Properties of synapse

1. ONE WAY CONDUCTION (BELL-MAGENDIE LAW)

According to Bell-Magendie law, impulses are transmitted only in one direction in synapse, i.e. from presynaptic neuron to postsynaptic neuron.

2. SYNAPTIC DELAY

During transmission of impulses via the synapse, there is a little delay in the transmission. This is called synaptic delay. This is due to the time taken for:

a) Release of neurotransmitter

b) Movement of neurotransmitter from axon terminal to postsynaptic membrane for mediator interaction with receptor

3. Action of the neurotransmitter to open the ionic channels in postsynaptic membrane

4. Mediator restoration.

The synaptic delay is one of the causes for the latent period of the reflex activity.

3. FATIGUE

The fatigue at the synapse is due to neuro-tansmitter substance, acetylcholine, level decreasing and mediator exhausting. After producing the action, this neurotransmitter is destroyed by acetylcholinesterase. Synapse is the mostly-fatigable structure in nervous system (compare: nervous fiber is practically non-fatigable).

4. SUMMATION

When many presynaptic excitatory terminals are stimulated simultaneously or when single presynaptic terminal is stimulated repeatedly, there is summation in postsynaptic neuron. This is called summation. Summation is of two types.

1) Spatial Summation

This occurs when many presynaptic terminals are stimulated simultaneously (for example, in central synapses).

2) Temporal Summation

It occurs when one presynaptic terminal is stimulated repeatedly. Also subliminal stimuli summation (3-5) to form EPSP can be proper example.

Thus, both spatial summation and temporal summation play an important role in the facilitation of response.

5. ELECTRICAL PROPERTIES

The electrical properties of the synapse are the EPSP and IPSP.

6. DECREASING TRANSFORMATION OF RHYTHM INTO FREQUENCY. 3-5 subliminal stimuli on entrance will give 1 action potential on exit.

7. To draw spine reflexes reflectory arcs, to call closage level.

Abdominal reflexes:

1. superior – it’s caused by puncture irritation of abdomen skin in parallel of rib arc; the reflexes arc is closed at D₆-D₈ segments of spinal cord (from D – dorsal);

2. intermediate – by similar irritation but at horizontal dimension at navel level; the reflexes arc is closed at D₉-D₁₀;

3. inferior- in parallel to groin plica; the reflexes arc is closed at D₁₁-D₁₂.

Plantar reflex - is a plantar flexion of foot toes as a response of puncture irritation of external plantar limb; the reflexes arc is closed at L5-S2 and is in sciatic nerve.

At injury of corresponding motor nerve and corresponding link of reflector arc the response reaction is decreased or disappeared (areflexy), muscular atony, atrophy are observed.

Biceps-reflex – is caused by irritation of muscle tendon above cubital joint by neurologic hammer. Answer reaction – hand flexion in cubital joint. The reflexes arc is closed at C₅-C₆. Afferent and efferent fibers are in muscular-cutaneous (skin) nerve structure.

Triceps-reflex- is caused by hammer shock on triceps-muscle tendon, on 1-1,5 cm upper of posterior process of ulna. Answer reaction- muscular contraction and antebrachium (fore-arm) extension. The reflexes arc is closed at C₆-C_8. The fibers are in medianus, radialis and muscular-cutaneous nerves.

Carpo-radialis reflex –is investigated by hummer shock onto awl-like processus of radius. Answer reaction – flexure in cubital joint and antebrachium pronation. Origin location: investigated person hand must be bended at obtuse angle in cubital joint; person’s examinated hand is supported by doctor’s hand at the locus between pronation and supination. The reflexes arc is closed at C₅-C₈. The fibers are in medianus, radialis and muscular-cutaneous nerves.

Knee jerk or patellar tendon reflex - is caused by light shock of hummer on musculus quadriceps femoris tendon. Answer reaction – tibia extension. The reflexes arc is closed at L₂-L₄. Sensor and motor fibers are in femoral nerve.

Чувствительное волокно – sensory (afferent) fiber.

Двигательное волокно – motor fiber

Задний рог серого вещества – grey substance posterior horn (corn)

Передний рог – anterior corn (horn)

Вставочный нейрон - associative neuron

Мышца – muscle

8. To draw pyramidal tract, to designate peripheral and central neurons.

Central or the 1^st neuron – pre-central gyrus, giant pyramids of Betz.

Peripheral neuron or the 2^nd – spine anterior corn.

9. To explain symptoms at pyramidal tract central and peripheral neuron damage.

Paralysis type	Central or spastic	Peripheral, sluggish or atrophic
Injuries location	Cortex motor projectional area or pyramidal fascicles	Spine anterior corn, peripheral nerves anterior fascicles and anterior fibers
Paralysis distribution	More often diffused	More often limited
Muscles tone	Hypertony, spasticity	Hypotony, atrophy
Reflexes	Deep reflexes are increased, abdominal and plantar are decreased or lost	Deep and skin reflexes are decreased or lost
Pathological reflexes	Some of them are present	Absent
Conjugating movement	Present	Absent
Degeneration reaction	Absent	Present

10. To draw superficial sensitivity conductive pathways.

Fig.22. Spinothalamic tracts and pathways for crude touch, pain and temperature sensations. Anterior spinothalamic tract carries crude touch sensation. Lateral spinothalamic tract carries pain and temperature sensations.

The 1^st neuron – spinal ganglion.

The 2^nd neuron – thalamus.

The 3^rd neuron – cortex post-central gyrus.

11. To draw prophound (deep) sensitivity conductive pathways.

Ways of Goll and Burdah.

Gracilis – of Goll, cuneatus or cuneate – of Burdah.

12. To call and to show reflexes of posterior brain that allows assessing cranial-cerebral nerves functions.

Corneal reflex – the investigated person looks up and towards. The investigator touches with thin paper strip to the inferior-exterior eyeside without touching the eyelashes. The reflex arc - orbital nerve (Vth pair ramus), pons, facial nerve. Decreasing or lost of corneal reflex is found out at trigeminal nerve, facial nerve, pons injuries, at shock, in course of narcosis.

Conjunctival reflex – is caused by touching to conjunctive. Answer reaction- eyelid close. Reflectory arc – see like at corneal reflex.

Superciliar reflex - is caused by hummer shock at superciliar arc limb. Answer reaction - eyelid closure. Reflex arc – orbital nerve, pons, facial nerve.

Mandibular reflex - the investigated person slightly opens his mouth. Masticatory muscles contraction is caused by hammer shock down on chip from one than from another side. Answer reaction – mandible lifting. This reflex can be absent under normal conditions.

13. What is the difference between static and static-kinetic reflexes of midbrain?

Static reflexes - tonic reflexes under resting conditions (while standing, sitting, head turns and inclinations, as well as arms movements, legs movements while sitting. Role: natural posture saving under rest.

Statho-kinetic reflexes – are realized at posture changings during movements and include:

• head straitening (from vestibular and skin receptors),

• trunk straitening (from skin proprioreceptors and skin receptors),

• Straitening, establishment reflexes (tone redistribution at posture changing).

Role: natural posture maintaining at movements.

14. Cerebellum. Probes of its functions assessment and injury main symptoms.