Lecture 4 - Action Potential + Synapses

Question 1

What is action potential?

Answer 1

the need for speed

Question 2

What are synapses?

Answer 2

where neurons connect

Question 3

What is the longest axon in the body?

Answer 3

from the end of the spinal cord to the legs

Question 4

What is an inactive state?

Answer 4

Sodium channels close spontaneously +can’t reopen, even if depolarized

Question 5

What is a refractory period?

Answer 5

Time needed for enough sodium channels to recover from inactive state to generate + sustain an action potential

Question 6

What is depolarization?

Answer 6

when there is an influx of sodium ions inside the cell (electrical potential of the cell membrane becomes more positive)

Question 7

What is the function of K+ channels?

Question 8

What occurs at the same time as the refractory period?

Answer 8

Hyperpolarization BUT refractory period is caused by channel inactivation

Question 9

Is there a large change in ion concentrations when the action potential is happening?

Answer 9

No

Question 10

Big Idea 1* - axons and its speed

Answer 10

need for speed has fostered evolution **bigger the axons, faster the neurons can send the signal down the axon and to other neurons

Question 11

What does increasing axon diameter affect do?

Answer 11

current can flow further and reduce axial resistance since a larger stretch of the axon can de depolarized
- for faster AP conduction

Question 12

What are negatives of increased axial conductance?

Answer 12

• space and energy costs (more ions to depolarize a bigger axon + ion concentrations change is going to be “burnt out” after multiple action potentials)
  -speed increases as he square root of the axial diameter increases

Question 13

What’s an alternative strategy to increase speed of signaling other than increasing axon diameter?

Answer 13

increased membrane “thickness” and keep axon diameter constant

Question 14

What is myelination?

Answer 14

multiple membrane wraps

Question 15

What is capacitance?

Answer 15

membrane’s ability to store charge (s.i unit=Farad,F)
*membrane’s electrical property

Question 16

Why do cell membranes make good capacitors?

Answer 16

• the thin, high-resistance lipid layer holds positive and negative charges are close enough to each to cancel each other out but still separate from each other

Question 17

What are effects of capacitance on rate of Vm?

Answer 17

• slows the rate of Vm change along a nerve cell or axon: a limiting factor in neural processing speed

Question 18

Relationship between membrane resistance and membrane capacitance

Answer 18

Increase membrane resistance (multiple membrane layers) causes decrease in membrane capacitance

Question 19

What are benefits of lowered membrane capacitance?

Answer 19

• Higher rm: less radial current, more axial current along axon
• Lower Cm: less time needed to charge membrane

Question 20

What are myelinated segments?

Answer 20

internodes

Question 21

What are unmyelinated sites and what is its importance?

Answer 21

nodes and the most radial current flows here

Question 22

Where are voltage-gated channels concentrated at?

Answer 22

the nodes

Question 23

Node of Ranvier

Answer 23

a small gap in the myelin sheath that covers a neuron’s axon

Question 24

Schwann Cells

Answer 24

myelinate periphery nerves

Question 25

Ganglion cells

Answer 25

nerve cells in the retina that send visual information to the brain

Question 26

Why are RGC axons myelinated only outside the retina, in the optic nerve?

Answer 26

myelin would diffuse the light coming into the retina - myelin isn't transparent

Question 27

What is white matter in the brain made of?

Answer 27

myelin (made of lipids)

Question 28

What is a synapse?

Answer 28

gap between neurons + responsible for functional connections between neurons

Question 29

What ion concentration changes at the synapse?

Answer 29

Ca 2+

Question 30

Amacrine cell

Answer 30

- neurons in the retina that process visual information -responsible for regulating signaling to retinal ganglion cells (RGCs). - first neurons in the visual system to fire action potentials.

Question 31

What are the functions of the chemical synapse?

Answer 31

- neurotransmitter released from presynaptic cells, activates receptors in postsynaptic cells - one-way transmission: pre (vesicles) - to postsynaptic (receptors) only

Question 32

What is the synaptic cleft?

Answer 32

gap between neurons where an electrical signal is converted into a chemical signal

Question 33

What are the functions of the electrical synapse (gap junction)?

Answer 33

- connexin proteins assemble open pores connecting cells - no gating: pores always open, little synaptic delay - current flows between cells, in either direction - act to synchronize electrical activity between cells, in active circuits and in conductive fibers (heart)

Question 34

Why are electrical synapses faster than chemical synapses?

Answer 34

- doesn't require time for the vesicles to sink and for post synaptic neurons to receive neurotransmitters

Question 35

*add picture of chemical synapse

Answer 35

- function of ligand-gated channels -reuptake -function of pumps -how does ca2+ ions get through?

Question 36

Why do you want signals to be quick and transient?

Answer 36

- allows our cells and brain to process information like breathing and walking more quickly

Question 37

What is the postsynaptic density?

Answer 37

-complex and evolved very early - thickening of the postsynaptic membrane of neurons that contains a high concentration of proteins -primary site for processing and transmitting signals at excitatory synapses

Question 38

Effect of drugs on reuptake

Answer 38

*some mood-altering drugs target neurotransmitter reuptake ex). cocaine blocks dopamine receptors in the neuron

Question 39

Excitatory neurotransmission

Answer 39

- membrane potential = + -depolarize

Question 40

Some examples of neurotransmitters

Answer 40

- glutamate (e) -acetylcholine (e) -glycine (I) -gaba (I)

Question 41

Inhibitory neurotransmission

Answer 41

- hyperpolarization - inside cells become more negative -decreased (-) membrane potential

Question 42

True of False: synapses are either inhibitory or excitory

Answer 42

true

Question 43

Difference between neurons and synapses in terms of excitatory and inhibitory

Answer 43

Neurons can have both excitatory and inhibitory postsynaptic input sites

Question 44

Can neurons only release one transmitter?

Answer 44

some neurons can release more than one transmitter type

Question 45

What is the output of a neuron usually?

Answer 45

(usually) excitatory or inhibitory

Question 46

Concept - neuron +neurotransmitter

Answer 46

a neuron will make and release the same neurotransmitter (s) at all of its axonal presynaptic endings