Muscle Tissue-Structure And Functions

Muscle Tissue

Muscle Tissue

• One of 4 primary tissue types, divided into:
• skeletal muscle
• cardiac muscle
• smooth muscle

Without these muscles, nothing in the body would move and no body movement would occur

Skeletal Muscles-

• Organs of skeletal muscle tissue
• are attached to the skeletal system and allow us to move
• Muscular System- Includes only skeletal muscles

Skeletal Muscle Structures

• Muscle tissue (muscle cells or fibers)
• Connective tissues
• Nerves

Blood vessels

6 Functions of Skeletal Muscles

• Produce skeletal movement
• Maintain body position and posture
• Support soft tissues
• Guard body openings (entrance/exit)
• Maintain body temperature

Store Nutrient reserves

Muscles serve specific functions in moving and positioning the body.

The same muscle may act as a prime mover, antagonist, synergist, or fixator under specific conditions.

The functions include.

A prime mover or agonist is the main muscle responsible for producing a specific movement of the body (e.g. concentric contraction).

Fixators steady the proximal parts of a limb while movements are occurring in distal parts.

A synergist complements the action of prime mover for example, by preventing movement of the intervening joint when a prime mover passes over more than one joint.

An antagonist is a muscle that opposes the action of a prime mover.

As a prime mover contracts, the antagonist progressively relax, producing a smooth movement

How is muscle tissue organized at the tissue level?

• Organization of Connective Tissues

Figure 10–1

Organization of Connective Tissues

• Muscles have 3 layers of connective tissues:
• Epimysium-Exterior collagen layer
• Connected to deep fascia
• Separates muscle from surrounding tissue
• perimysium- Surrounds muscle fiber bundles (fascicles)
• Contains blood vessel and nerve supply to fascicles

endomysium

3. Endomysium

• Surrounds individual muscle cells (muscle fibers)
• Contains capillaries and nerve fibers contacting muscle cells

Contains satellite cells (myogenic stem cells) that repair damage

Muscle Attachments

• Endomysium, perimysium, and epimysium come together:

• to form connective tissue attachment to bone matrix

i.e., tendon (bundle) or aponeurosis (sheet)

Nerves

Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system

Blood Vessels

• Muscles have extensive vascular systems that:
• supply large amounts of oxygen
• supply nutrients

carry away wastes

What are the characteristics of skeletal muscle fibers?

• Skeletal muscle cells are called fibers

Figure 10–2

Skeletal Muscle Fibers

• Are very long
• Develop through fusion of mesodermal cells (myoblasts- embryonic cells))
• Become very large
• Contain hundreds of nuclei –multinucleate

Unfused cells are satellite cells- assist in repair after injury

Germ layers

Structures originating from germ layers

Organization of Skeletal Muscle Fibers

Figure 10–3

The Sarcolemma

• The cell membrane of a muscle cell
• Surrounds the sarcoplasm (cytoplasm of muscle fiber)
• A change in transmembrane potential begins contractions

Transverse Tubules (T tubules)

• Transmit action potential – impulses through cell
• Allow entire muscle fiber to contract simultaneously
• Have same properties as sarcolemma

Filled with extracellular fluid

Muscle Striations

• A striped or striated pattern within myofibrils:
• alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

Figure 10–6 (1 of 5)

Level 1: Skeletal Muscle

Level 2: Muscle Fascicle

Muscle Contraction

• Is caused by interactions of thick and thin filaments

Structures of protein molecules (actin and myosin) detemine interactions

Skeletal Muscle Contraction

Figure 10–9 (Navigator)

The Process of Contraction

• Neural stimulation of sarcolemma:
• causes excitation–contraction coupling
• Cisternae of Sarcoplasmic reticulum(SR) release Ca2+:
• which triggers interaction of thick and thin filaments

consuming ATP and producing tension

What are the structural and functional differences between skeletal muscle fibers and cardiac muscle cells?

Structure of Cardiac Tissue

• Cardiac muscle is striated-involuntary muscle, found only in the heart

Figure 10–22

7 Characteristics of Cardiocytes

• Unlike skeletal muscle, cardiac muscle cells (cardiocytes):
• are small
• have a single nucleus

have short, wide T tubules

7 Characteristics of Cardiocytes

• have no triads
• have SR with no terminal cisternae
• are aerobic (high in myoglobin, mitochondria)

have intercalated discs

4 Functions of Cardiac Tissue

• –
• contraction without neural stimulation controlled
• Variable contraction tension:

• Extended contraction time

Prevention of wave summation and tetanic contractions

Role of Smooth Muscle in Body Systems

• Forms around other tissues
• In blood vessels:
• regulates blood pressure and flow
• In reproductive and glandular systems:
• produces movements
• In digestive and urinary systems:
• forms sphincters
• produces contractions
• In integumentary system:

arrector pili muscles cause goose bumps

Structure of Smooth Muscle

• Nonstriated tissue

Figure 10–23

8 Characteristics of Smooth Muscle Cells

• Long, slender, and spindle shaped
• Have a single, central nucleus
• Have no T tubules, myofibrils, or sarcomeres

Have no tendons or aponeuroses

8 Characteristics of Smooth Muscle Cells

• Have scattered myosin fibers
• Myosin fibers have more heads per thick filament
• Have thin filaments attached to dense bodies

Dense bodies transmit contractions from cell to cell

Functional Characteristics of Smooth Muscle

• Excitation–contraction coupling
• Length–tension relationships
• Control of contractions

Smooth muscle tone