The Nervous System

1. The Nervous System The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.

2. Neurons • Messages carried by the nervous system are electrical signals called impulses. • Impulses are transmitted by neurons

3. 3 Types of Neurons • Based on the direction in which an impulse travels • Sensory neurons – carry impulses from the sense organ s to the spinal cord • Motor neurons – carry impulses from the brain and the spinal cord to muscles and glands • Interneurons – connect sensory and motor neurons and carry impulses between them

4. Neurons (nerve cells)

5. Parts of a neuron • Cell body – The largest part of the neuron, contains the nucleus and cytoplasm • Dendrites – short branches off the cell body that carry impulses from the environment or from other neurons toward the cell body.

6. Axon – long fiber that carries impulses away from the cell body • Myelin sheath – insulating membrane located on the axon • has gaps in it called nodes, these nodes speed up the rate the impulse moves

7. The Nerve ImpulseThe resting impulse • The resting neuron has a positive charge outside the cell and a negative charge inside the cell. • This is caused by sodium and potassium pump which pumps sodium out and potassium into the cell. • Potassium can leak out of the cell faster than sodium which leaves a negative charge on the inside of the cell.

8. This leaves a positive charge outside the cell and a negative charge inside the cell membrane. • Resting potential – the electrical charge across the cell membrane of a neuron in its resting state http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

9. The Moving Impulse • An impulse begins when a neuron is stimulated by another neuron or by the environment. • The impulse travels down the axon away from the cell body and toward the axon terminals • Na+ flows into the cell reversing the resting potential

10. Action potential • Action potential – the change from a negative to a positive charge along the axon • As the impulse passes the K+ gates open up an allow K+ to flow out • This restores the resting potential http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

11. Threshold • The strength of an impulse is always the same • It either happens or it doesnt • Threshold – the minimum level of a stimulus that is required to activate a neuron.

12. The Synapse • At the end of the neuron, the impulse reaches an axon terminal. • This is where the neuron touches another cell. • The neuron can pass the impulse along to another cell. • This location is called a synapse.

13. Neurotransmitters • The chemicals used by neurons to transmit an impulse across a synapse to another cell