1. Neurology
VTT 235/245 Anatomy & Pathology

2. The Nervous System
 A complex communication and control
system.
 It monitors the animal’s internal and
external environments and directs
activities to maintain the well-being of
the body.

3. 2 Main Divisions
 Central Nervous System-
 Composed of the brain and spinal cord.
 Peripheral Nervous System-
 Consists of cord-like nerves that link the
CNS with the rest of the body.

4. Functions
 Sensory Functions-
 The nervous system senses changes from
inside/outside the body and conveys this
information to the spinal cord or brain.
 Integrating Functions-
 In the brain and spinal cord, the sensory
information is received, analyzed, stored,
and integrated to produce a response.

5. Functions…
 Motor Response Functions-
 Instructs the body to do something, such
as contract a muscle or cause a gland to
secrete its product(s).

6. Neurons & Supporting Cells

7. Neuroglia
 “Glial cells”, glia- greek for glue!
 Structurally and functionally supports
and protects neurons.
 Outnumbers neurons 10:1.
 Not directly involved in the transmission
of information or impulses.

8. Neurons
 Nerve cells.
 The basic functional
units of the nervous
system.
 Has a high
requirement for
oxygen.

9. Neuron Structure
 Central cell body- “stoma”
 Dendrites-
 Receive stimuli, or impulses, from other
neurons and conduct the stimulation to the
cell body.
 May also be modified into sensory
receptors that receive, or sense, stimuli
such as heat, cold, touch, pressure…
 Short, numerous, multi-branched
projections extending from the cell body.

10. Neuron Structure…
 Axons-
 Conduct nerve impulses away from the cell
body toward another neuron or effecter
cell.
 A cell that does something when stimulated.
 A single process can be very long.
 Often covered by a fatty substance called
myelin (white matter).

11. Neuron Structure…
 Myelin sheath-
 Actually cell membranes of specialized glial
cells called oligodendrocytes in the brain &
spinal cord, and Schwann cells in nerves
outside of the brain and spinal cord.
 These special glial cells are wrapped around
the axon.

12. Neuron Structure…
 Nodes of Ranvier-
 Small gaps in the
myelin sheath
between adjacent
glial cells.
 Works with the
myelin sheath to
enhance the speed of
conduction of nerve
impulses along the
axon.

13. Organization of the Nervous
System

15. CNS vs. PNS
 CNS- anatomically composed of the brain and
spinal cord.
 PNS- made up of components of the nervous
system that extend away from the CNS,
towards the periphery of the body.
 Cranial nerves- nerves of the PNS that
originate directly from the brain.
 Spinal Nerves- nerves of the PNS that
originate from the spinal cord.

16. Afferent vs. Efferent
 Afferent nerves-
 Conduct nerve impulses towards the CNS.
 Conducts sensations from the sensory
receptors in the skin and other locations in
the body to the CNS.
 Also called sensory nerves.

17. Afferent vs. Efferent…
 Efferent nerves-
 Conduct impulses from the CNS out toward
muscles and other organs.
 They cause skeletal muscle contractions
and movement.

18. Neuron Function

20. Resting State
 When a neuron is not being stimulated, it is in
a resting state.
 The cell membranes of neurons are
electronically polarized when at rest (like
tiny, charged batteries).
 Specially charged molecules located in the
neuron’s cell membrane pump sodium (Na+)
ions from inside the neuron to the outside.
 They also pump potassium (K+) ions from the
outside to the inside.

21. Resting State…
 This specialized molecule is called the
sodium-potassium pump.
 The action of the sodium-potassium
pump causes a higher concentration of
Na+ to accumulate outside the cell.
 The pump’s actions and the negative
charges inside the cell cause a higher
concentration of K+ to accumulate inside
the cell.

22. Resting State…
 This keeps the cellular membrane
between Na+ and K+ polarized.
 The distribution of positive and
negative charges creates a difference
in electrical charge across the
membrane.
 Inside the cell- negative
 This electrical difference in charges is
called the resting membrane potential.

23. Depolarization
 When an impulse from an adjoining neuron
stimulates another neuron, a set of specific
steps occurs, resulting in the nerve “firing” or
depolarizing.
 The Na+ channel opens and allows only Na+
ions to pass through it by passive diffusion
into the cell.
 Depolarization refers to this opening of the
Na+ channels and the sudden influx of many
Na+ ions.

