ch 9

motor neurons

(specialized nerve cells) stimulate muscles to contract

creatine phosphate (3 energy sources)

) During rest, creatine phosphate is produced and accumulates in the muscle cells (stores energy) b) When ATP levels fall, ADP reacts with creatine phosphate to produce ATP & creatine c) This reaction occurs rapidly and will maintain ATP levels as long as creatine phosphate is available; but these levels are depleted rapidly d) ATP and creatine phosphate provide enough energy to maintain muscle contraction for 8 - 10 sec.

actin myofilaments (thin)

- Composed of 3 different proteins o Fibrous actin (F actin): look like 2 strands of pearls twisted around each other • Composed of ~ 200 small globular proteins (Globular actin or G actin), each with a myosin binding site o Tropomyosin: elongated protein that winds along the groove of the F actin double helix o Troponin: composed of 3 subunits • one binds to actin • one binds to tropomyosin • one binds to Ca2+ - Tropomyosin & troponin make up the T-T Complex that lies over the actin myofilament when the muscle is relaxed, thus blocking the myosin binding sites on the actin

Myosin myofilaments (thick myofilaments)

- Composed of a protein called myosin shaped like 2 golf clubs twisted together so that there are 2 head portions attached to the rod portion of the molecule o the head regions extend towards the actin myofilaments and bind to the myosin binding sites on the G actin proteins forming Cross-Bridges which are important in muscle contraction o the heads are attached to the rod portion by a hinge region that can bend & straighten during contraction o the heads have ATPase activity (breaks down ATP), releasing energy used during contraction

nerve and blood supply

- In general, one nerve, one artery, and one or more veins serve each muscle. - Skeletal muscle has a RICH blood supply because muscle requires an almost constant supply of oxygen and nutrients. - Muscles give off large amounts of metabolic wastes that must be removed by veins. - Muscle capillaries, the body's smallest blood vessels, allow for exchange of oxygen / carbon dioxide and nutrients / metabolic wastes, among other exchanges between the blood and muscle tissues.

attachments

- When a muscle contracts, the movable bone (the muscle's insertion), moves toward the immovable bone (the muscle's origin).

Perimysium and fascicles (con tiss sheaths)

- layer of connective tissue that surrounds each fasciculus (bundle)

endomysium (conn miss sheaths)

- layer of connective tissue that surrounds each individual muscle fiber

muscle twitch

- the contraction of a muscle in response to a stimulus that causes an action potential in one or more muscle fibers, followed by relaxation; most normal activities involve sustained muscle contraction

tetanus pathology

1) Caused by a neurotoxin released by the bacterium Clostridium tetani (often found in soil); it's one of the most potent known toxins 2) The bacterium is an anaerobe that thrives in low oxygen environments; can get in through even a tiny pinprick or scratch, but deep puncture wounds or cuts are especially susceptible to infection with tetanus 3) The toxin is spread throughout the body via the blood & lymph vessels 4) The toxin causes the blocking of neurotransmitters from inhibitory motor neurons (which normally prevent overstimulation of the skeletal muscles) skeletal muscles enter a state of constant contraction and spasm 5) The first area that experiences the contractions is usually the mandible; therefore, tetanus is also referred to as "lockjaw" and is especially dangerous if swallowing and breathing muscles are affected 6) Incubation is ~ 2 weeks; complete recovery may take months 7) Immunization (tetanus antitoxin) is available

skeletal muscle fibers (reg of muscle fibers)

1) Do not go through mitosis after birth 2) Increase in size of skeletal muscle due to hypertrophy of existing cells

fast glycotic fibers

1) Intermediate type of fibers 2) Less common than the other two types 3) Contract quickly but are oxygen dependent

Slow Oxidative Fibers = Type I Muscle Fibers (diff myosin)

