A&P Ch 10

the 4 events of a twitch contraction

1) latent period 2) contraction period 3) relaxation period 4) refractory period

3 ways muscle fibers produce ATP

1. creatine phosphate 2. anaerobic glycolysis 3. aerobic respiration

*what are the 3 layers of connective tissue in skeletal muscles

1.Epimysium 2. Perimysium 3. Endomysium in order of most superficial to deep

skeletal muscle functions (6)

1.Produce skeletal movement 2.Maintain posture and body position 3.Support soft tissues 4.Guard entrances and exits 5.Maintain body temperature 6.Store nutrient reserves

b/w ages 30-50 yrs of age about what % of our muscle tissue is replaced by fibrous connective tissue and adipose tissue

10%

•Large motor units in large muscle groups control

= coarse movement (e.g., quadriceps)

Troponin describe it

A globular protein Binds tropomyosin to G-actin

motor unit composed

A single motor neuron + muscle fiber

•Glucose → pyruvic acid →

ATP, CO2, H2O and heat

Contraction cycle: initiation of contraction

Ca2+ binds to receptor on troponin molecule Troponin-tropomyosin complex changes Tropomyosin exposes actin's binding sites

Twitch: Contraction Phase

Ca2+ ions bind Tension builds to peak

Twitch: Relaxation Phase

Ca2+ levels fall active sites are covered and tension falls to resting level

cisternae

Cisternae: Concentrate Ca2+ (via ion pumps) Release Ca2+ into sarcomeres to begin muscle contraction

Contraction cycle: Relaxation

Contraction duration depends on: Duration of neural stimulus. Number of free calcium ions in sarcoplasm Availability of ATP - Ca2+ concentrations fall - Ca2+ detaches from troponin - Active sites are re-covered by tropomyosin

Skeletal muscles are voluntary muscles controlled by

Controlled by somatic motor nerves of the central nervous system (brain and spinal cord)

Energy sources of muscle metabolism what determines which energy source is used?

Energy sources: •Carbohydrate metabolism (primary source) •Fatty acids and amino acid metabolism (secondary sources) •Duration of muscle activity determines which energy source is used duration of muscle activity

glycogen is essential for

Essential for anaerobic glycolysis in an active muscle

type 2b muscle fibers contains

Few mitochondria, less myoglobin, few capillaries, appear pale (white)

SR forms what

Forms chambers (terminal cisternae) attached to T tubules

Nebulin describe it

Holds F actin( a structural protein) strands together controlled by Ca2+ v

Aerobic Respiration consists of

Krebs cycle and ETC

smooth muscle location

Located in walls of visceral organs and tunica media of blood vessels, in the walls of blood vessels, digestive, resp, urinary, and reproductive organs

Types of Skeletal Muscle Fiber: Type 1 (slow red Oxidative) has many

Many mitochondria Abundant myoglobin (red pigment-looks dark red, contains iron that binds oxygen)

consequences of aging on muscle tissue

Muscle strength and flexibility decreases Reflexes slow Slow oxidative fiber numbers increase

Contractile protein made up of

Myosin (thick) : always stays the same Actine (thin): always acts

Aerobic Respiration occurs when/ where

O2 is sufficient ( rest or light exercise) min- hours occurs in the mitochondria

Type 1 muscle fiber primary energy source

Primary energy source: Aerobic oxidative phosphorylation of fatty acids

cardiac muscles voluntary or involuntary?

Strong, involuntary contractions

Clinical Correlate: Rigor Mortis

- A fixed muscular contraction after death - Last 1 - 4 days Cause: - Ion pumps cease to function - Loss of all ATP - required for cross bridge separation from actin filaments during relaxation, keeps muscle in "twitch" - Ca2+ builds up in the sarcoplasm - Almost all myosin heads attached to actin in an abnormal way

Contraction cycle: Cross Bridge Detachment

- Returns to the original pivoted or flexed myosin light chains - Requires cleavage of ATP to ADP + P (phosphate) - Once regenerated, the myosin light chain binds to a new molecule of ATP for future cross-bridge coupling

Myosin

-A large-molecular-weight protein, which is also made of heavy and light chains -Light chains contain the actin-binding sites and ATP cleavage site

