BIO 203 lecture 11 objectives

Explain the ways in which different groups of skeletal muscles (agonists, etc.) interact to produce smooth, coordinated movements.

a. origins & insertions b. lever actions & leverages (first, second, & third class levers)

Explain mathematically how the force exerted by a muscle is proportional to its cross-sectional area, and how the work done by a muscle is proportional to its volume.

-force exerted by a muscle is proportional to its cross-sectional area -distance shortened during a muscle contraction is proportional to starting length work done= force x distance shortened

List four factors that control smooth muscle contractions.

1. nervous input from the autonomic nervous system 2. hormones & other substances in the the circulation 3. Substances produced within a metabolizing tissue can cause smooth muscle to relax (lack of oxygen, excess H+ & CO2) 4. Stretching (specifically visceral smooth muscles)

Define a motor unit and describe how motor units are important in controlling the force and rate of muscle contraction.

A motor unit is a motor neuron connected (with an axon) to muscle fiber(s). Motor units are important in controlling the force/rate of muscle contraction because as stimulus increases, force/rate of contraction increases.

Describe the causes of muscular atrophy.

Disuse atrophy: can occur in bedridden patients, astronauts, etc zero-gravity conditions: reduced use of muscle causes muscles to decrease in mass and volume myasthenia gravis: patient develops antibodies against acetylcholine receptors

Describe with diagrams what is meant by a first class lever, and give examples.

Fulcrum lies between the out-force and the in-force. ex: lifting the head, straightening arm at the elbow, movement of foot around the fulcrum of the ankle

Distinguish between isotonic and isometric contractions, and give examples.

Isotonic contractions are when a muscle shortens during contraction (when you bend your arm at the elbow). Isometric contractions occur when you carry a suitcase with your arm being constantly flexed. During isometric, the muscle length does not change but the tension developed increases sharply.

Explain what is meant by recruitment of motor units.

Motor recruitment is when many motor units, over time, become activated independently of each other. The central nervous system can increase the strength of a muscle contraction by activating these motor units.

Describe the two ways in which smooth muscle is organized, and describe their functions.

Multi-unit smooth muscle: unorganized cells, occur at separate cells rather than sheets. In iris of eye, walls of blood vessels, large passageways of the lungs, & arrestor pili muscle Visceral ("single unit"): wraparound sheets; found in hollow organs like stomach, intestine, urinary tract. Cells are close to one another & have gap junctions. responsible for per

Explain what is meant by muscle tone, and how it relates to posture and maintaining balance.

Muscle tone is when some fibers in partial contraction (some are contracted, some aren't). It is essential for maintaining posture and balance. If you faint, you lose your muscle tone & fall.

Contrast muscular hyperplasia and muscular hypertrophy

Muscular hyperplasia is an increase in the number of muscle fibers muscular hypertrophy is an increase in the size of muscle fibers. it increases the cross-sectional area of the muscle, increasing its volume

Describe the causes of muscular hypertrophy

Muscular hypertrophy is caused from repeated forceful contractions, exercise, testosterone, growth hormones

Describe the various types of skeletal muscle groupings and their functions.

flexor: decreases angle at joint extensor: increases angle at joint abductor: moves a bone away from the midline adductor: moves a bone toward the midline levator: produces an upward movement depressor: produces a downward movement supinator: turns the palm upward pronator: turns the palm downward sphincter: decreases the size of an opening tensor: makes a body part more rigid rotator: moves bone around its longitudinal axis

Describe with diagrams what is meant by a third class lever, and give examples.

out-force is at one end, in-force is in the middle, fulcrum is at the other end (fulcrum, in-force, out-force) ex: flexing the forearm at the elbow

Summarize in a table the similarities and differences between skeletal, smooth, and cardiac muscle.

look at pages 239 & 241 of lecture notes

Explain mathematically the advantage of having a lever system in the body. Illustrate with a diagram how the lever system activated by the biceps brachii muscle operates: discuss and calculate its advantages and disadvantages.

ratio of 1:7 (biceps brachia only has to shorten by 1 cm for every 7cm movement of the hand) disadvantage: to raise 20 kg, the biceps brachia must exert a force of 7 times that amount, equal to 140 kg

Describe the cells involved in muscle repair

satellite cells (stem cell that is really a quiescent myoblast) which divide and form myoblasts that can fuse to form new muscle cells

Describe, contrast and explain the response of a single muscle fiber and a whole muscle to electrical stimulation - define the threshold stimulus and the all-or-none phenomenon.

Single muscle fiber goes from no response to maximum response as stimulus is increased. This is called "all-or-none-response," meaning it contracts fully or not at all. When a single muscle fiber is exposed to a weak electrical stimulus, it doesn't contract. This weak electrical stimulus is called a sub threshold stimulus. As the strength of the stimulus increases, it becomes a threshold stimulus. The muscle contracts fully with a supra threshold stimulus. There is a progressive increase in the force of contraction of a whole muscle as stimulus increases. The strength of a whole muscle contraction can be varied (based on motor recruitment)

Describe how the mechanism of smooth muscle contraction differs from that of skeletal muscle.

Smooth muscle lacks troponin and tropmyosin. Instead, excitation-contraction coupling is mediated by the calcium bonding protein calmodulin.

Define tetanic contraction, and distinguish it from a twitch. What is fatigue in the context of a tetanic contraction?

Tetanic contraction occurs with a high frequency stimulant and has a progressive increase in forever time, and a twitch's force rapidly increases and reaches a maximum point, then rapidly decreases in force.

Explain the staircase ("treppe") effect.

The staircase/treppe effect occurs when the strength of each muscle twitch progressively increases up to a max value after a few seconds. It is caused mainly by a buildup of Ca++ in the sarcoplasm.