Nervous System
Parts of the Nervous System
• Brain
• Spinal Cord
• Nerves
Vocabulary to Know
• Homeostasis
– The regulation of steady, life-maintaining
conditions inside an organism, despite
changes in its environment
Nerve Cells
• Neurons
– Basic functioning units of the nervous
system
http://ilearn.senecac.on.ca/aahs/health/IHP/ottawa/anatomy/neuron/map/neuron.html
http://35.9.122.184/images/40-AnimalStructureAndFunction/
Neurons
• Made up of a cell body and branches
called dendrites and axons
– Dendrites receive messages from other
neurons and send them to the cell body
– Axons carry messages away from the
cell body
Any message carried by a neuron is called an impulse
Neurons
A message carried by a neuron is called
an impulse
Types of Neurons
• Sensory
• Motor
• Interneuron
Sensory Neurons
• Receive information
• Send impulses to the brain or spinal
cord
Interneurons
• Send impulses from sensory neurons
to motor neurons
Motor Neurons
• Conduct impulses from the brain or
spinal cord to muscles or glands
throughout your body
Synapse
• Small space across which an impulse
moves from an axon to the dendrites
or cell body of another neuron
Synapse
• An impulse reaches the end of an
axon
• Axon releases a chemical
• Flows across the synapse
• Stimulates the impulse in the dendrite
of the next neuron
• Impulse moves from neuron to neuron
http://www.med.harvard.edu/publications/On_The_Brain/Volume7/Number1/images/Neuron.jpg
An impulse moves in only one direction across a
synapse - from an axon to the dendrites or cell body of
another neuron.
http://mhln.com
Two Parts
• Central (CNS)
• Peripheral (PNS)
http://inside.salve.edu/walsh/cns_pns.jpg
Central Nervous System
• Brain
• Spinal cord
The Brain
• Coordinates body activities
• Made up of approximately 100 billion
neurons
• Divided into three major parts– the cerebrum
– the cerebellum
– the brain stem.
Cerebrum
•
•
•
•
•
Largest part of the brain
Thinking
Memory is stored
Movements are controlled
Impulses from the senses are
interpreted.
Cerebellum
• Interprets stimuli from eyes, ears,
muscles
• Controls voluntary muscle movements
• Maintains muscle tone
• Helps maintain balance
Brain Stem
• Connects brain to spinal cord
• Made up of the midbrain, the pons,
– Act as pathways connecting various
parts of the brain with each other
• Medulla
– controls involuntary actions
http://www.cbituk.org/GRAPHICS/brain.gif
The Spinal Cord
• Extension of the brain stem
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Peripheral
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Peripheral Nervous System
• Connects body to brain & spinal cord
• 12 pairs of nerves from your brain
(cranial nerves)
• 31 pairs from your spinal cord (spinal
nerves)
– Bundles of sensory and motor neurons
held together by connective tissue
http://www.christopherreeve.org/Research/Research.cfm?ID=178&c=21
Peripheral Nervous System
• Two divisions
– Somatic
– Autonomic
http://abdellab.sunderland.ac.uk/lectures/Parmacology/Pics/anatomy/PNS.GIF
Somatic Nervous System
• Controls voluntary actions
• Made up of the cranial and spinal
nerves that go from the central
nervous system to your skeletal
muscles
Autonomic Nervous System
• Controls involuntary actions-those not
under conscious control-such as your
heart rate, breathing, digestion, and
glandular functions
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/autonomic.gif
Reflexes
• Involuntary, automatic response to a
stimulus
• Involves a simple nerve pathway
called a reflex arc