3.1-3.2 Neurons

Question 1

action potential

Answer 1

the form of information of nerves

• a localized area of depolarization of the plasma membrane
• travels wave-like along an axon
• when it reaches the end of an axon, at a synapse, signal is transformed into a chemical signal, with release of neurotransmitter into the synaptic cleft

Question 2

synaptic transmission

Answer 2

release of neurotransmitter into a synaptic cleft

Question 3

neuron

Answer 3

has one or more dendrites (1 dendrite = bipolar neuron, >1 = multipolar)

• carries action potentials in 1 direction (away from cell body)
• soma = cell body with nucleus

Question 4

synaptic knobs

Answer 4

branching that occurs at the end of axons, which form connections with target cells

Question 5

synaptic cleft

Answer 5

the space between synaptic knob and target cell

Question 6

resting membrane potential

Answer 6

electrical potential across the plasma membrane, at -70 mV (net negative charge inside cell).

• established by two membrane proteins (Na/K, and K leak channels)
• the cell is polarized (negative inside)

Question 7

Na+/K+ ATPase

Answer 7

a membrane protein that pumps 3 Na+ ions out, two K+ ions in (banana-in, sweat the salt) per ATP (active transport)

Question 8

Leak channels

Answer 8

open all the time

- but relatively few sodium leak channels - membrane in impermeable to sodium (bananas leak)

Question 9

repolarization

Answer 9

after depolarization, membrane potential returns to -70 mV, caused by movement of ions into and out of the neuron through ion channels (AP is an electrochemical impulse)

Question 10

voltage-gated sodium channels

Answer 10

located on plasma membrane of axon - open to allow Na+ ions to flow down gradients into cell, threshold potential of ~-50 mV (meaning the v-gated Na channels are fully closed at -50 mV; at -50 mV the channels open), further opening gives the neuron a momentary positive charge

Question 11

repolarization

Answer 11

establishing the resting membrane potential again

1. V-gated sodium channels inactivate very quickly, cutting off flow of sodium into the cell. They remain inactivated until the membrane potential returns to resting values.
2. V-gated potassium channels open in response to membrane depolarization; they open more slowly than sodium channels, stay open longer, allowing K to leave the cell and going to -90 mV. They then close, but they close only at -90mV, and they do not close if the sodium channels are left open.
3. Potassium leaks, ATPase Na/K restore the resting potential

Question 12

Schwann cells

Answer 12

a type of glial cell, creates the myelin sheath, prevents ions from entering the neuron

Question 13

depolarization

Answer 13

change in membrane potential from -70 mV to a less negative or positive potential

Question 14

Myelin / saltatory conduction

Answer 14

increases the speed of transmission, forcing AP to jump from node to node, called saltatory conduction

reduces the area of membrane that is conducting, so that only the nodes of Ranvier are depolarized/repolarized, reducing the work needed by Na+/K+

Question 15

Axon

Answer 15

the wire

Question 16

myelination does not affect

Answer 16

1. refractory period or frequency of action potentials (this is based on V-gated sodium and potassium channels, not myelination)
2. the size of depolarization (APs are “all or nothing”)

It does affect speed of conduction

Note: speed and magnitude of AP is constant - “all of nothing”

Question 17

Glial cells

Answer 17

specialized, non-neuronal cells that provide structural and metabolic support for neurons - do not generate APs

• Schwann cells - form myelin
• Oligodendrocytes - form myelin
• Astrocytes - regulate neurotransmitter levels
• Microglia - cleaners
• Ependymal - produce CSF

Question 18

Equilibrium potential

Answer 18

during AP, movement of sodium/potassium is passive (gradient-driven); EP is when driving gradient force does not exist

Sodium is +50 mV (electrically sodium is pushed out and concentration-gradiently drawn in). Think: when the cell becomes permeable to Na, the membrane potential shoots up to +35 mV.

