Nervous Transduction

NERVOUS TRANSDUCTION

Haris Talha

SIGNAL TRANSDUCTION

Transduction in the nervous system typically refers to stimulus alerting events wherein a physical stimulus is converted into an action potential, which is transmitted along axons towards the central nervous system where it is integrated.

Electrical impulses jump from neuron to neuron in the brain through their branching nerve fibers. This movement of electrical potentials is called signal transduction.

MULTI DENDRITE NERVE

HOW IT IS GENERATED?

Depolarization:A decrease in the difference in voltage between the inside and outside of the 

neuron. Action Potential:

A short term change in the electrical potential that travels along a cell. Hyperpolarize:

To increase the polarity of something, especially the polarity across a biological membrane. Node of Ranvier:

A small constriction in the myelin sheath of axons. Salutatory Conduction:

The process of regenerating the action potential at each node of Ranvier.

NEURON NEURON or NERVE CELLS is defined as structural and functional unit of the nervous system. Neuron can be differentiated from other cells on the 2 basis. 1. Neurons has branches or processors called axons or dendrites 2. Neurons does not have centrosome

CLASSIFICATION Neurons are classified by 3 different methods:

A. Depending upon the number of poles

B. Depending upon functionC. Depending upon the length of axon

DEPENDING UPON THE NUMBER OF POLES

Base on the number of poles from which the nerve fiber arise , neurons are divided into three types

• Unipolar neurons• Bipolar neurons• Multipolar neurons

DEPENDING UPON THE FUNCTION

On the basis of function , nerve cells are classified into two types

• Motor or Efferent neurons • Sensory or Afferent neurons

Depending Upon The Length Of Axon

Under this classification the two types are present. Which are as follow:

• Golgi type 1 neuron• Golgi type 2 neuron

STRUCTURE

Neuron is made up of three parts 1. Nerve cell body 2. Dendrite

3. Axon Dendrites and axons forms the processes of neuron. Dendrites are short processes and the axon are long processes. Dendrites and axons are usually called nerve fibers.

NEURON THE FUNCTIONAL UNIT OF CNS

NERVE CELL BODYNerve cell body is also known as soma or perikaryon. it is irregular in shape. Like any other cell , it is constituted by a mass of cytoplasm called neuroplasm , which is covered by a cell membrane. The cytoplasm contains a large nucles , Nissl bodies , neurofibrils , mitochondria and golgi apparatus. Nissl bodies and neurofibrils are found only in nerve cells and not in other cells. Following are the organalles present in the cytoplasm:

• NUCLEUS• NISSL BODIES • NEUROFIBRILS• MITOCHONDRIA• GOLGI APPARATUS

DENDRITE

Dendrites are the branched process of neurons and it is branched repeatedly. Dendrites may be present or absent, if present it may be one or many in number. Dendrites has Nissl granules and neurofibrils.Dendrites transmits impulses towards the nerve cell body. Usually the dendrite is shorter than the axon

AXON

Axon is the longer process of the nerve cell. Each neuron has only one axon. Axon arises from axon hilock of the nerve cell body and it is devoid of nissl granules. Axon extend for a long distance away from the nerve cell body. length of longest axon is about 1 meter. Axon transmits nerve impulses away from the body.

ORGANIZATION & COVERING OF NERVE

Each nerve is formed by b bundles or groups of nerve fibers. Each bundle of nerve fiber is called a fasciculus. The whole nerve is covered by tubular sheath. which is formed by areolar membrane. This sheath is called epimeurium. Each fasciculus is covered by perineurium. And each nerve fiber is covered by endoneurium.

NERVE IMPULSE

• Nerve impulse is wave of electrochemical changes , which travel along the length of the neuron involving chemical reactions and movement of ions across the cell membrane.

MEMBRANE POTENTIAL

In neurons there are positive and negative ions, and a charge separating barrier is a plasma membrane. The

electrical potential that exists across a cell membrane is known as membrane

potential.

RESTING MEMBRANE POTENTIAL

When a neuron is at rest it is much more positive electrically outside then inside the cell membrane. The net difference in charge between inner side and outer side of a non-conducting neuron is called resting membrane potential. The major factors which are involved in resting membrane potential are as follows:

FACTORS

1.Sodium and potassium ions.2. Negative organic ions.3. Leakage of potassium ions from neurons.4. No conduction of nerve impulse.

SODIUM AND POTASSIUM IONS

Sodium ions are tenfold higher in concentration outside then inside the membrane surface. Potassium ions are twenty times more concentrated inside then outside. All the neurons have very active sodium and potassium pumps located in their cell membranes. By the splitting of ATP these pumps transport sodium and potassium out and potassium inside the cell, both against their concentration gradients. For every two potassium that are actively transported inward, three sodium are pumped out. So inside become more negative then the outside of the cell membrane or neurons.

