Anatomy Ch 10 Muscle Tissue

Front 1

Skeletal muscles

Back 1

are organs composed mainly of skeletal muscle tissue, but they also contain connective tissue, nerves, and blood vessels

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Each cell in skeletal muscle tissue

Back 2

is a single muscle fiber

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Skeletal muscles

Back 3

are directly or indirectly attached to the bones of the skeleton

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Our skeletal muscles perform the following six function:

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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

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Produce skeletal movement

Back 5

skeletal muscle contractions pull on tendons and move the bones of the skeleton

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Maintain posture and body position

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Tension in our skeletal muscles maintains body posture- for example, holding yoru head still when you read a book or balancing your body weight above your feet when you walk

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Support soft tissue

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Layers of skeletal muscle make up the abdominal wall and the floor of the pelvic cavity. These muscles support the weight of our visceral organs and shield our internal tissue from injury

Front 8

Guard entrances and exits

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Skeletal muscles encircle the openings of the digestive and urinary tracts. These muscles give us voluntary control over swallowing, defecation, and urination.

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Maintain body temperature

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Muscle contractions use energy, and whenever energy is used in the body, some of it is converted to heat. The heat released by working muscles keeps body temperature in the range needed for normal functioning.

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Store nutrient reserves

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When our diet contains too few proteins or calories, the contractile proteins in skeletal muscles are broken down, and their amino acids released into the circulation.

Front 11

A skeletal muscle contains:

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muscle tissue, connective tissues, blood vessels, and nerves

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Each muscle has three layers of connective tissue:

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1. an epimysium
2. a perimysium
2. an endomysium

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Epimysium

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a dense layer of collagen fibers that surrounds a skeletal muscle and is continuous with the tendons/aponeuroses of the muscle and with the perimysium

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perimysium

Back 14

a connective tissue partition that separates adjacent fasciculi in a skeletal muscle. divides muscle into a series of compartments. contains blood vessels and nerves

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fascicle

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bundle of muscle fibers in the compartments contained by the perimysium.

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endomysium

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the delicate connective tissue fibers that surrounds individual skeletal muscle cells, called muscle fibers

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endomysium, this flexible, elastic connective tissue layer contains:

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1. capillary networks that supply blood to the muscle fibers
2. Myosatellites, stem cells that take part in the repair of damaged muscle tissue
3. nerve fibers that control the muscle

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myosatellite cells

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stem cells that take part in the repair of damaged muscle tissue

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tendon

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at each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together to form a bundle known as s tendon. tendon attaches to skeletal muscles to bone

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aponeurosis

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a broad tendinous sheet that may serve as the origin or insertion of a skeletal muscle.

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myoblasts

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embryonic cells

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types of muscle tissue

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skeletal: striated, voluntary
cardiac: striated, involuntary
smooth: nonstriated, involuntary

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properties of muscle tissue

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excitability
contractility
extensibility
elasticity

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excitability

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-electrical- responds to electrical stimuli
-chemical- responds to chemicals at neurotransmitters sites

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contractility

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- ability to contract fully when stimulated

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extensibility

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- ability to stretch without being damaged

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elasticity

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- can return to original shape after contraction or extension

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muscle tissue:

each skeletal muscle is a discrete organ

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-- muscle tissue (fibers/cells)
-- connective tissue
-- blood vessels
-- nerve fibers

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muscle tissue:

striated

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--alternating light and dark bands (striations)

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muscle tissue:

voluntary

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-- its activity can be consciously controlled by neurons
-- most are also controlled subconsciously to some extent

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connective tissue components:

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endomysium
perimysium
epimysium
deep fascia
-tendon
-aponeurosis
superficial fascia (subcutaneous layer)

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endomysium:

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sheath of connective tissue surrounding individual fibers
--fascicle: bundle of fibers

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perimysium:

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collagen surrounding individual fascicle

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epimysium:

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fibrous connective tissue binding all fascicles together surrounds entire muscle

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deep fascia:

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dense irregular connective tissue external to epimysium binds muscle into functional group

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tendon:

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cord of dense regular connective tissue that attaches a muscle to the periosteum of a bone

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aponeurosis:

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connective tissue elements that extend as a broad, flat layer

