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176 Cards in this Set
- Front
- Back
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What type of nerves is the PNS mainly consisting of? |
Spinal Nerves: to and from the spinal cord Cranial Nerves: to and from the brain |
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What is the function of the nervous system |
Sensory input: information gathered by sensory receptors about internal and external changes Integration: Processing and interpretation of the sensory input Motor Output: Activation of effector organs (muscles and glands) produces a response |
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Sensory Division |
Afferent Somatic Sensory Fibers: convey impulses from skin, skeletal muscles, and joints to CNS Visceral Sensory Fibers: convey impulses from visceral organs to the CNS |
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Motor Division |
Efferent Transmits impulses from the CNS to effector Organs - muscles and glands two divisions Somatic nervous system autonomic nervous system |
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Somatic Nervous system |
Somatic motor nerve fibers conducts impulses from CNS to skeletal muscle Voluntary nervous system - conscious control of skeletal muscles |
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Autonomic Nervous System |
Visceral motor nerve fibers regulates smooth muscle, cardiac muscle, and glands involuntary nervous system two functional subdivisions - Sympathetic - Para sympathetic - work in opposition of each other |
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Histology of Nervous Tissue |
Highly cellular, little extracellular space (tightly packed) |
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What are the two principle cell types of the Nervous Tissue |
Neuroglia- Small cells that surround and wrap delicate neurons Neurons (nerve cells)- excitable cells that trasmit electrical signals |
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Neuroglia of the CNS |
CNS -Astrocytes -Microglial Cells -Ependymal Cells -Oligodendrocytes |
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Neuroglial of the PNS |
Satellite cells Schwann cells |
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Astrocytes |
Most abundant, versatile, branched glial cell Cling to neurons, synaptic endings, and capillaries Blood- Brain Barrier support and brace neurons control chemical environment around neurons respond to nerve impulses and Neurotransmitters influence neuronal functioning |
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Microglial Cells |
Defense cells in the CNS |
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Ependymal cells |
line the cerebrospinal fluid-filled cavities |
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Oligodendrocytes |
form the myelin sheths around the CNS nerve fibers |
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Satellite Cells |
Surround neuron cell bodies in the PNS Function similar to Astrocytes of CNS |
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Schwann Cells |
Neurolemmocytes surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers vital to regeneration of damaged peripheral nerve fibers |
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Neurons |
Structural Units of the nervous system large, highly specialized cells that conduct impulses extreme longevity (100+ years) Amitotic High metabolic rate- requires continuous supply of oxygen and glucose all have cell body (soma) and one or more processes (axons and dendrites) |
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Neuron Cell Body |
Perikaryon or soma Center of neuron Nuclei- clusters of neuron cell bodies in CNS Ganglia- groups of neuron cell bodies in the PNS |
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Neuron Processes |
two types of processes dendrites and axons Tracts- bundles of neuron processes in CNS Nerves- Bundles of neuron processes in PNS |
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Dendrites |
Function: receptive (input) region of neuron convey incoming messages toward cell body as graded potentials (short distance signals) dendritic spines- collect information |
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Axon- Structure |
axon hillock- cone shaped area of cell body long axons are called Nerve Fibers Axon Collaterals- occasional branches distal endings called axon terminals or terminal boutons |
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Axon- Function |
Conducting region of neuron; generates nerve impulses transmits them along Axolemma (neuron cell membrane) to axon terminal neurotransmitters are released from axon ternimal into a synapse lacks rough ER and golgi apparatus |
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transport along the axon |
molecules and organelles are moved along axons by motor proteins and cytoskeletal elements movement in both directions Anterograde- away from cell body -ex mitochondria, cytoskeleton elements, membrane parts, enzymes Retrograde- toward cell body -ex organelles to be degraded, signal molecules, viruses, bacterial toxins |
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Myelin Sheath |
composed of myelin - whitissh, protein-lipoid substances segmented sheath around most long or large-diameter axons -Myelinated Fibers function: protects and electrically insulates axon increases speed of nerve impulse transmission |
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Myelination in the PNS |
