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GHH Nervous Tissue

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General Histology and Histotechnique
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GHH Nervous Tissue

  1. 1. General Histology and Histotechnique (1st semester; 2012-2013)NERVOUS TISSUE - respond and integrates decision Motor or efferent neuronsNervous system - Carry information out of the brain and spinal cord- Complex, highly organized network of billions of going to the effectors neurons and even more neuroglia EffectorsComponents: - Cells and organs innervated by motor neurons Brain – contain 100 billion of neurons - Simply the muscle and glands. Cranial nerves and their branches- 12 pairs of left and right, emerge from the base of Nervous Tissue brain. - Responsible for communication and sending Spinal cord impulses.- It connects to the brain through the foramen Consists of Two principal kinds of cells: magnum- Spinal nerves – 31 pairs emerging from the spinal 1. Neurons/ nerve cells cord. 2. Neuroglia/ glial cells Spinal nerves and their branches Ganglia – small mass of nervous tissue and contains I. Neurons cell bodies of neurons - Responsible for most special functions attributes toLocation: outside of central nervous tissue, outside of the nervous system:the brain & spinal cord o Sensing- Closely associated with the cranial nerve and spinal o Thinking cord. o Remembering Enteric plexus – located on the walls of digestive o Controlling muscle activity tracts – G.I.T. o Regulating glandular secretionsFunction: Regulate the functions of Digestive system - Have the property of electrical excitability Sensory receptors  Capacity to produce- Either dendrites of sensory neurons action potential or- Specialized cells that monitor change in the internal responses to stimuli wall as well as the external environment. - Many neurons also contain LipofuscinEx. Pacinian corpuscles, ductile corpuscles  Pigments  Occur as clumps ofMajor structures of Nervous system yellowish brown granules in theThree Basic functions of Nervous System cytoplasm of neurons.  Product of neuronal1. Sensory function lysosomes that- Internal: increase in blood acidity accumulate as neuron- External: raindrop landing on arm ages.Sensory or afferent neurons Parts:- Neurons that carry information into the brain and spinal cord. 1. Cell body - Star shaped2. Integrative function Components:- Integrates (process) sensory information o Cytoplasm = Neuroplasm- Analyze, store, made decisions regarding o Plasma membrane = Neurolemma appropriate responses Organelles:Interneurons: neurons for integration o Mitochondria- Makes up vast majority of neurons in the body o Lysosomes o Golgi complex3. Motor function o Nissl bodies
  2. 2. General Histology and Histotechnique (1st semester; 2012-2013)- prominent clusters of rough endoplasmic reticulum SynapseFunction: - the site of communication between two neurons or- Produces proteins that are used by the cell body between a neuron and an effectors cell- Replaced cellular components Synaptic end bulb: bulb-shaped structure of axon- Used as a material for growth of neurons terminals.- Regenerate damage axons in PNS Varicosities: String of swollen bumps of axon terminals - Contains synaptic vesicles2. Processes  Stores chemical neurotransmitter  Triggers acetylcholinea. Dendrites (little trees) - Neurotransmitter - acetylcholine- receiving input portion of the neuron  Influenced the activity of other neurons, muscle fibers and gland cells.b. Axon (axis)- Propagates nerve impulses toward another neuron, Types of transport systems: a muscle fiber, or a gland cell.- A long, thin, cylindrical projection 1. Slow axonal transport - Slower systemParts: - Moves materials about 1-5mm per day1. Axon Hillock - Conveys axoplasm in one direction only- Resemble a small hill - From cell body to axon terminals- Cone- shaped elongation that joins the cell body - Supplies new axoplasm for developing or and the axon. regenerating axons - Replenishes axoplasm in growing and mature axon2. Initial segment - Carry materials from body to axon then back again- First part of axon*** 1 &2 Function: 2. Fast axonal transport- Responsible for the occurrence of impulses in an - Faster system axon known as trigger zone. - Capable of moving materials a distance of 200-400 mm per day3. Axoplasm – cytoplasm of axon - Uses proteins that function as motors to move materials in both directions – away from and4. Axolemma – plasma membrane that covers the toward the cell body – along the surface of axon. microtubules - Moves various organelles and materials that form5. Axon Collateral the membranes of the axolemma, synaptic and- Side branches of axons at right angle of the axon bulbs and synaptic vesiclesFunction: Provides modulation of axon/cell firing Clinical application6. Node of Ranvier- Neurofibril node Tetanus- Indentation between the axon connecting one from - Fast axonal transport is the route by which some the other. toxins and disease – causing viruses make their wayImportance: To speed-up the process of transmitting from axon terminals near the skin cuts to cell bodiessignals from the CNS to effectors cells (Muscle cell of neurons, where they can cause damage.glands). - Toxin produced by Clostridium tetanus is carried by fast axonal transport to the CNS disrupting the7. Axon terminal actions of motor neurons, causing prolong painful- Fine processes at end of the axon muscle spasms – condition called Tetanus.- Swell into bulb shaped structures- Synaptic end bulb Structural Diversity of Neurons
