Human: the nervous system and sense organs

The nervous system consists of two divisions: central (brain and spinal cord) and peripheral (nerves, ganglia).

Its main cell is the neuron: it has a cell body, short dendrites and a long axon. The dendrite receives excitation, and the long axon transmits it.

The form of activity of the nervous system is the reflex.

The reflex arc begins at the receptor:

1. Receptor
2. Sensory neuron
3. Nerve center
4. Motor neuron
5. Effector organ

Divisions of the brain: medulla oblongata, pons, cerebellum, midbrain, diencephalon and cerebral hemispheres.

The retina of the eye contains rods (night vision) and cones (color vision).

Key facts

• The medulla oblongata contains the respiratory center, and the cardiovascular center is also located here. The cerebellum controls the coordination of movement.
• In the spinal cord, gray matter is on the inside, and white matter is on the outside. In the cerebral hemispheres of the brain, gray matter (the cortex) is on the outside.
• Hearing receptors: the cochlea in the inner ear (organ of Corti). Balance: the vestibular apparatus.
• The autonomic nervous system: sympathetic (increases the activity of the heart) and parasympathetic (decreases the activity of the heart).
• The pupil of the eye regulates the amount of light, while the lens regulates the refraction of light rays (focusing).