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Anatomy and Physiology I > Chapter 11.1-11.4 and 11.7: Muscular Tissue > Flashcards

Chapter 11.1-11.4 and 11.7: Muscular Tissue Flashcards

1
Q

What are the universal characteristics of muscle?

A
  • excitability
    • to chemical signals / electrical changes across a plasma membrane
  • conductivity
    • local electrical change triggers a wave of excitation that travels along the muscle fiber
  • contractility
    • shortens when stimulated
  • extensibility
    • capable of being stretched between contractions
  • elasticity
    • returns to its original rest length after being stretched
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2
Q

What are the connective tissue wrappings around skeletal muscle?

A
  • Endomysium
    • around muscle cell
  • Perimysium
    • around muscle fasicle
  • Epimysium
    • around entire muscle
  • Tendons
    • attachments between muscle and bone matrix
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3
Q

What are the names for the plasma membrane and cytoplasm of a muscle cell and what are their components?

A
  • Sarcolemma: plasma membrane
  • Sarcoplasm: cytoplasm
    • myofibrils: protein cords
    • glycogen: stores glucose
    • myoglobin: stores some oxygen
    • multinucleate
    • mitochonrdia
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4
Q

What are(other) distinct, physical components of a muscle cell?

A
  • Sacroplasmic Reticulum (SR): smooth ER
    • terminal cisternae: dilated end sacs
    • stores calcium
  • T tubules
    • tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side
  • Triad
    • a T tubule and two terminal cisternae
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5
Q

What are the 3 types of proteins that make up sarcomeres?

A
  • contractile proteins
  • regulatory proteins
  • structural proteins
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6
Q

What are the types of myofilaments?

A
  • Thick filaments
    • made of several hundred myosin molecules
  • Thin filaments (actin)
    • contain active site that binds to the head of myosin
  • Regulatory proteins (turn contraction on and off)
    • tropomyosin: block active sites
    • troponin: small protein on each tropomyosin molecule
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7
Q

What are the given types of structural proteins?

A
  • Elastic filaments
    • titin (huge, springy protein)
      • helps stabilize and position thick filament
      • prevent overstretching and provide recoil
  • Dystrophin
    • links outermost actin to membrane proteins which link to endomysium
    • transfers forces of muscle contraction to connective tissue
    • genetic defects produce muscular dystrophy
      • used for diagnosis
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8
Q

What are striations?

A
  • result from precise organization of myosin and actin in cardiac and skeletal muscles
  • they are alternating A bands and I bands
  • A band
    • anisotropic
    • H band: middle of A, thick filaments only
    • M line: middle of H band
  • I band
    • isotropic
    • Z disc: provides anchorage for thin filaments and elastic filaments
      • bisects I band
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9
Q

What is sliding filament theory?

A
  • Thin filaments slide past the thick filaments, increasing amount of overlap
  • ATP needed
    • energizes myosin heads for power stroke
  • Calcium needed
    • uncovers attachment sites on actin
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10
Q

What is the nerve/muscle relationship?

A
  • skeletal muscle doesn’t contract unless stimulated by a nerve
  • if nerve connections are severed or poisoned, muscle is paralyzed
  • Denervation atrophy: shrinkage of paralyzed muscle when nerve remains disconnected
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11
Q

What are the motor neurons and motor units and their basic characteristics?

A
  • Somatic motor neurons
    • cell bodies in brain stem and spinal cord
    • axon lead to skeletal muscle
    • one motor neuron branches out to a number of muscle fibers
  • Motor unit
    • one nerve fiber and all the muscles innervated by it
    • average unit contains 200 muscle fibers
    • small units
      • fine degree of control
      • 3-6 fibers per neuron
      • eye and hand muscles
    • Large units
      • more strength than control
      • powerful contractions with hundreds of fibers
      • e.g. gastrocnemius (1000 muscle fibers per neuron)
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12
Q

What do the muscle fibers of one motor neuron do?

A
  • they are dispered throughout muscle
  • contract in unison
  • produce weak contraction over wide area
  • able to sustain long term contraction
    • motor units take turns contracting
      • partial contraction creates firmness (muscle tension)
  • effective contraction usually requires contraction of several motor units at once
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13
Q

What are the main components of the neuromuscular junction?

A
  • Synaptic knob
    • swollen end of nerve fiber
    • contains synaptic vesicles with acetylcholine
  • Synaptic cleft
    • gap between synaptic knob and sarcolemma
  • Schwann cell
    • envelopes and isolates Neuromuscular junction
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14
Q

What is the function of the neuromuscular junction?

A
  • nerve impulse from axon opens calcium channels
  • Ca+2 enters and causes synaptic vesicles to undergo exocytosis, releasing ACh into synaptic cleft
    • Muscle cell has millions of ACh receptors
  • Acetylcholine Esterase breaks down ACh, leading to relaxation
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15
Q

Define the following: voltage potential and resting membrane potential

A
  • Voltage potential (electrical potential)
    • a difference in electrical charge from one point to another
  • Resting membrane potential
    • About -90Mv in skeletal muscle cells
      • maintained by sodium/potassium pump
  • muscle fibers and neurons are excitable: their membranes exhibit voltage changes in response to stimuli
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16
Q

Describe the state of an unstimulated (resting) cell.

A
  • more anions on the inside of the membrane than the outside
  • make the inside of plasma membrane negatively charged
    • plasma membrane is electrically polarized with negative Resting Membrane Potential (RMP)
  • There are excess sodium ions in the ECF and excess potassium ions in the ICF
17
Q

Describe the state of a stimulated (active) muscle fiber.

