Chapter 10 muscle tissue

Property of muscle tissue: Ability to respond to stimulation by changing electrical state

Exitability

Property of muscle tissue: Ability to shorten and produce force

Contractility

Property of muscle tissue: Ability to stretch beyond resting length

Extensibility

Property of muscle tissue: Ability to return to original length

Elasticity

What proteins are involved with muscle contraction

Actin and myosin

What helps initiate contractions

Calcium

The arrangement of what provides visible striations

Actin and myosin

Connective tissue layer: Surrounds entire muscle

Epimysium

Connective tissue layer: Surrounds fascicle (bundle of fibers)

Perimysium

Connective tissue layer: Surrounds individual muscle fibers

Endomysium

Muscle fiber

A single muscle cell

Sarcolemma

Muscle cell plasma membrane

Sarcoplasmic reticulum

Stores, releases, and retrieves calcium

Myofibrils

Contractile structures inside muscle fibers

Sarcomere

Functional unit of contraction

Thin filaments

Primarily actin

Thick filaments

Primarily myosin

What is the Neuromuscular junction

Where a motor neuron communicates with a skeletal muscle fiber

Motor neuron

Nerve cell that stimulates muscle

ACh

Neurotransmitter that carries the signal to the muscle

Synaptic cleft

Space between neuron and muscle

Motor end plate

Specialized area of the sarcolemma containing ACh receptors

AChE

Enzyme that breaks down ACh

Step 1 in excitation contraction coupling: Excitation

A signal from nervous system generates action potential

Step 2 in excitation contraction coupling: Neurotransmitter release

Neuron releases ACh into the synaptic cleft

Step 3 in excitation contraction coupling: ACh binding

ACh binds to receptors on the motor end plate, Ion channels open causing depolarization (inside less negative)

Step 4 in excitation contraction coupling: Action potential

Depolarization triggers sodium channels to open, action potential them spreads alone sarcloemma

Step 5 in excitation contraction coupling: ACh breakdown

AChE breaks down ACh to stop continuous stimulation

Step 6 in excitation contraction coupling: T Tubules

Signal travels into muscle fiber through T tubules

Step 7 in excitation contraction coupling: Triad

The structural arrangement of a T tubule flanked by two terminal cisternae of the SR

Step 8 in excitation contraction coupling: Calcium releases

The signal causes the SR to release calcium into the muscle cell

Step 9 in excitation contraction coupling: Contraction initiation

Calcium binds to troponin, Which moves tropomyosin out of the way allowing myosin to attach to actin beginning contraction.

Excitation contraction coupling pathway

Signal→ ACh release and bind→ AP→ AChE→ T tubules→ Calcium→ Troponin→ Tropomyosin moves→ Contraction

What directly triggers the exposure of binding sites on actin

Calcium binding to troponin

Troponin function

Binds calcium

Tropomyosin function

Blocks binding sites

Power stroke

Myosin pulls actin

A signal from a motor neuron via ____ depolarizes the muscle fiber membrance and t tubules

ACh

What happens during a contraction

Myosin pulls actin toward center of sarcomere, Thin filament slide past thick filament, sarcomere shortens, actin and myosin filaments do not shorten themselves.

Cross bridge explanation

When a myosin head attaches to actin during muscle contraction

The cross bridge cycle continues as long as…

Calcium and ATP are available

Step 1 cross bridge cycle: Formation

Myosin heads attach to exposed binding sites on actin

Step 2 cross bridge cycle: Power stroke

Myosin heads bend and pull actin towards the center of the sarcomere as ADP & phosphate are released.

Step 3 cross bridge cycle: Bridge detachment

A new ATP molecule attaches to myosin, causing myosin to release actin.

Step 4 cross bridge cycle: Re-cocking myosin head

ATP breaks down to ADP + Phosphate which releases energy, this energy resets myosin head.

