The document discusses anatomy and physiology of the skin, ear, eye, and nervous system. It provides details on the layers of the skin, structures of the ear including common conditions like aural hematomas, important eye structures and how vision works, parts of the brain and spinal cord, and overview of the central and peripheral nervous systems.

1. THE NERVOUS
SYSTEM
Veterinary Physiology

2. The Skin
The skin is the largest organ in the body and performs regulatory functions, such as thermoregulation,
as well as providing protection against:
• Surface wear and tear
• Invasion against microorganisms
• Drying out of the body (desiccation)
The skin has three distinct layers…
1. Epidermis
2. Dermis
3. Hypodermis
Throughout the epidermis and dermis layers there
are hair follicles and oil and sweat glands.

3. The Epidermis
The epidermis is the ‘tough’ outer layer,
composed of stratified squamous epithelium.
Epidermis Cells
• Karatinocytes: produce keratin. Keratin is
tough, fibrous and waterproof giving the skin
its strength and resiliency
• Melanocytes: produces the skins
pigment/colour
• Merkel Cells: associated with the sensory
organs
• Langerhans Cells: these cells are macrophage
specific to the epidermis and are involved in
the immune response

4. Dermis
This is the second, deeper layer of the skin. It is highly fibrous and composed of…
• Dense connective tissue
• Collagen
• Elastin fibres
• Hair follicles
• Nerve endings
• Sebaceous and sweat glands
• Smooth muscles
• Blood vessels to bring nutrients and remove waste
• Nerves and sensory nerves to feel touch and pain
This helps support the skin and binds the epidermis to underlying tissues.

5. Hypodermis
• Composed of loose connective tissue and adipose tissue
• It is a thermoinsulator and mechanical shock absorber
• It is rich in adipose cells, blood and lymphatic vessels and nerves
• A reservoir for fluids, electrolytes and energy
• Without this layer, the skin would be at risk of tearing as it moves over bone and muscle

6. Pruritus – the Atopic Dog
Pruritus is an unpleasant sensation of the skin, provoking the desire to itch – it is often
caused by a parasitic infestation or allergic reactions.
Atopic means hypersensitivity to environmental allergies that have either been inhaled or in
contact with the skin.
Canine Atopic Dermatitis
This is a common pruritic skin disease, typically seen in young dogs. Commonly, it affects
the face, ears, feet, ventrum or perineum.
Usually, such cases result in otitis externa (discussed later)
and secondary bacterial and yeast infections.

7. The Ear
Malleus
(hammer)
Incus (anvil)
Staples (stirrup)
(Organ of
Corti)
(Tympanic
Membrane)

8. How Does an Animal Hear?
Sound waves are channelled towards the auditory canal
by the pinnae
The waves pass through the tympanic membrane and across
the middle ear via the auditory ossicles
The waves, now in the inner ear, move through the
endolymph in the cochlea to be detected by the organ of
Corti
The sensory hairs in the organ of Corti react to different
frequencies, dictating the nerve impulses sent to the brain
The nerve impulses are sent via the auditory nerve to the
temporal lobe in the brain for translation as sound

9. Aural Haematoma
Cause Pathogenesis Treatment
This is commonly seen in dogs and
is secondary to trauma or head
shaking due to otitis.
• The skin and cartilage separate
• The cartilage layers separate
• The perichondrium and cartilage
separate
Vessels rupture and bleed until
pressure builds up, ceasing
haemorrhage. Cartilage around the
haematoma degenerates and
granulation tissue fills the defects.
The pinna thickens and distorts in
shape during healing.
• Aspiration  inserting a syringe
to draw out all of the fluid
• Lancing
• Surgery

10. Ear Disease
Ear disease is classed as a skin disease! Otitis is any inflammation of the ear canal and becomes
chronic when the primary cause cannot be identified. Otitis can be externa, media, interna – it
usually starts as otitis externa then tracks down into otitis media then otitis interna.
Primary Causes
• Foreign Body
• Fungal Disease
• Parasites
Predisposing Factors
• Conformation
• Moisture
• Over Grooming
• Systemic Disease
• Obstructions
• Breed – bassets, spaniels, shar-
peis
Perpetuating Factors
• Bacterial infection
• Fungal infection
• Chronic inflammation
• Middle ear infection

