Human Physiology Unit Five

Muscle Characteristics Contractility Excitability Conductivity Extensibility Elasticity

Muscle Characteristics The ability to contract Contraction results in movement Contraction occurs due to sliding filaments

Muscle Characteristics Muscles contract due to nerve activity Muscles can be under voluntary or involuntary control

Skeletal Muscle Characteristics Appear striated Under voluntary control Quick response time due to nerve stimulation of independently contracting muscle fibers Results in body movement and balance

Smooth Muscle Characteristics Appear non-striated Under involuntary control Relatively slow response time due to stimulation produced by pacemaker potentials Results in internal organ movements and glandular secretions

Cardiac Muscle Characteristics Appear striated Under involuntary control Quick response time due to pacemaker produced action potentials

Cardiac Muscle Characteristics Intercalated discs connecting fibers produce simultaneous contraction Results in heart beats and the movement of blood

Muscle Anatomy

Muscle Anatomy

Filament Arrangement

Sarcomere Contraction The “all or none” law indicates that sarcomeres, when stimulated will contract fully - there is no partial contraction of sarcomeres

Actin Filament Composition

Myosin Action

The Power Stroke

Conduction in the Muscle Cell

Motor Unit

Muscle Contractions Graded responses are due to the number of motor units recruited during a muscle contraction The fewer the number of motor units recruited, the weaker the overall contraction The greater the number of motor units recruited, the stronger the overall contraction

Muscle Contraction Sequence of Events

Muscle Contraction Sequence

Muscle Contraction Sequence

Muscle Contraction Sequence

Muscle Contraction Sequence

Muscle Contraction Sequence

Muscle Contraction Sequence

Twitches and Summation

Summation and its Results

Contraction Types Isotonic contractions - contractions that result in the shortening of a muscle and movement Isometric contractions - contractions that do not shorten a muscle and result in no movement

Contraction Functions Isotonic contractions are used to produce movement in the body Isometric contractions are used to maintain tone, position and posture Tonus is an example of a graded response that is used to maintain position or posture

The Anatomy of a Muscle Spindle

Motor Neuron Types Lower motor neurons - neurons extending from the spinal cord that innervate skeletal muscle (Ex. - alpha and gamma motor neurons) Higher motor neurons - neurons found in the brain that process information and control muscle contractions through lower motor neurons

The Muscle Stretch Reflex

Reciprocal Enervation

The Crossed Extensor Reflex

Muscle Energy Sources ATP is necessary for energizing myosin cross bridges and accumulating Ca2+ at the end of contraction ADP cycles with ATP in the power stroke and is necessary for engaging and disengaging myosin cross bridges

Muscle Energy Sources At rest, skeletal muscle obtains most of its energy from the aerobic catabolism of fatty acids Creatine phosphate is a compound found in skeletal muscle that will donate its phosphate groups to ADP during times of sustained muscle activity

Muscle Energy Sources

Muscles and Oxygen Myoglobin is a pigment found in skeletal muscle cells that functions to take up and store oxygen for use in the cell Myoglobin provides a supply of ready oxygen for the production of the ATP needed for muscle contraction

Muscles and Oxygen Lactic acid is produced by muscles when they enter into anaerobic respiration due to limited oxygen amounts Lactic acid will be converted back to pyruvic acid in the liver after oxygen levels have returned to normal

Muscles and Oxygen Oxygen debt is the amount of oxygen needed to restore oxygen concentrations on hemoglobin (RBCs) and myoglobin (skeletal muscle), as well as the oxygen needed to convert lactic acid back to pyruvic acid (liver)

Atrophy vs. Hypertrophy Atrophy is the decrease in the mass and size of muscle tissue due to inactivity Hypertrophy is the increase in the mass and size of muscle tissue due to increased activity

Atrophy vs. Hypertrophy Steroid hormones will increase protein synthesis in muscle tissue, producing hypertrophy Testosterone, found in males, is one such hormone that naturally increasing muscle size in males