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superficial fascia

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(subcutaneous layer)

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layers of connective tissue

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epimysium
perimysium
endomysium

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epimysium

Back 40

surrounds whole muscle

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perimysium

Back 41

surrounds muscle bundles

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endomysium

Back 42

surrounds individual muscle fibers

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tendon:

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all three layers of connective tissue connect at each end of a muscle and form a tendon

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Aponeurosis:

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flat tendon-like structure where attachments are broad

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superficial fascia

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- separates muscle from skin
- contains areolar and adipose tissue

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deep fascia

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- holds muscle with similar functions together
- contains dense irregular connective tissue

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nerve supply

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- each muscle fiber (cell) is supplied with a nerve ending of a somatic motor neuron
-connected at the neuromuscular junction

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blood supply

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-Muscle tissue is well supplied with arteries
-- High oxygen requirement

-numerous veins
-- high metabolic waste production
-- 1 artery and 1 or more veins serve each muscle

-Blood vessels and nerve fibers enter central part of muscle and then branch

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skeletal muscle fiber microscopic anatomy

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- muscle cell = muscle fiber
- each fiber is a single multinucleate cell and runs the length of the muscle
- huge compared to most other human cells - can reach length of 30 cm (1 foot)
- each fiber is actually produced by the fusion of many cells during embryonic development
- muscle fiber --myofibrils--myofilaments (thick & thin)

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microscopic anatomy of skeletal muscle fiber

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- gigantic cells
- multinucleated
- striated

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muscle cell components

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sarcolemma
transverse tubules
sarcoplasm
myofibrils
sarcoplasmic reticulum
filaments
sarcomeres

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sarcolemma

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plasma membrane of muscle cell/fiber

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transverse tubules

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extend from sarcolemma into muscle fiber

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sarcoplasm

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cytoplasm of muscle fiber
- contains unusually large amounts of stored glycogen and myoglobin (oxygen-binding protein) not found in other cell types

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myofibrils

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contractile elements; made of muscle proteins (filaments)

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sarcoplasmic reticulum

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specialized ER; stores Ca
- active transport of Ca into SR
- keeps levels of Ca in sarcoplasm low-- would bind with P ions and form hydroxyapatite crystals, hard salts found in bone matrix, such calcified cells would die.

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filaments

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smaller subunits of myofibrils
- thick and thin filaments

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sarcomere

Back 58

"muscle segment" : functional units of muscle
- segment between specific areas of myofibrils (between Z-lines)
- smallest contractile unit of fiber
- sarcomere arrangement= repeating series of dark and light bands
--A- band: region of entire thick filament (dark)
--I - band: region of thin filament only (light)

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sarcolemma

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plasma membrane of a skeletal muscle fiber

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transverse tubules ( T tubules

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- extend from sarcolemma into the sarcoplasm
- channel electric impulses which trigger muscle contraction

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sarcoplasm

Back 61

cytoplasm of a skeletal muscle fiber

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myofibrils

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- multiple cylindrical structures in each muscle fiber
- contain bundles of thick and thin myofilaments

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sarcoplasmic reticulum

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- network of membranous channels surrounding each myofibril
- extends throughtout sarcoplasm
- terminal cisternae ( expanded ends of SR on either side of T tubule)
- triad ( two terminal cisternai and a T tubule)

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filaments

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contractile proteins
- myosin (thick)
- actin (thin)

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Thick filament

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- primarily protein= myosin
- myosin filament= many myosin molecules
--each thick filament within sarcomere contains about 200 myosin molecules
- each myosin molecule has distinctive structure: rod-like tail, or axis, which terminates in two globular heads (sometimes called "cross bridges" due to bindin)

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muscle proteins (thick filaments)

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-contain mostly myosin
- have heads (crossbridges) and tails
- function as motor protein

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muscle proteins (thin filaments)

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- contain mostly Actin
--looks like twisted double strand of pearls
-- binding site for myosin head
- tropomyosin covers binding site
- troponin holds tropomyosin in place

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titin filament

Back 68

- spans half a sarcomere, from Z disc to M line
- anchors a thick filament to Z disc and the M line
- very elastic
(accounts for the elasticity and extensibility of myofibrils)
(helps the sarcomere return to its resting length after a muscle has contracted or been stretched

