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118 Cards in this Set
- Front
- Back
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T/F. Electrical potentials exist across the membranes of essentially all cells of the body.
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True
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What is the concentration difference of ions across a selective membrane that can produce a potential
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Membrane potential
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What would happen if a membrane was only permeable to K+
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K+ would diffuse down its concentration gradient until electrical potential across the membrane countered diffusion.
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Two types of simple diffusion
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Potassium diffuse potential
Sodium diffuse potential |
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What is the electrical potential that counters net diffusion of K+
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K+ equilibrium potential
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What would happen if a membrane was only permeable to Na+
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Na+ would diffuse down its concentration gradient until potential across the membrane countered diffusion
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What is the electrical potential that counters net diffusion of Na+
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Na+ equilibrium potential
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What is the Goldman-Hodgkin-Katz equation
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The resting membrane potential that is closest to the equilibrium potential for the ion with the highest permeability
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Inhibiting the cells- "more negative"
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Hyperpolarization
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Neuron firing
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Depolarization
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What are the characteristics of cells at resting action potentials?
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-contain a high concentration of K+
-At rest, have membranes that are essentially permeable to K+ -Typically resting membrane potentials in neurons are -70 to -90 mv |
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Means positive to 0mV
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overshoot
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towards resting potential
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repolarization
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for action potential generation
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threshold
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What are rapid changes in the membrane potential
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Action potential
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What does an action potential begin and end with?
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Begins with sudden change from the normal resting negative potential to a positive membrane potential and then ends withan almost equally rapid change back to the negative potential
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This is the resting membrane potential before the action potential occurs
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Resting stage
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membrane rises rapidly in the positive direction due to sodium rushes into the cells
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Depolarization stage
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Membrane potential is rapidly back too the normal resting potential due to the closure of Na channel and diffusion of K ion to the outside of the cell
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Repolarization stage
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What is the depolarization stage caused by
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Sodium influx
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What is the range for repolarization
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+35 to -90 mv
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What is the range for depolarization
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-90 to +35 mV
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What is the range for absolute
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-90 to -80
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If a cell membrane receives another stimulus that cannot generate an action potential
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Refactory period
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What is the all or none principle?
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Either have it or dont have it
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Action potentials have 4 traits, what are they?
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1. are or none events- threshold voltage (+15mV to resting potential)
2. Are initiated by depolarization 3. Have constant amplitude 4. Have constant conduction velocity |
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Action potentials can be induced in nerve and muscle by what?
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Extrinsic stimulation
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If you give stimulus higher than normal action potential will be generated
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Relative refactory period- -80 to -90 mV
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What are large and small fibers
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Lrg- myelinated (cat)
Sm- Non-myelinated (squid) |
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What is the propagation phase
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Opening of Na+ channels generates local current circuit that depolarizes adjacent membrane which opens more Na+ Channels
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What surround the nerve axon forming a myelin sheath
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Schwann cells
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What decreases membrane capacitance and ion flow by 5000 fold
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Sphingomyelin
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A sheath that is interrupted every 1-3 min
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Node of Ranvier
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What is an immune-mediated inflammatory demyelinating disease of the CNS
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Multiple Sclerosis
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The resting potential of a typical central nervous system neuro is close to the Nerst potential for?
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K+
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According to the Goldman equation, a decrease in the extracellular concentraion of potassium ions cause the nerve cell membrae to ? moving the membrane potential ? the threshold for initiation of an action potential
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Hyperpolarize..... away from
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Wha percent of body mass is skeletal muscle?
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40
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What percent of body mass is smooth muscle and cardiac muscle?
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10
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Anatomy of Skeletal muscle
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Muscle --> Muscle fasciculus --> Muscle fibers --> myofibrils --> actin and myosin filaments
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During muscle contration what happens to the I band?
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It shortens
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Contraction results from the sliding action of interdigitating actin and myosin filaments
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Sliding filament
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What three things make up the actin filament
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1. F-actin
2. Tropomyosin 3. Troponin |
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What is F actin?
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-double-stranded helix
-composed of polymerized G-actin -ADP bound to each G-actin -myosin heads bind to active sites |
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What is tropomyosin?
