lecture 8 - brain and muscles Flashcards
cerebellum
interact w sensorimotor hierarchy. coordinate and modulate.
important for sequence motor learning.
compares M1, M2, motor signals from brain stem and somatosensory, vestibular systems
complex = 10% mass, 50% neurons.
also sensory, cognitive and emotional function.
cerebellar damage
devestates motor function. no precise control of direction, force, velocity. no adaptation to changign conditions
basal ganglia
interact with sensrimotor hierarchy
coordinate, modulate cortical activity. interconnect sensory and motor areas. role in high level cognition.
motor loop : cortical input -> BG -> thalamus -> motor cortex
cognitive - procedural/habit learning
2 major dorsolateral tracts
dorsolateral corticospinal tract
dorsolateral corticorubrospinal tract
dorsolateral corticospinal tract
direct
voluntary movement
m1 –> medulla (decussate) –> directly synapse on motor neurons of distal muscles.
only present in animals that can move digits independently
betz cells!
betz cells
large pyramidal cells in M1. axon at base of neocortex. terminate in lower regions of spinal cord on leg motor neurons. involved in rapid and powerful voluntary leg movements.
dorsolateral corticorubrospinal tract
indirect.
M1 –> red nucleus (decussate) –> medulla.
some terminate on trigeminal nerves, others to interneurons which innervate motor neurons of distal muscles.
2 major ventromedial tracts
ventromedial corticospinal tract
ventromedial cortico-brainstem-spinal tract
ventromedial corticospinal tract
direct
posture and locomotion - well learned task.
descend ipsilaterally, branches diffusely - no decussation. innervated both sides of spinal grey matter
ventromedial cortico-brainstem-spinal tract
indirect
feed into complex network of brain stem structures
each side carries both hemispheres. synapse on several spinal cord segments - control proximal trunk and limbs
brainstem structures in VM CBS tract
tectum - auditory (inferior colliuli - sound localization), and visual (superior colliculi - eye movement)
vestibular nucleus - balance, contributes to cerebellum
reticular formation - motor programs for complex species - specific movements.
well learned reflexes.
motor nuclei of cranial nerves - control facial muscles
similarities in dorsal and ventral tracts
project from M1
mediate voluntary movement
each composed of 2 tracts.
differences btw dorsal and ventral tracts
ventral more diffuse. activate proximal muscles. posture and whole body movement. species- specific activity.
doral - terminate contralateraly. activate distal muscles. limb movements. redundancy in tracts.
define motor unit
single motor neuron -> all fibers innervated.
neuron fires ALL muscle fibers of motor unit.
different number of muscle fibers innervated by each motor neruon. fewer fibers = more selective motor control.
skeletal muscles - direction of force, mtoor end plate
generate force in one direction only - contract muscle. * need opposing muscle group for opposite function
motor end plate = on each muscle fiber, activated by acetylcholine. activation contracts fiber
2 muscle fiber tyeps
fast - white
not highly vascularized. contract and relax quickly. tire quickly
slow - dark
highly vascularized. weaker, slower. sustained contraction = maintain activity indefinitely
2 categories of muscles required
flexor - bend/flex
extensor - straighten /extend
synergistic vs antagonistic muscles
synergistic = contraction produce same movement (either side of joint) antogonistic = contraction produce opposing movement (on same side of joint
2 types of contraction
isometric contraction: increased tention on tendon. no shortening/contraction of muscle. jsut hold
dynamic contraction: contraction followed by lengthening. movement
tension increased by
increse number of neurons firing
increasing firing rates of neurons.
monitor muscle tension
golgi tendon organ.
embedded in tendon. more tension - more pull on tendon.
high tension = feedback to inhibitory interneuron in spinal cord causes muscle to relax. other muscles increase contraction to make up for that
monitor muscle length
muscle spindle. embedded in intrafusal muscle in extrafusal muscle. extrafusal muscle contract, so do inrafusal - muscle spindle detect shortening.
stretch reflex
monosynaptic.
hit = tug tendon = lengthen of muscle. in response contract = kick.
muscle spindle sensory afferent nerves fire - cause gentral horn motor neruons to fire = kick.
withdrawal reflex
suddenly pull back when touch something painful
not monosynaptic. 1.6 msec to cross 2 synapses. one interneuron.
higher centres also turned on - multisynaptic - to deal with withdrawal.
reciprocal innervation
antagonistic muscle pairs counter-contract. allow for smooth & quick movements
recurrent collateral inhibition - renshaw cells
renshaw cell = small interneuron. motor neuron synapses on muscle AND renshaw. renshaw then inhibits motor neuron to silence it. = negative feedback loop to give itself rest.
walking as a reflex
reflex must be plastic - adjust to output.
with severed spinal cord, idnividual can walk when they have sensory feedback.
comple movements moved down to lower areas. so high areas?
high areas inform of goals and help with intentions but dont carry out reflex.
motor equivalence
sensorimotor system is plastic.
motor equivalence - same baasic movement carried out in multiple ways with different muscles
writing with hand or toe = similar font bc of motor equivalence
sensorimotor doesnt need conscious perception, just needs …
sensory feedback.
ebbinghaus illusion - consciously perceived differently, but sensorimotor preps finger gap to be same size.
species specific behaviours without practice & without limbs
- so engrained that they do same behaviour in same sequence to a tee. use alternate sensory feedback when missing limb.
central sensorimotor programs with practice
response chunking - learn sequence as a chunk
shift control lower levels- advantageous, frees up higher levels, greater speed at lower level, more parallel processing
sensorimotor learning
well -practiced sequence - shift sequence knowledge down to lower areas. hgiher association areas freed up.