plasma membranes of myelinating cells have less proteins -no channels or carriers -good electrical insulators -interlocking proteins bind adjacent myelin membranes Myelin sheath gaps -gaps between adjacent Schwann Cells -sites where axon collaterals can emerge -called nodes of ranvier Nonmyelinated fibers thin fibers not wrapped in myelin, surrounded by schwann cells but no coiling; one cell may surround 15 different fibers |
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Myelin Sheaths in the CNS |
formed by multiple, flat processes of oligodendrocytes, not whole cells can wrap up to 60 axons at once myelin sheath gap is present no outer collar of perinuclear cytoplasm thinnest fibers are unmyelinated white matter and gray matter
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White Matter |
regions of brain and spinal cord with dense collections of mylinated fibers |
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Gray Matter |
Mostly neuron cell bodies and nonmyelinated fibers |
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Functional Classification of Neurons |
Grouped by direction in which nerve impulse travels relative to CNS Three Types Sensory (afferent) Motor (efferent) Interneurons |
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Sensory |
Transmit impulses from sensory receptors towards CNS almost all are unipolar Cell Bodies in ganglia in PNS |
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Motor |
Carry impulses from CNS to effectors multipolar most cell bodies in CNS (except some autonomic neurons) |
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Interneurons (association neurons) |
Lie between motor and sensory neurons Shuttle signals through CNS pathways; most are entirely within CNS 99% of body's neurons most confined in CNS |
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Membranes Potentials |
Neurons (and muscle fibers) are highly excitable respond to adequate stimulas by generating an action potential (nerve impulse) |
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Basic Principles of Electricity |
Opposite charges attract each other Energy is required to separate opposite charges across a membrane Energy is liberated when the charges move toward one another If opposite charges are separated, the system has potential energy |
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Voltage |
is a measure of potential energy generated by separated charge measured between two points in volts Called potential difference or potential greater charge difference between points = higher voltage |
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Current |
is the flow electricalcharge (ions) between two points -can be used to do work |
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Resistence |
hindrance to charge flow insulator- substance with high electrical resistance conductor- substance with low electrical resistance |
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Ohms Law |
Current (I) = Voltage (V) / resistance (R) current and voltage is directly proportional no net current flow between points with same potential current inversely related to resistance |
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Role of Membrane Ion Channels |
Large transmembrane proteins serve as selective membrane ion channels Two main types of ion channels Leakage (nongated) channels- always open Gated- part of protein changes shape to open/close channel |
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Role of Membrane Ion Channels: gated channels |
Three Types Chemically Gated (ligand-gated) channels - open with binding of a specific neurotransmitter Voltage-Gated channels - Open and close in response to changes in membrane potential |
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Mechanically gated channels |
Open and close in response to physical deformation of receptors, as in sensory receptors |
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Gated Channels |
When gated channels are open -ions diffuse quickly across membrane along electrochemical gradients Ion flow creates an electrical current and voltage changes across membrane |
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Resting Membrane Potential |
Potential difference across membrane of resting cell Generated by differences in ionic makeup of ICF and ECF differential permeability of the plasma membrane ECF has higher [] of Na+ than ICF- balanced by Cl- ICF has higher [] of K+ than ECF- balanced by - charged proteins
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Depolarization |
decrease in membrane potential (towards zero and above) Inside of membrane becomes less negative than resting membrane potential Increases probability of producing a nerve impulse |
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Hyperpolarization |
An increase in membrane potential (away from zero) Inside of cell more negative than resting membrane potential Reduces probability of producing a nerve impulse |
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Graded Potential |
SAhort-lived, localized changes in membrane potential either depolarized or hyperpolarization triggered by stimulus that opens gated ion channels Current flows but dissipates quickly and decays |
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Action Potential |
Principle way neurons send signals principle means of long-distance neural communication occur only in muscle cells and axons of neurons brief reversal of membrane potential with change of ~100 mV do not decay over distance as graded potentials do |
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Properties of Gated Channels |
