Nerve System

 

A) Mechanism :

1) Resting potential :

1. Na+/K+ pump at membrane pump 3Na+ out and 2K+ in the membrane using energy
2. Membrane is more permeable to K+ than Na+ at rest. The tendency of K+ diffuse out is more than Na+ diffuse in along the concentration gradient , forming inside negative and outside positive

2) Action potential :

Arrival of action potential , which higher than threshold value

↓

Membrane is more permeable to Na+

↓

Rapid influx of Na+ across the membrane, and it is even enhanced, and it is even enhanced the permeability

↓

Depolarization begin (reversal of charge), action potential begin

↓

Reversal of charge cause decrease in permeability of Na+ and increase in permeability of K+

↓

K+ ion flow out cause Repolarization

↓

K+/Na+ pump pump K+ in and Na+ out restore resting potential

3) Transmittion between neurone :

• Upon arrival of action potential, the neutrotransmitter is released in vesicle, it diffuse across the synaptic cleft for relaying information to the opposite side.
• The post-synaptic membrane possesses receptors to specifically combine with the neutrotransmitter, leading to increase of permeability of Na+, thus increase in membrane potential. As more neutrotransmitter substance arrive until sufficient depolarization occurs and exceeds the threshold value, action potential is generated.

4) Rate of Transmittion :

1. Temperature
2. Diameter
3. Myelinated

• Unmyelinated nerve transmit nerve signal as countinous spread ,which is smooth progressive movement
• In myelined nerve , the myelin sheat is resistant, the signal can only occur at node of Ranvier. Depolarization occur from one node to another node, which spread as discountinous spread.

B) Brain :

1) Spinal cord :

1. Sensory neurone relay sensory impulses from limb receptor via spinal nerve to brain.
2. Motor impulses and interneurons relay moter impulses from brain via spinal nerve to limb muscle.
3. Reflex action

2) Medulla :

1. Maintain homostatic in body

3) Cerebellum :

1. Muscle tone
2. Sensitivity of tendon
3. Sensitivity of Organs of balance in ears

4) Cerebrum :

1. Control of voluntary action (initate of action)
2. Site of sensation (final station)
3. Association
4. Learning and memory

C) ANS :

Comparsion between Sympathetic Nervous System and Parasymthetic Nervous System :

Sympathetic Nerve System	Parasympathetic Nerve System
-Close to spinal cord	-Close to effectors
-Short preganglionic fibres, Long postganglionic fibres	-Long preganglionic fibres, Short postganglionic fibres
-Many postganglionic fibres	-Many preganglionic fibres
-Wide area effect	-Restricted area
-Widespread effect	-localized effect
-Excitatory homeostatic effect	-Inhibitory homeostatic effect
-Mobilizing energy for emergency use	-Save energy and restore to rest state
-Dominating during stressful	-Dominating during rest
-Noradrenaline	-Acetylcholine