11. Ear Disease - Pathogenesis
Otitis initially starts with the inflammation of the auditory canal, followed by hyperplasia of the
epidermis and ceruminous glands.This leads to excess production of cerumen (ear wax) and
accumulation of discharge.This has created a favourable environment for commensal
organisms, Malassezia and Staphylococcus so ulcers occur resulting in a secondary bacterial
infection.The diameter of the ear canal then decreases so the skin and cartilage ossify,
rupturing the tympanic membrane (ear drum).
It is diagnosed mainly by conducting an otoscopic exam but checking for parasites, diagnostic
imaging and cytology are also very helpful.

12. Ear Disease
Otitis Externa Clinical Signs Otitis Media & Interna Clinical
Signs
• Head shaking
• Ear scratching
• Malodour
• Crusting
• Pain
• Aural heamatoma
• Stenosis
• Scaling
• Exudation
• Deafness
• Pain on opening mouth
• Head tilt
• Vomiting
• Facial nerve damage
• Ruptured ear drum
• Vestibular defects
• Tonsillitis
• Discharge
Treatment:
• Allergy trials
• Cleansing solutions
• Ear flushing
• Systemic medication
• Topical medication
• Client education
• Surgery:
- Lateral Wall Resection  improves ear canal
drainage
- Total Ear Canal Ablation  Excises the entire
ear canal

13. Neonatal Hearing
Neonates are born deaf as their ears are sealed (so are their eyes) so they rely on vibration and
scent but are able to balance.Their ear canal opens around 2-4 weeks of age so it as at this stage
they begin to recognise sounds.
Congenital Deafness
Congenital deafness can either be acquired or inherited. It is common amongst certain breeds
such as BullTerriers, Dalmatians, Cocker Spaniels, white cats with blue eyes, merle and spotted
coats.
It can often go undetected until the animal is older as neonates use other sensory cues to aid
with feeding, elimination and locomotion.The best outcome for dogs suffering from congenital
deafness is client counselling and education. Although, the Dalmatian Club of America has an
official petition calling for the euthanasia of deaf puppies.

14. The Eye Pupil
Upper Eyelid
Iris
Limbus
Medial Canthus
Third EyelidConjunctiva
Lower
Eyelid
Lateral
Canthus

15. The Eye

16. The Eye – Important Structures
• Orbit
• Eyelids
• Conjunctiva
• Lacrimal System
• The Globe

17. Important Structures
The Orbit Eyelids Conjunctiva
• Bony fossa
• Separates eye from cranial skull
cavity
• Important for protection of they
eye and provides attachment
• Contains:
Eye, Extraocular Muscles,Optic
Nerve, Lacrimal Gland
• Dorsal and ventral folds of skin
lined with the palpebral
conjunctiva
• Meet at the lateral and medial
canthus, rest against the ocular
surface
• Cilia close to eyelid margin
• Third eyelid: nictitating membrane
and gland, aqueous portion of tear
film
• Lacrimal gland: aqueous portion of
tear film
• Meibomian glands: liquid part of
tear film
• Mucous membrane
• Lines eyelids and sclera
• Palpebral, bulbar, nictitans
• Contains:
Goblet cells, lymphoid tissue,
connective tissue, blood vessels
and nerves
• Prevents corneal desiccation
• Increases eyelid mobility
• Acts as a protective barrier

18. Lacrimal System The Globe Cornea Sclera
• Tears needed for it to be
able to function properly
• pH 6.8-8
• Maintains optimal
surface
• Removes any foreign
bodies
• Antibacterial
• Lets oxygen and
nutrients pass
• Drained into
nasolacrimal duct
• Blinking spreads the film
• Skin can become stained
if not functioning
correctly (epiphora –
typically seen in white
dogs)
• Outer:
Cornea and sclera to
support and maintain
shape. Clear to assist
with passage of light
• Middle:
Uvea to provide nutrition
and modify entering light
• Inner:
Retina and optic nerve to
converse the light
impulse to electrical
impulses for processing
• Clear
• Avascular
• Eye’s outermost lens
• Functions like a window
that controls and focuses
the entry of light into the
eye
• Thick fibrous outer layer
• Joins cornea at the
limbus
• Contains blood vessels
• Appears white in colour

