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NEURON STRUCTURE AND NERVE CELLS.
Prepared by :
MISHAL TKMSc Applied PsychologyPeriyar [email protected]
CONTENTS IN THIS PRESENSATION NEURON STRUCTURE OF NEURON COMPONENTS OF NEURON. CELL CELL ORGANELLS DNA STRUCTURE PROTEIN SYTHESIS-ROLE OF ER AND GOLGI. NERVE CELLS-GLIA AND NON GLIA .
Nerve cellsTwo Types of Cells in the Nervous System.
1.NeuronsReceive & transmit information to other cells.Around 100 billion to 1 trillion.2.Glia cellsDifferent functions but don’t transmit information like neurons.Around 9x more than neurons
Neuron It is the basic cell unit of the nervous
system.
Cells that act as the information conducting units of the nervous system.
Neuron’s componentsDendritesSoma / cell body.AxonPre synaptic terminals
Neuron structure
Neuron components.. Dendrites are branching fibers with a surface
lined with synaptic receptors responsible for bringing information into the neuron .
Some dendrites also contain dendritic spines that further branch out and increase the surface area of the dendrite.
Dendritic spines are the point of communication between two neurons.
Neuron components.. Cell body/ Soma - contains the nucleus,
mitochondria, ribosomes, and other structures found in other cells.
Also responsible for the metabolic work of the neuron.
Axon - thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles.
Single axon, extends out of an expansion of the cell body known as axon hillock.
Axon may have branches called axon collaterals.
Axons are covered with an insulating material called the myelin sheath with interruptions in the sheath known as nodes of Ranvier.
Axon collateral divides into small branches called teleodendria.
Knob called End foot or terminal button at teleodendrion.
Presynaptic terminals refer to the end points of an axon where the release of chemicals to communicate with other neurons occurs.
Information flow in a neuron.
Dendrites and axon are simply fluid filled extensions of the cell body.
Information flows from the dendrites to the cell body and axon .
Dendrites receives thousands of data.
But at single axon , data passes will be an average level and summarized version. And it is regulated by axon hillock.
Neuron consists of a flow of electrical current that begins on the dendrites and then travels along the axon to the terminals.
Each impulses reaches an end foot, the end foot releases a chemical into its synapse, and the chemical influences the electrical activity of the receiving cell. Thus passes the information.
The chemical is known as Neurotransmitter.
Like other cells , Neuron cell contain the following structures:
Membrane Nucleus Golgi body Mitochondria Ribosomes Endoplasmic reticulum
a. Smooth ER.b. Rough ER.
The cell
Cell has an outer cell membrane that separates it from its surroundings and allows it to regulate the materials that enter and leaves its domain.
The cell membrane envelops the cell body.
Its an impenetrable barrier.
Proteins embedded in the cell membrane serve as the factory’s gate, allowing some substances to leave or enter and denying the rest.
The nucleus – executive office, and a structure that contains the genes chromosomes .
Endoplasmic ReticulumThin tubes that transport newly
synthesized proteins to locations around the cell. Proteins may have ribosomes attached
The mitochondrion - structure that performs metabolic activities and provides energy that the cells requires.
Ribosomes - sites at which the cell synthesizes new protein molecules.
Lysosomes
DNA Structure The structure, type and functions of a cell
are all determined by chromosomes that are found in the nucleus of a cell.
Chromosomes are composed of DNA, (deoxyribonucleic acid).
DNA is arranged into a double helix structure.
Nucleotide, the building blocks of DNA
There are four different types of nucleotide possible in a DNA sequence, adenine, cytosine, guanine and thymine (can be replaced with A, C, G and T).
Thymine and adenine can only make up a base pair
Guanine and cytosine can only make up a base pair
Therefore, thymine and cytosine would NOT make up a base pair, as is the case with adenine and guanine.
Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase.
Protein synthesisThe X marked nucleotides are an example of a DNA sequence that would be used to code for a particular protein, with the sequence of these nucleotides determining which protein it is.
The sequence of these nucleotides are used to create amino acids, where chains of amino acids form to make a protein.
SUPPORT CELLS Glia are the other major components of the
nervous system that exchange chemicals with adjacent neurons.
The general term for support cells in the CNS is glia or neuroglia (glial cells, neuroglial cells). There are three types of neuroglial cells.
(1) Oligodendrocytes, (2) Astrocytes and , (3) Microglia.
Neuroglial cells (1) Oligodendrocytes, the myelin-
secreting cells of the CNS.
(2) Astrocytes, which provide physical and metabolic support for nerve cells.
(3) Microglia, or microglial cells (mesoglia), which are the phagocytes of the CNS.
Oligodendrocytes build the myelin sheath that surrounds the axon of some neurons.
Radial glia- guide the migration of neurons and the growth of their axons and dendrites during embryonic development.
Astrocytes helps synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon.
Microglia. These are the smallest of the glial cells, with
short twisted processes. They are the phagocytes of the CNS, considered part of the mononuclear phagocytic system.
They are believed to originate in bone marrow and enter the CNS from the blood.
In the adult CNS, they are present only in small numbers, but proliferate and become actively phagocytic in disease and injury.
Their alternate name, mesoglia, reflects their embryonic origin from mesoderm (the rest of the nervous system, including the other glial cells, is of neuroectodermal or neural crest origin).
Support cells in the PNS The support cells of the PNS are called
satellite cells and Schwann cells.
Satellite cells surround the cell bodies of the neurons in ganglia (ganglion cells).
These small cuboidal cells form a complete layer around the nerve cell body, but only their nuclei are visible in routine preparations. They help to maintain a controlled microenvironment around the nerve cell body, providing electrical insulation and a pathway for metabolic exchange.
Schwann cells: Schwann cells are responsible for the
myelination of axons in the PNS. A Schwann cell wraps itself, jelly roll-fashion, in a spiral around a short segment of an axon.
During the wrapping, cytoplasm is squeezed out of the Schwann cell and the leaflets of plasma membrane of the concentric layers of the Schwann cell fuse, forming the layers of the myelin sheath.
The blood-brain barrier is a mechanism that surrounds the brain and blocks most chemicals from entering.
The immune system destroys damaged or infected cells throughout the body.
Because neurons in the brain generally do not regenerate, it is vitally important for the blood brain barrier to block incoming viruses, bacteria or other harmful material from entering.
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