* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Nervous System - University of Nevada, Las Vegas
Types of artificial neural networks wikipedia , lookup
Haemodynamic response wikipedia , lookup
Apical dendrite wikipedia , lookup
Mirror neuron wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Electrophysiology wikipedia , lookup
Subventricular zone wikipedia , lookup
Neural oscillation wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Multielectrode array wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
End-plate potential wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Single-unit recording wikipedia , lookup
Neural engineering wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural coding wikipedia , lookup
Node of Ranvier wikipedia , lookup
Metastability in the brain wikipedia , lookup
Axon guidance wikipedia , lookup
Microneurography wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Neurotransmitter wikipedia , lookup
Pre-Bötzinger complex wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Central pattern generator wikipedia , lookup
Optogenetics wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neuroregeneration wikipedia , lookup
Synaptic gating wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Chemical synapse wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Nervous system network models wikipedia , lookup
Development of the nervous system wikipedia , lookup
Circumventricular organs wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Mammalian Physiology Nervous System Peripheral and Central UNLV 1 UNIVERSITY OF NEVADA LAS VEGAS PHYSIOLOGY, Chapter 6 Berne, Levy, Koeppen, Stanton Objectives • • • • • • Describe the organization of the nervous system Describe the central nervous system Discuss the different cell types in the nervous system Describe characteristics of axons Describe neuronal pools Discuss the peripheral nervous system – Sensory receptors – Somatic motor nerves 2 Basic Nervous System Functions 3 • Sensory Input – provides the central nervous system with information about the internal and external environment • Integration - CNS takes all the incoming information, interprets it, then selects an appropriate response • Motor Output - executes the central nervous system commands to effect the appropriate physical response Organization of the Nervous System • Central Nervous System (CNS) – Brain and spinal cord – Integration and command center • Peripheral Nervous System (PNS) – Neurons outside the CNS – Paired spinal and cranial nerves – Sensory division • Afferent fibers transmit impulses from receptors to CNS – Motor division • Efferent fibers transmit impulses from CNS to effector organs 4 Organization of the Nervous System 5 Central Nervous System CNS is comprised of brain, brain stem, and spinal cord Important structures include: -Medulla – cardiovascular & respiratory control -Cerebellum – motor control, motor learning -Hypothalamus – autonomic and endocrine control -Basal ganglia – motor control -Cerebral cortex – sensory perception, cognition, learning & memory, voluntary movement -Spinal cord – sensory input, reflexes, somatic and autonomic motor output 6 CNS Environment Local environment is controlled by -blood-brain barrier -buffering of neuroglia (astrocytes) -exchange between CSF and brain ECS Blood-brain barrier limits movement large molecules (proteins) and charged ions from the blood into the brain (Capillary endothelial cells of CNS have tight junctions) CSF has lower concentration of K+, glucose , and protein, but higher concentration of Na+ and Cl- than does blood (Table 6-5) 7 Regions of the Brain and Spinal Cord • • • • 8 White matter – dense collections of myelinated fibers Gray matter – mostly soma and unmyelinated fibers Sensory neurons enter via the dorsal root Motor neurons exit via the ventral root Histology of Nerve Tissue • The two principal cell types of the nervous system are: – Neurons – excitable cells that transmit electrical signals – Supporting cells – cells that surround and wrap neurons • The supporting cells (neuroglia or glial cells): – Provide a supportive scaffolding for neurons – Segregate and insulate neurons – Guide young neurons to the proper connections – Promote health and growth 9 Neuroglia: Astrocytes • • • Most abundant, versatile, and highly branched glial cells They cling to neurons and their synaptic endings, and cover capillaries Functionally, they: – Support and brace neurons (glial filaments in cytoplasm) – Anchor neurons to their nutrient supplies (capillaries & pia matter) – Control the chemical environment (take-up K+ & neurotransmitters) 10 Neuroglia: Microglia • Small, ovoid cells with spiny processes – Phagocytes that monitor the health of neurons – Remove cellular debris when CNS is damaged 11 Neuroglia: Ependymal Cells • Range in shape from squamous to columnar – Line the central cavities of the brain and spinal column – Form the epithelium that separates CNS from cerebral spinal fluid in the ventricles – Lie between the brain extracellular space and theCSF 12 Neuroglia: Oligodendrocytes • • • 13 Branched cells that wrap CNS nerve fibers – produce myelin sheath for neurons in the CNS One oligodendrocyte myelinates