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Questions and Answers
What does head pressing in an animal with a forebrain lesion indicate?
In an animal with a forebrain lesion, why does circling typically occur towards the side of the lesion?
What is the primary cause of stuporous behavior in a patient?
Which type of ataxia is characterized by drifting towards one side and a head tilt?
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What is the main difference between paralysis and paresis in neurological terms?
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Which type of gait abnormality is most likely to be associated with dysmetria and hypermetria?
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Which cranial nerve is responsible for the gag reflex in animals?
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Which cranial nerve innervates the trapezius muscle and can rarely show atrophy?
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Which nerve originates from the medulla and is the most caudal?
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Which region of the brain is primarily responsible for proprioception and limb placement?
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Which reflex involves repetitive flexion and extension of a joint in response to a single stimulus?
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In assessing animals, the cutaneous trunci reflex is used to help locate lesions affecting which part of the body?
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Which neurological abnormality would likely be associated with animals that keep their limbs in extension and exhibit generalized depression of reflexes?
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What is a possible cause of hamstring atrophy, crouched stance, and flinging forward of limbs in animals?
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Which type of lesion would be most likely to cause urinary retention due to increased tone of detrusor muscle and urethral sphincter?
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Which type of posture in ataxic animals involves rigidity in thoracic limbs with possible opisthotonus and flexed pelvic limbs, linked to cerebellum or cerebellar peduncle lesions?
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What type of posture indicates rigidity in all limbs with opisthotonus, often associated with brainstem (midbrain) lesions in ataxic animals?
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What does a head turn in ataxic animals typically indicate?
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Which syndrome is characterized by increased extensor tone in thoracic limbs and paresis to plegia in pelvic limbs, associated with T3-L3 myelopathy?
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What does opisthotonus in ataxic animals indicate?
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Which condition results in facial muscle contracture and a fixed grimace, as seen in tetanus?
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In ataxic animals, where is spasticity typically a sign of upper motor neuron lesions?
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Schiff Sherrington Syndrome is associated with which specific pattern of limb abnormalities?
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Torticollis in ataxic animals mainly involves:
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Rigidity in all limbs with opisthotonus is commonly associated with:
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Study Notes
Neurologic Exam and Lesion Localization
- Behavioral Changes: pacing, head pressing, circling, aggression, blindness, obsessive behavior, incontinence, and seizures due to forebrain lesions
- Head Pressing: due to disinhibition of the red nucleus in the midbrain, causing the animal to walk into walls
- Circling: towards the side of the lesion due to hemineglect
- Mentation: level of consciousness, including obtunded, stuporous, and comatose states
- Gait: ataxia, proprioceptive, vestibular, cerebellar, and paresis
- Reflexes: rule out systemic disease, assess reflexes in all limbs
- Posture: decerebrate, decerebellate, Schiff-Sherrington, and risus sardonicus
- Lesion Localization: central nervous system (CNS), peripheral nervous system (PNS), autonomic nervous system (ANS), and specific regions of the brain and spinal cord
Neuroanatomy
- CNS: brain and spinal cord
- PNS: nerves and muscles
- Intumescence: widening of the spinal cord where nerves come out
- Decussation: everything in the forebrain crosses over before going to the rest of the body
- Brainstem and Spinal Cord: ipsilateral, lesion on one side causes signs on the same side
- Encephalopathy: lesion to the brain
- Myelopathy: lesion to the spinal cord
- Lesions to PNS: radiculopathy, neuropathy, myelinopathy, junctionopathy, and myopathy
Upper and Lower Motor Neurons
- Upper Motor Neuron (UMN): cells that arise from the forebrain, brainstem, or cerebellum
- Lower Motor Neuron (LMN): cells that arise from spinal cord segments
- Ventral Nerve Roots: formed by the axons of the LMN
- Nerve Roots: combine to form named nerves
- Spinal Cord Segments vs Vertebrae: 8 cervical spinal cord segments, 7 cervical vertebrae, etc.
