Quiz on Muscles

What is muscle tone?

Also known as tonus. To maintain posture, passive partial contraction. A constant state of slight tension that serves to maintain muscle in a state of readiness. Tonus is due to alternate periodic activation of small # of motor units within the muscle by motor centers in the brain and spinal cord.

What happens in graded contractions?

An asynchronyzed train of impulses is sent to motor units, weight to induce tetanus (the smooth sustained contractions of skeletal muscle, leading to body movements) skeletal muscles are thus able to react to different loads accordingly. For example: the effort of muscles used in walking on the level ground is less than the effort those muscles expend in climbing stairs.

Grading

Means changing the strength of muscle contraction of the extent of shortening in proportion to the load placed on the muscle.

What are factors that affect muscle fatigue?

-reduction of creatine-P, ATP, glycogen -Increased levels of inorganic phosphate *may slow P release from myosin -Increased levels of lactate, H+, this change in pH -decreased calcium release: synapse, muscle -K+ leaves muscle fiber, leading to increased extracellular concentration, altering the membrane potential *changes Na+, K+, ATPase activity

Maximal stimulus

Any voltage that is greater than threshold and less than maximal is considered Suprathreshold/submaximal.

Incomplete tetanus

Each stimulus causes a contraction to be initiated when the muscle has partly only relaxed from the previous contraction. Muscle is never allowed to relax completely.

Muscle fatigue

Fatigue is defined as a decrease in the muscles ability to generate force. Their are two types of muscle fatigue: 1) central fatigue due to the CNS ( your muscle fatigue can do with your psychological) 2) Peripheral fatigue due to neuron or muscle ( Where it originated from). Ex: when her husband was running and his shoulder muscle started to hurt.

Asynchronous recruitment of motor units

Helps avoid fatigue. Different motor units take turns maintaining tension.

Motor Unit

Is a neuron and all the muscle fibers it innervates. The strength of skeletal muscle contraction is controlled by: 1. Activating a desired number of motor units within the muscle and 2. Controlling the frequency of motor neuron impulses in each motor unit.

Sciatic nerve

Is the largest and longest spinal nerve in the human body. Function: It delivers nerve signals to and from the muscles and skin of the thighs, lower legs and feet

Summation

It is a stronger contraction when the muscle fiber does not relax completely between action potentials. If a second stimulus is delivered immediately after the first, a second twitch may be produced that begins before the relaxation period has been completed on the previous twitch.

Recruitment

The increase of number of motor units being stimulated. This increase in the number of motor units stimulate will result in an increase in the strength of the muscular contraction.

Electromyogram

The recording obtained

Tetanus

The smooth sustained contractions of skeletal muscle, leading to body movements.

Latent period

The time between the beginning of the stimulus and the beginning of a visible response (contraction). During the latent period, impulses are spreading over the sarcolemma and calcium is being released.

Relaxation Period

The time period when the muscle lengthens or returns to its resting length. Release of tension.

Tetanus

When a muscle is stimulated at progressively greater frequencies, a frequency (the rate at which it occurs) is finally reached at which the successive contractions fuse (blend) together and there is no visible relaxation period between twitches. This smooth, sustained contraction is called tetanus. After the muscle is left in tetanus for a period of time it will fatigue.

What is dynamometer?

an instrument for measuring the force of muscular contraction.

Twitch

A muscle twitch is a is a contraction of a muscle in response to a stimulus that causes an action potential in one or more muscle fibers (an all or none). When a skeletal muscle is stimulated by a single electrical impulse of a given voltage, it quickly contracts and relaxes. A muscle twitch can be divided into three periods: 1. Latent period 2. Contraction period 3. Relaxation period

What causes muscle fatigue?

Fatigue is caused by reversible depletion (reduction in the #) of muscle's ability to generate force. If the muscle uses its energy sources faster than it can be generated by cellular metabolism, fatigue occurs. - reduction of creatine-P ,ATP, glycogen -increased levels of inorganic phosphate *may slow P release from myosin -increased levels of lactate, H+, this change in pH -decreased calcium release: synapse, muscle -K+ leaves muscle fiber, leading to increased extracellular concentration, altering the membrane potential *changes Na+,K+,ATPase activity.

How are waste products removed from the muscle?

Normally, by the circulatory system as the blood brings nutrients to them muscles for energy transformation. If certain waste products (Metabolites: a substances necessary for metabolism) aren't removed at an adequate rate, they will accumulate and chemically interfere with the contractile process, thereby hastening the onset fatigue. Some accumulated water products also stimulate pain receptors in surrounding connective tissue and induce cramping, genera sign of inadequate blood flow to the muscle.

What is the primary function of muscle?

Regardless of what type of muscle it is, its primary function is to convert chemical energy to mechanical work, such as movement of bones, soft body parts, or fluid through tube (blood vessels or digestive tract).

What happens during contraction?

Skeletal muscle cells convert chemical energy into thermal and mechanical energy, and, in the process, produce chemical waste products.

What types of movements are produced by graded contractions?

Smooth controlled movements of the body (such as walking, swimming, or jogging).

What does the contraction of skeletal muscle supply?

Supplies the "applied force" allowing for work to move an object (the load). Work= Applied force X load Skeletal muscle performs mechanical work when the muscle contracts an object is moved, and is lifting weight. If you exert less force, then the weight does not move and no work is done.

Complete Tetanus

Sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potential at very high rate. -no relaxation phase -aerobic respiration , breakdown of glucose with oxygen ->ATP -relaxation phase does not occur at all

Once you have lifted a light object

The brain recruits approximately the same # of motor units to keep the object up, but cycles between different motor units. The muscle fibers consume stored energy available in the muscle, and generate a force by contracting. As the muscle fibers deplete this fuel source, more energy must be created in order to continue contracting. By recruiting different motor units, motor units can relax and replenish (fill up again) their fuel sources.

What happens when a motor unit is activated?

The component of muscle fibers generate and conduct their own electrical impulses that ultimately result in contraction fibers. Although the electrical impulse generated and conducted by each fiber is very weak ( less than 100 micro bolts), many fibers conducting simultaneously induce voltage differences in the overlying skin that are large enough to be detected by a pair of surface electrodes (a conductor through which electricity enters or leaves an object).

Electromyography.

The detection, amplification, and recording of changes in skin voltage produced by underlying skeletal muscle contraction.

Threshold stimulus

The minimum amount of energy needed to make a muscle fiber contract. The minimum stimulus that will elicit a visible response.

What happens when a skeletal muscle is called on to perform mechanical work?

The number of motor units in the muscle activated by the brain is proportional to the amount of work to be done by the muscle; the greater the amount of work to be done, the greater the # of motor units activated. The brain determines he # of active motor units required for a muscle and associated tendons and joint capsules.

Contraction Period

The time period when the muscle fibers are shortening against their load. (Pulling their load). Sarcomeres are shortening as the actin filament slides over the myosin filament. Creation of force in muscle.

Who controls the skeletal muscle contractions?

They are controlled by the central nervous system (brain and spinal cord). For example, each somatic motor neuron that leaves the spinal cord innervates many different skeletal fibers.

What does summation and recruitment have in common?

They both result in an increase in the strength of the muscular contraction.

What factors may be responsible for gender differences when considering force generated and time to fatigue? Consider both anatomical and physiological factors in your discussion.

testosterone so RBC levels are higher than women