Each Na+ channel has two voltage- sensitive gates Activation gates - closed at rest; open with depolarizion allowing Na+ to enter cell Inactivation gates - open at rest; block channel once it is open to prevent more Na+ from entering cell Each K+ channel has one voltage-sensitive gate closed at rest opens slowly with depolarization |
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Generation of action potential: resting site |
All gated Na+ and K+ channels are closed only leakage channels for Na+ and K+ are open - this maintains the resting membrane potential |
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Generation of an action potential: Depolarizing Phase |
Depolarizing local currents open voltage-gated Na+ channels - Na+ rushes into cells Na+ influx causes more depolarization which opens more voltage-gated Na+ channels -> ICF At threshold (-55 to -50 mV) positive feedback causes opening of all voltage-gated Na+ channels to open -> a reversal of membrane polarity of +30mV |
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Generation of an Action Potential: Repolarizing Phase |
Na+ channel slow inactivation gates close Membrane permeability to Na+ declines to resting states - action potential spike stops rising Slow voltage-gated K+ channels open - K+ exits the cell and internal negativity is restored |
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Generation of Action Potential: Hyperpolarization |
Some K+channels remain open, allowing excessive K+ efflux - Inside of membrane more negative than resting state This causes hyperpolarization of the membrane (slight dip below below resting voltage) Na+ channels begin to reset |
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Role of the Sodium-Potassium Pump |
Repolarization resets electrical conditions not ionic conditions After repolarization Na+/K+ pumps (thousands of them in an axon) restore ionic conditions -3 Na+ pumped out of cell - 2 K+ pumped into cell |
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Threshold |
Not all depolarization events produce APs For axon to "fire," depolarization must reach threshold - that voltage at which the AP is triggered At threshold: - membrane has been depolarized by 15-20 mV - Na+ permeability increases - Na+ influx exceeds K+ efflux - the positive feedback cycle begins |
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All of None Phenomenon |
An AP either happens completely, or it does not happen at all |
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Propagation of an Action Potential |
Propagation allow AP to serve as a signaling device Na+ influx causes local currents - local currents cause depolarization of adjacent membrane areas in direction away from AP origin (toward axon's terminals) - Local currents trigger an AP there - This causes the AP to propagate AWAY from the AP origin Since Na+ channels closer to AP origin are inactivated no new AP is generated there |
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Absolute Refractory Period |
When voltage-gated Na+ channels open neuron cannot respond to another stimulus Absolute Refractory Period - Time from opening the Na+ channels until resetting of the channels - Ensure that each AP is an all-or-none event - Enforces one-way transmission of nerve impulses |
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Relative Refractory Period |
Follows absolute refractory period - Most Na+ channels have returned to their resting state - Some K+ channels still open - Repolarization is occuring Threshold for AP generation is elevated - inside of membrane more negative than resting state Only exceptionally strong stimulus could stimulate an AP |
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Conduction Velocity |
Conduction velocities of neurons vary widelt Rate of AP propagation depends on- - Axon Diameter - Large diameter fibers have less resistance to local current flow so faster impulse conduction -Degree of Myelination - Continuous Conduction in nonmyelinated axons is slower than saltatory conduction in myelinated axons |
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Conduction Velocity: Effects of Myelination |
Myelin sheaths insulate and prevent leakage of charge saltatory conduction (possible only in myelinated axons) is about 30 times faster - Voltage-gated Na+ channels are located at myelin sheath gaps - APs generated only at gaps - Electrical signal appears to jump rapidly from gap to gap |
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Conduction Velocity: Effects of Myelination |
Myelin Sheaths insulate and prevent leakage of charge Saltatory conduction (possible only in myelinated axons) is about 30 times faster - Voltage-gated Na+ channels are located at myelin sheath gaps - APs generated only at gaps - Electrical signal appears to jump rapidly from gap to gap |
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Nerve Fiber Classification |
Nerve Fibers classified according to: -Diameter -Degree of Myelination -Speed of conduction |
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Nerve Fiber Classification: Groups |
Group A fibers - large diameter, myelinated somatic sensory motor fibers of skin, skeletal muscles, joints Group B Fibers - Intermediate diameter, lightly myelinated fibers Group C Fibers - Smallest diameter, unmyelinated ANS fibers |
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The Synapse |
Nervous System works because information flows from neuron to neuron Neurons functionally connected by synapses |
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Synapse Classifications |