NEGATIVE ORGANIC IONS

The large numbers or organic ions such as (proteins, organic acids etc) are much more inside then outside of the membrane, where they are only in negligible concentration. This makes inside of the neuron much more negative

LEAKAGE OF POTASSIUM IONS FROM NEURONS

The cell membrane is virtually impermeable to all ions except potassium. As the membrane is slightly permeable to potassium, some of it leaks out of the cell . the loss of this positive ion from the neuron by diffusion account for more negative charges inside then out side the cell membrane of neuron.

NO CONDUCTION OF NERVE IMPULSE

In unstimulated state the neuron has a membrane potential of approximately -70mV.

INITIATION OF NERVE IMPULSE

A nerve impulse is initiated by an appropriate stimulus applied at one end of tha neuron and it results in remarkable localized change in the resting membrane potential . It disappears for a brief instant and is replaced by a new potential called Action or Active membrane potential which is in the form of impulse. During this state, the inner membrane surface become more positive than outside. This change is so brief that only a portion os the neuron is in the active membrane potential state.

FACTORS

1.Sodium and potassium ions movement.2.Charges are reversed.3. Passage of Nerve Impulse.4. Membrane potential.

SODIUM & POTASSIUM IONS MOVEMENT

The passage of nerve impulse is associated with increase in permeability of Sodium ions moving inwards upsetting the potential momentarily, making the inside more positive than outside .Neurophysiologists believe that the increased permeability is due to opening of specific pores in the membrane ,termed “sodium gates” .when these gates open, sodium ions rush into neuron by diffusion . Some K+ moves out.

CHARGES ARE REVERSED The inner side of the cell membrane has excess of positive ions as its internal surface, and the outer surface become more negative.

PROPAGATION OF NERVE IMPULSE

During active membrane potential, the neuron conducts the impulse in the form of nerve impulse.

MEMBRANE POTENTIAL

Active membrane potential of +0.05 volts (+50mv) exists. These changes occur along the length of the neuron till the impulse reaches synapse. Soon after passage of the impulse, the resting membrane potential is restored by the movement of a small number of ions especially potassium moving out. This neuron now is ready to conduct another impulse.

SALTATORY IMPULSE

It may be added that in myelinated neurons the impulse jumps from node to node. This is called Saltatory Impulse.

SYNAPSE

INTRODUCTION

Synapses are bridges Function of the synapse is to transfer electric activity (information) from one cell to another The transfer can be neuro-neuro or neuro-myo

PARTS OF SYNAPSE

Synapses consist of 3 parts: Pre synaptic end Synaptic cleft Post synaptic end

PRE-SYNAPTIC END

Efferent end of the synapseAxonPresynaptic end knobPresynaptic membrane

SYNAPTIC CLEFT

Intermediate zone between the two synaptic knobs Comprises of:

Synaptic gap Neurotransmitters

POST-SYNAPTIC END

Post synaptic membranePostsynaptic receptors Either muscle or postsynaptic knob

EVENTS OF TRANSMISSION

Calcium channels open

Neurotransmitter released

Receptors at post synaptic membrane activated

sodium channels open

Nerve impulse arrives

Nerve impulse is regenerated

DIFFERENCE BETWEEN SYNAPSEAND NEUROMUSCULAR JUNCTION

Structural difference NeurotransmittersInhibition and excitatory

NEUROTRANSMITTERS DEFINATION: Neurotransmitter is a chemical substance that acts as a mediator for the transmission of nerve impulse from one neuron to another neuron through a synapse. FUNCTION: The neurotransmitters are stored in tiny sac-like structures called vesicles at the end of axons. When an impulse, or nerve signal, reaches the end of the axon, the vesicles release a neurotransmitter into the small space between the adjoining cells (synaptic gap). Neurotransmitters diffuse across the synapse and bind to receptors in the receiving cell that are specific for the neurotransmitter.

IMPORTANT NEUROTRANSMITTERS

Acetylcholine. Serotonin. Dopamine. Norepinephrine. Tryptophan.

ACETYLCHOLINE Location:

1. Neuromuscular Junctions 2. CNS

Function: 1. Muscle Control 3. Sensory Response 2. Memory Formation 4. Excitatory

Receptors: 1. Nicotinic 2. Muscurinic

SEROTONINLOCATATION: 1. Gut 2. CNSFUNCTION: 1. Intestinal movement control 2. Mood regulation 3. Apitite 4. Sleep 5. Muscle controlRECEPTORS: 5-HT

DOPAMINE

LOCATION: Hypothalamus FUNCTION: 1. Voluntary motion 2. cognition 3. reward pathways RECEPTORS: D1 , D2 , D3 , D4 , D5

NOREPINEPHRINE

LOCATION: Adrenal Medulla FUNCTION: Fight or flight responce (increased heart beat , increased glucose level , increase oxygen to brain and muscles) RECEPTORS: Adrenergic

TRYPTOPHAN

LOCATION: Blood FUNCTION: Precursor to serotonin RECEPTORS: N/A

THE END

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