24. Depolarization…
 The inside of the neuron goes from a
negative charge to a positive charge.
 The significant change in electrical
charge is also referred to as the action
potential.

25. Repolarization
 Within a fraction of a second, the Na+
channels snap shut, halting the influx.
 At the same time, potassium channels
open and only allow K+ ions to pass
through them.
 K+ ions passively diffuse out of the cell
by a concentration gradient and positive
cell charge.

26. Repolarization…
 The outflow of K+ ions continues until
the channels close a split-second after
they have opened.
 This causes the charge inside the cell to
swing back in the negative direction.
 The change of the cell’s charge back to
negative is called repolarization.

28. All-or-Nothing Principle
 Not every depolarization stimulus
results in a complete depolarization-
repolarization cycle.
 The initial stimulus must be sufficient
enough to make the neuron respond.
 When the stimulus is strong enough to
cause complete depolarization, it is said
to have reached the threshold.

29. All-or-Nothing Principle…
 Regardless of how strong the initial
stimulus was, if it was sufficient enough
to achieve threshold, the action
potential would be generated and
conducted along the entire length of
the neuron with a uniform strength.

30. All-or-Nothing Principle…
 This phenomenon is called the all-or-
nothing principle, because either the
neuron completes a depolarization to
the maximum strength, or it does not
depolarize at all.

31. Refractory Period
 If a second threshold stimulus arrives
at the dendrites while the Na+ channels
are open or while K+ molecules are
moving through their open channels, the
stimulus is incapable of a second
depolarization.

32. The Synapse
How Neurons Communicate

33. The Synapse…
 Once the action potential has been
successfully conducted to the end of the
axon, the nerve impulse must be transmitted
to the next neuron or to the cells of the
target organ or tissue.
 Because two neurons do not physically touch,
the depolarization wave is unable to continue
to the next neuron.
 Instead, the neuron must release a chemical
that stimulates the next neuron or cell.

34. The Synapse…
 This perpetuation is called a synaptic
transmission.
 The synapse is the junction between
two neurons or a neuron and a target
cell.
 The synapse consists of a physical gap
between the two cells called the
synaptic cleft.

35. The Synapse…
 Presynaptic neuron- the neuron
bringing the depolarization wave to the
synapse and releasing the chemical to
stimulate the next cell.
 Neurotransmitter- the chemical
released from the presynaptic neuron.
 Postsynaptic neuron- the neuron that
contains the receptors that receive the
neurotransmitter.

36. The Synapse…
 On the postsynaptic membrane are
specialized proteins called receptors.
 The neurotransmitter binds with these
receptors and trigger a change in the
postsynaptic cell.
 The postsynaptic membrane receptors
are very specific about which
neurotransmitters they will allow to
bind.

37. Neurotransmitters
 Can be classified
into 2 categories-
 Excitory- usually
causes an influx of
Na+ so that the
postsynaptic
membrane moves
toward the
threshold.
 Inhibitory- moves
the charge away from
the threshold.

38. Neurotransmitters…
 Acetylcholine-
 Excitory or inhibitory, depending on its
location in the body.
 Excitory- at the junction between somatic
motor neurons that stimulates muscle fibers to
contract.
 Inhibitory at the site where nerves synapse
with the heart and slows the heart rate.

39. Neurotransmitters…
 Catacholamines-
 Norepinepherine- associated with the “fight-or-
flight” reactions of the sympathetic nervous
system.
 Epinepherine- released primarily from the adrenal
medulla to participate in the “fight-or-flight”
response.
 Dopamine-
 Found in the brain.
 Involved in autonomic functions and muscle control.
 Low dopamine= Parkinson’s disease.

40. Neurotransmitters…
 GABA & Glycine-
 GABA- gamma-aminobutyric acid.
 GABA is found in the brain, glycine is found
in the spinal cord.

41. Neurotransmitters…
 One postsynaptic membrane may have
multiple types of presynaptic neurons
across the synaptic cleft.
 By having both, the nervous system can
selectively increase or decrease the
activity of specific parts of the brain or
spinal cord.

