Ch07 Neurons and Electrical Signaling

APK2105C @ UF | Dr. Nguyen | Module 2 | Ch06 Neurons and Electrical Signaling

False

True or False: Neurons contain only ICF and no organelles.

axon

Synaptic vesicles travel along the ______ to release neurotransmitters.

microtubules; soma; axon terminals

Provide structural support and act as “tracks” that transport synaptic vesicles from the _______ to the _______ _______.

ion; electrical

Opening or closing of ____ channels on the neuron changes the _________ properties of the cell.

leak channels

Channels in neurons:

• allow passive movement of ions across the membrane

• always open

• located all over the neuron

ligand-gated channels

Channels in neurons:

• open or close following ligand-receptor binding

• densely located in dendrites and soma

voltage-gated channels

Channels in neurons that open or close following changes in membrane potential

Na+ and K+ channels

Voltage-gated channels that are most dense in the axon and axon hillock

Ca2+ channels

voltage-gated channels that are most dense in the axon terminal

bipolar neuron

Neuron w/ two extensions from the cell body that serves as a sensory neuron for special senses.

pseudo-unipolar neuron

Neuron w/ only one extension from the soma and that serves as a somatosensory neuron.

multipolar neurons

Most common neuron in the body.

afferent and efferent

What are the functional classes of neurons?

tract

Group of axons traveling together in the CNS (white matter)

nuclei

Group of neurosomas in the CNS (gray matter)

nerve

Group of axons traveling together in the PNS (organs)

ganglion

Group of neurosomas in the PNS

nerves; PNS

Are nerves or tracts organs? Where are they located?

nervous and connective

What two tissues make up nerves in the PNS (making them organs)?

oligodendrocytes

Glial cells in the CNS that form myelin sheaths

Schwann cells

Glial cells in the PNS that form myelin sheaths

True

True or False: Schwann cells wrap themselves around the axon to form the myelin sheath

membrane potential (Vm)

difference in voltage across the plasma membrane

inside; outside; negative

Membrane potentials are ALWAYS described as the potential inside/outside the cell vs inside/outside the cell. This means the inside of a neuron is 70mV more positive/negative relative to the outside of the neuron.

chemical driving forces (for Na+ and K+), Na+/K+ pump, differences in permeability

What are the 3 contributors to the resting Vm?

into

Na⁺ wants to move into/out of the cell.

out of

K⁺ wants to move into/out of the cell.

K+

To which ion is the (neuronal) membrane more permeable to?

equilibrium potential (E_x)

The V_m that counters the chemical force acting on an ion across the membrane, thereby putting the ion at equilibrium.

electrical; chemical

V_m is an electrical force, so the E_x of an ion is the exact chemical/electrical force needed to equally oppose the chemical/electrical force of an ion.

-94mV

What is E_K+ ?

60mV

What is E_Na+ ?

closer; Ex

The more permeable the membrane is to an ion, the ______ V_m will be to that ion’s ____.

leak channels

Channels that help establish/keep stable the resting V_m

gated channels

Channels that can be signaled top open or close in order to change the V_m

voltage; ligand

The two types of gated channels are _______- and _______-gated channels.

open; increased; closer to

As ion channels are signaled to open/close, the permeability to that ion is increased/decreased, which will drive the V_m closer to/father from that ion’s E_x

polarized

The plasma membrane is ________ at rest. There is a difference in voltage across the membrane.

graded potentials

Small, decremental changes in V_m that occur when ion channels are signaled to open or close. Can change in magnitude.

decreases

As the signal moves away from the stimulus site, its V_m increases/decreases.

axon hillock

Where do graded potentials converge?

True

True or False: Graded potentials can be hyperpolarizing or depolarizing.

hyperpolarizing

Is an IPSP hyperpolarizing or depolarizing?

depolarizing

Is an EPSP hyperpolarizing or depolarizing?

axon hillock

Where does graded potential summation occur?

False

True or False: One stimulus is usually enough to meet threshold and trigger an action potential.

temporal summation

process of adding together multiple graded potentials that occur at the same synapse in rapid succession, leading to a greater chance of reaching threshold for action potential generation.

spatial summation

process of adding together graded potentials from multiple synapses at different locations on the neuron, increasing the likelihood of reaching the threshold for action potential generation.

depolarization

What is phase 1 of an action potential?

repolarization

What is phase 2 of an action potential?

hyperpolarization

What is phase 3 of an action potential?

fast

During an action potential, the influx of Na⁺ ions is slow/fast.

slow

During an action potential, the efflux of K⁺ ions is slow/fast.

closed; open; open; open; open; closed

In voltage-gated Na⁺ channels (ONLY)…

• At resting membrane potential, the activation gate is open/closed and the inactivation gate is open/closed

• During depolarization, the activation gate is open/closed and the inactivation gate is open/closed.

• During repolarization, the activation gate is open/closed and the inactivation gate is open/closed.

subthreshold stimulus

A stimulus that is below the threshold and therefore unable to trigger an action potential.

threshold stimulus

A stimulus that is at the threshold and therefore triggers an action potential.

suprathreshold stimuli

A stimulus that is above the threshold and therefore triggers one or multiple action potentials

refractory period

Period during and immediately after an action potential in which the membrane is less excitable than at rest.

refractory; overlap

In comparison to graded potentials, action potentials cannot sum due to _________ periods that prevent ________ in APs.

frequency

Since action potentials are not graded, they “code” for the strength of a stimulus through their…

False

True or False: Action potentials can travel in either direction on an axon.

absolute refractory period

Period where a neuron CANNOT have another action potential during depolarization and repolarization no matter what.

relative refractory period; stronger; weaker

Period where a neuron CAN have another action potential BUT a stimulus must meet a certain threshold during hyperpolarization.

The earlier during hyperpolarization that a stimulus wants to produce an action potential, the stronger/weaker it has to be. The later, the stronger/weaker it has to be.

True

True or False: During hyperpolarization/relative refractory period, the threshold will ALWAYS have to be greater than -55mV.

True

True or False: If a threshold stimulus outlasts the refractory period, another action potential can occur.

more; supra; relative

Firing occurs ______ frequently w/ increasing ______-threshold stimuli b/c action potentials can be generated earlier and earlier in the _______ refractory period.

electrotonic propagation; Na+

Process where a nerve impulse travels along the neuron. When one site has an action potential, it signals the following area to open ____ channels, and so on.

False

True or False: When a subsequent site releases Na+, this will signal the previous site to open their channels again.

relative refractory state/period

Previous sites on a neuron will not respond to Na+ coming from subsequent site b/c they are in a…

False

True or False: Saltatory propagation can occur in both myelinated and unmyelinated axons.

saltatory propagation

Rapid transmission of electrical impulses on a myelinated neuron. Characterized by Na+ “zipping through” myelinated areas on the axon after depolarization at Nodes of Ranvier.

axon diameter and myelination

What are two factors affecting speed of propagation?

True

True or False: The larger an axon’s diameter, the faster the propagation.

A fibers

? fibers — large diameter, myelin present

B fibers

? fibers — small diameter, myelin present

C fibers

? fibers — small diameter, no myelin present

A fibers

Which nerve fibers are the fastest?

C fibers

Which nerve fibers are the slowest?

Tetrodotoxin (TTX)

Neurotoxin that blocks voltage-gated Na⁺ channels, which can be fatal

Novocaine

Local anesthetic that blocks voltage-gated Na⁺ channels