Lecture 10: Muscle Anatomy and Physiology Part 2

Question 0

Organization of a sarcomere

Answer 0

The sarcomere is the functional contractile unit in a skeletal muscle fiber.

Defined by the area between 2 adjacent Z discs

Myofibrils contain multiple and repeating sarcomeres

Each sarcomere shortens as the muscle fiber contracts

Question 1

Myotonic dystrophy

Answer 1

Inherited disorder part of muscular dystrophy

Prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use. For example a person may have difficulty releasing their grip on a doorknob

Question 2

Smooth muscle

Answer 2

Much smaller than skeletal muscle fibers

Has longer actin and myosin filaments

Myosin ATPase activity much slower

Myosin light chain plays regulatory role

Not arranged in sarcomere

Has less sarcoplasamic reticulum

• IP3-receptor channel is the primary calcium channel
• calcium also enters cell from extra cellular fluid

Question 3

Smooth muscle fibers

Answer 3

1. Found in the walls of viscera and blood vessels
2. Short fusiform cells (widest in the middle and tapered at each end)
3. One centrally located nucleus
4. No striations
5. Thin filaments attached to dense bodies
6. Under involuntary control

Question 4

Familial thoracic aortic aneurysm and dissection

Answer 4

Inherited condition that predisposes individuals to the development of aneurysms, dilations in a blood vessel, particularly in the thoracic aorta

Question 5

Electrical and mechanical events in muscle contraction

Answer 5

A twitch is a single contraction-relaxation cycle

Question 6

Properties of whole muscles

Answer 6

Tired muscles can’t generate much force.

• muscles fatigue when strong stimulation keeps a muscle in a state of tetanus too long.
• after resting, muscles will be able to co tract again; muscles may need to rest for minutes up to a day to fully recover

Question 7

Exercise and skeletal muscle

Answer 7

Muscle atrophy: a wasting of tissue that results in reduction of muscle size tone and power. This can be caused by a lack of stimulation (exercise) to the muscle.

Muscle hyper trophy: an increase in Muscle fiber size (not an increase in number of muscle fibers). Hypertrophy results from repetitive stimulation of muscle fibers. Mitochondria increases in number therefor the amount of ATP increases. Both myofibrils and myofilaments increase in number, all resulting in the muscle increasing in size.

Question 8

Mechanics of body movement

Answer 8

Isotonic contractions create force and move load

• concentric action is a shortening action
• eccentric action is a lengthening action

Isometric: contraction create a force without moving a load
- series elastic elements; sarcomeres shorten while elastic elements stretch resulting in little change in overall length

Question 9

Cardiac muscle fibers

Answer 9

Cardiac muscle fibers are found almost exclusively within the heart wall. They have the following qualities:

1. Striated
2. One or two nuclei
3. Form y- shaped branches
4. Join other adjacent cells to form junctions termed intercalated discs comprised of gap junctions
5. They are autorhythmic (able to generate a muscle impulse without nervous stimulation)
6. Under involuntary control

Question 10

Cardiac muscle

Answer 10

Shares features with both skeletal and smooth muscle:

• like skeletal: striated; sarcomere structure
• unlike skeletal: muscle fibers shorter; may be branched, have single nucleus
• like smooth: electrically linked to one another, some exhibit pacemaker potentials, under sympathetic and parasympathetic control as well as hormone control