19. The UvealTract
Iris Ciliary Body Choroid
• Visible coloured layer
• Hole in the centre – the pupil
• Movement of iris controls light
quality entering the eye
• Iris muscles circle the pupil in the
dog and criss-cross above and
below in the cat
• Sometimes pupil size can be
uneven (aniscoria)
• Located behind the iris between
the lens and the choroid
• Secretes aqueous humour which
flows from the posterior chamber
to the anterior chamber, causing
intraocular pressure
• Raise pressure = glaucoma
• Lowered pressure = hypotony
• Lies between the sclera and retina
• Contains a mirror like layer
responsible for the shine seen from
cats and dogs eyes
• Assists in re-stimulating the retinal
photoreceptors when light is
reflected back from it
• Increases visual sensitivity with low
light vision

20. The Lens The Retina
• Biconcave structure
• Avascular
• No pigments so light can enter
• Central portion of the lens is termed
the nucleus
• Hardening of portion seen in older
animals is known as nuclear sclerosis
• Inner most layer at the back of the
eye
• Contains the photoreceptor cells:
Rods – function in dim light, animals
have a large amount of these
Cones – function in bright light,
animals only have some colour
detection

21. Formation of an Image
The pupil allows entrance of light into the eye. Inside the glove, there are 3 chambers filled with
jelly like substances:
• Anterior Chamber
- Aqueous Humour
• Posterior Chamber
- Aqueous Humour
• Vitreous Chamber
-Vitreous Chamber
Functions
• Provide nutrients
• Remove waste products
• Maintain shape and maintain pressure of
globe to allow persistent light refraction

22. How do Animals See?
The amount of light that is allowed into the eye is determined by the size of the pupil which is
controlled by muscles of the iris.
Creation of an Image
• Light enters the eye and travels through the transparent cornea, through the aqueous and
vitreous humours then through the lens
• The lens changes shape by contraction or relaxation of the muscular ciliary body
• Light stimulates photoreceptors in the retina so impulses are sent along the optic nerve.There
are two types of photoreceptor: rods (white and black vision) and cones (colour vision). In dogs
and cats, only a few cones are present, it is mainly rods. So, they have dichromatic vision and
can struggle to distinguish between subtle shade differences.
• The optic nerve from each eye crosses at the optic chiasm and enters the cerebral cortex via the
midbrain

23. HumanVs. CatVision

24. SpeciesAdaptations
• Location of the eyes
• Field of vision
• Colour perception

25. Corneal Ulcers
REMEMBER: it is the outer portion of the globe that is clear, avascular and acts as the eyes
outermost lens.
The cornea consists of…
• Superficial epithelium
• Basement membrane (Bowman’s layer)
• Stroma
• Descemet’s membrane
• Endothelium

26. Corneal Ulcers
An ulcer occurs when there is inflammation of the cornea (keratitis). It can be the result of…
• Self trauma
• Foreign body
• Chemical irritation
• Scratches from another animal
• Plants, thorns, bushes
Clinical Signs
• Squinty eyes
• Hypersensitivity
• Rubbing the eye
• The eye can actually appear normal!
Diagnosis can be made through fluorescein
staining.The cornea should allow the liquid
to run off the eye but trauma causes an
indentation and disrupts the cells so the stain
sticks.The ulcer can then be seen.

27. Corneal Ulcers
Sometimes treatment is not needed as the ulcer can heal on its own but it is dependent on the
severity. It is most important to control the initiating factor and reduce inflammation and pain,
usually through antibiotics.The patient will likely need buster collar too!
Complications can occur and this include:
• Complicated ulcer
• Melting ulcer
• Indolent ulcer
The ulcer may only cause minor changes in vision…
• Entry of light disrupted
• Focussing power altered
• Blurry image

28. Hyperthyroidism & Secondary Retinal
Detachment
Hyperthyroidism is when the thyroid gland produces too much of the thyroid hormone thereby
increasing the metabolic rate of the animal. In turn, this increases the heart rate which could
lead to hypertension (high blood pressure). Should the blood pressure become too high, the
retina could haemorrhage or detach, possibly living the animal blind.

