The Neuron

Question 1

Neurons

Answer 1

Specialized cells of the nervous system that carry information using electrical impulses (action potentials)

Question 2

Nerves

Answer 2

Bundles of neuron fibers wrapped in connective tissue to create cable-like structures

Question 3

Neuroglia or “Glial Cells”

Answer 3

cells that support, protect and nourish neurons

Question 4

Cell Body

Answer 4

contains the cell’s organelles, relay action potentials from dendrites to axon(s)

Question 5

Nissl Substance

Answer 5

rough ER of a neuron, makes neurotransmitters (amino acids, small peptides or proteins)

Question 6

Dendrites

Answer 6

receives incoming messages and direct them toward the cell body

Question 7

Axon

Answer 7

Conducts electrical signals (action potentials) away from the cell body

Question 8

Synaptic Terminal

Answer 8

At the end of the axon, relays messages to other neurons or body cells, usually in the form of neurotransmitters

Question 9

Myelin Sheath

Answer 9

Insulates the axon and helps it conduct electricity more quickly (like Sheath on a wire)

made of closely spaced supporting (glial) cells, these are called Schwann Cells in nervs

Question 10

Nodes of Ranvier

Answer 10

small gaps in between the supporting cells

Helps nerve signals “hop” along the axon more quickly

Question 11

Membrane Potential

Answer 11

The driving force for the movement of ions across a membrane due to a difference in ion concentration inside relative to outside neuron cell membrane

Question 12

What happens when a neuron is “at rest”?

Answer 12

High [Na+] outside the cell, high [K+] inside the cell

the resting membrane potential is Negative: [K+] inside <[Na+] outside (inside more negative)

Question 13

If positive Ions leave the cell what happens to the cell membrane potential?

Answer 13

decreases (repolarizes)

Question 14

if positive ions enter what happens to the cell membrane potential

Answer 14

increases (depolarizes)

Question 15

Voltage-gated ion channels

Answer 15

passively allow the movement (diffusion) of one type of ion down their concentration gradient (from [high] to [low])

Question 16

what do ion pumps do?

Answer 16

actively move ions up (against) their concentration gradient using ATP (dephosphorylation)

the sodium-pottasium pump (Na+/K+ pump) is ALWAYS pumping to restore/maintain the restin potential

3 Na OUT 2K+ IN

Question 17

What is an action potential?

Answer 17

a wave of depolarization (positive membrane) that travels along a neuron

starts at the dendrites and ends at the synaptic terminals

Question 18

Action Potential Phases: Stimulation

Answer 18

a stimulus causes a slight increase in Na+ ions inside the cell which raises the membrane potential

sodium channels open if the stimulus raises the membrane potential above the threshold

Question 19

Action Potential Phases: Rising Phase (depolarization)

Answer 19

Sodium Ions diffuse (move) down their concentration gradient into the cell

the membrane potential rises and quickly becomes positive (depolarized)

Question 20

Action Potential Phases: Peak

Answer 20

Sodium channels close and inactivate (can’t open again right away during this refractory period)

potassium channels open

Question 21

Action Potential Phases: Falling Phase (repolarization)

Answer 21

potassium ions flow down their concentration gradient out of the cell

membrane potential decreases and becomes negative

potassium channels close

Question 22

Action Potential Phases: Recovery Phase

Answer 22

the sodium-potassium pump restores the resting potential and ion concentration gradients

for every ATP used:
- 3 sodium ions are pumped out
- 2 potassium ions are pumped in

Question 23

Action Potential Propagation (4 steps)

Answer 23

1. Stimulus: brings a section of neuron membrane above the threshold
2. Sodium: flow into the cell through voltage-gated Na+ channels
3. Na+ ions spread further down inside the membrane and cause nearby Na+ channels to reach their threshold and open
4. the Na+ channels that opened first quickly close and become inactive preventing the action potential from propagating (spreading) backwards

Question 24

How does Myelin Sheath speed up action potentials?

Answer 24

instead of ions needing to diffuse in and out all the way along the neuron membrane the action potential “hops” when Na diffuses through the cytoplasm to the next Node of Ranvier

Question 25

What is a Synapse

Answer 25

the connection between two neurons or between a neuron and another type of cell

allows the sending neuron (presynaptic neuron) to deliver its signal to a receiving cell (post-synaptic cell)

Question 26

Types of Synapse: Electrical Synapses

Answer 26

provides a direct channel between cells so that the action potential can physically “jump” from one cell to the next when Na+ ions flow through connexions (holes between cells)

Question 27

Types of Synapse: Chemical Synapses

Answer 27

convert the electrical signal (action potential) from the sending neuron (presynaptic neuron) to a chemical signal (in the form of neurotransmitters) that can cross the synaptic cleft and trigger a response in the receiving cell (either postsynaptic neuron or cell)

Question 28

Synaptic Cleft

Answer 28

small space between the synaptic terminal of one neuron and the next neuron