Neuronal Excitation

What is a synapse

Communication point between a neuron and another cell

What is a neuromuscular junction

Specialized synapse between a motor neuron and skeletal muscle fiber

What is synaptic transmission

Process of transferring information across a synapse

What is a presynaptic neuron

Neuron sending the signal

What is a postsynaptic neuron or cell

Neuron or cell receiving the signal

What is an action potential

Rapid electrical change in membrane potential that travels along the axon

What is a neurotransmitter

Chemical messenger released by a neuron that binds receptors on another cell

What is neuronal excitation

Making a neuron more likely to fire an action potential

What type of signal is an action potential

Electrical signal

What type of signal is a neurotransmitter

Chemical signal

Which neurotransmitters in this lecture are excitatory

Glutamate, acetylcholine, and norepinephrine

Which neurotransmitter in this lecture is inhibitory

GABA

What does polarized mean for a resting neuron

Inside of the neuron is negative relative to the outside

What happens when an excitatory neurotransmitter binds the postsynaptic neuron

Positive ions enter and depolarize the neuron

What is depolarization

Membrane becomes less negative and closer to firing

How does depolarization affect action potential likelihood

Makes an action potential more likely

What happens when an inhibitory neurotransmitter binds the postsynaptic neuron

Negative ions enter and hyperpolarize the neuron

What is hyperpolarization

Membrane becomes more negative

How does hyperpolarization affect action potential likelihood

Makes an action potential less likely

What is summation

Adding excitatory and inhibitory signals together

What is the axon hillock

Region where summed signals determine whether threshold is reached

What is threshold

Voltage level that must be reached to generate an action potential

What happens if summed input at the axon hillock exceeds threshold

An action potential is generated

What is propagation

Movement of an action potential along the axon

What is repolarization

Membrane returning toward its resting polarized state after depolarization

What are the main functions of the myelin sheath

Increases conduction speed and helps protect the axon

What is a Node of Ranvier

Gap in the myelin sheath where the action potential activates

What is saltatory conduction

Action potential effectively jumps from node to node along a myelinated axon

Why does myelin increase conduction speed

It allows saltatory conduction between Nodes of Ranvier

What is an axon terminal

End of the axon where neurotransmitters are released

What must happen for a neuron to produce an action potential

Summed inputs must exceed the cell threshold

What determines a neurotransmitters action on the next cell

The neurotransmitter released by the neuron

What does afferent mean

Sensory information traveling toward the CNS

What is a proprioceptor

Sensory receptor that detects body position and movement

What is proprioception

Ability to sense body position and movement without looking

What are Group I afferent fibers associated with

Proprioceptors and proprioception

What are the characteristics of Group I fibers

Myelinated, largest diameter, and fastest conduction

What is a mechanoreceptor

Sensory receptor that detects mechanical stimuli

What types of stimuli do mechanoreceptors detect

Touch, pressure, stretch, and vibration

What are Group II afferent fibers associated with

Mechanoreceptors such as touch and vibration

What are the characteristics of Group II fibers

Myelinated and slightly smaller and slower than Group I

What is a nociceptor

Sensory receptor that detects potentially tissue damaging stimuli associated with pain

What is a thermoreceptor

Sensory receptor that detects temperature changes

What do A-delta fibers detect

Sharp pain and cold

What are the characteristics of A-delta fibers

Myelinated, small diameter, and slower conduction

What do C fibers detect

Dull pain and warmth

What are the characteristics of C fibers

Unmyelinated, smallest diameter, and slowest conduction

What is the afferent fiber order from fastest to slowest

Group I, Group II, A-delta, C

What general factors increase nerve conduction speed

Larger diameter and more myelination

Which fibers cause the initial sharp pain after an injury

A-delta fibers

Which fibers cause the later dull aching pain after an injury

C fibers

How do the main afferent fiber types compare

Group I = proprioception, Group II = touch and vibration, A-delta = sharp pain and cold, C = dull pain and warmth

What does efferent mean

Motor information traveling away from the CNS

What are the two general neurons in a motor pathway

Upper motor neuron and lower motor neuron

What is an upper motor neuron

Motor neuron or pathway in the CNS that influences lower motor neurons

What is a lower motor neuron

Motor neuron that communicates with skeletal muscle

What do alpha motor neurons innervate

Extrafusal skeletal muscle fibers

What are extrafusal muscle fibers

Regular skeletal muscle fibers that generate force and movement

What is the main function of alpha motor neurons

Produce skeletal muscle contraction and force

What do beta motor neurons innervate

Extrafusal and intrafusal muscle fibers

What do gamma motor neurons innervate

Intrafusal muscle fibers

What are intrafusal muscle fibers

Specialized muscle spindle fibers involved in detecting stretch

What is the main function of gamma motor neurons

Adjust muscle spindle sensitivity for stretch and reflexes

How do alpha, beta, and gamma motor neurons differ

Alpha = extrafusal, beta = both, gamma = intrafusal

What is a motor unit

One alpha motor neuron and all muscle fibers it innervates

What characterizes a small motor unit

Small alpha neuron, few small muscle fibers, low force, and fatigue resistant

When are small motor units recruited during voluntary contraction

First

What characterizes a large motor unit

Large alpha neuron, many large muscle fibers, high force, and fatigues easily

When are large motor units recruited during voluntary contraction

Last

How do small and large motor units compare

Small = low force and fatigue resistant, large = high force and fatigue easily

What is intracellular stimulation in this lecture

Excitation of cell bodies by descending cortical input or reflexively

Which motor units are activated first during intracellular stimulation

Small motor units

Why are small neurons activated first during intracellular stimulation

They have greater membrane resistance and a larger voltage change

What does Ohms law state in this lecture

E = I × R

What do E, I, and R represent in Ohms law

E = voltage change, I = current, R = resistance

What is the voluntary motor unit recruitment order

Small motor units to large motor units

How can voluntary muscle force be increased

Increase firing rate or recruit additional motor units

Why do small motor units allow better graded control

Each recruited unit adds a small amount of force

What is extracellular stimulation

Excitation of nerve fibers by an external electrical stimulus such as TENS or NMES

Which nerve fibers are activated first during extracellular stimulation

Large nerve fibers

Why are large fibers activated first during extracellular stimulation

They receive greater current and have a larger voltage change

What is the extracellular stimulation recruitment order

Large motor units to small motor units

How do intracellular and extracellular recruitment differ

Intracellular recruits small first, extracellular recruits large first

Why does voluntary contraction allow better graded control

Small motor units are recruited first and add small amounts of force

Why does extracellular stimulation fatigue muscle more quickly

Large motor units are activated first and fatigue quickly