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ANATOMY & PHYSIOLOGY NERVE TISSUE Part 1 Instructor Terry Wiseth Nervous System Function 1) Sensory input stimuli 2) Integration process and interpret 3) Motor output activates effector organs “Stop light" “Taste food" 2 Nervous System Organization Central Nervous System (CNS) brain, spinal cord integration command center Peripheral Nervous System (PNS) cranial nerves, spinal nerves communication lines 3 Nervous System Organization Nervous System Organization Somatic Nervous System "voluntary" Sensory neurons convey information from cutaneous and special sense organs, body wall and limbs to the CNS Motor neurons that conduct impulses from CNS to skeletal muscle only 6 Autonomic Nervous System "involuntary" Sensory neurons convey information from receptors in viscera to CNS Motor neurons that conduct impulses to smooth muscle, cardiac muscle and glands 7 Autonomic Nervous System Branches of ANS Sympathetic involves expenditure of energy Parasympathetic restores or conserves energy 9 Branches of ANS two divisions have opposing actions ex: sympathetic speed up heart rate ex: parasympathetic slows down heart rate 10 Nerve Types 1) Neuroglia 2) Neurons 11 Nerve Types 1) Neuroglia Support neurons Nurture neurons Protect neurons 12 Nerve Types 2) Neurons Sense Think Remember Regulate gland function Control muscle movement 13 Neuroglia "glia cells“ Support neurons More numerous than neurons Make up half the mass of the brain 14 Neuroglia Able to multiply and divide Multiply and fill in areas of neurons that are destroyed by injury Brain tumors commonly arise from glia cells and are highly malignant 15 Neuroglia Types CNS Astrocytes Microglia Oligodendrocytes Ependymal cells PNS Neurolemmocytes Satellite cells 16 Neuroglia Types Astrocytes "nursing neurons“ Largest an most numerous glial cells Many processes Maintain proper balance of K+ for generation of nerve impulse Participate in neurotransmitter metabolism 18 Astrocytes Participate in brain development by assisting migration or neurons Provides link between neurons and blood vessels Form blood-brain barrier (BBB) Regulate entry of substances into brain 19 Blood Brain Barrier BBB allows diffusion only of lipid soluble substances across the astrocyte membrane surrounding the capillary Nicotine, ethanol, heroin 20 Blood Brain Barrier Water soluble substances may pass but only by mediated transport Glucose, amino acids 21 Parkinson’s Disease caused by a lack of the neurotransmitter dopamine normally produced by neurons of the brain Lack of dopamine causes the characteristic shaking and decreased muscle control 22 Parkinson’s Disease Administration of dopamine is not helpful because it cannot cross the BBB 23 Parkinson’s Disease Administration of L-dopa (a precursor of dopamine) reduces the symptoms because it can pass the BBB and is converted to dopamine by the CNS neurons 24 Microglia Derived from monocytes Small, phagocytic engulf bacteria clear away debris from dead cells may migrate to areas of injured nerve tissue 25 Oligodendrocytes Support neurons by twining around them and producing a lipid protein wrap called a myelin sheath Each oliodendrocyte wraps myelin around several axons 26 Ependymal Cells Derived from epithelial cells Many may be ciliated Line the fluid filled ventricles of the brain Form cerebrospinal fluid (CSF) and assist its circulation 27 Neurolemmocytes "Schwann cells“ produce myelin sheaths around PNS neuron axons each cell produces part of the myelin sheath around a single axon of a PNS neuron 28 Satellite Cells support neurons in ganglia clusters of the PNS Surround ganglion neuron cell bodies providing nutrients Satellite Cell Neuron 29 Neurons various sizes and shapes the basic functions of all neurons are more or less similar 1)receive and integrate inputs 2)relay their output to some other target cell 30 Neurons cell that has an excitable cell membrane capable of producing an electrical impulse communication between neurons passing of a chemical message from one nerve cell to another across space between them called the synapse 31 Neuron Anatomy 1) Soma 2) Dendrites 3) Axon 4) Synapse 32 Neuron Anatomy 1) Soma Nissl bodies Nucleus 33 Neuron Anatomy 2) Dendrites 34 Neuron Anatomy 3) Axon Neurolemma Schwann cell Node of Ranvier 35 Neuron Anatomy 4) Synapse synaptic knob synaptic cleft synaptic vesicles 36 Soma (Cell Body) lack spindle fibers necessary for cell division acts as a bridge between the dendrite and the axon 37 Soma (Cell Body) site of an extremely high rate of metabolism numerous mitochondria, ribosomes and endoplasmic reticulum 38 Nissl Bodies Clusters of ER and ribosomes Organelles of function