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121 Cards in this Set
- Front
- Back
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The master controlling and communicating system of the body
* functions *Sensory input *Integration *Motor output |
Nervous System
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monitoring stimuli
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Sensory input
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interpretation of sensory input
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Integration
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response to stimuli
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Motor output
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* Brain and spinal cord
* Integration and command center |
Central Nervous System
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* Paried spinal and cranial nerves
* Carries messages to and from the spinal cord and brain * Is broken into the somatic nervous system and the autonomic nervous system |
Peripheral Nervous System
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MOTOR DIVISION
* Conscious control of skeletal muscles (what I drive) |
Somatic Nervous System
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* Regulates smooth muscle, cardiac muscle, and glands
(what I don't think about) |
Autonomic Nervous System
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best known for mediating the neuronal and hormonal stress response commonly known as the flight or fight response.
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Sympathetic
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summarized by the phrase rest and response or rest and digest.
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Parasympathetic
(parasailors chill) |
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PERIPHERAL NERVOUS SYSTEM
- carry impulses from skin, skeletal muscls, and joints to the brain. |
Sensory afferent fibers
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PERIPHERAL NERVOUS SYSTEM
- transmit impulses from visceral organs to the brain |
Visceral afferent fibers
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PERIPHERAL NERVOUS SYSTEM
- transmits impulses from the CNS to effctor organs (memory device: motors are engines) |
Motor (efferent) division
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The tow principal cell types of the nervous system are:
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Neurons and Supporting Cells
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- excitable cells that transmit electrical signals
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Neurons
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- cells that surround and wrap neurons
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Supporting cells
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* provide a supportive scaffolding for neurons
* Segregate and insulate neurons * Guide young neurons to the proper connections * Promote health and growth |
Supporting Cells: Neuroglia
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* Most abundant, versatile, and highly branched glial cells
* They cling to neurons and their synaptic endings, and cover capillaries |
Astrocytes
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* funtionally, they:
* Support and brace neurons * Anchor neurons to their nutrient supplies * Guide migration of young neurons * Control the chemical environment- by removing excess ions, notably potassium, and recycling neurotransmitters |
Astrocytes
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- small, ovoid (egg shaped) cells with spiny processes
* Phagocytes that monitor the health of neurons |
Microglia
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- range in shape from squamous to columnar
* They line the central cavities of the brain and spinal column- their apical surfaces are also covered with microvilli, which absorb CSF |
Ependymal Cells
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- branched cells that wrap CNS nerve fibers form covering over the axon of a nerve called myelin
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Oligodendrocytes
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(neurolemmocytes)- surround fibers of the PNS
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Schwann Cells
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- Surround nuron cell bodies with ganglia(knots of nerves)
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Satellite cells
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* Structural units of the nervous system
* Composed of a body, axon, and dendrites * long-lived, amitotic, and have a high metabolic rate |
Neurons
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Their Plasma membrane function in:
* Electrical signaling * Cell-to-cell signaling during development |
Neurons
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* 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 |
Nerve cell body
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* armlike extensions from the soma
* Called tracts in the CNS and nerves in in the PNS * There are two types: axons and dendrites |
Processes
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* Short, tapering, and diffusely branched processes
* They are the receptive, or input, regions of the neuron * Electrical signals are conveyed as graded potentials ( not action potentials) |
Dendrites and Motor Neurons
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* Slender processes of uniform diameter arising from the hillock
* Long axons are called nerve fibers * Usually there is only one unbranched axon per neuron * Rare branches, if present, are called axon collaterals * Axonal terminal- branched terminus of an axon |
