Lecture 6: Brainstem and Cranial nerves (II) Flashcards
Visual pathway flow
Starts at the retina and the ret4inal ganglion cells go back and form the optic nerve and then some of the axons cross over and some don’t, where the cross over occurs is called the optic chiasma, and then they keep going back as the optic tract and innervate various structures like the superior colliculus and the lateral geniculate nucleus of the thalamus, then the axons from the lateral geniculate nucleus go back to the visual cortex which is the overall pathway, also have the superior colliculus pathway which shows how these axons go to various motor nuclei
Damage at the optic chiasm (cross over) causes …
Bitemporal hemianopsia - peripheral vison loss, nasal retina on each side damaged, the nasal retinas see the temporal visual fields, pituitary tumour or hypothalamus tumour can put pressure on the optic chiasm and cause this
Optic nerve
axons of the retinal ganglion cells
Optic chiasm
fibers originated from nasal retina cross over to the opposite side
Optic tract
contains crossed axons from nasal retina & uncrossed axons from temporal retina
Lateral geniculate nucleus of the thalamus
processes & relays visual information to visual cortex
Superior colliculus
visual reflex centres controlling the extrinsic eye muscles
Primary visual cortex (occipital lobe)
- processes basic visual information (contrast information & object orientation)
- conscious perception of visual images
Visual association ateas (occipital lobe)
processes visual information concerned with shape, colour & movement
next to primary visual cortex
Complex visual processing - ventral parts of temporal lobe
identify objects in the visual field (what)
ventral stream
Complex visual processing - parietal cortex
assess the spatial location of objects (where)
dorsal stream
Complex visual processing - frontal cortex
uses visual information to guide movement
Oculomotor nerves location
Cranial nerve III
Axons extend from ventral midbrain, goes forward & passes through the superior orbital fissure to the eye
Oculomotor nerves composition overall
Mixed nerves - chiefly motor
Somatic motor axons
Parasympathetic (autonomic) motor axons
Sensory (proprioceptor) afferents
Oculomotor nerves composition - Somatic motor axons
to four of the six extrinsic (muscles on the outside of the eye) eye muscles (inferior oblique muscle and superior, inferior and medial rectus muscles)
- move eyeball
- to levator palpebrae superior muscle - raising upper eyelid
Oculomotor nerves composition -Parasympathetic (autonomic) motor axons
- to constrictor muscles of iris (coloured part of the eye)- causing pupil to constrict
- to ciliary muscle –controlling shape of lens for visual focusing
Oculomotor nerves composition - Sensory (proprioceptor) afferents
information from the PNS to CS - information communicated from the eye muscles to the midbrain
Oculomotor nerves known as the …
eye mover
Provide most of the movement of each eye
Also - opening of eyelid, constriction of pupil, focusing
Damage to oculomotor nerves
Damage causes drooping upper eyelid, dilated pupil, double vision, difficulty focusing & inability to move eye in certain directions
muscles its innervating are affected
Trochlear nerves location
Cranial nerve IV
Axons emerge from dorsal midbrain, course ventrally around midbrain, pass through the superior orbital fissure to the eye
**Only cranial nerve emerging from dorsal brainstem
What cranial nerve is the only one to emerge from the dorsal brainstem?
