Download Types of neurons

Neurons and Impulses
Types of Neurons
Sensory
Motor
Interneurons
WAKE UP!!!
Sensory Neurons

INPUT carry signals from the outer parts of
your body (periphery) to the brain and spinal
cord (central nervous system)
Brain
Sensory
Neuron
Spinal
Cord
Motor Neurons

OUTPUT From the brain and spinal cord to
the muscles, glands and skin.
Interneurons

Interneurons
connect various
neurons within the
brain and spinal
cord.
Sensory
Neuron
Brain
Spinal
Cord
Motor
Neuron
Mirror Neuron
A mirror neuron is a neuron that fires both
when an animal acts and when the animal
observes the same action performed by
another – wikipedia, 2012
(http://en.wikipedia.org/wiki/Mirror_neuron)
Structures of a neuron
The cell body
Contains the cell’s Nucleus
 Round, centrally located
structure
 Contains DNA
 Controls protein
manufacturing
 Directs metabolism
Dendrites
Information
collectors
 Receive inputs from
neighboring
neurons
 Inputs may number
in thousands
 If receives enough
inputs the cell’s
AXON may
generate an output

Dendritic Growth
Mature neurons
generally can’t
divide
 But new dendrites
can grow
 Provides room for
more connections
to other neurons
 New connections
are basis for
learning

Axon
The cell’s output
structure
 One axon per cell, 2
distinct parts

 tubelike structure
branches at end that
connect to dendrites of
other cells
Myelin sheath
White fatty casing on
axon
 Acts as an electrical
insulator
 Not present on all
cells
 When present
increases the speed
of neural signals
down the axon.

Myelin Sheath
How neurons communicate
Neurons communicate by means of an electrical
signal called the Action Potential (AP)
 Action Potentials are based on movements of
ions between the outside and inside of the cell
 When an Action Potential occurs a molecular
message is sent to neighboring neurons
 Action Potential


Calcium Gated Channels = AP
Ion concentrations
Outside of Cell
K+
Na+
Cl-
Cell Membrane in resting state
K+
Na+
Cl-
Inside of Cell
A-
The Cell Membrane is Semi-Permeable
K+
Na+
Cl-
Outside of Cell
Cell Membrane at rest
K+
Na+
ACl-
Inside of Cell
Potassium (K+)
can pass through
to equalize its
concentration
Sodium and
Chlorine cannot
pass through
Result - inside is
negative relative
to outside
- 70 mv
Resting Potential

At rest the inside of the cell is at -70 microvolts
With inputs to dendrites inside becomes more positive
if resting potential rises above threshold an action potential starts to
travel from cell body down the axon
Figure shows resting axon being approached by an AP

Soduim-Potassium Pump



Neuron to Neuron
Axons branch out
and end near
dendrites of
neighboring cells
 Axon terminals are
the tips of the axon’s
branches
 A gap separates the
axon terminals from
dendrites
 Gap is the Synapse

Dendrite
Axon
Cell
Body
Synapse

axon terminals
contain small
storage sacs
called synaptic
vesicles
vesicles contain
neurotransmitter
molecules
Sending
Neuron
Axon
Terminal
Synapse
Neurotransmitter Release

Action Potential causes vesicle to
open
 Neurotransmitter released into
synapse
 Locks onto receptor molecule in
postsynaptic membrane
Locks and Keys

Neurotransmitter molecules
have specific shapes
 Receptor molecules have
binding sites
 When NT binds to
receptor, ions enter
positive ions (NA+ )
depolarize the neuron
negative ions (CL-)
hyperpolarize
Some Drugs work on receptors
Some drugs are
shaped like
neurotransmitters
 Antagonists : fit the
receptor but poorly
and block the NT

 e.g. beta blockers
 Agonists : fit
receptor well and
act like the NT
e.g. nicotine.
Summary








3 types of neurons
The cell membrane
Ion movements
Action potentials
Synapse
Neurotransmitters
Receptors and ions
Agonists and
antagonists