week five - nervous system, cranial nerves

Question 1

describe the olfactory nerve [CNI]

Answer 1

func = smell
sensory afferent olfaction
exits via : foramina on cribriform plate of ethmoid bone
distribution
1. olfactory cells in roof of nasal cavity in epi.
2. axons of olfactory nerves carry info&raquo_space;> cribriform plate&raquo_space;> olfactory bulbs in ant. cranial fossa
3. synapse w/ mitral cells –> send afferent fibres down olfactory tracts to reach central cee [onnections]+ contrat. bulb

Question 2

describe the optic nerve [CNII]

Answer 2

func : vision
sensory afferent vision [attached to brain via diencephalon]
exits via optic canal
divs.
1. optic n.
2. optic chiasm
3. optic tract

distribution
1. retina rods + cones detect light
2. retinal axons come tgt = forms optic n.
3. signal travels&raquo_space; n.&raquo_space; via optic foramen
4. cross over of fibres from temporal visual fields at optic chiasms [sup. to pit. gland]
5. runs in optic tract –> area of thymus
6. relayed to visual cortex
7. RHS visual field relayed to LHS lobe - vice versa !!

Question 3

reflect the divisions of the optic nerve in a simple drawing

Answer 3

x

Question 4

describe the oculomotor nerve [CNIII]

Answer 4

func
- motor = supplies 4/6 extraocular musc
- parasymp = pupil constriction, accomodation of lens

exits via superior orbital fissure [SOF] of sphenoid bone

motor efferent –> caries preganglionic parasym fibres –> ciliary ganglion near eyeball

distribution [motor]
1. exits SOF –> splits into sup.inf. divs.
2. sup.div runs ant. and sup. around eyeball&raquo_space;> supps sup.rectus
3. inf.div runs ant. and inf. arounf eyeball&raquo_space;> supps medial rectus + inf.rectus

distribution [parasym]
1. innervates ciliary musc of lens and sphincter musc of pupil
2. terminates in inf.oblique musc

Question 5

describe the trochlear nerve [CNIV]

Answer 5

func = motor innervation to sup.obl.musc of eye [turns downward + medially]
- smallest n. but longest intracrnial course
exits via SOF of sphenoid bone
distribution
- only CN to arise from dorsal surface of brainstem, from midbrain
- runs sup. above opthalmic n.

Question 6

describe the abducens nerve [CNVI]

Answer 6

func : innervates lateral rectus of eye [abductor of eye]
motor efferent somatic
exits via SOF of sphenoid
distribution
1. runs to cavernous sinus [close to internal carotid a.] to lateral rectus of eye
2. often first n. to be affected by sinus infection

Question 7

describe how eye movement is innervated

Answer 7

THREE CN involv.

1. oculomotor [supplies 4/6 musc - [super.med.inf rectus, inf oblique]
2. trochlear [motor supp. sup.obl]
3. abducens [motor supp. to lateral rectus musc]

Question 8

describe the facial nerve [CNVII]

Answer 8

func:
- special sensory [taste of ant. 2/3 tongue]
- motor [musc of facial expression, middle ear, stylohyoid musc, post.belly of diagastric
- parasymp [lacrimal, subling. + submand. glands]

Question 9

describe the vestibulocochlear nerve [CNVIII]

Answer 9

func: special sensory [afferent]
- hearing/balance

exits: internal acoustic meatus of temporal bone

distribution
1. through inner ear
2. vestibular part -receives input from semicirc. ducts [balance]
3. cochlear part - arises from cells in cochlear of ear [hearing]
4. these two n. come tgt to form CNVIII w/ facial n. branch

Question 10

describe the glossopharyngeal nerve [CNIX]

Answer 10

motor + sensory nerve
func:
- motor : stylopharungeus
- parasym: to parotid gland
- special sensory : post. third of tongue
- sensory : from post third of tongue, pharynx, middle ear cav., carotid sinus, body

exits: jugular foramen

distribution
1. parasym fibers leave skulls through foramen ovale of sphenoid bone as lesser petrosal n. for otic ganglion
2. inf. branches of n. = carotid sinus, pharyngeal, musc to stylopharyngeus, tonsilar and lingual branches

Question 11

describe the vagus nerve [CNX]

Answer 11

motor + sensory
func:
- motor : musc of pharynx + larynx [except stylopharyngeus]
- parasym: smoo musc of trachea, bronchi, digestive tract, cardiac musc of heart
- special : taste [epiglottis, palate]
- general sensory : tongue, pharynx, larynx, bronchi, heart, stomach, intestine

exits: jugular foramen
distribution
1. accompanies acc.n as it emerges from skull + connected to hypogloss.n. in sup. aspect of neck
2. descends through inf. part of neck as vagus n.
3. in thorax = joins w vagus n. from opposite site = forms cardiac, pulmonary and esophageal plexus
4. supps. organs and viscera of thorax + abdomen

Question 12

describe the accessory nerve [CNXI]

Answer 12

motor nerve
func: sternocledomastoid + trapezius
exit: jugular foramen
distribution:
1. series of rootlets [first 5 or 6 cervical segments] asc. through foramen magnum&raquo_space;> exits cranial cav. w/ vagus n. through jugular foramen
2. desc along int.carotid.a&raquo_space;> supps. sternocleidomastoid + trapezius

Question 13

describe the hypoglossal nerve [CNXII]

Answer 13

motor
func: intrinsic + extrinsic musc of tongue [except palatoglossus -innerv. by CNX]
exits: hypoglossal canal

distribution
1. leaves cranial cavity - joined by branch/es of cervical plexus conveying general somatic motor fibre and general sens branches
2. passes over angle of mand.&raquo_space;> curves anteriorly to enter tongue