A&P Excitable Membranes Lecture

Ligand-gated Ion Channel

Open or closes with response to a chemical signal

Voltage-gated Ion Channel

Opens or closes when membrane voltage changes

Leakage Ion Channel

Allows ions to leak through membrane at rest

Mechanically Gated Ion Channel

Opens or closes in response to physical stimulation

Resting Membrane Potential (RMP)

-70mV the charge on a resting membrane, slightly negative inside

Polarized Membrane

Membrane with a relatively negative inside and a positive outside

Sodium (Na+)

Positive ion, concentrated mainly outside cell

Potassium (K+)

Positive ion, concentrated mainly inside cell

Concentration Gradient

Ions tend to move from high to low concentration

Electrical Gradient

Opposite charges attract, like charges repel

Sodium-potassium pump

Uses ATP to move 3 Na+ out and 2 K+ in

K+ Leakage Channels

Allows K+ to leave the resting cell, contributes to negative interior

Graded Potential

Small, local voltage channel that varies with stimulus strength

Depolarization

Membrane becomes less negative, commonly from Na+ entering

Hyperpolarization

Membrane becomes more negative, making an impulse less likely

EPSP

Excitatory postsynaptic potential, moves the membrane towards threshold

IPSP

Inhibitory postsynaptic potential, makes reaching threshold harder

Threshold Potential

About -55mV, triggers action potential

Summation

Combining graded potentials to potentially reach threshold

Action Potential

Rapid electrical change that travels along neuron.

Depolarizing/Rising Phase

Voltage-gated Na+ channels open and Na+ enters

Peak of Action Potetnial

About +30mV, Na+ channels inactivate

Repolarizing/Falling Phase

K+ exits, making membrane negative again

After Hyperpolarization

Excess K+ exit temporarily making the membrane more negative than resting

All-or-none response

A full action potential occurs when threshold is reached, otherwise none occurs

Positive Feedback

Na+ entry causes more depolarization, opening additional Na+ channels

Absolute Refractory Period

A second action potential cannot occur

Relative Refractory Period

A second action potential is possible with a stronger stimulus

Propogation

Spread of an action potential along an axon

Synaptic Transmission

Communication between cells through neurotransmitter release

Calcium (Ca2+)

Enters the axon terminal and triggers neural transmitter release

Exocytosis

Vesicles fuse with the membrane and release neurotransmitters

Acetylcholine (ACh)

Neurotransmitter that binds receptors on target cells

Acetylcholinesterase (AChE)

Enzyme that breaks down acetylcholine

What are the three important voltages of membranes?

-70mV resting, -50mV threshold, +30mV peak

What is the order of an action potential?

Resting » threshold » depolarization » repolarization » after » hyperpolarization

Which ion enters during depolarization?

Na+

Which ion exits during repolarization?

K+

What happens at the axon terminal?

Ca+ enters » vesicles release ACh» ACh binds target receptors

What is the difference between EPSP and IPSP?

EPSP promotes reaching threshold, IPSP makes it harder