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. EyesLight, EarsSound

• 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