Trochlear nerve (4th cranial nerve)
Trochlear nerve composisotn
primarily motor (chiefly motor)
Supply somatic motor axons to (& carry proprioceptor axons from) the superior oblique muscle (which rotates the eye downward & laterally) [SO4 - superior oblique muscle innervated by the 4th cranial nerve]
- This muscle has a tendon that hooks around a pulley called a trochlea
- Provide eye movement
Trochlear nerve damage
Damage causes double vision & inability to rotate eye inferolaterally
double vision because not all muscles are working together to get clear vision
Trigeminal nerve location
cranial nerve V
3 major branches - ophthalmic division (VI), maxillary division (V2) and mandibular division (V3), one on each side
Axons extend from face to pons (S - sensory = large component) & pons to muscles (M - motor = small component)
Cell bodies of sensory neurons are located in large
trigeminal ganglion
Divisons of the trigeminal nerve
3 major branches - ophthalmic division (VI), maxillary division (V2) and mandibular division (V3)
Opthalamic division (V1) of trigeminal nerve
Axons run from face to pons via superior orbital fissure
Convey sensory impulses from skin of anterior scalp, upper eyelid & nose, & from nasal cavity mucosa, cornea & lacrimal (tear) gland - all of the sensory information from these structures is going to the pons via the superior orbital fissure
Maxillary division (V2) of trigeminal nerve
Axons run from face to pons via foramen rotundum
Convey sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek and upper lip
anaesthetised when getting upper teeth dental work
Mandibular division (V3) of trigeminal nerve
Axons pass through skull via foramen ovale
Convey sensory (pain, temp (hot and cold) but not taste from the tongue) impulses from anterior tongue (except taste buds), lower teeth, skin of chin, & temporal region of scalp
V3 has a motor branch - Supply motor axons to (carry proprioceptor axons from) muscles of mastication (chewing muscles)
Trigeminal nerve composition
Mixed nerves - mainly sensory
- Largest cranial nerves
- Main sensory nerve from face (transmitting afferent impulses from touch, temperature & pain receptors)
- Supply motor axons to muscles of mastication (V3)
Part of each nerve can be anaesthetised during dental procedures
Trigeminal nerve damage
Damage produces loss of sensation & impaired
chewing
Tic Douloureux (trigeminal neuralgia)
- inflammation of trigeminal nerve (pressure on nerve root)
- excruciating pain
- provoked by a sensory stimulus in area of supply (touching forehead for example)
- analgesics - partially effective
- Nerve cut in severe case to relieve pain (but causing sensation loss)
Abducens nerve location
Cranial nerve VI
Axons leave inferior pons & pass through superior orbital fissure to eye (lateral rectus muscle)
Abducens nerve function
Provide eye movement (abducts the eyeball - i.e. moves it from the midline )
Abducens nerve damage
Damage results in inability to rotate eye laterally & at rest eye rotates medially (lazy eye)
Facial nerves location
Cranial nerve VII
Axons emerge from pons, enter temporal bone via internal auditory meatus and run within bone (bony canal) (through inner ear cavity) before emerging through stylomastoid foramen; course to lateral aspect of face
Branches of the facial nerves from most superior to inferior
temporal zygomatic buccal (cheek) mandibular (mandible/jaw) cervical (neck)
Mandibular branches for both
trigeminal and facial nerves (do not get confused between the two)
Facial nerves composition
Mixed nerves
Major motor axons of face
- Supply motor axons to (convey proprioceptor impulses from) skeletal muscles of face (muscles of facial expression), except for chewing muscles served by cranial nerve V (trigeminal supplies this instead)
- Transmit parasympathetic (autonomic) motor impulses to lacrimal (tear) glands, nasal & salivary glands
- Convey sensory impulses from taste buds of anterior 2/3 of tongue - taste from anterior part of tongue through this nerve
Facial nerves damage
Damage produces sagging facial muscles & disturbed sense of taste (missing sweet, salty & umami)
Bells Palsy
facial nerve damage
usually unilateral not bilateral
characterised by paralysis of facial muscles (affected
side) & partial loss of taste sensation (because the facial nerve is not responsible for all of the taste information)
- viral infection causing inflammation of facial nerve
- symptoms: lower eyelid droops, corner of mouth sags, tears drip continuously, eye cannot be completely closed, paralysed face is ‘pulled’(to the other side). Treatment: steroids, rest
Vestibulocochlear nerve location
Cranial nerve 8
Axons arising from hearing & equilibrium apparatus (which is the cochlea and the semicircular canals) within inner ear of temporal bone, passing through internal acoustic meatus to enter brainstem at the pons- medulla border
more laterally arising than the facial nerves on the pons - medulla junction/inferior part of pons
Vestibulocochlear nerve composition
Purely sensory
Provide hearing (cochlea nerves) and sense of balance (vestibular nerves)
Vestibulocochlear nerve damage
Damage produces deafness, dizziness,
nausea, loss of balance and nystagmus (rapid involuntary eye movements)
Auditory pathway
