Skeletal Muscle

Question 1

What are the functions of muscle?

Answer 1

• Locomotion
• respiration
• digestion
• parturition
• blood and lymph circulation
• swallowing
• generation of body heat

Question 2

Describe the 4 specific muscle properties.

Answer 2

• contractility = ability to contract/ shorten
• excitability = capacity to receive and respond to stimulus
• extensibility = ability to be stretched
• elasticity = ability to return to original shape after being stretched.

Question 3

List the types of muscles.

Answer 3

• skeletal muscle :
  —> contracts rapidly
  —> located in trunks, extremities, head and neck
  —> voluntary movement
• smooth muscle :
  —> contracts slowly
  —> located in viscera and blood vessels
  —> involuntary movement
• cardiac muscle :
  —> contracts rapidly
  —> located in the heart
  —> involuntary movement

Question 4

What are the level of organisation of skeletal muscle.

Answer 4

• epimysium = sheath of connective tissue surrounding muscle
• fascicle = a small bundle or cluster of muscle fibers (cells)
• perimysium = connective tissue extensions from epimysium surrounding each fascicle.
• endomysium = connective tissue extensions from perimysium surrounding the muscle fibers and are attached to sarcolemma.
• muscle fiber :
  *muscle cell -> elongated shape
  *contains basic contractile units
  *pull is transmitted by endomysium, perimysium and epimysium to tendon to aponeurosis that is attached to bone.
• sarcolemma =
  *a thin cell membrane enclosing skeletal muscle fibers ( cell )
  *at each end of muscle fibers, sarcolemma fuses w/ tendon fiber – collect into bundles to form muscle tendons – connect the muscles to the bones
  -myofibrils =
  *several hundred - thousands in each muscle fiber
  *composed by linear series of repeating sarcomeres
  -sarcomere =
  *basic contractile unit of striated muscle
  **found between Z lines and Z discs
  *contain MYOFILAMENTS (thin and thick)
  *arrangement give rise to striations

Question 5

What is the significance of sarcoplasmic reticulum?

Answer 5

• specialised endoplasmic reticulum
• important for muscle contraction
• regulates calcium storage, release and reuptake
• bigger in fast contracting fibers (white)

Question 6

Why is mitochondria important?

Answer 6

• present in large numbers
• lie in parallel to the myofibrils
• supply contracting myofibrils w/ large amounts of energy in form of ATP
• Type 1 fibers (red) have more # of mitochondria

Question 7

Why are T Tubules significant?

Answer 7

• arranged transversely to myofibril
  –> periodic invaginations of sarcolemma
  –> contain ECF
• allow plasma membrane of muscle fiber to carry depol. of AP to interior of fiber.

Question 8

What are the different types of muscle fibers?

Answer 8

• Type 1 = red fibers
• Type 2 = white fibers
• Type 2A
  *Type 2B

Question 9

Describe Type 1 fibers.

Answer 9

• red fibers
• slow twitch
• slow contracting
• fatigue resistant
• rich in mitochondria
• rely on oxidative metabolism
• plentiful in muscles, main function is slow prolonged activity

Question 10

Describe type 2 fibers.

Answer 10

• type 2A and 2B
• fast twitch
• fast contracting
• easily fatiguable
  -less mitochondria
• rely on glycolytic metabolism

Question 11

What is the difference between type 2A and 2B?

Answer 11

2A =
*mixed oxidative-glycolytic
*fast contracting
*fatigue resistant
*intermediate between type 1 and 2B
*strong oxidative capacity
2B=
*fast contracting
*fast fatiguing
*glycolytic
* depend on glycogen for energy supply
—> athletic training can cause some 2B fibers to be converted to 2A.