Principles of Biology

1. Principles of Biology By Frank H. Osborne, Ph. D. Lab 8 - The Nervous System

2. Properties of the Sense Organs A. Sense organs receive stimuli from the outside world. B. A sense organ communicates with the central nervous system via a sensory neuron.

3. A. The eye 1. The eye has cells that respond to light intensity and color. 2. The optic nerve transmits impulses from the eye to the brain. 3. The brain interprets the impulses it receives from the eye.

5. B. The ear 1. Sound travels as a disturbance of the air molecules. 2. The eardrum vibrates when it is disturbed by the air. 3. Vibrations of the eardrum are transmitted mechanically to the cochlea. 4. Sensitive hair cells in the cochlea transmit the impulses to the brain via the otic nerve.

6. The ear 5. The brain decides which sounds are important. 6. The ear has semicircular canals that are used to sense balance.

8. The Sense Organs C. The skin 1. Touch receptors a. Touch receptors sense contact with outside things. b. Touch receptors are very close together in sensitive areas of the skin.

9. The Sense Organs 2. Thermal receptors a. Thermal receptors detect heat and cold. b. The heat receptors respond faster than do the cold receptors. 3. Pain receptors detect pain.

10. D. The nose 1. The olfactory receptors respond to substances in the air. 2. The olfactory receptors transmit impulses to the brain. 3. The brain determines what the smell is. 4. Olfactory fatigue results from a long-term exposure to a particular odor.

12. The Sense Organs E. The tongue 1. The tongue can taste substances that are sweet, salty, sour and bitter. 2. The brain determines the substance being tasted. This is done by combining taste sensations with smell sensations.

14. Reflex Action A. A reflex is a nervous system response that is automatic. B. Pathway of a reflex 1. A sensation is detected and an impulse is sent to the spinal cord using a sensory neuron. 2. The sensory neuron causes an associative neuron (interneuron) in the spinal cord to send an impulse to a motor neuron. 3. The motor neuron stimulates a muscle to contract.

15. Reflex Action C. The knee-jerk reflex 1. The hammer causes a stretch of the tendon below the kneecap. 2. The stretch receptors send an impulse to the interneuron via a sensory neuron. 3. The interneuron stimulates the motor neuron which causes the leg muscle to contract.

17. The End Lab 8 The Nervous System