many neurons CNS version of Schwann cells Neurons (Nerve Cells) • Structural units of the nervous system – Composed of a body, axon, and dendrites – Long-lived, amitotic (non-divisible), and have a high metabolic rate • Their plasma membrane functions in: – Electrical signaling – Cell-to-cell signaling during development 14 Neurons (Nerve Cells) Basic Elements -Soma (cell body) -Dendrites -Axon 15 Development of Neurons • • • The nervous system originates from the neural tube and neural crest The neural tube becomes the CNS There is a three-phase process of differentiation: – Proliferation of cells needed for development – Migration – cells become amitotic and move externally – Differentiation into neuroblasts 16 Axonal Growth • Guided by: – – – – – – • NCAM – – – – 17 Scaffold laid down by older neurons Orienting glial fibers Release of nerve growth factor by astrocytes Neurotropins released by other neurons Repulsion guiding molecules Attractants released by target cells N-CAM – nerve cell adhesion molecule Important in establishing neural pathways Without N-CAM, neural function is impaired Found in the membrane of the growth cone Nerve Cell Body (Soma) • • • • • • 18 Contains the nucleus and a nucleolus Is the major biosynthetic center Is the focal point for the outgrowth of neuronal processes Has no centrioles (hence its amitotic nature) Has well-developed Nissl bodies (rough ER) Contains an axon hillock – cone-shaped area from which axons arise Dendrites of Motor Neurons • • • • • 19 Short, tapering, and diffusely branched processes Extensions of neuronal cell body They are the receptive, or input, regions of the neuron Electrical signals are conveyed as graded potentials (not action potentials) (calcium spikes) Account for 90+% of surface area Axons • Structure – – – – – Slender processes of uniform diameter arising from the hillock Long axons are called nerve fibers Normally there is only one unbranched axon per neuron Axonal terminal – branched terminus of an axon Lack rough endoplasmic reticulum, free ribosomes, Golgi apparatus • Function – Generate and transmit action potentials – Secrete neurotransmitters from the axonal terminals – Axonal transport 20 Axonal Transport • • • Distribution of membrane and cytoplasmic components from soma to points along the axon (especially to axon terminus) Energy supplied by glucose Fast axonal transport – Membrane-bound organelles and mitochondria – Synaptic vesicles – 400 mm/day • Slow axonal transport – Cytoplasmic prioteins – 1 mm/day 21 Axonal Transport • Transport facilitated by microtubules – Organelles attach to microtubules – Movement triggered by calcium • Microtubule motor proteins are required for transport – Kinesin and Dynein • Axonal transport is bidirectional – Anterograde axonal transport (soma to axonal terminals) • Kinesin – replenishment of synaptic vesicles and enzymes responsible for neurotransmitter synthesis – Retrograde axonal transport (axonal terminals to soma) • Dynesin – return of synaptic vesicles to soma for lysosomal degradation 22 Myelin Sheath • • Whitish, fatty (protein-lipoid), segmented sheath around most long axons It functions to: – Protect the axon – Electrically insulate fibers from one another – Increase the speed of nerve impulse transmission 23 Myelin Sheath and Neurilemma Formation • • Formed by Schwann cells in the PNS A Schwann cell: – Envelopes an axon in a trough – Encloses the axon with its plasma membrane – Has concentric layers of membrane that make up the myelin sheath • Neurilemma – remaining nucleus and cytoplasm of a Schwann cell 24 Nerve Fiber Classification • Nerve fibers are classified according to: – Diameter – Degree of myelination – Speed of conduction • Functional: – Sensory (afferent) — transmit impulses toward the CNS – Motor (efferent) — carry impulses away from the CNS – Interneurons (association neurons) — shuttle signals through CNS pathways 25 Synaptic Transmission Neurons communicate across synapses using neurotransmitters –Released from presynaptic membrane –Binds to receptor on post synaptic membrane –Acetylcholine is neurotransmitter in PNS 26 Types of Synapses • • • Axodendritic – synapses between the axon of one neuron and the dendrite of another Axosomatic – synapses between the axon of one neuron and the soma of another Other types of synapses include: – Axoaxonic (axon to axon) – Dendrodendritic (dendrite to dendrite) – Dendrosomatic (dendrites to soma) 27 Synaptic Transmission • Excitatory postsynaptic potentials (EPSP) – Cause depolarization which may or may not reach threshold [↑ Na+ permeability] – Temporal summation: summing several EPSPs from one presynaptic neuron – Spatial summation: summing EPSPs from several different presynaptic neurons • Inhibitory postsynpatic potentials (IPSP) – Cause hyperpolarization [↑ Cl- permeability, ↑ K+ permeability] 28 Termination of Synaptic Transmission • Neurotransmitter bound to a postsynaptic neuron: – Produces a continuous postsynaptic effect – Blocks reception of additional “messages” – Must be removed from its receptor • Removal of neurotransmitters occurs when they: – Are degraded by enzymes (ie. Acetylcholinesterase) – Are reabsorbed by astrocytes or the presynaptic