RMP, GP, AP

fckass subject

Resting membrane potential

Unequal distribution of ions across the cell membrane

Inside of cell

Slightly negative

Outside of cell

Slightly positive

Resting membrane potential in neurons

-70 mV

Resting membrane potential in muscles

-90 mV

Threshold potential

-55 mV

Factor 1 of RMP

Unequal distribution of ions in the ECF and cytosol (ECF: Na+ and Cl-, Cytosol: K+ and anions like phosphates and amino acids)

Factor 2 of RMP

Inability of most anions to leave the cell

Factor 3 of RMP

Electrogenic nature of Na+-K+ ATPase pumps

Graded potential

Small deviation from the resting membrane potential

Decremental conduction

Occurs in dendrites and cell body of a neuron

Hyperpolarizing graded potential

Inside becomes more negative (more polarized)

Depolarizing graded potential

Inside becomes less negative or more positive (less polarized)

Stimulus strength effect on graded potential

Greater stimulus strength → larger amplitude

Summation

Adds graded potentials to increase chance of reaching threshold

Spatial summation

Multiple stimuli at different locations, same time

Temporal summation

Multiple stimuli at same location, different times

Action potential

Electrical signal or nerve impulse

Threshold stimulus

Generates one action potential

Suprathreshold stimulus

Generates multiple action potentials

Axon hillock

Trigger zone where nerve impulses arise and travel along the axon

Depolarization

Membrane becomes less negative (from -55 mV to +30 mV)

Voltage-gated Na+ channels

Open to allow Na+ into the cell → depolarization

Repolarization

Return to -70 mV as K+ exits the cell

Voltage-gated K+ channels

Responsible for repolarization

After-polarizing phase

Membrane potential becomes more negative than resting level (about -90 mV)

All-or-none principle

Action potential occurs completely (threshold) or not at all (subthreshold)

Absolute refractory period

Neuron cannot initiate another AP no matter how strong the stimulus

Relative refractory period

New AP can occur only if stimulus is stronger than normal

Continuous conduction

Occurs in unmyelinated axons; step-by-step and uses more ATP

Saltatory conduction

Occurs in myelinated axons; faster, jumps at Nodes of Ranvier

Myelin sheath

Multilayer lipid and protein covering around axons

Schwann cells

Produce myelin in PNS

Oligodendrocytes

Produce myelin in CNS

Nodes of Ranvier

Gaps in myelin sheath where impulses jump

Factor 1 affecting speed of propagation

Amount of myelination – faster with more myelin

Factor 2 affecting speed of propagation

Axon diameter – larger diameter conducts faster

Factor 3 affecting speed of propagation

Temperature – conduction slows when cooled

A fibers

Large myelinated nerve fibers

B fibers

Small myelinated nerve fibers

C fibers

Small unmyelinated nerve fibers

Synapse

Junction where neurons or neurons and effectors communicate

Presynaptic neuron

Neuron that sends the signal

Postsynaptic neuron

Neuron that receives and responds to the signal

Electrical synapse

Action potentials pass directly through gap junctions between neurons

Chemical synapse

Uses neurotransmitters to transmit signals across a synaptic cleft

Synaptic cleft

Space filled with interstitial fluid between presynaptic and postsynaptic neurons

Synaptic delay

Time needed for neurotransmitter diffusion (about 0.5 msec)

Acetylcholine and norepinephrine

Most common neurotransmitters in the PNS

Gamma-aminobutyric acid (GABA)

Most common inhibitory neurotransmitter in the CNS

Glutamate

Most common excitatory neurotransmitter in the CNS

Schizophrenia

Associated with increased dopamine levels

Parkinson’s disease

Associated with decreased dopamine levels