Loading....
Coupon Accepted Successfully!

 

Sequence of events

  1. Arrival of message in form of Action potential.               
  2. Opening of voltage gated Ca2+ channels.
  3. Fusion of vesicles with cell membrane & exocytosis.       
  4. Development of Post synaptic potential. 
  5. Post Synaptic potentials are integrated at axon hillock.          
  6. A P in the axon of the Post synaptic neuron
  1. Postsynaptic potentials are either brief depolarizations or hyperpolarizations of postsynaptic membrane kept brief by reuptake (rapid removal of transmitter substance by terminal button) and enzymatic deactivation (enzyme destroys transmitter - occurs for acetyclcholine by way of acetylcholinesterase).
  2. Nature of postsynaptic potential depends on type of ion channel opened by postsynaptic receptors at particular synapse:

Excitatory potentials (EPSP)occur when Na+  or Ca2+ enters cell

Inhibitory potentials (IPSP) produced by opening of K+ or Cl- channels

EPSP

 

Type

Timing

Cause

Site

1. EPSP

Latency : 0.5 ms

Peak : 0.5 – 1.5 ms

Time Constant : 3 ms

Na/Ca influx

 

2. Slow

Latency : 100 – 500 ms

Lasts : Several Seconds

K efflux

AutonomicGanglia cardiac muscle, smooth muscle, cortical neurons

3. Late slow

Latency : 1-5 Sec

Lasts : 10 – 30 min

K efflux

Symp. Ganglia

IPSP

 

Type

Timing

Cause

Site

IPSP

Latency 0.5 ms

Peaks: 0.5 –1.5 ms

Time consistent: 3 ms

Cl influx

K efflux

Na/Ca closure

 

Slow

Latency 100 – 500 ms

Lasts : Several seconds

K efflux

Auto. Ganglia, cardiac muscle,smooth muscle,cortical neurons

Aid to Memory

  1. Timing of EPSP & IPSP : Same
  2. Slow EPSP & IPSP : cause is K+
  3. No late slow IPSP.

 Fast & slow responses & post ganglionic neurons in sympathetic ganglia:
 

EPSP Type

Duration

 NT

Receptor

1. Fast

30ms

Ach

Nicotinic

2. Slow

30 S

Ach

M2

3. Late slow

4 min

GnRH

GnRH

IPSP  Slow

2 S

Dopamine

D 2

Snare Proteins

Main proteins that interact to produce synaptic vesicle docking and fusion in nerve endings i.e Synaptobrevin (V- snare protein) in vesicle membrane locks with Syntaxin (t- snare protein) in cell membrane

 

1.  Tetanus Toxin     act on Synaptobrevin ,block presynaptic release of inhibitory neurotransmitter in spinal cord leading to SPASTICITY     
                                                        

2.  Botulinum Toxins


 

Uses: To relieve achalasia (in LES), to remove wrinkles (in facial muscles)

Properties of Synaptic Transmission

  1. Synaptic delay (0.5 ms)
  2. Spatial summation & Temporal summation
  3. Facilitation-subliminal fringe
  4. Occlusion
  5. Fatigue
  6. Synaptic plasticity (For memory & learning a)Post tetanic potentiation b)habituation(inactivation of Ca2+ channels, decreased response) c) sensitization d)Long term potentiation e)LTD - Long term depression

 


Receptors:

Receptors can be classified as:

               i.         Tactile receptors

              ii.         Thermo receptors

            iii.         Nociceptors

            iv.         Proprioceptors

 

Thermoreceptors and nociceptors

 

Thermoreceptors and nociceptors are mainly naked nerve endings.
Proprioceptors : are stimulated by changes of position of body

  1. Muscle spindle
  2. Golgi tendon organ
  3. Joint receptors
  4. Vestibular receptors
 

Receptors can be further classified as on the basis of receptor adaptation as

  • Rapidly Adapting
  • Slowly Adapting

Adaptation is decrease in frequency of action potentials despite the maintenance of a constant strength stimulus

  • Rapidly Adapting (or phasic )

These include:

o   Pacinian corpuscles

o  Meissner’s corpuscles

o  Krause’s end bulb

  • Slowly Adapting (or tonic)

These include:

o  Merkel’s disc

o  Ruffini endings

o  C-mechanoreceptors





Test Your Skills Now!
Take a Quiz now
Reviewer Name