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 Based on the direction in which an impulse travels Sensory neurons – carry impulses from the sense organ s to the spinal cord 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 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 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 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. 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 Axon – long fiber that carries impulses away from the cell body Myelin sheath – insulating membrane located on the axon 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 Impulse The resting impulse The resting neuron has a positive charge outside the cell and a negative charge inside the cell. 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. 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. 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. 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 Resting potential – the electrical charge across the cell membrane of a neuron in its resting state http://highered.mheducation.com/sites/0072495855/student_view0/c hapter2/animation__how_the_sodium_potassium_pump_works.html http://highered.mheducation.com/sites/0072495855/student_view0/c hapter2/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. 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 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 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 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 As the impulse passes the K+ gates open up an allow K+ to flow out This restores the resting potential This restores the resting potential http://highered.mheducation.com/sites/0072495855/student_vi ew0/chapter14/animation__the_nerve_impulse.html http://highered.mheducation.com/sites/0072495855/student_vi ew0/chapter14/animation__the_nerve_impulse.html

11. Threshold The strength of an impulse is always the same 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. 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. At the end of the neuron, the impulse reaches an axon terminal. This is where the neuron touches another cell. This is where the neuron touches another cell. The neuron can pass the impulse along to another cell. The neuron can pass the impulse along to another cell. This location is called a synapse. This location is called a synapse.

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