Topic 1: Introduction to the Nervous System

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Topic 1: Introduction to the Nervous System

❖Name the parts of a generalised neuron & indicate the input, output and integration areas of the neuron.➢Neurons are the functional cell of the nervous system that transmit electrochemical messages called nerve impulses or action potentials to other neurons and effectors (muscles or glands).

Parts of a neuron :

➢Cell body (or soma): contains

relatively large nucleus with a prominent nucleolus and produces proteins needed for other parts of the neuron. Cluster of cell bodies = ganglia.➢Dendrites: [INPUT] highly branched ‘finger-like’ projections that receive information from other neurons.➢Axons: [INTEGRATION] long nerve fibres that are capable of propagating electrical impulses known as action potential through them from cell body to axon terminal (*Electrical impulses rarely travel the other way). Cluster of neuron axons = nerves ➢Axon terminal: [OUTPUT] nerve endings that make synaptic contacts with other neurons and effector cells, they also contain various kinds of neurotransmitters (chemicals which convey the message across the synaptic space). 2 / 4

➢Myelin sheath: the insulating cover of axons which increases the speed at which electrical impulses travel along the neuron (*Not all neurons have a myelin sheath, only the ones that need fast electrical impulses).➢A single neuron integrates it many inputs (inhibitory or excitatory) to produce a single output response (action potential or nerve impulse).oThis allows: large amounts of info to be processed very quickly and acted upon.List the roles of glial cells in the nervous system Ependymal cells The nervous system also contains specialised Glial cells which protect and support neurons.

There are four types of neuroglia:

Astrocytes:

o o o o Structural support Formation of scar tissue Transport of substances between blood vessels and neurons Communication with one another and with neurons Neurons Microglial cellCapillary Astrocyte e 3 / 4

oMop up excess ions and neurotransmitters oInduce synapse formation.

➢Oligodendrocytes:

oForm myelin sheaths in the brain and spinal cord (e.g. multiple sclerosis = myelin sheath deteriorates and signals slower) oProduce nerve growth factors

➢Microglia:

oStructural support oPhagocytosis (immune protection as normal body immune cells don’t get into the CNS).

➢Ependymal cells:

oForm a porous layer through which substances diffuse between the interstitial fluid of the brain and spinal cord and the cerebrospinal fluid.❖Explain in broad terms, what a membrane potential is, and what is required for it to exist.➢All cells have a membrane potential, which is a difference in charge between the inside and outside of cells.➢Only nerve cells and muscle cells can rapidly change their membrane potential as a means of creating a signal. This means these are excitable cells.➢In rest state the inside of nerve cells are negative in respect to the outside of cells.➢The voltage arises from differences in concentration of the electrolyte ions K + and Na + .➢Specific sodium channels and potassium channels are intrinsic to the membrane and selectively close and open to allow the passage of these ions across the membrane.➢At rest, sodium channels are mostly closed and potassium channels open, so potassium moves down the concentration gradient (out of the cell), making is less negative to the outside.➢This is known as resting membrane potential.➢The concentration gradient is maintained by active transport (using ATP) of sodium ions out of cell and potassium ions in.➢Known as the sodium-potassium pump.❖Describe how depolarisation and repolarisation are achieved in a neurone.➢Depolarisation is what allows neurons to signal, which is the rapid reversal of the membrane potential from its rest state.➢Thus, where the sodium channels are open allowing sodium ions into the cell making it positive to the outside.➢After the signal, repolarisation occurs, where sodium channels close and potassium channels open allowing potassium to move out of cell and stop sodium moving into cell, creating a resting membrane potential again (negative inside).➢A “wave” of depolarisation and repolarisation moves rapidly along the axon of neurones and more sodium channels open and close. ➢This process is known as nerve

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