Anatomy Sem 1 Exam 3

What are the 3 types of muscle tissues?

1. Skeletal

2. Cardiac

3. Smooth

4 Main Characteristic of Muscle tissue

1. excitability

2. contractability

3. extensibility

3. elasticity

4 main functions of muscle tissue

1. produce movement

2. maintain posture

3. stabilize joints

4. generate heat

Each skeletal muscle, as well as each muscle fiber, is covered in _________ tissue

Connective

Epimysium

surrounds entire muscle

Perimysium

surrounds fascicles within a muscle

Fascicles

Bundles of muscle fibers wrapped in perimysium

Endomysium

Surrounds individual muscle fibers

Skeletal muscle fibers

Long, cylindrical cells that contain multiple nuclei

Sarcolemma

Sarcoplasm

Sarcolemma= muscle fiber plasma membrane

Sarcoplasm= muscle fiber cytoplasm

What are the modified organelles of skeletal muscle?

Myofibrils

Sarcoplasmic reticulum (SR)+ (T Tubules)

Myofibrils

(4 main parts)

Densel packed, rod-like elements

that make up a muscle fiber

A single muscle fiber can contain thousands (80% of muscle volume)

4 parts:

1. Striations

2. Sarcomeres

3. Myofilaments

4. Molecular composition of myofilaments

Myofilament striations consist of what three things?

Dark A bands alternating with lighter I bands

Single contractile units called sarcomeres

A Bands

Thick filament regions

Lighter central H Zone which contains no thin filaments

I Bands

Thin filament regions

Bisected by Z Disc proteins called connectin, anchoring elastic and thin filaments

Sarcomere

The smallest contractile unit of a muscle fiber

From one Z disc to the next is a sarcomere

Myofilaments

The contractile proteins, actin and myosin, of muscle cells

Actin myofilaments

Thin filaments

Two strands of actin subunits

Extend across I bands and partway in the A band

Anchored to the Z Discs

What regulatory proteins do Actin contain?

Troponin= bound to actin ad tropomyosin- has Ca2+ bonding site

Tropomyosin

Troponin/tropomyosin complex regulates interaction between active sites on actin and myosin heads

Myosin Filaments

Thick filaments

Several myosin molecules (golf club shape)

Heads bond active sites on actin to form cross bridge

Heads are offset, resulting in staggered cross bridge locations

can bend/straighten at the hinge region

Extend the length of A bands

connected at the M line

ATPase activity, energy used for movement

What are the other (2) structures that support the myofilaments?

1. Elastic filaments= composed of protein titin/// holds thick filaments in place, provides recoil after stretch, resists excessive stretching

2. Dystrophin proteins= links filaments to proteins of the sarcolemma

Duchenne's muscular Dystrophy

caused by a dystrophia gene mutation (dystrophin protein)

Sarcolemma tears, increased apoptosis of muscle fibers, loss of muscle mass

sarcoplasmic reticulum= SR (smooth ER modification)

Network around each myofibril

Dilated end sacs (terminal cisternae) store calcium

Has Traverse t-tubules and triads

Transverse T-Tubules of the SR

Tunnel like in-folding structures

Penetrate the cell//carry electric current to the cell interior

Triads of the SR

Contains: T-Tubule and 2 terminal cisternae

Triad role in SR

T tubule contains integral membrane proteins that act as voltage sensors (sensors change shape in response to electrical current)

SR cistern membranes also have integral membrane proteins that control opening of calcium channels in SR cisterns

**When an electrical current impulse passes by, T Tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm

sliding filament model

Actin myofilaments sliding over myosin to shorten sarcomeres

>actin and myosin do not change in length

>shortening sarcomeres responsible for skeletal muscle contraction

In short= myosin heads "walk" along actin filaments, pulling actin towards line

Explain how muscle contraction is voluntary

Controlled by the CNS:

The brain makes the decision to move

Signal transmitted down spinal chord to motor neurons

Motor neurons activate muscle fibers

Neurons and muscle cells are excitable cells, can generate action potentials

AP can cross from neurons to muscle cells through ion channels

neuromuscular junction (NMJ)

The area where the motor neuron meets the muscle

What is the axon terminal separated from the muscle fiber by?