1) Large number of mitochondria, many blood capillaries and myoglobin (a dark pigment, similar to hemoglobin, which binds Oxygen and acts as a reservoir for it when the blood does not supply an adequate amount) 2) Contract slowly, but can sustain a contraction for a long time 3) Primary source of ATP synthesis = aerobic respiration 4) Examples: neck and postural muscles

Fast Oxidative Fibers = Type II Muscle Fibers

1) Lower concentration of myoglobin, fewer & smaller mitochondria, fewer blood vessels 2) Contract quickly but fatigue quickly 3) Have large deposits of glycogen & are well adapted to perform anaerobic respiration 4) Examples: eye muscles

smooth muscle fibers (region of muscle fibers)

1) Retains the greatest ability to regenerate, but still limited compared to other mitotically active tissue • In the uterus, mitosis occurs when needed during pregnancy

Mechanism of neuromuscular transmission of action potential

1) The action potential (impulse) reaches the presynaptic terminal of the axon 2) Voltage-gated Ca 2+ channels open 3) Ca 2+ enter the presynaptic terminal from interstitial fluid initiate release of ACh from synaptic vesicles (exocytosis) 4) ACh diffuses across synaptic cleft and binds to ACh receptors at motor end plate increases permeability of ligand-gated Na+ channels 5) Increased Na+ permeability Na+ diffuse into the cell results in depolarization of Postsynaptic membrane, resulting in an action potential in the muscle fiber - Now the action potential needs to get deep into the muscle fiber, to the myofilaments, in order for contraction to occur.

tetanus

2 conditions - a normal occurrence and a pathological condition

synaptic cleft

: the space between the axon terminal and the muscle fiber

threshold (full contraction)

: the weakest strength of a stimulus that causes a contraction

normal occurrence

A complete contraction of a muscle that occurs when the impulses are fired very close together and the SR does not have the time to allow for uptake of the Ca2+ in between each impulse sustained contraction

structure

A whole skeletal muscle is considered an organ of the muscular system because it's composed of skeletal muscle tissue, connective tissue, nervous tissue & vascular tissue

energy sources

ATP, the energy molecule used by living cells, provides the energy needed for muscle contractions; as long as adequate amounts of ATP are present, muscles can contract repeatedly for a long time • ATP synthesis = ATP breakdown

skeletal anatomy hierarchy

Each fasciculus is composed of numerous muscle fibers (muscle cells) - Muscle fibers consist of myofibrils and organelles (esp. mitochondria, sarcoplasmic reticulum) - Myofibrils are composed of myofilaments o Thick filaments - containing myosin o Thin filaments - containing actin

Anabolic Steroids and Muscle

Synthetic hormones taken to increase the size & strength of muscles (hypertrophy) 1) Pharmaceutical form of testosterone, altered so that the reproductive effects are minimized, but the effects on skeletal muscle are maintained 2) Introduced in the 1950s to treat muscle atrophy diseases 3) People who take large doses exhibit an increase in body weight and total skeletal muscle mass 4) Harmful side effects: testicular atrophy, sterility, cardiovascular disease (heart attack, stroke), abnormal liver function leading to liver cancer, aggressive behavior • When used by females: increase in muscle definition & body hair; decrease in pitch of voice

Physiologic Contracture

a condition resulting from extreme muscular fatigue where, due to a lavk of ATP within the muscle fibers, the formed cross-bridges cannot release between the myosin & actin myofilaments

z disk (z line)

a filamentous network of proteins forming a disk-like structure for the attachment of actin myofilaments

Acetylcholine (ACh):

a neurotransmitter composed of acetic acid & choline o Neurotransmitter: substance that stimulates or inhibits production of an action potential

tendon

a ropelike connection between the muscle and bone,

Aponeurosis:

a sheet-like covering of a bone or cartilage to the fascia of other muscles.

during contraction

a) Actin and myosin myofilaments stay the same length b) Actin slides past myosin myofilament, but myosin remains in the same position c) Z disks come closer to each other d) Sarcomeres get shorter