Axodendritic- btw axon terminals of one neuron and dendrites of others Axosomatic- btw axon terminals of one neuron and soma of others less common types Axoaxanal (axon to axon) dendrodendritic (Dendrite to dendrite) somatodendritic (dendrite to soma) |
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Presynaptic neuron |
Neuron conducting impulses toward synapse sends the information |
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Postsynaptic neuron |
in PNS may be a neuron, muscle cell, or gland cell - neuron transmitting electrical signal away from synapse - receives the information |
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Chemical Synapses |
Specialized for release and reception of chemical neurotransmitters typically composed of two parts Two parts separated by Synaptic cleft Electrical impulse changed to chemical across synapse, then back into electrical |
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Synaptic Cleft |
Fluid- filled space Prevents nerve impulses from directly passing from one neuron to next Transmission across synaptic cleft - clemical event - depends on release, diffusion, and receptor binding of neurotransmitters - ensures unidirectional communication between neurons
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Information transfer across Chemical synapsis |
AP arrives at axon terminal of presynaptic neuron Causes voltage-gated Ca2+ channels to open Synaptotagmin- protein binds Ca2+ and promotes fusion of synaptic vesicles with axon membrane Exocytosis of neurotransmitter into synaptic cleft occurs |
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Termination of Neurotransmitter effects |
Reuptake- by astrocytes or axon terminal Degradation- by enzymes Diffusion- away from synaptic cleft |
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Synaptic delay |
rate-limiting step of neural transmission |
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Postsynaptic Potentials |
Neurotansmitter receptors cause graded potentials that vary in strength with: - amount of neurotransmitter released - time neurotransmitter stays in area Types of postsynaptic potentials - EPSP- excitatory postsynaptic potentials - ISPS- inhibitory postsynaptic potentials |
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Excitatory Synapses and ESPSs |
Neurotransmitter binding opens chemically gated channels - allows simultaneous flow of Na+ and K+ in opposite directions Na+ influx greater than K+ efflux -> net depolarization called EPSP (not AP) EPSP help trigger AP if EPSP is of threshold strength - can spread to axon hillock trigger opening of voltage-gated channels, and cause AP to be generated |
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Inhibitory Synapses and IPSP |
reduces postsynaptic neuron's ability to produce an action potential - makes membrane more permeable to K+or Cl- - if K+ channels open, it moves out of the cell - if Cl- channels open, it moves into cell therefore neurotransmitter hyperpolarizes cell - inner surface of membrane becomes more negative -AP less likely to be generated |
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Synaptic Integration: Summation |
A single EPSP cannot induce an AP EPSPs can summate to influence postsynaptic neuron IPSPs can also summate Most neurons receive both excitatory and inhibitory from thousands of other neurons - only if EPSPs predominate and bring to threshold -> AP |
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Types of Summation |
Temporal Summation - one or more presynaptic neurons transmit impulses in rapid-fire order Spatial Summation - Postsynaptic neuron stimulated simultaneously by large number of terminals at the same time |
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Integration: Presynaptic Inhibition |
Excitatory neurotransmitter release by one neuron inhibited by another neuron via an axoaxonal synapse less neurotransmitter released smaller EPSPs formed |
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Integration: Synaptic Potential |
repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron - Ca2+ [] increases in presynaptic terminal and post synaptic neuron Brief high-frequency stimulation partially depolarizes postsynaptic neuron - chemically gated channels (NMDA receptors) allow Ca2+ entry - Ca2+ activated kinase enzymes that promote more effective responses to subsequent stimuli |
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Neurotransmitters |
Language of nervous system 50 or more neurotransmitters most neurons make two or more neurotransmitters - usually released at different stimulation frequencies Neurotransmitters are classified by chemical structure and by function |
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Classification of Neurotransmitters: function |
Can classify by -Effects - excitatory versus inhibitory -Actions - direct versus indirect |
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Classification of Neurotransmitters: Functions: Effects |
Neurotransmitter effects can be -excitatory (depolarizing) -inhibitory (hyperpolarizing) Effects determined by the neurotransmitter receptor to which it binds. Examples: -GABA and glycine usually inhibitory -Glutamate usually excitatory -ACh binds to at least two receptor types with opposite effects -ACh excitatory at neuromusclar junctions -ACh inhibitory in cardiac muscle |
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Classification of Neurotransmitters: Direct versus Indirect Actions Direct Action |
Direct Action- (ex. ACh) Neurotransmitter binds to and opens ligand/chemically-gated ion channel Promotes rapid responses by altering membrane potential |
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Channel-Linked (Ionotropic) neurotransmitter Receptors: Mechanism of Action |
