Brain Stem Tracts and Anatomy Flashcards
parts of the brain stem
in continuous order: midbrain, pons, medulla (oblongata)
pair of fiber bundles ventral to the midbrain in the brain stem
cerebral peduncles (feet) major tract of axons of voluntary motor neurons (corticospinal tract)
the large bulge ventral to the pons in the brain stem contains a massive series of neurons that project to overlying…
cerebellum
what do the medullary pyramids contain
corticospinal tracts (which are the same tracts that run through cerebral peduncles)
bulging out from the upper lateral portion of the medulla is a pair of ___, which contain neurons that project almost exclusively to the cerebellum
olives
inform cerebellum in errors in smooth execution of movement
where are the superior and inferior colliculus and what do they do
dorsal side of midbrain (two pairs of small mounds)
superior- vision (gaze)
inferior- auditory stimuli
where is the fourth ventricle
on top of the entire pons and part of the medulla
which cranial nerve is not a true cranial nerve (name and number)
cranial nerve XI (11), spinal accessory (motor)
exits through foramen magnum. arises from cervical spinal cord
which 3 cranial nerves do not arise from brain stem
I (olfactory), II (optic), XI (spinal accessory- motor)
the __ is home to cranial nerves III and IV
the __ is home to cranial nerves V, VI, VII, VIII
midbrain- III (oculomotor) and IV (trochlear)
pons- V (trigeminal), VI (abducens), VII (facial), VIII (vestibulocochlear)
the largest cranial nerve, and the only true pontine nerve (because it enters/exits directly from substance) is ___
cranial nerve V (trigeminal, mixed)
cranial nerves VI, VII, VIII are at pons-medulla junction
the only completely crossed cranial nerve is __
IV, trochlear (motor, eye movement)
name/number of the three sensory cranial nerves
I (olfactory), II (optic), VIII (vestibulocochlear- somewhat mixed though)
name/number of motor cranial nerves
III (oculomotor)- eye IV (trochlear)- eye VI (abducens)- eye XII (hypoglossal) XI (accessory)- cervical spinal cord
name/number of four mixed cranial nerves
V (trigeminal)
VII (facial)
IX (glossopharyngeal)
X (vagus)
cranial nerve I
olfactory, sensory
cranial nerve II
optic, sensory
cranial nerve VIII
vestibulocochlear, sensory (somewhat mixed)
cranial nerve III
oculomotor (motor)
cranial nerve IV
trochlear (motor)
cranial nerve VI
abducens (motor)
cranial nerve XII
hypoglossal (motor)
cranial nerve XI
accessory (motor)- cervical spinal cord
cranial nerve V
trigeminal (mixed)
cranial nerve VII
facial (mixed)
cranial nerve IX
glossopharyngeal (mixed)
cranial nerve X
vagus (mixed)
the axons of the corticospinal tract run down entire length of brain stem and cross at lower medulla levels at the ___?
pyramidal decussation
this tract runs down the entire length of the spinal cord and provides a way for the diencephalon (specifically the hypothalamus) to control sympathetic tone at spinal cord level
hypothalamic axons/fibers (hypothalamospinal fibers)
spinothalamic tract
ascending axons carrying sensation from limbs/trunk of pain/temp/itch
runs parallel (but it opposite direction) to descending hypothalamic axons
dorsal columns of brain stem
sensory axons that process touch, vibration, pressure, proprioception from tactile/ muscle position receptors at limbs and trunk
synapse on second neurons in lower medulla in dorsal column nuclei
the dorsal columns (sensory axons of limbs/trunk) synapse on dorsal column nuclei in lower medulla, which cross and form ___
medial lemniscus
every brain stem cross section will feature these 4 tracts:
corticospinal tract
descending hypothalamic fibers
spinothalamic tract
medial lemniscus
this tract descends medially and ventrally through the entire brain stem. what is?
corticospinal tract. always medial and ventral (front) through the midbrain to pons to medulla (goes top to bottom- descending)
medial brain stem strokes have potential to lesion what tract?
corticospinal tract (ventral and medial running)
after descending through the medial and ventral portion of the brain stem, the axons of the corticospinal tract cross at the lower medulla at the pyramidal decussation, and from there descend the spinal cord in the ____ portion of the ___ matter
corticospinal tract- lateral portion of spinal cord white matter
the corticospinal tract axons cross at pyramidal decussation, run through lateral portion of white matter in spinal cord, then synapse on lower motor neurons whose bodies are in the ___ of the spinal cord ___ matter
UMN- axons in lateral white matter of spinal cord
LMN- bodies in ventral horns of gray matter of spinal cord
spastic weakness or paresis develops from what kind of lesion? patient will also present with hyperactive muscle stretch reflexes
lesion in corticospinal tract (UMN). Paresis will be contralateral and below point of lesion
why does lesion of UMN in corticospinal tract result in hyperactive muscle stretch reflexes?
UMN have net inhibitory effect on muscle stretch reflexes, so loss of innervation disinhibits muscle stretch reflexes
Babinski sign, and what does it signify?
backwards cutaneous reflex (upgoing toes), signifies corticospinal tract lesion
hypothalamic axons descend through ___ portion of brain stem
lateral
a lateral brain stem vascular syndrome has the potential to affect what tract?
descending hypothalamic fibers which run through lateral portion of brain stem
ipsilateral central Horner’s syndrome is caused by disruption of what?
descending hypothalamic axons (hypothalamospinal fibers)
disruption in hypothalamus control over sympathetic innervation to face, scalp, smooth muscles in orbit
what are the three neurons of sympathetic pathway
- hypothalamus (above brain stem)- descends through entire brain stem, lateral portion
- upper thoracic spinal cord (T1-T3)- descend through sympathetic trunk
- superior cervical ganglion- provides all sympathetic innervation
patient presents with ipsilateral miosis (constricted pupil), ptosis (eyelid drooping), anhydrosis (loss of sweating), and orthostatic HTN (drop in bp from lying to standing). what is likely?
ipsilateral central Horner’s syndrome (loss of SNS input from hypothalamus)
orthostatic htn
bp drop from lying to standing