42. Stopping & Recycling
Neurotransmitters
 The body needs a way to stop the
neurotransmitter or the excitory or
inhibitory effect would continue.
 In the case of acetylcholine, it is
broken down into the enzyme
acetylcholinesterase.
 “-ase”- enzyme

43. Stopping Neurotransmitters
 If nothing breaks down
neurotransmitters, the effect
would continue indefinitely.
 Ex.- This is what happens with
organophosphate toxicity:
 The insecticide combines with
acetylcholinesterase and inactivates it.
 Overstimulation of acetylcholine receptors
results in vomiting, diarrhea, difficulty
breathing, and constricted pupils.

44. THE BRAIN
Cerebrum
Cerebellum
Diencephalon
Brainstem

45. The Brain

46. Cerebrum
 Made up of gray and white matter
fibers.
 The largest part of the brain.
 Responsible for higher-order behaviors:
 Learning
 Intelligence

47. Cerebrum…
 Receives and interprets sensory
information-
 Initiates nerve impulses to skeletal
muscles.
 Integrates neuron activity normally
associated with:
 Communication
 Emotional expression
 Memory

48. Cerebrum…
 The wrinkled appearance is due to folds called
gyri, separated by deep grooves called
fissures and more shallow grooves called sulci.
 The most prominent groove is the longitudinal
fissure which divides the cerebrum into the
right and left cerebral hemispheres.
 Each hemisphere is divided by sulci into lobes.
 Different lobes specialize in certain
functions.

49. Cerebellum
 Located caudal to the cerebrum.
 The second largest component of the
brain.
 Allows the body to have coordinated
movement:
 Balance
 Posture
 Complex reflexes

50. Diencephalon
 Serves as a nervous system passageway
between the primitive brainstem and
the cerebrum.
 Pituitary- the endocrine “master gland”
that regulates hormone production and
release.
 Thalamus- acts as a relay station for
regulating sensory inputs to the
cerebrum.

51. Diencephalon…
 Hypothalamus- and interface between
the nervous and endocrine systems.
 Plays a major role in:
 Temperature regulation
 Hunger
 Thirst

52. Brainstem
 The connection between the brain and
spinal cord.
 The most primitive part of the brain.
 Composed of: the medulla oblongata,
pons, and midbrain.
 Maintains basic body support functions.

53. Brainstem…
 Heavily involved in autonomic control
functions related to:
 The heart
 Respiration- including coughing, sneezing,
and hiccuping.
 Blood vessel diameter
 Swallowing
 Vomiting

54. Meninges
 A set of connective tissue layers that
surround the brain and spinal cord.
 They contain a rich network of blood
vessels that supply oxygen and nutrients
to the superficial tissues of the brain
and spinal cord.

55. Cerebrospinal Fluid
 The brain and spinal cord are bathed and
protected from the hard inner surfaces of
the skull and spinal column by CSF.
 It circulates between layers of meninges and
through cavities inside the brain and spinal
cord.
 The chemical composition may be involved in
the regulation of certain autonomic function,
such as respiration and vomiting.

56. Blood-Brain Barrier
 A functional barrier separating the capillaries
in the brain from the nervous tissue itself.
 The composition results in a cellular barrier
that prevents many drugs, proteins, ions, and
other molecules from readily passing from the
blood into the brain.
 In this way, the BBB protects the brain from
many poisons circulating in the bloodstream.
 Ex.- Ivermectin
 Parasites and insects don’t have a BBB so the drug kills them
by allowing it to reach target receptors in the brain.

57. Cranial Nerves
 A special set of 12 nerve pairs in the
peripheral nervous system that
originate directly from the brain.

