The Nervous System

Question 1

What are neurons?

Answer 1

specialized cells capable of transmitting electrical impulses and then translating those electrical impulses into chemical signals

Question 2

Name and describe the parts of the neuron

Answer 2

• Cell body/soma - nucleus, ER and ribosomes are located here
• Dendrites - appendages that receive incoming messages from other cells
• Axon hillock - located in between the cell body and the axon and it integrates incoming signals
• Axon - long appendage goes from the cell body to the nerve terminals
• Myelin sheath- a fatty membrane that insulates the axon prevents signal loss and speeds the conduction
• Nodes of Ranvier - small breaks in the myelin sheath
• Nerve terminal/synaptic bouton (knob)- enlarged and flattened structure to maximize transmission of the signal to the next neuron and ensure proper release of neurotransmitters

Question 3

What are action potentials?

Answer 3

transmission of electrical impulses down the axon

Question 4

What is the small space between neurons where neurotransmitters are released called?

Answer 4

synaptic cleft

Question 5

What is a synapse?

Answer 5

the combination of the nerve terminal, synaptic cleft and postsynaptic membrane

Question 6

What is a nerve?

Answer 6

a group of neurons bundled together in the PNS, can carry multiple types of information

Question 7

What are tracts?

Answer 7

bundles of axons in the CNS, carry only one type of information

Question 8

What are astrocytes?

Answer 8

nourish neurons and form a blood-brain barrier that controls the transmission of solutes from the bloodstream into nervous tissue

Question 9

What are ependymal cells?

Answer 9

line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber

Question 10

What are microglia?

Answer 10

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

Question 11

What are oligodendrocytes?

Answer 11

produce myelin around axons for the CNS

Question 12

What are Schwann cells?

Answer 12

produce myelin around axons for the PNS

Question 13

What are action potentials?

Answer 13

is a rapid rise and then fall of voltage across a cell membrane; they are used to send messages down axons to other neurons

Question 14

What is the cell’s resting membrane potential?

Answer 14

around -70 mV; this is the net electric potential difference that exists across the cell membrane, created by a movement of charged molecules across that membrane

Question 15

Describe the process of how the cell resting membrane potential is produced

Answer 15

Potassium
-Potassium has a higher concentration inside the cell than outside, which leads to passive diffusion of those ions outside through potassium leak channels
-Potassium is a positive ion and so it leaving the cell makes the cell a little more negative and the outside a little more positive
-However the negative gradient is attractive to the positive K ion so it will go back into the cell until an equilibrium potential of potassium at -90 mV is achieved
Sodium - same thing but reversed
- Sodium has a higher concentration outside the cell than in so sodium will leak INTO the cell through passive diffusion using sodium leak channels
- Sodium reaches equilibrium around +60 mV
The two concentration gradients partially cancel each other out and end up with a -70 mV membrane potential overall

Question 16

What is depolarization?

Answer 16

raising the membrane potential, Vm, from its resting potential; caused by an influx of sodium ions

Question 17

What is hyperpolarization?

Answer 17

lowering the membrane potential from its resting potential; caused by an influx of potassium ions

Question 18

What is the threshold value for action potentials?

Answer 18

-55 to -40 mV

Question 19

What is temporal summation?

Answer 19

refers to the integration of multiple signals near each other in time

Question 20

What is spatial summation?

Answer 20

refers to the integration of multiple signals near each in space

Question 21

Absolute Refractory period vs Relative Refractory period

Answer 21

Absolute - no amount of stimulation can cause another action potential to occur
Relative - there must be a greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than the resting value D

Question 22

What is impulse propogation?

Answer 22

the action potential moving down the axon segment by segment and initiating neurotransmitter release

Question 23

What is saltatory conduction?

Answer 23

when the ions hope from node to node because insulation is so effective

Question 24

How are neurotransmitters released?

Answer 24

(1) When the action potential reaches the terminal end, voltage gated calcium channels open
(2) Calcium coming into the cell allows for the fusion of vesicles containing neurotransmitters to be pushed out of the cell
(3) Neurotransmitters bind to receptors on the postsynaptic membrane
(a) If ligand-gated channel –> depolarized or hyperpolarized
(b) If G protein-coupled receptor –> changes in cyclic AMP or influx of calcium

Question 25

What are the three methods of neurotransmitters reuptake?

Answer 25

(1) Broken down by enzymes (ACh)
(2) Brought back to the presynaptic neuron using reuptake carriers (5-HT, DA, NE)
(3) May diffuse out of the synaptic cleft (NO)

Question 26

What is white matter?

Answer 26

matter in the brain that consists of axons encased in myelin sheaths

Question 27

What is grey matter?

Answer 27

matter in the brain that consists of unmyelinated cell bodies and dendrites

Question 28

What are the four regions of the spinal cord?

Answer 28

cervical, thoracic, lumbar and sacral

Question 29

What is the vertebral column?

Answer 29

protects the spinal cord and transmits nerves at the space between adjacent vertebrae

Question 30

Preganglionic neuron vs postganglionic neuron

Answer 30

Preganglionic neuron has its soma in the CNS and its axon travels to a ganglion in the PNS

Question 31

What is a monosynpatic reflex arc?

Answer 31

A reflex that is caused by a single synapse between the sensory neurons that receives a stimulus and the motor neuron responds to it; knee jerk reaction

Question 32

What is a polysynaptic reflex arc?

Answer 32

A reflex that is caused by at least one interneuron between the sensory and motor neurons; withdrawal reflex