Lecture 10: Spinal cord and Brainstem Control of motor function I

Question 1

Interneurons

Answer 1

30x as numerous as anterior motor neurons Small and highly excitable Capable of spontaneous actiity Responsible for most spinal cord integrative function

Question 2

Motor unit

Answer 2

composed of a single otor neuron and the muscle fibers it innervates Composed of extrafusal fibers

Question 3

Motor Neuron pool

Answer 3

Group of motor nuerons that innervate fibers within the same muslce

Question 4

Recruitment refers to the _______ in tension of uscle cotractions by the

Answer 4

increase, by the actiation of additional motor units (size principle)

Question 5

Small motor neurons

Answer 5

Innervate a few muscle fibers Lowest thresholds Fire first Geerate smallest force

Question 6

Large motor neurons

Answer 6

Innervate many muscle fibers highest thresholds fire last generate largest force

Question 7

Functions of Renshaw cells

Answer 7

Inhibitory cells in anterior horns of spinal cord recieive collateral branches from alpha motor neurons Transmit inhibitory signals to surrounding motor neurons Results in lateral inhibition Enhance fluidity of limb movement Trasmit inhibitory signals to same motor neuron results in reccurent inhibition

Question 8

Renshaw cells are inhibitory cells in _____ horns of spinal cord

Answer 8

anterior

Question 9

Muscle spindle (group Ia and II afferents)

Answer 9

Arranged in parallel with extrafusal fibers Detect both dynamic and static changes in muslce length

Question 10

Golgi tendon organ (group Ib afferets)

Answer 10

Arranged in series with extrafusal fibers Detect muscle tension

Question 11

Pacinian corpuslces (group II afferents)

Answer 11

Detect vibration

Question 12

Free nerve endings (Groups III and IV afferents)

Answer 12

Detect noxious stimuli

Question 13

Which nerve fiber group is not myelinated

Answer 13

Group IV

Question 14

Muscle spindle consists of ____ intrafusal fibers

Answer 14

3-12

Question 15

muscle spidle is innervated by

Answer 15

small gamma motor neurons (groups II afferents)

Question 16

Muscle spindle composition

Answer 16

3-12 intrafusal fibers that are innervated by small gamma motor neurons (group II afferents) Encapsulated within a sheath to form muslce spindle run parallel to extrafusal fibers

Question 17

Does the central region of a muscle spindle have contractile fibers

Answer 17

No, it functions as a sensory reeptor

Question 18

sensory fibers originate in what part of a muscle spindle

Answer 18

the central region stretching of central region of intrafusal fibers stimulates sensory fibers

Question 19

extrafusal fibers make up the _____ which are innervated by

Answer 19

muscle fibers, alpha neurons

Question 20

with finer movements, the number of muscle spindles required ____

Answer 20

increases

Question 21

What are the two types of intrafusal fibers

Answer 21

Nuclear bag fibers Nuclear chain fibers

Question 22

Nuclear bag fibers

Answer 22

detect rate of change in muscle length Innervated by group Ia afferents and dynamic gamma efferents Multiple nuclei located in a central “bag-like” configuration

Question 23

Nuclear chain fibers

Answer 23

Detect static chage in muslce length Innervated by group II afferents and static gamma efferents More numerous than nuclear bag fibers Multple nuclei arranged i a single row

Question 24

Nuclear bag fibers are nuclei that are concentrated in “bag” in ___ of receptor area

Answer 24

center

Question 25

nuclear chain fibers are nuclei that align in chain _____

Answer 25

throughout the receptor area

Question 26

Muscle spindle correts for increase in _______

Answer 26

muscle length (stretch)

Question 27

stimulation of sensory fibers in muscle spindles results from

Answer 27

Lengthening of entire muscle Contration of ends of intrafusal fibers

Question 28

Types of sensory fibers

Answer 28

Ia (primary fibers) * forms annulospiral ending * 17micrometers in diameter * Transmits at 70-120 m/sec II (secondary fibers * 8micrometers

Question 29

stimulation of sensory fibers in muslce spindle results in

Answer 29

stimulation of alpha-motor neurons, resulting in contraction and shortening of muscle

Question 30

Muslce Spindle gamma motor neurons

Answer 30

Innervate Intrafusal fibers Adjust sensitivity of muscle spindle coactivated with alpha-motor neurons stimulation results from lengthening of entire muslce

Question 31

Gamma motor neurons are about ____ the number of alpha motor neurons

Answer 31

half

Question 32

Types of gamma motor neurons

Answer 32

Agamma: 5 micrometers in diameter Supply small intrafusal fibers in middle of muscle spindle Gamma-dynamic Excite nuclear bag intrafusal fibers Gamma-static Excite nuclear chain intrafusal fibers

