Exam 3 Review:  Chapter 09:  Muscle Tone

muscle tone - The normal degree of vigor and tension in maintained in skeletal muscles by involuntary spinal reflexes; the resistance of skeletal muscle to passive elongation or stretch; the normal state of involuntarily controlled contractions of various skeletal muscle motor units which keeps all individual muscles in a state of partial contraction and ready to contract more forcefully if voluntary commands are received; this state is maintained by negative proprioceptive feedback systems.  [See question 9 below.]

muscle tension - The force generated when a muscle contracts; the condition or degree of a muscle being stretched or strained.

isotonic contraction - The type of skeletal muscular contractions in which the force applied by the muscle is sufficient to move the load, and as a result, the muscle shortens while its muscle tension remains relatively constant.

isometric contraction - The type of skeletal muscular contractions in which the force applied by the muscle is not sufficient to move the load, and as a result, the muscle does not shorten though its muscle tension or force of contraction increases.

hypotonia - A condition of diminished skeletal muscle tone in which the muscle exhibits diminished resistance to passive stretching; a symptom of various weakening diseases.

disuse atrophy - A wasting or decrease in size of a body organ, tissue, or part owing to a  lack of use, which may be caused by disease, injury, or immobilization; e.g., muscular atrophy of a person affected with paralysis.

muscular hypertrophy - A noncancerous enlargement of a muscle as a result of an increase in the size rather than the number of its constituent muscle cells; the common response of skeletal muscles to a program of exercise.

hyperplasia -  A noncancerous but abnormal increase in the number of cells in an organ or a tissue with consequent enlargement.

concentric contraction - The common type of isotonic contraction in which the muscle shortens to do work, e.g., when picking up an object or kicking an object.

eccentric contraction - The less common type of isotonic contraction in which the muscle lengthens to do work, e.g., when slowly lowering a heavy object that has been picked up or when walking up a steep hill; eccentric contractions are about 50% more forceful and often cause delayed-onset muscle soreness.

Describe:  

9. The physiological control or regulation of muscle tone.

Muscle tone is the normal degree of background contraction which is maintained in skeletal muscles by involuntary spinal reflexes. Muscle tone represents the resistance of skeletal muscles to passive elongation or stretching.  This state is maintained by negative proprioceptive feedback systems.  Various mechanoreceptors (stretch receptors) in tendons, ligaments and joint capsules as well as muscle spindles within the body of the muscle itself send continuous somatic sensory information, "proprioception," to control centers in the CNS, particularly in the gray matter of the spinal cord.  In response, the control centers initiate responsive, "random" motor commands to contract various motor units.  Since muscles are arranged in antagonist pairs and groups, as one muscle exerts a little contraction in response to the control center's commands, it stretches its antagonists, causing them to send proprioceptive sensory information back to the control center.  Thus, a normal state of involuntarily controlled contractions of various skeletal muscle motor units in different muscle groups occurs, which keeps all individual muscles in a state of partial contraction and ready to contract more forcefully if voluntary commands are received.  [Note:  See Chapter 13 for more information on stretch reflexes and the various mechanoreceptors.]

13. How muscle length (degree of stretch) affects the strength of muscle contraction.

There is an optimal muscle length, based on the degree of sarcomere operating length, which is approximately 70 - 130% of the sarcomere's normal resting length.  Within that range, muscle tension = contractile force generated, is maximized.  If the muscle length is out of the optimal range, whether longer or shorter, performance and muscle tension = contractile force are compromised.  In the optimal range , the potential number of myosin head to actin cross-bridges is maximized.  See Figures below.

14. The difference between Isotonic and Isometric contraction of a muscle.

isotonic contraction - the force applied by the muscle is sufficient to move the load, and as a result, the muscle shortens while its muscle tension remains relatively constant.

isometric contraction - the force applied by the muscle is not sufficient to move the load, and as a result, the muscle does not shorten though its muscle tension or force of contraction increases.