1. The Nervous System Ch. 36

2. Communication Center
Central Nervous System (CNS): system of nerves, the spinal cord, and the brain that receives signals from environment and sends out responses to those signals
Neurons: nerve cell; 3 sections
Dendrites: fan like branches that receive impulses
Cell body: main area of cell
Axon: long extension that sends impulses on to other neurons or body cells

3. Types of Neurons
Sensory neurons: receive signals from the environment and send impulses to the spinal cord and brain
Interneurons: nerves that make up the brain and spinal cord; process impulses and send response impulses to motor neurons
Motor neurons: react to impulses from brain and spinal cord; activate glands, muscles, etc..

4. How Neurons Send Impulses
Ion channels allow the inward flow of K+ and limit the flow of Na+
Concentration difference between Na+/K+ is made greater by Na+/K+ Pump
Membrane is polarized:
Inside has negative charge
Outside has positive charge
About -70mV difference (resting potential)
Impulse is sent as swift of K+ and Na+ across the membrane change the polarity of the cell (action potential)

5. Na+/K+ Pump
Concentration gradient of Na+ and K+ most be large so the flow of ions is fast
Na+/K+ Pump uses ATP to pull in K+ and push out Na+
1 ATP= 2 K+ in; 3 Na+ out
Also helps to repolarize membrane after impulse

6. Sending an Impulse Sending an impulse starts with an action potential
Stimulus must be strong enough to start action potential; pass threshold
Na+ channels in the nerve membrane open up; Na+ rush into cell down a concentration gradient
Inside cell changes from – to +
Shift causes other Na+ channels to open and signal moves like a wave down the axon

7. Sending an Impulse
After impulse, the K+ channels open and K+ rush out, changing the inside of the cell from + to –
Repolarizing (outside +; inside -) the area of nerve must happen to send another signal
Signals can “jump” down axon by traveling to pockets between myelin sheaths

8. White and Gray Matter Myelin sheaths increase signal transmission
Heavily myelinated nerves have a white color
Inner areas of the brain
Spinal cord nerves
Regular nerves have gray color
Outer areas of the brain
Body nerves

9. Neuron to Neuron Signals
Nerve cells don’t touch; signal “wave” has to be passed from cell to cell
Synapse: small space (10-20 nm) between neurons
Neurotransmitter: chemical signals that travel from axon of one neuron to the dendrite of the next neuron; triggered by Ca+ channels

10. Regions of the Brain 3 main sections:
Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from
Cerebellum- back of your brain; controls balance, senses, and coordination
Brain stem- connection between brain and spinal cord
Medulla oblongata- controls involuntary activities
Pons- connects areas in the brain
Midbrain- responds to signals and sends them to regions of the brain
Hypothalamus- connection between nervous and endocrine system

11. Layers of the Nervous System
Peripheral Nervous System (PNS): nerves that carry messages to and from the CNS
Two system in the PNS:
1) Somatic Nervous System:
- 12 nerves in the brain
- 31 nerves in the spine
- send information for all voluntary movement
Reflex: automatic response to set stimuli so to quickly minimize damage
- pulling back when burned

12. Layers of the Nervous System
2) Autonomic Nervous System:
- send impulses to organs in the body
- control involuntary movements
Two systems in the ANS:
Sympathetic Nervous System:
- controls organs during times of stress
- release of epinephrine
Parasympathetic Nervous System:
- controls organs during times at rest

13. Layers of the Nervous System