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-covers active sites
-prevents interaction with myosin |
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What is troponin?
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-I- binds actin
-T-binds tropomyosin -C-binds Ca2+ |
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What 3 things is the myosin molecule made up of?
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-two heavy chains (MW 200,000)
-Four light chains (MW 20,000) -Head region- site of ATPase activity |
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What is the theory for the mechanism of muscle contraction
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Binding of Ca2+ to troponin results in a conformational change in tropomyosin that uncovers the active sites on the actin molecule allowing for myosin to bind.
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What is the walk-along theory
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Attach, Power stroke, release
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What are the two things that can be measured in length-tension relationship?
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Passive tension
Total tension |
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Can active tension be measured directly?
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NO
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Tension required to extend a resting muscle
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Passive tension
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active tension and passive combimed
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Total tension
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What is used to compare tension generated by different sized muscles?
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Stress
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In skeletal muscle, maximal active stress is developed where?
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At normal resting length (approximately 2mm)
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What does stress do at longer and shorters lengths of the sarcomere?
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Declines
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When is contraction velocity zero?
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When max force= afterload force
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What happens to contraction velocity at an increased afterload?
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Decreases
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What is no afterload?
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Maximum velocity at minimum load
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What are two types of skeletal muscle
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Slow fibers
Fast fibers |
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What kind of fibers are oxidative, small diameter, high myoglobin content, high capillary density, many mitochondria, low glycolytic enzyme content?
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Slow fibers
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What kind of fibers are glycolytic, large diamenter, low myoglobin content, low capillary density, few mitochondria, high glycolytic enzyme content
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Fast fibers
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What fibers will be recruited first to power normal contractions?
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Motor units containing slow fibers
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What fibers help out when particularly forceful contraction is required?
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Fast fibers
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A collection of muscle fibers innervated by a single motor neuron
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Motor unit
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Characteristics of small motor unit
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-as few as 10 fibers/unit
-precise control -rapid reacting |
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Characteristics of large motor units
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-as many as 1000 fibers/unit
-coarse control -slower reacting |
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What is provided when motor units overlap?
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Coordination
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Two ways to increase strength
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1. recruit more motor units
2. increase frequency |
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Wha increase in contraction intensity as a result of the additive effect individual twitch contractions
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Force summation
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What results from an increase in the number of motor units contracting simultaneously
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Multiple fiber summation
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What results from an increase in the frequency of contraction of a single motor unit?
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Frequency summation
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What is it called when Ca2+ is responsible for frequency force summation
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Tetanization
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What happens if the muscle is stimulated before complete relaxation has occured?
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The new twich will sum with the previous one
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What happens if action potential frequency is sufficiently high?
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The individual contractions are not resolved and a fused tetanus contraction is recorded
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What happens before development of maximal contractile force?
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Myoplasmic Ca2+ falls
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Muscle remodeling- Growth
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Hypertrophy
Hyperplasia Hypertrophy and Hyperplasia Lenthening |
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What is caused by near maximal force development, increase in actin and myosin, and myofibrils split?
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Hypertrophy
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What is the formation of new muscle fibers and can be caused by endurance training?
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Hyperplasia
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What is increased force generation and no change in shortening capacity or velocity of contraction
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Hypertrophy and hyperplasia
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What are causes of atrophy
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Denervation/neuropathy
tenotomy Sedentary life style Plaster cast Space flight |
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Characteristics of muscle performace
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-degeneration of contractile proteins
-decreased max force of contraction -decreased velocity of contraction |
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Characteristics of atrophy with fiber loss
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Disuse for 1-2 years and it is very difficult to replace lost.
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In a typical nerve cell, the repolarization phase of the action potential is most likely caused by?
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Efflux of potassium ions from the cell
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The primary physiological basis for the length-tension curve of skeletal and cardiac muscle is?
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Degree of overlap of actin and myosin filaments
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What is a specialized synapse between a motorneuron and a muscle fiber?
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Neuromuscular transmission
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Where does neuromuscular transmission occur?
