Nervous System

Question 1

Define afferent neurons, efferent neurons, and interneurons.

Answer 1

Afferent: Body to CNS (ARRIVE at CNS)
Efferent: CNS to body (EXITS the CNS)
Interneurons: neurons that carry sensory info and deal w/ integration.

Question 2

What are: Dendrites, dendritic spines, axon hillock, axon, axon terminal, synapse, and synaptic cleft.

Answer 2

Dendrites: receive incoming information, contact point for neuron-neuron communication.

Dendritic Spine: increase area of synapses

Axon Hillock: where the axon originates in action potentials are initiated.

Axon: transmits action potential

Axon Terminal: releases neurotransmitters onto downstream target.

Synapse: neuron makes contact with another cell (target cell)

Synaptic Cleft: small gap, separating pre-post membrane.

Question 3

What does the CNS consist of?

Answer 3

Brain and Spinal Cord

Question 4

Where are the channels, Na+/K+ ATPase pumps, ligand-gated ion channels and voltage gated ion channels located on a neuron?

Answer 4

Located all over the cell

Question 5

What is the role of Na+ and K+ leak channels and Na+/K+ ATP pumps on a neuron?

Answer 5

And all around maintaining of resting millivolts. (Vm)

Question 6

Explain why a graded potential effect on the membrane potential is variable, while an action potential is all or none and always clips of membrane potential from -70Vm to +30Vm.

Answer 6

Graded potential equals ligand gated ion channels lead to more receptors with Neuro transmitters equals more ion channels open. Graded potential needs multiple graded potentials close together to trigger action potential.

Action potential is propagated down, axon, leading to Neuro transmitter being released which leads to binds of ligand gated channel on postsynaptic membrane, which leads to the sodium flow in which leads to the membrane depolarizing, which leads to enough voltage gated sodium on axon hillock opens which leads to generating action potential which leads to propagates plus releases action potential .

Question 7

For a voltage gated Na+ channel, what is the status of the voltage sensors, activation gate, and inactivation gate as a neuron cycles through an action potential and back to the resting state?

Answer 7

-70mV: voltage sensor goes down activation gate. -> depolarization as it hits -55mV(voltage sensors begin to rise). -> repolarize at +30mV(voltage sensors still up activation gate)

Question 8

In a neuron, how does the inactivation gate create an absolute refractory period that prevents firing another action potential?

Answer 8

Absolute refractory period is due to the inactivation gate blocking the channel.

Question 9

Why is a refractory period necessary?

Answer 9

Allows for an directional propagation of action potential’s. Action potential not just moving towards axon terminal.

Question 10

Define depolarization.

Answer 10

Towards positive +

Question 11

Define hyper polarization.

Answer 11

More negative- then Vm.

Question 12

Define repolarize.

Answer 12

Back towards negative -

Question 13

Resting potential.

Answer 13

Negative-, refers to inside the cell.

Question 14

The membrane potential in a neuron changes drastically going from rest to an AP. What occurs to move the membrane potential from -70mV to -55mV, +30mV, start to move back towards negative Vm, close to -94mV and finally returning to -70mV?

Answer 14

-70mV to -55mV: Neuro transmitters bind leading to ligand gated channel opens -> sodium influx depolarizes membrane -> voltage sensors rise.
Sodium influx depolarizes the cell and creates graded potential.
-55mV to +30mV: activation gate opens sodium rushes in, and the inside becomes positive at +30 in activation gate, undergoes an confirmational and gets inserted into channel.

Question 15

Describe what happens when an AP reaches the axon terminal the results of the post synaptic axon fireing AP. start with what happens with voltage gated calcium channels.

Answer 15

Vm goes +, calcium channel opens allowing calcium influx -> activated calmodulin -> NT’s release in synaptic cleft. NT’s bind to receptors -> channels open -> Na+ influx -> depolarize cell -> graded potential if enough Na+, the membrane potential -55mV will open the voltage gated Na+ channel -> AP will fire.

Question 16

In a neuron, how does the inactivation gate create an absolute refractory period that prevents firing another AP?

Answer 16

Absolutely refractory period is due to the activation gate blocking the channel.

Question 17

Why is a refractory period necessary?

Answer 17

Allows for unidirectional propagation of AP’s.
AP isn’t just moving towards the axon terminal.

Question 18

What ion gates are closed and open during repolarization of an AP?

Answer 18

Na+ ligand gated channels and K+ voltage gated channels are opened.

Question 19

How is repolarization affected by voltage gated K+ channels closing slowly?

Answer 19

The membrane is hyper polarized for a short amount of time.

Question 20

What is the effect of a very large graded potential Na+ influx?

Answer 20

Prevents hyper polarization and allows AP to fire quicker.

Question 21

How can the relative refractory period in an AP be overridden in order to fire the next AP sooner?

Answer 21

Can be overridden by a large graded potential. AP firing frequency is an indicator of stimulus intensity.

Question 22

How does neuron diameter and myelination speed up AP transmission rate?

Answer 22

Myelination shortens time an AP takes to move down the axon. Proportional to diameter, faster if larger, not bumping into walls, the bigger to the diameter of the less disruption of flow.