Brainstem Flashcards
brainstem
1) midbrain
2) pons
3) medulla
midbrain derives from?
mesencephalon
pons derives from?
metencephalon
medulla derives from?
myelencephalon
borders of midbrain
mammilary bodies (of diencephalon)
isthmus of brainstem (aka pontomesencephalic junction)
anatomy of midbrain
1) tectum
2) tegmentum
3) cerebral aqueduct
4) cerebral peduncles
tegmentum
contains grey matter which contains nuclei and white matter which contains fibre tracts
nuclei of midbrain
1) CN III nuclei
- oculomotor nuclei
- Edinger-Wespinal (EW)
2) CN IV nuclei
3) CN V nuclei
- part of mesencephalic nuclei
4) red nucleus - cerebellar circuitry
5) substantia nigra - basal ganglia (dopamine circuit)
tectum
- pretectal area
- corpora quadrigemini
pretectal area
junction of midbrain and diencephalon
corpora quadrigemini
2 superior colliculi (eyes) and 2 inferior colliculi (ears)
CN V nuclei in brainstem
1) mesencephali nuclei (midbrain and ponds)
2) main sensory nuclei and motor nuclei (pons)
3) spinal nuclei (pons and medulla)
fibres/tracts of midbrain
1) corticospinal tract
2) medial lemniscus
3) spinothalamic tract
- medial longitudinal fasciculus
- decussation of sup. cerebellar peduncles
cerebral aqueduct
separates tectum and tegmentum
cerebral peduncles
separated by interpeduncular fossa
nerves emerging from midbrain
CN III - emerges ventrally from interpeduncular fossa
CN IV - emerges dorsally, caudal to inferior colliculi
borders of pons
isthmus of brainstem (between midbrain and pons)
pontomedullary junction (between pons and medulla)
fourth ventricle
anatomy of pons
1) tegmentum
2) basal pons
3) part of fourth ventricle
4) cerebellar peduncles
pontine nuclei
1) CN V
- part of mesencephalic nucleus
- main sensory nucleus
- motor nucleus
- part of spinal nucleus
2) CN VI
3) CN VIII
- motor nucleus
- part of sensory nucleus
4) CN VIII
5) basal pontine nuclei - specific to basal pons
6) superior olivary nucleus
pontine fibres
1) corticospinal tract
2) medial lemniscus
3) spinothalamic tract
4) pontocerebellar fibres
cerebellar peduncles
connect brainstem to cerebellum
superior cerebellar peduncles (SCP)
middle cerebellar peduncles (MCP)
inferior cerebellar peduncles (ICP)
nerves that emerge from the pons
CN V
CN VI
CN VII
CN VIII
boundaries of the medulla
pontomedullary junction (between the pons and the medulla)
foramen magnum - contines as spinal cord
pontomedullary junction
imaginary line connecting inferior aspects of middle cerebellar peduncles
divisions of medulla
1) rostral - open medulla (caudal portion of fourth ventricle is “open” dorsally)
2) obex
3) caudal - closed medulla (ventricle is enclosed by medullar tissue and continues as central canal of spinal cord)
anatomy of medulla
1) tegmentum
2) pyramids
3) olives
4) part of fourth ventricle, part of central canal
5) posterior column
medullary nuclei
1) part of CN V (sensory)
2) part of CN VII (sensory)
3) part of CN VII (sensory)
4) CN IX (motor and sensory)
5) CN X (motor and sensory)
6) CN XII (motor)
7) inferior olivary nucleus
8) posterior column nuclei
inferior olivary nucleus
in olives, lateral to pyramids
posterior column nuclei
nuclei gracilis (medial)
nuclei cutaneous (lateral)
medullary fibres
1) corticospinal tract - in pyramids
2) medial lemniscus - starts at post. column nuclei
3) spinothalamic tract
pyramids
contain corticospinal tract, decussate at spinomedullary junction
posterior column of medulla
fasciculus gracilis (medial)
fasciculus cuneatus (lateral)
fourth ventricle
diamond-shaped, brainstem forms floor (dorsal surface of pons, open portion of medulla)
sulcus limitans