The synaptic cleft

What is at the Axon Terminal?

What part of Sarcolemma is related to this?

Axon terminal contains synaptic vesicles of acetylcholine (Ach)

Junctional folds on sarcolemma contain Ach receptors.

Big Picture of Muscle Fiber Contraction: 4 Steps biggest to smallest

1. Events at the NMJ

2. Muscle Fiber Excitation

3. Excitation-contraction coupling

4. Cross bridge cycling

Events at the NMJ

Largest Step of muscle fiber contraction:

1. AP arrives at axon terminal

2. Voltage gated calcium channels open, calcium enters motor neurons

3. Calcium entry causes release of Ach neurotransmitter into synaptic cleft

4. Ach diffuses across Ach receptors on sarcolemma (the junctional folds)

5. Ach bonding to receptors opens gates, allows Na+ to enter local muscle fiber, resulting in the end plate potential EPP

6. Acetylcholinesterase degrades Ach

Muscle fiber excitation

(3 steps)

Second step down of muscle fiber contraction:

1. Resting sarcolemma is polarized (RMP)= voltage exists across membrane-- inside=negative

2. Action potential is caused by changes in electrical charges

Occurs in 3 steps:

1. Generation of EPP

2. Depolarization

3. Repolarization

Excitation-contraction coupling

Third step down of muscle fiber contraction:

1. Events that transmit Action potential across sarcolemma (excitation) are coupled to sliding of myofilaments (contraction)

2. AP is sent along sarcolemma and down into t tubules, where voltage-sensitive proteins stimulate Ca2+ release from SR

3. AP is brief and ends before contraction is seen

Cross Bridge Cycling

Fourth step down of muscle fiber contraction

Voltage sensitive proteins in T-tubules change shape, causing sarcoplasmic reticulum to release Ca2+ into cytosol

Pre- Cross bridge cycling:

What does muscle fiber look like (tropomyosin)?

What happens that causes the cross-bridge cycle to begin?

Low intracellular Ca2+ concentration:

-tropomyosin blocks active sites on actin

-myosin heads cannot attach to actin

-muscle fiber remains relaxed

Voltage-sensitive proteins in T-tubules change shape, casuing SR to release Ca2+ into cytosol

Four Steps of Cross-Bridge Cycle

1. Cross bridge formation: high-energy myosin head attaches to actin thin filament active site

2. Working (power) stroke: myosin head pivots and pulls thin filament toward M line

3. Cross bridge detachment: ATP attaches to myosin head, causing cross bridge to detach

4. Cocking of myosin head: energy from hydrolysis of ATP "cocks" myosin head into high-energy state

>>>This energy will be used for power stroke in next cross bridge cycle

muscle relaxation

Original nerve stimulus stops

ACh breakdown in synaptic cleft

Ca2+ uptake into SR

Tropomyosin returns to blocking the active sies on actin

ATP required to break cross bridge (detachment)

Rigor Mortis

stiffness of the body that sets 3-4 hours after death

Deteriorating sarcoplasmic reticulum releases calcium

Calcium still actives cross bridging

Muscle contracts but cannot relax because muscle relaxation requires ATP (ATP no longer produced after death)

fibers remain contracted until myofilaments decay

Motor Unit

a motor neuron and all the muscle cells it stimulates

How do motor units sustain long term contraction?