Ligand/chemically-gated ion channels Neurotransmitter is the ligand Action is direct, immediate and brief Excitatory receptors are channels for small cations Inhibitory receptors allow Cl- influx that causes hyperpolarization |
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Classification of Neurotransmitters: Direct versus Indirect Action Indirect Action |
Indirect Action Neurotransmitter acts though intracellular second messengers, usually G protein signal transduction pathways Broader, longer-lasting effects similar to hormones Biogenic amines, neuropeptides,and dissolvedd gases |
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G Protein-Linked (Metabotropic) Neurotransmitter Receptors: MEchanism of Action |
Responses are indirect, complex, slow, and often prolonged Transmembrane protein complexes Cause widespread metabolic changes ex. Muscarinic ACh receptors, receptors that bind biogenic amines and neuropeptides |
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Acetylcholine (ACh) |
Released at -Neuromuscular junctions -by some ANS neurons -by some CNS neurons Degraded by the enzyme acetylcholinesterase (AChE) ACh pharmacology and toxicology -AChE blocked by nerve gas, causing tetanic muscle spasms -Botox inhibits ACh release |
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Acetylcholine receptors |
Nicotinic ACh receptor -excitatory -direct action -located on -skeletal muscles, ANS ganglia, CNS neurons -inhibited by the drug curare, causing muscle paralysis Muscarinic ACh Receptor -excitatory or inhibitory depending on receptor subtype -indirect action -located on parasympathetic postganglionic fibers in ANS |
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Biogenic Amines |
Catecholamines - dopamine, norepinephrine, and epinephrine - synthesized from amino acid tyrosine Indolamines - serotonin, sythesized from amino and tryptophan - histamine, sythesized from amino acid histidine Broadly distributed in brain imbalances associated with menth illness (depression, anxiety, schizophrenia) |
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Classification of Neurotransmitters: Chemical Structure: Peptides |
Peptides (neuropeptides) -Substance P - Mediator of pain signals - Endorphins - beta endorphins, dynorphin and enkephalins - act as natural opiates; reduce pain perception -Gut-Brain Peptides - Somatostatin and Cholecystokinin |
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Classification of Neurotransmitters: Chemical Structure: Purines |
ATP Adenosine - Potent inhibitor in brain - caffeine blocks adenosine receptors act in both CNS and PNS produce fast or slow responses induce Ca2+ influx in astrocytes |
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Classification of Neurotransmitters: Chemical Structure: Gases and Lipids |
Nitric Oxide (NO), Carbon monoxide (CO), Hydrogen sulfide gases (H2S) Bind with G protein- coupled receptors in the brain Lipid soluble Synthesized on demand No involved in learning and formation of new memories; brain damage in stroke patients, smooth muscles relaxation in intestines |
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Classification of Neurotransmitters: Chemical Structure: Endocannabinoids |
Act at same receptors as THC (active ingredient in marijuana) Lipid soluble Synthesized on demand Believed involved in learning and memory May be involved in neuronal development, controlling appetite, and suppressing nausea |
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Types of Circuits |
Circuits - patterns of synaptic connections in neuronal pools four types of circuits - diverging - converging - reverberating - parallel after-discharge |
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Diverging |
One input, many outputs |
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Converging |
Many inputs, one outputs |
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Reverberating |
signal travels through a chain of neurons, each feeding back to previous neurons |
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Parallel |
Signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell
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Endoneurium |
loose connective tissue that encloses axons and their myelin sheaths |
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Perineurium |
Coarse connective tissues that bundles fibers into fascicles |
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Epineurium |
tough fibrous sheath around a nerve |
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Sensation versus perception |
Sensation- Conscious awareness of stimuli Perception- Interpretation of meaning of stimulus |
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Classification of Sensory Receptors |
Based on- - type of stimulus they detect - Location in body - Structural complexity |
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Mechanoreceptors |
respond to touch, pressure, vibration, and stretch |
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Thermoreceptors |
sensitive to changes in temperature |
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Photoreceptors |
respond to light energy |
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Chemoreceptors |
respond to chemistry -smell, taste, changes in blood chemistry |
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Nociceptors |
sensitive to pain-causing stimuli - extreme heat or cold, excessive pressure, inflammatory chemicals player in detection- vanilloid receptor - ion channel opened by heat, low pH, chemicals respond to: - pinching, chemicals from damaged tissue, capsaicin |
