| A | B |
|---|
| Cerebellum | The part of the brain that controls baance. |
| Brain stem | The part of the brain that controls automatic activities and connects the brain and the spinal cord. |
| Neuron | A nerve cell |
| Synapse | A tiny gap between neurons. |
| Receptor cell | A cell that receives information about the environement and starts nerve impulses to send that information to the brain. |
| Cornea | A clear layer of the eye that light passes through |
| Iris | The part of the eye that controls the amount of light that enters . |
| Pupil | The black circle in the center of the irus. |
| Retina | The back part of the eye where light rays are focused. |
| Optic nerve | A bundle of nerves that carry impulses from the eye to the brain. |
| Eardrum | A thin tissue in the middle ear that vibrates when sound waves strike it. |
| Cochlea | The organ in the ear that send impulses to the auditory nerve. |
| Auditory nerve | A bundle of nerves that carry impulses from the ear to the brain. |
| Testis | The male sex organ that produces sperm cells (plural testes) |
| Skeletal system | The network of bones in the body. |
| Red marrow | The spongy material in bones that makes blood cells. |
| Osteoporosis | A disease in which bones become lighter and break easily. |
| Ligament | A tissue that connects bone to bone. |
| Voluntary muscle | A muscle that a person can control. |
| Involuntary muscle | A muscle that a person cannot control. |
