Exam 4 review

Muscle Tissue

Cells Specialized for contraction

Skeletal muscles move body by pulling on bones

Cardiac and smooth muscles control movements Inside body

Common properties of Muscle tissues

• Excitability (Responsiveness)

• Contractility (Ability of cells to shorten)

• Extensibility (Stretching)

• Elasticity (Recoil)

Functions of skeletal muscles

• Producing movement

• Maintaining posture and body position

• Supporting soft tissues

• Guarding body entrances and exits

• Maintaining boy temperature

• Storing nutrients

Skeletal muscles contain

• Skeletal muscle tissue

• Connective tissues

• Blood vessels

• Nerves

What are the three layers of connective tissue Skeletal muscles have?

• Epimysium

• Perimysium

• Endomysium

Epimysium

• Layer of collagen fibers that surrounds the muscle

• Connected to deep fascia

• Separates muscle from surrounding tissues

Perimysium

Surrounds muscle fiber bundles (fscicles)

Contains

• Collagen fibers

• Elastic fibers

• Blood Vessels Nerves

Endomysium

Surrounds individual muscle cells (muscle fibers)

Contains

• Capillary networks

• Myosatellite cells (stem cells) that repair damage

• Nerve fibers

Irregular Bones

Complex shapes with short, flat, notched or ridged surfaces. The vertebrae that form the spinal column, the bones of the pelvis, and several bones in the skull are examples of irregular bones.

Short Bones

Boxlike in appearance. Examples of short bones include the carpal bones (wrists) and tarsal bones (ankles) 

Flat Bones

Have thin, parallel surfaces. Flat bones form the roof of the skull, the sternum (breastbone), the ribs, and the scapulae (shoulder blades). They protect the underlying soft tissues and offer an extensive surface area for the attachment of skeletal muscles.

Long Bones

Relatively long and slender. They are located in the arm and forearms, thigh and leg, palms, soles, fingers and toes. The femur, the long bone of the thigh, is the largest and heaviest bone in the body.

Structure of a long bone

• Diaphysis

• Epiphysis

• Metaphysis

Diaphysis (shaft)

• Wall of compact bone

• The central space is called the medullary cavity (marrow cavity)

Epiphysis (wide part at each end)

Mostly spongy bone (trabecular bone)

Metaphysis

Where diaphysis and epiphysis mee

Structure of flat bones

For example, parietal bones of the skull 

consist of spongy bone between two layers of compact bone (cortex)

Within the cranium, the layer of spongy bone is called diplo

Characteristics of Bone

• Dense matrix due to deposits of calcium salts

• Osteocytes (bone cells) within lacunae are organized around blood vessels

• Canaliculi 

• Periosteum

Canaliculi

Narrow passageways that allow for exchange of nutrients, wastes, and gases

Periosteum

Covers outer surfaces of bones (except at joints)

Consists of outer fibrous and inner cellular layers

Membrane that cover outside of bones

• Except within joint cavities

Outer, fibrous layer and inner, cellular layer

Fibers are interwoven with those of tendons

Perforating fibers

• Fibers that become incorporated into bone tissue

• Increase strenght of attachements

Four types of Bone Cells

• Osteogenic cells

• Osteoblasts

• Osteocytes

• Osteoclasts

Osteogenic cells (osteoprogenitor cells)

• Mesenchymal cells that divide to produce osteoblasts

• Located in inner cellular layer of periosteum and in endosteum 

• Asist in fracture repair

Osteoblasts

• Immature cells that produce new bone matrix during osteogenesis (ossification)

• Osteoid - matrix produced by osteoblasts that has not yet become calcified 

• Osteoblasts surrounded by bone matrix become osteocytes

Osteocytes

Mature bone cells that do not divide

Live in lacunae between layers of matrix

Have cytoplasmic extensions that pass through canaliculi

Two major functions

• Maintain protein and mineral content of matrix

• Help repair damaged bone

Osteoclasts

Absorb and remove bone matrix

Large, multinucleate cells

Secreted acids and protein-digesting enzymes

• Dissolve bone matrix and release stored minerals 

• This osteolysis is important in homeostasis

Derived from the same stem cells that produce monocytes and macrophages 

Functions of periosteum

• Isolates bone from surrounding tissues

• Provides a route for blood vessels and nerves

• Participates in bone growth and repair

Transverse

Linear

Oblique, nondisplaced

Obilque, displaced

Spiral

Greenstick

Comminuted

Are Skeletal Muscle Involuntary and Voluntary?

