NROC64 lec 7: Spinal control of movement - nearly word-for-word what was said in lecture.doc

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14 Mar 2012
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NROC64: Lec 7/Chapter 13: Spinal Control of Movement
SAQ:
What is the McGurk Effect and explain it?
ANSWER:
Differing audiovisual input:
Lip movement doesn’t match with what you hear;
Seeing looks like dah, hearing (close eyes) = sounds like bah, cover ears = sounds like gah.
Integration of diff sensory inputs, gah being between dah and bah (the 2 ends). We perceive
speech sounds in a categorical fashion. We never say it’s something in between.
Slide 4: Motor Programs
Motor systems: muscles and neurons that control muscles directly
Generation of coordinated mvts which requires sensory input (motor control w
proprioception at the very least is what you need for something that’s coordinated
otherwise you just get some cramp where muscle is active but not functional or
in a coordinated way)
Parts of motor control:
oSpinal cord and how it influences coordinated muscle contraction
oBrainstem, cerebellum, basal ganglia, cerebral cortex where you have motor
programs that are sent down to the spinal cord (next week)
Slide 5: Overview of fxn’l units in motor system
Spinal Cord:
oHave local circuit neurons for reflexes
oHave lower motor neurons themselves which innervate skeletal muscles
oHave sensory input coming from the muscles that influence the system in
the spinal cord
Brainstem, cerebellum, basal ganglia, cerebral cortex:
oOn top, will focus on next week
Slide 8: Muscle types
2 types:
osmooth: digestive tract, arteries, related structures
ostriated:
cardiac
skeletal (somatic muscles)
Slide 9: Somatic musculature
Motor systems: muscles and neurons that control muscles directly, falls into 3 diff
groups depending on which parts of the skeleton is moves that way
oAxial (core) muscles: trunk mvt (turns etc;); PD patients have difficulty
with these muscles and have trouble initiating mvt with these muscles
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(particularly important for sleeping; PD patients sore in the morning b/c
didn’t turn during the night)
oProximal muscles: closer to the core = shoulder, elbow, pelvis, knee
oDistal muscles: fine motor control
Slide 10: Lower Motor Neuron
Spinal cord is thicker at Cervical and Lumbar levels has to do with the fact that they
innervate arms and legs respectively and you need more neurons there
When you look into these spinal segments, ventral horn is most relevant for today’s
topic b/c that’s where the soma of the lower motor neurons are located which then
innervate the muscles themselves
Lower motor neurons themselves are located in the ventral horn of the spinal cord
for sensory neurons the soma is located in the dorsal root, so NOT inside the
dorsal horn; the soma are found in spinal ganglion
upper motor neurons are innervating the lower motor neurons
Slide 11: Ventral horn
cervical and lumbar = swollen
ventral horn has 2 main axes:
ogoing from medial to lateral, have organization of neurons that are
innervating axial to distal muscles; neurons innervating the axial muscles
are located in medial part of ventral horn whereas neurons innervating the
distal muscles are situated in lateral part of ventral horn
ogoing from dorsal to ventral, have flexors located at the dorsal end and
extensors located at the ventral end; biceps = flexor and triceps = extensor
also illustrates concept of synergist/antagonist:
osynergist: contributing to same thing (ex: 2 flexors working synergistically)
oantagonist: flexor and extensor working in antagonistic way (inhibition of
triceps and excitation of biceps)
othey’re innervated differently
Slide 12: Alpha Motor Neurons
2 lower motor neurons:
oalpha
ogamma = proprioception
alpha motor neurons = relevant for contracting a muscle
so alpha motor neurons together with the muscle fibre that they synapse on form a
MOTOR UNIT; there can be one alpha neuron innervating several muscle fibres =
still a MOTOR UNIT
motor neuron pool: set of motor neurons that altogether innervate one muscle (ex:
biceps)
Slide 13: Graded Control of Muscle Contraction by Alpha Motor Neurons
strength and speed of contraction
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there is a continuum depending on what is required of the muscles to perform; at
least 3 mechanisms are involved:
o1) varying firing rate of motor neurons; more Ach release, temporal
summation
input from the motor neuron into the muscle (diagram); AP with
Ach release
degree of contraction measured in terms of force
increase in force as a result of the AP and then it declines again;
contraction of muscle and then it relaxes again over time
when you have more APs in rapid sequence, get temporal
summation; some contraction and some relaxation but the relaxation
isn’t complete and then the next contraction adds on top of that and
so forth
because APs are arriving more rapidly, have more stronger degree of
contraction and higher degree of force also
o2) recruit additional synergistic motor units
several muscle fibers in the same muscle = entire motor neuron pool
= maximum that’s possible simply have more muscle fibers
contracting increases force
o3) small and large motor neurons
another way to modulate force is to switch from small to large motor
neurons; large motor neurons will innervate more muscle fibers or
have stronger effect on the fibers that they innervate
the motor neurons themselves are controlled in 3 major ways
o1) input from upper motor neurons in brain into ventral horn
o2) lateral input on the level of the spinal cord segment in 2 possible ways:
a) there’s direct input thru sensory neurons (ex: proprioception,
pain)
b) there’s indirect input (ex: some reflexes actually work thru
multiple synapses indirectly thru interneurons that are sitting in the
segment of the spinal cord; interneurons can have inhibitory or
excitatory function)
Slide 14: Types of motor units
muscle fibers are just one aspect of the motor unit
1) red muscle fibers:
ored because contain large amount of mito and enzymes
oslow to contract but can sustain contraction for longer periods of time
omarathon runners
2) white muscle fibers:
ofew mito
oanerobic metabolism
ocontract and fatigue rapidly
oshort distance running
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