BIOL121: 06/01-02/26 (Mendel)

depolarization

decrease membrane potential (toward zero and above)

inside membrane become less negative

probability of producing impulse increases

hyperpolarization

increase in membrane potential (away from 0)

inside of membrane become more negative

probability of producing impulse decreases

graded potentials

short distance

short lived

dendrites and cell bodies

ligand-gated channels

action potential

long distance

long lived

axons (nerve impulse)

voltage gated channels

propagation

allows AP to be transmitted from axon hillock to axon terminal

one direction, does not stop

absolute refractory period

ensure each AP is all or none event

one way transmission of nerve impulses

ABSOLUTELY NO CAN HAPPEN

relative refractory period

most Na+ channels returned to resting state, some K+ channels still open, repolarization occurring

AP threshold is elevation, exceptionally strong stimulus required to stimulate another AP

action potential rate factors

AXON DIAMETER = larger diameter (myelin) have less resistance to flow, so have faster impulse

CONTINUOUS CONDUCTION = nonmyelinated axons, every part needs depolarization

SALTATORY CONDUCTION = myelinated axons, electrical signal “jumps” from one node of Ranvier to the next

presynaptic neuron

neuron conducting impulses toward synapse (send info)

postsynaptic neuron

neuron transmitting electrical signal away from synapse (receive info)

chemical synapse

1. AP arrives at axon terminal of presynaptic neuron

2. voltage gated Ca2+ channel open, Ca2+ enters axon terminal (down gradient ECF —> inside axon terminal)

3. Ca2+ causes synaptic vesicles to release neurotransmitter (exocytosis of NT into synaptic cleft)

4. NT diffuse across synaptic cleft and binds to specific receptors on postsynaptic membrane

5. binding of NT opens ion channels = graded potentials

   1. EXCITATORY (depolar) = ACh always says go

   2. INHIBITORY (hyperpolar) = Norepi depend on location

6. NT effects terminated

   1. REUPTAKE by astrocytes or axon terminal

   2. DEGRADATION by enzymes

   3. DIFFUSION away from synaptic cleft

axon terminal

presynaptic neuron

contain synaptic vesicles filled with neurotransmitter

neurotransmitter dumped to synaptic cleft

receptor region

postsynaptic neuron

receives neurotransmitter

usually on dendrite or cell body

ACh esterase stops ACh

postsynaptic potentials

EPSP (excitatory postsynaptic potential) = NT causes depolarization -70→ 0

IPSP (inhibitory postsynaptic potential) = NT causes hyperpolarization -70 → -80

summation by postsynaptic neuron

EPSPs can summate (add together)

TEMPORAL = cell stimulated multiple times (1 person poking)

SPATIAL = many receptors are stimuated (15 people poking)

cholinergic synapse

neuron releases ACh

most excitatory, synapses in CNS, neuron - neuron in PNS, neuromuscular/neuroglandular in ANS