1. health and fitness
2. disease

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COPYRIGHT ©2015. DENTIN, LLC. ALL RIGHTS RESERVED.
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Printed in the United States
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TABLE OF CONTENTS
CHAPTER 1
ANATOMICAL SCIENCES
Muscles ................................................................................................................................................ 7
Joints & TMJ ....................................................................................................................................... 16
Bone (Hard Tissue) ............................................................................................................................. 19
Tissues ................................................................................................................................................ 27
PDL & Gingiva ..................................................................................................................................... 35
Tooth Histology & Life Cycle .............................................................................................................. 37
Tooth Tissues ..................................................................................................................................... 40
Enamel Structures .............................................................................................................................. 44
Reproductive System ......................................................................................................................... 47
Gastrointestinal System ...................................................................................................................... 50
Respiratory System ............................................................................................................................ 55
Endocrine System ............................................................................................................................... 58
Urinary System ................................................................................................................................... 68
Lymphatic System .............................................................................................................................. 70
Nervous System ................................................................................................................................. 73
Cranial Nerves .................................................................................................................................... 80
Foramen .............................................................................................................................................. 90
Heart ................................................................................................................................................... 92
Arteries................................................................................................................................................ 98
Veins ................................................................................................................................................. 106
Blood ................................................................................................................................................ 111
Embryology ....................................................................................................................................... 113
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CHAPTER 2
BIOCHEMISTRY & PHYSIOLOGY
The Cell & Cell Division ..................................................................................................................... 117
Cell Membrane ................................................................................................................................. 119
Central Nervous System (CNS) ........................................................................................................ 124
PNS & ANS ....................................................................................................................................... 130
Nerve Transmision ............................................................................................................................ 131
Hormones ......................................................................................................................................... 135
Gastrointestinal Hormones ............................................................................................................... 142
Blood ................................................................................................................................................ 145
Heart Physiology............................................................................................................................... 151
Vitamins, Minerals, & Deficiencies .................................................................................................... 159
Physiologic Disorders ....................................................................................................................... 164
Metabolism ....................................................................................................................................... 168
Oral Cavity Physiology ...................................................................................................................... 171
Muscle .............................................................................................................................................. 173
Respiration ........................................................................................................................................ 177
Reproduction .................................................................................................................................... 180
Sensory Organs ................................................................................................................................ 182
Renal (Kidney) ................................................................................................................................... 185
Liver .................................................................................................................................................. 189
Gastrointestinal System .................................................................................................................... 191
DNA & RNA ....................................................................................................................................... 193
Compounds & Substances ............................................................................................................... 197
Chemistry.......................................................................................................................................... 199
Carbohydrates .................................................................................................................................. 203
Lipids ................................................................................................................................................ 206
Proteins & Amino Acids .................................................................................................................... 211
Enzymes ........................................................................................................................................... 217
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CHAPTER 3
MICROBIOLOGY & PATHOLOGY
Bone Disorders ................................................................................................................................. 225
Hormonal Disorders .......................................................................................................................... 229
Gastrointestinal Disorders ................................................................................................................ 232
Endocrine Disorders ......................................................................................................................... 234
Skin Disorders .................................................................................................................................. 236
Neurological Disorders ..................................................................................................................... 238
Cardiac & Cerebral Disorders ........................................................................................................... 239
Renal Disorders ................................................................................................................................ 244
Eye Disorders ................................................................................................................................... 247
Autoimmune Disorders ..................................................................................................................... 248
Immunology ...................................................................................................................................... 250
Cellular Disorders ............................................................................................................................. 259
Genetic Disorders & Mutations ......................................................................................................... 260
Respiratory Disorders ....................................................................................................................... 262
Blood & Hemodynamic Disorders .................................................................................................... 265
Liver Disorders .................................................................................................................................. 272
Inflammation & Necrosis ................................................................................................................... 275
Neoplasms (Tumors) ......................................................................................................................... 278
Infections .......................................................................................................................................... 289
Plaque, Caries, Calculus ................................................................................................................... 293
Cells & Organelles............................................................................................................................. 296
Pathogen Sterilization & Disinfection ................................................................................................ 299
Wound Healing, Grafts, & Teratology ............................................................................................... 302
Bacteria............................................................................................................................................. 305
Antibiotics ......................................................................................................................................... 317
Viruses .............................................................................................................................................. 321
Vaccines ........................................................................................................................................... 332
Fungi ................................................................................................................................................. 334
Parasites ........................................................................................................................................... 337
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CHAPTER 4
DENTAL ANATOMY & OCCLUSION
Tooth Anatomy ................................................................................................................................. 340
Eruption Sequence ........................................................................................................................... 343
Deciduous (Primary) Teeth ............................................................................................................... 346
Succedaneous Anterior Teeth .......................................................................................................... 350
Succedaneous Posterior Teeth ........................................................................................................ 357
Periodontium Anatomy ..................................................................................................................... 368
Tooth Histology & Development ....................................................................................................... 374
Enamel, Dentin, Cementum, Pulp..................................................................................................... 376
Parafunction & Erosion ..................................................................................................................... 381
Muscles & TMJ ................................................................................................................................. 382
Mandibular Movements & Positions ................................................................................................. 387
Posterior Contacts in Ideal MICP ..................................................................................................... 389
Anterior Contacts in Ideal MICP ....................................................................................................... 391
Curves of Spee & Wilson .................................................................................................................. 392
Centric Occlusion, Centric Relation, & Rest ..................................................................................... 393
Articulation, Occlusal Balance & VDO .............................................................................................. 396
CHAPTER 5
NBDE I TEST PEARLS
Anatomy & Physiology ...................................................................................................................... 405
Biochemistry & Physiology ............................................................................................................... 409
Microbiology & Pathology................................................................................................................. 414
Dental Anatomy & Occlusion ............................................................................................................ 418
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MUSCLES
SOFT PALATE-mobile fold attached to the hard palate that separates the oral cavity from the
nasopharynx. Attached laterally to the tongue by glossopalatine arches, and to the lateral wall of the
pharynx by pharyngopalatine arches.
• Palate salivary glands are in the posterolateral zone, derived from ectoderm and are separated
by C.T. septa.
Two arches formed by the anterior & posterior pillars of the Fauces:
1. glossopalatine arch (palatoglossal arch)-formed by anterior pillars. Palatoglossus muscle is
below this arch and elevates the tongue and narrows the fauces. It’s the posterior boundary of
the oral cavity, and anterior boundary of the fauces.
