N. System & Tissue Ch. 11, Pt.

Question 1

Neuron Function

Answer 1

They are highly irritable & respond to adequate stimulus by generating an action potential

Question 2

Role of Membrane Ion Channels

Answer 2

1. Leakage (nongated) channels: always open

2. Gated channels [3 types]

Question 3

3 types of gated channels

Answer 3

1. Chemically-ligand-gated channels
2. Voltage gated channels
3. Mechanically gated channels

Question 4

When gated channels are open, ions:

Answer 4

diffuse quickly across membrane along electrochemical gradients & ion flow creates an electrical current & voltage changes across the membrane

Question 5

Resting Membrane Potential

Answer 5

Potential difference cross membrane of resting cell

Question 6

RMP is generated by two things:

Answer 6

Difference in ion concentration in ICF & ECF

Differential permeability of the plasma membrane

Question 7

Difference in ion concentration:

Answer 7

• Lower concentration of Na+ & Cl- in ICF than in ECF

- Higher concentration of K+ & A- than in ECF

Question 8

Differential permeability of membrane

Answer 8

Impermeable to A-
Slightly permeable Na+
More permeable to K+

Question 9

The sodium potassium pump

Answer 9

stabilizes RMP by maintaining concentration gradients for Na+ & K+

Question 10

There is a negative interior of a cell at RMP due to

Answer 10

greater diffusion of K+ out of the cell than Na+ into the cell

Question 11

Changes in membrane potential include:

Answer 11

Depolarization & hyperpolarization

Question 12

Depolarization is when

Answer 12

the cell becomes more +
A reduction in membrane potential; toward zero
Increase chances of producing a nerve impulse

Question 13

Hyperpolarization is when

Answer 13

the cell becomes more - than at rest
An increase in membrane potential; away from zero
Reduces chance of producing a nerve impulse

Question 14

Membrane potentials that act as signals… two types

Answer 14

Graded & Action potential

Question 15

Graded Potential signals are

Answer 15

Incoming short-distance

Question 16

Action Potential signals are

Answer 16

Long distance of axons

Question 17

Graded Potentials

Answer 17

Short- lived local changes in membrane potential.
Depolarizations or hyperpolarizations
Spread locally; adjacent regions; wash out/die out

Question 18

Graded Potentials happen when

Answer 18

a stimulus causes gated ion channels to open.

Question 19

The magnitude in graded potentials

Answer 19

vary directly with the stimulus

Decrease in magnitude w/ distance as ions flow/diffuse through leak channels

Question 20

Action Potential is a

Answer 20

• Brief reversal of membrane potential with an amp of ~100mV [large disturbance]
• Occurs in muscle cells & axons of neurons
• Principal means of long distance neural communication

Question 21

Generation of AP includes

Answer 21

Resting state
Depolarization
Repolarization
Hyperpolarization

Question 22

Resting state

Answer 22

Only leakage channels are open.

All gated channels are closed.

Question 23

Depolarization

Answer 23

Depolarization local current open VG Na+ channels
Na+ influx
Threshold -55 to -50 mV positive feedback leads to opening of all Na+ channels & reversal of membrane polarity to +30 mV

Question 24

Repolarization

Answer 24

Na+ channel gates close
Membrane permeability to Na+ declines to resting levels.
Voltage-sensitive K+ gates open.
K+ exits cell & internal negativity is restored.
Na+/K+ pump

Question 25

Hyperpolarization

Answer 25

Some K+ channels remain open, excessive K+ efflux. | Slow closing gate.

Question 26

At threshold..

Answer 26

mebrane potential is depolarized by 15-20 mV Potassium permeability increases More Na in than K out Positive feedback cycle begins

Question 27

Subthreshold stimulus

Answer 27

weak loceal depolarization that doesn't reach threshold

Question 28

Threshold stimulus

Answer 28

Strong enough to push the membrane potential toward/beyond threshold.

Question 29

Stimulus intensity

Answer 29

Difference between weak/strong stimulus? Frequency of AP

Question 30

Conduction velocity

Answer 30

vary widely on effect of axon diameter (the larger the faster) & on degree of myelination

Question 31

Myelination effects

Answer 31

- Myelin sheaths insulate & prevent leakage of charge - Saltatory conduction is 30x faster - VG-Na channels are located at nodes and APs jump from node to node.

Question 32

Multiple sclerosis

Answer 32

Autoimmune disease that affects mainly young adults | Short circuiting of nerve impulses; slows & eventually stops

Question 33

Symptoms of MS

Answer 33

weakness loss of muscular control speech disturbances

Question 34

Regeneration of Peripheral Nerves

Answer 34

Cell body & neurilemmal tube is intact Stranded end of axon and myelin sheath degenerate Axon stump puts out several sprouts Regeneration tube guides lucky sprout back to its original destination; schwann cells produce nerve growth factors

Question 35

The synapse is a..

Answer 35

junction that transfers information from a neuron to another or to an effector cell.

Question 36

presynaptic neuron

Answer 36

conducts impulses towards the synapse | Delivers a message [NT]

Question 37

postsynaptic neuron

Answer 37

transmits impulses away from the synapse | Neuron responds to the stimulus & becomes more - or +

Question 38

Postsynaptic Potentials are

Answer 38

* Graded potentials | * Strength determined by amount of neurotransmitter release, time neurotransmitter is in the area

Question 39

Types of postsynaptic potentials

Answer 39

1.EPSP—excitatory postsynaptic potentials Any NT that causes depolarization 2.IPSP—inhibitory postsynaptic potentials Hypolarization prevents muscle contraction

Question 40

EPSP

Answer 40

NT binds to and opens chemically gated channels that allow simultaneous flow of Na+and K+in opposite directions •Na+influx is greater that K+efflux, causing a net depolarization •Helps trigger AP at axon hillock if it has threshold strength and opens the voltage-gated channels

Question 41

IPSP

Answer 41

* NT binds to and opens channels for K+or Cl– * Causes hyperpolarization * Reduces postsynaptic neuron’s ability to produce an action potential

Question 42

Integration: Summation; two types

Answer 42

temporal & spatial

Question 43

Temporal summation

Answer 43

1+ presynaptic neurons transmits impulses in rapid fire order

Question 44

Spatial summation

Answer 44

Postsynaptic neuron is stimulated by a large number of terminals at the same time

Question 45

Neurotransmitters

Answer 45

Most neurons make 2+ neurotransmitters, which are released at different stimulation frequencies •50+ NT have been identified