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The motor end plate
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Invagination in the moter endplate membrane
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Synaptic trough
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Characteristicsc of synaptic cleft
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- 20-30nm wide
- contains lrg quantities of acetylcholinesterase |
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Characteristics of subneural clefts
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- increase the surface area of the post-synaptic membrane
- Ach gated channels at tops -Voltage gated Na+ channel in bottom half |
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What are formed from budding golgi and are transported to the terminal by axoplasm streaming (300,000 per terminal)
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Synaptic vesicles
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What is formed in the cytoplasm and is transported into the vesicles (10,000 per)
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Acetylcholine
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What happens when Ach filled vesicles occasionally fuse with the post-synaptic membrane and release their contents?
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Miniature end-plate potentials in the post-synaptic membrane
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Steps for Ach Release
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1. AP begins in the ventral horm of spinal cord
2. Local depolarization opens voltage-gated Ca2+ channels 3. An increase in cytosolic Ca2+ triggers the fusion of -125 synaptic vesicles with the pre-synaptic membrane and release of Ach (exocytosis) |
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What do pre and post stand for?
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pre- motor neuron
post- muscle membrane |
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Ca2+ channels are localized around linear structures on the pre-synaptic membrane called?
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dense bars
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Where do vesicles fuse with the membrane
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In the region of the dense bars
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Ach receptors located at the top of subneural cleft
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Ach gated ion channels
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Located in bottom half of subneural cleft
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Voltage gated Na+ channels
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ACh released into the neuromuscular juncction binds to and opens what?
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nicotinic ACh receptor channels on the muscle fiber membranes
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Opening of nACh receptor channels produces what?
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An end-plate potential
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What will initiate an AP if the local spread of current is sufficient to open voltage sodium channels?
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End-plate potential
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What block nicotinic ACH channels by competing for ACh binding site and reduce amplitude of end plate potential leaving no AP?
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Curariform drugs
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What decreases the release of ACh from nerve terminals and is an insufficient stimulus to initiate an AP
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Botulinum toxin
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What are ACh-like drugs?
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metacholine, carbachol, nicotine
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What do ACh-like drugs do?
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bind and activate nicotinic ACh receptors and they are not destroyed by AChE
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What are Anti-AChE drugs
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neostigmine, physostigmine
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what do anti-AChE druges do?
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Block the degradation of ACh... prolong its effect
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What is the incidence/symptoms of Myasthenia Gravis?
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Paralysis-lethal in extreme cases when respiratory muscles are involved.
2 per 1,000,000 people/year |
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What is the cause of Myasthenia Gravis?
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It is an autoimmune disease characterized by the presence of antibodies against the nicotinic ACh receptor which destroys them and causes weak end plate potentials
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What is the treatment for Myasthenia Gravis?
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It is usually ameliorated by anti-AChE (neostigmine) because it increases the amount of ACh in nmj
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What are transverse tubules?
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-Invagination of the sarcolemma filled with extracellular fluid
-penetrate the muscle fiber, branch and form networks -Transmit APs deep into the muscle fiber |
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What is the sarcoplasmic reticulum?
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-Terminal cisternae and longitudinal tubules
-intracellular storage compartment for Ca2+ |
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What do terminal cisternae form?
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Junctional feet adjacent to the T-tubule membrane
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What is vertebrae skeletal muscle and where are they located?
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-Two tubule networks per sarcomere
-Located near the ends of myosin filaments |
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What is cardiac muscle and where is it located?
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-Single T-tubule network per sarcomere
-Located at the level of the Z disc |
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The junction between two terminal cristernae and a t-tubule
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The triad
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What is the sequence of events for EC coupling (skeletal muscle)?
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1. AP moves along T-tubule
2. The voltage change is sensed by the DHP receptor 3. Activate calcium channel and release calcium 4. Contraction occurs 5. Calcium is pumped back into SR. Calcium bind to calsequestrin to facilitate storage 6. Contraction is terminated |
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What is the sequence of events for EC coupling (Cardiac muscle)?
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1. AP moves along T-tubule
2. Activation of DHP receptors -voltage sensors that release a small amount of Ca into the fiber. 3. Ca then binds to the receptors releasing a large amount of Ca. 4. Calcium is pumped back into SR and back into T-tubule 5. Contraction is terminated |
