what is Synaptic plasticity

The changes that may occur in synaptic function after repeated stimulation is called plasticity. The effects may be either facilitation or inhibition.

Only chemical synapses exhibit plasticity, which appears to be due to functional and anatomical modifications of the synapse or both. These changes may be presynaptic or postsynaptic. Functional alterations are typically short term and involve changes in the effectiveness of existing synaptic connections, e.g.. increased release of neurotransmitter. This helps in short-term memory. Anatomical alterations are long term and consist of growth of new synaptic connections between the neurons. This helps in permanent memory.

1. Post Tetanic Potentiation or Facilitation (PTP)

When an excitatory presynaptic neuron is stimulated for a short time by a tetanizing current, the synapse becomes more excitable after cessation of the stimulus. There is an increase in postsynaptic potentials. This hyper excitable state lasting for few minutes to hours is called PTP. It is due to accumulation of large amounts of Ca” ions in the presynaptic endings, which in turn is caused by tetanizing current. The excess Ca” acccumulated in the presynaptic terminal facilitates trans- mission by increasing transmitter release. PTP participates in short-term me

2. Long-Term Potentiation (LTP)

It appears to be due to prolonged increase in excitability of the synapse following a brief tetanic stimulation of presynaptic afferents. This response may last a few days to few months. This appears to be due to:
a) An increase in glutamate release from presynaptic nerve endings due to persistent entry of Ca” ions.
b) An increase in Ca” influx into the postsynaptic nerve terminal, which activates various calmodulin-dependent enzymes that participate in neurotransmitter synthesis in the postsynaptic neuron.
c) Nitric oxide (NO) produced in the postsynaptic nerve terminal, diffuses into the presynaptic nerve terminal and enhances further release of glutamate from the presynaptic terminal and further facilitates LTP.
d) LTP is commonly seen in the hippocampal neurons and appears to participate in permanent memory.

3. Habituation or Fatigue

Repeated application of a stimulus sometimes causes the response to disappear. This type of response is called habitu- ation. This is brought about by gradual inactivation of Ca” channels and consequent reduction in the release of a neu- rotransmitter. This is also referred to as synaptic fatigue.

4. Sensitization

When a habituated stimulus is coupled with a noxious stimu lus there is an increase in the postsynaptic response. This is referred to as sensitization and is due to increased level of cyclic AMP via an increase in Ca” levels in the postsynaptic neuron. This response is transient but can be prolonged when the stimuli are repeated.

5. Long-Term Depression

Long-term depression may appear with repeated stimulation of inhibitory afferent inputs. LTD is just the opposite of LTP described earlier. This may be due to either partial or total inactivation of the Ca” channels. Nitric oxide (NO) appears to cause LTD in cerebelkam and LTP in hippocampus.

upper motor neuron lesion v/s lower motor lesion

Upper Motor Neuron Lesion:

  1. Damage occurs to the neurons that extend from the brain to the spinal cord.
  2. Results in spasticity or hypertonicity of muscles due to increased muscle tone.
  3. Causes hyperreflexia or exaggerated reflex responses.
  4. Can cause clonus or rhythmic contractions of a muscle in response to a stretch.
  5. Can result in Babinski sign or dorsiflexion of the big toe and fanning of the other toes upon stroking the sole of the foot.

Lower Motor Neuron Lesion:

  1. Damage occurs to the neurons that extend from the spinal cord to the muscles.
  2. Results in flaccidity or hypotonicity of muscles due to decreased muscle tone.
  3. Causes hyporeflexia or decreased reflex responses.
  4. Can cause muscle atrophy or wasting away of muscle tissue.
  5. Can result in fasciculations or involuntary twitching of muscle fibers.

sympathetic v/s parasympathetic system

Sympathetic Nervous System:

  1. Activated during “fight or flight” response to stress or danger.
  2. Increases heart rate, blood pressure, and respiration.
  3. Diverts blood flow away from digestive organs and towards skeletal muscles.
  4. Releases epinephrine and norepinephrine from adrenal glands to enhance the body’s response to stress.
  5. Dilates pupils and inhibits salivation.
  6. Stimulates glucose release from liver.

Parasympathetic Nervous System:

  1. Activated during periods of rest and relaxation.
  2. Decreases heart rate, blood pressure, and respiration.
  3. Increases blood flow to digestive organs.
  4. Promotes digestion and absorption of nutrients.
  5. Stimulates salivation and tears.
  6. Constricts pupils.
  7. Contracts bladder during urination.

spasticity v/s rigidity


  1. Increased muscle tone due to damage to the upper motor neurons in the brain or spinal cord.
  2. Results in stiff, tight muscles that can’t be easily moved.
  3. Often associated with hyperreflexia, or exaggerated reflex responses.
  4. Can cause muscle spasms or sudden, involuntary muscle contractions.
  5. Often seen in conditions such as stroke, cerebral palsy, and multiple sclerosis.


  1. Increased muscle tone due to damage to the basal ganglia or related brain regions.
  2. Results in resistance to passive movement, as if the muscles are locked in place.
  3. Often associated with hyporeflexia, or decreased reflex responses.
  4. Can cause cogwheel rigidity, or a ratchety feel to passive movement due to intermittent resistance.
  5. Often seen in conditions such as Parkinson’s disease and other movement disorders.

REM v/s NREM sleep

REM sleep

  1. Rapid Eye Movement (REM) sleep is characterized by rapid eye movements and vivid dreaming.
  2. The brain is highly active during REM sleep, with patterns similar to those seen during waking hours.
  3. Muscle tone is greatly reduced during REM sleep, leading to temporary paralysis of voluntary muscles.
  4. Heart rate and breathing become irregular.
  5. Typically makes up around 20-25% of total sleep time in adults.

NREM sleep

  1. Non-Rapid Eye Movement (NREM) sleep is divided into three stages of progressively deeper sleep.
  2. During NREM sleep, brain activity slows and becomes more synchronized.
  3. Muscle tone is generally maintained during NREM sleep, although it may be reduced in deeper stages.
  4. Heart rate and breathing become slower and more regular.
  5. Typically makes up around 75-80% of total sleep time in adults.

superficial v/s deep pain

superficial pain

  1. Originates from receptors located in the skin, mucous membranes, and other superficial tissues.
  2. Often described as sharp, prickling, or burning.
  3. Typically well-localized to the site of tissue damage.
  4. Can be triggered by a wide range of stimuli, such as temperature changes, chemical irritants, or mechanical pressure.
  5. Generally fades relatively quickly once the stimulus is removed.

deep pain

  1. Originates from receptors located in deep tissues such as muscles, tendons, and joints.
  2. Often described as dull, aching, or throbbing.
  3. May be poorly localized or difficult to pinpoint.
  4. Can be triggered by tissue damage, inflammation, or other types of stress or strain on the tissues.
  5. May persist even after the stimulus is removed.