The Nervous SystemCh. 36

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

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..

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)

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

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

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

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

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

Regions of the Brain• 3 main sections:

1) Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from

2) Cerebellum- back of your brain; controls balance, senses, and coordination

3) Brain stem- connection between brain and spinal cord

a) Medulla oblongata- controls involuntary activities

b) Pons- connects areas in the brainc) Midbrain- responds to signals and

sends them to regions of the braind) Hypothalamus- connection between

nervous and endocrine system

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

Layers of the Nervous System2) Autonomic Nervous System:

- send impulses to organs in the body- control involuntary

movementsTwo systems in the ANS:1) Sympathetic Nervous System:

- controls organs during times of stress

- release of epinephrine2) Parasympathetic Nervous

System:- controls organs during

times at rest

Layers of the Nervous System