UNIT 3: MUSCLES

Types of Muscle tissue

• Skeletal: striated and voluntary- moves body

• Smooth: involuntary, non-striated

• Cardiac: heart, involuntary

Skeletal muscle

• Epimysium: Covering of whole muscle

• Perimysium: Covers group of fibers= fasicle

• Endomysium: Covers each cell= muscle fiber

• Tendon- fibrous CT that extends from epimysium to connect muscle to bone

• Aponeurosis- broad sheet of CT– extension of muscle’s fibrous wrapping to merge with another muscle

• Fascia- fibrous CT around muscle, outside epimysium and tendon

• Whole muscle is an organ

Skeletal/Striated Muscle Fiber• Fiber= muscle cell

• Skeletal muscle made of bundles of fibers- extending the length of the muscle

Inside a Muscle Fiber

• Sarcolemma- plasma membrane

• Sarcoplasm- cytoplasm

• Sarcoplasmic reticulum (SR)- network of tubules and sacs similar to ER that works to pump and store Calcium ions for electrical impulse muscle contraction

• Triad: A T-tubule sandwiched between two ends of SR

• Transverse Tubules (T-tubules): extensions of plasma membrane (sarcolemma) that reach transversely, deeper through cell (in shape of T)– Carry nerve impulses into myofibril– Important for muscle contraction

• Muscle fibers made of Myofibrils –bundles of very fine fibers--are responsible for muscle fiber contraction; their contraction shortens the entire cell due to their attachment to the sarcolemma

Myofilaments

• Protein filaments consisting mainly of proteins:

• thin filaments- actin, troponin and tropomyosin

• thick filaments- myosin

• Thick and thin alternate

Actin

• Globular molecules look like beads, form 2 strands twisted around each other

Myosin

• Molecules shaped like golf clubs– “heads” stick out and are chemically attracted to actin

• Heads are called cross bridges– they try to bridge gap between filaments

Short Unit of myofibril= Sarcomere

• Sarcomere is contractile unit

Regions of sarcomere• A band- dArk, thicK wide stripe, contains myosin

overlapping actin• H band- in middle of A band- region of only

myosin• I band- lIght, thIn, either side of A-band, contains

actin only• Z line- dense plate/disk to which thin filaments

anchor at ends in I-band, marks ends of one sarcomere

Changes when muscle contracts

• Muscle contraction shortens muscle, units of muscle fibers overlap

• Sarcomere shortens

• H-band disappears, A now solid dark

• Z-lines become closer together

• I-band becomes thinner

Sliding Filament Theory• Flood of calcium ions binds to troponin,

moving them off the active sites of Actin they normally block

• Myosin heads bind to Actin and pull the thin filaments toward center of sarcomere

SHORTENS SARCOMERE & ENTIRE MUSCLE FIBER

• Muscle Contraction: shortens a muscle– Requires Calcium

• Calcium: charged ions released after nerve impulse- necessary to expose actin so myosin can bind

• Cross-bridge: myosin heads when they attach to actin

• Troponin: sits on Actin– Inhibits enzyme ATPase & Tropomyosin

• Tropomyosin– Blocks binding site for myosin on actin– Wraps around edge of actin

• Neuromuscular Junction: connection between nerve cell and sarcolemma of muscle fiber where electrical impulse starts

• Releases Acetylcholine

Steps of Contraction

1. Nerve impulse goes from neuron to NMJ releases ACh

2. ACh diffuses across NMJ and binds to muscle fiber electrical impulse

3. Impulse moves along sarcolemma, down T-tubules, to SR

4. Ca ions released from SR to sarcoplasm bind to troponin

5. Tropomyosin moves to expose actin

6. Energized myosin heads bind to actin and use energy from ATP to pull actin toward center

7. Thin filaments pulled together MUSCLE SHORTENS

Relaxation

1. After impulse Ca is pulled off troponin and SR reabsorbs it

2. Ca moved off of troponin tropomyosin moves back, blocking actin

3. Myosin cross-bridges can’t attach to actin anymore

4. Myosin & Actin aren’t connected MUSCLE LENGTHENS

Energy Sources for muscles

• ATP- acts like pulled rubber band tight– Pulls myosin off actin into cocked position– When it breaks down to ADP, it releases

energy, making myosin pull on actin

Energy Sources for muscles

• Myoglobin- attracts and stores oxygen– Replenishes oxygen lost in muscles during

exercise– Red color (contains Iron)

Energy Sources for muscles

• Creatine Phosphate (CrP)– Resynthesizes ATP

when muscles run out– Back up energy for 20

extra seconds contraction

– Only small amount of ATP stored in muscle

Energy Sources for muscles

• If you run out of ATP/CP muscle stiffness

• ATP is REQUIRED to detach myosin and turn off contraction

• After death… Rigor Mortis

Rigor Mortis in Meat- Cold shortening- Is meat stretchable? Why/why not?- Is meat muscle contracted?