terminals – Diffuse from the synaptic cleft • Synaptic Delay – Neurotransmitter must be released, diffuse across the synapse, and bind to receptors – Synaptic delay – time needed to do this (0.3-5.0 ms) – Synaptic delay is the rate-limiting step of neural transmission 29 Neural Integration: Neuronal Pools • Functional groups of neurons that: – Integrate incoming information – Forward the processed information to its appropriate destination • Serial Processing – Input travels along one pathway to a specific destination – Works in an all-or-none manner – Example: spinal reflexes • Parallel Processing – – – – 30 Input travels along several pathways Pathways are integrated in different CNS systems One stimulus promotes numerous responses Example: a smell may remind one of the odor and associated experiences Organization of a Neuronal Pool in the CNS Each input fiber divides numerous times providing innumerable terminal fibrils to synapse with the cell bodies (dendrites) of the neurons in the pool Input 31 Output Neuronal Pools • Simple neuronal pool – Input fiber – presynaptic fiber – Discharge zone – neurons most closely associated with the incoming fiber – Facilitated zone – neurons farther away from incoming fiber 32 Types of Circuits in Neuronal Pools • Divergent – one incoming fiber stimulates ever increasing number of fibers – Within a pathway to amplify the signal – Into multiple tracts to send the signals to separate areas 33 Types of Circuits in Neuronal Pools • • Convergent – opposite of divergent circuits, resulting in either strong stimulation or inhibition Convergence of signals – Multiple inputs from a single neuron – Inputs from multiple neurons 34 Types of Circuits in Neuronal Pools • 35 Reverberating circuit – chain of neurons containing collateral synapses with previous neurons in the chain making a positive feedback loop – continuous output signal - control of rhythmic activities such as sleep-wake cycle, breathing, walking etc Types of Circuits in Neuronal Pools • 36 Parallel after-discharge – incoming neurons stimulate several neurons in parallel arrays which stimulate a common output cell – complex neural functions such as calculations Peripheral Nervous System • Sensory (afferent) division – Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain – Visceral afferent fibers – transmit impulses from visceral organs to the brain • Motor (efferent) division – Transmits impulses from the CNS to effector organs – Somatic nervous system • Conscious control of skeletal muscles – Autonomic nervous system (ANS) 37 • Two divisions – sympathetic and parasympathetic • Regulates smooth muscle, cardiac muscle, and glands Sensory (Afferent) Receptors Classification • Special – Vision, hearing, taste, smell, balance • Superficial – Touch, pressure, vibration, tickle, heat, cold, pain, itch • Deep – Position, kinesthesia, deep pressure, deep pain • Visceral – Hunger, nausea, distension, visceral pain 38 Sensory Transduction • Response of a sensory receptor to a stimulus – Chemoreceptor – Mechanocreceptor – Photoreceptor 39 Sensory Coding • Stimulus intensity – Mean frequency of discharge (temporal summation) – Number of receptors activated (spatial summation) • Stimulus frequency – Intervals between discharges • • Pattern of nerve impulses Adaptation – Accommodation to stimulus (slow or rapid) 40 Neural Integration Integration: summation of information coming into the neuron. Spatial summation – summation of information coming into different places on the neuron. Temporal summation – summation of information coming into the neuron with time. 41 Sensory Coding Increasing frequency of discharge in response to increasing stimulus intensity Adaptation – signal stops when stimulus becomes constant Different pattern of discharge 42 Sensory Coding Pattern of discharge synchronized with stimulus frequency 43 Somatic Motor Neurons • • • • • • ά- motor neuron – efferent – extrafusal muscle fibers - voluntary control γ- efferent motor neuron – intrafusal muscle fibers - muscle spindle – proprioception Motor unit – ά-motor neuron, axon, and all the muscle fibers it innervates All the muscle fibers in a motor unit are the same type (I, IIa, IIb) Muscle fibers contract on an all or none basis – each fiber contracts fully when stimulated Force increases incrementally by – Recruitment (activating additional motor units) – Summation (increasing frequency of stimulation) 44 Skeletal Muscle Fiber Types Fiber types classified by: -Speed of contraction -Energy producing pathways -Fatigue resistance -Fiber diameter Fiber type determined by neural input pattern -Slow-twitch = tonic innervation pattern -Fast-twitch = phasic innervation pattern Fiber type also determined by trophic nerve substances (axonal flow) 45 Motor Unit Recruitment Size Principle Weaker motor units recruited first, those with smallest diameter axons: type I → type IIa → type IIb Type I – 0 to 50% maximum force Type IIa – 20% to 100% max force Type IIb – 80% to 100% max force 46 Size Principle for Recruitment In response to stretch, small motor neurons recruited first When stretch is released, large motor neurons are deactivated first Large motor neurons are more susceptible to inhibition 47