1. Physiology I (PHL 215)
Physiology of Muscles
Dr. Gamal Gabr

2. Muscular System Functions
Body movement (Locomotion)
Maintenance of posture
Respiration
Diaphragm and intercostals contractions
Communication (Verbal and Facial)
Constriction of organs and vessels
Heart beat
Production of body heat (Thermogenesis)

3. Typical cells Muscle cell=fiber Plasma membrane Sarcolemma Cytoplasm
Sarcoplasm
Endoplasmic reticulum
Sarcoplasmic reticulum (SR)
Many mitochondria
Multiple nuclei

4. Muscle cell structures not found in other cells
Myofibrils: bundles of very fine fibers
Thick and thin myofilaments: very fine fibers that make up myofibrils
Sarcomere: segment of myofibril between two Z lines; contractile unit
T tubules: transmit electrical impulses through cell

6. Thin filaments: actin, tropomyosin, troponin
Myofilaments
4 protein molecules that make up myofilaments: Myosin, actin, tropomyosin, troponin
Thin filaments: actin, tropomyosin, troponin
Thick filaments: mostly myosin

7. Properties of Muscle
Excitability: Capacity of muscle to respond to a stimulus Contractility: Ability of a muscle to shorten and generate pulling force Extensibility: Ability stretches when pulled Elasticity: Ability to return to original shape and length after contraction or extension

8. Muscle structure Connective Tissue Sheaths
Connective Tissue (CT) of a Muscle
Epimysium: Dense regular CT surrounding entire muscle
Separates muscle from surrounding tissues and organs
Perimysium: Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle
Contains blood vessels and nerves
Endomysium: Loose CT that surrounds individual muscle fibers
Also contains blood vessels and nerves
Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

10. Motor neurons
Stimulate muscle fibers to contract
Neuron axons branch so that each muscle fiber (muscle cell) is innervated
Form a neuromuscular junction
Capillary beds surround muscle fibers
Muscles require large amount of energy
Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

11. Energy for Muscle Contractions
ATP: adenosine triphosphate
CP: creatine phosphate
Glucose & Oxygen
Glucose stored in form of glycogen in muscle
Excess oxygen molecules in sarcoplasm bound to myoglobin

12. Anaerobic respiration
Allows body to avoid use of oxygen in short term
Produces lactic acid
Accumulation of lactic acid in muscles causes burning sensation

13. Types of Muscle Skeletal Attached to bones
Makes up 40% of body weight (Women’s skeletal muscle makes up 36% of their body mass, Men’s skeletal muscle makes up 42% of their body mass)
Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
Voluntary in action; controlled by somatic motor neurons
Smooth
In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
Functions: propel urine, mix food in digestive tract, regulating blood flow
Controlled involuntarily by endocrine and autonomic nervous systems
Cardiac
Heart: major source of movement of blood

14. Basic Features of a Skeletal Muscle
Muscle attachments
Most skeletal muscles run from one bone to another
One bone will move – other bone remains fixed
Origin – less movable attachment
Insertion – more movable attachment
Muscles attach to origins and insertions by connective tissue
Fleshy attachments – connective tissue fibers are short
Indirect attachments – connective tissue forms a tendon

15. Skeletal Muscle Structure
Composed of muscle cells (fibers), connective tissue, blood vessels, nerves
Fibers are long, cylindrical, and multinucleated
Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm - 4 cm in length
Striated appearance
Nuclei are peripherally located

16. Muscle Fiber Anatomy Sarcolemma - cell membrane
Surrounds the Sarcoplasm (cytoplasm of fiber)
Punctuated by openings called the transverse tubules (T-tubules)
Myofibrils -cylindrical structures within muscle fiber
Are bundles of protein filaments (=myofilaments)
Two types of myofilaments
Actin filaments (thin filaments)
Myosin filaments (thick filaments)
When myofibril shortens, muscle shortens (contracts)

17. Sarcoplasmic Reticulum (SR)
SR is an elaborate, smooth endoplasmic reticulum
Runs longitudinally and surrounds each myofibril
SR stores Ca++ when muscle not contracting
When stimulated, calcium released into sarcoplasm
SR membrane has Ca++ pumps that function to pump Ca++ out of the sarcoplasm back into the SR after contraction

18. Smooth Muscle Cells are not striated
Fibers smaller than those in skeletal muscle
Spindle-shaped; single, central nucleus
More actin than myosin
No sarcomeres
Not arranged as symmetrically as in skeletal muscle, thus no striations.

19. Smooth Muscle
Grouped into sheets in walls of hollow organs
Longitudinal layer: muscle fibers run parallel to organ’s long axis
Circular layer: muscle fibers run around circumference of the organ
Both layers participate in peristalsis

20. Cardiac Muscle
Found only in heart where it forms a thick layer called the myocardium
Striated fibers that branch
Each cell usually has one centrally-located nucleus
Fibers joined by intercalated disks

21. Disorders of Muscle Tissue
Muscle Fatigue
Lack of oxygen causes ATP deficit
Lactic acid builds up from anaerobic respiration
Muscle Atrophy
a decrease in the mass of the muscle
Weakening and shrinking of a muscle
May be caused
Immobilization
Loss of neural stimulation

22. Disorders of Muscle Tissue
Muscle Hypertrophy
Enlargement of a muscle
More capillaries
More mitochondria
Caused by
Strenuous exercise
Steroid hormones
Muscle Tonus
Tightness of a muscle
Some fibers always contracted