Modules 9-10

Neuron

Neuron

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

Dendrite

The bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body.

Axon

The extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands.

Myelin Sheath

Layer of fatty tissue segmentally encasing the fibers of many neurons, speeds up neural impulses as the impulse hops from one node to the next.

Action Potential

A neural impulse; a brief electrical charge that travels down an axon.

Threshold

The level of stimulation required to trigger a neural impulse.

Synapse

The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or cleft.

Neurotransmitters

Chemical messengers that cross the synaptic gaps between neurons.

Reuptake

A neurotransmitter's reabsorption by the sending neuron.

Endorphins

"Morphine within"--natural, opiatelike neurotransmitters linked to pain control and to pleasure.

Cell Body

The part of the neuron that contains the nucleus, which directs the manufacture of substances that the neuron needs for growth and maintenance.

Refractory Period

in neural processing, a brief resting pause that occurs after a neuron has fired; subsequent action potentials cannot occur until the axon returns to its resting state

all-or-none response

a neuron's reaction of either firing (with a full-strength response) or not firing.

agonist

a molecule that increases a neurotransmitter's action

antagonist

a molecule that inhibits or blocks a neurotransmitter's action

glial cells (glia)

cells in the nervous system that support, nourish, and protect neurons. They also play a role in learning, thinking, and memory.

Motor (efferent) Neurons

Neurons that carry outgoing information from the central nervous system to the muscles and glands.

Interneurons

CNS neurons that internally communicate and intervene between the sensory inputs and motor outputs

Nervous System

The body's speedy, electrochemical communication network--all the nerve cells of the peripheral and central nervous systems.

Central Nervous System

The brain and the spinal cord.

Peripheral Nervous System

The sensory and motor neurons that connect the central nervous system to the rest of the body.

Nerves

Bundled axons that form neural "cables" connecting the central nervous system with muscles, glands, and sense organs.

Somatic Nervous System

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

Autonomic Nervous System

The part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands.

Sympathetic Nervous System

The division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations.

Parasympathetic Nervous System

The division of the autonomic nervous system that calms the body, conserving its energy.

Reflex

A simple, automatic, inborn response to a sensory stimulus, such as the knee-jerk response.

Endocrine System

The body's "slow" chemical communication system; a set of glands that secrete hormones into the bloodstream.

Hormones

Chemical messengers, mostly those manufactured by the endocrine glands, that are produced in one tissue and affect another.

Adrenal Glands

A pair of endocrine glands just above the kidneys. They secrete the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which help to arouse the body in times of stress.

Pituitary Gland

The endocrine system's most influential gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.

sensory (afferent) neurons

neurons that carry incoming information from the body's tissues and sensory receptors to the brain and spinal cord