Module 5.1-5.2

Question 1

What are the 2 types of motor neurons?

Answer 1

Alpha and Gamma

Question 2

large, lower motor neurons of the brainstem and spinal cord. Innervate extrafusal skeletal muscle fibers branching multiple times at the muscle and are directly responsible of initiating muscle contraction.

Answer 2

Alpha

Question 3

are a type of lower motor neuron that take part in the process of muscle contraction. They represent about 30% of the nerve fibers going to skeletal muscle and are important in keeping muscle spindles taut, allowing the firing of alpha motor neurons to continue discharging, leading to muscle contraction. They are for volume control by providing real-time feedback about the status of a muscle.

Answer 3

Gamma Motor neurons

Question 4

True/False: An example of a motor unit would be an alpha and gamma motor neuron and all of the muscle fibers they innervate.

Answer 4

False:A motor unit consists of a single (not two) motor neuron and all of the muscle fibers it innervates.

Question 5

Known as the (“middleman”) are 30x more abundant than anterior motor neurons and are important for motor reflex circuitry. They serve as the main endpoint for signals coming from the brain. In some cases, are necessary for switching an excitatory input signal to an inhibitory output signal.

Answer 5

Interneurons

Question 6

provide pathways for multisegmented reflexes traveling up and down the cord for one or two segments. Important for sensing the relative position of body parts and strength of effort used in movement. Also important for connecting the sensory information from muscle tissue to the effector contraction response to maintain position.

Answer 6

Propriospinal Fibers

Question 7

(make up the bulk of the muscle and are attached to the bone by fibrous tissue extension called tendons). Think of skeletal muscle.

Answer 7

Extrafusal Fibers

Question 8

• Smaller than extrafusal
• Encapsulated in sheaths to form muscle spindle

Answer 8

Intrafusal fibers

Question 9

What is the primary function of the muscle spindle?

Answer 9

to set up a relax circuit to maintain muscle length. Stretching the muscle stimulates sensory type Ia and II afferent in spindle. Then type Ia fibers stimulate alpha MNs in spinal cord, contraction of EFFs. Original stretch is opposed and muscle length is maintained.

Question 10

Alpha motor neurons stimulate ________ muscle fibers

Answer 10

EXTRAFUSAL muscle fibers

Question 11

Gamma motor neurons stimulate __________ muscle fibers.

Answer 11

INTRAFUSAL/SPINDLE muscle fibers

Question 12

Dynamic gamma motor neurons innervate nuclear __________ intrafusal fibers

Answer 12

BAG intrafusal fibers

Question 13

Static gamma motor neurons innervate nuclear _________ and _________intrafusal fibers.

Answer 13

CHAIN and STATIC BAG

Question 14

The __________ senses muscle length and contraction velocity, and the ____________ senses muscle tension

Answer 14

MUSCLE SPINDLE, GOLGI TENDON ORGAN

Question 15

Both sensory _____ and _____ fibers sense displacement or the degree of muscle stretch whereas only sensory _____ fibers sense the rate of change or velocity of muscle shortening. Sensory _______ fibers detect the force of muscle contraction.

Answer 15

1. IA and II fibers sense displacement
2. IA fibers sense the rate of change or velocity of muscle shortening.
3. Sensory IB fibers detect the force of muscle contraction.

Question 16

What sensory fibers are using the tension in the Golgi tendon organ to provide information on the force generated by the contracting muscle

Answer 16

Ib sensory fibers

Question 17

Define the Response: Spindle is stretched slowly. Type Ia and Type II afferent impulses increase in proportion to degree of stretch.

Answer 17

Static Response:

Question 18

Define the Response: Center of spindle is stretched rapidly-Type Ia afferents impulses increase in proportion to rate of change of the length.

Answer 18

Dynamic Response

Question 19

True/False: In a reflex arc, afferent sensory axons from the dorsal root synapse in the spinal cord and communicate with motor neurons in the ventral root.

Answer 19

True

Question 20

What reflex is important for preventing jerkiness of body movements. Without an intact reflex circuitry, rapid oscillation between contraction and relaxation of a muscle.

Answer 20

Stretch Reflex

Question 21

In the doctor’s office, when the hammer strikes the patellar tendon, what is the order of the series of events that follows?

Answer 21

1. Quadriceps femoris muscle spindle stretches
2. Sensory neurons are stimulated from the stretch receptor
3. Interneurons and motor neurons are stimulated
4. Quadriceps contract and hamstring relaxes
5. Leg kicks

Question 22

is the observed muscle oscillation that usually indicates the interruption of corticospinal or other descending pathways that influence the reflex arc due to the spinal cord.

Answer 22

Clonus

Question 23

How does the patellar reflex occur?

Answer 23

• Strike patellar tendon with tendon hammer
• Muscle spindle stretches (in quadriceps femoris)
• Type Ia afferent stimulates alpha MN in L4 (without interneurons-monosynaptic reflex arc)
• Antagonistic flexor (hamstring) reflexes via inhibitory interneuron

Question 24

True/False: Muscle Response :the faster response that is derived from the direct activation of alpha motor neurons and a slightly delayed one is derived from the activation of gamma neurons

Answer 24

True

Question 25

Co- activation of alpha and gamma motor neurons causes contraction of both the __________ and the ends of the _______). This results in a __________ spindle with an intact stress response, and the feedback from the spindle via the _________ afferents reinforces the effects of activating the ______________.

Answer 25

extrafusal fiber, spindle
shortened, type IA
alpha motor neurons

Question 26

What are the two types of withdrawal reflex fibers?

Answer 26

A-delta fibers: thinly myelinated and rapidly convey temperature and pressure pain signals
- C-fibers: the slowest sensory fibers because they are unmyelinated. They convey information about the intensity of a painful stimulus and are typically associated with the slow burning pain sensations.

Question 27

TRUE/FALSE : Reflex arcs require polysynaptic circuits in order to provide the coordinated response of multiple motor units to a single stimulus signal.

Answer 27

True

Question 28

For the GTO reflex response, close _________ synapse(s) is/are required. Excess close ____________, ______________
stimulates sensory close ___ fibers, which synapse with a close __________ __________
to cause the muscle to close ______ in response.

Answer 28

2, tension/contraction, force

IB, inhibitory neuron

relax