in the production of neurotransmitters Darkened area around the nucleus are Nissl Bodies 39 Ganglia And Nuclei Grouped soma having similar functions Ganglia along spinal cord Nuclei within CNS Ganglia Nuclei 40 Dendrites Short, branched arms that stick out from the soma Receive incoming signals and carry them to the soma Dendrites Axon Soma 41 Dendrites Cell membrane of soma and dendrites sensitive to chemical, mechanical or electrical stimulation Stimulation leads to generation of action potential (nerve impulse) conducted along the axon 42 Axon Conduct impulse away from the soma Neurolemma Schwann cell Node of Ranvier 43 Neurolemma Axonal membrane found only in myelinated neurons Primarily in peripheral nervous system Neurolemma Axon 44 Schwann Cell Cells that wrap around the axons 45 Schwann Cell Form myelin A fatty protein sheath Whitish in color Acts as an electrical insulator Increase the speed and efficiency at which nerve impulses may be transmitted 46 Node of Ranvier Gaps located between neighboring Schwann cells on myelinated neurons 47 Node of Ranvier Action potential occurs at the node (gap) only Na+ diffusion occurs along inside of axon neurolemma to the next node 48 Node of Ranvier Synapse Gap that acts as a junction between axon of presynaptic neuron and dendrite of postsynaptic neuron Presynaptic axon ends in synaptic knob 50 Synapse Synaptic cleft Synaptic vesicles Synapse Direction of Nerve Transmission Synaptic Knob Contains numerous mitochondria and synaptic vesicles full of neurotransmitters Neurotransmitters act to excite or inhibit neighboring neurons 52 Synaptic Cleft Short distance between synaptic knob and postsynaptic dendrite is very small Place for regulation of transmission 53 Synaptic Cleft If a signal is too weak, it will not traverse the synaptic gap If the signal is strong enough, it will go on to excite the postsynaptic membrane, and thereby continue the transmission 54 Synaptic Cleft Many drugs that act on the nervous system interfere with activity in the synaptic cleft 55 Events of Synapse STEP ONE: Arrival of action potential at the synaptic knob Events of Synapse STEP TWO: Entry of extracellular Ca+2 and exocytosis of Acetylcholine Events of Synapse STEP THREE: Acetylcholine action promotes entry of Na+ into the presynaptic neuron initiating action potential Events of Synapse STEP FOUR: Breakdown of acetylcholine by acetylcholinesterase and reabsorption of choline by postsynaptic neuron knob Functional Classification 1) Sensory neurons (Afferent) Receptors 2) Motor neurons (Efferent) Effectors 3) Interneurons 60 Functional Classification Sensory neuron Interneurons Motor neuron Sensory Neurons Approximately 10 million sensory neurons in body Also known as Afferent fibers Carry information from receptors to central nervous system 62 Receptors May be a process of a sensory neuron May be a specialized cell which communicates with a sensory neuron Receptors 63 Receptors Extroreceptors Touch, temperature, pressure, sight, smell, touch, hearing Proprioreceptors Monitor position of skeletal muscles and joints Interoreceptors Monitor the activities of the viscera, taste, pain 64 Receptors Motor Neurons Approximately 1/2 million motor neurons in body Also known as Efferent fibers Carry signals from the CNS to the effector organs (muscles and glands) 66 Effectors Peripheral targets of motor neurons Change their activities in response to motor neuron impulse Skeletal muscle, cardiac muscle, smooth muscle, glands Motor End Plate 67 Interneurons Approximately 20 billion interneurons in body Located entirely within the CNS Interconnect other neurons 68 Interneurons Analysis of sensory input Coordination of motor output 69 Myelination Most neuron axons are surrounded by a myelin sheath 70 Myelination Protein lipid covering produced by neuroglia 1) Electrically insulates axon 2) Speeds up the transmission of nerve impulse through the axon 71 White Matter The major component of a cell membrane is the phospholipid bilayer Many layers of membrane stacked on top of one another creates a fatty appearance due to the presence of this phospholipid 72 White Matter Lipid has a glistening white appearance Such as fat found on meats Myelinated axons have a glistening white appearance 73 Gray Matter Areas containing mainly cell bodies tend to lack myelin Unmyelinated Axon Myelinated Axon 74 Neurolemma Neurolemmocytes (Schwann cells) wrap several times around a small portion of the PNS axon Myelin sheath is called a neurolemma 75 Neurolemma Neurolemma Neurolemma Neurolemma Neurolemma Neurolemma 1 2 Neurolemma 3 4 Neurolemma Aids regeneration of an axon if it is injured Forms a regeneration tube that guides and