Organisation of the nervous system and the structure of neurons SNAB Topic 8 Grey Matter Lesson 2 Learning Objectives Describe the organisation of the nervous system  Describe the structure and function of sensory, relay and motor neurones  Describe the role of Schwann cells and myelination  Key Notes Interesting Facts Questions What is the nervous system? The nervous system is an organ system whose purpose is to:  Transmit signals from sensory organs in the form of electrical impulses to the CNS  Process and store information  Produce effects in other effector organs  Anatomy of the Nervous System Nervous System Organisation The nervous system is subdivided into separate sub systems.  The most significant of these divisions is between the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).  Nervous System Organisation Diagram Central Nervous System This system consists of:  The Brain  The Spinal Cord  The CNS has the function of processing nervous impulses to and from the PNS  Anatomy of the Central Nervous System CNS: Evolutionary Overview      All animals have a CNS of varying complexity The CNS is one of the earliest features to form in the developing embryo of animals Not all animals have a brain, in fact the brain is a specialised folding of the spinal cord Mammals have the most complex CNS or any animal species Humans have the most complex CNS of any mammal Peripheral Nervous System The functions of the PNS are:  To detect external or internal stimuli  To transmit those stimuli to the CNS  To carry commands from the CNS to the bodies effector organs  Effector organs can either be muscles or glands  Somatic Nervous System This is the first subdivision of the PNS  Its function is:  The control of voluntary actions  The stimulation of skeletal muscle  Muscle Types     Muscle in humans is subdivided into three categories: Skeletal Muscle: Muscle attached to the skeleton which causes movement Smooth Muscle: Muscle which controls blood pressure, construction of the trachea and peristalsis in the intestines Cardiac Muscle: Heart Muscle, which does not need nervous impulses to contract (myogenic) Autonomic Nervous System This is the second subdivision of the PNS  Its function is:  To control involuntary responces  To stimulate smooth muscle, cardiac muscle and glands  [Cardiac muscle is self stimulating but the Autonomic Nervous System controls its rate or beating]  Anatomy of the Autonomic Nervous System Sympathetic Nervous System The autonomic nervous system is divided into two subdivisions: Sympathetic and Parasympathetic  The function of the Sympathetic Nervous system is:  To stimulate the body’s involuntary systems e.g. the “Fight or Flight” response  Anatomy of the Sympathetic Nervous System Parasympathetic Nervous System The function of this second division of the Autonomic Nervous System is:  To inhibit the body’s involuntary systems  It prepares for the “rest and digest” response, the opposite of “Fight or Flight”  Anatomy of the Parasympathetic Nervous System Checkpoint  What division of the nervous system transmits impulses to skeletal muscle? A. B. C. D. Sympathetic Parasympathetic Somatic Central The Neuron The Neuron cell is the “function unit” of the nervous system (Neurone is the official UK spelling)  Neurons are highly specialised cells which can carry electrical impulses along their membranes  Neurons can also communicate with other neurons across synapses by chemicals called neurotransmitters  Facts about the Neuron The brain alone has around 1 trillion neurons (1x1012)  Although only 10 µm wide neurons can be very long (e.g. 1 metre in humans, 20 metres in whales!)  Neurons for webs of connections. The brain consists of an estimated 1x1014 connections  Motor Neuron Diagram Structures of the Neuron I Cell Body: Contains the cells organelles (e.g.) nucleus. The site of protein production  Dendrites: Filaments of neuron membrane which carry electrical impulses towards the cell body  Axon: Long filament of neuron membrane which carries electrical impulses away from the cell body  Structures of the Neuron II Myelin Sheath: Fatty layer wrapped around the axon. The sheath is created by a specialist cell called a Schwann Cell  Node of Ranvier: Area of the axon membrane where there is a small gap in the myelin sheath  Terminal branches: Small filaments where the axon splits up  Types of Neuron Motor Neurons Connect the CNS to effectors (Muscles or glands)  The cell bodies of the motor neurons are found in the “grey matter” of the spinal tissue  [Axons of motor neurons exit the spinal column between vertebras in structures called ganglions]  Image of a Motor Neuron Sensory Neuron These carry impulses from sensory cells (e.g. rods and cones in the eye) to the CNS  Many sensory cells can be wired into one sensory neuron amplifying the stimulus  Image of a Sensory Neuron Relay Neuron Aslo know as interlink neurons  The function of these neurons is to link sensory and motor neurons in reflex responses  A reflex response is one which does not involve conscious thought  Image of a Relay Neuron Nerves Bundles of axons of sensory or motor neurons are held together by connective tissues  These are called nerves  Image or a Nerve Checkpoint  What part of the Neuron carries electrical impulses towards the cell body? A. B. C. D. Axon Dendrite Myelin Sheath Node of Ranvier Nerve Problems Nerve bundles can be subject to many disorders:  Nerves maybe pinched between bones or other tissue (especially painful when in the back between vertebrae)  Nerves maybe squashed causing temporary paralysis (dead leg!)  The Vulcan Nerve Pinch! Correct! Try Again!