Chapter 9: Muscles and Chapter 10 Test 3 (BIO 201 SUMMER 2019), A&P Lecture Ch. 8,9,11, Mastering HW Ch 9, Mastering Chapter 10 Activities, Ch. 7 Muscles A&P

what actually causes a muscle contraction and relaxation?

* cross bridge cycling * Ca2+ is pumped into the SR (sarcoplasmic reticulum), tropomyosin blockage is restored, and the muscle relaxes

repolarization (action potential)

* immediately after the depolarization wave passes, the sarcolemma permeability changes * Na+ channels close and K+ channels open * K+ diffuses out of the cell, restoring the electrical polarity of the sarcolemma ^^^ this is repolarization

Hyperpolarization: (action potential)

* more K+ diffuses out of the cell, making the membrane more polar than RMP ^^^ this is hyperpolarization * the ionic concentration of the resting state is restored by the Na+ K+ PUMP

sodium/potassium ATPase pump

* moves 3 Na+ (sodium) out of the cell and 2 K+ (potassium) into the cell for every ATP used * creates concentration gradients that is important to the cell function

multiple motor unit summation

* muscle contracts more vigorously as stimulus strength is increased * this phenomenon, called recruitment, brings more and more muscle fibers respond

nerve stimulus of skeletal muscle

* skeletal muscles are stimulated by motor neurons * each muscle fiber is innervated (connected) by an axon -- the axonal terminal is filled with synaptic vesicles -- the synaptic vesicles contain the neurotransmitter acetylcholine

neuromuscular junction

* the axonal ending and the muscle cell are very close but they do not touch -- the space between the two is called the synaptic cleft -- the muscle cell dips down a bit under the synaptic cleft and is highly fooled THIS IS A MOTOR END PLATE

as K+ leaves the cell: (RMP)

* the charge becomes more negative this negative charge attracts K+ back into the cell

resting membrane potential (RMP)

* the voltage across the cell membrane * this can be measured with very tiny probes; one inside the membrane and one outside * depending on the cell type RMP -- ranges from -5 to -100 m V * all cells are polarized

at low intracellular Ca2+ concentration: roles of ionic calcium (Ca2+) in the contraction mechanism

* tropomyosin blocks the binding sites on action * myosin cross bridges cannot attach to the binding sites on action * the muscle is relaxed

arrangement of the filaments in a sarcomere

Longitudinal section within one sarcomere - thick: myosin - thin: actin

myofilaments: M-lines

M-lines appear darker due to the presence of an anchoring protein

when the mvmt of K+ out of the cell equals the mvmt into the cell, the charge (RMP) is:

about -70 m V

calcium breaks down ______ in the axonal terminal?

ach

Minimum contraction

contraction caused by threshold stimulus

Period of contraction of muscle twitch

cross bridges form and cycling occurs; muscle shortens

sarcoplasm

cytoplasm of a muscle cell

Endomysium

fine sheath of CT surrounding each muscle fiber

latent period of muscle twitch

first few milliseconds after stimulation when excitation-contraction coupling is taking place (everything between stimulus and actin and myosin binding)

stimulus intensity and muscle tension

it doesn't matter how much we increase the stimulus, the maximum contraction will NOT go up

RMP is the:

most important in nerve and muscle cells even though all cells have one

muscle fiber

muscle cell

Sarcolemma

muscle plasma membrane

incomplete tetanus contraction

rapid stimuli, muscle has some time to relax between contractions

a cell becoming more negative =

repolarization

Na+ does try to move into the cell: (RMP)

the membrane is only slightly permeable to Na+

membrane potential is created by: (RMP)

the position of ions relative to the cell membrane

2 kinds of myofilaments

thick and thin

threshold stimulus

weakest stimulus that causes a response

I band

within the light I band is a dark line called the Z-disc or Z-line

trigger an action potential

you HAVE to release acetylcholine (Ach) to cause the action potential

motor unit: the nerve-muscle functional unit

• A motor unit is a motor neuron and all the muscle fibers it connects to • The number of muscle fibers per motor unit can vary from four to several hundred • Muscles that control fine movements (fingers, eyes) have small motor units • Large weight-bearing muscles (thighs, hips) have large motor units • Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle

Destruction of Acetylcholine

* ACh bound to ACh receptors is quickly destroyed by the enzyme acetylcholinesterase * This destruction prevents continued muscle fiber contraction in the absence of additional stimuli

neuromuscular junction con't

* ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma * binding of ACh to its receptors initiates an action potential in the muscle

roles of acetylcholine (Ach) w/ depolarization

* Ach binds to its receptors at the motor end plate * binding opens chemically (ligand) gated sodium channels * Na+ diffuses into the cell and the interior of the sarcolemma becomes less negative ^^^this is known as depolarization

depolarization and generation of an action potential: (action potential)