Axons: Structure
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* Generate and transmit action potentials
* Secrete neurotransmitters from the axonal terminals * Movement along axons occurs in two ways: * Anterograde * Retrograde |
Axons: Function
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toward axonal terminal
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Anterograde
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Away from axonal terminal
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Retrograde
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* Whitish, fatty (protein-lipoid), segmented sheath around most long axons
* It funtions to: * protect the axon * Electriacally insulate fibers from one another * Increase the speed of nerve impulse transmission |
Myelin Sheath
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A series of Schwann cells Sheath blocks ion movements Action potential must "jump" from node to node
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Myelin Sheath
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* 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 ____ ____ Neurolemma- remaining nucleus and cytoplasm of a Schwann cell |
Myelin Sheath and Neurolemma: Formation
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* Envelopes an axon in trough
* Encloses the axon with its plasma membrane * Has concentric layers of membrane that make up the ___ ____ |
A Schwann Cell
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- remaining nucleus and cytoplasm of a Schwann Cell
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Neurolemma
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* A Schwann cell surrounds nerve fibers but coinling does not take place
* Schwann cells partially enclose 15 or more axons |
Unmyelinated Axons
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* Both myelinated and unmyelinated fibers are present
* Myelin sheaths are formed by oligodendrocytes * Nodes of Ranvier are widely spaced * There is no neurilemma |
Axons of the CNS
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REGIONS OF THE BRAIN AND SPINAL CORD
- dense collections of myelinated fibers or axons, which connect various gray matter areas (the location of nerve cell bodies) of the brain to each other and carry nerve impulses between neurons |
White Matter
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REGIONS OF THE BRAIN AND SPINAL CORD
- mostly soma or cell bodies (neurons) and unmyelinated fibers. |
Gray Matter
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NEURON CLASSIFICATION
- three or more processes |
Multipolar
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NEURON CLASSIFICATION
- two processes (axon and dendrite) |
Bipolar
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NEURON CLASSIFICATION
- single, short process |
Unipolar
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NEURON CLASSIFICATION
- transmit impulses toward the CNS |
Sensory Afferent
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NEURON CLASSIFICATION
- carry impulses away from the CNS |
Motor (efferent)
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NEURON CLASSIFICATION
- shuttle signals through CNS pathways |
Interneurons (association neurons)
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* Neurons are highly irritable
* Action potentials, or nerve impulses, are: * Electrical impulses carried along the length of axons * Always the same regardless of stimulus * The underlying functional feature of the nervous system |
Neurophysiology
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- is the charge gradient across a membrane before any changes take place
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Resting potential
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Changes in membrane potential or the charge differential across membrane
- Changes are caused by three events: * Depolarization * Repolarization * Hyperpolarization |
Membrane Potentials
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- the inside of the membrane becomes less negative
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Depolarization
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- the membrane returns to its resting membrane potential
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Repolarization
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- the inside of the membrane becomes more negative than the resting potential
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Hyperpolarization
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* short-lived, local changes in membrane potential
* Decrease in intensity with distance * Magnitude varies directly with the strength of the stimulus * Sufficiently strong ___ ____ can intiate action potentials |
Graded Potentials
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* Voltage changes are decrementral- they fade as they progress
* current is quickly dissipated due to the leaky plasma membrane * Only travel over short distances |
Graded potentials
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* A brief reversal of membrane potential with a total amplitude of 100 mV
* Action potentials are only generated by muscle cells and neurons * They do not decrease in strength over distance * They are the principle means of neural communication * An action potential in the axon of a neuron is a nerve impulse |
Action Potentials
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* Na+ and K channels are closed
* Leakage accounts for small movements of Na+ and K+ * Each Na+ channel has two voltage regulated gates * Activation gates- closed in the resting state * Inactivation gates- open in the resting state |
Action Potential: Resting State
