The Nervous System
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
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
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
Dendrites (Receptors) Cell branches that receive impulses from other neurons or from receptors
Cyton The cell body – Contains a nucleus
Axon The branch of the cell that transmits impulses away from the cyton
Myelin Sheath The fatty insulation covering produced by the Schwann cells. Nodes of Ranvier – Area of no myelin * Myelin * Node of Ranvier * Schwann Cell
Terminal Branches Responsible for: – transmitting impulses to the dendrites of other neurons – Transmitting impulses to effectors
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
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
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
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
Grasshopper – Similar nervous system to earthworm – Has SENSORY ORGANS Eyes Tympanum- Detects sound Antennae- Sense and Touch
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