Synapses Flashcards
Features of synapses
- One way conduction
- Synaptic delay
- Summation
- Fatigue
- Occlusion
- Subliminal fringe
- Facilitation
- Divergence
- Convergence
- Reverberatory circuits
Anatomical classification of synapses
- Axoaxonic
- Axodendritic
- Axosomatic
Chemical classification of synapses
- Electrical
- Chemical
- Conjoint
Electrical synapses found in
cardiac muscle fibres
smooth muscle fibres of intestine
epithelial cells of lens of eye
Synaptic delay time
0.5msec for 1 synapse
Define summation
Facilitated response to repeated stimuli applied simultaneously or one after another
Properties of EPSP/IPSP
- can be summated
- local response
- does not get propagated
- does not follow all-or-none law
- due to opening of ligand gated Na+ or Ca+2 influx or closure of K+ channels for EPSP
- due to Ca+2 influx or K+ efflux or closure of Na+ channels for IPSP
Divergence is found in
- Reticular Activating System
- SNS
- Focal epileptic seizures
Convergence is found in
- Anterior horn cells
- Sensory tracts
- Retinal to visual cortex
Define reverberatory circuits and examples
Activity in neuronal circuits continues for longer periods even after cessation of stimulus
- Short-term memory
- Smooth decline and termination of movement
Define plasticity
- Changes that occur in synaptic function after repeated stimulus
- may be excitatory or inhibitory
- only by chemical syn.
- due to functional or anatomical modifications
- pre/post synaptic changes
Mechanisms of synaptic plasticity
- PTP
- LTP
- Habituation/Fatigue
- Sensitization
- Long term depression
PTP
When an excitatory presynaptic neuron is stimulated for a short time by tetanizing current, the synapse becomes more excitable after cessation of stimulus.
- inc. in post synaptic potentials
- due to accumulation of lots of Ca+2 in presynaptic endings
- helps in short term memory
LTP
Appears due to prolonged increase in excitability of synapse after brief tetanic stimulation of presynaptic afferents
- inc. glutamate release
- inc. Ca+2 influx into post syn. terminal
- NO produced in post syn. diffuses into pre syn. terminal to stimulate glutamate release
- permanent memory (hippocampal neurons)
Habituation
Repeated application of stimulus causes response to disappear.
Due to gradual inactivation of Ca+2 channels and reduction in NT release
