Nervous Tissue PDF

nervous tissue general architecture of the nervous system nervous system receive, process, integrate and respond to information enable perception and cognition control activities of somatic and visceral systems general architecture CNS - consist of brain...

nervous tissue general architecture of the nervous system nervous system receive, process, integrate and respond to information enable perception and cognition control activities of somatic and visceral systems general architecture CNS - consist of brain and spinal cord PNS - nerve fibres and nerve ganglia outside of brain and spinal cord, with special nerve endings functional division somatic nervous system (SNS) - voluntary, conscious control of body activities provides motor and sensory innovation to all parts of body does not include internal organs, cardiac muscles, smooth muscles, glands autonomic nervous system (ANS) - control over cardiac muscles, smooth muscles sensory innervation to internal organs and glands basic components of nervous system x neurons (nerve cells) process and integrates information to enable functions supporting cells glia/neuroglial cells - supporting and glue neural cell and hold them together - 90% of nervous system glial cells differentiated and developed from neural stem cells (neuroepithelial cells) multipotent cells neuroepithelial cells can develop into all kinds of neuroglial cells and neurons in CNS grey matter - neuronal cell bodies, neuropil (unmyelinated axons and dendrites), glial cells, and capillaries synaptic integration information process motor control sensory perception  white matter - glial cells and myelinated axons for transmitting signals in PNS ganglia - collection of nerve cell bodies outside CNS togt w supporting cells loacted where neuronal cell bodies r aggregate in diff locations (e.g cranial nerve ganglia, dorsal root ganglia) also have motor ganglia for sympathetic and parasympathetic system nerve bundles of myelinated and/or unmyelinated axons w supproting cells for transmitting signals all nerves are PNS except for optic nerve structure of nerve fibres physiological properties of neurons excitability conductivity secretion neurons gather and transmit electrochemical signals major components of neurons soma - containing nucleus and organelles blue spot in staining bc of prominent nucleus  dilated region of the neuron (Nissl bodies) contains nucleus and organelles protein producing cell dendrite - propagate electrochemical stimulation to soma usually branched w short extensions of cytoplasm of soma slightly larger diameter than axons form v large dendritic field for detecting stimuli from other neurons and ext environment significantly increases detecting areas for signals normally unmyelinated contain all organelles found in soma axon - conduct electrical impulses away from soma (projecting process from dendritic field) single usually, long and slender extension from soma and can be myelinated or unmyelinated  important structural features within axolemma (axoplasm) - cytoplasm within axon that lacks large organelles such as golgi apparatus, RER, free ribosomes and mRNA axon hillock - conical shape zone of transition between soma and axon initial segment - region of axon between apex of axon hillock and beginning of myelin sheath and site of action potential generation (initiation of action potential) synaptic terminal - axonal ends r ramified w branches called telodendria synapse - specialized contacts between neurons for transmission of info small junction across nerve impulse passes from axon terminal to neuron/muscle/gland cell neuron classification morphology psudounipolar neurons pseudo - fake looks like unipolar but not one axon and one dendrite fused tgt to form small stem w peripheral axon and central axon looks like theres one process but theres two sensory neurons neural cell bodies located in dorsal root ganglia or cranial nerve ganglia peripheral process links to sensory receptor and will conduct signal to CNS thru central axon bipolar neurons one v long dendrite, one v long axon found in olfactory cells one end is dendrite collecting stinuli and other send info to CNS multipolar neurons many processes w one long axon most of the prcesses r dendrites dendrites form field to collect stimuli one projecting axon sends signal away most of the neurons r this type function sensory functions pseudounipolar and bipolar detect stimuli motor functions multipolar neurons respond to stimuli example - neuron cell body located in ventral horn of spinal cord projects axons into effectors (muscles)  in symp and parasymp system -> two steps of motor neuron system presynaptic neurons postsynaptic neurons interneurons pyramidal cell found in motor cortex of brain, which r interneurons in charge of collecting signals from one neuron then sends signal to other neuron integration of information process, store, retrieve make decision small neurons forming networks w unmyelinated axons axonal transport within neurons as neurons cant divide in adulthood upon maturation, neurogenesis will decrease neurons produce all kinds of substances, can renew organelles and subcellular components within neuron n keep them fresh antrograde transport - transports components from cell body towards terminal end of axon retrograde transport - components move from terminal end back to soma synapse classification function chemical synapse electrical signals (ions) transferred to chemical signals then back to electrical conduction of impulses achieved by release of neurotransmitters from presynaptic neuron neurotransmitter diffuse across narrow