(Dr Adu's Lectures)

Front 1

The Nervous System

Front 2

Learning Objective

Back 2

Describe in detail thee general anatomy, structure and fucntions of the nervous system
Describe the general structure and functions of neurons

Front 3

Nervous System

Back 3

The nervous system (NS) performs a variety of complex tasks;

Detection of sensory information e.g. mechanoreception in the skin - merkel cells

Control of voluntary body movements

Front 4

Nervous System in Action #1

Back 4

Sensory input - NS constantly collects information from millions of receptors (e.g. pain receptors) that detect changes within and outside the body

Front 5

Nervous System in Action #2

Back 5

Integration - NS interprets and integrates the sensory information (inputs): makes decisions and sends instructions to alter tissue/organ behaviour appropriately

Front 6

Nervous System in Action #3

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Motor output - effector organs respond to instructions

Front 7

General functions of NS

Back 7

Sensory input - Integration - Motor output

Front 8

Functions of the Brain

Back 8

The brain is responsible for higher functions: cognition, learning, formation/storage and recall of memories, emotions, control of PNS function

Front 9

General Structure of the NS

Back 9

The NS is comprised of 2 major parts: the central nervous system (CNS), the peripheral nervous system (PNS)

The CNS includes the brain and spinal cord: complex organs consisting of neural tissue, blood vessels and protective connective tissue, interpret and integrate different types of sensory information

Initiate appropriate motor commands in response to sensory input

Front 10

The Peripheral Nervous System

Back 10

Contains all neural tissue outside the CNS including: different types of neuronal populations e.g. dorsal root ganglia, nerves that extend from these neuronal populations near the brain (cranial nerves e.g. IX & X nerves) and spinal cord (spinal nerves)

Nerves carry sensory information to the CNS and convey motor commands to peripheral (effector) tissues e.g. skeletal muscle

Front 11

Afferent and Efferent sub-divisions of the PNS

Back 11

The afferent division carries sensory information from receptors in the body to constantly inform the CNS of changes in the external and internal environment

The efferent division enables the CNS to adjust the activity of effector organs in response to changes in the external or internal environment to maintain homeostasis

Front 12

Functional Divisions of the PNS

(Efferent Division)

Back 12

2 sub-divisions:

Somatic Nervous System: comprised of somatic nerve fibers that carry impulses from the CNS to skeletal muscle (under voluntary control, degenerates in motor neuron disease)

Autonomic Nervous System (ANS): It consists of neurons that control the function of internal structures such as sweat glands or visceral organs such as the heart, it is not under conscious (voluntary) control

Front 13

Functional Divisions of the ANS

Back 13

Sympathetic nervous system

Parasympathetic nervous system (e.g. 10th cranial nerve)

Enteric nervous system

Front 14

Cellular Composition of the NS

Back 14

The NS is built from 2 types of cells:

Neurons (about 10 billion in the human brain)

Glia cells - by far the most numerous cell type of the NS, up to 50 times more glial cells than neurons in the CNS

Front 15

Characteristics of Neurons #1

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Neurons are the basic structural and functional unit of the nervous system

Highly specialised excitable cells that transmit information in the form of electrical impulses (APs) rapidly from one part of the body to another

With the exception of the hippocampus and olfactory epitheliun neurons can not be replaced once lost from the NS

They show remarkable longetivity - can function optimally over a lifetime (>100 years)

Front 16

Characteristics of Neurons #2

Back 16

They have extremely high metabolic rates - die within minutes without oxygen

In stroke - oxygen deprivation cause (motor neuron death in the brain cortex) hence, limb paralysis seen in stroke patients

Front 17

General Structure of Neurons #1

Back 17

A typical neuron has four morphologically distinct parts: neuronal cell body (perikaryon or soma), dendrites, axons, presynaptic terminal

The cell body contains the usual complement of organelles except centrioles

They have highly developed clusters of RER and ribosomes, termed Nissl bodies, synthesise the cells proteins and membrane components

Front 18

General Structure of Neurons #2

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During embryonic development, outgrowth of axons occurs at specific points on the cell body

In the CNS, most neuron cell bodies are located in nuclei - for example the Dorsal-Motor nucleus

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General Structure of Neurons #3

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The cell body and processes are supported by a cytoskeleton comprised of:

Actin filaments (microfilaments)

Neurofilament proteins - 3 type

Microtubules - regulate axon growth during development and also provide a track for axonal transport

Front 20

General Structure of Neurons #4

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Neurotransmission occurs in one direction - away from the cell body towards the axon presynaptic terminal

Movement of substances and organelles such as mitochondria can occur in both directions - retrograde and anterograde axonal transport

Front 21

Dendrites & Axons

Back 21

Cell bodies of neurons extend two types of processes:

Dendrites - short thin slender processes, information is received here from other neurons

Axons - each neuron has one axon, a tabular process, that generates and transmits nerve impulses - diameter ranges from 0.2 - 20 micrometer) - axons can be extremely long e.g. motor neurons

Front 22

Neuroglia (Glial Cells)

Back 22

In the CNS, there are 4 types: astrocytes, oligodendrocytes, microglia and ependymal cells

In the PNS, there are 2 types: Schwann cells and satellite cells

Front 23

Function of Glial Cells

Back 23

Generally provide support for neurons

Astrocytes have numerous processes that cling to neurons and synapses - holding them in place

Control chemical environment around neurons, for example clearance of glutamate neurotransmitters by astrocytes in the CNS

Front 24

Learning Objective

Back 24

Explain how the neuronal resting membrane potential is established and maintained

Front 25

Electrical signalling in neurons

Back 25

Neurons are electrically excitable cells

They use two types of eletrical signals to communicate