A
  • Sodium ion gates open into plasma membrane
  • Sodium flows into the cell down its gradient
    • These cations override negative charges in the ICF
  • Depolarization: inside of membrane becomes positive
  • Immediately, Sodium gates closed and Potassium gates open
  • Potassium rushes out of cell
    • concentration gradient and positive sodium charge
  • Repolarization–membrane is negative again
  • Overall (quick up and down) shift is Action Potential
18
Q

What is the difference between Resting Membrane Potential and Action Potential?

A
  • RMP
    • seen in a waiting excitable cell
  • Action Potenital
    • a quick event in a stimulated, excitable cell
    • self sustains down the length of a cell membrane
    • action potential at one point causes another to happen immediately in front of it, which triggers another (and so on)
      • this wave of excitation is called an “impulse”
19
Q

What are the 4 major phases of contraction and relaxation?

A
  • Excitation
    • process in which nerve action potentials lead to muscle action potentials
  • Excitation-contraction coupling
    • events that link action potentials on the sarcolemma to the activation of myofilaments therby preparing them to contract
  • Contraction
    • step in which the muscle fiber develops tension and may shorten
  • Relaxation
    • when stimulation ends, a muscle fiber relaxes and returns to its resting length
20
Q

What occurs during the excitation phase of contraction?

A
  • nerve signals open up voltage gated calcium channels in the synaptic knob
  • Calcium enters the knob and stimulates the release of ACh from synaptic vesicles onto synaptic celft
  • ACh diffuses across the cleft
  • two ACh molcules bind to each receptor and open its channels
  • Sodium enters, depolarization of membrane potential
    • -70 mV to +90 mV
  • Then Potassium leaves and potential hyperpolarizes
    • -90mV (hyperpolarization)
    • the quick voltage shift is called “end plate potential”
  • Voltage gate in end plate region opens nearby voltage gate channels producing an action potential that spreads over muscle surface
21
Q

What occurs during excitation/contraction coupling?

A
  • Action potential spreads down the t-tubules
  • Opens voltage-gated ion channels in t tubules and calcium channels in SR
  • Calcium leaves the SR and enters cytosol
  • Calcium binds to troponin in thin filaments
  • Troponin-tropomyosin complex changes shape and exposes active sites on actin
22
Q

What occurs during the contraction phase?

A
  • ATPase in Myosin head hydrolizes as an ATP molecule
  • Activates the head (“cocking it”)
    • ADP and P1 remain attached
  • Head binds to actin active site forming a myosin-actin cross bridge
  • Myosin releases ADP and P and flexes pulling thin filament over it (powerstroke)
  • Upon binding more ATP, myosin releases actin
    • process can be repeated
    • recovery stroke recocks head
    • Each stroke utilizes one molecule of ATP
23
Q

What occurs during the relaxation phase?

A
  • Nerve stimulation and ACh release stop
  • ACHhE breaks down ACh and fragments are reabsorbed into knob
  • Stimulation by ACh stops
  • Calcium pumped back into the SR by active transport
  • Tropomyosin reblocks the active sites of actin
  • Muscle fiber ceases to produce or maintain tension
  • Muscle fiber returns to its resting length
    • recoil of elastic components
    • contraction of antagonistic muscles
24
Q

Define the following: length/tension relationship and muscle tone (and tension)

A
  • the length/tension relationship means the amount of tension generated by a muscle depends on how stretched or shortened it was before it was stimulated
    • <em>If overly shortened before stimulated, a weak contraction results, as thick filaments just butt against Z discs </em>
    • <em>If too stretched before stimulated, a weak contraction results as minimal overlap between thick and thin filaments results in minimal cross bridge formation</em>
    • <strong>Optimum resting length</strong> produces greatest force when muscle contracts
  • Muscle tone is partial contraction to ensure resting muscles are near this optimal length (via nervous system)
  • Tension is force exerted by muscle as it contracts
25
Q

What is rigor mortis?

A
  • It is the hardening of muscles and stiffening of body beginning 3 to 4 hours after death
    • deteriorating SR releases calcium
    • deteriorating sarcolemma lets calcium enter cytosol
    • calcium activates myosin acting cross bridge
    • <strong>muscle contracts but cannot relax</strong>
      • relaxation requires ATP (body cannot make any)
      • fibers remain contracted until myofilaments decay
  • Peaks abut 12 hours after death, then diminishes in next 48 to 60 hours
26
Q

What cells make up cardiac and smooth muscle? Where do they receive innervation from?

A
  • myocytes
  • autonomic nervous system
    • (NOT somatic motor neurons)
27
Q

What is the tissue makeup of cardiac tissue?

A
  • Striated, short, thick cells
  • SR is less developed so must use Ca+2 from ECF
  • Cardiocytes joined by intercalated discs
    • Gap junctions and desmoses
  • Damaged cardiac muscle cells repair by fibrosis
  • Can contract without nervous stimulation
    • autorhythmic/autonomic
    • NS increases/decreases heart rate
  • slow contractions (to expel blood)
  • Almost all aerobic respiration
28
Q

What is the tissue makeup of smooth muscle?

A
  • No striations
  • Some lack nerve supply
  • Others use autonomic fibers with varicosities including synaptic vesicles
  • Myocytes connected by gap junctions
  • Capable of mitosis and hyperplasia
  • Injured smooth muscle regenerates well
  • Smooth muscle is slower than skeletal and cardiac
  • Form the walls of hollow organs
  • Acquires calcium from ECF

Anatomy and Physiology I (19 decks)

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