2. pharyngopalatine arch (palatopharyngeus arch)-formed by posterior pillars.
• Palatopharyngeus muscle-located below this arch, it elevates the pharynx, shuts the
nasopharynx, narrows the fauces, and aids in swallowing. During swallowing, muscular
contraction causes movements that seal off the oropharynx from the nasopharynx.
Palatopharyngeus muscle CAUSES MOVEMENTS THAT FORM A FOLD IN THE
POSTERIOR WALL OF THE PHARYNX.
PALATINE TONSILS-consist mostly of lymphoid tissue, found between the two arches in the “fauces
area”= passageway from the oral cavity to the oral pharynx.
Soft Palate-consists of 5 paired skeletal muscles:
1. Tensor veli palatini-tenses soft palate & opens mouth of auditory tube during
swallowing/yawning. It curves around pterygoid hamulus, so if hamulus fractures, it affects
tensor veli palatini. Its tendon loops around pterygoid hamulus.
2. Levator veli palatini-elevates soft palate.
3. Palatoglossus-draws soft palate down to the tongue, closing the oropharyngeal isthmus.
4. Palatopharyngeus-elevates pharynx, pulls palatopharyngeal arches toward midline, & closes
nasopharynx.
5. Muscularis uvulae-elevates uvula.
Pharyngeal plexus INNERVATES all soft palate muscles EXCEPT Tensor veli palatini (innervated by
nerve to the medial pterygoid) = branch of mandibular division of trigeminal nerve (V3).
Soft Palate receives blood supply from:
1. greater and lesser palatine arteries (descending palatine artery branches of maxillary artery)
2. ascending palatine artery (facial artery branch)
3. palatine artery (ascending pharyngeal artery branch)
Anterior zone of the palatal submucosa contains fat, and posterior zone contains mucous glands.
Soft palate ends posteriorly in the midline as a conical projection = UVULA
• Bifid uvula-results from failure of complete fusion of the palatine shelves.
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TONGUE-all tongue muscles (intrinsic & extrinsic) are innervated by Hypoglossal nerve (CN XII)
EXCEPT palatoglossus muscle (innervated by pharyngeal plexus of CNX).
•
Paired Extrinsic Tongue Muscles: originate on structures away from the tongue and insert onto
it causing tongue movements during speaking, food manipulation, cleaning teeth, and
swallowing:
1. Genioglossus-protrudes tongue apex through mouth (sticks out tongue). Origin is
superior genial spine of mandible. Insertion is dorsum of tongue. Innervation:
hypoglossal nerve.
2. Hyoglossus-depresses side of tongue. Origin is hyoid bone. Inserts on side of
tongue. CN XII.
3. Styloglossus-elevates and retracts tongue. Origin is styloid process of temporal
bone. Insertion: lateral side and dorsum of tongue. Innervation: hypoglossal nerve.
4. Palatoglossus-pulls tongue root up and back (elevates the tongue). Origin: palatine
aponeurosis. Insertion: side of tongue. Innervation: PHARYNGEAL PLEXUS of
Vagus.
•
Intrinsic Tongue Muscles: longitudinal, transverse, and vertical muscles alter tongue shape, and
are confined to the tongue and NOT attached to bone. All are innervated by HYPOGLOSSAL
NERVE. Intrinsic muscles are named based on the 3 spatial planes that they run.
•
Tongue develops from: copula, tuberculum impar, 2nd & 3rd brachial arches, & lateral lingual
swellings.
Tongue Blood Supply:
1. lingual artery (from tonsilar branch of facial artery)
2. ascending pharyngeal artery
3. veins drain into the internal jugular vein.
Tongue Lymph Drainage:
1. tip of tongue-drains into submental lymph nodes.
2. remaining anterior 2/3-drains into submandibular and deep cervical lymph nodes on both
sides.
3. posterior 1/3-drains into deep cervical lymph nodes on both sides.
CARDIAC MUSCLE FIBERS-make up the myocardium (thick, middle layer of the heart). It is striated
muscle that contains transverse tubules, a slow rate of calcium sequestration, and is inhibited by
acetylcholine.
• Have MORE mitochondria b/t myofibrils and richer in myoglobin than most skeletal muscle.
• Like skeletal muscle, contain mylofilaments (contractile units) and are STRIATED with actin &
myosin.
• Have LARGER t-tubules and LESS DEVELOPED sarcoplasmic reticulums than skeletal
muscle fibers.
• Cardiac muscle fibers are short, branched, and single or binucleated in contrast to skeletal
muscle fibers.
• Contain large, oval centrally placed nuclei, and strong, thin unions b/t fibers =
INTERCALATED DISCS.
o Intercalated discs-junctions b/t cardiac muscle cells that provide low resistance to
current flow. Contains desmosomes which are within the discs to attach cells, and gap
junctions to communicate electrical impulse from cell-to-cell.
•
Cardiac muscle fibers CONTRACT SPONTANEOUSLY WITHOUT NERVE SUPPLY. Cardiac
fibers respond to increased demand by increasing its fiber size = Compensatory hypertrophy.
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Cardiac and skeletal muscle fibers cannot mitotically divide. Certain smooth muscle fibers
can under hormonal influences (e.g. during pregnancy myometrium smooth muscle fibers of the
uterus increase in length and form new cells).
SKELETAL MUSCLE FIBERS-attaches to the skeleton responsible for voluntary body movement.
Consists of BUNDLES of very long, narrow, cylindric, multinucleated cells with regularly ordered
myofibrils = STRIATED (distinct transverse striations) that span a joint attached at either end by a
tendon. Comprises ~40% of a person’s body weight.
• slender ovoid or elongated nuclei, and are situated peripherally.
• CONTAIN transverse tubules (t-tubules) & WELL-DEVELOPED sarcoplasmic reticulum.
• FAST, FORCEFUL VOLUNTARY CONSCIOUS CONTRACTION caused by myofibrils (ACTIN &
MYOSIN) = contractile element proteins of skeletal muscle that reduces sarcomere length.
Actin Filaments (thin myofilaments 5-8nm diameter) is composed of:
1. Actin-globular actin (G-actin) molecules arranged in double spherical chains = fibrous actin
(F-actin).
2. Tropomyosin-long threadlike molecules that lie on the surface of F-actin strands and
physically cover actin binding sites during the resting state.
