Nerve and synapses

Question 1

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

Answer 1

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

Question 2

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

Answer 2

neurons

Question 3

What are synapses?

Answer 3

They are specialized sites where communication between neurons takes place.

Question 4

Describe the standard structure of a neuron.

Answer 4

All neurons have a cell body, several branching dendrites and a single axon that can vary in length that ends in a presynaptic terminal

Question 5

Describe the soma of the neuron.

Answer 5

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 6

Describe the dendrites of the neuron.

Answer 6

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

Question 7

Describe the axon of the neuron.

Answer 7

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 8

Describe the flow of information in the neuron.

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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 11

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

Answer 11

K+