Nervous System and Sense Organs

Chapter 49 Holt Modern Biology Vocab

The structures that control the actions and

reactions of the body in response to stimuli from the environment; a body formed by billions of specialized nerve cells

Nervous System

A nerve cell that is specialized to receive and

conduct electrical impulses

Neuron

A cytoplasmic extension of a neuron that

receives stimuli

Dendrite

An elongated extension of a neuron that

carries impulses away from the cell body

Axon

A sudden change in the polarity of the

membrane of a neuron, gland cell, or muscle fiber that facilitates the transmission of electrical impulses

Action Potential

The end of an axon

Axon Terminal

A layer of fatty material that surrounds certain

nerve fibers and that acts as an electrical insulator

Myelin Sheath

The junction of which the end of the axon of a

neuron meets the end of a dendrite or the cell body of another neuron or meets another cell

Synapse

A chemical substance that transmits nerve

impulses across a membrane

Neurotransmitter

The difference in electric potential between

the two sides of a cell membrane

Membrane Potential

The electric potential across the cell

membrane of a nerve cell or muscle cell when the cell is not active

(-70 mV)

Resting Potential

A short period of time after the stimulation of

a nerve during which the nerve cannot be stimulated

Refractory Period

Produce myelin in cells not in the brain or

spinal cord

Schwan Cells*

Gaps in a myelin sheath

Nodes of Ranvier*

The brain and spinal cord; controls flow of info

in the body

Central Nervous System

All of the nervous system except the brand

and spinal cord; cranial nerves, neck, chest, and pelvis nerves

Peripheral Nervous System

Upper part of the brain that receives sensation

and controls movement

Cerebrum

Outer part of the brain, coordinates muscle

movement, subconscious activities and balance

Cerebral Cortex

Connects cerebral hemispheres with spinal

cord, maintains breathing and circulation

Brain Stem

Part of the brain that directs incoming sensory

and motor signals to the proper region

Thalamus

Coordinates activities of nervous and

endocrine systems; controls homeostasis

Hypothalamus

Lower brain stem; controls circulation,

respiration, and other special senses

Medulla Oblongata

Back part of the brain; coordinates muscle

movement and, subconscious activities, and balance

Cerebellum

Collection of nerve fibers through which

impulses travel between the Central Nervous System and other parts of the body

Nerve

Specialized structure that contains the ends of

sensory neurons and responds to certain types of stimuli

Sensory Receptor

Nerve cell that conducts nerve impulses from

the Central Nervous System to the muscles and glands

Motor Neuron

Neuron located between the afferent neuron

and final neuron of the neural chain

Interneuron

Portion of the neural structure that provides

nerve connections to the skin, skeleton, and muscles of the body but not to the viscera, blood vessels, or glands

Somatic Nervous System

Involuntary movement in response to stimuli

Reflex

Part of the nervous system that controls the

involuntary actions

Autonomic Nervous System

Organ that receives stimuli and gives rise to

the senses such as sight, smell, hearing, and pain

Sense Organ

Tube which air enters the ear

Auditory Canal

Eardrum

Tympanic Membrane

Channel that connects the middle of the ear to

the mouth cavity

Eustachian Tube

Coiled tube found in inner ear; essential to

hearing

Cochlea

Fluid-filled canal in inner ear that helps

maintain balance and coordinate movement

Semicircular Canal

Light sensitive inner layer of the eye,

transmits signals to the brain

Retina

Transparent membrane that forms the front

portion of the eyeball

Cornea

Opening located in the center of the iris of the

eye, controls the amount of light let in to the eye

Pupil

Colored circular part of the eye

Iris

Convex transparent structure that focuses

light on the retina

Lens

Detect dim light Play a major role in non-color and night vision

Rods

Photoreceptor that distinguishes colors,

sensitive to bright light

Cones

Oval concentration of nerve endings on the

tongue, palate, and pharynx

Taste Bud

One of the bumps of tissue on the tongue

between which taste buds are embedded

Papilla

Responsible for the sense of smell

Olfactory Receptor

Substance that causes a change in an

organism’s physiological or physiological state

Drug

Drug that affects the central nervous system

Psychoactive Drug

Relying on a drug to function

Dependence

A state of being where you can no longer

control your drug use

Addiction

When more drugs are needed to get the same

effect

Tolerance

Uncomfortable symptoms produced when you

stop using a drug

Withdrawal

Drug that increases activity

Stimulant

Drug that relaxes

Depressant

Measures how much alcohol is in the blood

Blood Alcohol Concentration

Derived from the tobacco plant and causes

bad effects

Nicotine

Lung disease which breaks down alveoli and

reduces the area available for gas exchange

Emphysema