Lecture 18: Muscles, Tendons And Ligaments

Question 1

Muscles are..

Answer 1

A functional grouping of contractile cells containing the myofilament proteins actin and myosin
-generally do not divide in the adult but some regeneration can occur from undifferentiated stem cells

Question 2

Types or muscles

What are the 3 basic types of muscles, what are their basic properties?

Answer 2

Skeletal muscle: anchored directly or indirectly to skeleton

• responsible for voluntary movement
• tight pattern of cross-striations under microscope
• larger proportion of body weight (40%)

Cardiac muscle:

• only found in the heart
• continuous, rhythmic contraction
• branching striated fibres

Smooth muscle:

• even texture
• slow powerful involuntary contractions of viscera and blood vessels

Question 3

Skeletal muscle

List the properties of this type of muscle

Answer 3

Each fibre is multinucleated syncytium

• fusion of many individual myoblasts
• has peripheral nuclei, because bulk of cell is occupied by contractile myofilaments

Fibres act in parallel and largely in unison

• force proportional to cross-sectional area
• speed is proportional to length

Forces transduced to skeleton through CT sheath and tendon

Question 4

Skeletal muscles are comprised of:

How does the muscle contract?

Answer 4

Muscle fibres (=cells) which contain many internal myofibrils.
Myofibrils are formed from a chain of repeating units called sarcomeres. Each sarcomere contains thin filaments actin and thick filaments myosin.
Energy (ATP) causes myosin head to move along the actin filaments, shortening the myofibrils and contracting the muscle
Each muscle has an optimal length where the force is maximal- this occurs were the filaments are fully interdigitating without overlapping

Question 5

Cardiac muscle. What are its properties

Answer 5

Branching chains of striated muscle cells
-only found in the heart (myocardium)
-central nuclei: one per cell
Joined by specialised junctions-intercalated discs
Spontaneous, rhythmic contractile activity
-modulated by hormones and the autonomic nervous system
-responsive to body’s blood flow needs

Question 6

Smooth muscle:

What are its properties

Answer 6

Single, spindle-shaped cells
-no striations
-central nuclei
Grouped in sheets or bundles
-controlling hollow visceral organs eg gut, reproductive tract, urinary system, lungs
-may be longitudinal or circumferential
Spontaneous, slow, powerful contractions
-modulated by hormones and autonomic nervous system
-some specialised smooth muscle us under precise neural control eg iris sphincter
Must look at PowerPoint for all the visual images

Question 7

What are the properties of tendons

Answer 7

• Tight-packed, very regular parallel collagen fibres
• they concentrate the pull of muscles to bones
• enable muscles to act at a distant insertion
• may have an elastic component allowing energy recycling
• tendons can transit tension around corners like a rope and pulley via bony channels or via ligamentas loops (annular ligaments)
• were compressive forces become too great, bones often form within a tendon (sesamoid bones) eg patella in quadriceps tendon

Question 8

What are the values of elastic tendons?

Answer 8

Increase the efficiency of locomotion eg dog hock (ankle)