W5-L6: Reflex Arc and Innervation

Question 1

The reflex arc

Answer 1

The reflex arc is a neural pathway that controls an immediate, involuntary response to a stimulus, involving a sensory receptor, sensory neuron, integration center, motor neuron, and effector.explain

Question 2

What is a Motor unit?

Answer 2

Motor unit: makes up the functional unit of movement

• Consists of the anterior motor neuron and the specific muscle fibers it innervates

Question 3

How do muscle fibers differ in different muscles

Answer 3

The number of muscle fibers per
motor neuron generally relates
to a muscle’s particular
movement function

provide an example 9eyes_

Question 4

What is a Motor neuron pool?

Answer 4

collection of alpha motor neurons that innervate a single muscle

Question 5

The Anterior Motor Neuron

Answer 5

Consists of: cell body, axon, and dendrites

Question 6

What is a Myelin sheath?

Answer 6

bilayer lipoprotein membrane that wraps around the axon over most of its length

• Acts as an electrical insulator

Question 7

What are Nodes of Ranvier?

Answer 7

allows impulses to jump from node to node called saltatory conduction

• Allows the electrical current to travel down towards the motor end plate

Question 8

What is the NMJ?

Answer 8

Neuromuscular junction (motor Endplate)
NMJ represents the interface between the end of a myelinated motor neuron and muscle fiber

Question 9

How does Excitation occur in NMJ?

Answer 9

Excitation: Ach is released into synaptic cleft and elicits an end-plate potential and spreads to the extra junctional sarcolemma

Action potential travels down and enters the T-tubule system

Question 10

Inhibitory postsynaptic potential (IPSP) and
Excitatory postsynaptic potential (EPSP)

Answer 10

An inhibitory postsynaptic potential (IPSP) is a hyperpolarization of the postsynaptic membrane that makes the neuron less likely to fire an action potential.

An excitatory postsynaptic potential (EPSP) is a depolarization of the postsynaptic membrane that makes the neuron more likely to fire an action potential.

Question 11

What is A motor unit?

Answer 11

A motor unit contains only one specific muscle fiber type (type I or type II) or a subdivision of the type II fiber with the same metabolic profile

Question 12

Answer 12

Question 13

What is the All-or-None Principle?

Answer 13

• If a single nerve fiber is stimulated, it will always give a maximal response and produce an electrical impulse of a single amplitude.
• A motor unit does not exert a force gradation; either the impulse elicits an action, or it does not
• After the motor neuron fires and the impulse reaches the NMJ, all fibers of the motor unit fire simultaneously

Question 14

Force of muscle action varies from slight to maximal via what two mechanisms?

Answer 14

1. Increased number of motor units recruited
   - muscle generates considerable force when activated by all of its motor units
2. Increased frequency of motor unit discharge
   - repetitive stimuli that reach a muscle before it relaxes and increases the total tension

Question 15

What is Motor unit recruitment?

Answer 15

Motor unit recruitment describes adding motor
units to increase muscle force

Question 16

What is the Size Principle

Answer 16

• With increased muscle force, motor neurons with larger axons are recruited (size principle)
• Size principle: orderly recruitment of specific motor units to produce a smooth muscle action; allows the CNS to fine tune skeletal muscle activity to meet motor task demands
• Differential control of motor unit firing patterns represents major factor distinguishing skilled from unskilled performance