Chapter 11.1-11.4 and 11.7: Muscular Tissue Flashcards
What are the universal characteristics of muscle?
- 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
What are the connective tissue wrappings around skeletal muscle?
- Endomysium
- around muscle cell
- Perimysium
- around muscle fasicle
- Epimysium
- around entire muscle
- Tendons
- attachments between muscle and bone matrix
What are the names for the plasma membrane and cytoplasm of a muscle cell and what are their components?
- Sarcolemma: plasma membrane
- Sarcoplasm: cytoplasm
- myofibrils: protein cords
- glycogen: stores glucose
- myoglobin: stores some oxygen
- multinucleate
- mitochonrdia
What are(other) distinct, physical components of a muscle cell?
- 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
What are the 3 types of proteins that make up sarcomeres?
- contractile proteins
- regulatory proteins
- structural proteins
What are the types of myofilaments?
- 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

What are the given types of structural proteins?
- Elastic filaments
- titin (huge, springy protein)
- helps stabilize and position thick filament
- prevent overstretching and provide recoil
- titin (huge, springy protein)
- 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
What are striations?
- 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

What is sliding filament theory?
- 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
What is the nerve/muscle relationship?
- 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
What are the motor neurons and motor units and their basic characteristics?
- 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)
What do the muscle fibers of one motor neuron do?
- 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)
- motor units take turns contracting
- effective contraction usually requires contraction of several motor units at once
What are the main components of the neuromuscular junction?
- 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
What is the function of the neuromuscular junction?
- 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
Define the following: voltage potential and resting membrane potential
- 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
- About -90Mv in skeletal muscle cells
- muscle fibers and neurons are excitable: their membranes exhibit voltage changes in response to stimuli
Describe the state of an unstimulated (resting) cell.
- 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
Describe the state of a stimulated (active) muscle fiber.
- 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
What is the difference between Resting Membrane Potential and Action Potential?
- 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”
What are the 4 major phases of contraction and relaxation?
- 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
What occurs during the excitation phase of contraction?
- 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

What occurs during excitation/contraction coupling?
- 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

What occurs during the contraction phase?
- 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

What occurs during the relaxation phase?
- 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

Define the following: length/tension relationship and muscle tone (and tension)
- 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
What is rigor mortis?
- 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
What cells make up cardiac and smooth muscle? Where do they receive innervation from?
- myocytes
- autonomic nervous system
- (NOT somatic motor neurons)
What is the tissue makeup of cardiac tissue?
- 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
What is the tissue makeup of smooth muscle?
- 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