descending motor pathways Flashcards
motor system evolution
- reticular formation
- vestibular system
- tectum
- red nucleus
- cerebral cortex
- (later) pyramidal tract
reticular formation
random network of neurons that has a reticulospinal pathway that modifies excitability of neurons in the spinal cord
vestibular system
semicircular canals give us position in space, in relation to gravity
(up vs down)
tectum
contain superior and inferior colliculus for visual and auditory inputs
red nucleus
- primitive corticospinal tract
- has excitatory and controlling affects on more distal muscles
cerebral cortex
controlled lower stations in the motor pathway
somatotopic organization of ventral horn
more medial the muscle, the more medial the neurons are in gray matter
descending pathways
- lateral pathways
- medial pathways
lateral pathways control
distal musculature
- include: lateral corticospinal tract
skilled muscle movement
medial pathways control
axial and proximal musculature
- include: vestibulospinal, reticulospinal, tectospinal tracts
cells of motor cortex
giant pyramidal cells
physiology of motor cortex
- pyramidal cell fires impulses prior to muscle movement
- organized to produce simple movements of individual body parts
- determines direction, amplitude, speed and force of movement
- not organized to control individual muscles
somatotopy of motor cortex
motor area given to parts of the body that perform more precise and delicate movements compared to those that perform less precise movements
- movements not muscles!!
efferent pathway
- axons thru white matter
- to internal capsule
- to crus cerebri/cerebellar peduncle
- pyramidal fibers pierce the pons
- pyramids of medulla
- lateral corticospinal tract
other parts of the cerebral cortex that is involved with motor function
- premotor cortex
- supplementary motor cortex
premotor cortex
- affects motor cortex
- organizes neurons into more complex units of movement
- triggers movement of response to visual and other stimuli
- directs reaching and grasping movements
“preparation of movement”
supplementary motor cortex
- higher level of motion control
- concerned with mvmt that is self generated
- bilateral movements
corticobulbar tract
- cell bodies in motor cortex (lateral convexity)
- fibers leave through internal capsule
- exit in midbrain, pons, and medulla
- innervate cranial nerve motor nuclei
- crossed and uncrossed fibers
(motor cortex to cranial nerve nuclei)
corticobulbar tract interacts with these nuclei:
- trigeminal motor nucleus
- nucleus ambiguus
- facial motor nucleus (upper face)
- facial motor nucleus (lower face)
- hypoglossal nucleus
which nuclei have completely crossed tracts? (control contralateral sides)
- facial motor nucleus (lower face)
- hypoglossal nucleus
abducens and facial nerves
bell’s palsy symptoms
- droopy eyelid, dry eye, or excessive tears
- facial paralysis, twitching, weakness
- drooping corner of mouth, dry mouth, impaired taste
bell’s palsy can be caused by
lesion of CN VII
- lesion on left side = paralysis of left side of face
lower face nucleus receive input from
opposite side motor cortex face area only
the upper face gets inputs form
same side AND opposite side motor cortex
what if there is a lesion of motor cortex on opposite side?
- the axons will degenerate
- lost control of lower part of the face
- still have control of the upper half of the face bc it also receives same side signals
why is it bad if only the lower half of the face lost motor function?
- indicative of a stroke in dangerous area
- disrupted the cranial nerve (7?)
- motor cortex damages
jacksonian march
the spreading of seizure from primary location to other parts of the body (I.e. from thumb to face)
epilepsy is the result of
excessive activity of neurons
- opposite of a lesion
upper motor neuron lesion
- slight muscle atrophy
- no fasciculation
- hyperreflexia
- increased/spastic muscle tone
lower motor neuron lesion
- severe muscle atrophy
- fasciculation
- hyporeflexia
- decreased/flaccid muscle tone
spastic hemiplegia cause
stroke of left hemisphere
symptoms of spastic hemiplegia
- arm is flexed upward
- knee is straight out
- fingers are curled due to hyperactivity of stretch reflexes
- excess tone due to UMN lesion (no descending inhibition to blow out unnecessary reflexes
Babinksi Response Test
- in babies less than 1 year
- run finger along bottom of foot
- toes will flare and withdraw foot
when is the Babinski reflex suppressed?
- after 1 year of age
- helps ability to walk
- not present in adults (curl toes instead)
grasp reflex
- when anything touches a baby’s palm, fingers close
- reflex is outgrown unless damage to motor cortex
