Lecture 15/16 - Cranial Nerves Flashcards
what are the 12 cranial nerves
olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory spinal, hypoglossal
what nerves are motor, sensory or both?
olfactory = s
optic = s
oculomotor = m
trochlear = m
trigeminal = b
abducens =m
facial = b
vestibulocochlear = s
glossopharyngeal = b
vagus = b
accessory spinal = m
hypoglossal = m
where are the nerve cell bodies for SOMATIC MOTOR fibers in cranial nerves found
what are they considered
within nuclei (cluster of gray matter/nerve cell bodies) in the brain itself
these are considered lower motor neurons with the nerve cell bodies IN the CNS
where are the nerve cell bodies for SOMATIC SENSORY fibers in cranial nerves found
in the ganglia outside the CNS
they are like the sensory neurons in the spinal cord with the nerve cell body in the dorsal root ganglia
are the cranial nerves considered part of the CNS or PNS
PNS
what is the function, anatomy, clinical examination and examples of clinical disease for the olfactory nerve
function = conscious perception of smell
anatomy = chemoreceptors in nasal mucosa that detect odours and transmit sensory information to the axons of this nerve. The nucleus for this nerve is in the olfactory bulb and anterior olfactory nucleus in the forebrain
clinical exam = absence or decreased sense of smell is difficult to evaluate in an animal and generally not examined here. It is important to know that an animal that sniffs does not necessarily perceive odours
clinical disease = anosmia; absent sense of smell… hyposmia; decreased sense of smell
what is the function, anatomy, clinical examination and examples of clinical disease for the optic nerve
function = sensory visual perception and sensory component of the pupillary light reflex
anatomy = light entering retina activates photoreceptors that generate AP that are relay via retinal ganglion cells which form axons in the optic nerves. The optic nerves from each eye converge at the optic chiasm and there is some decussation, then optic tracts are formed by the continuation of the axons. the entire optic nerve and retina are actually part of the CNS - they are evolutionary modifications of a primitive tract rather than an actual peripheral nerve
-the fibers for conscious perception of vision synapse in the lateral geniculate nucleus (LGN). the post synaptic fibers form the optic radiation to the visual cortex (occipital region of brain)
-fibers for unconscious response to visual stimuli (pupils) pass to the pretectal area
clinical exam = pupillary light reflex and menace response
-PLR direct = shine light into the eye and observe for pupillary constriction in the SAME eye. abnormal result is LACK of constriction in response to light. this also tests CNIII
PLS indirect = shine light into one eye and observe the OTHER eye for pupillary constriction. Abnormal result is a lack of constriction
-menace response = while covering one eye, touch and then make a threatening gesture at the uncovered eye, looking for a blink response. in order for the blinkresponse to be produced, the retina, CNII, path to/through visual cortex, cerebellum and CNVII must be intact. ***This is a response, not a reflex
clinical disease = blindness (total or partial) observed by absence of PLR and menace response
what is the function, anatomy, clinical examination and examples of clinical disease for the oculomotor nerve
function = motor control of iris constrictor mucles (parasympathetic pupillary constriction). Somaticmotor innervation of some medial rectus and retractor bulbi muscle
anatomy = originates from nuclei in the rostral (anterior) ventral area of the midbrain (there are two nuclei on each side, 1 for eye movement, 1 for iris constriction)
clinical exam = eye position and abnormal PLR
-eye position; if nerve or somatic nucleus is damaged, ventrolateral strabismus results
-abnormal PLR = an inappropraite lack of constriction to the pupil. possible anisocoria
what is anisocoria
when one of your pupils is bigger than the other one
what is strabismus
when eyes do not line up in the same direction
what is the function, anatomy, clinical examination and examples of clinical disease for the trochelear nerve
function = motor innervation of the dorsal oblique muscle of the eye - this muscle helps to keep the visual world “steady” by counter-rotating the eye when head tilts to the side
anatomy = nucleus is located caudally in the midbrain (NOTE: this is the last cranial nerve that has nuclei in the midbrain)
clinical exam = lesions are hard to diagnose in dogs. in cats and horses (species with slit like pupils), a dorsolateral rotation of the affected eye can be observed
clinical disease = mild dorsolateral strabismus. also, abnormal movement of eyes when head is moved or gaze shifts laterally. Rotation of fundus (through ophthalmoscope)
what is the function, anatomy, clinical examination and examples of clinical disease for the trigeminal nerve
function = motor and sensory. SENSORY portions innervate face (pinnae, eyelids, cornea, oral cavity, mucosa of the nasal septum). The MOTOR component innervates the muscles involved with mastication
anatomy = nuclei located in the PONS. sensory component has three branches (ophthalamic, maxillary, mandibular). Ophthalamic branch innervates ocular region and MEDIAL canthi. Maxillary branch innervates nasal region and LATERAL canthi. Mandibular branch innervates the BUCCAL area.
-sensory component has a large ganglion called the trigeminal or gasserian ganglion which contains primary nerve cell bodies for sensory part of nerve
clinical exam = observe for blink response when checking the palpebral reflex. look for symmetrical response to stimulation of the nasal mucosa.
-palpebral relfex = stimulate the medial canthus, lateral canthus, or skin over mandible and look for a blink in response.
-stimulate nasal septal mucosa = use a cotton bud to touch the nasal mucosa of each side of the nasal septum and observe for symmetry of response
clinical disease = motor loss (masseter, temporalis muscle wasting, loss of jaw tone), sensory loss (absent palpebral reflex, lack of sensation in face)
what is the function, anatomy, clinical examination and examples of clinical disease for the abducens nerve
function = motor. innervates lacteral rectus and retractor bulbi muscles
anatomy = nucleus is located in the dorsal medulla (brainstem)
clinical exam = examine the position and movement of the eyes, look for the eye to be retracted, allowing the third eyelid to be extruded
clinical disease = medial strabismus and loss of lateral gaze, inability to retract globe
what is the function, anatomy, clinical examination and examples of clinical disease for the facial nerve
functions = sensory and motor. motor branches innervate facial muscles. sensory branches innervate the palate and cranial two thirds of the tongue (taste and proprioception). also parasympathetic innervation of glands (submandibular salivary, lacrimal)
anatomy = multiple specific nuclei are in medulla. innervation to the muscles and glands of the face: eyelids, lips, etc. Sensory fibers from tongue
clinical exam = observe facial asymmetry, droopy eyelids and lips, and inability to blink properly. observe menace response and palpebral reflex (is the animal able to blink in response to a threatening gesture or touching of the facial skin
-palpebral closure = brush finger across palpebral commissure, observe how tightly the animal is able to close its eye
clinical disease = facial paralysis
what is the function, anatomy, clinical examination and examples of clinical disease for the vestibulocochlear nerve
function = two branches. cochlear or auditory nerve has sensory function in hearing. vestibular nerve is involved in orienting the head and body
anatomy = vestibular portion consists of the vestibular nerve and the four vestibular nuclei in the brainstem (medulla). responsible for normal posture and coordination or eyes, head, neck, trunk and limbs. vestibular informaion is projected to CN III, IV, and VI via medial longitudinal fasciculus (MLF) and also to the cerebellum
-cochlear nerve travels together with the vestibular portion of CNVIII to the medulla
clinical exam = oculocephalic reflex tests: move head from side to side and observe symmetrical coordinated eye movement for NORMAL nystagmus.
observe for ABNORMAL nystagmus which occurs when the eyes move in a stationary animal. repeatedly back and forth (horizontal) up and down (vertical) or in circles (rotary or pendular). observe for vestibular ataxia, circling, head tilt
-hearing may be noted in history by owner