3. Troponin-small oval molecule attached to each tropomyosin.
Myosin Filaments (thick myofilaments 12-18nm diameter) composed of myosin which has two
components:
1. light meromyosin (LMM)-makes up the rod-like backbone of myosin filaments.
2. heavy meromyosin (HMM)-forms shorter globular lateral cross-bridges that link to actin
binding sites during contraction.
Skeletal muscle contracts when a stimuli from the nervous system excites individual muscle
fibers. This starts as a series of events leading to interactions b/t myosin (thick filaments) and actin
(thin filaments) of the sarcomeres of the fibers.
• Skeletal muscle fiber origin is the stationary attachment, and their insertion is the movable
attachment.
• Skeletal muscle fibers are classified by their fiber arrangement (parallel, convergent, circular, or
pinnate).
• Each skeletal muscle fiber is innervated by an axon of a motor neuron terminal at a motor
end plate (a large complex terminal formation by which an axon of a motor neuron
establishes synaptic contact with a skeletal muscle).
• The axon of a motor neuron is highly branched, thus one motor neuron innervates many
muscle fibers. When a motor neuron transmits an impulse, ALL fibers it innervates contract
simultaneously.
Skeletal muscle fibers are enclosed/covered by sheets of fibrous C.T. (fascia):
1. Endomysium-fine C.T. sheath surrounding an individual skeletal muscle fiber.
2. Perimysium-fibrous sheath surrounding a bundle of muscle fibers.
3. Epimysium-external C.T. sheath surrounding an entire muscle.
Sarcoplasmic reticulum-the organelle that releases & stores calcium ions during contraction and
relaxation of skeletal muscle. It’s a network membranous channels of tubules and sacs in skeletal
muscles that extends throughout the sarcoplasm. Similar to the endoplasmic reticulum of other cells.
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TOOTH TISSUES
PULP FUNCTIONS: MAIN FUNCTION of dental pulp is to FORM DENTIN (FORMATIVE).
1. Formative (main function)-peripheral layer of pulp cells gives rise to the odontoblasts that form
dentin.
2. Nutritive-pulp keeps organic components of the surrounding mineralized tissue supplied with
moisture and nutrients. Very rich blood supply that surrounds the odontoblasts.
3. Sensory-free nerve endings that contact the odontoblasts to sense extremes in temp, pressure,
or trauma to dentin or pulp which are perceived as pain.
4. Protective- Responds to external stimuli that may trigger formation of reparative or secondary
dentin.
PULP CAPPING is more successful in YOUNG TEETH because the apical foramen is larger AND
young pulp contains more odontoblastic cells, is very vascular, less fibrous, and has more tissue
fluid than adult pulp. YOUNG PULP LACKS COLLATERAL CIRCULATION.
As pulp ages, PULP SIZE & NUMBER OF RETICULIN FIBERS DECREASES.
•
As pulp ages reticulin fibers decrease (the pulp becomes less cellular and more fibrous).
The size of the pulp also decreases because of continued deposition of dentin.
•
As pulp ages, the number of collagen fibers and calcification (pulp stones or denticles)
within the pulp increases.
PULP contains MYELINATED & UNMEYLINATED NERVE FIBERS (afferent and sympathetic).
Sympathetic and afferent fibers are the primary nerves in dental pulp.
1. myelinated fibers are sensory
2. unmyelinated fibers are motor and regulate lumen size of blood vessels.
3. free nerve ending-the only type of nerve ending found in pulp. It’s a specific pain
receptor. Regardless of the source of stimulation (heat, cold, pressure) the only response is
PAIN.
4. Proprioceptors-respond to stimuli regarding movement (found in gingiva, skeletal muscle,
PDL, TMJ) BUT NOT FOUND IN PULP!
Anatomically, PULP is divided into two portions (CORONAL & RADICULAR PULP):
1. Coronal Pulp-located in the pulp chamber and pulp horns (CROWN portion of tooth).
2. Radicular Pulp-located in pulp canals (ROOT portion of tooth).
•
Accessory Canals extend from pulp canals through the root dentin to the PDL.
CENTRAL ZONE (PULP PROPER)-area that contains large nerves and blood vessels, lined
peripherally by a specialized odontogenic area that has 3 layers:
1. Cell-rich zone-contains fibroblasts = the most numerous cell type found in dental pulp.
2. Cell-free zone (zone of Weil)-rich in capillaries and nerve networks.
3. Odontoblastic layer-contains odontoblasts and lies next to predentin and mature dentin.
Odontoblasts are derived from ectomesenchyme.
DENTAL PULP CELLS: fibroblasts, odontoblasts, histiocytes (macrophages), and lymphocytes.
• Diseased pulp contains: plasma cells, PMN’s, monocytes, and eosinophils.
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PERIKYMATA-tiny valleys on the TOOTH (CROWN) SURFACE created by the termination of the
lines of Retzius, and travel circumferentially around the crown.
MATURATION OF ENAMEL is characterized by a percentage INCREASE in inorganic content and a
percentage DECREASE in water and organic content.
COMPARISON OF TOOTH TISSUES
Mineral Content
Color
Formative cells
Embryology
Repair
Aging
Sensitivity
Cells in mature
tissues
ENAMEL
96% (highest)
DENTIN
70%
CEMENTUM
50%
Translucent yellow
Ameloblast
Epithelial
No replacement,
some
remineralization
Wear, staining,
caries
Light yellow
Odontoblast
Ectomesenchyme
Physiological,
reparative,
secondary dentin
Increase in
secondary and
sclerotic dentin
Yes-only as pain
Cytoplasmic
extensions from
odontoblasts
Light yellow
Cementoblast
Ectomesenchyme
New cementum
deposition
None
None
Increased amount
with age (apex)
No
Cementocytes
PULP
0% (except
denticles/pulp stones)
Blood red
Dental Papilla
Ectomesenchyme
Can recover if mild
inflammation but
severe = death
Reduced size and
may be obliterated.
Yes
Odontoblasts and
other cell types
ORTHODONTIC MOVEMENT OF TEETH: always causes remodeling of alveolar bone proper to
accommodate teeth movement.
• If a tooth is tilted MESIALLY during orthodontics, the CORONAL HALF of the mesial wall
shows resorption due to osteoclastic activity, while the CORONAL HALF of the distal wall
shows deposition due to osteoblastic activity.
• A similar situation is the alternate loosening and tightening of a deciduous tooth before it is
lost caused by the alternate resorption (cementoclasts, osteoclasts) and apposition
(cementoblasts, osteoblasts) of cementum and bone.