Potassium are driven out by concentration gradient, driven in by electrical gradient. At -90 mV.

Question 19

Permeability

Answer 19

if the cell were completely permeable to K+, resting potential would be around -90 mV, which means there are a large number of K+ leak channels

Question 20

Refractory period

Answer 20

APs can pass through a neuron in 1/1000ths of a second, but a limit exists to how quickly it can conduct an AP after one has passed (a refractory period)

1. Absolute refractory period - neuron will not fire no natter how strong the depolarization induced. The V-gated sodium channels are inactivated (not closed)
2. Relative refractory period - Neuron can be induced to transmit an AP, but depolarization required is greater than normal due to hyperpolarization

Question 21

synapse

Answer 21

junction between axon terminus and the dendrites/soma/axon of a second neuron or an organ

Electrical and chemical

Question 22

electrical synapse

Answer 22

Electrical - two cytoplasms are joined by gap junctions. the AP will spread. important in smooth muscle and cardiac muscle

Question 23

chemical synapse

Answer 23

Chemical - ends of axons, where AP is converted to chemical signal

1. AP reaches end of axon, the synaptic knob
2. Depolarization of presynaptic membrane opens V-gated calcium channels
3. Calcium pours into the presynaptic cell, causing exocytosis of neurotransmitter stored in secretory vesicles
4. NT diffuse across the synaptic cleft
5. NT binds to receptor (ligand-gated) proteins in post-synaptic membrane
6. Opening of ion channels in post-synaptic cell alters membrane polarization
7. If the membrane depolarization of postsynaptic cell reaches threshold of V-gated sodium channels, an action potential is initiated
8. Neurotransmitter in synaptic cleft is degraded/removed, terminating the signal

Question 24

neuromuscular junction

Answer 24

between neuron and skeletal muscle;

1. action potential reaches a synapse
2. acetylcholine is released in synaptic cleft
3. acetylcholine binds to surface of post-synaptic cell membrane
4. opens sodium channel, depolarizing the postsynaptic cell membrane
5. Acetylcholine is degraded

Question 25

types of neurotransmitters

Answer 25

GABA (gamma-aminobutyric acid), serotonin, dopamine, norpinephrine

Question 26

excitatory NT

Answer 26

if it opens a channel that depolarizes a postsynaptic membrane

excitatory/inhibitory depends on receptor, not the neurotransmitter

Question 27

hyperpolarization (inhibitory NT)

Answer 27

to make the resting potential even more negative

Question 28

when happens when chloride enters a cell?

Answer 28

entry of chloride into a cell, more negative, inhibitory

Question 29

if an inhibitor of acetylcholinesterase is added to a neuromuscular junction, the postsynaptic membrane will…

Answer 29

…be depolarized longer with each action potential

1. inhibition means acetylcholine will remain in the synaptic cleft longer
2. acetylcholine-gated sodium channels will remain open longer with each AP
3. If the sodium channels are open longer, the depolarization of postsynaptic membrane will last longer

I guess by inhibitor they mean, re-uptake inhibitor

Question 30

threshold depolarization

Answer 30

around -50mV is required to open the voltage-gated sodium channels

• the release of NT is not generally sufficient to induce this degree of depolarization

Question 31

summation

Answer 31

a postsynaptic neuron decides to fire based on the effect of all the synapses impinging on a neuron, both excitatory and inhibitor

Question 32

EPSP/IPSPSs

Answer 32

Excitatory PostSynaptic Potentials

excitatory neurotransmitters causes postsynaptic depolarization, while inhibitory neurotransmitters induce postsynaptic polarization.

presynaptic neuron fires APs so rapidly that the EPSPs and IPSPs “pile on top of each other” - temporal summation

Question 33

spatial summation

Answer 33

EPSPs and IPSPs causes postsynaptic membrane to reach threshold voltage, and AP is fired

Question 34

the intensity of a presynaptic signal depends on

Answer 34

frequency of action potentials