Nerve/synapse I

Question 1

The nervous system is divided into two parts. Name and describe them.

Answer 1

Central nervous system: brain and spinal cord
Peripheral nervous system: nerves in arms, legs, intestines, etc. that feed into the CNS

Question 2

What are the 3 types of fibers present in the PNS? Describe what they are.

Answer 2

Afferent (sensory): brings signals in and towards the CNS
Efferent (motor): sends signals from CNS to muscles
Autonomic: sends signals from CNS to organs

Question 3

The smallest unit in the nervous system is the […]

Answer 3

Neuron

Question 4

What are the two distinctive characteristics of neurons?

Answer 4

They are electrical cells and they can talk to each other.

Question 5

What are synapses?

Answer 5

They are specialized sites where communication between neurons takes place.

Question 6

Describe the standard structure of a neuron.

Answer 6

All neurons have a cell body (soma), several branching dendrites, and a single axon that can vary in length and that leads to the presynaptic terminal.

Question 7

Describe the soma of the neuron.

Answer 7

This is where the nucleus and organelles, such as the mitochondria, are. It is also where chemical reactions and processes take place. It could survive if you removed all other parts of the cell.

Question 8

Describe the dendrites of the neuron.

Answer 8

They allow neurons to receive inputs from other cells and are highly branched to allow more synapses from which they can receive signals.

Question 9

Describe the axon of the neuron.

Answer 9

A neuron only has one axon, which allows it to send information to other neurons using an electrical impulse that propagates to the presynaptic terminal.

Question 10

Describe the flow of information in the neuron.

Answer 10

It comes in through the dendrites, travels into the soma, then travels down the axon towards the dendrites of another neuron.

Question 11

What is the resting membrane potential of the neuron? What is the cause?

Answer 11

Around -70 mV compared to the outside. This is due to a small excess of negatively charged ions inside the cell.

Question 12

Explain the two major causes of the voltage gradient in the neuron.

Answer 12

1. There is a concentration gradient of Na+ (a lot on the outside, little on the inside), K+ (a lot on the inside, little on the outside), Cl- (a lot on the outside, little on the inside), and other anions (a lot on the inside, little on the outside).
2. At rest, the neuronal membrane is only highly permeable to K+, which wants to flow out of the cell. So K+ will naturally leak out of the cell from leak channels down their concentration gradient, leaving behind unpaired negative ions that pull K+ back in.

Question 13

What equation can be used to calculate the resting membrane potential for a given ion?

Answer 13

The nernst equation.

Question 14

What is the equilibrium potential for K+?

Answer 14

-90 mV

Question 15

What is the equilibrium potential for Na+?

Answer 15

+70 mV

Question 16

What is the equilibrium potential for Cl-?

Answer 16

-80 mV

Question 17

Is the resting membrane potential equal to that of K+? Explain why or why not.

Answer 17

No, it is not. The resting membrane potential would be -90 mV if the membrane were only permeable to K+. However, at rest, there is also a small inward leak of Na+, which has a positive membrane potential of +70 mV. So, it averages out to around -70 mV.

Question 18

When the neuron is at rest, the dominant ion determining the membrane potential is […]

Answer 18

K+