chap 43 bio

Membrane potential

difference in electrical charge across a cell membrane; potential energy

Is membrane potential always the same along the entire neuron?

There is a large difference in charge across the membrane because the signal gets passed along the myelin sheath and is propagated by sodium and potassium ions.

Resting potential

membrane potential of a cell in its resting state when neuron isn’t communicating.

• Low concentration of sodium and chloride ions inside

• High concentration of potassium ions, proteins, and amino acids inside

• Permeable to sodium, potassium, and chloride ions

Sodium-potassium pump

pumps sodium OUT of the cell and potassium INTO the cell by the energy gained from receiving a phosphate group from ATP to ensure through active transport that the concentration of potassium is higher on the inside of the membrane and the concentration of sodium is higher on the outside

How can movement of ions through ion channels be regulated?

• Change in voltage; opening or closing the voltage gated ion channels 

• Ligand gated channels: an ion channel that opens in response to binding by a certain molecule 

Depolarization

resting state; membrane is polarized because the charges on the two sides are different; membrane becomes less polarized than before; membrane changes from highly negative to briefly positive

Repolarization

changes the membrane potential back to negative 

“all-or-none” event

refers to the 55mV threshold potential, if less than 55 action potential does not occur 

Threshold potential

membrane potential that will trigger an action potential in a neuron

Why are action potentials propagated in only one direction?

They are propagated in only one direction because sodium channels in the neuron are refractory

Refractory

no longer responding to stimuli that previously elicited a response

Myelin sheath

multiple layers of myelin from cell membranes of glial cells wrapped around axon and prevents ions from leaking out

Oligodendrocytes

glial cell that wraps around axons of some neurons and increases the speed of action potential

How does myelination affect the propagation of an action potential?

it speeds propagation by preventing cations from leaking out across the membrane as they spread down the axon

Neurotransmitters

chemical messengers that transmit info from one neuron to another and are found in synaptic vesicles

How is information transferred from one neuron to another?

Neurotransmitters located in the synapse transfer information from one neuron to another

Otto Loewi’s experiment

Otto loewi's experiment: isolated the vagus of the nerve and heart of a frog ; heart rate slowed when the nerve was electrically stimulated; took the solution from the neurotransmitter from the stimulated heart and inserted it to another frog heart without stimulating the heart, the heart rate slowed, which showed strong evidence of chemical transmission of signals by the nervous system

What causes the release of neurotransmitters into the synaptic cleft?

Action potential arrives at the axon , depolarization opens the voltage gated calcium channels; increase the calcium concentration and causes synaptic vesicles to fuse with the membrane and release neurotransmitters into the gap between the cells (exocytosis)

What is the role of calcium?

Calcium triggers the release of calcium

What happens once a neurotransmitter is released into the synaptic cleft?

Once the neurotransmitters are released it binds to the receptors to the postsynaptic cells

EPSP

• depolarization of a cell that makes the cell more likely to generate action potential 

  • Depolarization

  • Sodium flows into the cell

IPSP

• hyperpolarization that makes the cell likely to generate ATP

  • Hyperpolarization

  • Potassium flows out and chloride flows in