Chapter 11

A&P 1 Lecture

Universal characteristics of muscle

Excitability (responsiveness), conductivity, contractibility, extensibility, elasticity

Excitability (responsiveness)

To chemical signals, stretch, and electrical changes across plasma membrane

Conductivity

Local change triggers a wave of excitation that travels along the muscle fiber

Contractability

Shortens when stimulated

extensibility

capable of being stretched between contractions

Elasticity

Returns to original resting length after being stretched

Skeletal muscle

Voluntary, striated muscle attaches to one or more bones

Striations

Alternating light and dark transverse bands

Voluntary

Usually subject to conscious control

Skeletal muscle cell

Muscle fiber or myofiber

muscle fiber or myofiber

skeletal muscle cell

multinucleated

nucleus in skeletal muscle?

Endomysium, perimysium, epimysium

Skeletal muscle contains fibrous connective tissues:

fibrous connective tissues

the endomysium, perimysium, epimysium are what

Endomysium

Surrounds each muscle fiber

Perimysium

Bundles muscle fibers into fascicles

Epimysium

Surrounds entire muscle

Collagen

Stretches slightly under tension and recoils when released and resists excessive stretching

collagen

protects muscle from injury and returns muscle to its resting length

collagen

contributes to power output and muscle efficiency

extensible and elastic

collagen is somewhat_____

Sarcolemma

Plasma membrane

Sarcoplasm

Cytoplasm

Myofibrils

Long protein bundles occupying most of sarcoplasm

Multiple nuclei

Flattened and pressed against inside of sarcolemma

Mitochondria

Packed into spaces between myofibrils

Sarcoplasmic reticulum (SR)

Smooth ER that forms a network around each myofibril; calcium reservoir

Terminal cisternae

Dilated end-sacs of SR; cross muscle fiber from one side to another

T tubules

Tubular infolding of the sarcolemma which penetrate through the cell and emerge on other side

T tubules

signal sarcoplasmic reticulum (SR) wehn to release calcium which causes muscle contraction

Thick filaments

Made of several hundred myosin molecules

Thick filaments

Shaped like golf club, 2 chains interwinds to form a shaft-like tail, double globular myosin head

Thick filament heads

Directed outwards in a helical array (spiral) around bundle

thick filament heads

heads on one half of the thick filament angle to the left and the other half angle to the right, bare zone with no heads in the middle

Thin filaments

Fibrous actin, globular actin subunits, tropomyosin molecules, troponin molecule

Fibrous actin

2 intertwined strands

fibrous (F) actin

string of globular (G) actin subunits each with an active site that can bind to head of myosin molecules

Tropomyosin molecules

Blocks active site on G actin when muscle is relaxed; prevents myosin from binding

Troponin molecule

Small, calcium-binding protein (attaches to calcium) on each tropomyosin molecule

regulatory proteins

determine when the muscle fiber can and cannot contract: tropomyosin and troponin

contractile protiens

do the actual work of shortening the muscle: myosin (head) and actin (primary protein of thin filament

Elastic filaments

run through core of thick filament; anchor it to Z disc and M line

elastic filaments

help stabilize and position thick filament

elastic filaments

prevent overstretching and provide recoil

Titan

Huge, springy protein

titan

elastic filaments contain what protein

Dystrophin

Links actin in outermost myofilaments to membrane proteins that link to endomysium

dystrophin

transfers forces of muscle contraction to CT ultimately leading to tendon

dystrophin

genetic defects in ______ produce disabling disease muscular dystrophy (muslces loses the ability to contract)

Striations

Organized in a precise way in skeletal and cardiac muscle

A band

Dark, thick (myosin) filaments

H band

Lighter region in middle of A band; thick filaments only

M line

Middle of H hand; transverse protein complex that links thick filaments

I band

light, thin (actin) filaments

Z disc (Z-line)

Provides anchorage for thin and elastic filaments

Sarcomere

Segment of a myofibril from Z disc to Z disc

sarcomere

functional contractile unit of muscle fiber

Their individual sarcomeres shorten

Muscle cells shorten because:

Thick and thin filaments slide past each other

Z disc (Z lines) are pulled closer together as:

Length during shortening; only amount of overlap changes

Neither thick nor thin filaments change in:

Dystrophin and linking proteins also pull on extracellular proteins which transfers pull to extracellular tissue

During muscle shortening

Nerve-muscle relationship

Skeletal muscle cannot contract unless stimulated by a nerve: what is this

Somatic motor neurons

Nerve cells with cell bodies in brainstem and spinal cord; serve skeletal muscles

Somatic motor fibers

Axons (long extensions) of somatic motor neurons (nerve cells for contraction) that lead to skeletal muscle

Branches out to a number of muscle fibers

Each nerve fiber does what

Is supplied by only one motor neuron

Each muscle fiber:

Motor unit

One nerve fiber and all the muscle fibers innervated by it; behave as a functional unit

Muscle fibers of one motor unit

Dispersed throughout muscle (not clustered)

muscle fibers of one motor unit

contract in unison

muscle fibers of one motor unit

produce weak contraction over wide area

muscle fibers of one motor unit

motor units take turns contracting to provide long-term contraction (postural control)

Average motor unit

200 muscles fibers distributed across 100 fascicles

Small motor units

Fine degree of control and 3-6 muscles fibers per neuron

small motor units

eye and hand muscles are examples of what kind of moto unit

Large motor units

More strength than control

large motor units

powerful contractions supplied by _____ with hundreds of fibers

large motor units

quadriceps femoris and gastrocnemius controlled by motor units that may have 1,000 muscle fibers per neuron

Synapse

Point where a nerve fiber meets its target cell

Neuromuscular junction (NMJ)/ motor end plate

When target cell is a muscle fiber

Separate synapse with muscle fiber

Each terminal branch of the nerve fiber within NMJ forms:

Axon terminal/synaptic knob

Swollen end of nerve fiber; 1 per synapse, contains synaptic vesicles filled either acetylcholine (ACh)- part 1 on picture

Synaptic cleft

Narrow gap between axon terminal and sarcolemma- part 2 on image

Postsynaptic membrane/junctional folds of sarcolemma

Increase surface area holding ACh receptors- part 3 on image

Basal lamina

Thin layer separating muscle fiber and nerve ending from surrounding CT; contains acetylcholinesterase (AChE)- part 4 on image

Electrically excitable cells

Muscle fibers and neurons are what kind of cells

Plasma membranes exhibit voltage changes in response to stimulation

Why are muscle fibers and neurons electrically excitable (cell can respond to a stiumulus by producing an electrical signal) ?

Concentration differences in ions in intracellular fluid vs. extracellular fluid

Electrical activity depends on:

Voltage (electrical potential)

A difference in electrical charge from one side of the membrane to the other

Resting membrane potential

About -90 mV

about -90 mV

what is the resting membrane potential

resting membrane potential

maintained by sodium-potassium pump

unstimulated (resting) cell

More anions on the inside of the plasma membrane negatively charged in comparison to the outside

negatively charged in comparison to the outside

these more anions make the inside of the plasma membrane____ (resting cell)

Electrically polarized (charged) with a resting membrane potential (RMP)

The plasma membrane is: (resting cell)

Extracellular fluid (ECF)

where are there excess sodium ions (Na+) (resting cell)

Intracellular fluid (ICF)

where are there excess potassium ions (K+) (resting cell)

intracellular fluid (ICF)

in _____, there are also anions such as proteins, nucleic acids, and phosphates that cannot penetrate the plasma membrane, these anions make the inside of the plasma membrane negative charged in comparison to its outer surface (resting cell)

proteins, nucleic acids, phosphates

in the intracellular fluid, what anions cannt penetrate the plasma membrane (resting cell)

they make the inside of the plasma membrane negatively charged in compariosn to its outer surface

what do the anions proteins, nucleic acids, and phosphates do when they are in the ICF (resting cell)

Stimulated (active) muscle fiber or nerve cell

Na+ ion gates open in the plasma membrane and Na+ flows down its electrochemical gradient into the cell