Question 33

Brain areas controlling gamma fibers

Answer 33

Bulboreticular region of brain stem Cerebellum Basal nuclei Cerebral cortex

Question 34

Muscle spindle function

Answer 34

Dynamic stretch reflex Static reflex Prevents jerkiness of body movements (damping)

Question 35

Dynamic stretch relfex

Answer 35

Signals transmitted from primary nerve endings Elicited by rapid stretch or unstretch Opposes sudden changes to muscle length

Question 36

Static reflex

Answer 36

Transmitted by both primary and secondary endings causes degree of muscle contraction to remain relatively constant

Question 37

Stretch Reflex

Answer 37

Stretching of muscle stretches group Ia afferent fibers Group Ia afferents synapse directly on alpha-motor neurons of same muslce The muscle contracts and decreases tension on muslce spindle Synergistic muscles are activated and antagonistic muscles are inhibited

Question 38

Golgi tendon organ

Answer 38

Encapsulated sensory receptor through which tendon fibers pass arranged in series with extrafusal fibers 10-15 muscle fibers attached to each Golgi organ Golgi organ is stimulated by contracting or stretching of muscle Detects muscle tension Golgi tendon reflex is opposite of the stretch reflex Circuitry Type Ib afferent (16micrometers in diamter) —> inhibiotry interneurons–> anterior motor neuron

Question 39

The Golgi Tendon Organ is an encapsulated sensory receptor through which _____ pass and is arranged in a series with ____

Answer 39

muscle tendon fibers, extrafusal fibers

Question 40

The golgi tendon organ is stimulated by

Answer 40

contracting or stretching of muscle

Question 41

The golgi tendon reflex is opposite of the

Answer 41

stretch reflex

Question 42

Functions of premotor and supplementary motor areas

Answer 42

Premotor and supplementary motor cortices generate a plan for movement Transfer plan to primary motor cortex Signals generated here cause more complex patterns of movement than the more discrete pattern generated by the primary motor cortex Anterior part of the premotor cortex develops a “motor image” of the total muscle movement that is to be performed Supplementary motor cortex programs complex motor sequences and is responsible for mental rehearsal for a movement Image in posterior motor cortex excites each successive pattern of muscle activity required to achieve the image Posterior motor cortex sends signals to: Primary motor cortex basal nuclei and thalamus–> primary motor cortex

Question 43

posterior motor cortex sends signals to

Answer 43

Primary motor cortex Basal nuclei and Thalamus–> Primary motor cortex

Question 44

more than one half of the entire primary motor cotex is concerned with

Answer 44

controlling the muscles of the hands and the muscles of speech

Question 45

in the premotor area immediately above Broca’s area is a locus for

Answer 45

controlling voluntary eye movements

Question 46

Cells in the motor cotrex are organized into

Answer 46

verticle columns

Question 47

Cell in motor cotex are organized into verticle columns: each column stimulates

Answer 47

a group of synergistic muscles or even a single muscle

Question 48

Cell in motor cotex are organized into verticle columns: each column has ___ distinct layers

Answer 48

6

Question 49

Cell in motor cotex are organized into verticle columns: each column has 6 distinct layers. Pyramidal cells are in what layer

Answer 49

5th layer

Question 50

Cell in motor cotex are organized into verticle columns: each column has 6 distinct layers. Input signals enter layers ______

Answer 50

2-4

Question 51

Cell in motor cotex are organized into verticle columns:

Question 52

Cell in motor cotex are organized into verticle columns: Each column has 6 distinct lyaers. Neurons arising in ___ layer communicate with other regions of the cerebral cortex

Answer 52

6th

Question 53

Typical descending pathway consists of a series of ____ motor neurons: which are

Answer 53

2 Upper motor neurons (UMNs) Lower motor neurons (LMNs) Does not take into consideration the association neurons between UMNs and LMNs

Question 54

Upper motor neurons are entirely within the ____

Answer 54

CNS

Question 55

Upper motor neurons orgiinate in

Answer 55

Cerebral cortex Cerebellum Brainstem

Question 56

Upper motor neurons form _____

Answer 56

descending tracts

Question 57

Lower motor neurons begin in

Answer 57

CNS from anterior horns fo spinal cord from brainstem cranial nerve nuclei

Question 58

Lower motor neurons are made up of ______

Answer 58

alpha motor neurons (A-alpha)

Question 59

Lower motor neurons make up ___ and ___

Answer 59

spinal nerves and cranial nerves

Question 60

What are mirror neurons

Answer 60

A special class of neurons called mirror neurons becomes active when a person performs a specific motor task or when he or she observes the same task performed by others.

Question 61

What two parts of the body have the largest zones on the motor homunculus

Answer 61

Hands and Face