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Questions and Answers
What is the neurotransmitter released by the nerve that stimulates muscle contraction?
What is the neurotransmitter released by the nerve that stimulates muscle contraction?
Muscle fibers contract in a gradual manner rather than in an all-or-none fashion.
Muscle fibers contract in a gradual manner rather than in an all-or-none fashion.
False
What is the term for the pause between the nerve impulse and muscle contraction?
What is the term for the pause between the nerve impulse and muscle contraction?
latent period
The ________ is the gap between the nerve and muscle that is filled with interstitial fluid.
The ________ is the gap between the nerve and muscle that is filled with interstitial fluid.
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Match the following phases of muscle contraction with their descriptions:
Match the following phases of muscle contraction with their descriptions:
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What process occurs when muscle stimulation happens before relaxation is complete?
What process occurs when muscle stimulation happens before relaxation is complete?
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Fused tetanus occurs with evidence of relaxation between contractions.
Fused tetanus occurs with evidence of relaxation between contractions.
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Name the type of muscle fiber that is best suited for endurance and aerobic activities.
Name the type of muscle fiber that is best suited for endurance and aerobic activities.
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What is the primary function of muscles?
What is the primary function of muscles?
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Muscles use stored _____ for immediate energy during contraction.
Muscles use stored _____ for immediate energy during contraction.
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Which type of response is described as a single, brief contraction?
Which type of response is described as a single, brief contraction?
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Smooth muscles are voluntary and under conscious control.
Smooth muscles are voluntary and under conscious control.
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Match the types of muscle fibers with their characteristics:
Match the types of muscle fibers with their characteristics:
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Name the three types of muscles.
Name the three types of muscles.
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What happens to glucose during anaerobic glycolysis?
What happens to glucose during anaerobic glycolysis?
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The protein responsible for the contraction of muscle fibers is called _____ and is thick.
The protein responsible for the contraction of muscle fibers is called _____ and is thick.
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What is the role of creatine phosphate (CP) in muscle contraction?
What is the role of creatine phosphate (CP) in muscle contraction?
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Match the type of muscle with its characteristic:
Match the type of muscle with its characteristic:
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What describes an antagonistic pair of muscles?
What describes an antagonistic pair of muscles?
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The sliding filament theory pertains to how muscles relax.
The sliding filament theory pertains to how muscles relax.
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What is the role of ATP in muscle contraction?
What is the role of ATP in muscle contraction?
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The _____ is the basic unit of muscle contraction, defined by the distance between Z lines.
The _____ is the basic unit of muscle contraction, defined by the distance between Z lines.
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What is creatine phosphate's role in muscle cells?
What is creatine phosphate's role in muscle cells?
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Study Notes
Motor System
- Muscles produce movement, maintain posture, stabilize joints, and generate heat.
- Muscles are attached to bones at least two points; an origin (immovable) and an insertion (movable).
- Movement occurs when a muscle contracts, pulling on the insertion point. The origin remains stationary.
- Muscles work in pairs called antagonistic muscles. When one muscle contracts, the other relaxes. For instance, bicep contracts, tricep relaxes.
- Flexor muscle contracts to bend a joint. Extensor muscle relaxes to bend a joint.
- Muscle cells, also called muscle fibers, are elongated.
- Muscle contraction is due to the movement of microfilaments.
- When muscles contract, they shorten. When muscles relax, they lengthen.
- There are three types of muscle tissue: cardiac, smooth, and skeletal.
Muscle Types
- Cardiac muscle is involuntary, found in the heart, has striations, and each cell typically has a single nucleus. Cells are connected by intercalated discs.
- Smooth muscle is involuntary, found in walls of internal organs, lacks striations, and has a single nucleus per cell.
- Skeletal muscle is voluntary, found attached to bones via tendons, has striations, and each cell has multiple nuclei. Cells are surrounded and bundled by connective tissue.
Skeletal Muscle Characteristics
- Skeletal muscles are made of bundles of cells called muscle fibers.
- Muscle fibers have more than one nucleus each.
- Muscle fibers are enclosed in a membrane called sarcolemma.