stimulates regrowth of the axon 83 Neurolemma Nodes of Ranvier Intervals along the axon where there are gaps between the myelin sheath 85 Nodes of Ranvier Neurolemmocytes wrap (neurolemma) the axon segment between the two nodes 86 Nodes of Ranvier Oligodendrocytes myelinate many cells of the CNS in much the same manner as a neurolemmocyte myelinates parts of a single PNS axon 87 CNS Lacks Neurolemma Many broad flat processes spiral about CNS axons and deposit a myelin sheath Neurolemma is not formed 88 CNS Lacks Neurolemma Axons in the CNS display little regrowth after injury Due to absence of neurolemma and inhibitory influence exerted by CNS neuroglia 89 Myelin and Nerve Regeneration Possible only if the axon is myelinated Myelinated Axon Unmyelinated Axon 90 Regeneration of Nerve Tissue Neurons have very limited powers of regeneration Neurons lose the ability to divide at 6 months of age 91 Regeneration of Nerve Tissue Any neuron destroyed is permanently lost Only certain types of damage to neuron cells can be repaired 92 PNS Regeneration PNS dendrites and axons may be repaired: 1) If the cell body remains intact 2) If Schwann cells remain active 93 CNS Regeneration CNS shows little repair of damage to neurons Injury to brain or spinal cord is usually permanent Stroke Damage 94 CNS Regeneration Why does the CNS lack the ability for nerve cell regeneration? 1) Lack of neurolemma 2) Axon regrowth inhibition 3) Scar tissue formation 95 Lack of Neurolemma Axons of CNS are myelinated by oligodendrocytes and do not form neurolemmas 96 Axon Regrowth Inhibition Neuroglia of CNS inhibit axon regrowth Possibly the same mechanism that inhibits axonal growth during development once a target region has been reached 97 Scar Tissue Formation Astrocytes invade area forming scar tissues which act as physical barriers to regeneration 98 Neuronal Regrowth Neuronal tumor cells Tumor cells developing from neurons (rare) have the ability to divide Current research on neuronal regrowth is centered on how these tumor cells have gained the ability to reproduce 99 Neuronal Regrowth Brains of some songbirds Nerve tissue appears and disappears every year Researchers hope to find how songbirds are able to regenerate CNS tissues This gives new meaning to the phrase “Bird Brain” 100 Neuronal Regrowth Lack of mammalian CNS regeneration 1) Inhibitory influences from neuroglia 2) Absence of growth cues present during development 101 Neuronal Regrowth Developmental cues are electrical and chemical in nature Use electrical or chemical stimulation to promote axon regrowth EGF (1992) used to trigger mitosis Epidermal Growth Factor is the hormone which skin cells respond to divide and reproduce 102 Myelin Development Amount of myelin increases from birth to maturity Myelin presence greatly increases the speed of nerve impulse conduction 103 Myelin Development Infant response to stimuli are not as rapid or coordinated as those of older children or adults Myelination is still in progress 104 Diseases of the Myelin Sheath Destruction of the myelin sheaths Tay-Sachs disease Diabetes mellitus Multiple sclerosis 105 Diseases of the Myelin Sheath Results in slowed action potential and impaired control of skeletal and smooth muscle 106 Multiple Sclerosis (MS) Progressive destruction of myelin sheath in CNS neurons 107 Multiple Sclerosis (MS) Chronic, disabling disease affecting over 2.5 million people world wide Myelin sheaths deteriorate to scleroses (hardened scars or plaques) in multiple regions 108 Multiple Sclerosis (MS) Characteristics of the disease 1) Progressive loss of muscle strength 2) Strange sensations Demyelinated plaques formed in the brain from MS 109 Multiple Sclerosis (MS) Characteristics of the disease 3) Double vision occurs periodically 4) “Attacks" every year or two with periods of remission 110 Multiple Sclerosis (MS) Implications of a viral cause which precipitates the activation of killer Tcells to destroy myelin producing oligodendrocytes 111 Multiple Sclerosis (MS) 1993 FDA approved use of Betaseron (a form of interferon) Note greyish plaques around the ventricles 112 Multiple Sclerosis (MS) Demyelination in Spinal Cord Nerve Tracts What we call a nerve is actually many nerve axons bundled together by sheaths of tissues Endoneurium Perineurium Epineurium 114 Endoneurium A connective tissue wrapping enveloping individual axons 115 Endoneurium Perineurium A connective tissue wrapping bundles or fascicles of axons Perineurium 117 Epineurium A connective tissue sheath enveloping the nerve as a whole 118 Epineurium These connective tissue sheaths help to give peripheral nerves a certain toughness and resistance to tearing 119 End Nerve Tissue Part 1