Anaerobic Respiration (3 es)

a) The breakdown of glucose in the absence of oxygen b) 1 glucose molecule 2 ATP + lactic acid c) Not as efficient as aerobic respiration, but occurs faster, producing ATP in a short time d) During intense exercise (ex. sprinting) anaerobic resp. combined w/ the breakdown of creatine phosphate can provide the muscles with enough ATP for 2 - 3 minutes e) Limited by lactic acid buildup in muscle fibers

aerobic response (3 es)

a) The breakdown of organic molecules (including glucose, fatty acids, amino acids) in the presence of oxygen b) 1 glucose (up to ) 38 ATP + CO2 + H2O (much more efficient) c) As the muscles continue to contract, more blood carrying oxygen will go to them d) The process is more complex and takes longer than anaerobic (citric acid cycle & electron- transport chain) e) Resting muscles, or those undergoing long-term exercise (long-distance running or other endurance exercises) depend primarily on aerobic respiration for ATP synthesis

during relaxation

a) There is a low concentration of Ca2+ in the sarcoplasm, a high concentration in the SR b) The myosin binding sites on G actin are covered by the T-T complex, so no contact exists between actin and myosin

sub threshold (full contraction)

below threshold - no response occur

connective tissue sheaths epimysium

connective tissue sheath surrounding the entire muscle

posture maintance

constant muscle tone

A band (anisotropic band):

contains mainly myosin filaments in center (H zone), with overlapped myosin/actin at either end

sarcoplasm

cytoplasm

sarcoplasmic reticulum

endoplasmic reticulum

sacro

flesh

glycosomes

granules of stored glycogen that provide glucose during muscle cell activity for ATP production

sarcoplasmic reticulum def

highly-specialized, smooth endoplasmic reticulum that contains high [Ca2+] when the muscle fiber is relaxed

M line

in the middle of the H zone; consists of filaments that attach to the center of the myosin myofilaments & help hold them in place

smooth

involuntary non striated visceral

cardiac

involuntary striated

muscle mass

most of the bodys mvmd result from muscle contractions, 40-50% body weight is composed of muscle mass

myo

muscle

muscle fiber

muscle cell

sarcolemma

muscle cell membrane

movement

muscle contraction (involuntary and voluntary) - constriction of organs and vessels digestive tract - propels, mix food & water vessels - regulates blood flow

recruitment

o as the stimulus strength increases between threshold and maximum values, the number of motor units responding to the stimuli increases and the force of contraction produced by the muscle increases in a graded fashion

all-or-none law of skeletal muscle contraction

o if the muscle fibers of a motor unit are activated by the nerve sufficiently to contract (at or above threshold), those fibers will contract maximally

I band (isotropic band):

o includes a Z disk and contains mainly actin filaments

motor unit

o motor neuron + muscle fibers that it controls ♣ When an electrical impulse travels down the axon, all muscle cells innervated by the motor neuron contract simultaneously ♣ Motor units vary in size according to location and movement • In locations where delicate & precise movement is needed (eyes, fingers), 1 neuron may control only 2 to 3 muscle fibers • In locations where muscles perform more powerful but less precise contractions (leg), 1 neuron may control as many as 2000 fibers

presynaptic terminal

o the axon terminal ♣ Contains synaptic vesicles (ACh) and numerous mitochondria

Motor End Plate (postsynaptic membrane):

o the sarcolemma of the muscle fiber in the area of the junction ♣ Contains ACh receptors

latent lag phase (full contraction)

o the time between application of the stimulus to the motor neuron and the beginning of the contraction • ~ 2 milliseconds; during this time the Ca2+ is being released by the SR

elasticity

recoil to org length

myoglobin

red pigment stores oxygen

whole muscles

respond in a graded fashion oStrength of contractions can vary from weak to strong, depending on the number of motor units stimulated to contract multiple motor unit summation

motor units

respond in an all-or-none fashion o all the muscle fibers within a given motor unit contract or relax nearly simultaneously; that is, it's not possible for some of the muscle fibers of a motor unit to contract while others in the same motor unit relax

