Somatosensory System Part 2 SN

Question 1

What is a Motor Unit?

Answer 1

A single motor neuron and all the muscle fibres it innervates

Question 2

What is an Alpha Motor Neuron?

Answer 2

• Located in ventral (anterior) horn of gray matter in spinal cord.
• Innervates extrafusal muscle fibres
• Force generating muscle fibres

Question 3

What is a Gamma Motor Neuron?

Answer 3

Smaller and less numerous than alpha motor neurons

Innervates intramural muscle

Question 4

What is a Muscle Spindle?

Answer 4

Long Thin Fibres surrounded by extrafusal muscle fibers

Question 5

Where are muscle spindles the greatest concentration in?

Answer 5

In the Hand and Neck

Question 6

Why are Muscle Spindles the greatest concentration in hands and neck?

Answer 6

The most position (and velocity) sensitive areas.

Question 7

How many muscle spindles in the human body?

Answer 7

25,000 to 30,000

Question 8

How many muscles spindles in each arm and leg?

Answer 8

Average of about 4,000 in each arm and 7,000 in each leg

Question 9

What is the Number for the Rough Guess of Muscle Spindles?

Answer 9

38*(Muscle Mass)^1/3

Question 10

What is the function of muscle spindles?

Answer 10

Monitor changes in muscle length as a function of velocity.

Question 11

What are Group Ia Afferent?

Answer 11

Reference to sensory muscle (not skin)

• Sensory, large, myelinated, fast

Question 12

What is Extrafusal Muscle Fibres?

Answer 12

Outside Muscle Spindles

• Force Generating Muscle Fibres
• Innervated by alpha motor neurons

Question 13

What are Intrafusal Muscle Fibres?

Answer 13

Located inside the Muscle Spindles

• Controlled by gamma motor neurons

Question 14

What does Stimulation of Intrafusal Fiber Lead to?

Answer 14

Elongation of Muscle Spindle (maintains sensitivity to stretch)

Question 15

What are Nuclear Bag Fibers?

Answer 15

Thick and contain nuclei within central region

Contains Group Ia and II afferents

Question 16

What are Dynamic Nuclear Bag Fibers?

Answer 16

High frequency impulses relayed to CNS during muscle stretching (responsive during a dynamic muscle activity)

Question 17

What are Static Nuclear Bag Fibers?

Answer 17

Stopped (holding it in place) impulses that are transmitted when a muscle has shortened and held at a new length

Question 18

What are nuclear chain fibers?

Answer 18

Thin and Contain nuclei throughout
- Contains group II afferents (sensory) …static (responsive when muscle is held at a new length)

Question 19

What happens with y-motor (intrafusal) neuron activation?

Answer 19

Equatorial region gets longer and the polar region gets shorter

Question 20

What is Alpha-Gamma Co activation?

Answer 20

Stimulation of the ventral horn of grey matter of spinal cord.

Question 21

What is Low Threshold?

Answer 21

Discharges first

Question 22

What is High Threshold?

Answer 22

Needs a stronger stimulus

Question 23

What happens in alpha motor activation?

Answer 23

Muscle fibre shortens (physical change)

Question 24

What happens in gamma motor activation?

Answer 24

Muscle spindle lengthens

Question 25

What is the function of spinal reflexes?

Answer 25

Detect and regulate changes in muscle length and rate of muscle length change

Question 26

How does the muscle lengthen in spinal reflexes?

Answer 26

Stretches intra-and extrafusal muscle fibres (components will lengthen)

Question 27

How is the parallel muscle spindle lengthened?

Answer 27

The equatorial region of intramural muscle fibres is stretched

Ia afferent impulses when disturbed causes an action potential in the spinal cord

Question 28

What do synapses with alpha motor neurons cause?

Answer 28

Motor Unit Activation

Question 29

What is a Monosynaptic Reflex?

Answer 29

One chemical synapse activated by action potentials of alpha motor neurons

Question 30

Where are Golgi Tendon Organs situated?

Answer 30

At the junction between muscle tendons and where that tissue merges into active muscle; called musculotendinous junction.

Question 31

What is the function of the Golgi Tendon Organs?

Answer 31

• Monitors Muscle Tension (Force)
• Inhibitory effect to the same muscle and excitatory to the antagonist muscle
• Protective function under high loads
• “Fine Tunes” muscle force production for smooth movements
• Works with other sensory inputs

Question 32

What is Active Muscle Force?

Answer 32

• Due to Cross-Bridge cycling (contractile proteins will form reversible chemical bonds)
• Force Transfer.. Tendon lengthening (information generating through Ib afferent)

Question 33

What do linear regression lines demonstrate?

Answer 33

• Cat Soleus Muscle
• Positive Relationship

Question 34

What is the relationship between force and discharge rate?

Answer 34

As more force is produced, discharge increases due to Action Potentials from Force Transduces