HES 202- Week 2 Force Modulation and Muscle Spindles

Question 1

Describe Input resistance

Answer 1

Small MN’s (Type 1) have high input resistance (leads to greater response and easier to excite)

Question 2

What is Rheobase? What type of MN’s is the rheobase low?

Answer 2

Direct measure of the current that has to be put into a neuron to get it to fire- rheobase is low in small MN’s

Question 3

Is the conduction velocity in small MN’s slow or fast?

Answer 3

Slow

Question 4

Is the after-hyperpolarization (AHP) shorter or longer in large MN’s

Answer 4

Shorter

Question 5

Describe the size principle?

Answer 5

MU’s recruited from smallest to largest.

Question 6

What is a pro to the size principle and what is a con to the size principle?

Answer 6

Pro: Minimizes fatigue as slow twitch, fatigue resistant muscle fibres are activated first.
Con: Cannot selectively choose with MU’s to recruit

Question 7

What is recruitment threshold?

Answer 7

amount of force needed to ‘turn on’ motor unit

Question 8

Why does each MU produce partially fused tetanus?

Answer 8

Because units fire asynchronously with each other, the net force is smooth.

Question 9

What is electromyography? (EMG)

Answer 9

Recording of the electrical activity from the muscle

Question 10

What does an Indwelling EMG observe?

Answer 10

Somewhat invasive, but can observe a single motor unit.

Question 11

What is a surface EMG

Answer 11

A global view

Question 12

What is force modulation?

Answer 12

maximal voluntary contraction (MVC)

Question 13

Describe divergence? What happens?

Answer 13

A single neuron synapases on multiple nuerons

Question 14

Describe convergence? What happens?

Answer 14

Multiple neurons “converge” on fewer neurons

Question 15

What is intrafusal?

Answer 15

skeletal muscle

Question 16

What is extrafusal?

Answer 16

muscle spindles

Question 17

Where do afferent signals go?

Answer 17

signals go away from the brain

Question 18

Where do efferent signals go?

Answer 18

signals go towards the brain

Question 19

What is the role of afferent/sensory input?

Answer 19

Each afferent projects centrally to the spinal cord (reflexes) and to more superior structures

Question 20

Where is the cell body located in the afferent/sensory inputs

Answer 20

Cell body in the dorsal route ganglion

Question 21

How are afferents labeled?

Answer 21

Based on cross sectional diameter. 1 is the largest, 2, 3, and 4 being the smallest.

Question 22

What does conduction velocity depend on?

Answer 22

Depends on diameter. The larger the diameter, the faster the conduction

Question 23

What are found in most skeletal muscle?

Answer 23

Spindle/fusiform shaped receptors

Question 24

What types of muscles would have a higher density of spindles?

Answer 24

Hand muscles have a higher density of spindles, and more proximal muscles have fewer muscle spindles.

Question 25

What are the two types of receptors?

Answer 25

Bag which can be further described as Bag 1 (Dynamic) and Bag 2 (Static) and Chain static

Question 26

What are the two types of afferent and what do each of them innervate

Answer 26

Type 1a (primary)- length and velocity. Innervate bag 1, bag 2, and chain

Type 2 (secondary)- length. Innervate bag 2 and chain

Question 27

What does a microneurography record

Answer 27

single unit action potentials

Question 28

When you get a tendon tap, what does it stretch

Answer 28

stretches the intrafusal muscle fibers

Question 29

Which afferent is sensitive to tap and vibration

Answer 29

Primaries (1a) are very sensitive to taps and vibration and can stop firing on release

Question 30

What is the name of the only receptor that has its own efferent (motor) system

Answer 30

fusimotor or gamma system

Question 31

What types of Gamma MN’s does it consist of?

Answer 31

dynamic and static gamma MN’s

Question 32

Where doe alpha motor neurons send info to?

Answer 32

skeletal muscle

Question 33

where do gamma motor neurons send info to

Answer 33

muscle spindles

Question 34

Dynamic gamma sends info to…

Answer 34

Bag 1 (dynamic receptors)

Question 35

Static gamma sends info to…

Answer 35

Bag 1, Bag 2, and static

Question 36

Turning on the gamma system prevents what?

Answer 36

Prevents the spindle from becoming unloaded during shortening contractions and keeps it sensitive to stretch

Question 37

Gamma dynamic makes the spindle more…

Answer 37

velocity sensitive

Question 38

Gamma static makes the spindle more…

Answer 38

sensitive