29. Proptosis
Proptosis is the acute prolapse of the eye as a result of trauma – it is most common in
exophthalmic breeds, especially hamsters, but can be seen commonly in cats following a RTA for
example. It is a medical emergency:Traction on optic nerve and fractures of the orbit and jaw can
occur secondary, as well as the eyelids behind the globe going into spasm. It is also important to
keep the eye lubricated. It needs replacing if possible asap and if this is not an option, they eye
would have to be removed (enucleation).
What is affected when the eye prolapses?
• Medial, lateral, dorsal and ventral rectus muscles
• Retractor oculi muscle
• Dorsal and ventral oblique muscles

30. Proptosis
Risks?
• The eye itself may be severely damaged
• The structures surrounding the eye may be damaged (orbit, surrounding bone, eyelids,
lacrimal apparatus)
• Palpebral muscles (muscles of the eyelid) may be damaged
• 80% of animals with proptosis may lose sight
or ability to keep the eye in normal position

31. Entropion
Entropion is the abnormality of the position of the eyelid (inversion of the eyelids), commonly
due to loose skin. It is a painful condition which particularly Shar-Pei dogs are predisposed to.
To rectify this, the Holtz-Celsus procedure is carried out – this consists of the eyelids being
everted and stitched down then a small area of tissue being removed to pull the eyelid out and
open.

32. The Nervous System
The Central Nervous System (CNS)
• Brain
• Spinal Cord
The Peripheral Nervous System
• Cranial Nerves
• Spinal Nerves
Sensory System
Somatic Motor System
Autonomic System

33. The Brain
Cerebellum, pons,
medulla oblongata
Cerebrum, olfactory
bulbs, hypothalamus,
thalamus The brain controls and
coordinates and is protected by
the skull.
The cerebral hemisphere is divides
into lobes…
• Occipital
• Parietal
• Frontal
• Temporal
• Olfactory

34. Part of the Brain Location Function
Thalamus Deep within the posterior part of the
forebrain
Processing information from the sense
organs and relaying this to the cerebral
cortex
Hypothalamus Ventral to the thalamus Links nervous and endocrine system as it
secretes hormones. Influences the
control of the autonomic nervous system
by controlling a range of involuntary
actions.
Huge role in homeostasis! Regulates
body temperature, hunger, thirst and
osmotic balance of bodily fluids.
Midbrain Lies between the fore and hindbrain.
Overhung by cerebral hemispheres
Pathway for fibres running from hind to
forebrain. Carries sense of hearing and
sight
Cerebellum Dorsal surface of hindbrain Controls balance and coordination –
divided into outer cortex (grey matter)
and inner layer (white matter)
Pons Ventral to the cerebellum Contains centres that control respiration
Medulla Oblongata Extends from the pons Contains centres for respiration and
blood pressure

35. The Spinal Cord

36. Cranial Nerves
There are 12 pairs of cranial nerves.
An easy way to remember them is…
OLd
OPie
OCcasionally
Tries
TRIGonometry
And
Feels
VEry
GLOomy
VAGue
And
HYPOactive

37. Spinal Nerves
The pectoral limb (forelimb) is supplied by the brachial plexus.
Nerves in the forelimb…
• Radial Nerve  Supplies extensors of the elbow, carpal and digital joints
• Median Nerve  Innervates flexors of the paw
• Ulnar Nerve  Innervates flexors of the paw
The pelvic limb (hindlimb) is supplied by the lumbosacral plexus.
Nerves in the hindlimb…
• Femoral Nerve  innervates the quadriceps muscle and is therefore the extensor of the stifle
and flexor of the hip
• Sciatic Nerve  supplies innervation to the hamstring group

38. Intervertebral Disc Disease (IVDD)
15% of disc prolapses occur in the cervical segment of the spine with the most common clinical
sign being neck pain.
The remaining 85% occur in the thoracolumbar region and the clinical signs are usually ataxia
and pelvic limb paresis (weakness).
Disc disease can be classified…
• HansenType 1  Extrusion
• HansenType 2  Protrusion
In general, a prolapsed disc results in either compression or concussion of the spinal cord.