Cross bridge cycle flow

Formation→ Power stroke→ Myosin release actin→ Reset myosin head

Step 1 in muscle relaxation: Nerve signal stops

The motor neuron stops releasing ACh

Step 2 in muscle relaxation: ACh breakdown

AChE breaks down ACh, stopping muscle stimulation

Step 3 in muscle relaxation: Repolarization

Sarcolemma repolarize as ion channels close

Step 4 in muscle relaxation: Calcium reuptake

Calcium is pumped back into the SR

Step 5 in muscle relaxation: Tropomyosin blocks again

Calcium detaches from toponin, Allowing tropomyosin to cover myosin binding sites on actin again. Myosin can no longer bind to actin, muscle fiber relaxes.

Muscle relaxation flow

Signal stops→ ACh breakdown→ Repolarization→ calcium reup→ tropomyosin blocks again

Motor response pathway

Sensory afferent, CNS processing, Motor response efferent

Isotonic contraction

Muscle changes length

Concentric contraction

Muscle shortens

Eccentric contraction

Muscle lengthens

Isometric contraction

Muscle stays the same length

Length tension relationship

The force a sarcomere produces depends on its starting length

Frequency of stimulation: When a second stimulus arrives before the muscle has completely relaxed from the first

Wave summation

Frequency of stimulation: Occurs with increasing stimulus frequency, where partial relaxation occurs between contraction.

Incomplete tetanus

Frequency of stimulation: Occurs at very high stimulus, there is no relaxation between contractions

Complete tetanus

Treppe definition

Muscle contractions increase in efficiency after a period of dormancy

Importance of muscle tone

Stabilizes joints, maintains posture, keeps muscles ready for action.

Muscle tone disorder: Low muscle tone, floppy muscles and weakness

Hypotonia

Muscle tone disorder: High muscle tone, stiff and rigid muscles

Hypertonia

Type of muscle fiber: Slow, aerobic, last a longtime, posture/walking

Slow oxidative

Type of muscle fiber: Fast, High endurance, running/cycling

Fast oxidative

Type of muscle fiber: Fast but fatigues quickly, sprinting/heavy lifting

Fast glycolytic

The speed of a contraction depends on what

How quickly myosin ATPase breaks down ATP

Hypertrophy definition

Increase in muscle cell diameter due to addition of structural proteins (myofibrils) Leads to increase in muscle mass and strength

Atrophy definition

Loss of structural proteins and decrease in muscle mass

Sarcopenia definition

Age related atrophy, irreversible

Performance enhancing substances: Synthetic forms of testosterone that stimulate muscle formation

Anabolic steroids

Performance enhancing substances: Hormone that triggers RBC production, increasing oxygen

Erythropoietin

Performance enhancing substances: Facilitates muscle mass building, promotes healing of muscle and other tissue, fast recovery

Human growth hormone

Performance enhancing substances: Natural, provide quick burst of ATP, potentially increasing explosive power output

Creatine

What does the cardiac muscle tissue possess a high density of

Mitochondria and myoglobin

Desmosomes definition

Hold cells together during powerful contractions

Authorhythmicity definition

Ability to generate its own electrical impulses and contract rhythmically without external nervous simulation, due to pacemaker cells

True or false: the autonomic nervous system and hormones can adjust the hearts rate and force

True

Cardiac muscle plateau phase cause

Sustained influx of calcium ions

Instead of Z discs what does the smooth muscle use for actin

Dense bodies

Smooth muscle contraction pathway

Calcium concentration increases inside cell, calcium binds to calmodulin, complex activates myosin light chain kinase, MLCK phosphorylates myosin heads, myosin binds to actin

Single unit smooth muscle

Visceral, gap junctions, intestines, uterus, bladder

Multi unit smooth muscle

No gap junctions, independent contraction, iris, large airways, arrector pili

Hyperplasia

Increase in cell number

Hypertrophy

Increase in cell size

Depolarization

Na+ channels open causing Na+ to come in, making it more positive.

Repolarization

Na+ channels close causing K+ to come out, making it more negative.