58. Cranial Nerves
Colville p. 155
Nerve Type Function
I Olefactory Sensory Smell
II Optic Sensory Vision
Eye movement, pupil
III Occulomotor Motor size, focusing
lens
IV Trochlear Motor Eye movement
S: eye & face
V Trigeminal Mixed
M: chewing
VI Abducens Motor Eye movement

59. Face and scalp
movement,
VII Facial Mixed
salivation, tears,
& taste
VII
Vestibulocochlear Sensory Balance/hearing
I
S: 1/3 caudal tongue
IX Glossopharyngeal Mixed taste
M: swallowing &
salivation
S: GI tract, resp.,
M: larynx, pharynx,
X Vagus Mixed parasympathetic motor
to the abdominal
viscera & thoracic
organs
Skeletal muscles of the
XI Spinal Accessory Motor neck and shoulder
Accessory with vagus
Skeletal muscles of the
XII Hypoglossal Motor
tongue

60. I Olfactory bulb
II Optic chiasma
Pituitary gland
Cranial
nerves III
Cerebral
IV peduncle
V
VI Pons
VII
VIII
IX
X
XI Pyramid
XII

61. Spinal Cord
 The caudal continuation of the brain
stem outside the skull.
 It conducts sensory information and
motor instructions between the brain
and the periphery of the body.

62. Autonomic Nervous System

63. Autonomic Nervous System
 Controls many functions of the body on
a subconscious level.
 These autonomic functions are
performed by two divisions:
 Sympathetic nervous system
 Parasympathetic nervous system
 These two systems generally have
opposite effects on eachother.

64. IV. Pathology
By: Dr. Tuya Buchanan, DVM

65. Cerebral Pathology

66. Cerebral Trauma/ Hemorrhage
 Severe bruising
of the brain
causes capillary
rupture &
bleeding of the
brain resulting in
increased ICP
(intracranial
pressure)

67. Cerebellar Hypoplasia
 The cerebellum does not grow
properly
 Due to in utero viral infections or
injury, or just bad genetics
 Panleukopenia in cats
 Herpesvirus infections in dogs
 Vaccinating pregnant animals w/ MLV
 Problems are first noticed when the
young animal starts to ambulate

68. Cerebellar Hypoplasia (cont)
 Signs include:
 Ataxia
(incoordination)
 Hypermetria
(over reaching
when walking)
 Intention
tremors
 Broad-based
stance

69. Hydrocephalus
 Commonly referred
to as “water on the
brain”
 Characterized by a
dome-shaped head
 Either too much CSF
is produced or there
is inadequate
drainage

70. Cerebral Hypoxia
 Lack of oxygen to
the brain
 Numerous causes-
clots (“stroke”),
heart disease,
renal disease,
hyperthyroidism in
cats, parasites, etc.

71. Brain Tumors
 Can arise from any type of neuro cells
 Clinical signs depend on the location,
size, and degree of pressure they are
putting on the brain
 Glial tumors include astrocytomas &
oligodendrogliomas
 Meningiomas are another type of tumor

72. Brain Tumor in a Boxer

73. Strychnine Poisoning
 Strychnine blocks an inhibitory
neurotransmitter (glycine) in the
medulla & spinal cord
 So you end up with excitation of
neurons which results in muscle
rigidity & seizures
 Animals die from lack of oxygen to
vital body parts and exhaustion

74. Some Infectious Agents which cause
Cerebral Pathology

75. Rabies
 Rhabdovirus
 Furious Rabies- aggressive, snarling,
seizuring, drooling animal
 Dumb Rabies- depression, dementia,
hind-end weakness, & drooling
 Some animals will show obsessive
licking/self mutilation of an old wound
 No ante-mortem tests- need the
brain

76. Rabies (cont)

77. Rabies (cont)
Bad Raccoon! A Negri Body inside a neuron.
When seen this viral inclusion
body can mean only Rabies!

78. Distemper
 Caused by a Paramyxovirus
 The virus depletes the immune
system so the puppy is very prone to
secondary infections
 Starts out respiratory, then GI signs,
then neurological signs
 “hard pads” usually occur end-stage

79. Distemper (cont)
 Difficult to diagnose
ante-mortem
 Serology can be
very unrewarding
 Can do
immunoflourescent
assays for the virus
in conjunctival
scrapings (or wait
for necropsy)

80. Equine Encephalitis
 Caused by a virus
 3 forms: Eastern, Western, &
Venezuelan
 Horses have a fever, appear sleepy, and
may show incoordination of the rear-
end; it can progress to full paralysis and
death

81. Seizures
 A seizure is an episode of abnormal
electrical activity in the brain resulting in:
 loss or altered consciousness
 increased muscle tone
 involuntary urination & defecation
 Most seizures are grand mal but some may
be petit mal where there is not a complete
loss of consciousness and may only involve a
limb shaking or small body tremors