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Exteroceptors |
respond to stimuli arising outside body receptors in skin for touch, pressure, pain, and temperature Most special sense organs - photoreceptors for visions, mechanoreceptors for hearing, chemoreceptors for smell and taste |
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Interoceptors (visceroceptors) |
Respond to stimuli arising in internal viscera and blood vessels sensitive to chemical changes, tissue stretch, and temperature changes Sometimes cause discomfort but we are usually unaware of their workings |
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Proprioceptors |
Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles inform brain of one's movements |
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Classification by receptor structure |
simple receptors for general senses - tactile sensations (touch, pressure, stretch, vibrations), temperature, pain, and muscle sense receptors for special senses - vision, hearing, equilibrium, smell, and taste |
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Nonencapsulated nerve ending |
abundant in epithelia and connective tissues most nonmyelinated, small-diameter group C fibers; distal endings have knoblike swellings Respond mostly to temperature and pain; some to pressure-induced tissue movement; itch |
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Encapsulated Dendritic Endings |
Tactile corpuscles- discriminative touch Lamellar corpuscles- deep pressure and vibration Bulbous corpuscles- deep continuous pressure Muscle spindles- muscles stretch Tendon organs- stretch in tendons Joint Kinesthetic receptors- joint position and motion |
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Phasic Receptors |
Fast acting signal beginning or end of stimulus Examples: - receptors for pressure, touch, and smell |
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Tonic Receptors |
adapt slowly or not at all Examples - nociceptors and most propioceptors |
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Processing at the Circuit Level |
Pathways of three neurons conduct sensory impulses upward to appropriate cortical regions First Order sensory neurons -conduct impulses from receptor level to spinal reflexes or second order neurons in CNS Second Order sensory neurons -transmit impulses to 3rd order sensory neurons Third Order sensory neurons -conduct impulses from thalamus to somatosensory cortex (perceptual level) in brain |
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Processing at the Perceptual Level |
Interpretation of sensory input depends on specific location of target neurons in sensory cortex Perceptual detection -ability to detect a stimulus Magnitude estimation -intensity coded in frequency of impulses Spatial discrimination -identifying site or pattern of stimulus |
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Main Aspects of Sensory Perception |
Feature Abstraction -identification of more complex aspects and several stimulus properties Quality Discrimination -ability to identify submodalities of sensation Pattern recognition -recognition of familiar or significant patterns in stimuli |
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Perception of Pain |
Pain warns of actual or impending tissues damage-> protective action Painful stimuli include extreme pressure and temperature, histamine, K+, ATP, acids, and bradykinin impulses travel on fibers that release neurotransmitters glutamate and substance P Some pain impulses are blockedby inhibitory endogenous opioiods |
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Pain Tolerance |
All people perceive pain at same stimulus intensity pain tolerances varies "sensitive to pain"means low pain tolerance, not low pain threshold genes help determine pain tolerance,response to pain medications |
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Visceral and Referred Pain |
Stimulation of visceral organ receptors -felt as vague aching, gnawing, burning -activated by tissue stretching, ischemia, chemicals, muscle spasms Referred pain -pain from one body region perceived from different region -visceral and somatic pin fibers travel in same nerves; brain assumes stimulus from common region |
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Reflexes |
Inborn (intrinsic) reflex- rapid, involuntary, predictable motor response to stimulus Learned (acquired) reflex- result from practice or repetition Somatic- activate skeletal muscle Autonomic- activate visceral effectors (smooth or cardiac muscle or glands) |
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Receptor |
Site of Stimulus action |
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Sensory Neuron |
transmits afferent impulses to CNS |
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Integration Center |
either monosynaptic or polysynaptic region within CNS |
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Motor neuron |
conducts efferent impulses from integration center to effector organ |
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Effector |
muscle fiber or gland cell that responds to efferent impulses by contracting or secreting |
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Spinal Reflexes |
spinal somatic reflexes -integration center in spinal cord - effectors are skeletal muscle Testing of somatic reflexes important clinically to assess condition of nervous system - if exaggerated, distorted, or absent-> degenerageration/pathology of specific nervous system regions |
