Resting Membrane Potential

Resting Membrane Potential
Definition
A typical neuron at rest is more positive electrically outside than inside the cell membrane. This net difference in charge between the inner and outer surface of a non conducting neuron is -65mv is called the Resting Membrane Potential.
Factors Involved in Resting Membrane Potential
This popularity is due to the unequal distribution of ions across the neurolemma. The major factors which are involved in resting membrane potential are
Sodium and Potassium Ions

• There is a greater concentration of sodium ions outside than inside the membrane.
• Similarly potassium ions are concentrated muscle inside than outside the membrane.
• This is attributed to the activity of ATP driven sodium potassium pump in the neurolemma.

Action Potential
Definition
When neuron is stimulated reversal of the polarity of the neurolemma occurs, first changes to +40mv and then restores to -65mv again is called Action Potential.

This action potential is extremely rapid as it occurs in a few milliseconds.
Factors Involved in Action Potential
Sodium and Potassium Ions

• The change in potential across the membrane is due to the presence to sodium and potassium channels in the neurolemma.

Changes Associated with Action Potential
Sequence of membrane potential changes associated with an Action Potential.

• Resting Potential
• Sodium gates open and Na+ diffuses into the cell causing a depolarization of the membrane from negative to zero and then proceeds upto +40mv.
• Sodium gates close and potassium gates open.
• K+ diffuses out, causing a repolarization of the membrane.
• Sodium potassium pump restores original ion gradients and resting potential.

Propagation of the Impulse
Definition
When the action potential develops and spreads along the entire length of neurolemma, it is called propagation of nerve.
Synapse
Definition

The region where the impulse moves from one neuron to another is called a Synapse.
Components of Synapse
It consists of three components
1. Pre Synapting Membrane
2. Synaptic Cleft
3. Post Synaptic Membrane
1. Pre Synaptic Membrane
The membrane of axon terminal is called Pre Synaptic Membrane.
2. Synaptic Cleft
The narrow space between neurons is called Synaptic Cleft.
3. Post Synaptic Membrane
The membrane of dendrites of another neuron is called Post Synaptic Membrane.
Motor End Plate
When it is the membrane of muscle cell it is called motor end plate.
Neurotransmitter
The chemicals present in the vesicles which are released at the axon ending of the neurons, at synapse are called Neurotransmitter.
Mechanism of Impulse Through Synapse

• When an impulse is reached at axon terminals, the calcium channels are opened.
• From synaptic cleft calcium ions are diffused into the calcium channels.
• Due to this synaptic vesicles fuse with the pre-synaptic membrane, causing the release of neurotransmitter molecules into the synaptic cleft.
• The neurotransmitter bind to the receptors on the post-synaptic membrane, which generate action potential in the post-synaptic cell.
• The neurotransmitters are then reabsorbed by the pre-synaptic cells for reuse.

Examples of Neurotransmitter
Many different types of neurotransmitter are known. These are acetylcholine, norepinephrine, glycine, gab a, serotonin, dopamine etc.
Evolution of Nervous System
In different group of animals two types of nervous systems can be recognized, which are
1. Diffused Nervous System
2. Centralized Nervous System
1. Diffused Nervous System
Diffused Nervous System is found in cnidarians and Echinoderms.
Nervous System of Hydra

• In these animals, no anterior and posterior ends is present and their body is radially symmetrical.
• The nerves cells are found in the form of network throughout the body.
• The flow of information is not highly directional and it diffuses in all directions.
• The transmission of impulses is slow because of synapses involved.
• There is no brain but the nerve cells constitute the nervous system.

2. Centralized Nervous System
Centralized Nervous System found to varying degrees in more complex organisms from platyhelminthes to chordates including humans.
Nervous System of Planaria

• In these animals, definite anterior and posterior ends is present and their body is bilaterally symmetrical animals.
• It consists of an anterior brains (a concentration of neurons) which is connected with the Sensory Organs.
• From the brain arise two cord like nerves running longitudinally through the body.
• The two nerve cords are connected with each other at several points through the transverse nerves.
• They co-ordinated the movement of the two lateral sides of the body.