FORM & FUNCTION (Graded Potential)

Question 1

Action potential (AP) strength:

Answer 1

-always the same amplitude
-“all or nothing”
-stimulus strength effects the frequency
>stronger stimuli lead to more FREQUENT APs

Question 2

Sustained threshold stimulus:

Answer 2

-generate a train of Aps with an interval including the ARP and the RRP

Question 3

Sustained supra-threshold stimulus:

Answer 3

-generate a train of Aps within an interval including only the ARP

Question 4

Which part of the neurone will AP be initiated?

Answer 4

-axon hillock

Question 5

Types of electrical signals in excitable cells:

Answer 5

1. Action potential
2. Graded potential

Question 6

Graded potential:

Answer 6

-local signal proportional to the stimulus
-sub-threshold changes in membrane potential
-occurs primarily in dendrites and cell body

Question 7

Characteristics of graded potential:

Answer 7

-vary in amplitude based on duration and strength of the stimulus
-decremental nature

Question 8

Decremental nature of graded potentials:

Answer 8

-diminishes in strength over distance

Question 9

Role of graded potential in neural communication:

Answer 9

-serve as initial response to external changes

Question 10

Types of graded potential:

Answer 10

1. Receptor potential/generator potential
2. Postsynaptic potential
3. Endplate potential

Question 11

Receptor potential/generator potential:

Answer 11

-GP generated by sensory receptors at the nerve endings of the sensory neuron

Question 12

Postsynaptic potential:

Answer 12

-GP generated by NT binding to its receptor on the postsynaptic neuron

Question 13

Endplate potential:

Answer 13

-GP generated by NT binding to its receptor on the skeletal muscle fiber

Question 14

GP hyperpolarizing or depolarizing:

Answer 14

1. Excitatory postsynaptic potential (EPSP)
2. Inhibitory postsynaptic potential (IPSP)

Question 15

EPSP:

Answer 15

-depolarization
-Na+ channels on postsynaptic neurons are opened and Na+ enters the cell

Question 16

IPSP:

Answer 16

-hyperpolarization
-Cl- channels on postsynaptic neuron are opened and Cl- enters the cell

Question 17

GP: summation

Answer 17

1. Temporal summation
2. Spatial summation
   *AP can NOT be summated

Question 18

Temporal summation:

Answer 18

-successive, rapid input from a SINGLE pre-synaptic neuron is electrically summed

Question 19

Spatial summation:

Answer 19

-simultaneous input from more than one pre-synaptic neuron is electrically summed

Question 20

Propagation of electrical signals within a neuron:

Answer 20

1. Passive spreading
2. Active spreading

Question 21

Passive spreading:

Answer 21

-slow and small amplitude
-localized
-signal dies off with distance (stays within cell body)

Question 22

Active spreading:

Answer 22

-fast and large amplitude
-travel far
-signal is self-regenerated
-requires VG Na+ and K+ channels to be positioned along the path of propagation (can go down axon)

Question 23

Steps of AP propagation:

Answer 23

1. • enters cell
2. Current flows through activated patch membrane, depolarizes adjacent patch
3. Adjacent path reaches threshold, current flows, depolarizes adjacent patch
4. Continues in one direction as repolarized patch is refractory
   *after refractory period, the channel is ready to be activated again

Question 24

Distribution of Na+ and K+ channels in a neuron:

Answer 24

-soma: 50-75
-axon hillock: 350-500
-myelinated regions: <25
-nodes of Ranvier: 2000-12000
-axon terminal: 20-75

Question 25

Myelination:

Answer 25

-effectively reduces the distance an AP needs to travel -allows for ‘saltatory conduction’ (node to node conduction) -AP jumps from node to node

Question 26

Factors effecting conduction speed in neurons:

Answer 26

1. Myelination 2. Axon diameter

Question 27

Unmyelinated neurons:

Answer 27

-continuous -slower propagation of AP

Question 28

Larger diameter:

Answer 28

-faster conduction due to decreased resistance to the flow of electric current

Question 29

Smaller diameter:

Answer 29

-slower conduction

Question 30

Nerve fiber classification:

Answer 30

-A fibers -B fibers -C fibers

Question 31

A fibers:

Answer 31

-myelinated with large diameter -fast conduction speed -4 sub-classes Ex. somatic motor, touch pressure

Question 32

B fibers;

Answer 32

-myelinated -slightly smaller than A fibers -medium conduction speed Ex. visceral motor (preganglionic)

Question 33

C fibers:

Answer 33

-unmyelinated -small -slowest conduction speed Ex. visceral motor (postganglionic), slow pain, temperature

Question 34

GP vs. AP amplitude:

Answer 34

GP: proportional to strength of stimulus, small (10mV), decremental AP: strength coded in frequency, large (100mV), non-decremental

Question 35

GP vs. AP duration:

Answer 35

-GP: few ms to s -AP: very short, 3-5ms

Question 36

GP vs. AP channels:

Answer 36

-GP: ion channels (ligand gated, mechanosensitive, temperature gated) -AP: VG Na+ and K+ channels

Question 37

GP vs AP spread:

Answer 37

-GP: passive -AP: active

Question 38

GP vs. AP triggers:

Answer 38

-GP: external stimuli or NT release -AP: membrane depolarization to threshold (due to GP)

Question 39

GP vs. AP location:

Answer 39

-GP: any region of the membrane -AP: only in membrane with high concentration of VG Na+ and K+ channels