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Stretch and Tendon Reflexes |
to smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding: -length of muscle - from muscle spindles -Amount of tension in muscles - from tendon origins |
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The stretch Reflex |
Maintains muscle tone in large postural muscles, and adjusts it reflexively - causes muscle contraction in response to increased muscle length (stretch) How they work: stretch activates muscle spindles |
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The stretch reflex: Positive reflex |
Indicate: - sensory and motor connections between muscle and spinal cord intact - Strength of response indicated degree of spinal cord excitability Hypoactive or absent if peripheral nerve damage or ventral horn injury Hyperactive if lesions of corticospinal tract |
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The Tendon Reflex |
Postsynaptic reflexes Helps Prevent damage due to excessive stretch important for smooth onset andtermination of muscle contraction Produces muscle relaxation (lengthening) in response to tension - Contraction or passive stretch activates tendon reflex - afferent impulses transmitted to spinal cord - contracting muscle relaxes; antagonist contracts (reciprocal Activation) - Information transmitted simultaneously to cerebellum and used to adjust muscle tension |
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The Flexor Reflex |
Initiated by painful stimulus causes automatic withdrawal of threatened body part Ipsilateral and polysynaptic Protective; important Brain can override Crossed |
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Crossed Extensor Reflex |
Occurs with flexor reflexes in weight-bearing limbs to maintain balance Consists of ipsilateral withdrawal reflex and contralateral extensor reflex - stimulated side withdrawn (flexed) - Contralateral side extended |
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Superficial Reflexes |
Elicited by gentle cutaneous stimulation depends on upper motor pathways and cord-level reflex arcs Best Known: - Plantar Reflex - Abdominal Reflex |
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Plantar Reflex |
Stimulus - stroke of lateral aspect of sole of foot Response - downward flexion of toes Damageto motor cortex or corticospinal tracts -> abnormal response = Babinski's sign - Hallux dorsiflexes; only digits fan laterally - normal in infant to ~1 year due to imcomplete myelination |
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Abdominal Reflexes |
Cause contraction of abdominal muscles and movement of umbilicus in response to stroking of skin Vary in intensity from one person to another Absent when corticospinal tract lesions present |
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Spinal Nerves |
Only 7 cervical vertebrae, yet 8 pairs of cervical spinal nerves - 7 exit vertebral canal superior to vertebrae for which named - 1 exits canal inferior to C7 Other vertebrae exit inferior to vertebra for which named |
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Ventral and Dorsal Roots |
Each spinal nerve connects to the spinal cord via two roots Ventral Roots: - contain motor (efferent) fibers from ventral horn motor neurons - fibers innervate skeletal muscles Dorsal Roots - contains sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors Dorsal and ventral roots unite toform spinal nerves, which emerge from vertebral column |
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Rami |
Each spinal nerve branches into mixed rami Dorsal Ramus Ventral Ramus- larger Rami communicantes (autonomic pathways) join ventral rami in thoracic region Contain: Nerve plexuses- interlacing nerve network Lumbar and sacral roots extend as cauda equina |
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Plexuses |
Within plexus fibers criss-cross - each branch contains fibers from several spinal nerves - fibers from ventral ramus go to body periphery via several routes - each limb muscle innervated by more than one spinal nerve |
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Cervical Plexus and the neck |
Most branches form cutaneous nerves - innervate skin of neck, ear, back of head, and shoulders - other branches innervate neck muscles Phrenic Nerve - major motor and sensory nerve of diaphragm (receives fibers from C3-C5) - must be functional for respiration - irritation -> hiccups |
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Branchial Plexus: Five Important Nerves |
Axillary Musculocutaneous Median Ulnar Radial |
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Axillar |
Innervates deltoid, teres minor, and skin and joint capsule of shoulder |
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Musculocutaneous |
innervates biceps brachii and brachialis, coracobrachialis, and skin of lateral forearm |
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Median |
Innervates skin, most flexors, forearm pronators, wrist and finger flexors, thumb opposition muscles |
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Ulnar |
Supplies flexor carpi ulnaris, part of flexor digitorum profundus, most intrinsic hand muscles, skin of medial aspect of hand, wrist/finger flexion |
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Radial |
Innervates essentially all extensor muscles, supinators, and posterior skin of limb |
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Lumbar Plexus |
Innervates thigh, abdominal wall, and psoas muscle Femoral Nerve- innervates quadriceps and skin of anterior thigh and medial surface of leg Obturator Nerve- passes through obturator foramen to innervate adductor muscles |
