Ch 26 - Neurologic examination and localisation Flashcards
What are the six components of a neuro exam?
- Sensorium and behaviou
- Posture and gait
- Postural reactions
- Spinal reflexes, muscle mass and muscle tone
- Cranial nerves
- Cutaneous sensation
What is the reticular activating system?
A collection of nuclei that are located throughout the brainstem for the thalamus to the medulla which functions to arose the cerebrum
Abnormalities in which parts of the brain would cause an abnormality of sensorium (mentation)
The cerebral hemispheres or the RAS within the brainstem
What are the two broad categories of abnormalities influencing the sensorium?
- Abnormalities in the level of mentation (depressed/obstunded/stuporous/comatose)
- Abnormalities in the quality of mentation (aggression, hyperactivity, hysteria etc)
Define obtundation, stupor and coma
- Obtundation - state of decreased arousal with response to voice or touch
- Stupor - Arousal to vigourout stimul but response is incomplete or inadequate
- Coma - Sustained unresponsiveness to stimuli
Define decerebrate and decerebellate rigidity
- Decerebrate rigidity - Opisthotonus with rigid extension of all 4 limbs. Typicall associated with midbrain or rostral cerebellar lesions. Always have a severe impact on mentation and the menace response
- Decerebellate rigidity - Opisthotonus with rigid extension of all 4 limbs but with hip joint flexion. Results from severe cerebellar lesions. Does not always effect mentation
Define pleurothotonus
Deviation of the head and neck to one side. May indicate a lesion in the mid-to-rostral brainstem or cerebral lesions
What areas of the CNS cause an abnormality in gait?
Anywhere from the midbrain caudally
What are the key upper motor neuron tracts which function in gait generation?
Reticulospinal and rubrospinal tracts
Name the unconscious and conscious general proprioceptiv tracts
Unconscious
- spinocerebellar tracts
Conscious
- Fasciculus gracilus (PL)
- Fasciculus cuneatus (TL)
What is the modified Frankel score?
Grading scheme used with respect ot strength, proprioception and sensory function.
Opposite to what we use in the clinic (grade 0 most severe)
What are the three forms of ataxia?
- General proprioceptive ataxia (disruption of ascending general proprioceptive tracts relaying spatial information and degree of muscle tone of the limbs, trunk and neck)
- Vestibular ataxia
- Cerebellar ataxia
What abnormalities can be seen in animals with vestibular ataxia? Where is the neurolocalisation?
- Loss of balance and orientation
- Abnormalities in CNV and VII possible on ipsilateral side
- Ipsilateral UMN paresis and general proprioceptive ataxia
- Located in central vestibula system (vestibular nuclei in the rostral medulla)
Define dysmetria as seen with cerebellar ataxia
A disturbance in the rate, range and force of movement manifested as a hypermetric gair with sudden bursts of motor activity
How can cerebellar dysmetria be differentiated from general proprioceptive dysmetria?
Can be challenging!
- general proprioceptive will often involve stiffness due to UMN paresis
- Presense of other vestibular signs (head tilt, nystagmus etc)
What is required for normal postural reactions??
All major sensory (general proprioceptive) and motor (UMN and LMN) components of the CNS and PNS are intact
What pathways are tested with postural reactons?
- Conscious proprioception (proprioceptive pathways projecting to the contralateral somesthetic (sensory) cerebral cortex)
- Unconscious proprioception (proprioceptive pathways projecting to the cerebellum)
Cannot be clinically seperated!
Describe the pathway of postral reactions
Sensory nerves of PNS -> enter spinal cord vis dorsal roots -> Ascend in ipsilateral dorsal and dorsolateral funiculi -> remains ipsilateral to level of midbrain -> contralateral thalamus and ultimately cerebral hemisphere
What kind of postural reactions will results from a unilateral proencephalic lesion?
Contralateral postural reaction deficits with normal gait
What are the two most uselful postural reaction tests?
Hopping and placing
Define reflex
What is required for a normal reflex?
A reflex is a stereotypic response to a specific stimulus that occurs independant of volition (using your own will)
A normal reflex required an intacta afferent (Sensory) arm of the reflex arc and an intact efferent (motor) arm of the reflex arc.
Sensory arm = muscle spindle or golgi tendon organ, sensory nerve, dorsal nerve root and spinal cord segment
What nerve and spinal cord segments does the patellar reflex test?
- Femoral nerve
- L4-L6
- Graded as absent (0), hyporeflexive (+1), normal (+2), hyperreflexive (+3), clonic (+4)
What nerve does the biceps brachii refles test? What spinal cord segments?
- Musculocutaneous nerve
- C6-C8
- Slight flexion of elbow or movement of skin over the muscle is normal response
What nerve does the triceps brachii reflex test?
What spinal cord segments?
- Radial nerve
- C7-T2
- Slight extension of the elbow or visible contraction of the muscle normal
Where do you apply pressure for a withdrawal-flexor reflex? What nerve and spinal segments does this test in the FLs and HLs?
Apply pressure to the base of the toenail, should result in full flexion of all joints
Forelimbs:
- dorsal thoracic, axillary, musculocutaneous, median, ulnar and radial nerves. C6-T2
Hindlimbs
- Sciatic nerve, L6-S1
How will a patient walk with sciatic nerve paralysis?
