Terms
A soft, spongy organ that weighs between two and three pounds; makes it possible to move, think, and learn
Brain
Unconscious actions such as jerking your hand away when you touch something hot
Reflex actions
A large bundle of nerve fibers at the back of the eyeball; carries messages from the rods and cones to the sight center in the brain
Optic nerve
The part of the ear that can be seen; catches waves of sound
Outer ear
Nerve cells; bundles of fibers that carry messages from one part of the body to the other
Nerves
The half of your cerebrum that communicates with the left side of your body
Right hemisphere
Nerve endings that send messages to your brain whenever your skin comes into contact with something outside your body
Sensory receptors
The colored part of the eye; causes the pupil to become larger or smaller according to the amount of light entering the eye
Iris
The part of the ear including the hammer, anvil, and stirrup; amplifies and transmits sound to the inner ear
Middle ear
The part of the brain connected to the spinal cord; controls involuntary muscles and activities of the body
Brain stem
The half of your cerebrum that communicates with the right side of your body
Left hemisphere
12 pairs of nerves which branch directly from your brain stem
Cranial nerves
The dark opening in the center of the iris through which light passes
Pupil
A thin membrane of skin that separates the outer ear from the middle ear
Eardrum
A long bundle of nerve fibers that extends from the brain stem and is protected by the spinal column
Spinal cord
Consists of your brain and spinal cord and acts as your body's computer, controlling the functions of each of the body's systems
Central nervous system
Fibers that inform your body of the things in its environment - things you feel, see, hear, smell, taste, etc.
Sensory nerve fibers
The part of the eye that causes light rays which pass through it to bend and focus on the retina
Lens
The small tube that carries sound waves from the outer ear to the eardrum
Auditory canal
The lower, back part of the brain; controls balance and coordinates skeletal (voluntary) muscle activity
Cerebellum
Made up of the nerves that control the involuntary actions of your body and all the other nerves that branch out into the body; serves as the messenger systems, carrying information from the brain to each part of the body
Peripheral nervous system
Fibers that carry messages from the brain and spinal cord to the muscles
Motor nerve fibers
The inner layer of the eye where images are formed
Retina
The tube that connects the middle ear to the back of the pharynx
Eustachian tube
The upper part of the brain; controls thought, memory, and learned behavior
Cerebrum