Organization of the Brain Stem

neuro lectures 5, 6
where are the nucleus gracilis and nucleus cuneatus located? which is medial?
in the caudal medulla (closed)
what happens at the nucleus gracilis/cuneatus?
fibers that have been traveling in the fasciculus gracilis and fasciculus cuneatus (dorsal column) synapse in their respective nuclei.
where do the projections from the nucleus gracilis/cuneatus go?
the axons from neurons in the nucleus gracilis and cuneatus travel ventrally across the midline as the internal arcuate fibers and bundle as the medial lemniscus
where does the medial lemniscus go after it is formed from the internal arcuate fibers?
the medial lemniscus continues to run rostrally through the upper medulla, pons and midbrain, it eventually terminates in the thalamus
what information is carried in the medial lemniscus?
touch, pressure, vibration and conscious proprioception from the contralateral side of the body
what is the difference between the medial lemniscus and the dorsal column?
"dorsal column" is the name given to the tract in the spinal cord, "medial lemniscus" is the name given to the tract in the brain stem
what happens to the spinothalamic tract once it enters the brain stem?
recall that the spinothalamic tract crossed over in the spinal cord, it just runs anterolaterally through the brainstem, at the level of the pons it runs adjacent to the medial lemniscus, also projects to the thalamus
what kind of information is carried by the spinothalamic tract in the brain stem?
pain and temperature sensation from the contralateral side of the body
what happens to the spinocerebellar pathway in the brainstem?
travels up the lateral side of the brain stem through the medulla, joins with axons from the external cuneate nucleus and enters the cerebellum through the cerebellar peduncles
what is the function of the external cuneate nucleus?
fibers carrying proprioceptive information from the upper half of the body have been running in the dorsal column system, they synapse in the external cuneate nucleus, 2nd order fibers from the ext. cuneate nucleus then enter the cerebellum
why is there no evidence of the spinocerebellar tract in the midbrain?
the fibers are destined for the cerebellum, so they have already left the brain stem pathways before the level of the midbrain
what information is carried by the spinocerebellar tract in the brainstem?
unconscious proprioceptive information from the lower body
what is the pathway of the corticospinal tract through the brainstem?
the corticospinal pathway descends from the motor cortex and travels in a column on the ventral surface of the pons and medulla, at the spino-medullay junction, the fibers of the tract cross over (pyramidal decussation) and run in the lateral funiculus on the contralateral side
main sensory trigeminal nucleus
information about discriminative touch from the ipsilateral face, conjunctiva and cornea, sends axons across the midline to asced to the thalamus with the medial lemniscus
spinal trigeminal nucleus relays pain and temperature information from which body areas?
ipsilateral face (CN 5), typmanic membrane, ext. auditory meatus and skin behind ear (CN 7), posterior 1/3 of tongue, pharynx, ext. auditory meatus again (CN 9, 10)
what sensory information does the main sensory trigeminal nucleus relay from other nerves?
cutaneous senation from tympanic membrane, ext. auditory meatus and skin behind ear (CN 7), posterior 1/3 of tongue, pharynx and ext. auditory meatus again (CN 9, 10)
mesencephalic trigeminal nucleus
relays proprioceptive information from muscles and joints of ipsilateral face and jaw, participates in reflex circuits with motor trigeminal nucleus to control force of bite
motor trigeminal nucleus
carries neurons that control the muscles of mastication and tensor tympani muscle (ispilateral)
what afferent information is carried by the facial nerve?
taste from anterior 2/3 of tongue (to nucleus solitarius), pain, temperature and cutaneous information from the tympanic membrane, ext. auditory meatus, skin behins ear (to main and spinal trigeminal nuclei)
nucleus of the solitary tract
recieves taste fibers from facial nerve for anterior 2/3 of tongue, projects to thalamus, also receives taste fibers from the glossopharyngeal nerve for the posterior 1/3 of tongue and from the vagus nerve for the epiglottis and pharynx
facial motor nucleus
receives input from bilateral cortex, spinal trigeminal nucleus and main motor nucleus of V, composed of 2 subnuclei, one controls lower facial muscles, the other controls upper facial muscles
why does upper motor neuron damage to facial motor cortex cause lower facial paralysis?
unilateral damage to the motor cortex knocks out inputs to the facial motor nucleus, but the upper motor cortex from the other side still functions and allows for control of upper facial muscles, lower facial muscles are paralyzed
why does a lesion in the facial nucleus cause Bell's palsy?
a lesion in the facial nucleus cuts off both sides of cortical input, leading to complete paralysis of the upper and lower facial neurons on one side
superior salivatory nucleus
receives inputs from the nucleus of the solitary tract and hypothalamus, innervates lacrimal gland (tearing) and sublingual and submandibular salivary glands
why do people with Bell's palsy have hyperacusis?
the facial motor nucleus also innervates the stapedius muscle, when that innervation is lost the muscle can't "clamp down" on the bone, the bones vibrate more and noises seem louder
what visceral afferents are carried with the glossopharyngeal nerve and where do they go?
taste information from the posterior 1/3 of the tongue projects to the nucleus solitarius, chemo/baroreceptive information from the carotid body is fed into local brainstem circuits
inferior salivatory nucleus
receives inputs from the solitary tract and nucleus and hypothalamus, innervates parotid gland
nucleus ambiguus
innervates the muscles of the pharynx and larynx and is important in vocalization and swallowing, fibers travel along vagus and glossopharyngeal nerves
what visceral afferents are carried by the vagus nerve and where do they go?
taste information from the epiglottis and pharynx travel to the nucleus solitarius, also carries chemo/baroreceptive information from the aortic arch, and feeling of nausea, satiety and fullness from the viscera (not sure where they go)
dorsal motor nucleus of the vagus
houses motor neurons that innervate cardiac muscle, lungs, esophagus and stomach
occlusion of which artery causes lateral medullary syndrome?
posterior inferior cerebellar artery (PICA)
what are the characteristics of lateral medullary syndrome (aka Wallenberg's)? what structure was damaged to cause the deficit?
hoarseness/dysphagia (nucleus ambiguus), loss of pain/temp on ipsi face (spinal trigeminal nucleus/tract), ipsi ataxia (inf. cerebellar peduncle), vertigo (vestibular nucleus), decreased taste ipsi (nucleus solitarius), horner's syndrome (descending sympathetics)
what are the 3 defining characteristics of horner's syndrome?
ptosis (drooping eyelid), miosis (small pupil), anhydrosis (lack of sweating)