Sensorimotor (4)

Question 1

What is a motor unit?

Answer 1

A motor unit is one motor neuron and all the muscle fibers it controls. When the neuron fires, all its fibers contract together.

Question 2

What do small and large motor units do?

Answer 2

Small motor units (like in fingers and face) allow fine control. Large motor units (like in legs and back) control big, strong movements.

Question 3

What happens at the neuromuscular junction?

Answer 3

The neuron releases acetylcholine, which makes the muscle fiber contract.

Question 4

What is a motor pool?

Answer 4

A motor pool is all the motor neurons that connect to one muscle.

Question 5

What are fast and slow muscle fibers?

Answer 5

Fast fibers contract quickly and with more force but get tired fast. Slow fibers contract slowly and with less force but last longer.

Question 6

What are flexors and extensors?

Answer 6

Flexors bend a joint, like the biceps. Extensors straighten a joint, like the triceps.

Question 7

What are synergistic and antagonistic muscles?

Answer 7

Synergistic muscles work together to make the same movement. Antagonistic muscles work in opposite directions.

Question 8

What are the two types of muscle contractions?

Answer 8

Isometric contraction tightens the muscle without movement. Dynamic contraction tightens and moves the muscle.

Question 9

What the receptor organs of tendons and
muscles?

Answer 9

Golgi tendon organ: A sensory receptor located in the tendons, where the muscle meets the tendon.

Muscle spindle: A sensory receptor found inside skeletal muscles.

Question 10

How do spindle fibers and Golgi tendon organs differ in what they sense?

Answer 10

Spindle fibers: Detect muscle stretch and change in length. They sense when a muscle is being extended too quickly.

Golgi tendon organs: Detect muscle tension or force generated during contraction. They monitor how hard the muscle is pulling.

Question 11

How do spindle fiber and Golgi tendon reflexes differ in the number of muscles involved?

Answer 11

Spindle fiber reflex: Involves one muscle (monosynaptic reflex) — the same muscle that is stretched contracts in response.

Golgi tendon reflex: Involves two muscles (disyanptic reflex) — the contracting muscle relaxes while the opposing (antagonist) muscle is activated.

Question 12

What are the effects of spindle fiber and Golgi tendon reflexes on muscle activity?

Answer 12

Spindle fiber reflex: Increases muscle contraction to resist stretch and maintain posture or muscle tone.

Golgi tendon reflex: Decreases muscle contraction to protect the muscle and tendon from damage caused by excessive tension.

Question 14

What is the withdrawal reflex and what triggers it?

Answer 14

The withdrawal reflex is a polysynaptic reflex that pulls a body part away from a painful stimulus, such as touching a hot object. It is triggered by pain receptors in the skin.

Question 15

How does the withdrawal reflex pathway work?

Answer 15

1. Painful stimulus activates sensory receptors.
2. Signals travel via afferent neurons to the spinal cord.
3. Interneurons relay the signal to motor neurons of flexor muscles.
4. Flexor muscles contract, pulling the limb away.
5. Additional multisynaptic pathways, some involving the cortex, coordinate further muscle activity.

Question 16

How is the withdrawal reflex different from the stretch reflex?

Answer 16

Stretch reflex: monosynaptic, involves one synapse, causes contraction to resist stretch.

Withdrawal reflex: polysynaptic, involves interneurons and sometimes the cortex, causes flexor muscles to contract to move away from danger.

Question 17

What is the purpose of the withdrawal reflex?

Answer 17

To protect the body from harmful stimuli by quickly withdrawing the affected limb and coordinating additional movements.

Question 18

What is reciprocal innervation?

Answer 18

A: It is when antagonist muscles are controlled so that when one contracts, the other relaxes, allowing smooth and coordinated movement.

Question 19

How does reciprocal innervation work in the spinal cord?

Answer 19

Sensory input excites excitatory interneurons → contracts agonist.

Sensory input excites inhibitory interneurons → relaxes antagonist.

This coordinates movement automatically.

Question 21

What is recurrent collateral inhibition?

Answer 21

It is when a motor neuron momentarily inhibits itself after firing through a feedback loop in the spinal cord.

Question 22

Which spinal cord cells mediate recurrent collateral inhibition?

Answer 22

Renshaw cells, small inhibitory interneurons that receive input from the motor neuron and inhibit it in return.

Question 23

Why is recurrent collateral inhibition important?

Answer 23

It prevents overworking a single motor neuron and spreads muscle contraction to other neurons in the motor pool, allowing smooth and sustained movement.

Question 24

What makes walking a complex sensorimotor reflex?

Answer 24

It integrates visual, somatosensory, balance, and spinal cord feedback to produce coordinated movement of trunk, legs, feet, and arms.

Question 25

How is walking controlled by the spinal cord?

Answer 25

The spinal cord can generate walking patterns without the brain if sensory feedback (like treadmill motion) is present, as shown in transected cat experiments.