• During active tooth eruption, there is apposition of bone on all alveolar crest surfaces and on
all walls of the bony socket. Permanent teeth move OCCLUSALLY & BUCALLY when
erupting.
• In a newly erupted tooth, the junction between tooth surface and the crevicular epithelium
consists of a basal lamina-like structure between enamel and epithelium.
Apical abscesses of MANDIBULAR SECOND & THIRD MOLARS have a marked tendency to
produce cervical spread of infection MOST RAPIDLY.
Attachment of muscles may determine the direction/route that an infection will take, channeling
the infection into certain tissue spaces.
•
INFECTIONS OF MANDIBULAR TEETH (Especially 2nd & 3rd molars) perforate the bone
below the buccinator causing swelling of the lower half of the face. The infection spreads
medially from the mandible into the submandibular and masticatory spaces. It pushes the
tongue forward and upward. Further spread cervically may involve the visceral space and lead
to edema of the vocal cords and airway obstruction.
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MAJOR SALIVARY GLANDS (parotid, submandibular, & sublingual) are compound tubuloalveolar
glands that deliver salivary secretions into the mouth by way of large excretory ducts (Stenson’s,
Wharton’s, and numerous small Rivian ducts).
• Parasympathetic innervation controlling salivation originates in cranial nerves VII and IX.
Major Salivary Glands: Parotid (purely serous), Submandibular (submaxillary-mixed with serous
demilunes), & Sublingual Glands (mixed with serous demilunes).
• All major salivary glands are compound tubuloalveolar glands (their ducts branch
repeatedly (compound) and their secretory portions are tubular and composed of small sacs
(alveoli or acini).
•
Salivary gland
EPITHELIUM.
striated
ducts
are
composed
of
SIMPLE
LOW
COLUMNAR
PAROTID GLANDS-LARGEST salivary gland, and is PURELY SEROUS. The parotid glands are below
and just anterior to the ear. It divides into deep and superficial lobes with the stylomandibular tunnel
(encloses facial nerve) being the dividing line. Thus, part of the parotid lies superficial to the mandibular
ramus, and another portion lies deep.
• STENSON’S DUCT-drains the parotid gland. Stenson’s duct pierces the buccinator muscle
and crosses the masseter muscle where it drains into the vestibule of the mouth opposite the
maxillary second molar.
•
Innervation: receives parasympathetic secretomotor innervation from glossopharyngeal
nerve (via lesser petrosal nerve), otic ganglion, and auriculotemporal nerve (V3 branch).
•
Facial nerve (CN7), retromandibular vein, & external carotid artery LIE INSIDE the parotid
gland. EXTERNAL CAROTID ARTERY and its terminal branches (superficial temporal and
maxillary arteries) within the parotid, supply the parotid.
•
If a needle is advanced to far posteriorly during an inferior alveolar block injection,
anesthesia of the mandibular teeth will NOT OCCUR because the needle has entered the
PAROTID GLAND.
•
As a result of a mandibular block injection, a patient can develop paralysis of the muscles of
facial expression due to depositing anesthetic solution into the parotid gland.
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PANCREAS-a triangular organ that lies across the posterior abdominal wall. It’s a retroperitoneal
organ (except a small part of its tail which lies in the lienorenal ligament). The pancreas head and
neck rests in the curve of the duodenum, and its body stretches horizontally behind the stomach,
and its tail extends to the spleen. PANCREAS IS BOTH AN ENDOCRINE & EXOCRINE GLAND with
groups of special cell scattered among glandular alveoli.
1. Islets of Langerhans (Endocrine Portion)-3 types:
• Alpha cells-secrete glucagon which counters the action of insulin. Increase blood
sugar.
• Beta cells-secrete insulin that helps carbohydrate metabolism. Decrease blood sugar.
• Delta cells-secrete somatostatin which inhibits growth hormone.
• *degeneration of the Islets of Langerhans cells lead to DIABETES MELLITUS.
2.
Acinar Cells (Exocrine Portion)-produce pancreatic juice that contains trypsinogen and
other digestive enzymes. Trypsinogen is then converted to trypsin in the small intestine.
The primary histologic characterstic of the pancreas is groups of special cell scattered among glandular
alveoli.
PANCREAS DUCTS (2):
1. Duct of Wirsung-MAIN EXCRETORY DUCT OF PANCREAS that begins at the tail, joins the
common bile duct from the gallbladder to form the hepatopancreatic ampulla (ampulla of
Vater) before opening into the duodenum. Ampulla of Vater discharges bile and pancreatic
enzymes into the duodenum.
2.
Santorini’s duct-an accessory pancreatic duct that begins in the lower portion of the pancreas
head and opens into the duodenum.
THYROID GLAND-located in the neck, just below the larynx (Adam’s apple). Its two lateral lobes (one on
each side of the trachea) join with the isthmus-a narrow tissue bridge that contracts the trachea to
give the gland its butterfly shape.
• Thyroid gland is a very vascular organ that receives its blood supply from superior and
inferior thyroid arteries. It is innervated from glandular branches of the three cervical
ganglia of the sympathetic trunk. Lymph from the thyroid gland drains laterally into the deep
cervical lymph nodes.
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THE CELL
PROTOPLASM-a viscous, translucent, watery material that is the primary component of plant and
animal cells. It contains a large percentage of water, inorganic ions (potassium, calcium, magnesium,
and sodium), and naturally occurring organic compounds (proteins, lipids, and carbohydrates). Types of
protoplasms:
1. Nucleoplasm-the protoplasm of the cell nucleus that plays a role in reproduction.
2. Cytoplasm-the protoplasm of the cell body that surrounds the nucleus, converts raw materials
into energy. A clear, thin film of protoplasm (cell membrane) always surrounds the cytoplasm.
Ectoplasm-the outer part of the cytoplasm.
3. Cytoplasm is the site of most synthesizing activities and contains:
• Cytosol-viscous, semitransparent fluid that is 70-90% water.
•
Organelles (mitochondria,
peroxisomes)
ribosomes,
vacuoles,
lysosomes,
centrosomes,
•
Metaplasm (cytoplasmic inclusions)-lifeless substances (yolk, fat, starch) that may
be stored in various parts of the cytoplasm. Examples: glycogen (carbohydrate
deposits in liver cells), fat deposits, pigment granules (deposits of colored
substances). Two types of pigment granules:
1. Lipofuscin-yelllowish-brown substance that increases in quantity as cells age.
2. Melanin-abundant in epidermis of the skin and retina.
ORGANELLES:
1. Centrosomes-organelle that contains centrioles (short cylinders adjacent to the nucleus that
take part in cell division).
