NERVOUS SYSTEM: I

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• NERVOUS SYSTEM I
• L3
• Last lecture
• Generation and propagation of AP
• This lecture
• Synaptic transmission
• EPSP IPSP
• Importance of post synaptic neuronal integration
• Possible drug, disease and toxin effects on
  synaptic transmission

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Synaptic Transmission
Signal at synapse either excites or inhibits the
postsynaptic neuron Two types 1.Excitatory
synapse more Na and less Kchannel Excitatory
postsynaptic potential (EPSP) 2. Inhibitory
synapse K Cl- channels, Inhibitory
postsynaptic potential (IPSP)
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Diversity in synaptic form allows the nervous
system to achieve diversity and flexibility.
Meditation, for example is a complex
psycho-physiological behavior which presents an
enigma for physiologists. It utilizes the
existing brain circuits to generate a unique
perceptual-sensory experience (using EPSP IPSP
in controlled way). This results in varying
degree of somato-visceromotor relaxation.
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An excitatory postsynaptic potential (EPSP) is a
graded depolarization that moves the membrane
potential closer to the threshold for firing an
action potential (excitement).
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An inhibitory postsynaptic potential (IPSP) is a
graded hyperpolarization that moves the membrane
potential further from the threshold for firing
an action potential (inhibition).
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The membrane potential of a real neuron typically
undergoes many EPSPs (A) and IPSPs (B), since it
constantly receives excitatory and inhibitory
input from the axons terminals that reach it.
Feel impulse of the singer in this song Nobody
wanna see us together But it don't matter no
Cause I got you babe (by Akon from Konvicted
album)
All emotions, body activities are controlled by
both Eg surgeon, musician, magician, writer,
scientist, manager, student
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Chat with each other GP, AP, NT signaling
Axo-axonal communication (here, between A B)
can modify classical synaptic communication
(here, between B C) this can result in
presynaptic inhibition or presynaptic
facilitation.
Note the Terminal B must have receptorsfor the
signal released from A.
Convergence of input (one cell is influenced by
many others) Divergence of output (one cell
influences many others)
Brain 100B neuron 1014 synapses
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Importance of post synaptic neuronal integration
examples Letdown of milk EPSP brings about
collection of milk in the cisterns (collecting
ducts) IPSP occurs in presence of a stranger or
barking dog etc (mechanism is not understood
fully) Appearing for interview/examination
- involves both Neuronal Physiology of
Urination involves both (mechanism is understood
to some extent)
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Neuronal Physiology of micturition

• Urination is controlled by a postsynaptic neuron
• When neuron fires, bladder contracts
• As bladder starts to fill with urine and become
  stretched, a reflex is initiated that ultimately
  produces EPSP in postsynaptic neuron.

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EPSP-IPSP Urination...
As bladder becomes progressively filled,
frequency of AP is progressively increased in
presynaptic neuron that signals postsynaptic
neuron.
When frequency becomes great enough that the EPSP
are summed to threshold, the postsynaptic neuron
generates AP that stimulates bladder.
Partial filling of bladder does not cause
sufficient excitation, so no generation of AP and
no urination.
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EPSP-IPSP Urination...
If the time is inopportune
Under this situation IPSPs could be produced at
bladder postsynaptic neuron by presynaptic inputs
originating in higher levels of brain responsible
for voluntary control of micturition.
These voluntary IPSPs in effect cancel out the
reflex EPSP. The postsynaptic neuron remains at
resting potential and does not have an AP for
bladder contraction. (upto certain threshold)
Supplying urine sample for laboratory evaluation-
higher center generate EPSP to cause micturition
even the bladder is partially filled with urine.
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Possible drug, disease and toxin effects on
synaptic effectiveness
a) Altering the synthesis, axonal transport
(local anesthetics, polio, MS ), storage, or
release of a neurotransmitter (clostridium
botulinum toxin) b) Modifying neurotransmitter
interaction with the postsynaptic receptor
(a-bunagatoxin from cobra snake) c)
Influencing neurotransmitter reuptake (cocaine)
or destruction d) Replacing a deficient
neurotransmitter with a substitute transmitter.
http//news.bbc.co.uk/2/hi/science/nature/7608465.
stm
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• Examples of drugs that alter synaptic
  transmission
• Cocaine
• Blocks reuptake of neurotransmitter dopamine at
  presynaptic terminals
• Strychnine
• Competes with inhibitory neurotransmitter glycine
  at postsynaptic receptor site
• Tetanus toxin
• Prevents release of inhibitory neurotransmitter
  GABA, affecting skeletal muscles

Read article from this webpages http//www.drugs.c
om/enc/attention-deficit-hyperactivity-disorder-ad
hd.html http//news.bbc.co.uk/2/hi/health/6425977.
stm (Use of hyperactivity drug soars)