Contraction cycle: Myosin Action

-Actin binds myosin → forming cross-bridges -Myosin heads pivot, called the power stroke or twitch - Thin filaments of sarcomere slide toward M line, alongside thick filaments - The width of the A band stays the same (A Always stays the same) - Z lines move closer together - ADP and phosphate group, located in the myosin head, are released

Skeletal Muscle fibers derived from

-Almost all derived from mesoderm -Except: dilator pupillae, and sphincter or the iris, derived from neuroectoderm

actin composed of

-Are two twisted rows (F-actin) of globular G-actin -The active sites on G-actin strands bind to myosin -Contributes to the cross-bridge formation

Clinical Correlate: Myasthenia Gravis

-Autoimmune disease -Antibodies attack the postsynaptic nicotinic Ach receptors in the NMJ -Muscles are weaker with repetitive movements -Presentation: ptosis, diplopia, muscle weakness at the end of the day

Clinical Correlate: Plantar Fasciitis

-Chronic irritation of the plantar aponeurosis at its origin on the calcaneus -Treatment includes ice, heat, stretching, weight loss, prosthetics, steroid injections, and/or surgery

What are the 3 types of proteins

-Contractile Generate force of contraction -Regulatory On and off switch for contraction -Structural Align thick and thin filaments Provide elasticity and extensibility Link the myofibrils to the sarcolemma and extracellular matrix

*Perimysium

-Dense irregular connective tissue -Surrounds muscle fiber bundles (fascicles - groups of 10 - 100 muscle fibers) -Contains blood vessel and nerve supply to fascicles

Skeletal Muscle attachments

-Endomysium, perimysium, and epimysium come together: -At ends of muscles, form connective tissue attachment to bone matrix -Form: tendon (bundle) or aponeurosis (sheet, wide tendon)

*Epimysium

-Exterior dense irregular connective tissue -Connected to deep fascia -Separates muscle from surrounding tissues

Muscle Fatigue is the inability to maintain force of contraction after prolonged activity due to what (4)

-Inadequate release of Ca2+ from SR -Depletion of creatine phosphate (CP), oxygen, and nutrients -Build up of lactic acid and ADP Insufficient release of ACh at NMJ

Levels of organization of skeletal muscles from smallest to largest (7)

-Myofilament -Sarcolemma -Myofibril -Muscle cells -Muscle fiber -Muscle fasciculus -Whole muscle

somatic motor neurons

-Neuron that stimulates skeletal muscle contraction -Axon extends from brain or spinal cord to a group of skeletal muscle fibers -Forms the neuromuscular junction (NMJ)

*Endomysium

-Surrounds individual muscle cells (muscle fibers) -Contains capillaries and nerve fibers contacting muscle cells -Contains myosatellite cells (stem cells) that repair damage

Types of proteins in myofilaments

-Thin filaments: Made of the protein Actin (A) for (A)ction -Thick filaments: Made of the protein Myosin

Anaerobic glycolysis: lactic acid removal

The Cori Cycle - The removal and recycling of lactic acid by the liver - Liver converts lactate to pyruvate - Glucose is released to recharge muscle glycogen reserves

Twitch: Latent period

The action potential moves through sarcolemma Causing Ca2+ release

A Band: Zone of overlap

The densest, darkest area on a light micrograph where thick and thin filaments overlap

Type 2b muscles fibers found where

Typically, small muscles, with large number of NMJs Examples: muscles that move the eye, digits, weightlifting, throwing a ball

Tropomyosin describe it

a double strand, at rest occupies the potential myosin binding site on actin prevents actin-myosin interaction

The sarcoplasmic reticulum (SR) is

a membranous structure surrounding each myofibril

wave summation occurs when

a second action potential triggers muscle contraction before the first contraction has finished

wave summation results in

a stronger contraction causes increasing tension or summation of twiches

The sarcoplasmic reticulum helps transmit

action potential to myofibril

•Hormonal Regulation of Glycogen by Insulin (exercise) ↓ energy needs (e.g., walking) → what kind of metabolism

aerobic metabolism → oxidation of circulating glucose and fatty acids •Extract more energy: 1 molecule of glucose ≈ 38 ATP •Sustains muscle activity longer

muscle tone is maintained by

alterinating b/w active and inactive motor units

•Hormonal Regulation of Glycogen by Insulin (exercise): ↑ energy needs (e.g., sprinting) → what kind of metabolism?

