Transcript 1. Cell body - greinerudsd

The Neuron
An everyday
(every second!)
use of active
transport
The Nervous System
Controls and
coordinates
functions
throughout the
body and responds
to internal and
external stimuli.
What makes up the Nervous System?
• The basic unit of structure and function of the
nervous system is a neuron (nerve cell).
Structure of a Neuron
4. Myelin sheath:
insulating membrane
*increases speed of
impulse*
1. Cell body:
Contains the nucleus
and other cell
organelles
Nucleus
Axon terminals
1. Cell body
4. Myelin sheath
Nodes
3. Axon
3. Axon: long, thin extension of the cell
body
*Function: sends nerve impulses away
from the cell body*
(Remember “A” for away!)
2. Dendrites
2. Dendrites:
Short, branched
extensions of the cell body
*Function: receive stimuli*
3 Main Types of Neurons
1. Sensory Neurons (sensory = of the senses)
-send impulse from sense organs to spinal cord & brain
2. Interneurons (inter- = between)
-relay messages between sensory and motor neurons
3. Motor Neurons (motor = causing motion)
-send impulse from brain and spinal cord to effectors
(glands or muscles)
Which are sensory?
Which are motor neurons?
How do Neurons Communicate?
1. Dendrites receive the signal (action potential) which then
travels down to the axon of the first neuron.
2. When the signal reaches the end of the axon, the axon
releases chemicals called neurotransmitters.
ex. acetylcholine, norepinephrine, dopamine, serotonin
3. Neurotransmitters enter into the space between the 2
neurons, called the synaptic cleft.
4. Neurotransmitters bind to receptors on dendrites of the
next neuron thereby passing on the signal.
The Neuron
• The internal “solution” of the cell
has a characteristic concentration
of sodium versus potassium ions
• called: RESTING POTENTIAL
– More Na+ outside, more K+ inside
– Takes Energy to maintain this
• A signal is produced when this
internal “solution” changes
• Called: ACTION POTENTIAL
The Resting Neuron
When a neuron is at rest
– There is a certain amount of ions inside & outside of cell
– This difference in charges is called the resting potential (-70mV)
• The nerve cell membrane pumps sodium (Na+) out of
the cell and potassium (K+) into the cell
• Works by active transport
• Net result = more K+ inside the cell and more Na+ outside the cell
• The cell membrane leaks K+ back out of the cell
– Diffusion
– Causing the negative charge inside the cell
– Also, organelles inside contribute to the negative charge
The Moving Impulse
• An impulse begins when a neuron is stimulated by
another neuron or by the environment
– Causes movement of ions across the membrane
– Na + rushes in
 What kind of transport is this?
• This is called an
action potential
• Also called “depolarization (+30mV)
• Impulse travels down axon away from the cell body to
the axon terminal
• at 110 m/sec (225 mph)
• After impulse passes, K+ flows out of the cell
• “repolarization” (-70mV)
What is an action potential?
• A sudden reversal
of membrane
potential.
• “Resting” is when
the pump is active
• “Action” is when
the sodium is
diffusing into axon
Threshold
• Strength of impulse is always the same
– It is an all or nothing response
• Minimum level of stimulation to cause an
impulse is call the threshold
• What happens when the action potential
reaches the end of the axon?
The Synapse
The area where an
impulse is transferred
between 2 neurons
• Synaptic cleft
separates the axon
terminal from the
dendrites of the
adjacent neuron
The Synapse
• The terminals contain tiny sacs (vesicles) that
contain neurotransmitters
 chemical signals
• Impulse triggers release of neurotransmitters
into the synaptic cleft (via exocytosis)
– Neurotransmitters diffuse across gap & bind to
receptors on the adjacent neuron
– Cause the impulse to continue
(if threshold is reached)
• Neurotransmitters are either broken down or recycled
• This is where drugs interfere
The Synapse = junction between two neurons
Section 35-2
Direction of Impulse
Dendrite of
adjacent neuron
Axon
Vesicle
Receptor
Axon
terminal
Synaptic cleft
Neurotransmitter
How do Neurons Communicate?
1. Dendrites receive the signal (action potential) which then
travels down to the axon of the first neuron.
2. When the signal reaches the end of the axon, the axon
releases chemicals called neurotransmitters.
ex. acetylcholine, norepinephrine, dopamine, serotonin
3. Neurotransmitters enter into the space between the 2
neurons, called the synaptic cleft.
4. Neurotransmitters bind to receptors on dendrites of the
next neuron thereby passing on the signal.