Neuro Exam 3 - Old Material

define neuroanatomical diagnosis

neurolocalization of a specific lesions rather than medical diagnosis of overall disease

discuss central and peripheral lesions

central - involve the brain and/or spinal cord

peripheral - elsewhere

discuss focal, multifocal, and diffuse lesions

focal - lesion affects one area; that is, all clinical signs can be explained by a single, localized lesion; ex. IVDD

multifocal - affect 2+ areas that are not anatomically adjacent; ex. HBC with brain trauma and peripheral nerve damage

diffuse - affect a large continuous area; ex. toxin ingestion may result in diffuse nervous system involvement (tremors, seizures, mentation changes, dyspnea, etc.)

recognize that lesions of the nervous system interrupt pathways; demonstrate understanding of this concept

interruption of a pathway will result in loss of motor or sensory function below that point

CNS vs. PNS vs. ANS

CNS - central nervous system - those parts that are housed within the axial skeleton (brain and spinal cord)]

PNS - peripheral nervous system - spinal nerves and cranial nerves, (nerves from anatomy)

ANS - autonomic nervous system - includes both CNS and PNS structures; can be subdivided into sympathetic and parasympathetic

motor vs. sensory

motor / efferent - impulses carried from the CNS to the periphery

sensory / afferent - impulses carried from the periphery to the CNS

somatic vs. visceral

somatic - impulses carried to or from the skeletal muscle, skin, bones

• somatosensory - sensation of pain, temperature, touch, proprioception

• somatomotor - motor to skeletal muscle

visceral - impulses carried to and from smooth muscle, cardiac m., glands

• viscerosensory - visceral pain (organ distension, traction, ischemia) and monitoring of homeostasis (blood pressure, pH, pO2, pCO2)

• visceromotor - autonomic responses

neurons vs. neuroglia

neurons - possess membranes that can generate electrical impulses and transfer impulses to adjacent nerve cells, somatic structures, and visceral structures at synapses

neuroglia - neural support cells, which account for 90% of the total number of nervous system cells

discuss mentation / sensorium

a descriptor of level of consciousness and reaction to external stimuli

the client’s observations are very important here; they have a better understanding of their animal’s normal behavior and are more likely to notice subtle changes

additionally, patients often behave quite differently at the clinic than they do at home

possible mental states: BAR, QAR, depressed, obtunded, stupor, coma, demented

understand the continuum of mentation

BAR / QAR →

depressed / lethargic / sedate →

obtunded →

stupor →

coma

BAR / QAR

bright alert responsive

quiet alert responsive

depressed / lethargic / sedate

less active than normal

normal response to stimuli

obtunded

decreased responses to stimuli

stupor

only responsive to deep pain stimuli

coma

no response to any stimuli

demented / disoriented / delirium

unusual responses to stimuli, restlessness, apparent confusion

list lesions that can affect mentation

forebrain

• cerebrum (particularly frontal / parietal lobes or the limbic system

• thalamus

brainstem (specifically the reticular formation

list lesions that do not affect mentation

spinal cord

neuromuscular disease

cerebellum (with no additional cerebral involvement)

discuss why decreased mentation doesn’t always mean neuro disease

it is important to note that a patient may have decreased mentation because they don’t feel well; for instance, a patient with a high fever will be lethargic

additionally, a recumbent animal does not necessarily have altered mentation; for instance, a patient with a cervical spinal cord lesion can be recumbent with normal mentation

discuss signs of damage for frontal lobe

adversive syndrome

• wide, propulsive circles toward lesion

• head deviated toward lesion (head is turned, not tilted)

• usually no ataxia, paresis, or paralysis

normal → obtunded, or demented

personality changes (often aggression)

compulsive activity

delays in onset of movement

lack of conscious perception of touch and pain

head pressing

discuss signs of damage for parietal lobe

adversive syndrome

• wide, propulsive circles toward lesion

• head deviated toward lesion (head is turned, not tilted)

• usually no ataxia, paresis, or paralysis

normal → obtunded, or demented

personality changes (often aggression)

compulsive activity

delays in onset of movement

lack of conscious perception of touch and pain

hemineglect

discuss signs of damage for temporal lobe

there is a great deal of decussation in the pathway between the spiral organ and the temporal lobe

because of this, damage to one temporal lobe will not cause deafness

discuss signs of damage for occipital lobe

cortical blindness (PLR intact)

in humans, damage to the visual association cortex is documented to lead to visual hallucinations

discuss signs of damage for piriform lobe

damage to both sides results in loss of olfaction

list the brain regions which constitute the brainstem

mesencephalon (midbrain)

metencephalon (cerebellum and pons)

myelencephalon (medulla oblongata)

unilateral lesion → ipsilateral signs

explain why brainstem lesions are often severe

a lesion of the midbrain or pons can stop the ascending fibers of the ARAS from reaching the thalamus, which can result in coma

a lesion of the medulla can effect the reticular formation, including the cardiovascular and respiratory centers; this is generally fatal

in cases of brainstem trauma, recovery is rare; those animals who do recover will suffer neurological deficits

discuss the ascending reticular activating system

input to the ARAS comes from all modalities (except proprioception) and from every segment of the spinal cord (via spinoreticular tract) and brainstem