anaerobic metabolism → primary fuel is intracellular glucose and glycogen •Does not sustain long muscle contraction

between 50-80 yrs how much more of muscle tissue is replaced by fibrous connective tissue and adipose tissue

another 40%

A band: H band (zone)

area around the M line has thick filaments but no thin filaments

Type 2a skeletal muscle energy source

both oxidative metabolism (aerobic) and anaerobic glycolysis multiple mitochondria, myoglobin, and glycogen

What does acetylcholinesterase do?

breaks down extra acetylcholine in the synaptic cleft ( the target for pharmacologic paralysis in neuromuscular blockade)

Myofibril are made up of

bundles of myofilaments

I Band: Z line

centers of the I bands ends the sarcomere

isometric contraction muscle contracts but does not

change in length

what are sarcomeres

contractile units of muscle and structural units of myofibrils forms visible pattern within myofibrils

•Hormonal Regulation of Glycogen by Insulin (Lipid and protein metabolism) occurs during what

during a state of starvation

Type 2a skeletal muscle fiber what kind of contraction

fast, intermediate oxidative glycolytic

•Hormonal Regulation of Glycogen by Insulin (Lipid and protein metabolism) muscles use what for energy by third week only use what

fatty acids and keytones •By third week of starvation, muscle operates entirely on fatty acids

•Small motor units control

fine movement (e.g., extra ocular muscles)

muscle tone keeps muscles

firm

motor unit recruitment

for weak muscle process in which the # of active motor units increases - weakest motor units are recruited first followed by stronger motor units - motor units contract alternately to sustain contractions for a longer period of time

Acronyms for sarcomere

from Z to shining Z A Always stays the same Actin Acs

Type 2b energy source

glycolysis (anaerobic)

unfused tetanus

held contraction twitched reach maximum tension if rapid stim continues and muscle is not allowed to relax, twitches reach max level of tension

•Hormonal Regulation of Glycogen by Insulin (exercise) Aerobic Exercise: At the onset, what supplies energy

hepatic glycogenolysis supplies 40% of energy

The strength of a contraction depends on what

how many motor units are activated

concentric isotonic contraction: which is greater muscle tension or load muscle shorten or lengthens

if muscle tension > load muscle shortens

eccentric isotonic contraction: which is greater muscle tension or load muscle shorten or lengthens

if muscle tone is < load muscle lengthens

fused tetanus

if stimulation freq is high enough, muscle never begins to relax and is in cont contraction

•Hormonal Regulation of Glycogen by Insulin (Well fed state) increases what

insulin

Glucose → pyruvic acid →

lactic acid

Glucose is utilized as energy source for

longer periods of activity

Skeletal muscle fibers developed through fusion of

mesodermal cells (myoblasts)

Change in Transmemebrane potential on sarcolemma begins what

muscle contraction

Thick filament Contains

myosin and titin

muscle tone is est by

neurons in the brain and spinal cord that excite the muscles motor neurons damage to either causes the muscle to be flaccid

skeletal muscle cells contains hundreds of what

nuclei

Why do we continue to breathe heavily for a period after stopping exercise?

o2 dept: replenish CP stores convert lactate into pyruvate reload O2 onto myoglobin

What is the Triad

one T tubule and two terminal cisternae

What is the sarcolemma?

plasma membrane of a muscle cell surrounds the sarcoplasm (cytoplasm of muscle fibers)

type 2a skeletal muscle adapts quickly to muscles used for what

rapid contractions and short burst of activity muscles used for sprinting and walking intermediate in color and energy metabolism

T tubules have the same properties as what

sarcolemma

Type 2b muscle fibers last

short duration, fatigues quickly

What are the 3 types of muscle tissue?

skeletal, cardiac, smooth

I Band: Titin

strands of protein from tips of thick filament to the Z line stabilizes the filament

type 2b muscle fibers adapt for

strong, fast, short duration contraction

Are skeletal muscles voluntary or involuntary?

