Ruminant Neurologic Exam – Comprehensive Study Notes

Neuroanatomy and Physiology

• Central Nervous System (CNS)
  • Cerebrum, Cerebellum, Brainstem, Spinal cord, Reticular Activating System (RAS)
  • Spinal cord segmental regions: C1{-}C5, C6{-}T2, T3{-}L3, L4{-}L6
  • Thalamus/Hypothalamus (forebrain cortex)
• Peripheral Nervous System (PNS) ― everything outside the CNS
  • Cranial nerves (CN I–XII)
  • Lower motor neurons (LMN) & spinal nerves
  • Nociceptors, neuromuscular junctions, autonomic ganglia, etc.
• Somatic vs. Autonomic Divisions
  • Somatic: voluntary movement (somatic sensory & motor fibers)
  • Autonomic: involuntary (visceral sensory & motor fibers)
  • Sympathetic = “fight or flight”
  • Parasympathetic = “rest & digest”
• Afferent vs. Efferent pathways
  • Afferent (sensory) → CNS; Efferent (motor) ← CNS
  • Multiple fiber types may coexist in a single nerve “highway”

Key Terminology

• Fiber types
  • Somatic Afferent (SA), Somatic Efferent (SE)
  • Visceral Afferent (VA), Visceral Efferent (VE)
• Upper Motor Neuron (UMN)
  • Cell body & axon entirely within CNS (cortex → brainstem/spinal cord)
• Lower Motor Neuron (LMN)
  • Cell body in brainstem/spinal cord; axon exits via nerve → muscle/gland
• Lesions at the UMN–LMN junction may show mixed UMN & LMN signs

Clinical Fiber‐Type Examples

• Palpebral reflex OS absent
  • Afferent: CN V (trigeminal, SA)
  • Efferent: CN VII (facial, SE)
• Vagus nerve contains all fiber types (SA, SE, VA, VE)
• Oculomotor nerve: VE (parasympathetic pupillary constrictor) + SE (extra-ocular)
• Spinocerebellar tracts = afferent (GP information)
• Sympathetic/Parasympathetic nerves = VE and VA (not only VE)

Neurologic Examination (General Principles)

• Primarily an exercise in careful observation
• Aim: Explain all clinical signs with a single lesion (unless multifocal)
• Global algorithm (simplified)
  • No gait deficits → consider cranial disease types
  • Forelimb vs. hindlimb severity differentiates cervical, thoracolumbar, or lumbosacral lesions
  • Presence/absence of cranial nerve signs directs localization (cerebrum, cerebellum, brainstem, etc.)

Mental Status Evaluation

• Brainstem (RAS) → arousal; lesions cause obtundation, stupor, coma, abnormal respiratory patterns
• Cerebral cortex (thalamus/hypothalamus) → behavior, cognition, voluntary movement, temperature regulation
• Key questions: Is patient aware of examiner? How does it interact with herd mates?

Cranial Nerve Overview

• Cranial nerve composition may be sensory, motor, or both; one modality can be lost independently
• Quick reference (assessment highlights)
  • CN II: menace & PLR
  • CN III: eye position, PLR; lesion → ventrolateral strabismus, ptosis, mydriasis
  • CN V: facial sensation, palpebral, jaw tone
  • CN VII: facial symmetry, blink, ear & muzzle movement
  • CN VIII: head/eye position, physiologic nystagmus, hearing
  • CN IX/X: swallow, laryngeal movement (endoscopy)
  • CN XII: tongue tone & symmetry

Muscle Mass, Tone, & Symmetry

• Atrophy or asymmetry suggests cranial-nerve or LMN pathology
• Common in calves after dystocia; other differentials: trauma, inflammation, neoplasia

Important Muscle–Nerve Pairs

• Trigeminal n. → muscles of mastication (masseter, temporalis)
• Hypoglossal n. → tongue
• Facial n. → facial expression muscles
• Radial n. → forelimb extensors

Spinal Reflexes

• Withdrawal (flexor) reflex
  • Forelimb: axillary, median, ulnar nerves
  • Hindlimb: sciatic (lateral dermatome SA, stifle flexion SE) & femoral (medial dermatome SA, hip flexion SE)
• Front limb extensor (weight-bearing) → radial n. (triceps, digital extensors)
• Patellar reflex (stifle extension) → femoral n.

