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Nervous System Basics:
Neurons
Ch. 40
I. Neuron Structure
A. Neuron- Basic unit of
nervous system
1. AKA Nerve Cell
2.Conduct impulses
B. Consists of a cell body,
dendrites and an axon
I. Neuron Structure
C. Dendrites
1. Branch off the cell body
2. Receives impulses and sends
them to the cell body
a. “Sensors/Feelers”
D. Cell Body (Soma)
1. Contains nucleus
2. Contains other organelles
3. Interprets impulse and sends it to
the axon
I. Neuron Structure
E. Axon
1. Conducts the impulses
2. AKA “Nerve Fiber”
3. Myelin Sheath- White, fatty
tissue layer that covers the
axon
a. Insulates & aides in
relaying impulses faster
I. Neuron Structure
E. Types of Neurons
1. Sensory Neurons
a. Takes nerve impulses
from sensory receptors in
the skin, eye, ear, etc to the
brain & spinal cord
I. Neuron Structure
2. Motor Neuron
a. Takes nerve impulses
from the brain & spinal
cord to muscles or
glands
I. Neuron Structure
3. Interneurons
a. Lie in between other
neurons
b. Ex: Between a sensory
neuron & a motor neuron
c. Located in spinal cord
and brain
II. Relaying an Impulse
A. Shoulder Tap
1. Sensors in the skin “feel”
the tap.
2. Sensory neurons send an
impulse to the brain.
3. The brain interprets the
message.
II. Relaying an Impulse
A. Shoulder Tap (cont.)
4. The brain sends a
response down a motor
neuron to neck muscle.
5. The muscles contracting
in the neck cause the head
to turn.
II. Relaying an Impulse
B. A Resting Neuron
1. Potassium ions (K+) and
sodium ions (Na+) inside
and around the axon
membrane are involved in
transmitting impulses
II. Relaying an Impulse
2. Na+/K+ Pump
a. Uses active transport to
move 3 Na+ out for every 2 K+
that goes in.
b. This causes the inside of
the neuron axon to be slightly
more negative than the
outside.
II. Relaying an Impulse
c. The membrane is said
to be polarized.
R est
N
P eace
=
=
=
Resting neuron
Negative charge
“Poloarized”
II. Relaying an Impulse
C. Transmitting the Impulse
1. When a stimulus excites
an neuron, gates in the
axon membrane open and
let Na+ move in.
a. This causes the inside
to change to a slightly
positive charge
II. Relaying an Impulse
b. This change in charge is
called depolarization.
c. As depolarization occurs,
the Na+/K+ pump works to
return the axon to its resting
state
1) This is called
repolarization
2) See website
II. Relaying an Impulse
d. The gates don’t open at
the same time, they open as
the impulse moves down
the axon.
1) Wave-like
2) See website
II. Relaying an Impulse
D. Speed of Impulses
1. Myelinated neurons are
much faster
a. myelinated: 100 m/sec
b. nonmeyelinated: 10 m/sec
2. The impulse actually jumps
from one node of ranvier to the
next
III. Connecting Neurons
A. Neurons lie axons to
dendrites (end of one to
beginning of the next), but
they don’t actually touch.
1. Synaptic Cleft- The gap
between two neurons
III. Connecting Neurons
B. When the impulse reaches
the axon terminal (end),
neurotransmitters are
released into the synaptic
cleft.
1. Acetylcholine (muscle)
2. Norepinephrine (neurons)
III. Connecting Neurons
C. When the neurotransmitter
reaches the dendrites of the
next neuron, it signals it to
open the Na gates and send
the impulse down the axon.
RECAP
-What is a neuron?
-What are the main parts of a
neuron?
-What are the types of neurons?
-What is the charge of the inside
when a neuron is resting
RECAP
-What are the steps in
transmitting an impulse?
-How does the message of the
impulse get across the
synaptic cleft?