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