Lecture 8: Nerve 1

Question 1

Describe the structure of a nerve from out to in:

Answer 1

Whole nerve -> fascicles -> bundles of neurons -> axon

Question 2

Describe the structure of a neuron:

Answer 2

A neuron is a single cell
Dendrites -> cell body (soma) -> axon -> synaptic terminals

Question 3

What are the 3 different types of neurons?

Answer 3

1. Multipolar - multiple local inputs at soma (motor neurons, CNS)
2. Unipolar - dendrites distal from soma (sensory neurons)
3. Anaxonic - no distinct axon, axonless (CNS neurons)

Question 4

How do neurons communicate with eachother?

Answer 4

1. The pre-synaptic neuron contains neurotransmitter vesicles and releases these in the electrical-chemical conversion
2. A chemical synapse occurs between the 2 neurons which allows for regulation (dampening or potentiation) of the signal
3. The post-synaptic neuron contains neurotransmitter receptors - this is where the chemical-electrical conversion occurs

Question 5

Where is the input zone of a neuron?

Answer 5

Dendrites and cell body (soma)
* Receives input - local potentials
* Chemically-gated ion channels

Question 6

Where is the integration zone of a neuron?

Answer 6

Axon hillock
* Summates the local potentials -> generates action potential
* Voltage-gated ion channels

Question 7

Where is the action potential zone of a neuron?

Answer 7

Axon
* Sends an action potential down the axon
* Voltage-gated ion channels

Question 8

Where is the output zone of a neuron?

Answer 8

Axon terminals
* Releases neurotransmitter to initiate a response in target cell
* Voltage-gated ion channels

Question 9

Describe the ion gradients in bioelectricity:

Answer 9

• There are concentration gradients and electrostatic forces
• Both can act simultaneously in the same or opposite direction
• If they exactly balance, ions will stop moving - EQUILIBRIUM

Question 10

What are the relative levels of Na+ and K+ in the ECF and ICF?

Answer 10

ECF:
High Na+ - 142mM
Low K+ - 4mM
ICF:
Low Na+ - 12 mM
High K+ - 150mM

Question 11

What is equilibrium potential?

Answer 11

The membrane potential when the 2 opposing forces of an ion are balanced

Question 12

What is resting membrane potential (RMP)?

Answer 12

The combined permeabilities and gradients of all the ions (Na+, K+, Cl-, & others) involved, and is approximately -70mV

Question 13

What is the threshold value for an action potential?

Answer 13

-60mV

Question 14

What is depolarisation?

Answer 14

Becoming more positive

Question 15

What is repolarisation?

Answer 15

Becoming more negative but still above RMP

Question 16

What is hyperpolarisation?

Answer 16

More negative than RMP

Question 17

What is overshoot?

Answer 17

More positive than zero

Question 18

What are local potentials?

Answer 18

• Small (graded) local changes – depolarises or hyperpolarises the membrane to different levels (can cause action potential)
• Does not propagate, amplitude decreases with distance – short distances
• Temporal and spatial summation
• Chemically gated ion channels

Question 19

What are action potentials?

Answer 19

• All or nothing – either the same size action potential or no action potential at all
• Depolarizes to the same level (+30 mV) each time
• Propagates down the axon without loss of amplitude - long distances
• Voltage-gated ion channels

Question 20

Give 3 examples of different stimuli and their receptors:

Answer 20

1. Touch on a skin pressure receptor
2. Pain on a nociceptor
3. Light hits photoreceptor

Question 21

Describe the local depolarisation between neurons:

Answer 21

• Neurotransmitter from the pre-synaptic cell binds to the receptor on the postsynaptic cells
• Chemically gated Na+ channels will open
• Na+ will flow into cell
• Causes a local depolarisation

Question 22

What happens if an excitatory neurotransmitter binds?

Answer 22

Adrenaline/epinephrine:
Na+ enters neuron bringing membrane potential closer to threshold - depolarising

Question 23

What happens if an inhibitory neurotransmitter binds?

Answer 23

Serotonin:
Cl- enters neuron moving membrane potential away from threshold - hyperpolarising