  3. 3. General Histology and Histotechnique (1st semester; 2012-2013)Neurons display great diversity in size and shape - Multiply and divide in the mature nervous system - Supporting tissues of the brain and spinal cordA. According to function Types:1. Motor neuron- Transmit impulses to the motor cells 1. Astrocytes - Largest neuroglia2. Sensory neuron - Star shape with long processes- Transmit impulses from neurons to the senses Functions: - Help maintain appropriate chemical environment3. Associative neuron for the generation of action potential- Neurons connecting motor from sensory neuron - Provides nutrients to neurons - It takes up excess neurotransmitters and participateB. According to number of nerve process in the metabolism of neurotransmitters1. Multipolar neurons Two types of Astrocytes:- Have a several dendrites and one axon a. Protoplasmic astrocyte - Abundance of cyplasmic granules2. Bipolar neurons - Found in gray matter- One dendrites and One AxonLocation: Retina of the eye, inner ear, olfactory area of b. Fibrous astrocytethe brain. - Long-slender - Found in white matter3. Unipolar neurons- Sensory neurons that originate from the embryo as 2. Oligodendrocyte bipolar - Round/oval body- One dendrite and One axon - Few processes - Smaller than astrocyteC. According to size and shape Functions: - It forms the supporting network around the CNS1. Interneurons neuron- Occupy 90% of the total neurons of the body - Produce myelin sheath around axon of CNS neuronsFunction: Carry impulses from one neuron to another 3. Microgliaa. Pyramidal cells - Small cells- Pyramid like shape - Fewer than oligodendrocyte- Center of cerebral cortex - Derived in mesodermal cells  Largest part of brain - It gives rise to monocyte and macrophages Functions:b. Purkinje cells - It protects CNS cells from diseases- Found in the cerebellum - Engulfed microorganisms - Clear away debris/dead cellsc. Renshaw cells/ Inhibitory interneuron- Stellate cells 4. Ependymal cells- Found in the spinal cord - Epithelial cells and arranged in single layer with microvilli and ciliaII. Neuroglia - Shape: Columnar  cuboidal- Constitute about half the volume of CNS - Ciliated- 5-50 time more numerous than neurons Functions:- Do not generate action potential
  4. 4. General Histology and Histotechnique (1st semester; 2012-2013)- It lines the ventricles of brain and central canal of 3. Gives color to the white matter in the CNS spinal cord- It forms the CSF (cerebrospinal fluid); assist in 2. Unmyelinated nerve fiber circulation - No myelin sheath - Surrounded by coat of neuroglial plasma membrane5. Schwann cells - Fiber is enclosed by the Schwann cell only in PNS- Flattened cell - Fiber is not unsheathed in CNS- Encircles the PNS axon - Impulse is conducted as a continuous wave of- Produces myelin sheath around the single axon of voltage reversal to the end of the axon. PNS neuronFunction: Neuroglial cells that produces Myelin sheath:- Participate in the regeneration of PNS axon. 1. Schwann cells in PNS6. Satellite cell - Begin to form myelin sheath around axon during- Surrounds neurons cell body fetal development neurolemma: sheath of SchwannFunction: enclosing myelin sheath.- Support neurons in ganglia - Aids in regeneration that forms regeneration tube that guides and stimulates regrowth of axon. Nodes of Ranvier: gaps in myelin sheathNerve fibers- General term for any process (axon of dendrite) 2. Oligodendrocytes in CNS projecting from the cell body of a neuron - Myelinated parts of many axons in the same- It is also a connective tissue manner that a Schwann cell myelinates part of a single PNS axonConnective tissue sheaths: - Neurolemma is not present - Nodes of Ranvier present but few in number1. Epineurium - Axon in CNS display little regrowth after injury due- Encircles the entire nerve to absence of neurolemma - Certain diseases such as multiple sclerosis and Tay-2. Perineurium sachs diseases destroy myelin sheath- Wrapped around individual fascicles*** 1&2 – composed of dense connective tissue Gray and White Matter3. Endoneurium White matter- Surrounds the individual axon - Aggregations of Myelinated processes from many- Loose Areolar connective tissue neurons - In spinal cord, white matter surrounds an inner coreTypes of Nerve fibers: of gray matter shaped like a butterfly or the letter H.1. Myelinated nerve fiber- With myelin Gray MatterNodes of Ranvier – gaps in the myelin sheath - Contains neuronal bodies, dendrites, unmyelinatedInternodes axons, axon terminals, and neuroglia - Looks grayish rather that white because there isSignificance of myelin sheath: little or no myelin in these areas. 1. Increase speed of nerve impulse transmission - In the brain, a shell gray matter covers the surface due to node of ranvier by salutatory conduction: of the largest portions of the brain, the cerebrum electrical alteration jumps as current flow from and cerebellum. one node of ranvier to another 2. Electrically insulates the axon of neuron

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