2. Peroxisomes-contain oxidases, enzymes capable of reducing oxygen to hydrogen peroxide and
hydrogen peroxide to water. Beta-oxidation of very long chain fatty acids begins in peroxisomes.
3. Ribosomes-sites of most protein synthesis.
4. Mitochondria-threadlike structures within the cytoplasm that provide most of body’s ATP (fuels
cellular activities).
5. Vacuoles-store and excrete various substances within the cytoplasm.
6. Lysosomes-digestive bodies formed in the golgi apparatus that break down foreign or
damaged materials in cells. Contain hydrolytic enzymes.
7. Cytoskeletal elements-form a network of protein structures.
8. Endoplasmic Reticulum (ER)-organelle & extensive network of membrane-enclosed tubules in
the cell cytoplasm involved in protein and lipid synthesis, and transport these metabolites
within the cell.
• granular (rough surfaced ER)-has ribosomes attached to the membrane surface.
• agranular (smooth surfaced ER)-no ribosomes, but enzymes that synthesize lipids.
CELLULAR COMPONENTS:
1. Golgi Apparatus-synthesizes COMPLEX CARBOHYDRATES that combine with protein
produced by RER to form secretory products (e.g. lipoproteins). Procollagen filaments are
produced by the golgi apparatus.
2. Endoplasmic Reticulum-extensive network of internal membrane-enclosed tubules. RER is covered
with ribosomes and produces certain proteins. Smooth ER contains enzymes that synthesize lipids.
Involved in coordinating protein synthesis. Two types of ER:
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Plasma
Mast
Schwann
Sertoli
Leydig
Fibroblast
Osteoblast
Odontoblast
Ameloblast
T-lymphocytes
B-lymphocytes
Alpha cells
Beta cells
CELLS & THEIR PRIMARY FUNCTION
PRIMARY FUNCTION
Antibody Synthesis
Mediators of inflammation on contact with antigen
Form myelin sheath around axons of the PNS
Produces testicular fluid
Produces testosterone
Produces collagen and reticular fibers
Forms bone matrix, gives rise to osteocytes
Forms dentin
Forms enamel
Cell-mediated immunity
Differentiate into plasma cells
Produce glucagon (in pancreas)
Produces insulin (in pancreas)
CELL
Sustentacular
Pyramidal
Endothelial
Ependymal
Clara
Ganglionic
Globular
Prickle
Fibroblast
Chromaffin
Purkinje
Goblet
Interstitial
Islet
Juxtaglomerular
Mesenchymal
CELLS & THEIR PRIMARY FUNCTION
PRIMARY FUNCTION
Internal ear (organ of Corti), taste buds, olfactory epithelium
Cerebral cortex (cerebrum)
Lining blood and lymph vessels, endocardium (inner layer)
Lining the brain ventricles and spinal cord
Terminal bronchioles
In a ganglion peripheral to the CNS
Transitional epithelium (kidney, ureter, bladder)
Stratum spinosum of epidermis
Most common cell of connective tissue
Adrenal medulla and paraganglia of SNS
Cerebellar cortex (cerebellum)
Mucous membranes of respiratory and intestinal tracts
C.T. of ovary and testis
Pancreas
Renal corpuscle of kidney
Found between ectoderm and endoderm of embryos
CELL
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CENTRAL NERVOUS SYSTEM (CNS)
CEREBRUM-divided into right and left hemispheres connected by nerve fibers = CORPUS
CALLOSUM. Each hemisphere has 4 lobes:
1. Frontal Lobes-control skilled motor behavior (speech, mood, thought, and planning for the
future). In most people, the control of language is situated predominantly in the left frontal lobe.
2. Parietal Lobes-interpret sensory input for the rest of the body and control body movement.
3. Occipital Lobes-interpret vision.
4. Temporal Lobes-generate memory and emotions (contains the limbic system).
CEREBELLUM-functions to maintain muscle tone, coordinate voluntary muscle movement, and control
balance. Cerebellum lies below and posterior to the cerebrum just above the brainstem (pons,
midbrain, & medulla). It is morphologically divided into two lateral hemispheres and a middle portion.
Its function is to coordinate voluntary muscular activity, maintaining equilibrium, and
coordination.
BRAINSTEM-lies immediately inferior to the cerebrum, just anterior to the cerebellum. Brainstem
consists of:
1. Midbrain-connects dorsally with cerebellum, and contains large voluntary motor nerve tracts.
2. Pons-connects the cerebellum with the cerebrum, and links the midbrain to the medulla
oblongata; serves as the exit point for cranial nerves V, VI, and VII. Pons is the primary link
between the nervous and endocrine systems.
3. Medulla Oblongata-is the lowermost portion of the vertebrate brain, continuous with the
spinal cord. It joins the spinal cord at the level of the foramen magnum. It contains the cardiac,
vasomotor, and respiratory centers of the brain, serving as an autonomic reflex center to
maintain homeostasis, regulating respiratory, vasomotor, and cardiac functions. Mediates
reflexes like blinking, coughing, vomiting, swallowing. It’s the origin of the VAGUS NERVE.
LIMIBIC SYSTEM-the PRIMITIVE BRAIN area deep within the TEMPORAL LOBE of the brain.
Limbic system initiates basic drives: hunger, aggression, EMOTIONAL feelings, sexual arousal, and
screens all sensory messages traveling to the cerebral cortex.
HYPOTHALAMUS-a collection of nerve cells at the base of the cerebrum (CNS) that regulates or
affects body temperature, water balance, appetite, sleep, pituitary secretions, emotions,
carbohydrate metabolism & autonomic nervous system functions (e.g. sleep and wakeful cycles).
Hypothalamus is a collating center for information concerned with good body health and in turn, much
of this information controls secretions by the pituitary gland.
• hypothalamus controls many vital processes associated with the autonomic nervous
system (ANS). Hypothalamus is involved in regulating body temperature, water balance,
appetite, GI activity, sexual activity, sleep, and emotions of fear and rage. Hypothalamus
also regulates the release of pituitary gland hormones, thus, it greatly affects the
ENDOCRINE SYSTEM.
