1. The Nervous System

2. Function of the nervous System
1. Receive information 2. Respond to information 3. Maintain homeostasis

3. Stimulus: what causes the nervous system to respond
Receptor: what receives the stimulus (if it’s an external stimulus, the receptor is a sense organ – eyes, ears, nose, mouth, skin)
Effector: what responds to the stimulus (muscle or gland)
Response: final action taken in response to the stimulus

4. Neurons Neuron: nerve cell – carries messages throughout the body
Nerve impulse: electrical or chemical signal that travels from one neuron to another

5. Neuron Structure
All neurons are alike in that they have the same structures, but each type of neuron looks different.
Dendrite: takes signals to the cell body
Cell body: houses the nucleus and other organelles (makes up the gray matter in the brain)
Axon: takes signals/impulses away from the cell body (makes up the white matter in the brain)
Myelin: substance that covers the axon; it speeds up the impulse and protects the axon
Myelinated axon: impulse travels 5-30 m/sec
Unmyelinated axon: impulse travels m/sec

6. Neuron Structure Continued…
Node of Ranvier: the space between each myelin “link”
Axon Tips (presynaptic terminal): release chemicals (neurotransmitters) into the space between the neurons in order to carry impulses from one neuron to another.
Synapse: space between neurons
Neurotransmitter: chemical released by the axon tips that helps the impulse travel across the synapse to another neuron or to a muscle/gland

7. Nodes of Ranvier
Axon Tips
**Impulse starts in the dendrite  cell body  axon  axon tip  synapse  dendrite of another neuron or to the muscle/gland

8. -The impulse carried by the neuron is electrical - The impulse carried through the synapse is chemical -If the axon tips did not release the neurotransmitters, the impulse would stop at the axon tips.

9. Nerve: a bundle of nerve fibers
Nerve Fiber: axon or dendrite; they are often arranged in parallel bundles covered with connective tissue
Nerve: a bundle of nerve fibers

11. Types of Neurons
Sensory Neuron: picks up internal or external stimuli and converts it to a nerve impulse, then sends it to the interneuron
Interneuron: in the brain/spinal cord; takes impulse from sensory neuron and interprets it; decides if further action should be taken, then sends message, if necessary, to the motor neuron
Motor Neuron: takes the impulse from the interneuron and sends it to a muscle/gland (effector); the muscle contracts in response or a gland releases a hormone.

12. Interneuron
Sensory Neuron
Motor Neuron

13. Example: you put your hand on a hot pot and then move your hand
Stimulus (hot pot)  receptor (hand)  sensory neuron  interneuron  motor neuron  effector (muscle in the hand/arm)