Download 2. Peripheral Nervous System

Honors Biology
Powerpoint #3
Unit 8 – Chapter 35
The Senses Activities
 Brain
 Spinal
Cord
 Peripheral Nerves:
Neurons
 Coordinates
the body’s response
to changes in its internal and
external environments.
Relays messages, processes
information and analyzes information.
 Includes:

◦ Brain
◦ Spinal Cord

Sensory Division:
transmits impulses
from sense organs to
central nervous system.
◦ What are sense
organs?
 Organs designed to
pick up stimuli.
 (ie eyes, ears, nose,
skin)
 Motor
Division: transmits
impulses from the central nervous
system to muscles.
 Network
of Neurons makes up the
peripheral Nervous System.
sensory receptor (sensory input)  integration  (motor output)  effector
1.
Sensory Input
triggered by stimuli
conduction of signals to
brain
2.
Integration
interpretation of sensory
signals by brain
3.
Motor output
conduction of signals to
effector cells (i.e.
muscles, gland cells)
reflex arc pdf

Sensory neuron
interneuron

Without brain processing
motor neuron

Dendrite - conducts “signal” toward the cell body -- [input
zone]
◦ often short, numerous & highly branched
◦ signal comes from sensory cell or neighboring neuron

Axon - usually a single fiber -- [conducting zone]
◦ conducts signal away from cell body to another neuron or effector cell

Axon Ending
◦ a cluster of branches (100’s to 1000’s)
◦ relays signal to next neuron / effector cell
How a nerve impulse is transmitted
1) Resting - The neuron is POLARIZED (-70mV)
There is a slightly negative charge on the inside, and a
positive charge on the outside
◦
◦
◦
◦
This balance is maintained by the sodium-potassium pump
Pumps Na+ (sodium) outside
Pumps K+ (potassium) inside
Some K+ sneaks back out through channels
How a nerve impulse is transmitted
2) Action Potential - stimulus causes opening of Na+
gates, allowing Na+ to rush in
•
This changes the neuron from polarized to de-polarized
•
This is all-or-none, meaning a stimulus must exceed a
threshold for the action potential to occur
How a nerve impulse is transmitted
2) Action Potential - stimulus causes opening of
Na+ gates, allowing Na+ to rush in
•
Intensity of the stimulus is based on the number of
neurons that exhibit action potential.
•
Speed on impulse based on diameter of axon &
amount of myelination.
How a nerve impulse is transmitted
3) Repolarization – K+ moves outside, Na+ stays
inside
◦ After inside flooded with NA+, K+ gates open and let K+
Out (while NA+ gates close)
4) Refractory period – When the Na+/K+ balance
returns to normal (K+ on inside and Na+
outside)
• During this time the neuron will not respond to
new impulses
•
•
Neurons DON’T touch
The gap between the axon of one neuron, and the
dendrites of another is called the SYNAPSE
1. Action potential happens
2. Neurotransmitter is released by axon ending
1. Neurotransmitter is a chemical that sends a
signal
3. Neurotransmitter binds to dendrite membrane
of next neuron
4. Excitation or inhibition of the membrane occurs
5. Neurotransmitter is ‘recycled’

Resembles chain of beads

Allows signal to travel faster because impulse “jumps”
from node of Ranvier to node of Ranvier (with myelin
sheath (225 mph / without 11 mph)