•
Hypophyseal Portal Vessels-carry hypothalamic releasing factors to anterior lobe of
pituitary gland (adenohypophysis).
THALAMUS-a large ovoid mass of gray matter that RELAYS ALL SENSORY STIMULI (except
olfactory) as they ascend to the cerebral cortex. Thalamus is a collection of nerve cells at the base of
the cerebrum.
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SENSORY ORGANS
EAR-consists of three major parts:
1. External Ear-consists of the external part (pinna) and ear canal. It receives sound waves.
•
Auricle (pinna)-directs sound waves.
•
External auditory canal (meatus)-contains hair and cerumen (brown earwax); serves
as a resonator.
2. Middle Ear (tympanic cavity)-an air-filled cavity in the temporal bone that communicates
anteriorly with the nasopharynx via the Eustachian (Auditory) tube (pharyngotympanic tube).
Middle ear communicates posteriorly with the mastoid air cells and the mastoid antrum
through the aditus ad antrum. Eustachian tube serves to equalize air pressure in the tympanic
cavity and nasopharynx.
•
Auditory tube-regulates pressure.
•
Ossicles (malleus (hammer), incus (anvil), stapes (stirrup)-three small bones
linked together to transmit sounds.
•
Stapedius muscle (smallest skeletal muscle in the body) and tensor tympani
muscle.
•
Middle ear infections (otitis media) are quite prevalent and may become
extensive due to connection to both the mastoid air cells and the nasopharynx by
way of the Eustachian tube.
3. Inner Ear-formed by a bony labyrinth and a membranous labyrinth. Consists of the acoustic
apparatus, vestibular apparatus, semicircular canals, and a bony and membranous laryrinth:
•
Vestibule apparatus (saccule and utricle)-associated with sense of balance.
•
Semicircular canals-concerned with equilibrium.
•
Cochlea (contains two membranes: vestibular and basilar)-portion of inner ear
responsible for hearing.
•
Organ of Corti-a spiral organ that contains hair cell receptors for hearing and is
responsible for sound perception.
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BONE DISORDERS
FRACTURE-the most common bone lesion. Healing of fractures involves 3 phases:
1. Inflammatory phase-characterized by formation of a blood clot.
2. Reparative phase-characterized by formation of a callus of cartilage, replaced by a bony
callus (compact bone).
3. Remodeling phase-the cortex is revitalized.
Reasons Fractures Fail to Heal (non-union):
1. Ischemia-the navicular bone of the wrist, femoral neck, and lower third of the tibia are all poorly
vascularized and thus, subject to coagulation necrosis after a fracture.
2. Excessive mobility-pseudoarthrosis or a pseudojoint may occur.
3. Interposition of soft tissue-between the fractured ends.
4. Infection-most likely with compound fractures.
Fat embolism-is most often a sequela of fractured bones due to the mechanical disruption of bone
marrow fat and by alterations in plasma lipids.
Osteochondroma-a benign tumor made of bone and cartilage, found most frequently near the ends
of long bones. Most common in patients 10-25 years old.
OSTEOCHONDROSES-a group of diseases that affects the growth plate during childhood, resulting
in abnormal bone growth and deformity. Their cause unknown. Different diseases affect different bones,
characterized initially by degeneration and aseptic necrosis followed by regeneration and reossification.
Types of Osteochondroses:
1. Osgood-Schlatter Disease-inflammation of bone and cartilage at the top of the SHINBONE.
Usually develops between ages 10-15 more common in athletic boys. Major symptoms: pain,
swelling, and tenderness at the top of the shin. It usually involves the tibial tubercle of the
knee.
2. Legg-Calve-Perthes Disease-destruction of the growth plate in the neck of the thighbone.
Develops between ages 5-10, more common in boys. Caused by poor blood supply to the
neck of the thighbone. Main symptoms are hip pain and problems walking.
3. Scheuermann’s Disease-relatively common condition in which backache and humpback
(kyphosis) are caused by changes in vertebrae. Usually begins in adolescence, affecting
mostly boys. Symptoms are rounded shoulders and persistent mild backache.
4. Kohler’s bone Disease-a rare form of inflammation of bone and cartilage (osteochondritis)
affecting one of the small bones (navicular bone) in the foot. Usually affects children (boys 3-5
years). Symptoms are swollen foot with limping.
OSTEOMALACIA-caused by VITAMIN D DEFICIENCY in adults. Characterized by a gradual softening
and bending of the bones with varying severity of pain. This softening of the bones occurs b/c the
bones contain osteoid tissue that failed to calcify due to lack of vitamin D.
•
All bones are effected, specifically their epiphyseal growth plates. It is identified radiographically
by diffuse radiolucency that can mimic osteoporosis. Bone biopsy is often the only way to
differentiate between osteoporosis and osteomalacia.
•
Osteomalacia is the ADULT FORM OF RICKETS, appearing more in women. It may be
asymptomatic until fracture occurs.
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TYPE III Hypersensitivity Reactions:
1. SERUM SICKNESS-an acute, self-limited disease that occurs 6-8 days after injecting a
foreign protein (bovine albumin), characterized by fever, arthralgias, vasculitis, & an acute
glomerulonephritis. Serum sickness is an example of a systemic Arthus reaction.
•
Serum sickness is a reaction that is a type of immune complex disorder (Type 3
hypersensitivity) that results when patients are given large doses of foreign serum
(most often horse serum). The antigens in these serums stimulate an immune response.
Immune complexes form between the residual antigens and circulating antibody. These
antigen-antibody complexes are then deposited at certain body sites (joints, kidneys, and
vessel walls).
2. ARTHUS REACTION-another type of immune complex disorder that involves severe local
sensitivity at the site of injection of antigen. This reaction requires prior sensitization. When
an antigen-antibody complex initiates such a reaction in alveoli, symptoms include fever, cough,
and difficulty breathing. Symptoms typically develop over 4-6 hour period. The attack subsides
within a few days.
3. SYSTEMIC LUPUS ERYTHEMATOSUS (Lupus)-an autoimmune disease that results in
episodes of inflammation of joints, tendons, and other C.T. and organs.
HISTAMINE DOES NOT PLAY A ROLE IN ABOVE TYPE 3 HYPERSENSITIVITY REACTIONS.