- Plantigrade (tibial nerve dysfunction) and often walking on dorsal surface of paw (fibular nerve dysfunction) but can continue to bear weight due to an intact femoral nerve allowing stifle extension
What does a corssed extensor reflex in a laterally recumbent animal indicate?
An UMN lesion on the side of the limb extension (should be inhibited by desceding UMN tracts in a normal animal)
What nerves are responsible for the perineal reflex?
Branches of the sacral and caudal segments of the spinal cord through the pudendal nerves
What is the pathway of the cutaneous trunci muscle reflex?
- Sensory input from regional segmental spinal nerves into the spinal cord
- Relayed cranially to segments C8 and T1
- SYnapses to LMN of both lateral thoracic nerves which innervate the cutaneous trunci muscle
Whats causes increased mucle tone in UMN lesions?
Much of the descending UMN influence provides for inhibition of extensor musculature. And UMN lesion therefore leads to loss of inhibition and overactivity of the extensors and hypertonia
List the 6 steps in the stepwise approach to cranial nerve evaluation
- Vision and PLR
- Palpebral fissure and third eyelid symmetry
- Eyeball position and movement
- Vestibular function
- Facial and trigeminal nerve function
- Tongue and laryngeal-pharyngeal function
List the 12 cranial nerves
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Vestibulocochlear
IX - Glossopharyngeal
X - Vagus
XI - Accessory
XII - Hypoglossal
What CN are tested by vision and PLR?
CN II, III and VII
What nerves are assessed with palpebral fissue and third eyelid symmetry?
CN III, V and sympathetic nerves
What is the two-neuron system of the autonomic nervous system?
- A preganglionic neuron with its cell body within the CNS
- A ganglionic neuron located in the PNS along with an effector muscle
Which spinal cord segments are home to the preganglionic sympathetic neurons which innervate the eye?
Where do they travel after leaving the vertebral column?
- T1-T3
- Course through cranial thoracic cavity, through the brachial plexus to joint the descending fibres of the vagus, form the vagosympathetic trunk which courses in the carotid sheath to the cranila cervical ganglia
- Synapse in the cranila cervical ganglia, enter the cranial cavity, join axons of the ophthalmic branch of trigeminal nerve, exits through the orbital fissue and ultimately innervates the dilator musc of the pupil
What CN are assessed by eyeball position?
CN III, IV, VI, VIII
- III - ventrolateral strabismus
- VIII - medial strabismus
- IV - Lateral rotation of the dorsal pupil
Which cranial nerves does the palpebral refelx test?
CN V and VII
Which CNs are asessed by tongue and laryngeal/pharyngeal function?
IX, X, XI, XII
What are the three forms of cutaneous sensory receptors?
- mechanoreceptors (touch)
- thermoreceptors (temperature)
- nociceptors (noxious stimuli)
Describe the noxious stimuli neural tracts
Noxious stimulus -> afferent impulse which enters spinal cord through dorsal nerve roots -? bilateral tracts in lateral funiculi - > continue through medulla oblongata, pons, and midbrain to specific nuclei in thalamus -> relayed to somesthetic area of cerebral cortex
What is an autonomous zone?
A cutaneous area innervated by a single nerve
What are the autonomous cutaneous zones of the forelimb and their associated nerves?
- Palmer surface of paw - median and ulnar n
- lateral aspect of digit V - ulnar
- Dorsal paw and lateral antebrachium - radial
- Caudal antebrachium - Ulnar n
- Medial antebrachium - musculocutaneous n
What are the autonomous cutaneous zones of the hindlimb and thier associated nerves?
- Dorsal paw - fibular nerve
- Plantar paw - tibial nerve
- Medial aspect of limb - saphenous n (branch of femoral)
What are the 5 major regions of neurolocalisation?
- Prosencephalon
- Mid-to-caudal brainstem (midbrain, pons, medulla oblongate)
- Cerebellum
- Spinal cord
- LMN/neuromuscular system
List some clinical scenarios which can cause confusion regarding the T3-L3 neurolocalistion
- Schiff-Sherrington (disruption of ascending inhibitiroy axons for the border cells in the dorsolateral border of the ventral grey matter column of L1-L4
- Spinal shock - LMN signs in the HLs, commonly accompanied by Schiff Sherrington (transient disconnect between the facilitatory descending UMNs and spinal cord motor neurons
What does a LMN unit consist of?
- Alpha-motor neuron (nerve cell body) in ventral grey matter
- Ventral nerve root
- Spinal nerve
- Nerve plexus
- Named nerves of the limb
- NMJ
- Muscle
What are the three braod categories of LMN disease?
- Neuropathy
- Myopathy
- Junctionopathy
What is a mixed nerve?
A nerve in which sensory (afferent) fibers run toghether with the axons of LMN within the nerves
What is the most common sign associated with diffuse CNS disease?
What are some differentials?
- Fine, whole body tremor
- DDx: disorder of myelin formation, meningitis, metabolic disease, degenerative disease (kysosomal storage disease), toxicity