Voluntary

What type of Appearance does Cardiac and Skeletal Muslce has?

Straited Muscle

Sarcolemma

• Plasma membrane of a muscle fiber

• Surrounds the sarcoplasm (cytoplasm of a muscle fiber)

• A sudden change in membrane potential initiates a contraction

Myofibrils

Lengthwise subdivisions within a muscle fiber

Responsible for muscle contraction

Made of bundles of protein filaments (myofilaments)

Two types of myofilaments

• Thin Filaments

• Thick Filaments

Thin Filaments

Composed primarily of actin

contains F-actin, nebulin, tropomyosin, and troponin proteins

Filamentous actin (F-actin)

• Twisted strand composed of two rows of globular G-actin molecules

• Active sites on G-actin bind to myosin 

Nebulin

• Holds the F-actin strand together

Tropomyosin

Troponin

Thick Filament

Composed primarily of myosin

Each contains about 300 myosin molecules

Each myosin molecule consists of

Tail

• Binds to other myosin molecules

Head

• Made of two globular protein subunits

• Projects toward nearest thin filament

Core of titin recoils after stretching

Sarcomeres

The smallest functional units of a muscle fiber

Interactions between filaments produce contraction 

Arrangement of filaments accounts for the striated pattern of myofibrils

• Dark bands (A bands )

• Light bands (I bands)

A band

• M line

• H band

• Zone of overlap

M line

• In center of A band

• Proteins stabilize positions of thick filaments

I band

• Contains thin filaments but no thick filaments

• Z lines

• Titin

Tropomyosin

• Covers active sites on G-actin

• Prevents actin-myosin interaction

Troponin

• A globular protein

• Binds tropomyosin, G-actin, and Ca2+

Sliding-filament theory

During a contraction:

1. H bands and I bands narrow

2. Zones of overlap widen

3. Z lines move closer together

4. The width of the A band remains constant

Thus, thin filaments must slide toward the center of sarcomere

Isotonic Contractions

Skeletal muscle changes length

• Resulting in motion

Isotonic concentric contraction 

• Muscle tension > load (resistance)

• Muscle shortens

Isotonic eccentric contraction

• Muscle tension < load

• Muscle elongates

Isometric Contractions 

• Skeletal muscle develops tension that never exceeds the load

• Muscle does not change length

Cardiac Muscle Cells

• Found only in the heart

• Have excitable membranes

• Striated like skeletal muscle cells

Structural characteristics of cardiac muscle tissue

Are small

Are typically branched with a single nucleus

Have short, wide T tubules

• No triads

Have SR with no terminal cisternae

Are almost totally dependent on aerobic metabolism 

• Contain lots of myoglobin, many mitochondria

Contact each other via interclated discs

Intercalated discs

• Specialized connections

• Join sarcolemmas of adjacent cardiac muscle cells by gap junctions and desmosomes

• Functions include:

Stabilizing positions of adjacent cells

Maintaining the three-dimensional structure of tissue

Allowing ions to move from one cell to another

• So cardiac muscle cells beat in rhythm

Functional characteristics of cardiac muscle 

Automaticity 

• Contraction without neural stimulation 

• Controlled by pacemaker cells

Nervous system can alter pace and tension of contractions 

Contractions last 10 times longer than those in skeletal muscle, and the refractory periods are longer 

Wave summation and tetanic contractions are prevented due to special properties of sarcolemma

Smooth Muscle Tissue

Integumentary system

• Arrector Pili muscles erect hairs

Cardiovascular and respiratory systems

• Regulates blood pressure and airflow

Digestive and urinary systems

• Forms sphincters

• Moves materials along and out of the body

Reproductive system

• Transports gametes and expels fetus

Structural characteristics of smooth muscle

Long, slender, spindle-shaped cells

– Single, central nucleus

– No T-tubules, myofibrils, or sarcomeres

• Non-striated muscle

– Scattered thick filaments with many myosin heads

– Thin filaments attached to dense bodies

• Dense bodies connect adjacent cells, transmitting contractions

– No tendons or aponeuroses

Functional characteristics of smooth muscle tissue

• Excitation–contraction coupling

• Length–tension relationships

• Control of contractions

• Smooth muscle tone