Muscle Contraction, Agonists, and Antagonists
Agonists, Antagonists, and Synergists
Agonists: These are the main muscles responsible for movement. They produce most of the force required for a particular action.
Antagonists: These muscles oppose the primary mover (agonist). They play a protective role and help control the movement of the agonist.
Synergists: These muscles assist the primary movers.
Muscle Contraction
Muscle contraction occurs when tension is applied to the bones via the tendons, resulting in torque on a joint.
Types of Muscle Actions
- Isometric: The muscle generates tension, but no joint movement occurs. The speed and angle are equal to zero.
- Concentric: This involves the shortening of the muscle. The force generated is greater than the resistance.
- Eccentric: This involves the lengthening of the muscle. The force of resistance is greater than the force generated by the muscle.
Energy Systems
- Aerobic: The cell uses oxygen to produce energy.
- Anaerobic: Does not necessarily need oxygen to produce energy. Produces less power.
Muscle Fiber Types
- Type 1 Fibers: Slow-twitch, and appropriate for long-duration, sustained aerobic activities.
- Type 2 Fibers: Fast-twitch, strong, short-duration, and use anaerobic metabolism.
Key Concepts in Muscle Physiology
Strength: The amount of force a muscle or muscle group can exert against a resistance in one maximal effort.
Motor Unit: A group of muscle fibers innervated by a single motor axon.
Muscle Spindle: Senses the degree of muscle stretch and the speed of muscle stretch. It is attached to muscle fibers.
Golgi Tendon Organ: Signals to stop muscle contraction. It is not located within the muscle fibers.
Contraction: The shortening of muscle fibers due to myosin interaction.
Muscular Action: An activation of muscle that contributes to movement or stabilization of the musculoskeletal system. Muscle action depends on the position of the segment in relation to gravity or applied resistance.
Joint Receptors: Their function is to inform about joint position.
Nervous System Components
Central Nervous System (CNS): Consists of the brain and spinal cord. It has the ability to modify and coordinate force for the implementation of movements through sensory feedback from joint receptors, muscles, and tendons.
Peripheral Nervous System (PNS): Composed of the peripheral nerves and receptors that capture different tasks.
Sensory System: Captures and sends information to parts of the CNS.
Motor System: Carries information related to movement.
Muscle Growth and Loss
Hypertrophy: An increase in the size of muscle fibers.
Hypotrophy: A decrease in the number of myofibrils and the size of the fiber.
Atrophy: A reduction in cell size resulting from the loss of proteins and other cellular materials.
Cross-Sectional Area (CSA): Related to the amount of force a muscle can produce. A larger CSA indicates a greater capacity to produce force.
Role of Calcium in Muscle Fiber
When an impulse reaches the sarcoplasmic reticulum, it releases calcium. This calcium binds to troponin, initiating action by withdrawing tropomyosin molecules from the active sites of actin filaments. This unblocking allows the myosin cross-bridges to attach to actin. The interaction between actin and myosin filaments results in muscle fiber shortening and force generation.
Termination of Muscle Contraction
Muscle contraction continues until calcium is depleted.