little groove found in the fourth ventricle, divides motor vs sensory structures
nerves that emerge from medulla
CN IX
CN X
CN XII
hypoglossal trigones
motor area medial to sulculs limitans, XII nucleus
facial colliculus
cranial continuation of hypoglossal trigone, site of facial nerve loop, site of abducens (VI) nucleus
vagal trigone
motor area medial to sulcus limitans, doral (motor) nucleus of X
reticular formation
appears as diffuse network of nuclei and tracts throughout brainstem
functions of reticular formation
1) regulation of respiratory and circulatory systems
2) consciousness/ wakefulness/ sleep (RAS/ARAS)
functional organization of cranial nerves in the brainstem
SENSORY:
1) special sensory (Sp)
2) somatic sensory (Ss)
3) visceral sensory (Vi)
MOTOR:
1) autonomic (visceral) motor (A)
2) branchial motor (B)
3) somatic motor (Sm)
somatic motor
motor neurons controlling muscles of the body
branchial motor
motor neurons controlling muscles derived from teh branchial (pharyngeal/gill) arches
- ex. larynx, pharynx, superficial face
autonomic/visceral motor
preganglionic autonomic fibres, control visceral muscles
somatic sensory
pain, temperature, mechanical stimuli from the body
visceral sensory
sensory info from viscera, autonomic nervous system
special sensory
sensory info from “special senses”
- visual, vestibular, olfactory, auditory
CN I components
Sp - smell
CN II components
Sp - vision
CN III components
Sm - oculomotor nucleus (midbrain)
A - Edinger-Westphal nucleus (midbrain)
CN IV components
Sm - trochlear nucleus (midbrain)
CN V components
Ss - mesencephalic nucleus (midbrain + pons)
Ss - main sensory nucleus (pons)
Ss - spinal sensory nucleus (pons + medulla + spinal cord)
B - motor nucleus (pons)
CN VI components
Sm - abducens nucleus (pons)
CN VII components
Ss - spinal trigeminal nucleus (geniculate ganglion)
Vi - nucleus of solitary tract (pons + medulla)
A - superior salivatory nucleus (pons)
B - facial nucleus (pons)
CN VIII components
Sp - cochlear nuclei (pons)
Sp - vesibular nuclei (pons + medulla)
CN IX components
Ss - spinal trigeminal nucleus (superior ganglion of IX)
Vi - nucleus of the solitary tract (medulla)
A - inferior salivatory nucleus (medulla)
B - nucleus ambiguus (medulla)
CN X components
Ss - spinal trigeminal nucleus (superior ganglion of X)
Vi - nucleus of the solitary tract (medulla)
A - dorsal motor nucleus of vagus (medulla)
B - nucleus ambiguus (medulla)
CN XI components
B - acessorry spinal nucleus (spinal cord)
CN XII components
Sm: hypoglossal nucleus (medulla)
somatic motor nerves
III, IV, VI, XII
- simplest of cranial nerves (only belong to one category except III)
- nuclei adjacent to midline
EOM motor nuclei
III - MR, SR, IR, IO, levator
IV - SO
VI - LR
oculomotor nuclei
1) central caudal nucleus - levator (bilateral)
2) dorsal nucleus - IR (ipsilateral) and SR (contralateral)
3) intermediate nucleus - IO (ipsilateral)
4) ventral nucleus - MR (ipsilateral)
CN III lesions
- lateral strabismus
- ptosis
-mydriasis
lateral strabismus
LR is unopposed as there is no pull from MR to keep it even, associated with diplopia (double vision)
ptosis
dropping eyelids - central caudal nucleus (levator) affected
mydriasis
dilated pupil - dilator muscle unopposed as EW is affected causing the sphincter muscle to not function properly (autonomic)
CN IV lesions
affects down and out eye movement, diplopia when reading or descending stairs
CN VI lesions
medial strabismus
medial strabismus
MR is unopposed as LR does not pull to keep the eye even
horizontal conjugate eye movements
involve CN III (MR), CN VI (LR), and medial longitudiinal fasciculus