Pathway from the sensory receptors to the brain …. Stimulation of an inner hair cell in the cochlea which generates an action potential which runs down the vestibulocochlear nerve and then it follows a pathway innervating various collections of nerves (don’t need to know names of the pathway just appreciate there is one), so the action potential runs in the vestibulocochlear nerve to the cochlear nucleus of that nerve then in turn these neurons innervate the superior olivary nucleus which then goes and innervates the inferior colliculus which we know is a part of the auditory pathway and it crosses to the other side here and then from the inferior colliculus information is conducted up to the thalamus but now to the medial geniculate body and from here it goes up to the primary auditory cortex and another name for this is the transverse temporal gurus
Glossopharyngeal nerves location
Cranial nerve 9
Axons emerge from medulla & leave skull through jugular foramen - it is the first nerve that emerges from the medulla
Glossopharyngeal nerves composition
Mixed nerves with sensory and motor component
Glossopharyngeal nerves function
• Supply motor axons to (carry proprioceptor fibers from) a pharyngeal muscle - stylopharyngeus (skeletal muscle)
• Provide parasympathetic motor axons to parotid
salivary gland (smooth muscle)
- Sensory axons conduct taste & general sensory impulses from pharynx & posterior 1/3 of tongue
- Conducting sensory impulses from chemoreceptors (detect oxygen levels and determine whether you are hypoxic or not) in the carotid body & pressure receptors of carotid sinus
Provide control over swallowing, salivation, gagging, sensations from posterior 1/3 of tongue, control of blood pressure & respiration
Glosspharyneal nerve damage
Damage results in loss of bitter & sour taste, and impaired swallowing
Vagus nerve location
Cranial nerve 10
Axons emerge from medulla, pass through skull via jugular foramen, descend through neck region into
thorax & abdomen
Vagus nerve composition
mixed nerve
motor
Supply motor axons to (carry proprioceptor fibers from) skeletal muscles of pharynx & larynx
- Parasympathetic motor fibers supply heart, lungs & abdominal viscera
sensory axons
conducting sensory impulses from thoracic &
abdominal viscera
- transmitting sensory impulses from chemoreceptors in the carotid & aortic bodies, & pressure receptors of carotid sinus
- conducting sensory impulses from taste buds of posterior tongue & pharynx
Vagus nerve is the only cranial nerve to do what
The only cranial nerve extending beyond the head &
neck to the thorax & abdomen
Majority of vagus nerve motor axons are
Majority of motor axons are parasympathetic
Overall function of vagus nerve
Provide swallowing & speech;
• regulate activities of major viscera
Vagus nerve damage
Damage causes hoarseness or loss of voice, impaired swallowing & digestive system mobility
Fatal if both are cut - critical for heart and lungs to maintain function
Accessory nerves location
Cranial nerve 11
Accessory to vagus nerve
Cranial root (lateral medulla) - through jugular foramen - joins vagus nerve (X)
Spinal root (spinal C1-C5) - through foramen magnum - to neck muscles
Cranial root of accessory nerves
Cranial root joins with axons of vagus nerve (X) to supply motor axons to larynx, pharynx & soft palate
Accessory nerve composition
mixed nerves - primarily motor
Damage to cranial root of accessory nerves
Damage causes hoarseness or loss of voice & impaired swallowing
Spinal root of accessory nerves
Spinal root supplies motor axons to (conveys proprioceptor impulses from) trapezius &
sternocleidomastoid muscles, therefore provides head, neck & shoulder movement
Damage to spinal root of accessory nerves
Damage causes impaired head, neck & shoulder movement. eg. unable to shrug on one side if unilateral injury
Hypoglossal nerves location
(below tongue)
Cranial nerve 12
- Axons arise by a series of roots from medulla, exit from skull via hypoglossal canal to tongue
- Axons emerge between the pyramid & olive
Hypoglossal nerves composition
primarily motor
Supply somatic motor axons to (convey proprioceptor impulses from) intrinsic & extrinsic muscles of tongue
Provide tongue movements of speech, food manipulation & swallowing
Damage to hypoglosaal nerves
Damage causes difficulties in speech & swallowing Both sides - inability to protrude tongue
One side - tongue deviates (leans) towards injured side & results in ipsilateral atrophy eventually
Olfactory - sensory function? motor function? parasympathetic fibres?
yes (smell)
No
No
Optic - sensory function? motor function? parasympathetic fibres?
yes (vision)
No
No
Oculomotor - sensory function? motor function? parasympathetic fibres?
No
Yes
Yes
Trochlear - sensory function? motor function? parasympathetic fibres?
No
Yes
No
Trigeminal - sensory function? motor function? parasympathetic fibres?
Yes (general sensation)
Yes
No
Abducens - sensory function? motor function? parasympathetic fibres?
No
Yes
No
Facial - sensory function? motor function? parasympathetic fibres?
Yes (taste)
Yes
Yes
Vestibulocochlear - sensory function? motor function? parasympathetic fibres?
Yes (hearing and balance)
No
No
Glossopharyngeal - sensory function? motor function? parasympathetic fibres?
Yes (taste)
Yes
Yes
Vagus - sensory function? motor function? parasympathetic fibres?
yes (taste)
Yes
Yes
Accessory - sensory function? motor function? parasympathetic fibres?
No
yes
No
Hypoglossal - sensory function? motor function? parasympathetic fibres?
No
yes
no
Reticular formation
DO NOT FORGET TO DO THE LAST FEW SLIDES OF THIS LECTURE !!!!