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Sacral Plexus |
Longest and thickest nerve of body innervates hamstring muscles, adductor magnus, and most muscles in leg and foot composed of two nerves; tibial and common fibular |
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Innervation of skin: Deratomes |
Area of skin innervated by cutaneous branches of single spinal nerve all spinal nerves except C1 participate in dermatomes extent of spinal cord injuries ascertained by affected dermatomes most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness |
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Cranial Nerves |
Olfactory Optic Oculomotor Trochlear Trigemial Abducens Facial Vestibulocochlear Glossophsaryngeal Vagus Accessory Hypoglossal
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Olfactory |
Purely sensory; carry afferent impulses for sense of smell |
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Optic Nerve |
Purely sensory; carry afferent impulses for vision |
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Oculomotor Nerve |
Chiefly motor nerve; contain a few proprioceptive afferents. |
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Trochlear Nerves |
Primarily motor nerves; supply somatic motor fibers to (and carry proprioceptor fibers from) one of the extrinsic eye muscles, the superior oblique muscle, which passes through the pulley-shaped trochlea |
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Trigeminal Nerves |
Ophthalmic Divisions - convey sensory impulses from skin of anterior scalp, upper eyelids, and nose Maxillary Division - Convey sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek Mandibular Division - Convey sensory impulses from anterior tongue, lower teeth, skin of chin |
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Abducens Nerves |
Primarily motor; supply somatic motor fibers to lateral rectus muscle, an extrinsic muscle of the eye. Convey proprioceptorimpulses from same muscle to brain |
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Facial Nerves |
Mixed nerves that are the chief motor nerves of face. five branches: temporal, zygomatic, buccal, mandibular, and cervical |
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Vestibulocochlear Nerves |
Mostly sensory. Vestibular branch transmits afferent impulses fromsense of equilibrium, and sensory nerve cell bodies are located in vestibular ganglia. Cochlear branch transmits afferent impulses for sense of hearing, and sensory nerve cell bodies are located in spiral ganglia within cochlea |
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Glossopharyngeal Nerves |
Mixed nerves that innervate part of the tongue and pharynx. proxide somatic motorfibers to, and carry proprioceptorsfibers from, a superior pharyngeal muscle called the stylopharyngeus, which elevates the pharynx in swallowing |
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Vagus Nerve |
Mixed nerves.Nearly all motor fibers are parasympathetic efferents, except those serving skeletal muscles of pharynx and larynx.Parasympathetic motor fibers supply heart, lungs, and abdominal viscera and are involved in regulating heart rate, breathing, and digestive system activity |
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Accessory Nerves |
Mixed nerves, but primarily motor in function. Supply motor fibers to trapezius and sternocleidomastoid muscles, which together move head and neck, and convey proprioceptor impulses from same muscles |
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Hypoglossal Nerves |
Mixed nerves, but primarily motor in function. Carry somatic motor fibers to intrinsic and extrinsic muscles of tongue, and proprioceptor fibers from same muscles to brain stem. Hypoglossal nerve control allows tongue movements that mix and manipulate food during chewing, and contribute to swallowing and speech |
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Primary Mover |
Agonist Major responsibility for producing specific movement |
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Antagonist |
Opposes or reverses particular movement prime mover and antagonist on opposite sides of joint across which they act |
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Synergist |
Help prime movers - adds extra force to same movement - reduces undesirable or unnecessary movement |
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Fixator |
synergist that immobilizes bone or muscle's origin gives prime mover stable base on which to act |
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Naming Skeletal Muscles |
Location Shape Size Direction of fibers Number of origins Location of attachments Muscle action |
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Lever System |
Lever - Rigid bar (bone) that moves on a fixed point called fulcrum (joint) Effort - Force (supplied by muscle contraction) applied to lever to move resistance (load) Load - resistance (bone+tissues+any added weight) moved by the effort |
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The Muscles of facial expression insert on |
Dermis |
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Which is not a muscle of mastication |
Glossus Muscles |
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Accessory muscles of respiration include the________ and the _________________ |
Sternocleidomastoids, scalenes |
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The pectoralis major muscle inserts on the |
Humerous |
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Which is not an intrinsic muscle of the hand |
Adductor pollicis longus |
