Download Nervous System and Action Potential

Body Systems
• All our body systems
work together to maintain
homeostasis within our
bodies.
• Nervous
• Circulatory (includes
respiration)
• Lymphatic
• Digestive
• Excretion (includes
integumentary)
• Endocrine
• Immune
Nervous System
• Our nervous system allows us to
understand what is happening around us
as well as within us.
• It allows us to develop inferences to
explain the observations we make using
our five senses.
• It is a network of cells (called neurons) that
send electrical messages (called
impulses) to and from our cells, tissues,
and organs.
Neurons
Neuron parts
* Parts of the neuron
include:
1. Cell body, 2. dendrites,
3. axon,
and 4. axon terminals.
2.
* The axons are covered
with a myelin sheath.
There are nodes
separating the Schwann
cells that make up the
myelin sheath. As the
impulse travels along the
axon, it travels from node
to node; thereby,
increasing the speed at
which an impulse can
travel down a nerve cell.
4.
1.
3.
Movement of an Impulse
• Without nodes
•
http://www.ship.edu/~cgboeree/actionpot.html
• With nodes
The cell body
of a neuron:
note that in
contains all the
cell organelles
found in
eukaryotic
cells
Types of Neurons
• Sensory Neurons:
carry impulses from
our senses and our
body to our CNS.
• Motor Neurons: carry
impulses from our
CNS to our body
(either another
neuron, gland cell, or
a muscle cell).
• Interneurons:
connect sensory and
motor neurons.
Example of a Motor Neuron
Sensory Neuron
• Typically the cell body
of a sensory neuron is
found protruding from
the middle of the
axon.
How is an electrical impulse sent
along a neuron: Resting Potential
Outside of cell
Inside of cell
• Sodium/Potassium pumps
actively pump (3) Na+ out of
the cell and (2) K+ into the cell.
• Na+ channels are closed so
Na+ are not able to move into
the cell.
• This generates a separation of
charges so that the inside of
the cell is relatively – and the
outside is relatively +.
• The cell will remain in this
state (at rest) until it is
stimulated.
How is an electrical impulse sent
along a neuron: Action Potential
• A nerve impulse starts when a stimuli such as
light waves (eye), chemicals in scents or food
(nose or tongue) , pressure (touch/organs),
sound waves (ear), or another chemical,
disturbs a neuron in its resting potential.
• This causes Na+ channels to open and the Na+
diffuse (flood) into the cell leading to a more
positive charge inside than outside.
• This sudden reversal of charges (or voltage)
causes other sodium channels nearby to open
and the action potential continues down the
neuron.
Action Potential
At rest.
At the leading edge of the impulse, the
sodium gates open. The membrane
becomes more permeable to Na+ ions
and an action potential occurs.
As the action potential passes, potassium gates
open, allowing K+ ions to flow out.
The action potential continues to move along the
axon in the direction of the nerve impulse.
How is an electrical impulse sent
along a neuron: Repolarization
• The sodium/potassium
pumps return the cell to a
resting state by actively
pumping (3) Na+ out of
the cell and (2) K+ into
the cell.
•
http://www.brookscole.com/chemistry_d/temp
lates/student_resources/shared_resources/a
nimations/ion_pump/ionpump.html
An action potential will continue down a
neuron until it reaches the axon terminal.
Direction of a nerve impulse: travels from the dendrites to the
axon terminal
• At the
axon
terminal of
a neuron
there is
either 1.
another
neuron, 2.
a gland
cell, or 3. a
muscle
* However, neurons don’t actually touch cell.
other cells regardless if that cell is
another neuron, a gland cell, or a muscle
cell.
Synapse: The space between neurons
(because neurons don’t touch).
Synapse Animation
• Here’s what happens at the synapse:
• http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/s
ynapse.htm
Neurotransmitters
• They trigger Na+ channels to
open so the sodium ions
diffuse into the neuron.
Na+ channel closed
The red dot are
neurotransmitters sitting on
the sodium channels
The black dots are Na+
ions
Na+ channel open
http://www.ship.edu/~cgboeree/actionpot.html
Examples of neurotransmitters
• Acetylcholine: Neuron to
muscle
• Muscle Contractions;
stimulates neurons
• Dopamine: Neuron to
neuron
• Associated with the
pleasure center of the
brain; involved in feelings
of enjoyment in regards
to food and sex.
• Certain drugs cause the
release of dopamine or
inhibit its reuptake.
• Serotonin: Neuron to
neuron
• Involved in sexuality and
appetite.
• An imbalance can lead to
depression and
bipolarism.