Nerve Signals

Question 1

How is the transmission of an electrical impulse down a neuron generated?

Answer 1

By the movement of Na+ and K+ ions

Question 2

What is resting potential?

Answer 2

• a resting neuron has a net positive charge on the outside and a net negative charge on the inside
• the potential difference across the membrane is -70mv
• resting potential results from accumulation of Na+ ions on the outside of the membrane

Question 3

Describe excitation

Answer 3

Na+ channels in the membrane open and Na+ rushes into the cell via facilitated diffusion

(Ligand-gated ion channel transport)

-this causes a reversal of charge (depolarization)

Question 4

Describe action potential

Answer 4

Upon depolarization, the potential difference across the membrane changes to between +30 and +40mV

(Voltage gated transport)

-action potential moves down neuron like a wave by triggering the opening of adjacent Na+ channels

Question 5

Describe repolarization

Answer 5

SOPI
After the action potential has moved through an area, sodium-potassium pumps use ATP to move Na+ ions out of the cell and K+ ions in
-pump moves ions 3:2 (Na+ : K+)
-as a result, resting potential is reestablished (+O-I, -70mV)

Question 6

Refractory period

Answer 6

Nerve cell cannot fire again until resting potential has been reestablished (1-10 ms)
-ensures that signal travels in 1 direction (gates close)

-myelinated cells transmit impulses faster because the action potential jumps between the nodes of Ranvier

Question 7

All or nothing

Answer 7

Transmission of an impulse down a neuron is an all or nothing event

Minimum level of a stimulus required to produce an impulse is called the threshold level (-55mV)

• managed by axon hillock
• intensity of all generated impulses same despite discrepancies in stimuli
• larger stimuli will have more frequent impulses than smaller stimuli

Question 8

What are synapses?

Answer 8

Small spaces between neurons or effectors (muscles/glands)

Question 9

Describe synaptic transmission

Answer 9

Neurotransmitters (NT) are used to transmit impulses across a synapse

• Axon terminal of the presynaptic neuron contains vessels that hold NT and upon stimulation release them
• NT diffuse across synapse and initiate an impulse in the postsynaptic neurons

Question 10

2 types of synapses

Answer 10

1. Electrical
   -very rare
   Presynaptic and postsynaptic cells are in direct contact
   -allows current to flow through instantly
2. Chemical
   - make up majority of synapses
   - delays transmission as NT is released, diffusion, and binding of NT across synapse
   - allows neurons to receive input from hundreds to thousands at the same time
   - action potential reaches axon terminal
   - Ca2+ gates open and flow into cytosol
   - triggers Pr in synaptic vesicles to fuse w cell membrane
   - NT is released through exocytosis
   - NT binds to postsynaptic receptor, opening ion channels for AP to continue