1. Structure of a Neuron

2. 1. cell body 2. nucleus 3. dendrites 4. axon 5. Schwann cell nucleus 6. myelin sheath 7. node of Ranvier 8. Schwann cell 9. terminal branches 10. synaptic knobs

3. Impulses Along a Neuron Dendrites receive the nerve impulse and carry it toward the cell body, which contains the nucleus. The axon carries the impulse from the cell body toward the synaptic knobs where it will be transferred to other neurons.

5. Myelinated vs. Unmyelinated Myelinated neurons (those that have a myelin sheath) carry nerve impulses faster than unmyelinated ones because the impulse jumps from one node of Ranvier to the next, instead of traveling the whole length of the axon.

6. Normal Neural Pathway Specialized receptors (light, sound, taste, touch, odors) react to a stimulus and generate nerve impulses in the sensory neurons around them. The sensory neurons carry the impulse to the spinal cord and then to the brain where interneurons interpret the sensory information.

7. The interneurons send out impulses to motor neurons which cause a response by an effector (muscle or gland).

8. Reflex Arc Pathway The simplest neural pathway is called a reflex arc and it does not involve the brain. The pathway is: receptor, sensory neuron, interneuron in spinal cord, motor neuron, effector.

9. Reflex Arc

10. The fact that the “decision” is made in the spinal cord saves the time that it would take the nerve impulse to travel through the many circuits of the brain. A faster response time can save the body from further damage. Reflexes are protective mechanisms that are important in maintaining homeostasis.