Ben Allinbsa04@ic.ac.uk

1. Cells of the nervous system2. Neuronal structure and function3. Organisation of the nervous system4. The Central Nervous System5. The Peripheral Nervous System6. The Autonomic Nervous System

Neurone – One cell, made up of soma, axon and dendrite

Nerve – bundles of axons all held together. Ganglion - an encapsulated collection of

neuronal cell bodies in the peripheral nervous system

Nuclei – an Unencapsulated collection of neuronal cell bodies in the central nervous system.

Neurones Astroglia Oligodendroglia Microglia Schwann cell

Neurones - Structure Neurones - Types

Basic cell of the nervous system

Soma Axon Dendrite

Sensory Motor Inter-neurone

To carry electrical signals from one part of the body to another.

Mechanisms of conduction:◦ Resting potential◦ Action potential◦ Saltatory conduction

+ -

a) Na+ is extracellularb) K+ is intracellularc) Membrane more

permeable to K+d) Diffusion down a

[gradient]e) Charge is carried

with the ionsf) Accumulation of

charge repels diffusion of more ions

Stimulation causes flow of positive ions into the neurone. Some voltage gated Na+ channels open Na+ enters the neurone DOWN its [gradient] Threshold (-55mV) is reached all voltage gated Na+

channels open. Massive influx of Na+ inside of neurone becomes

positive (+30mV). This is depolarisation. At +30mV, Na+ channels close, lots of K+ channels are

open. Neurone enters refractory period K+ flows out, no more Na+ flowing in. This is

repolarisation. Inside of neurone becomes very –ve. This is

hyperpolarisation. K+ channels close and the charge returns to that of the

resting potential

Stimulation Threshold Depolarisation Channel inactivation – refractory period Repolarisation Hyperpolarisation Restitution

Segment of neurone becomes +ve. Adjacent segments are more negative Spread of +ve ions to area of –ve charge. Adjacent area become more +ve Threshold is reached Voltage gated channels are opened Depolarisation occurs Action potential is spread along the neurone

Organisation:◦ Neurone is one ‘nerve

cell’◦ Neurone is surrounded by

endoneurium◦ Bundles of neurones form

a fascicle◦ Fascicles are surrounded

by perineurium◦ Bundles of fascicles form

a nerve◦ Nerves are surrounded by

epineurium

Astroglia Oligodendroglia

The support cell Structural Remove

neurotransmitters Secrete neurotrophic

factors Form BBB Form scars

CNS Myelin forming cell Long processes Each process attaches

to a neurone Produces myelin

proteins and lipids Myelin forms a tight

sheath around the neurone

Die in Multiple Sclerosis

Microglia Schwann Cell

Brain Macrophages Formed from the bone

marrow Form ‘foot processes’

on blood vessels Immune surveillance –

detect when pathogens are present

Mount an inflammatory response

PNS myelin producing cell

One Schwann cell for one neurone.

Play a role in peripheral nerve regeneration

4 divisions of the Nervous system:◦ Central Nervous System (CNS)

Brain and Spinal Cord◦ Peripheral Nervous System (PNS)

Peripheral nerves and ganglia◦ Autonomic Nervous System (ANS)

Combination of CNS and PNS that controls ‘housekeeping functions’ and innervates the viscera (organs)

◦ Somatic Nervous System Combination of CNS and PNS that controls sensation

and motor function.

Consists of:◦ Brain

Cerebral cortex Brain stem Cerebellum

◦ Spinal cord

Cerebral cortex Diencephalon Cerebellum

Midbrain Pons Medulla

Consists of:◦Frontal lobe, Parietal lobe, Occipital

lobe, Temporal lobe

Frontal

Temporal Occipital

Parietal

3 layers, Dura Mater, Arachnoid and Pia Mater

Right hemisphere

Left hemisphere

Two types of neurones◦ Motor have soma (nucleus) in the spinal cord

Carry information away from the central nervous system◦ Sensory have soma in the dorsal root ganglion

Carry information towards the central nervous system Roots (ventral and dorsal) are formed from

collections of neurones emerging from the spinal cord.

Roots then combine to form spinal nerves. Spinal nerves combine at plexi to form

peripheral nerves. Peripheral nerves carry information to and from

the muscles, skin, organs etc.

What is the ANS?◦ Function

Structure Receptors Neurotransmitters

Combination of central and peripheral neurones that control homeostasis and perform housekeeping functions in the body.

Two divisions:◦ Sympathetic – Fight or flight◦ Parasympathetic – Rest and Digest

Two divisions, two structures Sympathetic:

◦ short preganglionic fibres, long post ganglionic fibres.

◦ Ganglia form the sympathetic chain◦ Emerges from thoraco-lumbar spinal cord◦ Adrenal medulla

Parasympathetic◦ Long pre-ganglionic fibres, short post-ganglionic

fibres◦ Cranial and sacral regions of the spinal cord

Two neurotransmitters:◦ Acetyl Choline (ACh)◦ Noradrenalin (NA)

Parasympathetic:◦ Exclusively ACh

Sympathetic◦ ACh pre-ganglionic fibres◦ NA post-ganglionic fibres◦ Sweat glands the exception – use ACh

SCHEMATIC DIAGRAM OF THE AUTONOMIC NERVOUS SYSTEM

Para

sym

pC

ran

ial

sacr

al

Sym

path

eti

c –

thora

cic/

lum

bar

ACh Effectororgan

ACh

NA

Adrenalmedulla

A (and NA) via bloodstream

AChEffectororgane.g. sweat gland

ACh = acetylcholine A = adrenaline (epinephrine) NA = noradrenaline (norepinephrine)

AN

S

Effectororgan

Effectororgan

Post

Post

Post

ACh

ACh

ACh

Pre

Pre

Pre

Pre

ACh Noradrenalin

nAChR: ◦ post ganglionic fibres◦ Ion channel linked◦ Fast acting

mAChR:◦ Effector organs◦ G-protein linked◦ Slow acting

Four types◦ All G-protein linked◦ α1 – smooth muscle

contraction◦ α2 – inhibit adrenalin

release◦ β1 – Inotropic effect on

heart◦ β2 –

Broncho/vasodilation

Cells of nervous system Generation of an action potential Organisation of the CNS and PNS Structure, function and receptors of the ANS