* Ach from the neuron binds to receptors in the motor end plate and causes sodium channels to open * Na+ flows into the cell * inside of the cell becomes positive

the cell membrane is impermeable to: (RMP)

* Cl- (chloride) because there is no pump allowing them to move * A- (protein anions) because theyre too big

graded muscle responses

* Graded muscle responses are: -- Variations in the degree of muscle contraction -- Required for proper control of skeletal movement * Responses are graded by: -- Changing the frequency of stimulation -- Changing the strength of the stimulus

Depolarization

* Na+ diffuses into the cell and the interior of the sarcolemma becomes less negative * initially, this is a local electrical event called end plate potential * later, it ignites an action potential that spreads in all directions across the sarcolemma

sarcoplasmic reticulum (SR)

* SR is an elaborate, smooth endoplasmic reticulum * terminal cisternae (lateral sacs) are enlarged areas of the SR * function: store Ca2+ between contractions Ca2+ is critical for contractions

T tubules

* T tubules are projections of the sarcolemma that occur at every junction of an A band and I band * 1 T tubule plus 2 terminal cisternae = triad

ultrastructure of myofilaments: Thick filaments

* Thick filaments are composed of the protein myosin. * Each myosin molecule has a rod-like tail and two globular heads - Tails-interwoven to form a fiber - Heads * looks like two golf clubs wrapped together * each thick filament contains approximately 200 molecules of myosin

ultrastructure of myofilaments: thin filaments

* Thin filaments are chiefly composed of the protein actin * Each actin molecule looks like 2 strands of pearl twisted together and the pearls are G action * tropomyosin is a protein that spirals around the actin and blocks the active sites where myosin binds * troponin attaches tropomyosin to the actin and regulates contraction

muscle twitch

* a muscle twitch is the response of a muscle to a single, brief threshold stimulus * a single stimulus results in a single contractile response

at higher intracellular Ca2+ concentrations: roles of ionic calcium (Ca2+) in the contraction mechanism

* additional calcium binds to troponin * calcium-activated troponin undergoes a conformational (shape) change * troponin pulls tropomyosin away from actin's binding site * myosin head can now bind and cycle * this permits contraction (sliding of the thin filaments by the myosin cross bridge) to begin

propagation of an action potential: (action potential)

* change in the charge causes voltage gated Na+ channels to open * Na+ flows into the cell in those areas ^^^ this is now depolarization * do a "wave" * once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle

when a nerve impulse reaches the end of an axon at the neuromuscular junction:

* voltage-regulated calcium channels open and allow Ca2+ to enter the axon * Ca2+ inside the axon terminal causes synaptic vesicles to fuse with the axonal membrane and releases ACh into the synaptic cleft via exocytosis

sliding filament model of contraction

* when a muscle contracts, thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a great degree -- distance between z discs is reduced -- I band shorten -- H zone disappear * in the relaxed state, thin and thick filaments overlap only slightly

what do all of these light and dark areas mean in myofibrils?

- all of these bands are caused by the arrangement of myofilaments

myofilaments: Z-disc

- coin-shaped sheet of proteins (connections) that anchors the thin filaments

myofibrils

- densely packed, rodlike contractile elements that run parallel to the length of the cell - makes up most of the muscle volume

muscle attach: directly or indirectly

- directly: epimysium of the muscle is fused to the periosteum of the bone - indirectly: CT wrappings extend beyond the muscle as a tendon or aponeurosis - indirect attachments are more common: they are more durable and take up less room on the bone and across the joint

microscopic anatomy of a skeletal muscle fiber

- each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma - fibers are up to hundreds of centimeters long - each cell is produced by fusion of embryonic cells - sarcoplasma has numerous glycosomes and lots of myoglobin

3 connective sheaths of skeletal muscle

- endomysium - perimysium - epimysium Think of a 3 pack of gum: - endomysium is the wrapper around each piece of gum - perimysium is the package of one gum pack - epimysium is the plastic holding all 3 gum packages together

myofilaments: Thin filaments

- extend across the I band and partway into the A band

Myofilaments: Thick Filaments

- extend the entire length of an A band - H-zone is only thick filaments

skeletal muscle tissue

- has obvious stripes called striations - controlled voluntarily - contracts rapidly but tire easily - responsible for overall motility - is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds

smooth muscle tissue

- in walls of hollow visceral organs, like the stomach, bladder, respiratory system - forces food and other substances thru internal body channels - it is not striated and is involuntary

attachments of skeletal muscles

- most skeletal muscles span joints and are attached to bone in at least two places - insertion and origin - when muscles contract the movable bone, the muscles insertion, moves toward the immovable bone, the muscles origin

glycosomes

- stored glycogen - broken down to glucose=energy

cardiac muscle tissue

- striated but not voluntary - contracts at a fairly steady rate set by the hearts pacemaker - neural controls allow the heart to respond to changes in bodily fluid

a sarcomere is:

