Nervous System
Cells
Ch 12
*By the end of this, you
should be able to answer all of
Obj. 12 questions.
What are the parts of the
motor division?
• Somatic nervous system
– Conscious control of skeletal muscles
• Autonomic nervous system (ANS)
– Regulate smooth muscle, cardiac muscle,
and glands
– Divisions – sympathetic and
parasympathetic---Ch 14 Objective
Cells of The Nervous System
• Glia
– Support the neurons
• Neurons
– Excitable cells that initiate and conduct
impulses that make all nervous system
functions possible.
Glia
• FIVE MAJOR TYPES TO CONTINUE
ON NEXT SLIDES
Astrocytes
• Largest and most numerous type of
glia
• Transfer nutrients from blood to
neurons
• Cells extension connect to neurons and
capillaries
• Forms the Blood Brain Barrier
Microglia
• Small, usually stationary cells
• In inflamed brain tissue, they
enlarge, move about and carry on
phagocytes
Ependymal cells
• Form thin
sheets that
line fluidfilled cavities
in the CNS
• Some produce
fluid and
others aid in
circulation of
the fluid
Oligodendrocytes
• Hold nerve fibers together and
produce myelin sheath
Schwann cells
• Found only in PNS
• Support nerve fibers and form myelin
sheaths
• Gaps in the myelin sheath are called
nodes of Ranvier
• Cell body: functional
portion
• Dendrites: short
extensions that
receive signals
• Axon: long extension
that transmits
impulses away
Myelinated Neurons
• Many vertebrate peripheral neurons have an insulating sheath around
the axon called myelin which is formed by Schwann cells.
• Myelin sheathing allows these neurons to conduct nerve impulses
faster than in non-myelinated neurons.
Saltatory Conduction in Myelinated
Axons
Myelin sheathing has bare patches of axon called nodes of Ranvier
Action potentials jump from node to node
Fig. 48.11
Nerve Impulse - The Action Potential
At rest, the inside of the neuron is slightly negative due to a higher
concentration of positively charged sodium ions outside
When stimulated past threshold, sodium channels open and sodium
rushes into the axon, causing a region of positive charge within the
axon.
The region of positive charge causes nearby sodium channels to open.
Just after the sodium channels close, the potassium channels open wide,
and potassium exits the axon.
This process continues as a chain-reaction along the axon. The influx of
sodium depolarizes the axon, and the ourflow of potassium repolarizes
the axon.
The sodium/potassium pump restores the resting concentrations of
sodium and potassium ions
http://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swf
Repolarization, Hyperpolorization,
and Refractory Period in the
Action Potential…
Answering Obj. #9…we are going to
explore this in the virtual action
potential lab!! (But before then, check
out the page number given on your
objective sheet).
Types of Synapses
• Electrical synapses- Occur where cells
joined by gap junctions allow an action
potential to simply continue along a post
synaptic membrane
• Chemical synapses- occurs where
presynatptic cells release chemical
transmitters [neurotransmitters] across a
tiny gap to the postsynaptic cell possibly
inducing an action potential there.
http://www.blackwellpublishing.com/matthe
ws/nmj.html
Neurotransmitters
• Means by which neurons communicate with
one another.
• FOUR CLASSES OF NEUROTRANSMITTERS:
– Acetylcholine
– Amines
– Amino Acids
– Other small transmitters
Acetylcholine
• Unique chemical structure; acetate with
choline
• Deactivated by acetycholinesterase,
with the choline molecules being
releases and transported back to
presynaptic neuron to combine with
acetate.
Amines
• Synthesized from amino acid
molecules
• Found in the various parts of the
brain
Amino Acids
• Most common neurotransmitter
• Stored in synaptic vesicles in the PNS
Other small transmitters
• Nitric Oxide derived from an amino acid
• NO from a postsynaptic cell signals the
presynaptic neuron, providing feedback
in a neutral pathway.