strong, quick, voluntary

titin

structural protein that recoils after stetching

myofibrils are lengthwise

subdivisions within muscle fibers

tendon vs aponeurosis

tendons: chords of connective tissue (bundle) aponeurosis: sheets of connective tissue

isotonic contractions: does muscle length change

tensions is constant while muscle length changes

*Twitch Contraction

the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron

A band : M line

the center of the A band At the midline of the sarcomere

•Each skeletal muscle fiber receives neural input from a motor unit via

the neuromuscular junction (NMJ)

A band

thick bands

I band

thin band

Structural proteins made up of

titin, nebulin, alpha-actin, myomesin, dystrophin

Transverse tubules (T Tubules) transmits what

transmits the action potential through cell allows the muscle fiber to contract simulatenously

Regulatory protein madeup of

troponin (thin) Tropomyosin (thin)

Muscle tone is a small amount of tension in muscle due to

weak involuntary contractions of its motor units

type 2b muscle fiber is what color fast, intermediate, or slow

white glycolytic fast

muscle metabolism: at rest muscles can consume what % of body O2 and during exercise it can reach what %

•ATP is constantly required for cross-bridge formation •At rest muscles can consume 30% of the body's oxygen, during exercise it can reach 90%

Excitation-Contraction Coupling:

•Action potential depolarizes dihydropyridine (DHP) receptors → Ryanodine receptor(RyR) on the sarcoplasmic reticulum (SR) open → release of Ca2+ → Ca2+ binds to troponin on sarcomere → initiate contraction

skeletal muscles are attached to

•Attached to bone or cartilage (some exceptions)

Muscle metabolism: Glucose

•Available in the well-fed sate Insulin increases the intracellular transportation of glucose

lactic acid goes to (2)

•Bloodstream → liver → glucose or •Accumulates in muscle and bloodstream → sore muscles

cardiac muscles are bound with

•Bound with intercalated discs

* Glycolysis

•Catabolism of glycogen •Occurs in the cytosol, does not require oxygen •Can be aerobic or anaerobic •1 molecule of Glucose → 2 molecules of Pyruvic Acid → net gain of 2 molecules of ATP

Sources of glucose

•Diffusion from blood into muscle fiber or •Glycolysis

creatine phosphate

•Energy-rich molecule found in muscle fibers •Rapid source of energy (ATP), first source of energy for muscle contraction •Allows contraction for 15 seconds •ADP + Creatine phosphate (enzyme creatine kinase) → ATP + Creatine •Inactive muscle restores creatine to creatine phosphate

Smooth muscle descriptions and regenerative capacity

•Grouped, non-striated, mononucleated fusiform cells •Can undergo hypertrophy and hyperplasia (increase in number)

•Hormonal Regulation of Glycogen by Insulin (exercise) Aerobic Exercise: As time progresses

•Hepatic gluconeogenesis •Resting muscles transforms glycogen → lactate → hepatic conversion to glucose → redistribution to active muscle

smooth muscle innervated by

•Innervated by ANS

what is the skeletal system innervated by?

•Innervated by somatic nervous system

cardiac muscle description and repair capacity

•Irregular branched, striated, mononucleated cells Cells cannot regenerated, may go through hypertrophy

smooth muscle lacks

•Lacks troponin

Skeletal muscles descriptions and repair capacity

•Large, elongated, striated, multinucleated fibers •Limited repair capacity, but can grow in size (hypertrophy) •Mature cells do not go through mitosis

•Hormonal Regulation of Glycogen by Insulin (Well fed state): Absence of insulin → opposite effects to maintain systemic glucose levels

•Liver mobilizes glycogen •Adipose tissue mobilizes fatty acids •Skeletal muscle there is glycogenolysis

Muscle metabolism: Glycogen

•Major storage of glucose •Major storage sites: liver and skeletal muscles •Hepatic glycogen sustains blood glucose levels •Muscle glycogen provides a glucose source during muscle contraction

What 4 tissues are skeletal muscles composed of?

