Lecture 10: Control Of Motor Function Flashcards
What fibers give rise to A(delta) fibers?
- alpha motor neurons
What is a single motor neuron of extramural fibers that act on specific muscle fibers?
- motor unit
What is the purpose of the motor neuron pool?
- this group of motor neurons innervate fibers writhing the same muscle
When multiple motor units are activated to increase the tension of muscle tension refers to what?
- recruitment
What is recruitment?
- increasing the tension of muscle contractions by activating additional motor units
What is the difference of how many fibers a small motor neuron and a large motor neuron innervate?
- small= few fibers
- large= multiple fibers
Small and large motor neurons have different thresholds. What is the difference?
- small= lowest threshold
- large= highest threshold
Large and small motor neurons differ in which fire. How do they differ?
- the small neurons fire first, while the larger neurons fire last.
How do small and large motor neurons differ in relation to force generated?
- small neurons generate smallest forces while the largest generated much larger forces.
What are Renshaw cells?
- inhibitory cells of anterior horns of spinal cord, that receive collateral branches from alpha motor neurons
What signals to Renshaw cells release?
- release an inhibitory signal to other motor neurons.
- this results in lateral inhibition and enhances the fluidity of limb movement.
What type of signaling and from what structure will recurrent inhibition be generated?
- inhibitory signals are generated by the Renshaw cells, acting on the same motor neuron to produce recurrent inhibition
Renshaw cells are able to transmit inhibitory signals to the same motor neuron, resulting in:_________
- recurrent inhibition
What are the different kinds of muscle sensors?
- muscle spindle ( Ia, II afferent)
- Golgi tendon organ (Ib afferent)
- pacinian corpuscle (II afferent)
- free nerve endings (III, IV afferent)
The muscle spindle muscle sensors are arranged how, and produce what function?
- parallel with the extramural fibers
- these detect both dynamic and static changes in muscle length
The Golgi tendon muscle sensor is primarily responsible to what?
- detects the muscle tension and therefore should be arranged in series with extrafusal fibers
What do pacinian corpuscles most likely detect?
- vibration
Describe the components that form the muscle spindle.
- innervation by small gamma motor neurons, that are encapsulated within a sheath. This sheath will then run parallel with muscular fibers
Where are no contractile fibers contained that act as a sensory receptor for the muscle?
- the muscle spindle
How is the muscle spindle able to function as a sensory receptor?
- the stretching of the central region of the intrafusal fibers generates a response.
- therefore this structure (muscle spindle) functions to detect muscle length changes
What type of function will consist of increased muscle spindle numbers?
- finer movement require more spindles
What are the types of intrafusal fibers?
- nuclear bag fibers
- nuclear chain fibers
What is the function of nuclear bag fibers?
- detect the rate a muscle length changes
- innervated by Ia afferent and dynamic gamma efferent
- bag like configuration
What do nuclear chain fibers do to function as an intrafusal fiber in the muscle spindle?
- detect static changes in muscle length
- group II (afferent) gamma (efferent) fibers
- more numerous and contain multiple nuclei in a single row
What happens when the sensory fibers from the central region of intrafusal fibers are stimulated?
- stimulation occurs when the muscle lengthens and activates the alpha motor neurons, which will cause contraction and shortening of the muscle.
What are spindle gamma motor neurons?
- fibers that innervate intrafusal fibers and adjust the sensitivity of the muscle spindle.
- these are coactivated with alpha motor neurons that are stimulated from a muscle being stretched.
What are the different gamma motor neurons taht are stimulated?
- gamma dynamic stimulate nuclear bag intrafusal fibers
- gamma static stimulate nuclear chain intrafusal fibers
What is in control of the gamma motor neurons?
- bulboreticular region of brain stem
- cerebellum
- basal nuclei
- cerebral cortex
What role does the muscle spindle play within dynamic stretch?
- signals are transmitted to primary nerve endings, that are elicited by rapid stretch or unstretch
- this will oppose sudden muscle length changes
What is the function of static reflex of the muscle spindle?
- this reflex is stimulated by primary and secondary endings that allow for degrees of contraction to remain constant
The combination of dynamic stretch reflex, and static reflex of the muscle spindle provide what function?
- provides damping which prevents jerkiness with body movements.
What are the nerve fibers that play a significant role in the Golgi tendon organ?
- Ib afferent synapse with an inhibitory interneuron, that synapse with an anterior motor neuron
Why is a person unable to inhibit the knee-jerk reflex?
- this consists of a Monosynaptic reflex, which prevents a inhibition from other neurons, that would occur in Polysynaptic reflexes.
Understand the flexor and crossed extensor reflexes on figure 55-9
.
What is after discharge?
- the results of persistent neural activity in Polysynaptic circuits.
Therefore it will prevent muscle from relaxing for some amount of time.
What are the functions of the premotor and supplementary motor areas?
- generate plan for movement
- premotor cortex develops a “motor image” of the muscle movement that will be performed
- supplementary cortex mentally rehearses a movement
What does the supplementary motor cortex do?
- provides sequence for complex motor sequences and is responsible for mental rehearsal of a movement
What does the premotor cortex do?
- develop a diagram of what the total movement will look like with respect to the muscle.
Where will more complex patterns of movement be generated? More complex than what the primary motor cortex could form.
Premotor and supplementary motor areas.
Where does the posterior motor cortex send its signal sequence?
- primary motor cortex into the basal nuclei and thalamus and then into the primary motor cortex.
What is an interneuron?
- responsible to spinal cord integrative function that is small, highly excitable, and reacts spontaneously