intercellular space (synaptic cleft) electrical synapse (gap junction) electrical signals (ions) directly moved from one synapse to another mainly present in smooth muscle cells, cardiac muscle cells and retinal cells morphology axosomatic synapse axodendritic synapse (80% of all excitatory synapses) axoaxonic synapses (enhance or inhibit other synapses) structure of synapse presynaptic terminal and presynaptic membrane - synaptic vesicles containing neurotransmitters  postsynaptic terminal and postsynaptic membrane - contain membrane receptors and iron gates (protein coupled or inotropic) to recieve chemical signals synaptic cleft - narrow space (20-30 nm) between pre and post synaptic membrane direction of neurotransmission one way transmission initiated by depolarization of presynaptic membrane modulated by positive/negative feedback of presynaptic auto receptors, adjacent neurons or environment general structure and function of glial cells I large population of supportive non-excitable cells in nervous system unlike neurons - can divide and multiply throughout life become source for brain tumor subtypes central neuroglia (CNS) astrocytes largest cell type many branches do not form myelin irregular shaped with many processes two types fibrous mainly in white matter long unbranched processes astrocytoma is most common adult primary brain tumor protoplasmic mainly in gray matter  shorter, thicker, highly branched processes functions physical and metabolic support for neurons provides nutritions and trophic factors buffering K+ and neurotransmitters -> keep extracellular K+ low, keep electrolyte balance provide guidance for migrating neurons -> astrocytes span entire thickness of brain forming scaffold structure maintain and facilitate BBB (blood brain barrier = active metabolic filter) processes stretch from blood vessels to neurons ends of processes expand, forming end feet that cover large areas on outer surface of vessel/axolemma participating in injury responses (astrogliosis) phagocytize neuronal debris and fill space to form glial scar after injury reduce spreading and persistence of inflammatory cells maintain and repair of BBB oilgodendrocytes microglia ependymal cells peripheral neuroglia (PNS) schwann cells - myelin sheath provide protection for multiple axons at the same time white lipid electrically insulating layered structure formed by specific types of glial cells surrounds and protects axon accelerates transmission of action potential along axon (0.5-2 m/s to 80-120 m/s) axon regeneration in PNS interrupted at regular intervals by nodes of ranvier, covered part is internode one schwann cell forms myelin sheath wrapping around 1 internodal segment of 1 axon in PNS one oligodendrocyte sends out multiple processes to form myelin sheath wrap around 1-several internodal segments up to 50 axons in CNS  saltatory conduction along myelinated axon increases resistance so signal jumps how myelination forms initiated when schwann cell mesaxon or processes of oligodendrocyte surround axon mesaxon wrap around axon in spiraling motion, forming cocentric layer cytoplasm squeezed out from between membrane of concentric layers decreases capacitance across cell membrane and increases electrical resistance perineuronal satellite cells locate within ganglia surrounding nerve cell bodies controlling micro-environment provide electrical insulation and pathway for metabolic exchange analogous to schwann cells do not form myelin located close to neural cell body in ganglia provide metabolic support and protection unmyelinated axons in PNS schwann cells cover length of axon abutting tightly nodes of ranvier do not form axons fit into grooves in surface of schwann cells single axon or group of axons enclosed in single groove of schwann cell large schwann cells can have 20+ grooves in CNS bare, not embedded in glial cell processes lack of basal lamina or connective tissue microglia (CNS) smallest neuroglia immune surveillance cells  antigen presenting cells production of inflammatory factors (NO, cytokinds) activated during injury, stationed within CNS when activated microglia become enlarged and amoeboid shaped phagocytosis surveillance presenting antigens ependymal cells (CNS) epithelial like cells lining of ventricle (fluid filled cavities) columnar epithelium lack external lamina forming choroid plexus found in brain for CSF (cerebrospinal fluid) production neural stem cells self renewing, multipotent adults stem cells generating main phenotypes of nervous system generated throughout adults life via neurogenesis differentiate to replace lost or injured neurons or glial cells neurogenesis occurs in SVZ (subventricular zones) of lateral ventricles and dentate gyrus of hippocampus injury response of nervous system neuronal injury include neurla degeneration and regeneration  different between PNS and CNS in PNS injury, much debris is present debris is toxic, secreting inhibitory factors to inhbitor regen vasculation (blood vessels) provides inflammatory cells and macrophages which remove debris schwann cells form myelination and axon will grow back to function if schwann cells do not grow fast enough -> functional deficit in CNS bc of BBB, debris removal by microglia is not very fast astrocyte form glial scar and cut of regeneration route debris still present and releasing inhibitors - so cannot regenerate demyelinating diseases characterized by preferential damage to myelin sheath lose ability to transmit electrical impulses along nerve fibres, causing physical mental and psych problems several immune mediated diseases affect myelin shealth (multiple sclerosis)