The Nervous System Ch. 36
Jan 04, 2016
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