basic neurochemistry

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Basic Neurochemistry

Mr. Dharmesh Kheni

Training team

Presented by:-

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ORGANIZATION OF NERVOUS SYSTEM

NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM

AUTONOMIC NERVOUS SYSTEM SOMATIC NERVOUS SYSTEM

BRAIN SPINAL CORD

PARASYMPATHETIC SYMPATHETIC

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Brain

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The Neuron

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The Neuron

Axon

DendritesSoma

Axon Terminals

Myelin Sheath

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The Neuron

• Soma (cell body) – contains nucleus, cytoplasm, organelles

• Dendrites – receive info

• Axon – transmits info

• Myelin sheath – covers the axon to increase transmission speed (cause of sensory and motor disturbances in multiple sclerosis)

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Neuron

• Basic functional unit of nervous system

• Unique features of neuron:

– Excitability

– Conductivity

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What is a synapse?

• A synapse is the junction between 2 neurones.

• There is a very narrow gap of about 20nm between neurones called the synaptic cleft.

• A nerve impulse cannot cross the synaptic cleft, so nerve impulses are carried by chemicals called neurotransmitters.

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SYNAPSE

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Action Potential/Impulse conduction

• The information in neuron is passed from one to another in the form of nerve signal i.e. Action potential, which is due to its unique features of excitability and conductivity.

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Action Potential

• Nerve signals are transmitted by action potential

• Any stimulus - Mechanical

Physical

Biochemical

Sudden change in resting membrane potential

C

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Resting membrane potential

• Normally there is an excess of positive charges outside the cell

• Inside of the cell is negative with respect to outside

• Called as Resting membrane potential

Normal Resting Membrane Potential is -70mv

Due to unequal no. of ions on either side of the membrane

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Resting membrane potential

• Following are the ions which play important role in generating resting membrane potential :

- Sodium ions ( +vely charged) - Potassium ions ( +vely charged) - Chloride ions ( -vely charged) - Organic ions ( e.g. proteins) :-vely

charged

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Resting membrane potential

• Na+K+Pump actively pump 3 Na+ outside the neuron for each 2 K+ inside the neuron.

• Thus Most of the sodium ions remain

outside of the cell and Potassium ions are inside the cell.

• This creates negative potential inside the resting neuron -70mv

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Action PotentialResting stage : - 70mv Any stimulus – Mechanical, Physical or Biochemical Change in resting membrane potential (from -70mv to +30mv)

This change in RMP causes opening of voltage gated Na+ channel

More entry of Na+ inside the neuron

Reaches Maximum electropotential +30 to 35mv This gradual increase in charge is called as

depolarization

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• Depolarization:

Each action potential begins with a sudden change from the normal resting negative membrane potential to a positive potential

• Repolarization :

After depolarization the action potential ends with equally rapid change back to negative potential

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The Synapse

• Axon terminal releases neurotransmitters.

• Neurotransmitters cross the synapse and bind to receptors on another neuron.

• Neurotransmitters released, taken up again by first neuron.

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NEUROTRANSMITTERS

• Chemicals produced by the body that are released from the nerve endings

• Enable passage of impulses from one neuron to another across the synapse

• Act on their specific receptors (glycoprotein structures on the cell membrane)

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Neurotransmitter

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MAO

Post Synaptic neuron

Pre Synaptic neuron

Fate of Neurotransmitter

COMT

Vesicles

Auto Receptor

Post Synaptic Receptors

Neurotra

nsmitters

Reuptake Channels

Diffusion of NTs

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Post Synaptic neuron

Pre Synaptic neuron1.Fate of Neurotransmitter

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Post Synaptic neuron

Pre Synaptic neuron

Reuptakechannel

2.Fate of Neurotransmitter

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Auto Receptorprevents further release

Post Synaptic neuron

Pre Synaptic neuron

3.Fate of Neurotransmitter

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MAO Auto Receptorprevents further release

Post Synaptic neuron

Pre Synaptic neuron

Reuptakechannel

4.Fate of Neurotransmitter

COMT

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COMT

Auto Receptorprevents further release

Post Synaptic neuron

Pre Synaptic neuron

Reuptakechannel

5.Fate of Neurotransmitter

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Auto Receptorprevents further release

Post Synaptic neuron

Pre Synaptic neuron

Reuptakechannel

6.Fate of Neurotransmitter

Diffusion of NTs

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Neurotransmitters• Excitatory :

- Stimulate neurons

e.g. Noradrenaline, Dopamine, Histamine, Serotonin, Glutamate etc.

Acetyl-choline (neuromodulator)

• Inhibitory :

- Suppress the neurons

e.g. GABA (Gamma-Amino-Butyric-Acid)

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Neurotransmitters

• Acetylcholine – movement (respiratory paralysis)

• Serotonin – mood, sleep, appetite, anxiety (depression, obsessive-compulsive disorder, panic disorder)

• Dopamine – motivation, pleasure (schizophrenia, Parkinson’s)

• Epinephrine and Norepinephrine – attention, anxiety, stress (epilepsy, mania in bipolar disorder)

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Gama Amino Butyric Acid

• It is primarily an inhibitory neurotransmitter responsible for Sleep, prevents anxiety & stress signals & has an overall calming effect on the brain.

• It has three receptors GABAA, GABAB

& GABAC

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NEUROTRASMISSION

• A neuron generates and propagates an action potential along its axon, then transmits this signal across a synapse by releasing neurotransmitters, which trigger a reaction in another neuron or an effector cell (eg, muscle cells; most exocrine and endocrine cells).

• The signal may stimulate or inhibit the receiving cell, depending on the neurotransmitter and receptor involved.

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Blood brain barrier: A mechanism that creates a barrier between brain tissues and circulating blood; serves to protect the central nervous system.

Propagation: passing of electrical impulse within neuron by exchange of Na+ and K+ across the axonal membrane.

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The Blood-Brain Barrier• Endothelial cells in blood vessels in the

brain fit closely together• Only some molecules can pass through• Protects the brain from foreign molecules

and hormones and neurotransmitters from other parts of the body

• Can be damaged by infections, head trauma, high blood pressure, etc.

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