• special senses

• touch

• pain

these neurons synapse in the reticular formation; RF neurons synapse on the thalamic nuclei; from here, there are projections to all parts of the cortex

ARAS: sensory neurons → RF → thalamus → internal capsule → cortex

functions of reticular system:

• regulation of consciousness and alertness

• sensory modification

• regulation of muscle tone

• contains central pattern generators for voluntary and involuntary actions

• regulation of ANS

summarize the function of the ascending reticular activating system in relation to regulation of consciousness and alertness

sensory inputs travel cranial to the reticular formation, then thalamus, and then activate areas of the cerebral cortex

ex:

• your dog is sleeping peacefully, you open a bag of treats, suddenly your dog is awake

• auditory stimuli goes not only to auditory cortex, but to the reticular formation

• the ARAS activates the entire cortex, thus allowing your dog to be awake and alert

• without a reticular formation, the cortex doesn’t respond to sensory inputs

localize a brain lesion when given a list of clinical signs

soma

cell body

contains organelles and cytoplasm

receives signals from adjacent axons

axon

sends and receives signals

each neuron has a single axon which can have many branches

dendrite

receive signals

remainder of the neuronal processes

myelin sheath node / node of ranvier

gaps between myelinated segments

nuclei

collection of nerve cell bodies in the CNS

ganglia

collection of nerve cell bodies in the PNS

tract

bundle of nerve fibers in the CNS

nerve

bundle of nerve fibers in the PNS

list the types of traumatic peripheral nerve injury

• compression - most severe is crushing

• traction - most severe is avulsion

• laceration - most severe is complete transection

• ischemia - most severe is total loss of blood flow

explain what occurs upon axonal and general neuronal injury in the PNS

when an axon is completely severed, we refer to the portion with the cell body as the proximal segment and the isolated portion as the distal segment

proximal segment undergoes some degeneration, then it may:

• regenerate (1-5 mm/day) to original or different synapse site

• lead to neuronal death

• become the site of neuroma formation

distal segment undergoes Wallerian degeneration (total degeneration) because protein synthesis occurs at the soma

• myelin requires contact by axon to remain intact, so it too degenerates

• schwann cells may remain intact or degenerate over time

damaged neurons can regenerate back to their original site if the cell body survives and the regenerating axon can make contact with distal schwann cells (which secrete chemotropic factors)

factors that decrease likelihood of functional nerve regrowth:

• damage near the soma

• severe and/or crushing injury

• misalignment of segments

• scar tissue formation

• old age of patient

CNS vs. PNS axonal injury

PNS axons are more likely to heal than CNS because:

• in CNS, the entire neuron is likely to die with axonal damage

• more efficient phagocytosis and debris removal in PNS

• schwann cells are better equipped to re-myelinate than oligodendrocytes

• PNS axons have endoneurium which guides the proximal segment toward the distal segment

explain what occurs upon axonal and general neuronal injury in the CNS

location of injury is important:

• superficial - fibroblasts in meninges synthesize collagen

• deep - proliferation of astrocytic processes; not as effective as fibroblasts

CNS injury commonly results in degeneration and necrosis of neurons:

• space-occupying lesions - hemorrhage, abscess, tumor → compressive

• lesions which impede blood flow - cardiac arrest, hypovolemic shock, thrombosis → ischemic

• other - infection, toxins, trauma, nutritional deficiencies

the BBB protects the CNS from initial infectious insult; however, once infected the brain lacks efficient mechanisms to combat spread and damage

axonal injury in the CNS typically results in wallerian degeneration, as well as degeneration of the entire neuron

those neurons that do survive will typically only regenerate a few millimeters, at which point synapses with adjacent neurons can occur

cases of functional recovery after CNS lesions typical involve compensatory adaptations by other neural networks, rather than a regeneration of damaged neurons

name the types of synapses (electrical, chemical) and what structures can receive a presynaptic terminal (neuron, skeletal muscle, smooth muscle, cardiac muscle, glandular cell)