KINS 158 Neuromotor Basis for Motor Control

The human nervous system is divided into two major divisions. What are they and what is each responsible for?

1. Central NS - Brain, brainstem, cerebellum, and spinal cord

   • Responsible for processing information and generating motor

   commands

2. Peripheral NS - All neural structures outside the skull and vertebral column,

• Linking the CNS to the rest of the body

What does the term neuromotor system mean?

Refers specifically to the components of

the nervous system that coordinate and control voluntary,

purposeful movement.

What is the neuron responsible for?

Transmits information throughout the nervous system

Structure of a Neuron: Cell Body

1. The cell body contains the nucleus. What is the nucleus responsible for?

2. What is the role of the cell body?

1. Regulates homeostasis of neuron

2. Synthesizes a large quantity and variety of proteins used as neurotransmitters.

Structure of a Neuron: Dendrites

1. What are dendrites responsible for?

1. primarily responsible for receiving information from other neurons

Structure of a Neuron: Axon

1. What is the role of the axon?

2. What are the branches of the axon called?

3. They are covered by myelin. What is this?

4. What do the axon terminals do?

1. Responsible for sending information from the

   neuron.

2. Collaterals

3. a cellular

   membrane that speeds up the transmission of neural

   signals along the axon

4. a signal transmission relay station for

   neurotransmitters

Sensory Neurons

1. Transmit information from the ___ to the ___

2. Sensory neurons are Pseudounipolar. What does this mean?

3. Where is the cell body of sensory neurons located?

1. Transmit information from the periphery to the CNS

2. Appear to have a single projection from the cell body

3. Cell body of sensory neurons located at the dorsal root

   ganglion of the spinal nerve

Motor Neurons

1. Transmit information from the ___ to ____ by activating ___

2. Alpha Motor Neurons - Where are they located and what do they do?

3. Gamma Motor Neurons - What do they do?

1. Transmit information from the CNS to muscles by activating muscle

   contraction

2. Alpha Motor Neurons

• Located predominantly in spinal cord

• Axons synapse on skeletal muscle fibers to create the motor unit

3. Gamma Motor Neurons

• Activity regulated through alpha-gamma coactivation

• Regulates sensitivity of intrafusal fibers (muscle spindles) to maintain accurate level

of proprioception

Interneurons

1. What are these?

2. Transmits information between?

1. Specialized neurons that originate and terminate in the brain or spinal cord

2. • Axons from the brain and motor neurons

   • Axons from the sensory nerves and the spinal nerves ascending to the

   brain

What are the two ways cells communicate?

1. Action Potentials - Rapid electrical impulses that travel along

   a neuron’s axon, allowing information to

   move within a single neuron

2. Synaptic Transmission - process by which neurons communicate with

   each other—or with muscles and glands—

   through the release of neurotransmitters

   across the synaptic cleft

Action Potential

A - Resting membrane potential

1. During resting membrane potential, what does the inside and outside of the cell look like?

2. How is the cell maintained at this state?

1. Inside the cell → High concentration of K⁺ (potassium).

   • Outside the → High concentration of Na⁺ (sodium) and Cl⁻ (chloride).

2. Sodium-potassium pump (Na⁺/K⁺ pump) → pumps 3 NA⁺ out and 2 K⁺ in.

   1. Leak channels: allow K⁺ to slowly leak out, further keeping the negative resting potential.

Action Potential

B - Depolarization

1. What 3 stages occur during depolarization?

1. Stimulus (e.g., neurotransmitter from another neuron) causes Na⁺ ligand-gated channels to open slightly → Na⁺ enters cell, makes inside less negative (small depolarization).

2. If membrane potential reaches threshold (~ -55 mV), an action potential fires.

3. Voltage-gated Na⁺ channels open, Na⁺ rushes in → rapid depolarization to +40 mV

Action Potential

C - Repolarization and Hyperpolarization

1. How does depolarization and hyperpolarization occur?

1. Voltage-gated K⁺ channels open, K⁺ flows out → repolarization.

2. extra K⁺ leaving, making the inside too negative (below –70 mV) → Hyperpolarization

Action Potential

D - Return to Resting Potential

1. Explain this stage

1. Na⁺/K⁺ pump restores ion balance.

Action Potential - Refractory Periods

1. What is the refractory period?

2. What is absolute refractory period?

3. What is relative refractory period?

1. Period when neuron cannot fire another action potential

2. Na⁺ channels unresponsive; neuron cannot fire again

3. Stronger stimulus required to trigger another potential

1. Absolute

2. Relative

Action Potential: Propagation of the Signal

1. Depolarization at one segment triggers…?

2. Myelin sheath (lipid-rich insulation) increases speed and efficiency by:

1. Depolarization at the next, spreading the signal along the axon

2. 
   

a. Preventing current leakage.

b. Allowing current to "jump" between Nodes of Ranvier (saltatory conduction). Nodes of Ranvier: Gaps in myelin/ rich in voltage-gated Na⁺ channels

Graded Potentials

1. What do graded potentials do?

2. What is EPSP?

3. What is IPSP?

1. change the membrane potential slightly (by a few millivolts) and can add up

(summate) over time and space.

2. Excitatory Postsynaptic Potential - a small depolarization of the postsynaptic

membrane that makes the neuron more likely to fire an action potential

3. Inhibitory Postsynaptic Potential - a small hyperpolarization that makes the neuron less likely to fire an action potential

Summation

1. Summation of graded potentials can trigger…?

2. What is temporal summation?

3. What is spatial summation?

1. The firing of an action potential

2. many potentials from one neuron trigger threshold point

3. potentials from many neurons trigger threshold point

1. What is the all-or-none law?

2. Once triggered, does the action potential speed up?

1. Neurons either fire or don’t — action potentials are not graded by stimulus intensity.

2. No. Once triggered, the action potential always has a constant amplitude and speed

Synapses

1. What is a synapse?

2. What is the most common type of synapse?

3. Are synapses electrical or chemical?

1. Specialized junctions where neurons communicate

2. Axodendritic synapse

3. Both

Chemical Synaptic Transmission

1. Explain the 5 stages

1. Action potential arrives at the axon terminal,

→ triggers the voltage gated Ca+ channels

2. Triggers synaptic vesicle mobilization

3. Vesicles fuse with the membrane (exocytosis) and

release neurotransmitters into the synaptic cleft.

4. Neurotransmitters bind to receptors on the

postsynaptic neuron → change its membrane

potential (excitation or inhibition).

5. Neurotransmitters are removed from the synaptic

cleft:

• Enzymatic breakdown (e.g., acetylcholinesterase).

• Reuptake into the presynaptic neuron (e.g., SSRIs

serotonin reuptake blocking).

The Motor Unit

1. One motor unit =

2. What is the Neuromuscular Junction?

1. the alpha motor neuron and all the muscle fibers it innervates

2. Connection site between alpha motor neuron and muscle fibers

Motor unit recruitment

1. Muscle force depends on?

2. More motor units activated = ?

3. Motor unit recruitment follows what principle?

1. Muscle force depends on how many muscle fibers are active

2. More motor units activated → greater force output.

3. Size Principle

• Recruitment starts with small, weak motor units.

• Progresses to large, powerful motor units as force demand increases