Chapter 43 Part II

Question 1

Action potentials

Answer 1

have all or nothing response: no matter, what the intensity of the stimulus, the amplitude of the action potential is the same

 Enough depolarization to graded potentials will push the neuron past –the threshold— at the axon hillock
* This causes an action potential

Question 2

How are action potentials acheived?

Answer 2

by voltage gated ion channels/voltage-activated channels

At rest these channels are closed, like a “gate”/ not conducting ions across the membrane

Voltage-dependent channels, dependent on voltage difference across the membrane

**when the membrane potential changes a reaches a certain threshold, channel undergoes change and “opens,” allowing ions to flow through the channel

Example: Na+ and K+ voltage gated ion channels

Question 3

Explain the steps of an action potential

Answer 3

1) depolarization occurs when voltage-gated Na channels open on axon hillock; Na rushes in, producing “spike” of depolarization

At the top of the curve, Na gates close and voltage gate K gates open
2) K leaves the cell, resulting in repolarization

3) hyperpolarization briefly occurs as K channels take time to close; Na/K pumps will kick in, resets the resting membrane potential

Question 4

Myelin

Answer 4

made up of Glia Cells

Question 5

Two types of Glia cells

Answer 5

Schwann cells and Oligodendrocytes

Question 6

Schwann cells

Answer 6

• Type of glia cell
• Wrap around neurons in the PNS, forming myelin sheaths
• Can only myelinate small segment of single axon

Question 7

Oligodendrocytes

Answer 7

• In CNS
• Can myelinate multiple axons simultaneously(different than schwann cells), process extends to wrap around several axons at once

Question 8

Similarities of Schwann cells and Oligodendrocytes

Answer 8

Both types of glia cells maintain the health and function of nervous system by providing support and insulation

Question 9

Propagation of Action Potentials

Answer 9

 Electrical signal/action potential travels down the axon of a neuron
* Action potential generated in neuron triggers the opening of votlage-gated ion channels
* Allows ions to flow across the membrane and depolarize the “next” region of the axon
* Depolarization triggers opening of voltage-gated ion channels in the next segment of the axon
* Process repeats down length of axon
* Facilitated by myelin shealth
* Allows for efficient communication between neurons

Question 10

Summary of Propagation of Action Potential

Answer 10

1) Na+ enters axon, attracting negative charges and repelling positive charges
2) charge spreads; membrane downstream depolarization (at next ion channel)
3)downstream voltage-gated channel open in response to depolarization; results in new action potential

Question 11

Saaltatory Conduction

Answer 11

Action potential travels down a myelinated axon, “jumping” from one node of Ranvier to the next

Done instead of propagation continuously down axon; allows signal to travel more quickly and use less energy instead of unmyelinated axon

Question 12

Nodes of Ranvier

Answer 12

: small gaps in myelin sheath where axon membrane is exposed to extracellular fluid

Concentration of voltage-gated ion channels are high at nodes

Allows for rapid depolarization and propagation of action potential

Question 13

Synapse

Answer 13

gap between axon terminal and target cell

Question 14

Synaptic/axon terminal

Answer 14

Action potential will continue to propagate until it reaches the end of the axon

Site where neuron communicated with other cells (Other neurons, Muscle cells, Gland cells)
 Releases neurotransmitters
 Receives feedback fron other cells in form off (Neurotransmitters, Neuromodulators, Signaling molecules)

When AP reaches terminal, it will cause an influx of ions from voltage gated channels into the cell; Causes release of neurotransmitter via exocytosis

Question 15

Neurotransmitters

Answer 15

chemical messengers that bind to receptors on the target cell; Tranmsit signal across the synapse

Question 16

Three main structures of synapse

Answer 16

presynaptic terminal, synaptic cleft, and postsynaptic membrane

Question 17

Presynaptic terminal

Answer 17

end of the axon that contains synaptic vesicles, which store and release neurotransmitters

Contains voltage gated ion channels responsible for generating and propagating action potentials

Question 18

Synaptic Cleft

Answer 18

o Narrow gap between presynaptic terminal and postsynaptic membrane
o Filled with extracellular fluid
o Site of neurotransmitter diffusion

Question 19

Postsynaptic terminal

Answer 19

membrane of target cell that receives signal from presynaptic terminal

o Contain receptors that bind to neurotransmitters
o Receptors initiate response in target cell
o Leads to generation of action potential

Optimized for rapid and efficient communication between cells; Plays role in sensation, movement, cognition, behavior

Question 20

Types of Neurotransmitters

Answer 20

EPSP, IPSP

Question 21

EPSP

Answer 21

excitatory postsynaptic potentials

make postsynaptic action potentials more likely
* Depolarization, Na+ inflow

Question 22

IPSP

Answer 22

make postsynaptic action potentials less likely
* Hyperpolarization, K+ outflow or Cl- inflow

inhibitory postsynaptic potentials

Question 23

Simultaneous EPSPs and IPSPs

Answer 23

may cancel each other out

Question 24

Peripheral Nervous system

Answer 24

receives info from environment