week 7 motor control Flashcards
Organization of neural structures involved in the control of movement
Organization of control of movement
Motor neuron cell bodies are located and arranged how?
- located in ventral horn of spinal cord
- Arranged logically along body axis.
within the ventral horn of the spinal cord
there is a medial-to-lateral topographical map of body muscles
In addition to sensory input and motor outputs, there are many _______________ in the spinal cord that create networks to control simple motor behaviors (ex: reflexes, balance, coordination)
interneurons
define a motor unit
- an a-motor neuron and all of the muscles it innervates
- two kinds:
- small (few fibers)
- large (many fibers)
a muscle fiber is only innervated by one a-motor neuron BUT
it takes many a-motor neurons to innervate all the fibers in a complete muscle
How does the brain encode a command for force?
rate coding; the rate of AP coming from the brain
what are the three different types of motor neurons? what is different about them?
- fast fatigable
- fast fatigue resistant
- slow
- training can change the amount/proportion of these (ex: long distance runners would build more fast fatigue resistant)
With increased motor unit size, a-motor neurons exhibit:
- increase in:
- cell body size
- dendridic complexity
- short term EPSP potentiaton with repeated activation
- axonal diameter (faster conduction)
- # of axonal branches (more muscle fibers innervated)
- decrease in:
- input resistance
- excitability
- Ia EPSP amplitude
- PSP decay constant
- duration of after-hyperpolarization
a-motor neurons vary in:
- cell size
- excitability
- axon branches
- dendrites
- synapses received
- input resistance
what types of summation do motor neurons perform and what does this look like?
- temporal summation
- spatial summation (NOT mutually exclusive)
what is the size principle? why?
smaller motor units depolarize sooner than big motor units
- this is bc smaller cell bodies have higher input resistance, which makes it easier to reach AP threshold with few EPSPs
- input resistance refers to the amount of resistance a neuron puts on the flow of electrical current (higher = current cant leave = bigger change in neuron membrane potential)
smaller motor units excite _______ muscle fibers, meaning there is ____ ______.
smaller motor units excite FEWER muscle fibers, meaning there is LESS FORCE.
Small and large units can be innervated by the same ____________ ________ __________ and as firing rate ___________ , _________ motor units are recruited
Small and large units can be innervated by the same DESCENDING MOTOR PATHWAYS and as firing rate INCREASES , LARGER motor units are recruited
Motor neuron recruitment in the cat medial gastrocnemius muscle under different behavioral conditions
Effect of stimulation rate on muscle tension
The number of active motor units and their rate of firing both increase with voluntary force
(this is an entire motor neuron pool)
a-motor neurons cause __________________
MUSCLE BODIES TO CONTRACT
what do y-motor neurons do?
ADJUST LENGTH OF MUSCLE SPINDLES
what do Ia and II afferents do?
carry feedback about stretch from muscle spindle to the spinal cord a-motor neurons
Stretch reflex circuitry : How spinal circuits modulate motor unit activity.
what is the role of γ-motor and a-motor neurons in regulating muscles
- During normal movements, your brain
sends commands to both α-motor
neurons and γ-motor neurons to
coordinate them. - This ensures muscles spindles stay
sensitive and stretch reflexes don’t
interfere with intended movements. - y-motor neurons stop firing when a-motor neurons are stimulated and they are not, but when both stimulated they fire nonstop
Golgi tendon organ makeup
- made up of the capsule (outside)
- and collagen fibrils (inside)
Golgi tendon organs (GTO) and their role in the negative feedback regulation of muscle tension
- Golgi tendon organs (GTO) relay force info back to spinal cord.
- Here the GTO is also exciting an excitatory interneuron (purple) to activate antagonist muscle group.