Chapter 10: muscle tissue

Myofibrils

(hundreds to thousands per cell) -Bundles of myofilaments (contractile proteins) enclosed in sarcoplasmic reticulum -Make up most of the cell's volume

sacroplasmic reticulum

- Has pumps that import Ca2+ into sarcoplasmic reticulum where it binds to calmodulin and calquestrin -Has channels that allow Ca2+ to be released into surrounding sarcoplasm to trigger contraction

Epimysium

Dense irregular connective tissue wrapping whole muscle

What changes occur in muscle in response to exercise?

Endurance exercise leads to better ATP production (e.g., more mitochondria) -Resistance exercise leads to hypertrophy oMuscle increases in size due to increases in synthesis of contractile proteins oMuscle also increases glycogen reserves and mitochondria oAlso appears to stimulate limited amount of hyperplasia (increase in number of fibers)

These events occur during contraction

Exposure of active sites on actin, cross bridges are formed and released, power stroke.

Because large amounts of ATP are stored in muscle fibers, it does not need to be continuously synthesized in order to sustain muscle contractions.

False

Incomplete tetanus occurs when action potentials are produced so rapidly that the muscle completely contracts without any relaxation.

False

Source of ATP depends on intensity and duration of exercise

For a 50-meter sprint (less than 10 seconds) oATP supplied primarily by phosphate transfer system -For a 400-meter sprint (less than a minute) oATP supplied primarily by glycolysis after first few seconds -For a 1500-meter run (more than a minute) oATP supplied primarily by aerobic processes af

Sacroplasm (cytoplasm)

Has typical organelles plus contractile proteins and other specializations

During muscle contraction, this region shortens:

I band and H zone

When Ca2+ binds to troponin, it triggers crossbridge cycling

Troponin and tropomyosin move so actin is exposed.

Energy is needed to make muscles contract and relax.

True

Recovery consumption is used to restore homeostasis after the following:

a. increase in body temperature b. changes in intracellular ion concentrations c. changes in extracellular ion concentrations d. changes in hormone levels

These statements about creatine phosphate are true:

accumulates in cells to store energy , ADP reacts with it to produce ATP, creatine kinase is used as a catalyst

These are the most important neurotransmitters that regulate smooth muscle:

acetylcholine and norepinephrine

These events occur during contraction except:

active transport of Ca+ back into sarcoplasmic reticulum

Johnny's primary source of energy comes from this as he runs on his treadmill for 30 minutes every morning:

aerobic respiration

These statements about myosin myofilaments are all true except:

attached to the Z disc

This statement is true about anaerobic respiration:

can produce ATP rapidly

Each muscle cell (fiber) is surrounded by this tissue:

endomysium

Connective tissue components

epimysium, perimysium, endomysium

This kind of contraction results in an increase of tension, but the length of the muscle does not change:

isometric

This condition would be found within the leg muscle cells of a good sprinter:

large deposits of glycogen

These conditions occur in both physiologic contracture and rigor mortis

low levels of ATP , cross-bridges are formed , Ca2+ builds up in the sarcoplasm, active transport of Ca2+ slows or stops

This stimulus results in the greatest force of contraction because all motor units of a muscle are responding:

maximal

These are all properties of smooth muscle except:

responds in all-or-none fashion to action potentials

•What are the parts of a muscle cell (fiber)?

sarcoplasm, multiple nuclei, sarcolemma

Depolarization must reach this value in a cell to trigger an action potential:

threshold

Perimysium

-Dense irregular connective tissue wrapping fascicle -Houses many blood vessels and nerves

isometric contraction

Although tension is increased, it is insufficient to overcome resistance -Muscle length stays the same -E.g., holding a weight while

Troponin binds to this:

G actin, calcium ions, tropomyosin

Sarcoplasm includes

Myofibrils, sarcoplasmic reticulum, terminal cisternae

These conditions occur in both physiologic contracture and rigor mortis except:

Release of cross-bridges

The depolarization of cardiac muscle results from the influx of both Na+ and Ca2+ across the plasma membrane.

True

Waves of contraction traverse an entire sheet of visceral (unitary) smooth muscle due to the numerous gap junctions that allow action potentials to pass directly from cell to cell.

True

fatigue

reduced ability to produce muscle tension -Primarily caused by a decrease in glycogen stores during prolonged exercise

These structural characteristics apply to cardiac muscle:

single, centrally located nucleus, striated

These statements about creatine phosphate are true except:

supports intense exercise for up to 3 minutes

Characteristics of Skeletal Muscle Tissue

•Excitability: ability to respond to a stimulus by changing electrical membrane potential •Conductivity: involves sending an electrical change down the length of the cell membrane •Contractility: exhibited when filaments slide past each other -Enables muscle to cause movement •Elasticity: ability to return to original length following a lengthening or shortening •Extensibility: ability to be stretched

What is the hierarchy of structures in a muscle?

- a whole muscle contains many fascicles -A fascicle consists of many muscle fibers -muscle fiber is a muscle cell -Muscle fibers contain myofibrils (bunch of myofilaments) •In addition to the muscle cells, a skeletal muscle contains nerves, blood vessels, and connective tissue.

