Download Neural Pathways

Neural Pathways
• information is carried via chains of
neurons
• neurons secrete chemicals that cause
changes in adjacent neurons
• chemicals travel between the axon of
one neuron and the dendrites of
another
Nerve Impulses (Action Potentials)
• routes traveled by nerve impulses are
called neural pathways
• one type of neural pathway is a reflex arc
• the simplest and quickest
• consists only of 2 neurons
• bypasses the brain
impulse generated by stimulus
-pres., temp.,
chem. changes
dendrites of sensory neuron
axon of sensory neuron
synapse (space b/w 2 neurons) -chemical signals
sent across gap
dendrites of motor neuron
axon of motor neuron
synapse
effector organ
-muscle that puts nerve
signals into effect
reflex (quick, jerky response)
How Do Impulses Travel?
-like a spark along a fuse, or
like a volleyball :)
1. membrane of the neurons has a positive
charge on the outside (excess Na+) and
a negative charge on the inside
2. when stimulated, Na+ channels open
temporarily becomes + and
and Na+ rushes in -inside
outside 3. channels then automatically close very
quickly, but this causes the neighboring
channels to open
4. it proceeds like a wave along the
membrane to the tip of the axon
5. then it arrives at the synapse
** when an impulse encounters a section
covered with myelin, it jumps over it –
saltatory conduction **
What Happens When an
Impulse Arrives at a Synapse?
Synapse
• where the axon of one neuron meets
the dendrites of another (empty
space)
1. when an impulse reaches the synaptic
-of the
knob, neurotransmitters are released
presynaptic
into the synaptic cleft
neuron
-from vesicles
2. neurotransmitters initiate an impulse in
the postsynaptic neuron and will then
cause the Na+ channels to open in that
neuron (excite)
-by binding to the proteins
3. the impulse will continue thru the axon
** some neurotransmitters may inhibit the
impulse (stop conduction) and NOT
open up the Na+ channels**
Examples of
Neurotransmitters
1. Endorphins
• inhibit conduction of pain impulses
-release of these increases during exercise
2. Serotonin, Norepinephrine, Dopamine
• conduct pleasurable impulses
• if there is a serotonin deficiency, may
lead to depression
• serotonin reuptake inhibitors (SSRI’s)
-blocks the uptake of serotonin back into presynaptic knob
2-Neuron Reflex Arc
volleyball
students