Physiological Factors Affecting Testing

ByProf. Dr. Samy A. Nasef

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

6 Functions of Skeletal Muscles

1. Produce skeletal movement

2. Maintain body position and posture

3. Support soft tissues

4. Guard body openings (entrance/exit)

5. Maintain body temperature

6. Store Nutrient reserves

Organization of Connective Tissues

Muscles have 3 layers of connective tissues:

1. Epimysium-Exterior collagen layer

Connected to deep fascia

Separates muscle from surrounding tissue2. perimysium- Surrounds muscle fiber bundles

(fascicles)

Contains blood vessel and nerve supply to fascicles 3. endomysium

3 .Endomysium

Surrounds individual muscle cells (muscle fibers)

Contains capillaries and nerve fibers contacting muscle cells

Contains satellite cells (stem cells) that repair damage

Muscle Attachments

Endomysium, perimysium, and epimysium come together:

at ends of muscles

to form connective tissue attachment to bone matrix

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

What are the characteristics of skeletal muscle fibers?

Skeletal muscle cells are called fibers

Figure 10–2فاروس سنتر صوتك اسرة

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

The Sarcolemma

The cell membrane of a muscle cell

Surrounds the sarcoplasm (cytoplasm of muscle fiber)

A change in transmembrane potential begins contractions

All regions of the cell must contract simultaneously

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

Myofibrils- 1-2um in diameter Lengthwise subdivisions within muscle fiberMade up of bundles of protein filaments (myofilaments)Myofilaments - are responsible for muscle contraction

2 Types of MyofilamentsThin filaments:

made of the protein actin

Thick filaments: made of the protein myosin

Sarcoplasmic Reticulum (SR)

A membranous structure surrounding each myofibril Helps transmit action potential to myofibrilSimilar in structure to smooth endoplasmic reticulumForms chambers (terminal cisternae) attached to T tubules

فاروس سنتر صوتك اسرة

A Triad

Is formed by 1 T tubule and 2 terminal cisterna

CisternaeConcentrate Ca2+ (via ion pumps)

Release Ca2+ into sarcomeres to begin muscle contraction

فاروس سنتر صوتك اسرة

Structural components of the Sarcomeres

Figure 10–4

-The contractile units of muscle-Structural units of myofibrils -Form visible patterns within myofibrils

فاروس سنتر صوتك اسرة

InterActive Physiology: Contraction of Whole MusclePLAYPLAY

Tension Produced by Whole Skeletal Muscles

Depends on:internal tension produced by muscle fibers

external tension exerted by muscle fibers on elastic extracellular fibers

total number of muscle fibers stimulated

Motor Units in a Skeletal Muscle

Figure 10–17

Motor Units in a Skeletal Muscle

Contain hundreds of muscle fibers

That contract at the same time

Controlled by a single motor neuron

InterActive Physiology: Contraction of Motor UnitsPLAYPLAY

Recruitment (Multiple Motor Unit Summation)

In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated

Maximum Tension

Achieved when all motor units reach tetanus

Can be sustained only a very short time

Sustained Tension

Less than maximum tension

Allows motor units to rest in rotation