Fundamentals of the Nervous System and Nervous Tissue

Flashcards on Fundamentals of the Nervous System and Nervous Tissue.

Resting Membrane Potential

The potential difference across the membrane of a resting cell, approximately -70 mV in neurons.

Voltage

A measure of potential energy generated by separated charge, measured in volts (V) or millivolts (mV).

Current

The flow of electrical charge (ions) between two points, which can be used to do work.

Resistance

Hindrance to charge flow; substances with high resistance are insulators, while those with low resistance are conductors.

Ohm’s Law

Gives the relationship of voltage, current, and resistance: Current (I) = Voltage (V) / Resistance (R).

Leakage (nongated) channels

Ion channels that are always open.

Gated channels

Ion channels in which part of the protein changes shape to open or close the channel; can be chemically, voltage, or mechanically gated.

Chemically gated (ligand-gated) channels

Open only with the binding of a specific chemical (e.g., a neurotransmitter).

Voltage-gated channels

Open and close in response to changes in membrane potential.

Mechanically gated channels

Open and close in response to physical deformation of receptors, as in sensory receptors.

Electrochemical gradient

The combination of electrical and chemical gradients that drives ion flow across a membrane.

Polarized

The state of a membrane when there is a charge difference across it.

Sodium-potassium pump (Na+/K+ ATPase)

Stabilizes the resting membrane potential by maintaining concentration gradients for Na+ and K+; pumps three Na+ ions out of the cell while pumping two K+ ions back in.

Graded Potentials

Short-lived, localized changes in membrane potential that are triggered by a stimulus that opens gated ion channels, resulting in depolarization or hyperpolarization.

Action Potentials

Brief reversal of membrane potential with a change in voltage of ~100 mV; the principal way neurons send signals over long distances.

Depolarization

Decrease in membrane potential (moves toward zero and above) making the inside of the membrane less negative; increases the probability of producing an impulse.

Hyperpolarization

Increase in membrane potential (away from zero) making the inside of the membrane more negative; decreases the probability of producing an impulse.

Resting state (Action Potential)

All gated Na+ and K+ channels are closed; only leakage channels are open, maintaining the resting membrane potential.

Threshold

The point at which depolarization must reach for an axon to "fire" and trigger an action potential. Typically between -55 to -50 mV.

All-or-None Phenomenon

An action potential either happens completely, or does not happen at all.

Refractory Period

Time in which neuron cannot trigger another AP because voltage-gated Na+ channels are open, so neuron cannot respond to another stimulus.

Absolute Refractory Period

Time from opening of Na+ channels until resetting of the channels; ensures that each AP is an all-or-none event and enforces one-way transmission of nerve impulses.

Relative Refractory Period

Follows the absolute refractory period; most Na+ channels have returned to their resting state, some K+ channels are still open, and the threshold for AP generation is elevated.

Continuous Conduction

Slow conduction that occurs in nonmyelinated axons.

Saltatory Conduction

Occurs only in myelinated axons and is about 30 times faster than continuous conduction; electrical signal appears to jump rapidly from gap to gap.

Group A Fibers

Largest diameter, myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints that transmit at 150 m/s (~300 mph).

Group B Fibers

Intermediate diameter, lightly myelinated fibers that transmit at 15 m/s (~30 mph).

Group C Fibers

Smallest diameter, unmyelinated fibers that transmit at 1 m/s (~2 mph); include ANS visceral motor and sensory fibers that serve visceral organs.