��STRUCTURE & FUNCTION �OF NERVE CELLS�

�Dr. Subhash Meena

Asst. Professor,

Deptt. Of Psychology,

Rajghat, Varanasi

Introduction

• Nervous tissue consist of two types of cells:

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NEURONS

NERVE CELLS (NEURON)

• Specific cells that transport electrical nerve impulse.
• Transport impulse from one part to others part of body.
• Property:
• Electrical excitability (ability to produce action potential and impulse in response stimuli).
• Once they arise, action potentials propagate from one point to the next along the plasma membrane due to the presence of specific types of ion channels.

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Basic Structure of the Neuron

• Cellular Membrane

2 layers of fat molecules which allow some small uncharged particles to flow in & out of the cell

Protein channels allow a few charged ions to cross the membrane but most chemicals are kept out

• Nucleus

Structure containing chromosomes

Basic Structure of the Neuron

• Mitochondria

Provides the cell with energy

Requires fuel & oxygen to function

• Ribosomes

Site of protein synthesis

• Endoplasmic Reticulum

Thin tubes that transport newly synthesized proteins to locations around the cell

Proteins may have ribosomes attached

Nerve Cells

• Nerve fiber is a general term for any neuronal process (dendrite or axon)
• The site of communication between two neurons or between a neuron and an effectors cell is called a synapse.
• (Neuron 🡪 synapse 🡪 neuron)
• Impulses transmit into neuron at synapse through dendrite process and carry incoming impulse towards cell bodies. Then transfer away from cell body by axon.

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CELL BODY

• Contains:
• Nucleus
• Surrounded by cytoplasm that includes typical organelles such as:
• lysosomes, mitochondria and a Golgi complex
• Nissl bodies (prominent cluster of rough endoplasmic reticulum) :
• sites of protein synthesis in neurons that was used to replace cellular components, as a material for growth of neurons and to regenerate damaged axons in the PNS.

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Cell body

• Characteristics:
• Different sizes with others
• Protoplasma have granules
• Neurons cells cannot divide like others cell body
• Form grey matter in brain and spinal cord
• Cells have one or more fibers (axons and dendrite) will form white matter nervous system’s organs .

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DENDRITE

• Dendrite’s shorter processes terminating mostly near the nerve cell body. They touch the others neuron at synapse.
• Are conductive in nature :
• receive and carry incoming impulses towards cell bodies.
• Have same structures like axons, but are usually shorter and branching.
• In motor neuron, they forms part of synapses.
• In sensory neuron, they form the sensory receptors that respond to specific stimuli.

AXON

• Each neuron has one axon.
• Originates from a special region of the cell body called the axon hillock.
• Axon may have branches along their length known as axon collaterals.
• Axon collaterals is divide into many fine processes known as axon terminals.
• Axon terminals:
• Longer than dendrites , sometimes about 1 metre.

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AXON

• Has a long central core of cytoplasma called axosplasma .
• The cytoplasma is surrounded by plasma membrane axolemma.
• Together axoplasma with axolemma is called as axis cylinder of the nerve fiber.
• Axon:
• the conducting region of the neuron.
• It generates nerve impulses and transmit them (typically away from the cell body.)

AXON

• Insulated by myelin sheath �It gives white colour to the nerve fiber.
• Has a series of Schwann cell plasma membrane and also known as neurolemma.
• There are tiny areas of exposed axolemma between adjacent Schwann cells, called nodes of Ranvier.
• Nodes of Ranvier:
• Assist in rapid transmission of nerve impulse.

(the speed of transmission of nerve impulse slower in non-myelinated fibers.)

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Functions of Myelin Sheath

Neurolemma

• A series of Schwann cell plasma membrane -
• Thin membrane surrounding the myelin sheath that found only around axons in the Peripheral Nervous Sytem.
• When the axon is injured, neurolemma assists regenerations.
• It forms a regeneration tube that guides and stimulates growth of the axon.

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Properties of neuron

Classification of Neuron

Classification of neuron

Classification of neuron

Classification of neuron

Classification of neuron

Nerve Impulse

• The electrical activity in the membrane of a neuron.
• Ways by which information is transmitted within the nervous system along the axons of the neurons.

Types of neuron

Types of neuron: Sensory or Afferent Nerves

• Nerve that transmit impulse from peripheral body through spinal cord to the brain to be interprets.
• Example: from skin.
• When action potentials are generated by sensory receptors on the dendrites of these neurons, they are transmitted to the spinal cord by the sensory nerve fibers.
• The impulse may then pass to the brain or to connector neurons of reflex arcs in the spinal cord.
• Sensory receptors 🡪 action potentials 🡪 dendrites 🡪 sensory nerve fibers 🡪 spinal cord 🡪 brain / connector neuron of spinal cord.

Types of neuron: Sensory or Afferent Nerves

• Sensory nerves from peripheral nerve are non-myelinated and not have neurolemma. From small division called as sensory nerve ending.
• Stimulation; pain, hot temperature 🡪 impulse transmit to sensory nerve 🡪 brain

Types of neuron: Motor or Efferent Nerves

• Nerve that send impulse from brain to spinal cord. Then it goes to skeletal muscle to contract.
• Brain 🡪 spinal cord 🡪 skeletal muscle (contract).
• The nearer motor nerve to muscle, it lost its myelin sheath and neurolemma.
• The nerve branches into filament and ends at Motor End Plate.

Types of neurons

STRUCTURE & FUNCTION: NEUROGLIA

• It is about half the volume of the Central Nervous System (50%).
• It held nervous tissue together.

Glial cells

Physically support neurons and produce the myelin sheath

Glial cells also maintain a homeostatic environment around the neurons and remove debris by phagocytosis

Glial cells

There are several types of glial cell. They do not transmit nerve impulses but provide neurons with physical support.

Some types of glial cell cause myelination of axons by surrounding them with tightly packed layers of plasma membrane

Layers of membrane

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Other types of glial cells provide neurons with essential chemicals and keep the chemical composition of the fluid around the neurons constant (i.e. maintain a homeostatic environment around the neurons).

axon

6 Types of Neuroglia

Differences between Neuroglia & Neuron

General Functions of Neuroglia

Neuroglia: Astrocytes

Neuroglia: Oligodendroglia / oligodendrocyte

Neuroglia: Microglia

Neuroglia: Ependymal cells

• 2 types of glia in the PNS
• Satellite cells
• Surround clusters of neuronal cell bodies in the PNS
• Unknown function
• Schwann cells
• Form myelin sheaths around the larger nerve fibers in the PNS.
• Vital to neuronal regeneration

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Neuroglia

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