Endomysium

-Areolar connective tissue wrapping individual fiber -Delicate layer for electrical insulation, capillary support, binding of neighboring cells

Sarcolemma (plasma membrane)

-Has T-tubules (transverse tubules) that extend deep into the cell -Sarcolemma and its T-tubules have voltage-gated ion channels that allow for conduction of electrical signals

terminal cisternae

-blind sacs of sarcoplasmic reticulum -Serve as reservoirs for calcium ions -Combine in twos with central T-tubule to form triads

Multiple nuclei (individual cells are multinucleated)

-cell is formed in embryo when multiple myoblasts fuse -Some nearby myoblasts become undifferentiated satellite cells for support and repair of muscle fibers

List the events occurring at a neuromuscular junction in order.

ACh binds to receptors on postsynaptic membrane ligand-gated Na+ ion channels depolarization of sarcolemma choline is reabsorbed by presynaptic membrane

What's the difference between aerobic respiration and anaerobic respiration?

Aerobic respiration takes place in the mitochondria and requires oxygen and glucose, and produces carbon dioxide, water, and energy. ... Anaerobic respiration also produces energy and uses glucose, but it produces less energy and does not require oxygen.

Clinical View: Anabolic Steroids as Performance-Enhancing Compounds

Anabolic steroids -Synthetic substances that mimic testosterone -Require prescription for legal use -Stimulate manufacture of muscle proteins -Popular performance enhancers -Side effects include oIncreased risk of heart disease and stroke oKidney damage and liver tumors oTesticular atrophy, breast development in males oAcne, high blood pressure, aggressive behavior oGrowth of facial hair and menstrual irregularities in women

True statement about mysofilaments

Are thicker than actin, makeup the h zone, attach to filaments that form the m line.

What changes result from lack of exercise?

Atrophy: decrease in size due to lack of use oE.g. someone wearing a cast oInitially reversible, but becomes permanent if extreme

Functions of Skeletal Muscle

Body movement -Move bones, make facial expressions, speak, breathe, swallow •Maintenance of posture -Stabilize joints, maintain body position •Protection and support -Package internal organs and hold them in place •Regulating elimination of materials -Circular sphincters control passage of material at orifices •Heat production -Help maintain body temperature

Crossbridge cycling: four repeating steps

Crossbridge formation •Myosin head attaches to exposed binding site on actin 2)Power stroke •Myosin head pulls thin filament toward center of sarcomere •ADP and Pi released 3) Release of myosin head •ATP binds to myosin head causing its release from actin 4) Reset myosin head •ATP split into ADP and Pi by myosin ATPase •Provides energy to "cock" the myosin head

Sarcoplasmic reticulum

Internal membrane complex similar to smooth endoplasmic reticulum

The resting membrane potential occurs when:

K+ ions diffuse out of the cell

effects of aging

Loss of muscle mass with age -Slow loss begins in person's mid-30s due to decrease in activity -Decreased size, power, and endurance of skeletal muscle -Loss in fiber number and diameter (decrease in myofibrils) -Decreased oxygen storage capacity -Decreased circulatory supply to muscles with exercise •Reduced capacity to recover from injury -Decreased number of satellite cells -Fibrosis: muscle mass often replaced by dense regular connective tissue oDecreased flexibility

eccentric contraction (isotonic)

Muscle lengthens as it contracts oE.g., in the biceps brachii when lowering a load

concentric contraction (isotonic)

Muscle shortens as it contracts oE.g., in the biceps brachii when lifting a load

isotonic contraction

Muscle tension overcomes resistance resulting in movement -Tone stays constant, but length changes

This statement best describes the muscle property of extensibility:

Muscles can stretch when needed

What is the first step in the process of contraction?

Neuron excites muscle fiber -Calcium enters synaptic knob oNerve signal travels down axon, opens voltage-gated Ca2+ channels oCa2+ diffuses into synaptic knob oCa2+ binds to proteins on surface of synaptic vesicles -Synaptic knob releases ACh oVesicles merge with cell membrane at synaptic knob: exocytosis oThousands of ACh molecules released from ab

Causes of fatigue

Other possible causes of fatigue -Problems of excitation at neuromuscular junction oInsufficient Ca2+ to enter synaptic knob oDecreased number of synaptic vesicles -Problems with excitation contraction coupling oAltered ion concentrations impair action potential conduction and Ca2+ release from sarcoplasmic reticulum -Problems with crossbridge cycling oExcessive Pi slows release of Pi from myosin head oLess Ca2+ available for troponin (some Ca2+ is bo

Given the following: 1. Ca2+ ions are actively transported back into sarcoplasmic reticulum 2. Troponin-tropomyosin complexes move to inhibit cross-bridge formation 3. Muscle fibers lengthen passively These events best describe: a. treppe c. contraction phase b. lag phase d. relaxation phase

Relaxation phase

Events in muscle relaxation

Termination of nerve signal and ACh release from motor neuron -Hydrolysis of ACh by acetylcholinesterase -Closure of ACh receptor causes cessation of end plate potential -No further action potential generation -Closure of calcium channels in sarcoplasmic reticulum -Return of Ca2+ to sarcoplasmic reticulum by pumps -Return of troponin to original shape -Return of tropomyosin blockade of actin's myosin binding sites -Return of muscle to original position due to its elasticity