Ch. 12: Nervous Tissue

neuron

neuron

A nerve cell; the basic building block of the nervous system.

dendrites

part of neuron that receives stimuli from the environment or from other neurons

axon

part of neuron that carries information towards other cells

cell body

Largest part of a typical neuron; contains the nucleus and much of the cytoplasm

myelin

a fatty covering around the axon of some neurons that speeds up transmission of the neural impulse

Nodes of Ranvier

Gaps in the myelin sheath of the axons. Action potentials can 'jump' from node to node, thus increasing the speed of conduction.

multiple sclerosis

The immune system attacks myelin, forming scar tissue (sclerosis) which gives the disease its name. This damage interrupts nerve impulses traveling to and from the brain and spinal cord.

neuroglia

Supporting cells ("glue") of the nervous system that support, insulate, and protect neurons but do not transmit nerve impulses

action potential

A neural impulse; a brief electrical charge that travels down an axon. The action potential is generated by the movement of positively charged atoms in and out of channels in the axon's membrane. It is an "all-or-nothing" event.

axon terminal

the end ("terminal") of the axon on the presynaptic cell

synaptic vesicles

contain neurotransmitters

presynaptic cell

neuron that transmits a signal toward the synapse

postsynaptic cell

The neuron, muscle, or gland cell that receives the signal from a neuron

synaptic cleft

space separating presynaptic and postsynaptic membranes

Acetylcholine (ACh)

neurotransmitter widespread in CNS and PNS

polarized membrane

An axon membrane at rest where the inside of the cell is negative (-70 mv) compared with the outside of the cell

depolarized membrane

An axon membrane that becomes less negative (closer to 0 mv) than the resting potential of -70 mv

repolarized membrane

An axon membrane that is restored to its resting potential of -70 mv after depolarization

hyperpolarization

A change in the axon membrane potential from -70 mV (resting) to -90 mV, becoming more negative

sodium channels

voltage-gated channels in the axon's plasma membrane that allow sodium to move into the cell

potassium channels

voltage-gated channels in the axon's plasma membrane that allow potassium to move out of the cell

sodium-potassium pump

A protein pump in the plasma membrane of an axon that restores the membrane to its original polarized condition by using ATP to pump sodium ions out of the cell and potassium ions into the cell

calcium channels

voltage-gated channels in the presynaptic terminal that allow calcium to enter and trigger the release of acetylcholine

resting potential

The difference in electric charge between the inside and outside of a neuron's cell membrane (more K ions inside, more Na ions outside); -70 mv

threshold

The level of stimulation required to activate a neuron

all-or-none principle

If the threshold is reached the action potential in the axon occurs either 100% or not at all.

central nervous system

A division of the nervous system consisting of the brain and spinal cord

peripheral nervous system

A division of the nervous system consisting of all sensory and motor neurons that are not part of the brain or spinal cord

somatic nervous system

the division of the peripheral nervous system that controls the body's voluntary skeletal muscles

autonomic nervous system

the division of the peripheral nervous system that controls involuntary activity of smooth and cardiac muscle, and internal organs and glands.

sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations; the "GAS"

parasympathetic nervous system

the division of the autonomic nervous system that calms the body, conserving its energy; the "BRAKE"

reaction time

the amount of time needed for your brain to respond to a stimulus and initiate a response

gray matter

Grayish nervous tissue of the CNS containing unmyelinated axons, neuron cell bodies, and dendrites

white matter

Whitish nervous tissue of the CNS consisting of neurons and their myelinated axons