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Anatomy & Physiology

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Nervous Tissue & Homeostasis excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue. together with endocrine system: responsible for maintaining homeostasis

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Differences in Nervous & Endocrine Control of Homeostasis NERVOUS ENDOCRINE rapid responder action potentials slow, prolonged response releases hormones

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Structures of the Nervous System total mass of 2 kg (~3% of total body mass) Skull Spinal Cord Spinal Nerves Cranial Nerves Ganglia Enteric Plexus Special Senses & other Sensory Receptors

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Major Structures of the Nervous System

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Functions of the Nervous System 3 basic functions: 1. Sensory 2. Integrative 3. Motor

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Sensory Function sensory receptors detect internal & external stimuli sensory (afferent) neurons carry this sensory information to spinal cord & brain thru cranial & spinal nerves

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Integrative Function integrate: process nervous system takes information from sensory neurons & processes that information, analyzes it, stores some of it & makes decisions for appropriate responses served by interneurons (connect 1 neuron to another neuron Perception : conscious awareness of sensory stimuli occurs in brain

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Motor Function served by motor (efferent) neurons carry info from brain/spinal cord effectors (muscle or gland) thru cranial or spinal nerves results in muscles contraction or gland secreting

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Quick Quiz What terms are given to neurons that carry input spinal cord & brain? What terms are given to neurons that carry output out of the brain & spinal cord?

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Organization of the Nervous System

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Histology of the Nervous System 2 cell types 1. Neurons 2. Neuroglia

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Neurons nerve cells that possess electrical excitability : ability to respond to a stimulus & convert it into an action potential stimulus: any change in environment that is strong enough to initiate an action potential

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Direction Action Potential Travels

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Action Potential electrical signal that propagates along surface of neurolema (membrane) begins & travels due to movement of ions between interstitial fluid & inside of neuron thru specific ion channels once begun it travels rapidly @ constant strength

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Parts of a Neuron

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Parts of Neuron: Cell Body contains nucleus, cytoplasm, typical organelles, + Nissl bodies clusters of RER make materials for: growth of neuron regenerate damaged axons in PNS

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Dendrites little trees input portion of neuron usually, short, tapering, highly branched their cytoplasm contains Nissl bodies, mitochondria

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Axon propagates action potentials another neuron muscle fiber gland cell

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Parts of an Axon joins cell body @ cone-shaped elevation: axon hillock part of axon closest to hillock = initial segment jct of axon hillock & initial segment where action potential arises so is called the trigger zone

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Parts of an Axon axoplasm: cytoplasm of an axon axolemma: plasma membrane of axon axon collaterals: side branches along length of axon (most @ 90) axon terminals: axon divides into many fine processes

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Synapse site of communication between 2 neurons or between a neuron & effector cell synaptic end bulbs: tips of some axon terminals swell into bulb-shaped structures synaptic vesicles: store neurotransmitter many neurons have >1 neurotransmitter, each with different effects on postsynaptic cell

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Types of Neurons Functional Classification Structural Classification Sensory Interneurons Motor use # processes extending from cell body 1. Multipolar neurons 2. Bipolar neurons 3. Unipolar neur ons

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Multipolar Neurons several dendrites with 1 axon includes most neurons in brain & spinal cord

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Bipolar Neuron 1 main dendrite & 1 axon retina, inner ear, olfactory area of brain

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Unipolar Neuron are sensory neurons that begin in embryo as bipolar during development axon & dendrite fuse then divide into 2 branches (both have characteristic structure & function of an axon) 1 branch ends with dendrites (out of CNS) 2 nd branch ends in axon terminal (in CNS) cell bodies of most found in ganglia

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Unipolar Neuron

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Purkinje Cells found in cerebellum

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Pyramidal Cells in cerebral cortex of brain

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Neuroglia (Glia) ~50% vol of CNS glue do not generate or propagate action potentials multiply & divide in mature nervous systems glioma : brain tumors derived from glial cells very malignant, grow rapidly

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Glial Cells of the CNS 1. ASTROCYTES 2. OLIGODENDROCYTES 3. MICROGLIA 4. EPENDYMAL CELLS

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Astrocytes star-shaped largest & most numerous of glial cells functions: 1. physically support neurons 2. assist in blood-brain-barrier (bbb) 3. in embryo: regulate growth, migration, &interconnections between neurons 4. help maintain appropriate chemical environment for propagation of action potentials

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Oligodendrocytes few trees smaller & fewer branches than astrocytes Functions: 1. form & maintain myelin sheath on axons in CNS 2. 1 oligo. myelinates many axons

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Microglia small cells with slender processes giving off many spine-like projections function: 1. phagocytes remove cellular debris made during normal development remove microbes & damaged nervous tissue

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Ependymal Cells single layer of cuboidal to columnar cells ciliated & have microvilli function: 1. line ventricles of brain & central canal of spinal cord 2. produce, monitor, & assist in circulation of cerebrospinal fluid (CSF) 3. form bbb

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Neuroglial Cells of the PNS Schwann cells Satellite cells

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Schwann Cells functions: 1. myelinate axons in PNS 1 Schwann cell myelinates 1 axon 2. participate in axon regeneration

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Satellite Cells flat cells that surround cell bodies of neurons in PNS ganglia functions: 1. structural support 2. regulate exchange of materials between neuronal cell bodies & interstitial fluid

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Myelination myelin sheath: made up of multilayered lipid & protein (plasma membrane) covering function: 1. electrically insulates axon 2. increases speed of nerve impulses

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Myelinated & Unmyelinated Axons

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Nodes of Ranvier gaps in myelin sheath 1 Schwann cell wraps axon between nodes of Ranvier

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Myelin amount increases from birth to maturity infants responses slower & less coordinated as older child or adult in part because myelination is a work in progress thru infancy

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Demyelination loss of myelin sheath see in disorders: multiple sclerosis Tay-Sachs side effect of radiation therapy & chemotherapy

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Gray Matter of the Nervous System contains: neuronal cell bodies dendrites unmyelinated axons axon terminals neuroglia

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White Matter of the Nervous System composed of: myelinated axons

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