39. The Anatomy of a Normal Disc
Gel like, acts as a
shock absorber
Intervertebral discs form
cartilaginous joints between
the vertebrae

40. Classifying Disc Disease:Type 1, Extrusion
An analogy to help us understand the meaning of extrusion and protrusion is by comparing the
disc to a jam doughnut!
If we were to stand on a jam doughnut, the jam explodes out. In terms of the intervertebral disc,
the jam would be the nucleus pulposus extruding through the annulus fibrosus into the spinal
cord. It is common in chondrodystrophic breeds such as Daschunds or Bassett Hounds.
Clinical Signs…
• Non ambulatory
• Pelvic limb para paresis
• Poor proprioception
• Absent or abnormal withdrawal reflexes
• Absence of deep pain perception

41. Classifying Disc Disease:Type 2, Protrusion
Pressing down on the jam doughnut with the palm of our hand lightly does not create enough
pressure for the jam to come out. However, it does mean that the doughnuts circumference
expands. In terms of the intervertebral disc, this means that as the nucleus pulposus degenerates,
the annulus fibrosis protrudes so the disc bulges. It is common in larger breeds of dogs, such as
GSDs.
Clinical Signs…
• Yelping in pain
• Reluctance to jump or climb
• Low head carriage and arched back
• Reluctance to move head and neck
• Restlessness and panting

42. IVDDTreatment
Diagnosis of IVDD is made through obtaining a clinical history and diagnostic imaging (x-ray,
MRI, CT).
Mild cases can be medically managed using good analgesia such as NSAIDs, opioids and/or
muscle relaxants or acupuncture.Whichever route is taken, strict rest is key!!
For more moderate and severe cases, surgical intervention may likely be necessary.The surgery
carried out can either be:
• Ventral Slot  opening created ventrally through the IVD and vertebral endplates
• Hemilaminectomy  removal of one half of the vertebral arch
• Dorsal Laminectomy

43. Nursing a PatientWith IVDD
• Padded bed to reduce the risk of pressure sores
• Sternal recumbency for good bilateral lung expansion
• Offer food and water little and often and place bowls close to patient
• Assist with urination and defaecation, could place urinary catheter or express bladder
• Keep bedding clean to avoid urinary/faecal scolding
• Environmental enrichment (e.g. play music, toys, put patient in busy area of the ward)
• Analgesia under theVS’ instructions
• Turn every 2-4 hours if in lateral recumbency
• Physiotherapy – massage, warm package joints
• Grooming, owner visits

44. Obturator Nerve Paralysis
This nerve originates from the lumbosacral plexus and leaves the pelvic cavity through the
obturator foramen. It sits very close to the medial aspect of the shaft of the ilium, supplying
motor innervation to the adductor muscles of the hind limb.
The nerve is likely to be damaged during parturition, as it passes along the inside of the bovine
pelvis.Therefore, prolonged or excessive traction on the calf can in turn put pressure on this
nerve, damaging it.
Clinical Signs
• Wide base stance
• Recumbency
• Hind limbs extended forward
Treatment
• If spotted early enough, the cow should be moved to
prevent complications involving the adductor muscles
• Good footing
• Shackle hind limbs
• Deep bed
• Analgesia
• Food/water near patient

45. Performing a Neurological Examination
Neurological examinations are commonly undertaken for investigation into abnormal gait.To
begin with, assessment of the animal’s behaviour and visual clues can be indicators of where the
issues lie.
Individual limbs need to be assessed and can be done by flexing and extending the limb to
determine how the muscles respond to manipulation, the tone of the muscles and the
symmetry of the muscles.
The next stage of the tests is dynamic testing and this is broken down into three phases…
• Proprioception
• Local Reflexes
• Sensation

46. Proprioception –The 6 BasicTests
• Knuckling
• Paper SlideTest
• Placing
• Hopping
• Wheelbarrowing
• Extensor PosturalThrust

47. Proprioception
Test Knuckling Paper SlideTest Placing
Normal The animal will sense the
foot is in the wrong
position and reposition is
instantly
The animal will return their
leg to the normal position
The animal should see or
feel the table is there and
bring their front paws up
and place them on the
table
Abnormal The paw will remain in that
position
The leg goes beyond 10
degrees from the vertical
and the dog is unaware
Limbs are not placed

48. Proprioception
Test Hopping Wheelbarrowing Extensor PosturalThrust
Normal Senses when to hop Moves forward evenly on
both forelimbs
As the animal approaches
the ground, they should
extend their hind limbs and
take a couple of steps back
upon landing
Abnormal Does not hop, the leg may
drag
May stumble or knuckle
over as they walk
Hind limbs don’t extend, no
steps are taken

