Transcript The Nervous System

The Nervous System &
Neurons
Unit 9
Chapter 35-2
Overview of the Nervous
System
• STRUCTURES: brain, spinal
cord, & peripheral nerves (1)
• FUNCTION: Recognizes and
coordinates the body’s
response to changes in its
internal and external
environments (2)
Overview of the
Nervous System
• The ultimate
control of all the
organ systems
is done by the
nervous system.
A. Neurons
• Neurons are nerve
cells that carry
electrical impulses
through the body (3)
• Impulse = message
(4)
• Neurons are
classified according
to the direction an
impulse travels.
• 3 Types of Neurons
– 1. Sensory: carry impulses from sense
organs to the brain (5)
– 2. Motor: carry impulses from brain to
muscles & glands (6)
– 3. Interneurons: connect sensory and
motor neurons and process impulses (7)
Interneuron
Sensory Neuron
Motor Neuron
Reflex Arc
Sensory Neuron
Interneuron
Motor Neuron
• Structure of a Neuron (8)
Nucleus
Dendrites
Axon
terminals
Cell body
Myelin sheath
Nodes
Axon
– 1. Dendrites: receive impulses (9)
– 2. Cell body: contains nucleus &
cytoplasm, largest part of cell
– 3. Axon: transmit impulses away
from cell body (10)
– 4. Myelin Sheath: covering that
insulates the axon, sending the
impulse faster and give it a
whitish appearance (11)
– Neurons with axons that have myelin make up
“white matter” in the brain, while neurons without
myelin are called “gray matter”
– 5. Nodes: gaps in the myelin
sheath where membrane is
exposed
– Impulses jump from one node to
the next
– 6. Axon terminals: transmits
impulse (message) to next cell (12)
II. Transmission of an Impulse
• A nerve impulse is an electrical
message.
• At rest, no impulse is being sent.
• The neuron must be stimulated
(receive input) to send a impulse.
+
A. Resting Neuron
+ ---- +
+
• When resting, neuron is not transmitting an
impulse
– inside of cell has a net negative charge –
– outside of cell has a net positive charge +
• The cell membrane has Membrane Potential,
the potential to carry an electrical current
because there is a difference in charge
– The ions sodium (Na+) and potassium (K +) cause
the potential
(K+)
• Sodium-potassium pumps in the nerve cell
membrane pumps sodium (Na+) ions out of the
cell and potassium (K+) ions into the cell by
means of active transport.
• As a result, the inside of the cell contains
more K+ ions and fewer Na+ ions than the
outside.
B. Stimulated Neuron
• An impulse begins when a neuron is
stimulated by another neuron or the
environment
• The stimulated impulse must reach
threshold, the minimum impulse
strength needed to create a new
impulse (all or none)
• At the leading edge of the impulse,
gates in the sodium channels open
allowing positively charged sodium
(Na+) ions to flow into the cell.
• This reversal of charges is called the
nerve impulse or ACTION POTENTIAL
(13)
• As the action potential passes, gates
in the potassium channels open,
allowing potassium (K+) ions to flow
OUT of the cell
• This restores the negative potential in
the axon.
1.
The action potential continues to move
along the axon in one direction toward
the axon terminals.
At Rest
------------2.
Action Potential
++---------3.
----++----4.
---------++-
Action Potential
•
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter45/animations.html#
C. Synapse
• The synapse is at the end
of the axon terminals
where a neuron can
transfer an impulse to
another cell (14)
• The small space between
cells is the synaptic cleft
• Terminals contain
vesicles filled with
neurotransmitter
• Neurotransmitters are
chemical signals of
neurons that transmit
an impulse across the
synapse to another cell
(15)
• Ex: epinephrine,
norepinephrine,
acetylcholine,
histamine, seratonin,
dopamine, melatonin
Steps of Transmission
1. Action Potential reaches axon terminal
2. Causes Neurotransmitter to be released
into synaptic cleft
3. Neurotransmitter binds to receptors on
next cell.
4. Channels open, which can create a new
action potential
http://highered.mcgrawhill.com/sites/0072437316/st
udent_view0/chapter45/ani
mations.html#
Major Neurotransmitters &
Their Effects
Major Neurotransmitters &
Their Effects