- Muscle fibers contain myofilaments, which are contractile protein threads.
- Myofilaments are of two types: actin (thin) and myosin (thick).
- Myofilament arrangement forms sarcomeres (contractile units between Z lines).
- Sarcomeres contain the A band (darker, myosin), I band (lighter, actin), and H zone (middle of A band). The Z line joins actin filaments.
- The sliding filament theory describes how muscles contract.
Sliding Filament Theory
- The sliding filament theory is a working model of muscle contraction.
- Calcium (Ca) binds to actin to expose binding sites for myosin.
- Myosin heads bind to actin, forming cross bridges and pulling actin filaments towards the center of the sarcomere.
- ATP provides the energy for the myosin head to detach from actin.
- This cycle of binding, pulling, and detaching shortens the sarcomere, resulting in muscle contraction.
Muscle Stimulation
- Skeletal muscles need nerve stimulation to contract.
- Motor units consist of a single motor neuron and the muscle fibers it controls.
- The motor neuron's signal arrives at the neuromuscular junction. The nerve and muscle do not make direct contact.
- The neuromuscular junction is the site where the nerve and muscle meet; there is a synaptic cleft (gap) filled with interstitial fluid.
- At the junction, a neurotransmitter (acetylcholine) is released from the nerve across the synapse.
- The neurotransmitter attaches to receptors on the muscle cell membrane (sarcolemma), making the membrane permeable to sodium.
- Sodium entry triggers an action potential in the muscle fibers. This initiates the sliding-filament mechanism, causing contraction.
Muscle Contraction
- Muscle contraction starts with a nerve impulse stimulating muscle cells. Each muscle cell contracts in an all-or-none way.
- The pause between nerve impulse and contraction is called the latent period.
- The contraction phase is the shortening of the muscle due to actin and myosin filaments' contraction.
- The relaxation phase occurs when filaments relax, returning the muscle to resting length.
Graded Responses
- Graded responses are different degrees of skeletal muscle shortening.
- Twitch is a single, brief contraction (not normal muscle function).
- Summation (build-up) of contractions leads to tetanus (sustained contraction).
- Unfused (incomplete) tetanus involves some relaxation between contractions.
- Fused (complete) tetanus is a sustained contraction without any relaxation.
Fast and Slow Twitch
- Three types of myosin: I, IIa, and IIx.
- Type I (slow-twitch) used for endurance activities; slow ATP breakdown (aerobic).
- Type IIa (fast-twitch) used for speed; fast ATP breakdown (anaerobic).
- Type IIx (fast-twitch) similar to IIa.
Muscle Response to Strong Stimuli
- Muscle force depends on the number of stimulated fibers.
- More fibers contracting mean greater tension.
- Muscles continue to contract until they run out of energy.
Energy for Muscle Contraction
- Muscles use ATP for energy. ATP bonds break to release energy.
- Direct phosphorylation uses creatine phosphate (CP) to regenerate ATP from ADP. (CP is a high-energy molecule in muscle tissue)
- Aerobic respiration breaks down glucose to create CO2, H2O, ATP, and requires ongoing oxygen.
- Anaerobic glycolysis breaks down glucose to produce pyruvic acid (and some ATP) without oxygen. Pyruvic acid is converted to lactic acid.
Muscle Fatigue
- Muscle fatigue occurs when a muscle is unable to contract.
- Oxygen debt results when oxygen must be replenished to rid the body of lactic acid build-up (acidic environment)
- Lactic acid build-up and lack of ATP limit muscle contraction.
Effects of No Exercise (Atrophy)
- Atrophy is a decrease in muscle mass. This happens in muscles that aren't contracted frequently enough.
Effects of Exercise (Hypertrophy)
- Hypertrophy increases muscle size, strength, efficiency, and fatigue resistance.
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Description
This quiz explores the muscular system, detailing muscle functions, types, and the mechanics of muscle contractions. It covers the distinctions between cardiac, smooth, and skeletal muscles, as well as the concept of antagonistic muscle pairs. Test your knowledge on how muscles contribute to movement and stability!