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Closed in the resting state
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Activation gates
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Open in the resting state
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Inactivation gates
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* Na+ permeablility increases; membrane potential reverses
* Na+ gates are opened; K+ gates are closed * Threshold- a critical level of depolarization (-55 to -50 mV) * At threshold, depolarization becomes self-generating |
Action Potential: Depolarization Phase
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* Sodium inactivation gates close
* Membrane permeablility to Na+ declines to resting levels * As sodium gates close, voltage-sensitiv K+ gates open * K+ exits the cell and internal negativity of the resting neuron is restored |
Action Potential: Repolarization Phase
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* Potassium gates remain open, causing an excessive efflux of K+
* This efflux causes ________ of the membrane (undershoot) * The neuron is insensitive to stimulus and depolarization during this time |
Action Potential: Hyperpolarization
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* Repolarization
* Restores the resting electrical conditions of the neuron * Does not restore the resting ionic conditions * Ionic redistribution back to resting conditions is restored by the sodium-potassium pump |
Action potential: Role of the Sodium-Potassium Pump
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Name the phases of the action potential:
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Resting state
depolarization phase repolarization phase hyperpolarization |
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* Na+ influx causes a patch of the axonal membrane to depolarize
* Positive ions in the axoplasm move toward the polarized (negative) portion of the membrane * Sodium gates are shown as closing, open, or closed |
Propagation of an Action Potential (Time = 0ms)
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- membrane is depolarized by 15 to 20 mV
* Established by the total amount of current flowing through the membrane * Weak (subthreshold) stimuli are not relayed into action potentials * all or none phenomenon- action potentials either happen completely, or not at all |
Threshold and Action potentials
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- action potentials either happen completely, or not at all
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All-or-none phenomenon
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* Time from the opening of the Na+ activation gates until the closing of inactivation gates
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Absolute Refractory Period
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* Prevents the neuron from generating an action potential
* Ensures that each action potential is separate * Enforces one-way transmission of nerve impulses |
Absolute Refractory Period
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* The interval following the absolute refractory period when:
* Sodium gates are closed * potassium gates are open * Repolarization is occurring * The threshold level is elevated, allowing strong stimuli to increase the frequency of action potential events |
Relative Refractory Period
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* Conduction velocities vary widely among neurons
* Rate of impulse propagation is determined by: * Axon diameter- the larger the diameter, the faster the impulse (think about hose diameter and water delivery) * Presence of a myelin sheath- myelination dramatically increases impulse speed |
Conduction Velocities of Axons
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* Current passes through a myelinated axon only at the nodes of Ranvier
* Voltage-gated Na+ channels are concentrated at these nodes * Action potentials are triggered only at the nodes and jump from one node to the next * Much faster than conduction along unmyelinated axons |
Saltatory Conduction
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* An autoimmune disease that mainly affects young adults
* Symptoms: visual disturbances, weakness, loss of muscular control, and urinary incontinence * Nerve fibers are severed and myelin sheaths in the CNS become nonfunctional scleroses * Shunting and short-circuiting of nerve impulses occurs |
Multiple Sclerosis
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* The advent of disease-modifying drugs including interferon beta-1a and -1b, A vonex, Betaseran, and Copazone:
* Hold symptoms at bay * Reduce complications * Reduce disability |
Multiple Sclerosis: Treatment
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- cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue
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Nerve
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Connective tissue coverings include:
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Endonerium
Perineruium Epineurium |
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loose connective tissue that surrounds axons
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Endoneurium
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course connective tissue that bundles fibers into fascicles
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Perineurium
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tough fibrous sheath around a nerve
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Epineurium
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Even if the sensitive living axons ar damaged, the conduit made up of epineurium and perineurium will often survive and provide a pathway for regrowing nerves.
