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Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function
• What does the nervous system do?
• Action Potentials—rapid transmission
of messages
• Reflex arc (simple somatic function)
and autonomic function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function
• What does the nervous
system do?
• Action Potentials—rapid transmission of
messages
• Reflex arc (simple somatic function) and
autonomic function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What does the nervous system do?
• Sensory input—brings information in (last part
of this presentation shows what kind of information)
• Processing information (brain and spinal cord—won’t
go into details in this class)
• Motor output—initiates response
– Muscles—movement
– Glands—secretion
This is all
we can do!
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
sensory
movement
Processing—this is the complicated part
that 10,000 neurobiologists are working on
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function
• What does the nervous system do?
• Action Potentials—rapid
transmission of messages
• Reflex arc (simple somatic function) and
autonomic function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Action potentials
• Ability to sense environment, process information
rapidly and respond requires rapid transmission of
messages within body
• Ability to transmit messages rapidly unique to
animals
• Accomplished by cell membrane changes called
action potentials
• Happens in nervous tissue cells called neurons and
in muscle cells
• Focus for now on neurons
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Neurons
• Main cells of nervous system
• Transmit rapid messages
called action potentials
• Axon carries message
• Dendrites connect to other
cells, usually neurons or
muscle cells
• Cell body contains nucleus,
maintains cell function
• Single neuron carries
message to and from
periphery (axons over 1 meter
long but barely visible in cross
section in microscope)
• Most neurons never die or
divide (undergo mitosis) after
initial nervous system
development (life-time cells!)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Myelin sheath
• Single nerve contains
hundreds or thousands of
axons
• Each axon is surrounded by
a myelin sheath
• Myelin is a fat-based
insulating substance that
isolates neurons and helps
speed of action potential
propagation (more later)
• Myelin is contained within
cells that wrap around axon
called Schwann cells
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Types of neurons
• Sensory neurons (bundled in
nerves) bring information in from
virtually every tissue, structure
and organ of body (except brain
and spinal cord—thus brain
surgery with no anesthesia)
• Motor neurons (bundled in
nerves) to every muscle and
gland, including blood vessels
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
How do neurons carry messages?
• ACTION POTENTIALS
– Unique to animal nerve and muscle tissue
– Ability to rapidly carry an ion diffusion
mediated change in voltage along the cell
membrane
– Only neurons and muscle cells can do it
– Here’s how (more or less)….
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Resting potential
• At rest, one-third of total body
energy used in neurons and
muscle cells maintaining resting
potential
• Sodium-potassium “pump” actively
moves + ions out of cell so that
inside cell is -70mV relative to
outside
• Happens at sub-microscopic
molecular level (“pump” is protein
structures in cell membrane)
• Happens at micro-time scale (in
1000’s of a second)
• Constantly maintains resting state
for all neurons and muscle cells so
they are ready to “fire”
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Action Potential—cell membrane “depolarizes”
• A stimulus causes Na+ and
K+ “gates” to open
• Positive ions rush in
changing cell interior
voltage to +40 mV relative
to outside cell
• Stimulus at one end of cell
causes adjacent membrane
“gates” to open so that
action potential
“propagates” or moves
along cell membrane. This
is how message is rapidly
transmitted (at about 100
Miles per hour)
• “Gates” are actually protein
structures in cell
membrane)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Role of myelin sheath/Schwann cells
• Myelin in Schwann cells wrapped around axon means that action
potential can jump to nodes where cell membrane is exposed
• This is called saltatory (“jumping”) propagatino of action potential
• It saves energy (so entire membrane doesn’t depolarize) and makes
action potential move faster
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Speed of depolarization or ion movement
• Immediately after
depolarization,
sodium potassium
pump returns cell to
resting state (resting
potential
• Voltage change from
negative resting
potential to positive
actino potential and
back to negative
resting potential can
all happen within
3/1000 of a second
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Synapse
• What happens when
action potential
arrives at end of
axon?
• Neurotransmitter is
secreted to stimulate
connecting neurons
or muscle cells
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function
• What does the nervous system do?
• Action Potentials—rapid transmission of messages
• Reflex arc (simple somatic
function) and autonomic
function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Total Nervous Function
• Sensory neurons—action potential brings
message to brain or spinal cord with sensory
input information from sensory receptors
• Motor neurons—action potential takes message
away from brain or spinal cord with motor output
command (for movement to muscle cells or
secretion to gland cells)
• Within brain and spinal cord, action potentials
among neurons process information allowing for
decision-making—what is the motor response to
the sensory input?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Simplest case—spinal cord reflex
NOTE: Image
shows single
neuron but pain
would stimulate
many neurons
that are become
bundled
together in
nerve. Motor
output would
also be carried
by many
neurons that
stimulate many
muscle cells
causing
movement
response.
• Sensory neurons action potential bring in pain information from skin
• Neurons of spinal cord process information, take decision
Larry M. Frolich, Ph.D.
• Motor neurons carry output to muscles to move limb away Biology
fromDepartment,
pain
Yavapai College
Autonomic function
• Spinal cord reflex example is “voluntary” or somatic function
• Most visceral organs (digestive system, glands, etc.), blood flow
(heart, blood vessels) have autonomic “involuntary” control
• Same principles, same kinds of action potential
• Control is sub-conscious
• Always dual control or innervation:
– Sympathetic: Speed up (“fight or flight”) response
– Parasympathetic: Slow down (“meditative”) response
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function
• What does the nervous system do?
• Action Potentials—rapid transmission of
messages
• Reflex arc (simple somatic function) and
autonomic function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
How does sensation happen?