HYPERSENSITIVITY REACTION COMPARISON
Reaction Type
I
II
III
IV
V
Alternate
Name
Allergy
(immediate)
Disorders
Mediator
Description
Atopy, anaphylaxis,
asthma, hay fever
IgE
Fast response (minutes);
involves mast cells and
basophils
Immune
complex
disease
Cell-mediated
immune
memory
response,
antibodyindependent
Thrombocytopenia
Rheumatic Heart
Goodpasture’s Syndrome
Erythroblastosis fetalis
Grave’s Disease
Myasthenia Gravis
Serum sickness
Rheumatoid Arthritis
Lupus
Contact dermatitis
Multiple Sclerosis
Mantoux test
TB
Sarcoidosis
Transplant Rejection
Autoimmune
disease
Graves’ Disease
Myasthenia Gravis
Cytotoxic,
antibodydependent
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IgM or IgG
Complement
MAC
Cellular destruction via MAC
IgG
Complement
Neutrophils
Circulating immune complex
deposited in vessel walls of
joints and kidney
Helper T-cells
Th1 cells activate macrophages
to cause an inflammatory
response and tissue damage
IgM or IgG
Complement
Testing with Coombs Test
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IMMUNOLOGY
MAIN FUNCTION of the IMMUNE SYSTEM is to prevent or limit infections by microorganisms
(bacteria, viruses, fungi, and parasites). Protection is provided by cell-mediated and antibodymediated (humoral) arms of the immune system:
1. CELLULAR IMMUNITY-a specific acquired immunity involving T cells. It acts to resist
most intracellular pathogens (bacteria and viruses). It involves soluble factors from Tlymphocytes (lymphokines) and macrophages (monokines).
• Cell mediated immunity (arm) consists primarily of T-lymphocytes (e.g. helper T cells
and cytotoxic T cells).
2. HUMORAL IMMUNITY (antibody-mediated immunity)-immunity produced by the
activation of the B-lymphocyte population which produces immunoglobulins (IgA, IgD,
IgM). Circulating antibodies are produced by plasma cells (are differentiated B cells) within
lymphatic tissue. The key to humoral immunity is the ability of antibodies to react
specifically with antigens. This type of immunity provides PROTECTIONS AGAINST
ENCAPSULATED BACTERIA.
• Antibody-mediated immunity (humoral immunity) involves B-lymphocytes & plasma
cells.
Complement & Phagocytes are two other MAJOR IMMUNE SYSTEM COMPONENTS.
NATURAL (INNATE) IMMUNITY-immunity that occurs naturally as a result of a person’s genetic
constitution or physiology, and does not arise from a previous infection or vaccination. It is
nonspecific, does not improve after exposure to the organism, and its processes have no memory.
•
Natural immunity (innate) is resistance not acquired through contact with an antigen.
ACQUIRED IMMUNITY-occurs AFTER EXPOSURE to an agent, improves upon repeated exposure,
and is specific. It is mediated by antibody and T-lymphocytes (T helper and cytotoxic T cells). The cells
responsible for acquired immunity have long-term memory for a specific antigen. Acquired immunity is
specific, improves after repeated exposure, and has “long-term” memory for an antigen.
ACQUIRED IMMUNITY-occurs naturally and artificially. It can be ACTIVE or PASSIVE.
•
Naturally (innate) Active immunity-person is exposed to an antigen and the body produces
antibodies.
•
Naturally (innate) Passive immunity-antibodies (IgG) passed from mother to fetus during
pregnancy and IgA passed from mother to newborn during breast-feeding.
•
•
Artificially Active immunity-vaccination with killed, inactivated, or attenuated bacteria or toxoid.
Artificially Passive immunity-injection of immune serum or gamma-globulin.
ACTIVE IMMUNITY-the host actively produces an immune response consisting of antibodies and
activated helper and cytotoxic T lymphocytes. The main advantage of active immunity is
RESISTANCE IS LONG TERM (years). The major disadvantage is its SLOW ONSET.
PASSIVE IMMUNITY-antibodies are preformed in another host. It is not as permanent and does not
last as long as active immunity. Main advantage is IMMEDIATE AVAILABILITY OF ANTIBODIES;
the major disadvantage is the SHORT DURATION (months).
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HYPERSENSITIVITY-an exaggerated immunological response upon re-exposure to a specific antigen
(positive skin test after having a disease). HYPERSENSITIVITY REACTIONS:
1. TYPE I (anaphylactic type) immediate hypersensitivity: a specific cytotropic antibody (IgE) binds
to receptors on basophils and mast cells and reacts with a specific antigen. IgE antibody mediatedmast cell activation and degranulation. Ex: “Hay fever”, asthma, anaphylaxis.
•
During a Type I hypersensitivity reaction, leukotrienes and prostaglandins D2 are generated
from Arachidonic acid. Also causes atopic allergies.
2. TYPE II (cytotoxic type) cytotoxic antibodies: cytotoxic (IgG, IgM) antibodies form against cell
surface antigens. Complement is usually involved. Ex: Autoimmune hemolytic anemias,
antibody-dependent cellular toxicity (ADCC), Goopasture disease.
3. TYPE III (immune complex type) immune complex disease: Antibodies (IgG, IgM, IgA) formed
against exogenous or endogenous antigens. Complement and leukocytes (neutrophils,
macrophages) are often involved. Ex: Autoimmune disease (SLE, rheumatoid arthritis), most
types of glomerulonephritis.
4. TYPE IV (cell-mediated type)-delayed type hypersensitivity: Mononuclear cells (T lymphocytes,
macrophages are the cellular infiltrates) with interleukin and lymphokine production. Ex:
Granulomatous diseases (tuberculosis, sarcoidosis).
5. TYPE V (auto-immune Disease)-reaction that occurs when IgG antibodies directed toward cell
surface antigens have a stimulating effect on their target. Ex: Graves Disease (antigen-antibody
complex on the follicular cell surface causes excess secretion of thyroid hormone as if were TSH).
