Neuron Physiology

Multipolar Neurons

a neuron that has many extensions protruding from cell body; structural classification of neuron

Dendrites

Highly branched extensions of the neuron that receive incoming signals and transmit signals toward the cell body

Axon Hillock (trigger zone)

Cone-shaped region of the neuron cell body where action potentials are initially triggered.

axon

A single, relatively long extension of a neuron that transmits action potentials along its length to synaptic knobs.

neurolemmocyte (Schwaan Cell)

Glial cell that forms myelin of peripheral neurons.

Myelin

Fatty insulation around an axon; formed by neurolemmocytes (for peripheral neurons).

Synaptic Knob

Terminal swelling at the end of an axon; contains neurotransmitter.

Neurotransmitter

Chemical released by a neuron that causes a physiologic response in another cell (e.g., muscle cell, gland cell, another neuron).

Membrane potential

Charge difference across a membrane; measured in millivolts (mV).

Resting membrane potential

Membrane potential (e.g., -70 mV) of an unstimulated, "resting" neuron.

Depolarization

Membrane potential becomes more positive than the RMP.

Repolarization

The return of a depolarized membrane back to its resting value (the RMP).

Hyperpolarization

Membrane potential becomes more negative than the RMP.

Graded potential (local potential)

Small, short-lived, local changes in membrane potential.

Synapse

Junction between two neurons.

• Synaptic cleft: Narrow space between the presynaptic and postsynaptic neurons.

• Presynaptic neuron: Neuron that releases neurotransmitter into the synaptic cleft as a result of an action potential reaching the synaptic knob.

• Postsynaptic neuron: Neuron that binds neurotransmitter released from a presynaptic neuron.

Postsynaptic potential (EPSP and IPSP)

Graded potentials that occur in postsynaptic neurons.

• Excitatory postsynaptic potentials (EPSPs): Depolarizing postsynaptic potential.

• Inhibitory postsynaptic potentials (IPSPs): Hyperpolarizing postsynaptic potential.

Summation

Cumulative effect of multiple postsynaptic potentials on the membrane potential at the axon hillock.

Threshold

Voltage necessary to open voltage-gated ion channels at the axon hillock (e.g., -55 mV).

Action Potential (AP; nerve impulse)

Large fluctuation of the membrane potential due to sequential opening and closing of voltage-gated channels at the axon hillock and along the axon.

Continuous Conduction

Propagation of an action potential along an unmyelinated axon.

Saltatory Conduction

Propagation of an action potential along a myelinated axon.

Node of Ranvier (neurofibril node)

Portion of axon between adjacent neurolemmocytes; not covered in myelin and contains voltage-gated ion channels.

receptive segment

dedrites; cell body

receive input from other neurons

Initial segment

axon hillock

initiation of action potential

conductive segment

axon and terminal branches

propagation of action potential

Transmissive Segment

synaptic knobs

release of neurotransmitter