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Nervous system
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What is the Nervous System?
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“A complex network of nerve cells and fibres that transmit messages to and
from the brain and spinal cord to various parts of the body”
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Allows body to react to its environment
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Receives and interprets internal and external stimuli
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Basic functions:
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Sensation – Perception of changes/events occurring inside and outside the
body Such changes are known as stimuli, Cells that monitor them are
receptor
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Reaction - Motor response
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Structure and Function:
Divided into two main parts:
Central Nervous System (CNS) –
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Brain
Spinal cord

Peripheral Nervous System (PNS) –
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Cranial nerves
Spinal nerves
Autonomic nerves

Components of the Nervous System:

Nervous Tissue:
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Controls & coordinates activities of the body
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Specialised elongated cells that transmit electrical impulses from one end to
another
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Dendrites -conduct nerve impulses toward the body
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Myelin Sheath –coats the axon, allows nerve impulses to travel faster
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Neurilemma - sheath of connective tissue which surrounds the whole axon
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Epineurium – outer connective tissue which surrounds whole nerve
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What do nerve endings do?
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Located at end of the axon
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At end of each nerve fibre is a specialised nerve ending
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Bi - polar – one axon and one dendrite (Interneuron) number 1
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Pyrimidal cell number 4
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Intercalated neurone:
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Lies between a sensory neurone and a motor neurone
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Ganglion – collection of cell bodies
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By altering the relationship between; negative charge of the cell contents,
positive charge of the cell membrane
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Causes exchange of ions between the inside and the outside of the neuron
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Na+ move in, K+ outwards across the neuron cell membrane =
Depolarization
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An impulse is transmitted to another neuron
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Nerve fibre must recover before it is able to conduct another impulse
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Recovery time = a few thousandths of a second
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The effects of the nervous system depend on:
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Number of nerve impulses transmitted per second
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Type of neuron stimulated; Some have an excitatory effect and Others have
an inhibitory effect
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Synapse = microscopic gap between one neuron to another
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The Synapse:
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The synapse consists of a swelling containing a chemical transmitter
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Others include: Noradrenaline and Adrenaline
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The chemicals either: Conduct the impulse across the synaptic ending to the
next neuron
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Presence of calcium ions is essential for transmission of nerve impulses
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What are the components of a coordinated nerve pathway?
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Stimulus; Any change inside or outside the body
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For example: Sight, Touch, Pain and Change in BP or
pH
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The stimulus provokes a
change in behaviour
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Coordinators; Brain and spinal cord (CNS) receive info in the form of nerve
impulses from receptors
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Effectors; Muscles and glands produce a response e
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contraction or
secretion
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Somatic and Visceral systems:

Visceral sensory and motor nerves:
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Associated with the visceral body systems respiratory and digestive
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Impulses transmitted by visceral motor nerves from CNS to smooth muscle
and glandular tissue, where they initiate a response
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Stimuli carried by the somatic sensory nerves towards CNS
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The Central Nervous System
Development of the CNS:
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Within the embryo the CNS develops as a hollow neural tube
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As it develops peripheral nerve fibres grow out laterally
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Anterior end becomes the brain
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The brain is made up of:
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Forebrain - cerebrum, thalamus, hypothalamus and associated structures
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Hindbrain – cerebellum, pons and medulla oblongata
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Right and left cerebral hemispheres
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They are linked by a tract of white matter known as the corpus callosum
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Damage to the forebrain can cause personality change
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The surface of the cerebrum
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the cell bodies lying deep inside the brain tissue
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Gyri (up folds)
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Fissures (deep crevices)
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The Tissue of the Cerebral Hemispheres:

Thalamus, hypothalamus and pituitary:
Frontal:
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The centre of voluntary movement
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Contains areas for the control of fine and complicated muscle movements
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Parietal:
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Collects, recognises and organises sensations of pain, touch, temperature,
position and movement

Occipital:
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Contains the centres for awareness and correlation of auditory stimuli
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Temporal:
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The posterior part of each hemisphere
Involves visual perception and visual memory

Has a role in eye movement:
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Frontal - motor functions
Parietal - receives & interprets information
Temporal - hearing & smell
Occipital - eyesight