Cutaneous Reflexes

• Cutaneous trunci (panniculus)
  • Skin pinch from wing of ilium to T2; lesion 1–4 vertebrae cranial to absent contraction
  • If response present at ilial level, don’t test cranial dermatomes
• Perineal reflex routinely evaluated during TPR

Gait & Proprioception

• Small ruminants: placing & hopping tests; can flip feet like small animals
• Large ruminants: lift a leg & push laterally; use environmental challenges

Nociception

• Perform last to preserve compliance
• Pain information often gathered earlier (neck ROM, flexor reflexes)
• Absent deep pain = poor prognosis

Neurolocalization by Region

• Cerebrum
  • Mentation change: lethargic → obtunded → stuporous → comatose
  • Abnormal behaviors: compulsive circling, wandering, abnormal vocalization, seizures
  • Visual deficits: cortical blindness (normal PLR but absent menace/dazzle)
  • Postures: Opisthotonus (hyper-extension of neck & limbs), Head pressing
• Cerebellum
  • Base-wide stance, intention tremors, truncal sway, hypermetria, ataxia WITHOUT LMN weakness
  • Menace absent despite normal vision (cortex intact)
• Vestibular system (summary table)
  • Peripheral (CN VIII): ipsilateral head tilt, horizontal nystagmus, no proprioceptive deficits, normal mentation
  • Central (brainstem): ipsilateral head tilt, positional/vertical nystagmus, proprioceptive deficits, altered mentation
  • Paradoxical (cerebellum): contralateral head tilt, positional nystagmus, ipsilateral proprioceptive deficits
• Brainstem
  • Multiple cranial nerve deficits (all originate here)
  • RAS involvement → somnolence, respiratory pattern changes
• Spinal cord localization (UMN vs. LMN)
  • C1{-}C5: tetraparesis, fore = hind severity
  • C6{-}T2: front limbs worse than rear (LMN front, UMN rear)
  • T3{-}L3: rear limbs UMN signs; front normal
  • L4{-}S: LMN rear limbs; tail/bladder may be affected

Case-Based Clinical Correlates

1. Absent palpebral OS, muzzle deviation R, ear drop L, ptosis OS
   → CN V afferent deficit, CN VII efferent deficit; somatic efferent fibers of CN VII affected
2. Vagus nerve functions (baroreceptors, peristalsis, HR, arytenoid abduction) use SA, SE, VA, VE fibers
3. Cow with obturator/sciatic injury post-calving
   • Expect decreased/absent pain response hind limbs & perineal reflex → LMN lesion
4. Listeriosis cow: depression + jaw & swallow deficits; CN V, IX, X; lesion in brainstem
5. Post-enucleation OD lacks menace, dazzle, PLR OD
   • Prioritized lesion sites: optic chiasm > optic nerve OD > retina OD
6. Neonatal calf dog-sitting, absent patellar reflexes bilaterally, no medial dermatome sensation
   • LMN problem; bilateral femoral nerve paralysis (SE & SA fibers) likely from traction injury during dystocia; atrophy absent due to acute timeline (<48 h)
7. Left CN VIII lesion
   • Head tilt L, horizontal nystagmus fast phase R, leaning L, no proprioceptive deficits → peripheral vestibular disease
8. CN III lesion OS
   • Ventrolateral strabismus, ptosis, mydriasis OS; PLR absent direct OS but consensual present; SE & VE fibers affected

Practical / Ethical / Real-World Notes

• Early, precise neurolocalization guides prognosis & therapy (e.g., listeriosis vs. peripheral nerve injury)
• Assisted deliveries carry risk of femoral/obturator/sciatic neuropathies; gentle traction & proper positioning mitigate damage
• Absence of deep pain → humane euthanasia discussions

Formulas, Numbers, & Quick Facts

• Spinal segments: C1{-}C5,\;C6{-}T2,\;T3{-}L3,\;L4{-}S
• Cranial nerve count: 12 pairs (I–XII)
• Patellar reflex arc = femoral\;n. \ (L4{-}L6\;spinal\;segments)
• Cutaneous trunci lesion localization = lesion site = \text{absent level} + 1{-}4\;vertebrae\;cranially

Study Tips

• Memorize cranial nerve modalities & assessments; practice interpreting PLR/menace discrepancies
• Use the regional algorithm (slide 12) to narrow spinal vs. intracranial lesions quickly
• Correlate specific reflex losses with segmental nerve/cord anatomy (e.g., absent withdrawal → sciatic/femoral vs. radial)