Unit 3: Biological Bases

Neuron

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

Cell body

Part of the neuron that contains the nucleus; the cell's life-support system.

Dendrites

Neuron's bushy, branching extensions that receive and integrate messages, conducting impulses towards the cell body.

Axon

Neuron extension that passes messages through its branches to other neurons or to muscles or glands.

Myelin sheath

Fatty tissue layer segmentally encasing the axon of some neurons; enables faster transmission of neural impulses.

Glial cells (glia)

Cells in the nervous system that support, nourish, and protect neurons; involved in learning, thinking, and memory.

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.

Refractory period

A brief resting pause 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.

Synapse

The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

Neurotransmitters

Chemical messengers that cross the synaptic gap between neurons, influencing whether the neuron will generate a neural impulse.

Reuptake

A neurotransmitter's reabsorption by the sending neuron.

Endorphins

Natural, opiate-like neurotransmitters linked to pain control and pleasure.

Agonist

A molecule that increases a neurotransmitter's action.

Antagonist

A molecule that inhibits or blocks a neurotransmitter's action.

Nervous system

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

Central nervous system

The brain and spinal cord.

Peripheral nervous system

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

Nerves

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

Sensory (afferent) neurons

Neurons that carry incoming information from sensory receptors to the brain and spinal cord.

Motor (efferent) neurons

Neurons that carry outgoing information from the brain and spinal cord to muscles and glands.

Interneurons

Neurons within the brain and spinal cord that communicate internally and process information between sensory inputs and motor outputs.

Somatic nervous system

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

Autonomic nervous system

Part of the peripheral nervous system that controls the glands and muscles of internal organs.

Sympathetic nervous system

Division of the autonomic nervous system that arouses the body, mobilizing its energy.

Parasympathetic nervous system

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

Reflex

A simple, automatic response to a sensory stimulus.

Endocrine system

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

Hormones

Chemical messengers manufactured by endocrine glands that travel through the bloodstream and affect other tissues.

Adrenal glands

Endocrine glands that sit above the kidneys and secrete hormones that help arouse the body in times of stress.

Pituitary gland

Regulates growth and controls other endocrine glands; the most influential gland in the endocrine system.

Lesion

Tissue destruction; brain lesions can be naturally or experimentally caused.

EEG (electroencephalogram)

An amplified recording of electrical activity waves across the brain's surface.

MEG (magnetoencephalography)

A brain imaging technique that measures magnetic fields from the brain's natural electrical activity.

CT (computed tomography) scan

A series of x-ray photographs taken from different angles to create a composite representation of a slice of the brain's structure.

PET (positron emission tomography) scan

A visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a task.

MRI (magnetic resonance imaging)

A technique that uses magnetic fields and radio waves to produce images of soft tissue; shows brain anatomy.

fMRI (functional MRI)

A technique for revealing blood flow and brain activity by comparing successive MRI scans.

Brainstem

The oldest part and central core of the brain, responsible for automatic survival functions.

Medulla

The base of the brainstem; controls heartbeat and breathing.

Thalamus

The brain's sensory control center; directs messages to sensory receiving areas