4d
Properties of synapse

1.convergence & divergence

2.Law of forward (1 way) conduction

  1. Susceptible to hypoxia
  1. Fatigue/ habituation
  1. Synaptic delay

6.summation

7.Occlusion

8 Subliminal fringe

  1. Plasticity

Convergence

When many presynaptic neurons
have synaptic connections with a
single post synaptic neuron

Divergence

1 presynaptic neuron may have
synaptic connections with
many post synaptic neurons

  • some presynaptic terminals
    release excitatory neurotransmitters
  • & some of them may release
    inhibitatory neurotransmitters
  • all these information
    (excitatory or inhibitory)
    are integrated
  • which decides
    the onward effect

This causes magnification of
the information

( info coming to 1 neuron
gets transmitted to
so many neurons)

  • in chemical synapses,
    impulse is always transmitted
    frm presynaptic
    terminal-to-postsynaptic terminal
    & never in the opposite direction
  • an impulse conducted
    antidromically
    up the axons of the
    ventral roots
    dies out after d
    epolarizing the cell bodies of
    the spinal motor neurons

Cause:
this is because

  • the presynaptic terminal has the
    neurotransmitter containing vesicles
    &
  • the postsynaptic terminal has
    the receptors

significance:

  • since axons conduct impulse
    in either direction with equal ease,
    the synapse makes a 1 way gate
    for impulse travel
    -this is necessary for orderly
    neural function

Synapses are more
susceptible to hypoxia
than the nerve

if there is lack of O2 & incr
in H+ ino conc.
the synaptic transmission is
effcted.

mechanism:

  • repeated stimulation
    of presynaptic neuron
    leads to decrease
    & finally disappearance
    of the postsynaptic response

cause:
due to

  • exhaustion of neurotransmitters
    ( as its synth is not as rapid
    as its release
    due to
    gradual inactivation
    of Ca2+ channels
    which decr the intracellular Ca2+
  • acclimitaion of waste products
  • refractiveness of the
    postsynaptic membrane
    to the neurotransmitter

fatigue is always
reversible
-after rest & nutrition

is the time taken required
for the passage of impulse
frm presynaptic to
postsynaptic terminal
normal- 0.5msec

cause:
time is required

  • for therelease of NT
  • for diffusion of NT thru the
    synaptic cleft to the
    postsynaptic membrane
  • for the action of NT on
    the postsynaptic membrane/
    for opening of ion channels
  • for the diffusion of ions, &
    changes in resting MP

ultimately-time is reqiured for
the development of AP

sinificance

  • conduction along
    a chain of neurons is slow
    -if there are many synapses in the chain
  • it's possible to determine if
    a given reflex pathway is
    monosynaptic or polysynaptic
    -by measuring the delay in
    transmission of impulse
    frm dorsal root to ventral root
    across the spinal Cord
  • require subminimal stimulation
    which produces EPSP

temporal
summation

spatial
summation

  • when 2 or more
    presynaptic neurons
    are stimulated with
    subminimal stimuli

the stimuli are
summated to produce
a response

  • if(one) presynaptic neuron
    is stimulated repeatedly
    with subminimal stimuli

the stimuli are
summated to produce
a response

(impulse frm
several neurons
at the same time)

( several impulse frm
one neuron
over time)

  • when 2 afferent excitatory nerves
    to a skeletal muscle are
    simultaneously stimulated,
    it is sometimes seen that
    the tension produced
    by the muscle is less than
    the sum of the tension
    produced by each
    stimulated seperately

this is because
some motor neurons
which are common to both
are excited maximally
when either is stimulated
seperately

they give no greater response
when they are
stimulated together

this decr in respose
is due to presynaptic fibers
sharing postsynaptic fibers

thus occlusion
is due to
afferent fibers overlapping
in their central distribution

  • the capability of
    being molded/changed
    depending on
    past experiences
  • when 2 afferent nerves
    to a skeletal muscle
    are stimulated at the same time,
    2 areas of depolarization
    are produced.

each depolarization
fully activates
a certain no.of neurons

these 2 depolarization
also causes
certain no.of neurons to
be stimulated subminimally

when both are stimulated
the subminimal stumuli
are summated
-to produce an AP

synaptic conduction
thus can be
increased(strengthened)
or
decreased(weakened)
upon past experience

these changes can be
presynaptic
or
postsynaptic
in location

& play an important
role in
learning & memory