Transcript The Nervous System

The Nervous System
Anatomy and Physiology
Nervous System Functions
• 1. Sensory-receptors gather information
and pass it on toward the CNS
• 2. Integrative-in the spinal cord or brain,
we put information together and make sense
of it
• 3. Motor-carry impulses to effectors such
as muscles and glands
Basic Structures
• Central nervous
system (CNS) consists
of brain and spinal
cord only
• Peripheral nervous
system (PNS) are
nerves outside the
CNS
Basic Structures
• Neurons are the nerve
cells that can transmit
the electrical impulse
• Neurons are
surrounded by support
cells called neuroglial
cells
• There are 5 types of
neuroglial cells
Neuron Structure
• Cell body with
nucleus
• Dendrites: branching
fibers that RECEIVE
impulses
• Axon: long fiber that
SENDS the impulse
on
Neuron Structure
• Axon is often wrapped
in cells called
Schwann cells
• A Schwann cell has its
own nucleus and is
made of myelin
• Nodes of Ranvier are
the spaces between
Schwann cells
Types of Neurons
• Sensory neurons carry
information from sensory
receptors to the CNS
(AFFERANT)
• Interneurons relay
impulses within the CNS
• Motor neurons carry
impulses from CNS to
effectors ( EFFERENT)
Types of Neurons
• Bipolar: only two
fibers—one dendrite
and one axon
• Unipolar: single fiber
from the cell body
which splits into
dendrite and axon
• Multipolar: many
dendrites; one axon
Identify which
neuron is
unipolar,
bipolar, and
multipolar.
Identify which
is the sensory
neuron, the
interneuron,
and the motor
neuron
The Nerve Impulse
• The membrane of
a resting neuron is
POLARIZED
• This means that
there is a different
electrical charge
on the outside of
the membrane as
compared to the
inside
Resting Potential
Resting Potential
•
•
•
•
More positive ions outside than inside
Result of actively pumping out sodium ions (Na+)
Potassium ions are also involved (K+)
Three Na+ ions are pumped out for every two K+ ions
pumped in.
Becoming Polarized
Sodium Potassium Pump
Resting Potential
• More positive outside the membrane than inside
(POLARIZED)
• This charge difference is called a potential difference
• Holds potential energy which can be released in the form of
an electrical impulse
Action Potential
• When stimulated, the
membrane of the neuron
opens the channels and
lets the Na+ rush inside
• This is
DEPOLARIZATION
• This releases the potential
energy in the form of a
current down the neuron
membrane
Like a Wave
Depolarization of
one section
stimulates the next
section of
membrane
Action Potential
Back to Resting Potential
After the wave, or current, of
depolarization has passed,
ions are restored to resting
potential
This means Na+ are again
pumped out, setting up a
more positive charge outside
the neuron
Odds and Ends
• Threshold must be
reached to trigger
depolarization
• Each nerve fiber has
an ALL OR NONE
RESPONSE
Reflex Arc
• Minimum of three
neurons
• Sensory to inter to
motor neuron
• Fastest responses go
only to the spinal cord,
not all the way to the
brain
Reflex Arc
Reflex Arc
Reaction Time
• Is the time between
stimulation and the
beginning of the
response
• Sensory neuron to
interneurons in brain,
then motor neuron
Reaction Time
• Can get shorter, as we practice
• Use the same pathway over and over
• Learned behavior
Bell Ringer
• Which nerve would be faster at transmitting
an impulse: 2 mm in diameter, or 4.5 mm
in diameter
• Which neuron would be faster at
transmitting an impulse: one with Schwann
Cells, or a bare axon with no Schwann cells
• How is multiple sclerosis related to
Schwann cells?