82. Seizures (cont)
 Seizures have either an intracranial
or an extracranial cause
 Intracranial seizures are caused by
primary CNS disease (problem is
inside the brain itself)
 Extracranial seizures are caused by
organ dysfunctions or toxins which
have secondary effects on the brain
(problem is outside the brain)

83. Intracranial Causes of Seizures
 Brain tumors- primary or those that
metastasize to the brain
 Bacteria (abscesses)
 Viruses (distemper)
 Protozoa (toxoplasmosis)
 Fungal
 Hydrocephalus
 Idiopathic epilepsy

84. Extracranial Causes of Seizures
 Hypoglycemia
 Liver disease
 Renal disease
 Hypocalcemia
 Toxins- strychnine, lead,
organophosphates

85. Spinal Cord Pathology

86. Wobbler Syndrome
 In horses, known as Cervical Stenotic
Myelopathy
 In dogs, known as Caudal Cervical
Spondylomyelopthy
 Either way, it’s a malformation of the
cervical spine causing cord compression

87. Wobbler (cont)
 Breeds of dogs include
Dobermans, Great Danes,
& Basset Hounds
 Affected dogs are mostly
young adults
 Signs range from hind-end
weakness to tetraplegia,
neck pain, & the neck is
flexed ventrally

88. Wobbler (cont)
 Seen in young,
rapidly growing
horses, especially
Thoroughbreds
 Over nutrition is a
big contributing
factor
 Signs consist of limb
weakness and
incoordination

89. Vertebral Fractures
 Usually secondary to trauma (HBC) or
bone pathology (osteomyelitis)
 Spinous process fractures do not usually
cause problems
 Problems arise when the spinal cord
becomes compressed or is also
fractured

90. Fractures (cont)

91. Spinal Cord Concussion
 Usually secondary to trauma, such as HBC
 Due to severe bruising of the cord, the
motor nerves do not function properly
 These dogs can look completely paralyzed
but radiographs +/- CT scan will show no
abnormalities
 With time and steroids, there will be
improvement

92. Intervertebral Disc Disease (IVDD)
 Affects dogs, rarely cats
 Disease can occur anywhere in the
spinal tract but the lumbosacral and
cervical regions are most common
 Can have partial or complete
herniation of the disc up into the
spinal cord
 Typically a degenerative process
 Dachshunds, Beagles, Pekingese, etc.

93. IVDD (cont)
 Clinical signs can be acute or chronic
 Severity of signs depends on the degree of
spinal cord compression
 Signs progress from ataxia/incoordination &
loss of conscious proprioception >> paresis
(muscle weakness) >> paralysis >> loss of deep
pain sensation
 Animals with acutely compressed cords can
be very painful while there may be little to
no pain with chronic compression

94. IVDD (cont)

95. IVDD (cont)

96. Degenerative Myelopathy
 Most common in German Shepherds & Welsh
Corgis
 A progressive degeneration of the axons &
myelin of the white matter of the SC
 Dogs are usually > 5 yrs old and develop a
gradual onset of non painful ataxia &
weakness in the pelvic limbs
 Poor prognosis; most are euthanized within 1-
3 yrs

97. Spinal Neoplasia
 Relatively common in dogs & cats
 Tumors are classified according to their
relationship with the spinal cord & meninges
 Extradural: outside the dura mater; compress SC;
most common SC tumor in dogs/cats
 Intradural-extramedullary: in the subarachnoid
space; compress SC
 Intramedullary: inside the SC itself; least
common type

98. SC Neoplasia (cont)

99. Laboratory
CSF Analysis

100. Evaluation
 Evaluation is important to patients with
neurologic disease.
 Helpful in evaluating patients with
unexplained fever.

101. Collection Sites
 Atlantooccipital
 Lumbosacral

102. Analysis
 Examination of CSF should consist of:
 Physical characteristics-
 Color
 Turbidity
 Total nucleated cell count (TNCC)
 Erythrocyte count
 Protein concentration
 Cytologic examination

103. Analysis…
 Analysis of CSF should be done as
quickly as possible.
 The low protein concentration of CSF cause
the cells to degenerate rapidly.

106. Dissection