Transcript Neural transmission

Neural transmission
Beauty in the nervous system?
The Neuron is the Fundamental “working unit” of the
nervous system
In most respects the neuron is
like other cells of our body
But is different in that it can produce
electrical impulses near its cell body region
That move down the axon and lead to the release
of specialized neurochemicals (neurotransmitter
substances) at the Synapse
Synaptic release of Neurotransmitter substances
may in turn affect “postsynaptic” neurons; mostly in
the dendritic regions
Historical perspective:The
“Reticular Theory
• The nervous system was thought to be a
continuous network of fibers…no
individual cells
The “Golgi stain” helped us to
visualize individual neurons
And led to: The Neuron Theory
There are many types of neurons:Some
common types of neurons
This is our “Model Neuron”
The Neuron is also different in that the axon
is typically myelinated by “glial cells”
The Shwann cell
Oligodendrocytes ( a member of the
glia family)
There are many types of glial cells: all are thought
to primarily provide support functions
The Neuronal communication process can
be thought of as an “electro-chemical” event
• How is the electric signal produced?
• How is the Chemical event produced?
The Neuron is Like a little battery
We use an Oscilloscope to
visualize electric charge
The resting Membrane potential
(RMP)
Ions are responsible for the charge
of a neuron
Cations +
Anions-
At Rest, ionic substances have different concentrations inside
vs. outside the neural membrane
Passive vs Dynamic neural
responses
Comparison Between Passive Potential and Active Potential
Description
Passive Potential
Active Potential
Amplitude
Graded with stimulus
intensity
Always the same size
Stimulation
Requires very little
Requires a 15-20 mV
change
Summation
Adds the stimuli strengths
Only one potential at a
time
Spread
Decay with distance
Actively regenerated
Duration
As long as the stimulus
Constant duration
Main channels used
Non-gated channels
Voltage-gated channels
Hyperpolarization and
Depolarization
• Hyperpolarization- makes the RMP more
negative
• Depolarization-makes the RMP more
positive
Comparison Between Passive Potential and Active Potential
Description
Passive Potential
Active Potential
Amplitude
Graded with stimulus
intensity
Always the same size
Stimulation
Requires very little
Requires a 15-20 mV
change
Summation
Adds the stimuli strengths
Only one potential at a
time
Spread
Decay with distance
Actively regenerated
Duration
As long as the stimulus
Constant duration
Main channels used
Non-gated channels
Voltage-gated channels
What is special
about “threshold?”
The forces of Diffusion:
Concentration Gradients
The forces of Diffusion
across a semi-permeable
membrane
Diffusion also occurs across
electrostatic gradients
The neural membrane is a semipermeable membrane
The Neurons membrane separates
the different ions
The membrane controls diffusion
By opening or closing
Ion channels
If ion channels are open; diffusion
across concentration and
electrostatic gradients will occur
Triggering the release of RMP
energy
• How does threshold depolarization trigger
a dynamic response?
– Changes membrane permeability
• Activating/opening ion channels
• -”Voltage-gated” Na+ ion channels
– Open only when a critical level of depol occurs
– Other ion channels then become involved
Refractory period
Once triggered, the AP is all or
none, and “one-way.”
Saltatory Propagation
Myelenation and size affect speed
Multiple sclerosis (MS) is a chronic, potentially debilitating disease that
affects the central nervous system, which is made up of the brain and
spinal cord. Doctors and researchers think the illness is probably an
autoimmune disease, which means that your immune system attacks
part of your body as if it's a foreign substance.
•
•
•
•
•
•
Multiple Sclerosis is an incurable debilitating disease of the central nervous
system. MS affects young to middle aged adults.
Approximately 4 million worldwide have this disease. 400,000 of these
people live in the United States. It can affect anyone, and can strike at
anytime without warning. Once you develop this disease it will be with you
for the remainder of your life, as there is no cure or known cause.
Multiple Sclerosis is a degeneration of the myelin sheath surrounding
nerves in the brain and spinal cord. The part of the body effected by this
disease is dependant on the nerves that are damaged.
Typical symptoms may include one or more of the following: loss of muscle
coordination, unsteadiness, fatigue, speech difficulties, vision degradation,
loss of bowel and bladder control and numbness in the extremities.
Many people with MS are unable to walk without assistance, requiring
wither canes, walkers or wheelchairs. A percentage are bed ridden and
unable to care for themselves in any way, required around the clock care.
Resetting the RMP
Action Potential at the
Terminals
The Synapse: PRESYNAPTIC and POSTSYNAPTIC
processes
PRESYNAPTIC Exocytosis
Excocytosis involves microtubules
Exocytosis
•
•
•
•
•
Voltage-dependent Ca++ channels
Ca++ influx
Vesicular migration
Vesiclular fusion
Release of NTs into synapse
NTs release into synapse
Classical NTs
NTs
Terminology
Acetylcholine/ACH
Serotonin/5-HT
GABA (gamma-amino-butyric acid)
Glutamate/Glu
Norpinephrine /NE
Dopamine /DA
Enkephalin/Endorphin
Post synaptic effects
Cholinergic
serotonergic
+/+/-
GABA-ergic
-
Glutamatergic
Adrenergic
Dopaminergic
+
+/+/+/-
Many other neurotransmitters are derived from precursor proteins, the so-called
peptide neurotransmitters. As many as 50 different peptides have been
shown to exert their effects on neural cell function.
POSTSYNAPTIC PROCESSES:
NT receptors
EFFECTS OF NTs?
Many factors, but all lead to:
• IPSPs: inhibiitory post synaptic potentials
– Hyperpolarization
– Decrease probability of action potential
• EPSPs: excitatory post synaptic potentials
– Depolarization
– Increase probability of action potential
Neural Integration
Neural Integration occurs mainly at axon
hillock and can occur spatially or
temporally
Axon Hillock
EFFECTS OF NTs?
• EPSP or IPSP
– Depends on receptor subtype
Most General division of NT
receptors- IONOTROPIC
RECEPTORS
Metabotropic Receptors
Effects depend on receptor subtype
And
circuits
NT-receptor interactions must stop!
Enzymatic degradation
Eg…
Effects of Nerve gas exposure
Neuromuscular
Effects
•Twitching
•Weakness
•Paralysis
•Respiratory
failure
Autonomic
Nervous
System Effects
•Reduced Vision
•Small pupil size
•Drooling
•Sweating
•Diarrhea
•Nausea
•Abdominal pain
•Vomiting
Central Nervous
System Effects
•Headache
•Convulsions
•Coma
•Respiratory
arrest
•Confusion
•Slurred speech
•Depression
•Respiratory
depression
Reuptake
Here are the SSRIs approved by the Food and Drug Administration (FDA)
specifically to treat depression, with their generic, or chemical, names followed by
available brand names in parentheses:
Citalopram (Celexa)
Escitalopram (Lexapro)
Fluoxetine (Prozac, Prozac Weekly)
Paroxetine (Paxil, Paxil CR, Pexeva)
Sertraline (Zoloft)
These medications may also be used to treat conditions other than depression.
Side effects of SSRIs
All SSRIs have the same general mechanism of action and side effects. However,
individual SSRIs have some different pharmacological characteristics. That means
you may respond differently to certain SSRIs or have different side effects with
different SSRIs.
SSRI possible side-effects
Side effects of SSRIs include:
Nausea
Sexual dysfunction, including reduced
desire or orgasm difficulties
Dry mouth
Headache
Diarrhea
Nervousness
Rash
Agitation
Restlessness
Increased sweating
Weight gain
Drowsiness
Insomnia
Drugs may affect neural
transmission in different ways