1. Nervous System Part 1

2. Nervous System
The nervous system is one of the two control systems of the body
The other being the endocrine system
These two systems have a lot of interaction!
Made of neurons and neuroglia
Nervous tissue!

3. Nervous System Organization

4. Neurons There are three classifications of neurons
Sensory Neurons
Interneurons
Motor Neurons
Interneurons form the central nervous system (CNS)
Sensory and motor neurons form the peripheral nervous system (PNS)

5. Neuron Structure Neurons have three general structures:
Soma (cell body)
Axon (signal transmission)
Dendrite (signal reception)
Some neurons look rather different but all have these three parts in some way

6. Central Nervous System
Composed of the brain and spinal cord
Contains many tracts (bundles of axons) leading from one area to another
These are all interneurons, signaling each other and storing information
This is how we think and remember!

7. Peripheral Nervous System
The PNS consists of organs called nerves which are sheaths of neuronal axons covered in connective tissue
There are 12 pairs of cranial nerves and 31 pairs of spinal nerves
Peripheral nerves sending signals towards the brain are afferent nerves, while nerves sending signals to the body are efferent nerves
Afferent nerves make up our senses (chapter 12, not covered in this class)

8. Cranial & Spinal Nerves
When a nerve ends at a particular body part it is said to innervate that region
The cranial nerves project out of the brain and innervate the body directly from the brain
Include the optic nerve (eye) and the vagus nerve (organs)
The spinal nerves branch out from the spinal cord and each innervates a region of the body
Named for which vertebral gap they come out of

9. Cranial vs. Spinal Nerve
Both afferent and efferent nerves (sensory and motor neurons) are bundled in each cranial and spinal nerve
The spinal cord contains the cell bodies (somas) of the PNS neurons in clusters called ganglia (sing. ganglion)
Only the axons stick out into the rest of the body
The axon of the neuron can be regrown if the soma is intact!

10. Examples of Cranial vs. Spinal Nerve Activities

11. Action Potentials
Recall: Sodium inrush depolarizes a cell membrane, before potassium rushes out and repolarizes the membrane again
This brief flicker back and forth of voltage triggers adjacent voltage-gated ion channels to open
Propagates the action potential as a wave of ions rushing across the membrane

12. Speed of Conduction
Action Potentials may be sped up if there is myelin on the axon
Myelin is a dense, fatty material, with gaps called Nodes of Ranvier
Myelin conducts the voltage from one Node of Ranvier to the next much more quickly
Only some neurons (e.g. skeletal motor neurons) are myelinated

13. More on Myelin
Heavily myelinated nervous tissue appears white, while unmyelinated tissue appears gray
White matter vs. Gray matter
If myelin is stripped off (by, for example, the immune system) there are no voltage-gated ion channels underneath it and the neuron fails to send signals
This is the cause and effect of Multiple Sclerosis, which paralyzes myelinated neurons while leaving other neurons intact

14. Release of Neurotransmitters
Once the action potential reaches the end of a neuron, voltage-gated calcium channels open and allow calcium into the neuron
The neuron attaches to another neuron or to another organ at a synapse
The calcium stimulates the release of synaptic vesicles into the synapse
These vesicles contain neurotransmitters that have an effect on the target cell

15. That’s our show!
Next class: last new material before exam #2!