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Nerve Fiber Structure
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* Nerve fibers are classified according to:
* Diameter * Degree of myelination * Speed of conduction |
Nerve fiber classification
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* A juction that mediates info transfer from one neuron:
* To another neuron * To an effector cell * Presynaptic Neuron * Postsynaptic neuron |
Synapses
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- conducts impulses toward the synapse
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Presynaptic neuron
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- transmits impulses away from the synapse
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Postsynaptic neuron
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Name the types of synapses
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Axodendritic
Axosomatic Axoaxonic Dendrodendritic Dendrosomatic |
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- synapses between the axon of one neuron and the dendrite of another
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Axodendritic
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- synapses between the axon of one neuron and the soma of another
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Axosomatic
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Axon to axon =
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Axoaxonic
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dendrite to dendrite =
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Dendrodendritic
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dendrites to soma =
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Dendrosomatic
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* Are less common than chemical synapses
* Correspond to gap junctions found in other cell types * Are important in the CNS in: * Arousal from sleep * Mental Attention * Emotions and memory * Ion and water homeostasis |
Electrical Synapses
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* Specialized for the release and reception of neurotransmitters
* Typically composed of two parts: * Axonal terminal of the presynaptic neuron, which contains synaptic vesicles * Receptor region on the dendrites or soma of the postsynaptic neuron |
Chemical Synapse
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Steps of an ____ ____
* At rest the outside of the membrane is more positive than inside. * Sodium moves inside the cell causing an action potential, the influx of positive sodium ions makes the inside of the membrane more positive than the the outside. * potassium ions flow out of the cell, restoring the resting potential net charges. * Sodium ions are pumped out of the cell and potassium ions are pumped into the cell, restoring the orginal distribution of ions. |
Action Potential
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* Neurotransmitter must be released, diffuse across the synapse, and bind to receptors
* Synaptic delay- time needed to do this (0.3-5.0ms) * Synaptic delay is the rate-limiting step of neural transmission |
Synaptic Delay
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* Neurotransmitter receptors mediate changes in membrane potential according to:
* The amount of neurotransmitter released * The amount of tim the neurotransmitter is bound to receptors |
Postsynaptic Potentials
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* Chemicals used for neuronal communication with the body and the brain
* 50 different neurotransmitters have been identified * Classified chemically and functionally |
Neurotransmitters
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What are these?
* Acetylcholine * Biogenic amines * Amino acids * Peptides * Nove messengers: ATP and dissolved gases NO and CO |
Chemical Neurotransmitters
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* First neurotransmitter identified, and best understood
* Released at the neuromuscular junction * Synthesized and enclosed in synaptic vesicles * Degraded by the enzyme acetylcholinesterase * Released by: * all neurons that stimulate skeletal muscle * some neurons in the autonomic nervous system |
Neurotransmitters: Acetylcholine
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Neurotransmitters: ____ ____
* include: * Catecholamines- dopamine, norepinephrine, and epinephrine * Indolamines- serotonin and histamine * Broadly distributed in the brain * Play roles in emotional behaviors and our biological clock |
Biogenic Amines
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- is believed to play an important role as a neurotransmitter, in the modulation of anger, aggression, body temperature, mood, sleep, sexuality, and appetite as well as stimulating vomiting
* In addition, ___ is also a peripheral signal mediator. For instance, serotonin is found extensively in the human gastrintestinal tract, and the major storage place is platelets in the blood stream. * If neurons that make ___ are abnormal in infants, there is a risk of sudden infant death syndrome (SIDS). * Several classes of drugs target the 5-HT system including some antidepressants, antiemetics, antipsychotics, and antimigraine drugs as well as the psychedelic drugs and empathogens |
Serotonin
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____ - has important roles in behavior and cognition, motivation and reward, inhibition of prolactin production, sleep, mood, attention, and learning and is a precursor for norephrine and epinephrine.
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Dopamine
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_____- underlies the fight-or-flight response, directly increasing heart rate, triggering the release of glucose from energy stores, and increasing blood flow to skeletal muscle.
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Norepinephrine
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_____- when secreted into the bloodstreeam it rapidly prepares the body for action in emergency siturations. The hormone boosts the supply of oxygen and glucose to the brain and muscles, while suppressing other non-emergency bodily processes (digestion in particular).
* Because of its suppressive effect on the immune system, epinephrine is used to treat anaphylaxis and sepsis. |
Epinephrine
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_____- invovled in local immune responses and allergies as well as regulating physiological funtion in the gut and acting as a neurotransmitter.
