Cell Phys Lecture 5

Front 1

Diameter of nerve

Back 1

Conduction velocity increases with diameter. The internal resistance decreases when the diameter increases.

Front 2

Length constant

Back 2

Any graded potential will decay as it travels away from the site of origin. The longer the length constant, the less the potential decays as it travels => for neurons, the longer the length constant the better.

Front 3

Length constant equation

Back 3

The larger the membrane resistance (fewer open channels - rm) the less likely a charge will escape from the cell. Neurons with smaller internal axial resistance (larger diameter - ri) the easier for a signal to flow

Front 4

Time constant

Back 4

How fast at a given point will the voltage change. How quickly does the action potential travel from threshold to peak ? The shorter the time = the better the conductance

Front 5

Time Constant Equation

Back 5

Time constant = Rm x Cm
Rm = membrane resistance (you want small so current can enter the cell quicker)
Cm = membrane capacitance (you want less capacitance, this will allow less charge to be held and more current to enter the cell => shorter time constant)

Front 6

Myelin & Length constant

Back 6

Increases length constant by:
- increasing nerve diameter
- increasing membrane resistance and decreasing internal resistance

Front 7

Myelin & Time constant

Back 7

Decreases time constant by:
- Decreasing capacitance (ability to hold a charge)
- Increases internal membrane resistance, but not as great an effect

Front 8

Multiple Sclerosis

Back 8

autoimmune disease that causes the degeneration of CNS myelin => reduced action potential rate and alterations in CNS function

Front 9

Non decremental electrical conduction (unmyelinated)

Back 9

threshold is reached => Na channels open => depolarize section of membrane (action potential) => domino effect where depolarizing travels down length of nerve

Front 10

All or nothing

Back 10

All action potentials must reach past a certain threshold, or there will be no signal conduction

Front 11

Saltatory conduction

Back 11

Myelin restricts transmembrane ion flow to nodes of ranvier (areas of high density voltage-sensitive Na channels). AP's only occur in these nodes, effectively skipping the signal along

Front 12

Ganglia

Back 12

collection of synapses , including cell bodies and nerve endings

Front 13

Synaptic Transmission

Back 13

action potential => voltage gated Ca channels open in pre-synaptic axon => vesicles release transmitter => cross synaptic cleft => bind to ion channel on postsynaptic membrane => change postsynaptic membrane to trigger response

Front 14

Altering transmitter release

Back 14

- Stopping transmitter release
- Ca-channel blockers
- Altering level of extracellular Ca

Front 15

Post synaptic receptor antagonist

Back 15

the antagonist can be a drug or ligand that has an affinity for the receptor but causes no reaction when bound to it

Front 16

Transmitter degradation

Back 16

acetylcholine - acetylcholinesterase
norepinephrine - monoamine oxidase (MAO)
catechol-O-methyl transferase (COMT) - gegrades catecholamines (dopamine, epinephrine, and norepinephrine)

Front 17

Transmitter disposal

Back 17

dopamine re-uptake inhibitor for the neurotransmitter dopamine by blocking the action of the dopamine transporter (DAT), effectively not uptaking the neurotransmitter

Front 18

Excitatory Post- Synaptic Potential

Back 18

presynaptic neurotransmitter opens ligand-gated NA channels causing a Na-ion influx and partial depolarization of the postsynaptic membrane. Makes the cell easier to excite - one is insufficient to generate an action potential

Front 19

Inhibitory Post- Synaptic Potential

Back 19

presynaptic neurotransmitter opens ligand-gated Cl channels causing a Cl-ion influx and partial hyperpolarization of the postsynaptic membrane. Makes the cell harder to excite

Front 20

Spatial Summation

Back 20

multiple axons innervate the same dendrite or cell body, can be excitatory or inhibitory
ENHANCED BY LONG LENGTH CONSTANT

Front 21

Temporal Summation

Back 21

A train of action potentials from a single axon acts on the same dendrite or cell body, can be excitatory or inhibitory
ENHANCED BY LONG TIME CONSTANT