internuclear neurons from abducen’s nucleus go to contralateral med. long. fasciculus which then goes to oculmotor nuclei
hypoglossal nuclus
all intrinsic and extrinsic tongue muscles
ipsilateral projections
CN XII lesion (unilateral)
tongue deviates toward weak side, atrophy
branchial motor nerves
V, VII, IX, X, XI
- innervate striated muscle of branchial arch origin
- all but CN XI contain fibres of other components
- each CN has one major function
major function of CN V
major sensory nerve for head (Ss)
major function of CN VII
nerve for facial expression (B)
major function of CN IX
taste and pharyngeal sensations (Vi)
major function of CN X
outflow to thoracis and abdominal viscera (A)
major function of CN XI
motor nerve for sterncleidomastoid and trapezius muscle (B)
CN XI lesion
certain head movements altered, shrugging of shoulders weakened
motor nucleus of facial
muscles from 2nd branchial arch
- muscles of facial expression
- middle ear (stapedius muscle)
corneal reflex
corneal reflex
combination of sensory by V and motor by VII
trigeminal motor nucleus
muscles of 1st pharygeal arch
- muscles of mastication
- middle ear (tensory tympani muscle)
jaw-jerk reflex
glossopharyngeal motor nucleus
muscles involved in speaking and swallowing
vagus motor nucleus
pharyngeal and laryngeal muscles
gag reflex
gag reflex
sensory by glossopharyngeal, efferent by vagus
visceral (automic) motor nerves
major: X
minor: III, VII, IX
CN X autonomic nuclei
ambiguus nucleus - preganglionic fibres to heart, some othre organs of thorax and neck
dorsal motor nucleus - preganglionic parasympathetic fibres of enteric nervous system, supplies thoracic and abdominal viscera
Edinger-Westphal nucleus
visceral motor
projects to ipsilaterally ciliary ganglion
- sphincter mucle: contracts iris to make pupil smaller
- ciliary muscle: accomodation
facial visceral motor
superior salivary nucleus: goes to salivary, nasal, palatine, and lacrimal glands
glossopharyngeal visceral motor
inferior salivary nucleus: goes to otic ganglion (preganglionic) and parotid gland (post ganglionic)
somatic sensory nuclei
CN V
minor contributions (sensory from outer ear):
CN VII - geniculate ganglion
CN IX - superior ganglion of IX
CN X - superior ganglion of X
mesencephalic nucleus (V)
primary sensory input cell body, muscle spindles of jaw,
jaw jerk-reflex
main sensory nucleus (V)
touch and jaw position - ventral trigeminothalamic tract
inside of mouth info - dorsal trigeminothalamic tract
ventral trigeminothalamic tract
crossed
join medial lemniscus
terminate on VPM thalamus
dorsal trigeminothalamic tract
uncrossed
to VPM (separate area than medial lemniscus goes to)
spinal trigeminal nucleus (V)
crude touch, temperature, pain (head and face)
spinal trigeminal tract
spinal trigeminal tract
crossed
joins sppinothalamic tract
terminates at VPL, VPM, and other nuclei
visceral sensory nuclei
VII, IX, X
all involved in sensing info from taste buds and/or viscera
main nucleus is nucleus solitarious
special senses nuclei
I - smell
II - vision
VIII - hearing and balance
medial lemniscus
The medial lemniscus carries information about touch, vibration, and proprioception from the spinal cord to the thalamus
lateral lemniscus
The lateral lemniscus carries information about sound from the cochlear nucleus to the inferior colliculus
spinothalamic tract
a sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory area of the thalamus
corticospinal tract
The corticospinal tract, AKA, the pyramidal tract, is the major neuronal pathway providing voluntary motor function. This tract connects the cortex to the spinal cord to enable movement of the distal extremities
