Mechanism of stimuli transmissio

Mechanism of Impulse Generation

Nerve Impulse

Unstimulated (resting) neurons have an electric charge across their cell membranes. The inside of the membrane is negative in comparison to the outside while it is at rest because positive and negative ions are concentrated on either side of the membrane. A nerve impulse is a localized reversal of charge on the membrane of a nerve cell that spreads like an electric current. An action potential is the name given to this abrupt electrical change in the membrane. As a result, an action potential or nerve impulse is a chain of quick-moving cellular events. Rapid movement of sodium and potassium ions across the cell membrane causes this electric change. The membrane quickly returns to its initial state after the reversal (in less than one thousandth of a second) so that it can be stimulated once more.

• Depolarization: Loss of polarization, more specifically, loss of the charge difference between the interior and exterior of a muscle or nerve cell's plasma membrane as a result of a change in permeability and the migration of sodium ions inside the cell.
• Repolarization: It describes the change in membrane potential that makes it go from a positive value to a negative value immediately following the depolarization phase of an action potential.
• Resting membrane potential of nerve fiber: Cellular resting membrane potential is the potential difference between the ions in a membrane's interior and exterior. There are -75 mV.
• Threshold potential: The minimum depolarization required to start an action potential in a membrane potential. It is -55 mV for the nerve fiber. In a nerve fiber, depolarization ends at +35 mV.

Synapse

The synapse establishes a functional connection with the membrane of another neuron. Synapses are specialized junctions used to transmit electrical impulses from one neuron to the dendrite (or cell body) of the following neuron. The synaptic deft, a tiny fluid-filled space between two neurons, exists. The actual location where an impulse is sent from one neuron to another is the synaptic cleft.

Mechanism of Stimuli Transmission

The simple movement of an action potential (nerve impulse) along a neuron is what constitutes the transmission of stimuli. Normally, a nerve impulse only travels in one direction. The movement of impulses from their source to their effector regions involves multiple neurons. The synaptic knobs, a tiny vesicle found at the ends of axons, are filled with neurotransmitters like dopamine and acetylcholine. Presynaptic neuron refers to the neuron that sends impulses to the synapse. The presynaptic neuron releases its neurotransmitter into the synaptic cleft between the cells in response to stimulation. The subsequent cell, known as the postsynaptic neuron, is stimulated by the neurotransmitter as a chemical signal (neuron that transmit signals away from synapse). Specialized spots, or receptors, are present on the receiving membrane, which is typically a dendritic, and are prepared to pick up and react to particular neurotransmitters. The postsynaptic neuron's receptors are then contacted by the neurons. This causes the following neuron to be stimulated, and the stimuli are transmitted from one neuron to the following. Because the electrical impulse "jumps" from node (space) to node in the myelin sheath rather than moving continuously along the fiber, a myelinated nerve fiber conducts impulses more quickly than an unmyelinated fiber of the same size.

Neurotransmitters

The chemicals released from a presynaptic neuron that connect with particular receptor sites on a post synaptic neuron are known as neurotransmitters. Each neuron communicates with other neurons using neurotransmitters. The three most important neurotransmitters are acetylcholine, norepinephrine, and epinephrine, often known as adrenaline, noradrenaline, and norepinephrine. The neurotransmitter released at the neuromuscular junction, or the synapse between a neuron and a muscle cell, is acetylcholine (Ach). The autonomic nervous system makes use of all three of the aforementioned neurotransmitters. Endocrine cells found in various organs throughout the body release a number of neurotransmitters, which are also hormones, into the bloodstream.

Reflex Arc (Reflex Action)

An automatic, predictable motor reaction to a particular stimuli is known as a reflex. Reflex actions include blinking of the eyes, jerking of the knees, and quick movement of the hand away from hot items. Both the brain and the spinal cord are integrated with these reflexes. Both internal and exterior stimuli are taken in, analyzed, and responded to as the nervous system works. Reflex arcs or reflex actions refer to a seamless transition from stimulus to response that occurs within the nervous system. This is the nervous system's fundamental functional pathway. A typical reflex arc has the following components:

• Receptor: A receptor is the end of a dendrite or a specific type of receptor cell, such as those found in a particular sense organ, that senses stimuli.
• Sensory neuron: A sensory neuron is a cell that sends impulses to the central nervous system.
• Inter neuron: Cells within the CNS that are located between neurons. These neurons can act inside the brain, transmit signals to various parts of the spinal cord, or transfer impulses to and from the brain.
• Motor neuron: A cell that transports impulses away from the central nervous system is a motor neuron.
• Effector: A muscle or gland that executes a response outside of the central nervous system.

A reflex arc can consist of just two neurons, one motor and one sensory, connected by a synapse in the central nervous system. Reflex arcs that simply need this few neurons are extremely uncommon. One of the few examples in humans is the knee-jerk reflex. Most reflex arcs in the central nervous system involve dozens or even hundreds of connecting neurons.