- the smallest contractile unit of a muscle - runs z-disc to z-disc

sarcomere structure

- thin (actin) filament - elastic (titin) filament - thick (myosin) filament

myofilaments: H-zone

- thin filaments do not overlap thick filaments in the lighter H-zone - H-zone contains thick filaments only

A band

- within the A band, there is a lighter H zone that appears in relaxed muscle - in the middle of the H zone is a dark M line

striations and sarcomeres (in myofibrils)

-- with a light microscope we see light and dark bands

nerve and blood supply of skeletal muscle

-Each muscle is served by one nerve, an artery, and one or more veins -Each skeletal muscle fiber is supplied with a nerve ending that controls contraction

roots for muscles

-myo -mys -sarco

sequential events of contraction

1) Cross bridge formation: myosin cross bridge attaches to actin filament 2) power stroke: myosin head pivots and pulls actin filament toward M line 3) Cross bridge detachment: new ATP attaches to myosin head and the cross bridge detaches 4) "Cocking" of the myosin head: energy from hydrolysis of ATP cocks the myosin head into the high energy state

excitation-contraction coupling

1) action potential is generated and propagated along the sarcolemma to the T-tubules 2) action potential triggers Ca2+ release 3) Ca2+ bind to troponin, blocking action of tropomyosin release 4) contraction via crossbridge formation 5) removal of Ca2+ by active transport 6) tropomyosin blockage restored, contraction ends

3 phases of muscle twitch

1) latent period 2) period of contraction 3) period of relaxation

structure and organization of skeletal muscle

1) muscle 2) fascicle 3) muscle fiber 4) myofibril or fibril 5) sarcomere 6) myofilament or filament

characteristics of muscle tissue

1. Excitability or irritability: ability to receive and respond to stimuli 2. Contractility: ability to shorten forcibly 3. Extensibility: ability to be stretched or extended beyond resting length 4. Elasticity: ability to recoil and resume the original resting length after being stretched

2 types of gated channels

1. chemically (ligand) gated 2. voltage gated

Muscle functions

1. produce movement: mvmt of whole body, blood, urine, food etc 2. maintain posture: fights gravity to maintain our sitting or standing posture 3. stabilize joints 4. generate heat: heat is a waste product of contractions but is significant source of our stable body temp

dark bands

A bands

Epimysium

CT that surrounds the entire muscle

period of relaxation of muscle twitch

Ca2+ is pumped back into the SR; actin and myosin separate; muscle lengthens; muscle tension returns to zero

the cell membrane is very permeable to: (RMP)

K+ * according to its concentration gradient: K+ wants to diffuse out of the cell

wave summation contraction

Frequently delivered stimuli (muscle does not have time to completely relax) increases contractile force

light bands

I bands - think 'illumination'

a cell becoming less negative =

depolarization

synaptic cleft

gap between the axonal terminal (presynaptic) and the muscle cell (postsynaptic)

RMP evenly distributed =

if there were only passive processes, eventually Na+ and K+ would be equally distributed across the membrane

the muscle is relaxed when?

myosin is blocked from action

the inside of the cell is _________ relative to the outside

negative * even though we are talking about positive ions, we are looking at relative charge

ach is?

neurotransmitter found in synaptic vesicles of the axonal terminal

muscle response to varying stimuli

notice that there is an increase in strength of the contraction, this is because we're adding contractions onto existing contractions

voltage gated channels

open in response to a change in charge * think of a garage door opener, you need an electrical signal not a actual key

chemically (ligand) gated channels

open in response to something binding to them ex: acetylcholine receptors in the motor end plate * think of a lock on a door, you need a key to open it

myoglobin

oxygen storing molecules

insertion and origin

points where muscles attach to bones, name used depends on mvmt of the bone

cross bridge cycle

sequence of events between binding of a cross-bridge to actin, its release, and reattachment during muscle contraction

Aponeurosis

sheets of connective tissue

3 types of muscle tissue

skeletal, cardiac, smooth

complete tetanus contraction

smooth and sustained contraction ex: holding a book or holding your arm out

maximum contraction or response

strongest contraction that a muscle can have

Perimysium

surrounds group of muscle fibers called fascicles