Motor 1 Flashcards
describe the hierarchy of the motor system
highest: cerebral cortex
middle: brain stem
lowest: spinal cord
the final common pathway for movements
a motoneurones in spinal cord
upper motor neurones
connect cerebrum and brain stem with spinal cord
lower motor neurones
connect cranial nerve nuclei in brainstem and spinal cord with muscles
white matter
tracts of axons carrying information to and from the brain
- ascending: sensory information to the brain
- descending: carry commands to motor neurons
grey matter
sensory and motor nuclei
list the white matter tracts
lateral
- corticospinal
- rubrospinal
ventromedial
- medullary recticulospinal
- pontine reticulospinal
- vestibulospinal
- tectospinal
function of lateral tracts
control voluntary movements
axons from cortex
- CST
- RST
functions of medial tracts
control posture and locomotion
axons from brainstem
- VS: stabilises head and neck
- TS: ensures eyes remain stable as body moves
- reticulospinal tracts: reflexly maintain balance and body position
describe the lower motor neurone distribution
medial ventral horn (posture and balance)
- innervate axial and proximal limb muscles
lateral ventral horn (voluntary movements)
- innervate distal limb muscles
describe sensory inputs at all levels
spinal cord: proprioceptors, touch, pain
brainstem: vestibular system informs about balance
cortical level: visual, olfactory, auditory, emotional, intellectual cues
spinal cord reflexes
simple building blocks for movement
brainstem nuclei control spinal reflexes and integrate them into higher order reflexes that control posture and balance
describe stretch reflex
muscle stretch stimulates muscle spindles
activates sensory 1a afferent nerves firing of APs
causes muscle contraction and muscle shortens to previous length
describe inverse stretch reflex
muscle contracts and shortens which pulls on the tendon
activates sensory 1b afferent nerves firing of APs
muscle inhibited and relaxes rapidly
describe flexor/withdrawal reflex
polysynaptic and protective
ipsilateral flexion and contralateral extension in response to pain
can reflexes be overridden
yes from voluntary input from CNS
descending voluntary excitations of a motoneurones overrides inhibition from GTOs and maintains muscle contraction
what is the clinical relevance of reflexes
assesses integrity of the whole spinal cord circuit
help spinal level localisation of a problem
primary motor cortex
pre-central gyrus or area 4
pre motor areas
area 6
contains:
- premotor area
- supplementary motor area
where are somatotopic maps of the body located
human cortex
- pre motor area: innervates proximal motor units
- supplementary motor area: innervates distal motor units
describe the process of making decisions
areas 5 & 7 (prefrontal and parietal cortex): involved in decidint which actions/movements to take
area 6: axons converge here and plan how to carry this out
area 4: doing the action
decision making neurones
PMA (area 6) neurones fire APs one second before a movement occurs
mirror neurones
PMA (area 6) also fire when others make the same specific movement
allows understanding of actions/intentions of others
when do PMA (area 6) neurones fire
movement is made
movement is imagined
movement is done by someone else
deciding the direction of a movement
each neurone has a preferred direction but the responses of all neurones are combined to produce a population vector
feedback mechanisms controlling movement
change in body position
rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones
correct postural instability
feedforward mechanisms
before movements begin
brainstem reticular formation nuclei initiate feedforward anticipatory adjustments
to stabilise postural instability
basal ganglia motor loop
a loop of information cycles from the cortex through the thalamus and basal ganglia and back to the cortex (SMA)