HYPERSENSITIVITY REACTION COMPARISON
Reaction Type
I
II
III
IV
V
Alternate
Name
Allergy
(immediate)
Disorders
Mediator
Description
Atopy, anaphylaxis,
asthma, hay fever
IgE
Fast response (minutes);
involves mast cells and
basophils
Immune
complex
disease
Cell-mediated
immune
memory
response,
antibodyindependent
Thrombocytopenia
Rheumatic Heart
Goodpasture’s Syndrome
Erythroblastosis fetalis
Grave’s Disease
Myasthenia Gravis
Serum sickness
Rheumatoid Arthritis
Lupus
Contact dermatitis
Multiple Sclerosis
Mantoux test
TB
Sarcoidosis
Transplant Rejection
Autoimmune
disease
Graves’ Disease
Myasthenia Gravis
Cytotoxic,
antibodydependent
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IgM or IgG
Complement
MAC
Cellular destruction via MAC
IgG
Complement
Neutrophils
Circulating immune complex
deposited in vessel walls of
joints and kidney
Helper T-cells
Th1 cells activate macrophages
to cause an inflammatory
response and tissue damage
IgM or IgG
Complement
Testing with Coombs Test
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TOOTH ANATOMY
OCCLUSAL SURFACE-chewing surface of POSTERIOR teeth that consists of cusps, ridges, and
grooves. The occlusal surface is bounded mesiodistally by the marginal ridges and buccolingually
by the cusp ridges.
•
Anterior teeth DO NOT HAVE an occlusal surface.
OCCLUSAL TABLE-that area of a tooth bordered facially and lingually by the crests of the cuspal ridges
of facial and lingual cusps, and mesially and distally by the crests of the marginal ridges.
INCISAL EDGE-the cutting edge or biting surface of ANTERIOR teeth.
ANATOMIC CROWN-the part of the tooth covered by enamel.
CLINICAL CROWN-the part of the tooth visible in the oral cavity. It may be larger or smaller than
the anatomic crown. The anatomic crown is shorter than the clinical crown of a tooth during gingival
recession.
INTERPROXIMAL SPACE-triangular space between adjacent teeth cervical to the contact area. The
sides of the triangle are the proximal surfaces of the adjacent teeth, the apex of the triangle is the
area of contact of two teeth, and the base of the triangle is the alveolar bone.
•
Interproximal space is normally occupied by the interdental papilla.
EMBRASURES-triangularly shaped spaces between the proximal surfaces of adjacent teeth.
Embrasures diverge buccally, cervically, lingually, and occlusally from the area of contact.
•
Pronounced developmental grooves are usually associated with embrasures between
permanent maxillary canines and first premolars; and between permanent mandibular canines
and first premolars.
•
LARGEST incisal/occlusal embrasure is between the maxillary lateral incisor & canine.
•
Each contact area has 4 Embrasures: BUCCAL, LINGUAL (larger than buccal),
OCCLUSAL/INCISAL, & CERVICAL.
•
Embrasure Functions: spillways to direct food away from the gingiva, make teeth more selfcleansing, protect gingival tissue from undue frictional trauma, while providing the proper
degree of tissue stimulation.
EMBRASURES DO NOT CONTRIBUTE TO ARCH STABILITY.
§ Embrasures also make the natural hygienic factors in the mouth more effective by exposing
tooth surfaces to oral fluids and the mechanical cleansing action of the tounge, lips, and
cheeks.
PROXIMAL CONTACTS-areas where mesial & distal surfaces of adjacent teeth in the same arch
make contact.
•
Support neighboring teeth to stabilize the dental arches.
•
Prevent food particles from entering interproximal spaces.
•
Protect interdental papillae of the gingiva by shunting food toward the buccal and lingual
areas.
•
Form embrasures.
•
Loss of proximal contact may result in periodontal disease, malocclusion, food impaction, or
drifting of teeth.
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PRIMARY MAXILLARY SECOND MOLAR strikingly resembles the PERMANENT MAXILLARY FIRST
MOLAR (but they are smaller). Primary second molars are larger than primary first molars, and resemble
the form of the permanent first molars.
•
Crown is greater F-L > M-D.
•
May have a FIFTH CUSP (Cusp of Carabelli).
•
Has a prominent M-B cervical ridge and oblique ridge.
•
MB cusp is EQUAL in size or slightly larger than the M-L cusp.
•
MB pulp horn is the largest and longest.
•
PRIMARY FIRST MOLAR is the primary tooth with the most noticeable morphologic deviations
from permanent teeth.
•
PRIMARY SECOND MOLAR has the greatest F-L diameter of all primary teeth.
PERMANENT MANDIUBLAR FIRST MOLAR morphology closely resembles the PRIMARY
MANDIBULAR SECOND MOLAR. However, some differences include:
1. Relative size of the distal cusp. The primary second molar’s M-B, D-B, and distal cusp are
almost equal in size. The distal cusp of the permanent molar, however, is smaller than the other
two cusps.
2. From the buccal aspect, the primary mandibular second molar has a narrow M-D calibration at
the cervical portion of the crown compared with the calibration mesiodistally on the crown at
contact level. The mandibular first permanent molar, accordingly, is wider at the cervical portion.
3. Groove patterns are different on the occlusal surface.
4. Primary tooth has more divergent roots to allow for eruption of the second premolar.
5. Primary tooth has a more prominent facial crest of contour.
PERMANENT MANDIBULAR 1st MOLAR
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PERIODONTIUM ANATOMY
1. Soft uncalcified tissues are dental pulp, gingiva, and PDL.
2. Cementoenamel junction does not contribute to stabilization and protection of the dental arches.
Facial embrasures, occlusal embrasures, proximal contact areas, and horizontal and vertical overlap
do contribute to stabilize and protect the dental arches.
3. Opening of the nasopalatine canal is located at the anterior midline of the palate.
PERIODONTAL LIGAMENT (PDL) & GINGIVA
PERIODONTIUM (“attachment apparatus”)-tissues that invest and support the teeth. Periodontium
consists of the gingiva, PDL, cementum, alveolar and supporting bone.
3 Features of the Human Dentition that directly affect PDL heath and its hard tissue anchorage in
terms of resisting occlusal forces:
1. Anterior teeth have slight or no contact in the intercuspal position.
2. occlusal table is less than 60% of the overall faciolingual width of the tooth and is generally
at right angles to the long axis of the tooth.
3. mandibular molar crowns are inclined 15-20° toward the lingual, while the root apices are
positioned more facially.
PDL PRINCIPAL FIBERS (collagen fibers)-a connective tissue that consists of bundles of collagen
fibers grouped according to the direction they extend from the cementum of the root to the alveolar
bone. PDL principal fibers connect the root cementum to alveolar bone and are distinguished by their
location and direction. Principal fibers are sometimes classified as belonging to the general group of
alveolodental fibers.
1. Alveolar Crest Fibers-extend from the cervical cementum of the tooth to the alveolar crest that
function to counterbalance the occlusal forces on the more apical fibers and resist lateral
movements.
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