Presented by: Cynthia Xue, DVM, DACVIM (LAIM), Assistant Professor, Clinical Sciences
Contact: cxue@rossvet.edu.kn
Outline:
Neuroanatomy/physiology
The neurologic exam
Neurolocalization
Outcomes:
Recognize abnormal clinical signs associated with neurologic dysfunction
Emphasize neurolocalization skills
Important structures:
Cerebrum
Cerebellum
Brainstem
Spinal cord
Reticular Activating System (RAS)
Spinal segments: C1-C5, C6-T2, T3-L3, L4-L6
Thalamus/Hypothalamus
Comprises everything outside the CNS:
Cranial Nerves (CN I-XII)
Lower Motor Neurons
Spinal Nerves
Nociceptors
Neuromuscular Junctions
Voluntary actions: Somatic sensory and motor fibers
Involuntary actions:
Visceral sensory fibers
Visceral motor fibers
Sympathetic and Parasympathetic divisions:
Fight or Flight
Rest & Digest
Nerves as "highways" for information transfer:
Afferent pathways: Sensory fibers relay info INTO the CNS
Efferent pathways: Motor fibers relay info FROM the CNS
Types of fibers:
Afferent: Somatic and visceral sensory fibers
Efferent: Somatic and visceral motor fibers
Absent palpebral reflex (OS):
Affected CNs: Trigeminal (CN V) for afferent, Facial (CN VII) for efferent
Symptoms: Muzzle deviation, ear drop, ptosis OS
Vagus Nerve: Mixed fiber types pertaining to visceral functions.
Oculomotor Nerve: Primarily motor for pupillary dilation and globe position.
Spinocerebellar tracts: Afferent neurons relaying proprioception.
Vagus Nerve Fiber Composition: SA, SE, VA, VE - all types involved.
False Statement: Parasympathetic and sympathetic nerves contain visceral afferent fibers, not only efferent.
Afferent Neurons: Carry sensory information from receptors in skin and organs to the CNS; cell bodies outside the spinal cord.
Efferent Neurons: Carry motor information from the brain to the PNS; cell bodies located in the ventral horn of the spinal cord.
UMNs: Cell bodies within the CNS; project to another CNS area.
LMNs: Cell body in brainstem/spinal cord; projects to organ/gland/muscle in PNS.
Understanding neuroanatomy aids in diagnosing lesions affecting both UMN and LMN, showing signs of weakness related to both types.
Described as an observational exercise (Fecteau et al. 2017).
Aim of neurologic exam: One lesion should explain all clinical signs.
Utilize algorithms to differentiate lesions based on symptoms such as gait deficits, cranial nerve signs, and leg abnormalities.
Evaluation of mental status essential for differentiating intracranial vs extracranial lesions.
Key questions:
Awareness of presence?
Social interaction with herd mates?
Assess functional aspects of cranial nerves:
Loss of sensory (afferent) vs motor (efferent) capabilities can indicate nerve damage.
CN | Function | Assessment |
---|---|---|
I (Olfactory) | Smell | Not routinely performed |
II (Optic) | Vision | Menace & PLR tests |
III (Oculomotor) | Eye movement & pupil constriction | PLR and eye position |
IV (Trochlear) | Eye movement | Eye position tests |
V (Trigeminal) | Sensation & motor to masticatory muscles | Palpebral reflex |
VI (Abducent) | Eye movement | Globe retraction |
VII (Facial) | Facial expression | Facial symmetry and reflexes |
VIII (Vestibulocochlear) | Balance & hearing | Response to noise |
IX (Glossopharyngeal) | Sensory & motor to pharynx | Ability to swallow |
X (Vagus) | Pharynx/larynx functions | Swallowing observation |
XI (Spinal accessory) | Motor to cervical muscles | Muscle atrophy observation |
XII (Hypoglossal) | Tongue movement | Tongue strength and symmetry |
Myopathy may be indicated by asymmetry or atrophy, linking cranial nerve or LMN damage.
Common issues in cattle due to dystocia.
Withdrawal (Flexor) Reflex: Assess sensory and motor pathways in limbs by leg flexion in response to stimulus.
Patellar Reflex: Tests femoral nerve by assessing stifle extension upon tendon tapping.
Different assessment methods required for ruminants vs. smaller animals, especially in dynamic environments.
Pain response observations can be integrated into earlier exam portions for compliance.
Definitions of pain sensation levels: normal, decreased, absent.
Suspected nerve injuries to assess pain response in hind limbs, perineal reflexes, linking neuroanatomy to clinical signs.
Recognizing clinical signs related to specific brain regions:
Cerebrum: behavioral changes, seizures, blindness.
Cerebellum: posture and ataxia without weakness.
Brainstem: cranial nerve abnormalities.
Postures: Opisthotonus, head pressing.
Behavioral Manifestations: Abnormal vocalizations.
Gait/Balance: Wide stance, truncal sway, ataxia.
Reflexes: Absent menace response, intention tremors.
Recognize common clinical signs to specify lesions and relate them to neurological pathologies across different systems.