The Cranial Nerves

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Transcript The Cranial Nerves

The Cranial Nerves
Honors Anatomy & Physiology
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• 12-pair
• named “cranial” because each passes thru a
foramina of the cranium
• part of PNS
• each with roman numeral (order from anterior
 posterior in which nerves arise from base
of brain) & a name that indicates nerve
• classified as:
1. sensory
2. motor
3. mixed (sensory & motor)
Cranial Nerve I: Olfactory
• olfact = to smell
• sensory
• olfactory epithelium on superior surface of
nasal cavity just inferior to cribiform plate of
ethmoid bone
• olfactory receptors are bipolar neurons
– each: single odor-sensitive dendrite
– their unmyelinated axons join above plate form rt or lt
olfactory nerves
Course of Olfactory Nerve
• olfactory nerves end in pair of olfactory bulbs:
masses of gray matter resting just above
cribiform plate where they synapse with next
neurons in olfactory pathway
Course of Olfactory Nerve
• axons of these neurons make up the olfactory
tracts  posteriorly to primary olfaction
center in temporal lobe
Cranial Nerve II: Optic Nerve
• optic = eye
• sensory
• rods & cones in retina: receptors initiating
visual signals & relay them  bipolar cells 
optic ganglion neurons  their axons join
forming optic nerves
• pass thru optic foramen  optic chiasm: a
cross-over of medial half of each eye to
opposite side (lateral half does not cross
Optic Tracts
• from optic chiasm  optic tracts
– most axons  thalamus  synapse with neurons whose
axons  primary visual area of occipital lobe
– some axons synapse with motor neurons in midbrain
extrinsic eye muscles
Cranial Nerve III: Oculomotor
• oculo = eye
• mixed, mainly motor
• its motor nucleus in
ventral part of midbrain
• 2 branches pass thru
superior orbital fissure
Oculomotor Nerve Extrinsic Muscles
of Eye
Superior Branch
• axons innervate:
1. superior rectus
2. levator palpebrae
superioris (upper eyelid)
Inferior Branch
axons innervate:
medial rectus
inferior rectus
inferior oblique
Oculomotor Nerve
• inferior branch also:
– parasympathetic innervation to intrisic muscle of eye
(smooth muscle)
1. ciliary muscle: adjusts lens for near/far vision
2. circular muscle of iris: contracts/relaxes in response to
amt of light (pupils constrict/dilate)
Oculomotor Nerve: Sensory
• proprioception: nonvisual perception of
movements & positions of body
Cranial Nerve IV: Troclear Nerve
trochle = pulley
mixed, mainly motor
smallest of the 12 cranial nerves
only 1 that arises from posterior of midbrain
Cranial Nerve IV: Troclear Nerve
• motor:
• axons from nucleus in midbrain  superior
orbital fissure
• innervates superior oblique muscle
• sensory: proprioception in superior oblique
Trigeminal Nerve
• largest of 12 cranial nerves
• mixed:
– sensory: ganglion in temporal bone
– motor: neurons in pons
Cranial Nerve V: Trigeminal Nerve
• tri: has 3 branches
1. Ophthalmic: sensory only: upper eyelids, eyes,
lacrimal glands, upper nasal cavity, side of nose,
forehead, anterior ½ of scalp
2. Maxillary: sensory only: mucosa of nose, palate,
part of pharynx, upper teeth, upper lip, lower
3. Mandibular: sensory: anterior 2/3 of tongue
(not taste), cheek, lower teeth
motor: muscles of mastication
Cranial Nerve VI: Abducens Nerve
• ab: away / ducens: to lead (nerve impulses
causes abduction of eyeball)
• mixed mainly motor
• nucleus in pons (motor): innervates lateral
rectus muscle
• sensory: proprioception in lateral rectus
Cranial Nerve VII: Facial Nerve
• mixed
• sensory:
– taste buds anterior 2/3 of tongue, proprioceptors in face & scalp
• motor:
– nucleus in pons
– innervates muscles of facial expression + stylohyoid muscle &
posterior belly of digastric muscle
• parasympathetic: lacrimal glands, palatine glands,
salivary glands: sublingual & sub-mandibular
Cranial Nerve VIII: Vestibulocochlear
• vestibule:small cavity; cochlear: snail-like
• mixed, mainly sensory
• 2 branches
1. Vestibular:
2. Cochlear:
motor: hair cells of spiral organ
Cranial Nerve IX: Glossopharyngeal
• glosso:tongue, pharyngeal: throat
• Mixed
• sensory: taste buds & somatic sensory receptors on
posterior 1/3 tongue, proprioceptors in swallowing
muscles, baroreceptors (stretch) in carotid sinus,
chemoreceptors in carotid bodies
• motor: from nuclei in medulla, exit thru jugular
foramen, innervate stylopharyngeus muscle (elevates
pharynx & larynx)
• parasympathetic: motor: stimulate parotid gland to
secrete saliva
Cranial Nerve X: Vagus Nerve
• vagus: wanderer, vagrant
• mixed
• distributed from head  abdomen
Vagus Nerve
• sensory:
skin of external ear
taste buds in epiglottis & pharynx
proprioceptors in muscles of neck & throat
baroreceptors in arch of aorta & chemoreceptors in aortic
– visceral sensory receptors in most organs of thorax &
abdominal cavities
Vagus Nerve
• parasympathetic motor:
– heart & lungs
– glands in GI tract
– smooth muscle of airways, esophagus, stomach, gall
bladder, small intestine, most of large intestine
Cranial Nerve XI: Accessory Nerve
• mixed
• originates from both the brainstem & spinal
• cranial root:
– motor: from medulla thru jugular foramen
– supplies voluntary muscles of pharynx, larynx, & soft
• spinal root:
– mixed, mainly motor
– motor:
Cranial Nerve XI: Accessory Nerve
• spinal root:
– mixed, mainly motor
– motor: neurons in anterior gray horn of C1 – C5  axons
come together  fpramen magnum  jugular foramen
– innervates sternocleidomastoid & trapezius muscles
– sensory: proprioceptors in muscles it supplies
Cranial Nerve XII: Hypoglossal
• hypo: below, glossal: tongue
• mixed
• sensory:proprioceptors in tongue muscles 
• motor: nucleus in medulla  hypoglossal
canal  muscles of the tongue (speech,
Development of the Nervous System
• begins developing in 3rd
wk from a thickening of
ectoderm called the
neural plate
Development of the Brain & Spinal