Neurologic Deficits
- Hemineglect: animal ignores one side of their world due to decussation
- Nystagmus: involuntary side-to-side or circular motion of the eyes
- Dysmetria: inability to control distance, speed, and range of motion
- Hypermetria: overflexion and overextension of the limb
- Localizing Neurologic Deficits: to specific neuroanatomic regions (CNS vs PNS)
- UMN vs LMN: assess reflexes and tone of limbs, prognosis
Cranial Nerves
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Olfactory Nerve (I): typically not assessed, avoid irritating substances
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Optic Nerve (II): menace response, pupillary light reflex, fundic exam
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Oculomotor Nerve (III): innervates dorsal, ventral, and medial rectus, ventral oblique, and pupillary sphincter
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Trochlear Nerve (IV): innervates dorsal oblique
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Abducent Nerve (VI): innervates lateral rectus and retractor bulbi
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Trigeminal Nerve (V): comes from the pons, 3 branches (ophthalmic, maxillary, and mandibular)
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Facial Nerve (VII): originates from the medulla, motor to muscles of facial expression, sensory to inner ear pinna, parasympathetic for lacrimal/nasal gland secretions
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Vestibulocochlear Nerve (VIII): originates from the medulla, maintains posture and balance, detects acceleration and deceleration, coordinates eye movement### Assessing Cochlear Function
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Deafness in animals can be assessed by testing hearing in both ears, but a crude method is to clap loudly once; a more objective way is to use brainstem auditory evoked response with electrodes.
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The glossopharyngeal (IX), vagus (X), and cranial nerves originate from the caudal medulla and nucleus ambiguus, innervating the oropharynx, larynx, and esophagus.
Assessing Cranial Nerves
- The oropharynx is associated with the gag reflex (sensory: X, motor: IX, X, and XII), and an animal usually licks after (tongue, XII).
- Swallowing involves the sensory nerve X and motor nerves IX, X, and XII.
- The larynx is innervated by the recurrent laryngeal nerve (branch of vagus nerve) and accessory XI (spinal accessory nerve).
- The hypoglossal nerve (XII) is the most caudal cranial nerve, coming from the medulla.
Assessing Proprioception and Motor Function
- Proprioception is the sense of where limbs are in space, graded similarly to cranial nerves.
- Paw placement and hopping tests are used to assess proprioception, requiring minimal strength but some strength.
- Forebrain, brainstem, and spinal cord lesions can cause delayed or absent paw placement and hopping.
- Wheelbarrowing, extensor postural thrust, and hemiwalking/hemistanding tests are also used to assess proprioception and motor function.
Segmental Spinal Cord Reflexes
- Reflexes must be evaluated in conjunction with other neurological abnormalities to be reliable.
- Graded 0-4, reflexes are absent, weak, normal, exaggerated, or display clonus.
- Thoracic limb reflexes include the withdrawal or flexor reflex, which is polysynaptic and involves multiple synapses and interneurons.
- Myotatic reflexes are monosynaptic, involving a direct response to muscle stretch, and include the biceps, triceps, and extensor carpi radialis reflexes.
Pelvic Limb Reflexes
- The withdrawal or flexor reflex is also reliable in the pelvic limb, primarily involving the sciatic nerve.
- Hamstring atrophy, crouched stance, dropped hock, and flinging limb forward when walking are signs of sciatic nerve deficits.
- Other reflexes include the patellar reflex (femoral nerve, L4-L6), hock flexion (tibial nerve), stifle flexion (sciatic nerve), and hip flexion (femoral nerve).
Other Reflexes
- The cutaneous trunci reflex is helpful for narrowing down the location of a lesion but should not be used to change localization.
- The perineal reflex (pudendal nerve) is a reliable test for sacral spinal cord or pudendal nerve lesions.
- The Babinski reflex (extensor toe) is normally absent in adults but present in newborns.
- Crossed extensor reflexes result from lesions in ipsilateral descending pathways, signifying UMN disease, likely chronic.
- Hyperpathia and hyperesthesia are not helpful for localization, but nociception (deep pain) determines prognosis for paralyzed patients.
Bladder Function
- Lesions to S1-S3 (pelvic and pudendal nerve) can cause decreased tone of detrusor muscle and urethral sphincter, leading to incontinence.
- Lesions cranial to S1 (UMN lesion) can cause increased tone of detrusor muscle and urethral sphincter, leading to firm bladder and urinary retention.
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Description
Understand how to perform a neurologic exam and observe behavior changes indicating forebrain lesions. Learn about symptoms like head pressing, circling, blindness, and seizures.