Ganglia:
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Deeper in the brain
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Groups of grey matter = ganglia or nuclei
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Sagittal section of the Brain:
Thalamus:
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Found deep within the tissue of the forebrain at the base of the cerebral
hemispheres
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The Epithalamus holds the pineal body – involved in the regulation of gonad
hormones
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g
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Helps control the ANS affecting sweating, shivering, vasodilaton and
vasoconstriction
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The regulation of body temperature
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Midbrain:
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Short length of brain between fore & hindbrain
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Contains
centres for control of muscle, sight, hearing and balance
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Damage results in coma
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Divided in to 2 hemispheres
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Receives info from semicircular
canals of inner ear and muscle tissue
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Fine adjustments are made by the cerebellum
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Forms a bridge of nerve fibres between cerebellar hemispheres
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The Medulla Oblongata:
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Extends from the pons to where the spinal cord passes through the foramen
magnum of the skull
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Contains the centres responsible for control of HR, respiration and BP
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The Spinal Cord:
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Extends from medulla oblongata
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Narrows and breaks up into a group of spinal nerves forming the cauda
equina
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Protection of the CNS:
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Skull – cranial bones strong, support
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Ventricular system
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The Ventricular system:
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Derived from hollow neural tube of the embryo
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A central canal runs along the entire length of spinal cord
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Cerebral aqueduct; midbrain
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Lateral ventricles (two); come from the third, ventricle, one inside each,
cerebral hemisphere
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Clear fluid, resembles plasma but no protein
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Circulates in the ventricular system and bathes outer surface of CNS in the
subarachnoid space
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Provides
antibacterial effect
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Cross section through the Cerebral Hemispheres to show the Meninges:
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Dura mater:
Tough fibrous layer
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In the veretebral canal there is a space between the dura mater and the
surrounding vertebra: the epidural space
The epidural space is used as site for anaesthesia
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More delicate and cushions the CNS
It helps the diffusion of oxygen and nutrients into the nervous tissue
Between the dura mater and the arachnoid mater is the subdural space
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The subarachnoid space is filled with cerebrospinal fluid
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Contains small blood capillaries, which supply the underlying nervous tissue
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Neuroglial cells surround blood capillaries
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Protect brain from harmful substances or substances not needed by brain
urea, certain proteins and antibiotics
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The action of general anaesthetic agents relies on their ability to pass through
the blood – brain barrier and affect the neurons in the brain
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Peripheral Nervous System and Autonomic Nervous System
Consists of all nerves given off from CNS
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Spinal nerves – leaving the spinal cord
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Cranial Nerves: Ventral surface of the Canine Brain:
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12 pairs
They leave the brain via foramina in the skull
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Some supply structures some distance from the point at which they leave the
brain e
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the vagus nerve (X) is the longest in the body
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Referred to by their name and a Roman numeral
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Nerves leave vertebral canal by the intervertebral foramina, one to the left and
one to the right
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Spinal nerves supply whole musculoskeletal system
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Supply the nerves to the limbs
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Contains
cerebrospinal fluid
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It consists of the cell bodies of the neurons and non-myelinated nerves
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White matter; Surrounds the grey matter
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The nerve fibres are in organised tracts running
towards the brain and away from the brain
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Does not have to be learned
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Involves only nerve pathways in spinal cord, using appropriate spinal nerve
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Pedal
Palpebral
Panniculus
Patella
Anal
Pupillary light response

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Sensory nerves carry nerve impulses received by sensory receptors in
organs
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Polysynaptic Reflex Arcs:
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Involve at least one intercalated neuron in the pathway
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g
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The paw is pinched
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A motor impulse is sent to the muscles of the leg
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A Severed Spinal Cord:
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A reflex is unconscious
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However, if an animal bites/yelps, indicates that it has felt pain
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This conscious response indicates the spinal cord is intact
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Considered to be a visceral motor system
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Control is unconscious = involuntary
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Prepares body for stress or excitement
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↑metabolic rate
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↑ rate and depth of respiration to ↑ amount of oxygen to the tissues
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Prepares body for stress or excitement
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↑metabolic rate
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↑ rate and depth of respiration to ↑ amount of oxygen to the tissues

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