1. The Nervous System

2. Regulation The control and coordination of life activities – All organisms use chemicals to regulate life activities – Multicellular animals have NERVE CONTROL – Allow for organisms to maintain HOMEOSTASIS

3. Stimulus: – Any change in the external or internal environment that initiates a RESPONSE Response: – A change in BEHAVIOR Stimuli are detected by RECEPTORS – Sensitive to a particular type of stimulus Ex. Eyes  Light, Ears  Sound Effectors: – Organs that produce a response to a stimulus Ex. Muscles and Glands

4. Neuron Specialized cells which are responsible for transmitting IMPULSES from one part of the body to another Impulse: – Electrical and chemical changes that travel through neurons – Causes the release of NEUROTRANSMITTERS from terminal branches – **Neuron-Nerve-Ganglia-Brain Made up of 4 main parts

5. Dendrites (Receptors) Cell branches that receive impulses from other neurons or from receptors

6. Cyton The cell body – Contains a nucleus

7. Axon The branch of the cell that transmits impulses away from the cyton

8. Myelin Sheath The fatty insulation covering produced by the Schwann cells. Nodes of Ranvier – Area of no myelin * Myelin * Node of Ranvier * Schwann Cell

9. Terminal Branches Responsible for: – transmitting impulses to the dendrites of other neurons – Transmitting impulses to effectors

10. Synapses Junction between adjacent nerve cells Some nerve cells have junctions with muscles or glands – Chemicals released stimulate contraction of the muscle, or secretion by the gland

11. Neurotransmitters Chemicals that are secreted by the terminal branch into the synapse between neurons Carry impulses from one cell to the next – Ex. Acetylcholine and Noradrenaline

12. Amoeba – No true nervous system Paramecium – System of FIBRILS that transmit impulses to cilia Regulates LOCOMOTION and INGESTION Some species of Protozoans have EYESPOTS Receive stimuli and generate impulses to produce a response Hydra – Contain specialized cells similar to neurons, but do not have a central nervous system – Cells connect to form a NERVE NET Impulses travel in any direction

13. Earthworm – Has neurons organized into distinct structures and organs which form a TRUE NERVOUS SYSTEM Brain: – Mass of ganglia located on the dorsal side of the worm, near the head Ventral Nerve Cord – Main nerve – Connected to the brain and runs along the length of the animal on the ventral side (Belly) Nerve Branches – Series of smaller nerves that branch to all parts of organism – Impulses are generated by receptors and travel through the nerves to reach muscles and glands

15. Grasshopper – Similar nervous system to earthworm – Has SENSORY ORGANS Eyes Tympanum- Detects sound Antennae- Sense and Touch

16. A Lateral view B Dorsal view 1 Antenna 2 Brain (cerebral ganglion) 3 Compound eye 4 Tympanum 5 Ganglion 6 Beginning of the Dorsal Nerve Cord 7 Segmental nerves 9 Ventral nerve cord