* Histaminergic action is known to modulate sleep- high produces wakefulness * Histamine is released as part of the human orgasm. |
Histamine
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Neurotransmitters: ______
* Include: * Substance P- mediator of pain signals * Beta endorphin, dynorphin, and enkephalins * Act as natural opiates; reduce pain perception * Bind to the same receptors as opiates and morphine * Gut-brain ____- somatostatin, and cholecystokinin |
Peptides
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Neurotransmitters: ____ ____
* ATP * Is found in both the CNS and PNS * Produces excitatory or inhibitory responses depending on receptor type * Induces Calcium wave propagation in astrocytes * Provokes pain sensation |
Novel Messengers
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Neurotransmitters: Novel Messengers
* ____ ____ * Is involved in learning and memory * The endothelium (inner lining) of blood vessels use ____ ____ to signal the surrounding smooth muscle to relax, thus resulting in vasodilation and increasing blood flow production of ____ ____. * is elevated in populations living at high-altitudes, which helps these people avoid hypoxia. * Viagra is a compound that metabolizes to release ____ ____. |
Nitric oxide
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- is the main regulator of cGMP- (cylic guanosine monophosphate) a second transmitter in the brain.
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Carbon Monoxide
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Functional Classifications of ______
* Two classifications: exitatory and inhibitory |
Neurotransmitters
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_____ neurotransmitters cause depolarizations (e.g. glutamte)
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Excitatory
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_____ neurotransmitters cause hyperpolarizations [eg. GABA (Gamma (y)- aminobutyric acid) and glycine]
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Inhibitory
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Functional Classifications of _____
* Some neurotransmitters have both excitatory and inhibitory effects * Determeined by the receptor type of the postsynaptic neuron * Ex: acetylcholine * Excitatory at neuromuscular junctions with skeletal muscle * Inhibitory in cardiac muscle |
Neurotransmitters
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NEUROTRANSMITTER RECEPTOR MECHANISMS
* _____ neurotransmitters that open ion channels * promote rapid responses * ex: ACh and amino acids |
Direct
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NEUROTRANSMITTER RECEPTOR MECHANISMS
____: neurotransmitters that act through second messengers * Promote long-lasting effects * EX: biogenic amines, peptides, and dissolved gases |
Indirect
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G Protein-Linked Receptors: ____
* G protein-linked receptors activate intracellular second messengers including Calcium, cGMP, diacylglycerol, as well as cAMP * Second Messengers * Open or close ion channels * Activate kinase enzymes * Phosphorylate channel proteins * Activate genes and induce protein synthesis |
Effects
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Neural transmitter ____ and ____
* Diseases that afect the function of signal transmission can have serious consequences. Parkinson's Disease has a deficiency of the neurotransmitter dopamine. Progressive death of brain cellsincreases this deficit, causing tremers, rigidity and unstable posture. L-dopa is a chemicla related to dopamine that eases some of the symptoms (by acting as a substitute neurotransmitter) but cannot reverse the progression of the disease |
problems and effects
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* The bacterium CLOSTRIDIUM TETANI produces a toxin that prevents the release of GABA. GABA is important in control of skeletal muscles. Without this control chemical, rgulation of muscle contraction is lost; it can be fatal when it effects the muscles used in breathing.
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Neural transmitter problems and effects
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CLOSTRIDIUM BOTULINUM produces a toxin found in improperly canned foods. The botulism toxin causes the progressive relaxation of muscles, and can be fatal.
* A wide range of drugs also operate in the synapses: cocaine, LSD, caffeine, and insecticides |
Neural transmitter problems and effects
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* Functional groups of neurons that:
* Integrate incoming information * Forward the processed info to its appropriate destination |
Neural Integration: Neuronal Pools
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* The nervous system orginates 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 |
Development of Neurons
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