L20 - Action Potentials

Question 1

What is a neuron?

Answer 1

A cell specialized to conduct electrochemical impulses called nerve impulses or action potentials

Question 2

What does the neuron cell body consist of?

Answer 2

Soma (contains the nucleus)

Dendrites (receive information, the hairy projections of the soma)

Axon (fiber that extends from soma to connect signals to other neurons)

Question 3

What is the Myelin sheath in the neuron responsible for?

Answer 3

Connect with other cells and membrane surfaces

Important for transmission of nerve impulses or action potentials

Question 4

How do transmembrane proteins permeate the membrane?

Answer 4

Ion channels

Question 5

What is the resting potential (homeostasis) of an ion?

Answer 5

-70 microvolts (MV)

Question 6

True or false, any ion can permeate gated-ion channels

Answer 6

False

Question 7

What are the key steps for the generation of an action potential?

Answer 7

1. Chemical stimulus applies
2. Membrane potential breaks threshold (goes from -70 to -60mV)
3. When the voltage reaches the threshold ion channels enter, allowing positive ions to rush into the cell
4. Once it reaches the peak it returns to normal.

Question 8

What happens if the membrane potential doesn’t reach -60 mV when trying to generate an action potential?

Answer 8

It doesn’t reach the threshold and it returns to the resting membrane potential (-70mV)

Question 9

Where along the neuron does the action potential travel to connect with another neuron?

Answer 9

The axon

Question 10

What chemical rushes into a neuron when the action potential threshold is reached?

Answer 10

Sodium (Na+)

Question 11

After an action potential, what is the term for the membrane potential returning to normal?

Answer 11

Hyperpolarization

Question 12

What is the term for when Sodium enters and an action potential is rising (getting closer to 0)?

Answer 12

Depolarisation

Question 13

What chemical enters once the action potential reaches its peak (30mV) to return the membrane potential to normal?

Answer 13

Potassium

Question 14

Explain the steps of repolarisation

When does it happen exactly?

Answer 14

At 30mV voltage-gated potassium channels open

Potassium (+) move OUT of the cells (repolarization)

Membrane potential drops

Question 15

During depolarisation, the membrane is within the absolute refractory period. What does this mean?

Answer 15

The membrane cannot respond to further simulation

Question 16

During repolarization the membrane is in the relative refractory period, what does this mean?

Answer 16

The membrane can respond to larger than normal stimulus.

Question 17

A stronger response requires a stronger action potential.

True or False

Answer 17

False

A stronger response has a quicker ‘rate’ at which action potentials occur.

Question 18

Summarise the ion channels opening and closing during an action potential.

Answer 18

Sodium (Na) channel opens

Potassium (K) channel opens

Sodium channels inactive

Potassium channels inactive

Question 19

What are the two properties that determine the velocity of propagation of an action potential?

Answer 19

Myelination (faster in myelinated axons than unmyelinated)

Diameter (faster in larger diameter axons than smaller diameter axons)

Question 20

Where does the action potential occur?

Answer 20

Only at the nodes of Ranvier

Question 21

What is the all-or-none law for action potentials?

Answer 21

The size of the action potential is unaffected by increases in the intensity of stimulation beyond the threshold level.

Question 22

What is the refractory period?

Answer 22

A period during which further stimulation cannot cause another action potential.

Question 23

How is the strength of a stimulus conveyed with action potentials?

Answer 23

Conveyed by the rate of neural firing (spikes/sec)

Question 24

What is synapatic transmission?

Answer 24

Sending of action potential to other neurons so it can travel in the brain.

Question 25

Where does synaptic transmission occur?

Answer 25

At the axon terminals which are at the tips of the axon’s branches

Question 26

What does pre-synaptic and post-synaptic mean?

Answer 26

Pre-synaptic = where it’s coming from

Post-synaptic = where it’s going to

Question 27

Is synaptic transmission chemical or electrical?

Answer 27

Chemical

It uses calcium (positive)

Question 28

What are the steps of synaptic transmission?

Answer 28

1. Arrival of action potential at axon terminal
2. Voltage-gated Ca2+ (calcium) channels opsn and Ca2+ enters presynaptic neuron
3. Neurotransmitter released into synaptic cleft (via exocytosis)
4. Synaptic vesicle fuses to cell membrane

Question 29

What part of the synaptic process determines the effect of the neurotransmitter?

Answer 29

The synaptic receptor

(not the neurotransmitter per se)

Question 30

What are the 4 types of neurotransmittors than neurons can produce (biochemical classification)

Answer 30

amino acids (e.g. GABA)

monoamines (e.g. dopamine)

acetylcholine (own class)

neuropeptides (larger molecules, e.g. oxycocin)

Question 31

What are Glial cells useful for?

Answer 31

They are a structural support cell (glial = glue)

Form things like the blood-brain barrier and help guide neurons during development.

(10x more of these than neurons)