ch. 14 - brain control of movement Flashcards
the brain influences activity of…
the spinal cord
- voluntary movements
strategy
association areas of neocortex, basal ganglia
tactics
motor cortex, cerebellum
execution
brain stem, spinal cord
sensorimotor system
sensory info used by all levels of the motor system
lateral pathways
- voluntary control of distal musculature
- under direct cortical control
ventromedial pathways
- control of posture and locomotion
- under brain stem control
coritcospinal tract (pyramidal tract)
- crosses at junction of medulla and spinal cord
- terminate in dorsolateral region of ventral horns and intermediate gray matter
rubrospinal tract
- starts in midbrain at the red nucleus
- crosses over in pons
- travels with axons of corticospinal tract
- role reduced in humans
lesions in lateral pathways cause…
- deficit in fractionated movement of arms and hands
- paralysis on contralateral side after stroke
ventromedial pathways
- originate in brain stem
- terminate on spinal interneurons controlling proximal and axial muscles
- use sensory info to maintain balance
vestibulospinal tracts
- head movements and balance
- from vestibular nuclei of the medulla
- one projects bilaterally down spinal cord to cervical circuits (head and back muscles)
- other ipsilaterally to lumbar spinal cord (upright and balanced posture)
tectospinal tract
- from superior colliculus (input from vision, somatosensory, auditory)
- produces orienting response
pontine reticulospinal tract
- originate from reticular formation of the brainstem,
- controlled by cortex
- enhances antigravity reflexes of the spinal cord
medullary reticulospinal tract
- originate from reticular formation of the brainstem,
- controlled by cortex
- liberates antigravity muscles from reflex
what areas make up the motor cortex?
4 and 6
area 4
primary motor cortex or M1
area 6
higher motor area
premotor area (PMA)
- lateral region
- connects to reticulospinal neurons that innervate proximal motor units
supplementary motor area (SMA)
- medial region
- axons to distal motor units directly
before motor actions, must have info from…
- somatosensory
- visual
- proprioceptive
area 5 receives input from…
areas 3, 1, 2
area 7 receives input from…
higher order visual cortical areas (like MT)
anterior frontal lobes
abstract thoughts, decision making, and anticipating consequences of action
area 6
actions converted into signals specifying how actions will be performed
per roland
monitored cortical activation accompanying voluntary movement (PET)
evarts
demonstrated importance of area 6 in planning movement
“ready”
parietal and frontal lobes
attention and alertness
“set”
SMA and PMA
strategies devised
“go”
area 6
basal ganglia is made up of..
- caudate nucleus
- putamen
- globus pallidus
- subthalamic nuclei
- substantia nigra
basal ganglia aids in…
selection and initiation of willed movements
basal ganaglia: input and output
- striatum receives input from cortex
- globus pallidus output to thalamus
basal ganglia gives input to..
VL nuclues
basal ganglia motor loop
cortical activation of putamen excites SMA and gives “go” signal
hypokinesia
increased inhibition of the thalamus by basal ganglia
hyperkinesia
decreased output of basal ganglia
parkinson’s
- hypokinesia
- trouble initiating willed movements due to increased inhibition of thalamus (VL) by basal ganglia
symptoms of parkinson’s
- bradykinesia (slow)
- akinesia (difficulty starting)
- rigidity and tremors of hand and jaw
organic basis of parkinson’s
degeneration of dopaminergic substantia nigra inputs to striatum, so no release of VL from inhibition
dopa treatment
facilitates production of dopamine to increase SMA activity
huntington’s disease symptoms
- hyperkinesia
- dyskinesia (abnormal movement)
- dementia
- impaired cognitive ability
- personality disorder
chorea
spontaneous, uncontrollable and purposeless movements with fast irregular flow, flicking movements
hemiballismus
- hyperkinesia
- violent, flinging movement on one side of the body
general role of basal ganglia
- focus activities from widespread regions of the cortex onto the SMA
- serve as filter to prevent inappropriate movements from being expressed
M1
lowest threshold for elicitation of movement by electrical stimulation (strong connections to motor neurons and spinal interneurons)
betz cells
pyramidal cells in cortical layer 5
sources of input to betz cells
- cortical areas ( 6 and 3, 1, 2)
- thalamus (which relays info from the cerebellum)
betz cells project to…
spinal cord and brain stem
force and direction of movement is encoded by…
activity from several neurons in M1
where are all cells active for every movement?
motor cortex
activity of each cells represents
a single vote
direction of movement
determined by a tally and averaging
malleable motor map - experimental rats
- microstimulation of M1 cortex normally elicits whisker movement
- cut nerve that supplies whisker movement
- microstimulation now causes forelimb movement
cerebellum
control sequence timing of muscle contractions
cerebellar lesions produce
- ataxia
- uncoordinated
- inaccurate movements
dysynergia
decomposition of synergistic multijoint movements
dysemtria
overshoot or undershoot target
anatomy of cerebellum
- folia and fissures increase surface area
- divided into 10 lobules
- 10% of brain volume, more than 50% of neurons
vermis
- divides hemispheres
- sends output to brain stem area that contribute to ventromedial pathways (axial musclature)
cerebral hemispheres
contribute to lateral pathways, especially cerebral cortex
motor loop through lateral cerebellum
- layer V pyramidal in sensorimotor cortex project to pons
- potine nuclei project to cerebellum
- lateral cerebellum projects back to motor cortex via thalamus
importance of motor loop through lateral cerebellum
- proper execution of planned voluntary multijoint movements
- movement, direction, timing, force