•Muscle tissue (muscle cells or fibers) •Connective tissues •Nerves •Blood vessels

•Hormonal Regulation of Glycogen by Insulin (exercise)

•Muscle's metabolic needs ↑ •Potential energy sources: glucose, glycogen, fatty acids, and proteins

Anerobic Glycolysis occurs during

•Occurs during heavy exercise (low oxygen supply) → anaerobic conditions

anerobic respiration characteristics (4) 1) less or more atp 2) faster or slower 3) require 02 or doesn't 4) provides evergy for how long

•Produces less ATPs •Faster •Does not require oxygen •Provides energy for about 2 minutes

what regulates glycogen

•Regulation of glycogen •Allosteric enzymatic regulation •Hormonal regulation by insulin

•Hormonal Regulation of Glycogen by Insulin (exercise) Aerobic exercise: later in lengthy exercise skeletal muscle glucose use inc or dec?

•Skeletal muscle glucose use ↓ •Fatty acid oxidation ↑ and provides nearly all energy needs for aerobic exercise metabolism

aerobic respiration: fast or slow more effective or less

•Slower process, but more effective •More ATP (30-32 molecules)

cardiac muscles controlled by

•Under the control of the specialized intrinsic pacemaker cells •Influenced by the autonomic nervous system (ANS)

Clinical correlate: Nutritional Deficits (scurvy) deficiency of what

•Vitamin C deficiency •Vitamin C is needed in the production of collagen •Leads to bone disease in growing children •Hemorrhages and healing defects in children and adults

Clinical correlate: Nutritional Deficits (Rickets (children)/ Osteomalacia (adults)) deficiency of what

•Vitamin D deficiency → hypocalcemia and activation of PTH •→ bone mass in adults (osteopenia) •→ bowing of legs in children

smooth muscle voluntary or involuntary

•Weak, involuntary contractions

•Hormonal Regulation of Glycogen by Insulin (Lipid and protein metabolism) onset of starvation causes

•→ rapid protein turnover •→ amino acid release to the liver •→ stimulate gluconeogenesis •→ brain uses this as an alternate source of energy •→ ↓ brain's need for glucose •→ ↓ protein breakdown

Type 1 sustains what kind of contractions

(Slow to contract, slow to fatigue) Sustain prolonged contractions Endurance muscles, maintain posture (e.g., postural muscles of the back) Example: Endurance activity such as marathon runners

Myofilaments are made up of Bundles of myofilaments form Myofilaments are responsible for

-protein filaments (repeated sections of sarcomeres) Bundles of myofilaments form myofibrils responsible for muscle contractions

The contraction cycle summary

1) SR releases calcium ions into sarcoplasm 2) Calcium binds to troponin 3) Troponin moves tropomyosin away from myosin bid sites on actin 4) Contraction cycle begins: 5) ATP hydrolysis (ATP →ADP + phosphate group) → myosin head is in cocked position ready to bind actin 6) Myosin and actin bind → cross-bridge formation 7) Power stroke → myosin head pivots, ADP + phosphate group are released 8) Detachment of myosin from actin → myosin binds another ATP, detaches from actin

NMJ (neuromuscular junction): Steps during a contraction process

1) An action potential (AP) is propagated through the pre-synaptic neuron reaching the synaptic cleft (to be transferred to the myocyte) 2) Acetylcholine (Ach) is released from the synaptic vesicles into the synaptic cleft 3) Myocyte's post-synaptic membrane, the motor end plate, contains nicotinic Ach receptors 4)Ach receptors are transmembrane Na+ and K+ channels, which increase influx of cations and depolarize the membrane propagating the impulse to the T-tubule system 5) Excess Ach is hydrolyzed by the enzyme acetylcholinesterase into acetate and choline 6) Choline is reabsorbed by presynaptic neuron and used for production of more ACh

Thin filaments have what 4 contractile/regulatory components

1) actin (contractile) 2) tropomyosin (regulatory) 3) Troponin (regulatory) 4) Nebulin (structural)

two types of isotonic contraction

1. Concentric 2. Eccentric

•Hormonal Regulation of Glycogen by Insulin (Well fed state) •Insulin in the liver does what insulin in skeletal muscles does what

Inhibits gluconeogenesis and increases glycogen production •Increases glucose transport into the cells → glucose phosphorylation → enters metabolic pathway → ends in ATP production