They take turn resting

Allows for posture control

Motor Units: Fine control

Small motor units contain as few as 20 muscle fibers per nerve fiber (eye muscles)

Motor Units: Strength Control

Gastrocnemius muscle (calf) has 1000 fibers per nerve fiber

Muscle Twitch

simplest contraction resulting from a muscle fiber's response to a signle actionpotential from the motor neuron

Muscle fiber contracts quickly, then relaxes

Myogram

a chart of the timing and strength of a muscle's contraction

3 Phases of Muscle Twitch

1. Latent period= events of excitation- contraction coupling

>>> no Muscle tension seen

2. Period of contraction= cross bridge formation (myosin attaching to actin)

>>>tension increases

3. Period of relaxtion= Ca2+ reentry into the SR

>>>Tension declines to zero

Muscle contracts faster than it relaxes

Isotonic Contraction

muscle shortens because muscle tension exceeds load

Isotonic contraction (concentric)

Muscle shortens and does work

(biceps brachii while picking up a book)

Isotonic contraction (eccentric)

Muscle lengthens and generates force

(biceps brachii while laying down a book)

Isometric contraction

Tension increases but does not exceed load, no change in muscle length

ATP supplies the energy needed for the muscle fiber to...

(4 reasons)

1. Move and detach cross bridges

2. Pump calcium back into the sarcoplasmic reticulum

3. Pump Na+ out of and K+ back into the cell after excitation-contraction coupling

4. Contractile acitvites

Available stores of ATP deplete in _____

4-6 seconds

ATP is regenerated quickly by 3 mechanisms:

1. Direct phosphorylation of ADP by creatine phosphate (CP)

2. Anaerobic pathway= glycolysis and lactic acid formation (only two ATP per glucose)

3. Aerobic pathway= respiration w/ oxygen; makes way more ATP

Aerobic Endurance

Length of time muscle contracts using aerobic pathways

Light to moderate activity which can continue for hours

Anaerobic Threshold

Point at which muscle metabolism converts to the anaerobic pathway

Fatigue

(3 possible causes)

Physiological inability to contract despite continued stimulation

Ionic Imbalances= Levels of K+, Na+, and Ca2+ can change, disrupting the membrane potential of the muscle cell

Decreased ATP and increased magnesium (unimportant)

Decreased glycogen= stored in liver and skeletal muscle

Note that Lack of ATP is rarely a reason for Fatigue

EPOC

Excess Postexercise Oxygen Consumption

Recovery requires extra oxygen ("oxygen debt")

For a muscle to return to its pre-exercise state:

>>Oxygen reserves are replenished

>>Lactic acid is reconverted to pyruvic acid (pyruvate)

>>Glycogen stores are replaced

>>ATP and creatine phosphate reserves are resynthesized

The force of contraction depends on the number of cross bridges attached, which is affected by 4 factors:

1. Number of muscle fibers= simulated (recruitment)= the ore motor units recruited, the greater the force

2. Relative size of fibers= the bulkier the muscle, the more tension can develop (hypertrophy with exercise)

3. Frequency of stimulation (temporal/wave)= the higher the frequency, the greater the force

>>stimuli are added together

4. Degree of muscle stretch (length-tension relationship) = muscle fibers with sarcomeres that are 80-120% their normal resting length generate more force

If sarcomere is less than 80% resting length...

filaments overlap to much and force decreases

If sarcomere is greater than 120% of resting length...

Filaments do not overlap enough and force decreases

Hypertrophy with muscles

Muscles increase in size with regular exercise

How fast a muscle contracts (velocity) and how long it can stay contracted (duration) is influenced by

3 things

1.muscle fiber type

2.Load

3. Recruitment

Slow oxidative/slow twitch fibers/type I fibers

(where at?)

more mitochondria capillaries "dark meat"

Adapted for aerobic respiration and resistant to fatigue

Postural muscles of the back (100msec/twitvh)

Fats glycolytic/ fast twitch fibers/ type II fibers

(where at?)

rich in enzymes for glycogen-lactic acid system "white meat"

SR releases calcium quickly, so contractions are quicker (7.5 msec/twitch)

Extraocular muscles, biceps, brachii

How are proportions of slow oxidative vs fast glycolytic muscle fibers determined?

Genetically determined

Can be modified slightly

Load (muscle contraction/duration)

Muscles contract fastest when no load is added

The greater load...

the shorter duration of contraction

the slower the contraction

Recruitment (muscle contraction/duration)

The more motor units contracting, the faster and more prolonged the contraction

What are the four stages of cellular respiration?