49. Local Reflexes
Test Myotatic Reflex – Patellar Reflex Withdrawal Reflex – Pedal Reflex
HowTo Gently percuss (tap) the patellar
ligament
Pinching in-between digits, usually
hindlimb
Normal Involuntary contraction of the
quadriceps muscle group causing
reflex extension of the stifle
Flexion or withdrawal of the limb
Abnormal Absence of the reflex Limb is not withdrawn. Absence of
deep pain sensation

50. Physiology of the PedalWithdrawal Reflex
A reflex arc is a fixed response to stimuli which is a rapid and automatic response done
unconsciously. It uses only nerve pathways in the spinal cord. Examples include: pedal, anal,
patellar, panniculus, palpebral.
The pedal reflex arc is a polysynaptic reflex. Pain stimuli aggravates nociceptors (sensory nerve
fibres) in the skin of the foot.These fibres then form excitatory synapses with interneurons in the
spinal cord.The impulse is therefore transmitted from nociceptors, through interneurons and to
motor neurons.The motor neurons cause rapid contraction of relevant muscles to retract the
legs but inhibitory neurons prevent antagonistic muscles.
This can be used during anaesthesia to evaluate the depth of the GA.

51. Sensation
Panniculus Reflex
This is tested by a quick pin prick or gently running artery forceps in the
thoracolumbar area. Normally, this will result in a quick twitch of the subcutaneous
muscle along the back.

52. Neurological Examination: the Cranial Nerves
Nerve Function How toTest Normal Abnormal
Olfactory Smell Ability to find food or
react to non-irritating
chemicals
Will find food or have
a negative reaction
Unable to find food or
doesn’t respond to
chemical
Optic Vision Tracking: drop a
cotton wool ball and
the animal should
watch it fall
Menace: make a
threatening gesture
towards each eye to
stimulate a blink
Pupillary Light
Reflex: shine a bright
focal light, the pupil
should constrict
Should follow the
cotton wool.
Blink reflex should be
present – wont work in
rabbits or animals
under 3 months. Make
sure to not waft air
into the eye
Both pupils should
constrict (indirect
response)
Dysfunction of the
optic nerve will cause
lack of vision and a
decreased pupillary
light reflex on the
affected side

53. Nerve Function How toTest Normal Abnormal
Oculomotor Eye Movements –
innervates the
constrictor muscles
of the pupils
Pupillary Light Reflex
Observation of the
eyes position
Both pupils should
constrict
Lack of pupillary light
reflex because of lack
of innervation to the
constrictor muscles
to the pupils
Trochlear Eye Movements Observation of the
eyes position
Eye looks straight
forward
Eye doesn’t look
straight forward, in
an abnormal position
Abducent Eye Movement Observation of the
eyes position
Eye deviation
Vestibulocochlear Hearing and Balance See animals
response to a loud
noise
A loud noise evokes a
response
No response evoked

54. Nerve Function How toTest Normal Abnormal
Trigeminal Facial Sensation
Supplies the
masticatory
muscles/jaw muscle
tone and movement
Facial Sensation:
Touch the philtrum of
the nose with a pen
and the dog should
turn their head away
Palpebral: gently
touch the medial and
lateral canthus of the
eye, should blink
JawTone: palpate
masticatory muscles
Move their head away
Blink reflex
Good jaw tone
No response to facial
sensation
Reduced jaw tone and
maybe atrophy of the
muscles of mastication
Facial Innervate muscles of
facial expression
Blink
Symmetry of the face
Perform menace
response and
palpebral reflex to see
if the animal can blink
Normal symmetry and
good blink reflex
Asymmetry, inability
to blink

55. Nerve Function How to Test Normal Abnormal
Glossopharyngeal Swallowing (gag
reflex)
Stimulate the back of
the throat – can
externally pinch just
above the larynx (only
if dog isn’t aggressive!)
Gag reflex is
stimulated
Gag reflex is not
stimulated
Vagus Laryngeal Function
(bark)
See if the dog can bark
normally!
Can’t bark, abnormal
noises
Accessory Neck Position &
Musculature
Palpate the muscles of
the neck
Weakness and atrophy
of the muscles
Hypoglossal Tongue Movement &
Position
Observe tongue for
muscular control when
lapping water and
licking
Good use of the
tongue, can lap water
efficiently
The tongue may
deviate from its
normal position (hang
out the side of the
mouth for example)

