Human Anatomy Unit 4 NERVOUS SYSTEM: NEURAL TISSUE Overview •  Includes all neural 8ssue in the body •  2 divisions 1.  Central (CNS) 2.  Peripheral (PNS) –  Afferent •  Sensory •  Info to CNS •  Receptors –  Efferent •  Motor •  Info from CNS •  Effectors PNS Organiza8on •  Soma8c –  Skeletal muscle –  Soma8c motor •  CNS controls skeletal muscle –  Soma8c sensory •  Sensory info from muscles to CNS •  Autonomic (Visceral) –  Gut structures –  Visceral motor •  Autonomic nervous system (ANS) •  Sympathe8c division •  Parasympathe8c division –  Visceral sensory Nervous System Organiza8on Cellular Organiza8on •  2 dis8nct types of cells 1.  Neurons •  Transfer and processing informa8on in the nervous system 2.  Neuroglia •  Cells that support and protect neurons Neuron Anatomy Soma Dendrites Axon (telodendria) Synap8c bulb Axon hillock Myelin Neuroglia CNS Glial Cells •  Astrocytes –  Inters88al environment –  Blood‐brain barrier –  Structural support –  Repairing damaged nervous 8ssue –  Neuron development •  Oligodendrocytes –  Not all nerves in the CNS are myelinated –  myelin •  Microglia –  macrophage •  Ependymal cells –  Cerebral spinal fluid (CSF) CNS Glial Cells PNS Glial Cells •  Schwann cells –  Myelin •  All peripheral nerves are myelinated –  Nodes of Ranvier •  Axolemma –  Neuron plasma membrane •  Neurilemma –  Superficial cytoplasmic covering •  Satellite cells Schwann Cells Neurons Neural Development and Growth •  Stem cells differen8ate into neurons or glia (before birth) •  Each neuronal daughter cell differen8ates and sends out processes that will be axons and dendrites •  Growth cone –
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Forms a 8p at the end of an axon Directs the route and final target for the axon Guided along glial cells Synapses become ac8ve before matura8on •  Determines final func8on •  Apoptosis –  Programmed cell death –  50‐70% of neurons and synapses in developing CNS Neural Regenera8on •  Severed neurons can be repaired as long as the damage –  Occurs outside of the CNS –  Does not damage the soma •  Slow process –  1mm/day Types of Synapses Structural Classifica8on of Neurons •  Anaxonic neuron –  CNS –  Special sense organs •  Bipolar neuron •  Pseudounipolar neuron –  Con8nuous axon‐dendrite processes –  Soma is off to the side –  Visceral sensory neurons –  Axons may be myelinated Single dendrite Centrally located soma Between axon and dendrite •  Mul?polar neuron –  Mul8ple dendrites Special senses (vision, –  Single axon smell, hearing) –  Not myelinated –  Most common in CNS –
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•  Soma8c motor neurons •  All axons are myleninated Structural Classifica8on of Neurons Func8onal Classifica8on of Neurons •  Sensory neurons –  Afferent division of PNS –  Deliver info to CNS –  Pseudounipolar neurons •  Afferent fibers •  From sensory receptors to spinal cord or brain •  Motor neurons •  Interneurons Func8onal Classifica8on of Neurons Sensory Neurons •  Afferent division of PNS •  Soma?c sensory neurons –  Deliver info to CNS •  Outside world •  Our posi8on in it –  Receptors located in the belly of muscles •  Monitor tension •  Monitor stretch –  Pseudounipolar neurons •  Afferent fibers •  From sensory receptors to spinal cord or brain •  Visceral sensory neurons –  Transmit info on internal condi8ons –  Status of organ systems Func8onal Classifica8on of Neurons Sensory Neuron Receptors •  Types –  Exteroreceptor (soma8c sensory receptors) •
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External environment Touch Temperature Pressure Special senses (vision, hearing, olfac8on) –  Proprioceptor (soma8c sensory neurons) •  Posi8on and movement of skeletal muscles and joints –  Interoreceptor (visceral sensory neurons) •
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Diges8ve, respiratory, cardiovascular, urinary, reproduc8ve systems Sensa8ons of deep pressure Pain Taste Func8onal Classifica8on of Neurons Motor Neurons •  Efferent division of PNS •  Mul8polar neurons •  S8mulates or modifies the ac8vity of –  Peripheral 8ssue –  Organ –  Organ system •  Soma8c nervous system •  Visceral nervous system (Autonomic nervous system) Func8onal Classifica8on of Neurons Soma8c Nervous System •
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Soma8c motor neurons Innervate skeletal muscles Cell bodies within CNS Axons extend to neuromuscular synapses Most ac8vi8es are consciously controlled Func8onal Classifica8on of Neurons Autonomic Nervous System •  Visceral motor neurons •  2 neuron system –  Preganglionic fiber •  Soma in the brain or spinal cord •  Control neurons in peripheral ganglia –  Postganglionic fiber •  Soma in a peripheral ganglia •  Control the peripheral effectors –  2 divisions of the ANS •  Sympathe8c –  “Fight or Flight” •  Parasypathe8c –  “Rest and Repose” Peripheral Effectors: Smooth muscle Cardiac muscle Glands Func8onal Classifica8on of Neurons Interneurons •  Connect neurons within the CNS –  Sensory ‐ ‐> Sensory –  Motor ‐ ‐ > Motor –  Sensory ‐ ‐ > Motor •  Analysis of sensory inputs •  Coordina8on of motor outputs •  May be excitatory or inhibitory based on the effect on the postsynap8c membrane of other neurons The Synapse •  Communica8on from a neuron to an effector •  A nerve impulse triggers events that transfers informa8on •  Chemical –  Vesicular synapse –  Neurotransmiber released from presynap8c membrane –  Binds to receptors on postsynap8c membrane •  Electrical –  Gap junc8ons The Structure of a Synapse Anatomical Organiza8on of the Nervous System Central Nervous System Peripheral Nervous System •  Center •  Nucleus •  Ganglia –  Collec8on of nerve cell bodies •  Neural cortex –  Superficial gray maber •  Tracts –  White maber •  Columns •  Pathways –  Ascending (sensory) –  Descending (motor) –  Collec8on of nerve cell bodies –  Gray maber •  Spinal nerves –  White maber –  Emerge from the spinal cord –  All mixed nerves •  Cranial nerves –
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White maber Emerge from the brain Sensory Motor mixed Anatomical Organiza8on of the Nervous System