Neurons and the Nervous System

"biology section of psych

natural selection

the principle that, among the range of inherited trait variations, those contributing to reproduction and survival will most likely be passed on to succeeding generations

neuron

a nerve cell; the basic building block of the nervous system

sensory neuron

a neuron that carries incoming information from the sensory receptors to the brain and spinal cord

motor neuron

a neuron that carries outgoing information from the brain and spinal cord to muscles and glands

interneuron

a neuron within the brain and spinal cord that communicates internally and intervenes between the sensory and motor outputs

reflex arc

a relatively direct connection between a sensory and motor neuron that allows an extremely rapid response to a stimulus, often without conscious brain involvement.

dendrite

the bushy, branching extensions of a neuron that receive neurotransmitters 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

a layer of fatty tissue that segmentally encases the axon of neurons; enables greater transmission speed of neural impulses

resting potential

the electrical charge of the axon in its inactive state, when the neuron is ready to "fire"

action potential

nerve impulse caused by a change in the electrical charge across the axon's membrane

depolarization

the process during the action potential when sodium ions rush into the axon, causing the interior to become more positive

threshold

the level of stimulation required to trigger a neural impulse

all-or-nothing principle

concept that an action potential occurs either full-blown or not at all

synapse

junction between the axon terminal buttons of one neuron and the dendrites of the next neuron

neurotransmitters

chemical messengers that cross the synaptic gap, binding to receptor sites and transferring signals from one neuron to the next

reuptake

reabsorption by the sending neuron of neurotransmitters after an action potential

multiple sclerosis

a chronic disease of the central nervous system marked by damage to the myelin sheath, which causes tremors, weakness, loss of coordination

nerves

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

central nervous system (CNS)

the brain and spinal cord

peripheral nervous system (PNS)

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

somatic nervous system

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

autonomic nervous system

division of the peripheral nervous system that controls the glands and muscles of internal organs (such as the heart)

sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations (fight of flight)

parasympathetic nervous system

the division of the autonomic nervous system that calms the body, conserving its energy (rest and digest)

agonist

a drug or other chemical that enhances or mimics the effects of neurotransmitters

antagonist

a drug or other chemical that inhibits the effects of neurotransmitters

glial cells

cells in the nervous system that support, nourish, and protect neurons

refractory period

a short rest period between action potentials when positive ions are pumped outside the axon

acetylcholine

a neurotransmitter that influences learning, memory, and muscle movement

myasthenia gravis

a chronic autoimmune disease that causes serious weakness of voluntary muscles by interrupting ACh functioning at the synapse

norepinephrine

a neurotransmitter that influences attention, arousal, concentration

serotonin

a neurotransmitter that influences well-being, happiness (as well as the sleep cycle and digestion)

dopamine

a neurotransmitter that influences reward and pleasure and the coordination of movement

GABA

a calming neurotransmitter that inhibits the firing of neurons

glutamate

an excitatory neurotransmitter that strengthens synaptic connections

endorphins

neurotransmitters that are natural "opiates" that reduce pain and induce euphoria

substance P

a neurotransmitter involved in the transmission of pain messages to the brain

endocrine system

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

hormones

chemical messengers manufactured by the endocrine glands that travel through the bloodstream, affecting other tissues

pituitary gland

the most influential gland; it releases growth hormone and regulates other glands

adrenaline

a hormone secreted by the adrenal glands, especially during stress, increasing blood circulation, breathing rates, and carbohydrate metabolism in preparing muscles for exertion