The Nervous system

1. 35.2 The Nervous system

2. Controls and coordinates functions throughout the body. Responds to external and internal messages. • The body’s • communication system

3. Specialized cells of the nervous system Transmit electrical signals called impulses in onlyone direction. 3 types sensory neurons-send signals from sensory receptors  brain motorneurons – send signals from the brain muscles & glands interneurons –carry impulses between sensory & motor neurons Neurons

4. Nucleus Axon terminals Cell body Myelin sheath neuron anatomy Axon Dendrites Nodes

5. Dendrites– carry impulses from the environment to the cell body Axons– carry impulses away from the cell body Cell body – where the metabolic activity of the cell takes place functions Myelin sheath – an insulating membrane surrounding the axon

6. A nerve impulse is similar to the flow of electrical current through a wire. When the neuron is NOT sending an impulse, the inside is negative and the outside is positive Nerve impulse – resting neuron Na+ and K+ ions move across the cell Membrane via the sodium-potassium pump

7. The Moving impulse • An impulse begins when a neuron is stimulated by another neuron or the environment • Action potential- When an impulse is sent the charge reverses inside the cell – it becomes positive • Threshold – the amount of stimulus required to activate the neuron

8. The moving impulse • An impulse begins when a neuron is stimulated strong enough to reach athreshold. The impulse travels rapidly down the axon towards the terminal end.

9. Direction of impulse Dendrite of Adjacent neuron axon vesicle receptor Axon terminal Where impulses aretransferredfrom one neuron to another. Chemicals diffuse across a small gap between the cells Neurotransmitters- are the chemicals that transfer impulses from one neuron to another. Receptors of the neighboring neuron pick up the chemical message, and a new impulse begins. Neuro- transmitter The Synapse

10. In a fraction of a second after binding to the receptors, the neur0transmitter molecules are released. They are re-absorbed back into the axon terminal

11. Review questions What are the 4 parts of a neuron? What is a threshold? How does a message move from one neuron to another?