6.5 neurons & synapses

Question 1

label diagram of a neuron

Answer 1

see ipad

Question 2

resting potential

Answer 2

Sodium ions tend to try and diffuse into the cell through Na ion channels.
Potassium ions tend to try and diffuse out of the cell through K ion channels.
Although both channels are closed, there is some “leakage”.

Question 3

central nervous system (CNS)

Answer 3

Main control
Consists of the Brain, Spinal Cord, and the Brain Stem.

Question 4

peripheral nervous system (PNS)

Answer 4

connects body to central nervous system (CNS)
2 branches: somatic & autonomic nervous system

Question 5

2 main processes involved in communication between neurons

Answer 5

The Nerve Impulse (a series of action potentials along the neuron)

Synaptic transmission (neurotransmitters from one neuron interact with another neuron).

Question 6

sodium potassium pump

Answer 6

The Na+/K+ pump is essential to the proper functioning of neurons.
Ions are distributed unequally across the membrane of the axon. This creates an difference of charges inside and outside the cell (called a membrane potential).

Question 7

action potential

Answer 7

Describes the rapid change in charges across the membrane when a neuron is firing.
There are 3 main stages:
1. Depolarization
2. Repolarization
3. Refractory period

Question 8

action potential - depolarization

Answer 8

A sudden change in membrane potential. The (relatively) negative interior rapidly becomes (relatively) positive.
When a stimulus is applied to the neuron, sodium channels open in the membrane of the axon.
Outside the membrane, there is a high concentration of Na+ ions. Sodium ions enter the cell (passive transport).
The membrane potential becomes more positive (~ +50 mV)

Question 9

action potential - repolarization

Answer 9

The membrane potential is returned to a (relatively) negative charge inside the cell.
The sodium channels close and the potassium channels open.
Positive K+ ions diffuse (facilitated) out of the neuron, thus making it more negative.

Question 10

Action Potential - Refractory Period/Hyperpolarization

Answer 10

The potassium channels stay open slightly longer than needed.
K+ ions leave the cell, and the potential becomes more negative than the resting potential (about -80mV).
This prevents further action potentials (as the cell is too negative) for approx. 2ms
The benefit: impulses can move in only one direction.

Potassium ion channels close.
The Na+/K+ pumps restore the resting potential

Question 11

what does it mean that the Na+ and K+ channel proteins are voltage-gated?

Answer 11

they are activated when the membrane potential (voltage) changes.
When depolarization occurs in one location on the axon, it triggers the opening of other Na+ channel proteins in the next segment of the axon.
Thus, depolarization spreads along the length of the axon. Like a wave at a sporting event :)

Question 12

synaptic transmission

Answer 12

The transmission of an impulse from one neuron to another

Question 13

synapses

Answer 13

The junction between two neurons is called a synapse. It is a small, fluid-filled space. The action potential, representing the stimulus signal, must cross this space.

Question 14

synaptic transmission

Answer 14

The influx of Na+ ions at the axon terminal triggers the opening of voltage-gated Ca2+ channels.
There is a rapid influx of Ca2+ ions across the membrane. (Passive)
The calcium ions trigger the fusion of vesicles containing chemicals known as neurotransmitters to the cell membrane.
Neurotransmitters are released through exocytosis into the synapse.
The neurotransmitter travels across the synapse to the next neuron’s membrane, where it binds to specific protein receptors on the post-synaptic neuron.
This causes Na ion channels to open and the action potential is triggered anew.
The neurotransmitter is then usually broken down and reabsorbed into the pre-synaptic neuron, to be recycled.