1. glycolysis

2. pyruvate oxidation (the transitional phase)

3. citric acid cycle (Kreb's cycle)

4. oxidative phosphorylation

>>>ETC

>>>chemiosmosis

Where is smooth muscle found?

walls of hollow organs

Respiratory, digestive, urinary, reproductive, circulatory (except in smallest blood vessels)

NOT IN HEART

Varicosities

In smooth muscle cells:

Bulbous swellings of nerve fibers (instead of skeletal NMJ)

Store and release Neurotransmitters

What are the varicosities of smooth muscle innervated by ?

The autonomic nervous system (rest and digest) not the CNS

Smooth muscle fibers are usually connected ________________________________________ whereas skeletal muscle fibers are ________________.

Smooth muscle fibers are usually electrically connected via gap junctions whereas skeletal muscle fibers are electrically isolated

Gap Junctions in Smooth Muscle Cells

Specialized cell connections that allow depolarization to spread from cell to cell

Smooth Muscle SR

(Two Important details)

Less Elaborate SR and no T-Tubules

SR does store Ca2+, but most of the calcium comes from extracellular origins

Caveolae

Pouch-like infoldings in Smooth muscle cells

Caveolae contain numerous Ca2+ channels that open to allow rapid influx of extracellular Ca2+

Smooth muscles have no ____________ or __________, but they do contain ____________________________________.

no striations and no sarcomeres, but they do contain overlapping thick and thin filaments

calmodulin

Protein in smooth muscle that binds to Ca2+

No troponin complex in smooth muscle

How are thick and thin filaments arranged in smooth muscle ?

Thick and thin filaments arranged diagonally

Myofilaments are spirally arranged, causing smooth muscle to contract in corkscrew manner

Structural Framework of Smooth Muscle Cells:

Intermediate filament-dense body network

Non contractile intermediate filaments resist tension

Dense bodies= proteins that anchor filaments to sarcolemma at regular intervals

>>>correspond to Z discs of skeletal muscles

During contraction, areas of the sarcolemma between dense bodies bulge outward

>>>Makes the smooth muscle cell appear puffy by microscopy

What happens to a smooth muscle cell during contraction? (Dense Bodies)

Areas of the sarcolemma between dense bodies bulge outward

• Makes the smooth muscle cell appear puffy by microscopy

Some smooth muscle cells are self-excitatory- what does this mean?

They depolarize without external stimuli

Act as pacemakers for sheets of muscle

Contraction in smooth muscle is different from skeletal muscle in the following ways:

(4 ways)

Some Ca2+ still obtained from SR, but mostly comes from extracellular space

Ca2+ binds to calmodulin, not troponin

Activated calmodulin then activates myosin kinase (myosin light chain kinase)

Activated myosin kinase phosphorylates myosin head, activating it

>>>Leads to crossbridge formation with actin

7 criteria for naming muscles

1. Location

2. Shape

3. Size

4. Direction of fibers/fascicles

5. # of origins

6. Location of attachments

7. Action

(any criteria can be combined!)

Rectus Muscle fibers

fibers that run straight

Transversus muscle fibers

fibers that run at right angles

Oblique muscle fibers

fibers that run at angles to imaginary defined axis

Flexion

a movement that decreases the angle between two body parts.

extension

a movement that increases the angle between two body parts

Abduction

Movement away from the midline of the body

Addcution

Movement toward the midline of the body

A muscle that crosses on the anterior side of a joint produces ___________

flexion

A muscle that crosses on the posterior side of a joint produces _____________

extension

A muscle that crosses the lateral side of a joint produces______________

Abduction

A muscle that crosses on the medial side of a joint produces ____________

adduction

What muscle produces a smile?

Zygomaticus major

What muscle produces a pucker?

Orbicularis Oris

What muscle produces a pout?

Mentalis

What muscle produces angry eyebrows?

Corrugators Supercilli

What muscle produces a blink?

Orbicularis Oculi