• Sensory receptors respond to stimulus
from body or environment
• These receptor cells trigger action
potential in connecting sensory neurons
• Spinal cord and/or brain interpret and
analyze information
– Where?
– What?
– How much/how strong?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Sensory fields in brain
• For conscious somatic sensory perception, large
fields in brain organize information spatially
– Visual cortex forms visual field or complete visual
image
– Sensory cortex maps touch sensation from entire skin
surface
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What can we sense—sensory all over body
• Cutaneous receptors of skin
• Bring touch, pressure, pain, heat cold
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What can we sense—sensory all over body
• Proprioception—gives body position by sensing muscle tension
• Allows touching nose with eyes closed
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Special senses—in head
•
•
•
•
•
Taste
Smell
Vision
Hearing
Equilibrium
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Taste
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Smell
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Vision—eye as optical device
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Vision—retina
receptors
respond to
light
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Hearing
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Equilibrium
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Nervous Function--review
• What does the nervous system do?
• Action Potentials—rapid transmission
of messages
• Reflex arc (simple somatic function)
and autonomic function
• What can we sense?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What does the nervous system do?
• Sensory input—brings information in (last part
of this presentation shows what kind of information)
• Processing information (brain and spinal cord—won’t
go into details in this class)
• Motor output—initiates response
– Muscles—movement
– Glands—secretion
This is all
we can do!
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Neurons
• Main cells of nervous system
• Transmit rapid messages
called action potentials
• Axon carries message
• Dendrites connect to other
cells, usually neurons or
muscle cells
• Cell body contains nucleus,
maintains cell function
• Single neuron carries
message to and from
periphery (axons over 1 meter
long but barely visible in cross
section in microscope)
• Most neurons never die or
divide (undergo mitosis) after
initial nervous system
development (life-time cells!)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Action potentials
• Ability to sense environment, process information
rapidly and respond requires rapid transmission of
messages within body
• Ability to transmit messages rapidly unique to
animals
• Accomplished by cell membrane changes called
action potentials
• Happens in nervous tissue cells called neurons and
in muscle cells
• Focus for now on neurons
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
How do neurons carry messages?
• ACTION POTENTIALS
– Unique to animal nerve and muscle tissue
– Ability to rapidly carry an ion diffusion
mediated change in voltage along the cell
membrane
– Only neurons and muscle cells can do it
– Here’s how (more or less)….
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Resting potential
• At rest, one-third of total body
energy used in neurons and
muscle cells maintaining resting
potential
• Sodium-potassium “pump” actively
moves + ions out of cell so that
inside cell is -70mV relative to
outside
• Happens at sub-microscopic
molecular level (“pump” is protein
structures in cell membrane)
• Happens at micro-time scale (in
1000’s of a second)
• Constantly maintains resting state
for all neurons and muscle cells so
they are ready to “fire”
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Action Potential—cell membrane “depolarizes”
• A stimulus causes Na+ and
K+ “gates” to open
• Positive ions rush in
changing cell interior
voltage to +40 mV relative
to outside cell
• Stimulus at one end of cell
causes adjacent membrane
“gates” to open so that
action potential
“propagates” or moves
along cell membrane. This
is how message is rapidly
transmitted (at about 100
Miles per hour)
• “Gates” are actually protein
structures in cell
membrane)
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Speed of depolarization or ion movement
• Immediately after
depolarization,
sodium potassium
pump returns cell to
resting state (resting
potential
• Voltage change from
negative resting
potential to positive
actino potential and
back to negative
resting potential can
all happen within
3/1000 of a second
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Total Nervous Function
• Sensory neurons—action potential brings
message to brain or spinal cord with sensory
input information from sensory receptors
• Motor neurons—action potential takes message
away from brain or spinal cord with motor output
command (for movement to muscle cells or
secretion to gland cells)
• Within brain and spinal cord, action potentials
among neurons process information allowing for
decision-making—what is the motor response to
the sensory input?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Simplest case—spinal cord reflex
NOTE: Image
shows single
neuron but pain
would stimulate
many neurons
that are become
bundled
together in
nerve. Motor
output would
also be carried
by many
neurons that
stimulate many
muscle cells
causing
movement
response.
• Sensory neurons action potential bring in pain information from skin
• Neurons of spinal cord process information, take decision
Larry M. Frolich, Ph.D.
• Motor neurons carry output to muscles to move limb away Biology
fromDepartment,
pain
Yavapai College
How does sensation happen?
• Sensory receptors respond to stimulus
from body or environment
• These receptor cells trigger action
potential in connecting sensory neurons
• Spinal cord and/or brain interpret and
analyze information
– Where?
– What?
– How much/how strong?
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What can we sense—sensory all over body
• Cutaneous receptors of skin
• Bring touch, pressure, pain, heat cold
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
What can we sense—sensory all over body
• Proprioception—gives body position by sensing muscle tension
• Allows touching nose with eyes closed
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Special senses—in head
•
•
•
•
•
Taste
Smell
Vision
Hearing
Equilibrium
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College
Average number of neurons in the human brain: 100 billion
Average number of neurons in an octopus brain: 300 billion
Rate of neuron growth during development of a fetus (in the womb): 250,000 neurons/minute
Diameter of a neuron: 4 to 100 microns
Longest axon of a neuron: around 15 feet (Giraffe primary afferent axon from toe to neck)
Velocity of a signal transmitted through a neuron: 1.2 to 250 miles/hour
Larry M. Frolich, Ph.D.
Biology Department, Yavapai College