Rigor Mortis in Meat

• Electrical stimulation- flexes and relaxes muscles immediately after animal is butchered

HOMEWORK due MON

• Research Protein Powder (supplement)

• Write a paragraph or bullets explaining…– What does it do? How does it work?– Does it build muscle?– Who should take it?

Muscle Tension•Twitch- a single stimulation triggers a quick jerk of a muscle•Lasts <0.1sec – phases: latent, contraction, relaxation

Kahoot: What happens after a motor neuron stimulus, before contraction happens?

Summation

• A series of stimuli occur rapidly so muscle doesn’t have time to relax in between contractions

Tetanus: smooth, sustained muscle contractions (common)

• Incomplete tetanus: shorts periods of relaxation occur between peak tension

• Complete tetanus: more frequent stimuli make peaks of tension seem to fuse into a single, sustained peak constant contraction

Motor Units

• Motor unit=neuron (nerve cell) + muscle fibers to which it attaches

• Motor neurons branch and can attach to many muscle fibers

• One motor unit may stimulate a small or large part of a muscle

• Less muscle fibers per motor unit = more precise movement (ex: fingers)

Effects of Lactic Acid• When do your muscles burn?

• Exercise uses anaerobic processes (no oxygen) in short term

produces lactic acid• Lactic acid accumulates when less Oxygen

available• Why do you still breathe heavily AFTER you

stop exercising?

Types of muscle fibers• White (Fast): have little myoglobin, fastest

twitch speed, few mitochondria, muscles fatigue quicker– Example: in eyes & fingers for quick motions

• Red fast: lots of myoglobin & oxygen, moderate twitch speed/fatigue resistance

• Red slow: slow twitch speed, most myoglobin, able to stay contracted longer, not easily fatigued; postural muscles

• Most muscle tissues contain mixture of red and white fibers

• Athletic training can produce changes in mix of fiber types

Kahoot question!

Which person would have the highest concentration of Red SLOW muscle fibers?

Kahoot question!

• Which body part would have the highest concentration of White muscle fibers?

Muscle Tone- Tonic

• Tonic Contraction: low level of continuous contraction Muscle tone

– Even though muscle relaxes, small number of motor units stay contracted

– Important for maintaining posture

– Falling asleep…

– Defined calf muscles…

Muscle Tone- Isotonic

• Isotonic contraction: “same tension”

muscle changes in length but tension/tone stays constant

myosin cross bridges “WIN” tug-of-war

Isotonic Contraction

– Concentric: muscle shortens• Pick up a book

– Eccentric: muscle lengthens• Lower the book you picked up

muscle contracts and gets longer

Muscle Tone- Isometric • Isometric contraction: increased tension (work) but

no movement (same length)

– Motions usually combination of both types– Example: Shoulder

• Isometric holds it in place• While arm moves: Isotonic

• Youtube vid: https://www.youtube.com/watch?v=PHTUlwCnCe8

Kahoot questions!

• What type of contraction?

Cardiac muscles- in between skeletal and smooth

• Automaticity- instead of nerve junction, cardiac muscle stimulates itself

• Aerobic- uses oxygen– Can’t sustain tetanus– Doesn’t fatigue easily

Smooth Muscles• Non-striated: random arrangement of

myosin/actin

• Anchored filament- filaments connected to plasma membrane, then crisscross the cell– When muscle contracts, it “balls up”– More freedom of movement

• Lack of motor neuron stimulation- self-excitation

Smooth Muscle

• Single unit smooth muscle arranged in sheets• Act as large unit to push contents along organ

– Example: in digestive system

• Multiunit smooth muscle has many independent cells– neurons attached to give more precise controlled movement• Example: in skin – goosebumps

in eye– dilate pupils

All or nothing concept

• What is the difference between lifting a light weight and a heavy weight?– Type of contraction?

All or nothing concept

• A BUNDLE of muscle FIBERS contract all or nothing – when stimulated by SINGLE motor unit

• The ENTIRE muscle does NOT contract all or nothing

• More motor units recruited= stronger overall contraction; more work