Ch. 4: The Nervous System

Question 1

What is the cell body?

Answer 1

nucleus of a neuron that also has the endoplasmic reticulum and ribosomes

also called the soma

Question 2

What is the role of dendrites?

Answer 2

recieve incoming messages from other cells

Question 3

What is the role of the axon hillock?

Answer 3

integrates incoming signals and wil initiate an action potential if the threshold is met

Question 4

What is the role of myelin and the myelin sheath?

Answer 4

fatty membrane that prevents signal loss or crossing signals
increases the speed of conduction in the axon

Question 5

What are oligodendrocytes?

Answer 5

produce myelin in the CNS

Question 6

What are Schwann cells?

Answer 6

produce myelin in the PNS

Question 7

What are the nodes of Ranvier?

Answer 7

small breaks in the myelin sheath with exposed areas of the axon

Question 8

What are glial cells?

Answer 8

structural and supportive roles

Question 9

type of glial cell

What are astrocytes?

Answer 9

noursh neurons and form blood-brain barrier
control what enters nervous tissue from blood

Question 10

What are ependymal cells?

Answer 10

line ventricles of the brain and produce cerebrospinal fluid

Question 11

What are microglia?

Answer 11

phagocytic cells that ingest and break down waste products and pathogens in CNS

Question 12

Explain the steps of an action potential.

Answer 12

1. resting potential -70 mV (more K+ than Na+ which makes it negative)
2. depolarization, sodium gates open and sodium enters the cell
3. when the cell reaches +35 mV the sodium channel closes
4. repolarization, triggers potassium channels to open and let potassium out of the cell
5. hyperpolarization, overshoot of K+ out of the cell
6. refactory period, when no action potential can occur
   absolute refactory period: no amount of stimulation can cause another action potential
   relative action potential: must be greater than normal stimulation to cause an action potential

action potential moves down axon to trigger NT release

Question 13

What causes an action potential to be faster?

Answer 13

shorter length of axon has lower resisitance and faster conduction
greater cross-sectional areas have less resistance and faster propogation (much larger effect on speed)

Question 14

What is saltatory conduction?

Answer 14

signal hopes from the nodes of Ranvier
myelin prevents ions to travel through so the membrane is only permeable to ion flow at the nodes of ranvier

Question 15

What is white and grey matter?

Answer 15

in the brain and spinal cord
white matter has axons with myelin sheaths
grey matter has unmyelinated cell bodies and dendrites
- in the brain the white matter is deeper than gery matter
- in the spinal cord white matter is outside the cord and grey matter is deep within

Question 16

Explain the connection between the spinal cord, sensory, and motor neurons.

Answer 16

sensory neurons bring information to the back of the spinal cord (cell bodies of sensory neurons are in dorsal root ganglia) and motor neurons exit the spinal cord at the front of the spinal cord

Question 17

What is a monosynaptic reflex arc?

Answer 17

single synapse between sensory neuron that recieves the stimulus and the motor neuron that responds to it
knee-jerk reflex

Question 18

What is a polysynaptic reflex arc?

Answer 18

there is at least one interneuron between the snesory and motor neurons
withdrawl reflex

Question 19

Explain what happens at the nerve terminal and the synapse.

Answer 19

1. action potential reaches nerve terminal
2. calcium channels open
3. calcium influx causes versicles with NTs to the presynaptic membrane
4. exocytosis of NTs into synaptic cleft
5. NTs bind to receptors on postsynaptic fell (ligand-gated ion channes or G protein-coupled recpetors)

Question 20

How are Neurotransmitters cleared from the postsynaptic receptors?

Answer 20

1. enzymatically broken down
2. absorbed back into presynaptic cell by reuptake chanels
3. diffuse out of the synaptic cleft