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sarcomeres

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-functional (contractile) units of skeletal muscle
- Z discs: separate one sarcomere from the next
- A bands: appear dark
- I bands: appear light

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muscle shape

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Parallel
Fusiform
Circular
triangular
unipennate
bipennate
multipennate

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functions of muscle tissue

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produce body movement
stabilizing body position
storing and moving substances in the body ( circulation, respiration, digestion)
generation heat (thermogenesis)
communication (speaking/writing)

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A bands; appear dark

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H zone: contains thick but no thin filaments
Zone of overlap: contains both thick and thin filaments
M line: in middle of sarcomere

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I bands: appear light

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only thin filaments
extend from A band of one sarcomere to A band of the next sarcomere

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contraction of relaxation of skeletal muscle fibers

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the sliding filament mechanism

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contraction cycle

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1. when stimulated, crossbridges attach to myosin binding site on actin
2. each cross bridge attaches and detaches several times during a contraction
3. crossbridges act like tiny ratchets to propel thin filaments towards center of sarcomere
4. thus, sarcomere is shortened
- distance between Z lines is shortened
- I bands and H zones are shortened
- A bands move closer together, but don not change in length

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myosin heads

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produce sliding of actin on myosin

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The ATP- binding site

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in the head is an open cleft

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when ATP is bound and hydrolyzed,

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the cleft closes, distorting the head, and the head binds firmly to actin

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the head

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then overcomes the distortion, creating the power stoke that moves actin on myosin

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neuromuscular junction

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controls contractions
contact between neuron and sarcolemma

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synapse

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region where nerve cell communicates with other cell through the release of neurotransmitters called Acetylcholine (Ach)

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synaptic gap

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space between the synaptic terminal and the sarcolemma

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synaptic end bulbs

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expanded end of axonal branches

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motor end plate

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location on the sarcolemma where acetylcholine receptors are found

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steps in contraction

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-nerve impulses (axon)--Ach via exocytosis in synaptic cleft
-Ach diffuses across synapse + to receptors on sarcolemma
- action potential then spreads all over via T tubules
-Sarcoplasmic reticulum releases calcium ions
-calcium ions bind with troponin exposing myosin binding site
-muscle fibers then contract

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steps - relaxation

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-release of Ach stops
-release of calcium ions stops
-calcium is actively pumped back into sarcoplasmic reticulum

-calcium ions detach from troponin

-tropomyosin covers up myosin binding site
-cross bridges cannot attach

-contraction stops

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where does the energy come from?

Back 87

ATP (adenosintriphosphate)

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ATP

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-provides energy for contractions
-needed to detach cross bridges
-needed to pump calcium ions back into the sarcoplasmic reticulum
-needs to be regenerated for contractions to continue

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ATP regeneration

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-resting skeletal muscle needs little ATP
-excess ATP is temporarily stored as creatine phosphate
-creatine phosphate used to form ATP to supply quick bursts of energy

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anaerobic respiration

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-occurs in sarcoplasm
-provides ATP during peak levels of muscular activity
-requires no oxygen
-produces small amounts of ATP
-produces lactic acid as byproduct

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aerobic respiration

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-occurs in mitochondria
-requires oxygen
-produces vast amounts of ATP
-provides 90% of ATP for activities that last more than ten minutes

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creatine phosphate: details

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-excess ATP in resting muscle forms creatine phosphate
-creatine phosphate 3-6 times more plentiful than ATP within muscle
-its quick to breakdown provides energy for creation of ATP
-sustains maximal contractions for 15 sec (100 meter dash)
-Athletes tried creatine supplementation - gain muscle mass but shut down bodies own synthesis (safety?)

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anaerobic cellular respiration: details

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-ATP produced from glucose breakdown into pyruvic acid during glycolysis - if no oxygen present (pyruvic converted to lactic acid which diffuses into the blood
-glycolysis can continue anaerobically to provide ATP for 30 to 40 seconds of maximal activity (200 meter race)

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aerobic cellular respiration: details

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ATP for any activity lasting over 30 seconds
-if sufficient oxygen is available, pyruvic acid enters the mitochondria to generate ATP, water and heat
-provides 90% of ATP energy if activity lasts more then 10 minutes