56. Peripheral Nervous System - Divisions
Peripheral Nervous System
Sensory System Autonomic SystemSomatic Motor System
Transmits information
to the CNS
Parasympathetic and
sympathetic divisions
which control glands,
heart and smooth
muscles
Controls Skeletal
Muscles

57. Autonomic Nervous System
This nervous system supplies the cardiac muscle, smooth muscle and glandular tissue and can
be divided into:
• Parasympathetic – rest & digest
• Sympathetic – fight or flight
Nerves for the parasympathetic system arise from the brain and sacral region.
Nerves for the sympathetic system arise from the thoracolumbar region

58. Neuron
Direction of impulse

59. How a Nerve Impulse isTransmitted
The nerve impulse begins in the dendrites and moves to the Dendron into the cell body.The
impulse leaves via the axon hillock, down the axon and once it reaches the axon terminals
stimulates calcium channels to open.Vesicles have already begun to drift towards the presynaptic
membrane and the calcium stimulates the release of neurotransmitters so acetylcholine is
released into the synaptic cleft.The acetylcholine molecules combine with the post synaptic
membrane, exciting the membrane so nerve impulses can be transmitted across the gap. Once at
the postsynaptic membrane, cholinesterase is released.

60. Seizuring
Seizuring is caused by paroxysmal discharges from groups of neurons, which arise as a
result of excessive excitation or loss of inhibition.
3 Stages of Seizuring
1. Pre Ictal
2. Ictal
3. Post Ictal

61. Seizuring
Seizure Classification:
• Intracranial  structural/functional (brain tumour, idiopathic epilepsy)
• Extracranial  reactive (toxins, metabolic disorders, infectious diseases)
o Generalised (‘grand mal’) Seizure)  a seizure affecting the entire body, electrical activity
affecting all/most of the brain, a loss of consciousness, tonic-clonic, mastication, salivation,
urination/defaecation, nystagmus
o Partial/Focal Seizure  a seizure affecting a single area of the body, electrical activity affects
one small part of the brain, no loss of consciousness, twitching, repetitive movement, possible
mastication, salivation

62. Major Spinal Nerves
Pectoral Limb Pelvic Limb
• Radial nerve
• Median nerve
• Ulnar nerve
• Supplied by nerves from the brachial plexus
• Formed from C6-C8 andT1-T2
• Femoral nerve
• Tibial nerve
• Saphenous nerve
• Sciatic nerve
• Supplied by nerves from the lumbosacral
plexus
• Formed from L3-L7 and S1-S2

63. Radial Nerve Paralysis
The radial nerve:
• Innervates extensor muscles of the elbow
• Innervates extensors of the carpus and digits
• Carries sensation from dorsal forepaw and proximal forelimb
Therefore, if the radial nerve is damaged, these functions cannot be carried out.
Clinical Signs
• Monoparesis (weakness of one limb)
• Knuckling
• Delayed or absent proprioception
• Cannot weight bear or extend forelimb
• Skin sensation of dorsal metacarpus and
phalanges reduced
• Muscle atrophy
• Proximal radial paralysis  elbow drops,
limb is usually dragged

64. Radial Nerve Paralysis
Causes
• Trauma, e.g. RTA
• Overstretching
• Prolonged recumbency in
heavy animals
• Fractures
• Nerve lesions
• Damage or inflammation to
the nerve prevents impulses
being sent through the motor
neurons to the muscle fibres
Treatment
• Physiotherapy
• Medication – NSAIDs
• Time
• Amputation if none of the above
work

65. Equine Post Anaesthesia Neuropathy
Pathophysiology
The ischaemic muscle starts to swell due
to capillary damage and fluid leakage,
increasing hydrostatic pressure.The
vessel collapses which affects other
muscle groups and the nervous tissues
also become hypoxic.
Prevention
• Proper positioning to minimise
pressure
• Sufficient padding
• Removal of head collars
• Symptomatic treatment