Excitability:

respond to a stimulus

contractility

shorten forcefully (results in movement)

during muscle relaxation

skeletal muscle relaxes when the nervous impulse (action potential) stops a) At the synapse (neuromuscular junction), the ACh that diffuses across the synaptic cleft and binds to the ACh receptors on the motor plate end is quickly broken down by acetylcholinesterase (AChE) (so that it doesn't act as a constant stimulus) to acetic acid and choline b) Choline molecules are reabsorbed by the presynaptic terminal and then combined with the acetic acid produced within the cell to form ACh that's packaged into vesicles, ready for another action potential c) Ca2+ gates on the SR membrane close, Ca2+ pumped back in to SR, Ca2+ move from troponin

extensibility

stretch beyond norm resting length, still contract

direct attachment

the epimyseium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage.

indirect attachment

the muscle's connective tissue wrappings extend beyond the muscle either as a:

cardiac muscle fibers (region of mf)

thought to be post-mitotic tissue; when there is injury to the heart wall (as in a myocardial infarction - heart attack), non-contracting fibrous connective tissue replaces the cardiac muscle • Recent studies show regeneration promise: undifferentiated stem cells were directly injected into muscle tissue and they differentiated into heart muscle cells

t tubules

tunnel-like folds along the sarcolemma surface that extend deep into the muscle fiber and lie near the sarcoplasmic reticulum; conduct impulses from the cell surface down to the SR

skeletal

voluntary striated

body movements

walking, manipulating objects with hands

production of body heat

• (thermogenesis) muscle contraction work by-product: heat (~85%)

excersize effects

• A muscle increases in size (hypertrophies), and increases in strength and endurance in response to exercise o Increase in metabolic enzymes, myofibrils, sarcomeres & mitochondria; more capillaries • A muscle that is not used decreases in size (atrophies) o Decrease in metabolic enzymes, myofibrils, sarcomeres & mitochondria; less capillaries o Severe atrophy (elderly, limited mobility) involves irreversible decrease in # of muscle fibers can lead to paralysis

sliding filament model

• Actin and myosin myofilaments don't change in length during contractions; the actin slides over the myosin; the position of the myosin remains the same, but the position of the actin changes. • When sarcomeres shorten myofibrils also shorten muscle fibers shorten muscle bundles shorten muscle contacts

Action potentials across the neuromuscular junction

• Membrane potentials o Plasma membranes are polarized there's a voltage or electrical difference across the plasma membrane ♣ Resting membrane potential: inner surface of p.m. is negatively charged, outer surface is positively charged (ion concentration differences) ♣ Action potentials (electrical signals): reversals of the resting membrane potentials inner surface of the p.m. becomes positively charged compared to the outer surface o due to diffusion of ions through ion channels in the membrane

muscle fatigue

• Results from ATP depletion • Without adequate ATP levels in muscle fibers, cross-bridges cannot function normally

oxygen debt

• The additional oxygen that must be taken into the body after vigorous exercise to restore all systems to their normal states

Excitation-Contraction Coupling

• The mechanism by which an action potential causes contraction of a muscle fiber • Involves the sarcolemma, T tubules, sarcoplasmic reticulum, Ca2+ , troponin, tropomyosin

sarcomeres

• Units of organization found in skeletal and cardiac muscle, making these types of muscle appear striated. Each sarcomere lies between two Z disks (Z lines). • Depending on the distribution and interconnection of myofilaments a number of "bands" and "lines" can be distinguished in the sarcomeres:

stabilize joints

•some muscles keep joints from falling apart when other muscles cause those joints to move. This is just as important as the movement itself. Ex: rotator cuff muscles in the shoulder keep the ball-and-socket joint of the should from dislocating every time we throw a ball or raise an arm.