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Questions and Answers
What are myofibrils primarily composed of?
What structure separates one sarcomere from the next?
What gives skeletal muscle its striated appearance?
Which bands in the sarcomere consist solely of actin?
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What are the dark-staining bands in the sarcomere called?
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What happens to the sarcomeres during muscle contraction?
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How do the actin and myosin myofilaments interact in the sarcomere?
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What defines a sarcomere within skeletal muscle?
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What occurs during muscle contraction according to the sliding filament model?
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What characteristic of muscle fibers allows them to respond to stimuli?
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What is the role of gated channels in muscle fibers?
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What defines the resting membrane potential of muscle cells?
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During muscle relaxation, what happens to the sarcomeres?
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What primarily causes the charge difference across the cell membrane?
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What happens to muscle fibers when they are stimulated?
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Which type of ion channel allows continuous ion movement across the membrane?
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What is one of the mechanisms of muscle fatigue?
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What can cause muscle soreness following vigorous exercise?
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What is meant by oxygen deficit during exercise?
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Which characteristic is unique to smooth muscle cells?
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What distinguishes cardiac muscle cells from skeletal muscle cells?
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What happens to breathing after exercise ceases?
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How do muscle fibers respond to prevent structural damage from fatigue?
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Which type of muscle is characterized by being non-striated and spindle-shaped?
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What is the primary function of the sternocleidomastoid muscle?
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How many heads does a triceps muscle have?
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Which of the following muscles are considered muscles of mastication?
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Where does the sternocleidomastoid muscle insert?
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What are abductors and adductors responsible for?
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Which statement about biceps muscle is true?
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Which of the following is NOT a muscle of facial expression or mastication?
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What is the origin of the sternocleidomastoid muscle?
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Which muscle is primarily responsible for extending the elbow?
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Which muscle acts as an abductor of the upper limbs?
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Identify the muscle that elevates the ribs.
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Which muscle is located in the pelvic diaphragm?
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What is the primary function of the Levator ani muscle?
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Which muscle is primarily identified as the 'flexing muscle' of the arm?
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What role does the latissimus dorsi play in upper limb movement?
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Identify the muscle that is located between the ribs.
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Study Notes
Skeletal Muscle Structure
- Skeletal muscle is made up of bundles of protein filaments called myofibrils.
- Myofibrils are made up of two types of myofilaments: actin (thin filaments) and myosin (thick filaments).
- Actin and myosin are arranged into repeating units called sarcomeres.
- The myofilaments in the sarcomere are responsible for the mechanical aspect of muscle contraction.
The Sarcomere
- The sarcomere is the basic structural and functional unit of skeletal muscle.
- Sarcomeres are connected end to end to create myofibrils.
- Z disks are networks of protein fibers that serve as anchors for actin myofilaments and separate one sarcomere from the next.
- A sarcomere extends from one Z disk to the next Z disk.
- The organization of actin and myosin myofilaments gives skeletal muscle its striated appearance and its ability to contract.
- The myofilaments slide past each other, causing the sarcomeres to shorten.
- Each sarcomere consists of two light-staining bands separated by a dark-staining band.
- Light bands, consisting only of actin, are called I bands and extend from the Z disc toward the center of the sarcomere to the ends of the myosin myofilaments.
- Dark bands are called A bands and extend the length of the myosin myofilaments.
- Actin and myosin myofilaments overlap for some distance on both ends of the A band, which allows for contraction.
Neuromuscular Junction
- The neuromuscular junction is the point of contact between a motor neuron and a muscle fiber.
- It is where the motor neuron releases acetylcholine, which binds to receptors on the muscle fiber, triggering muscle contraction.
Sliding Filament Model
- When a muscle contracts, the actin and myosin myofilaments in the sarcomere slide past one another and shorten the sarcomere.
- When sarcomeres shorten, myofibrils, muscle fibers, muscle fascicles, and muscles all shorten to produce muscle contraction.
- During muscle relaxation, sarcomeres lengthen.
Excitability of Muscle Fibers
- Muscle fibers are electrically excitable.
- Electrically excitable cells are polarized, meaning the inside of the cell membrane is negatively charged compared to the outside.
- A voltage difference, or electrical charge difference, exists across each cell membrane.
- This charge difference is due to differences in the concentrations of ions on either side of the membrane.
Ion Channels
- The phospholipid bilayer is impermeable to ions. Membrane proteins, called ion channels, permit ions to pass through the membrane.
- Leak channels allow for the slow leak of ions down their concentration gradient.
- Gated channels may open or close in response to various types of stimuli.
Resting Membrane Potential
- The electrical charge difference across the cell membrane of an unstimulated cell is called the resting membrane potential.
- Muscle cells (fibers) have a resting membrane potential but can also perform action potentials.
- The resting membrane potential is due to the inside of the membrane being negatively charged in comparison to the outside of the membrane which is positively charged.
- Action potentials are due to the membrane having gated channels.
Muscle Fatigue
- Muscle fatigue is a state of physiological inability to contract a muscle.
- Mechanisms of fatigue include:
- Acidosis and ATP depletion due to either an increased ATP consumption or a decreased ATP production
- Oxidative stress, which is characterized by the buildup of excess reactive oxygen species (ROS; free radicals)
- Local inflammatory reactions
Muscle Soreness
- Muscle soreness, often experienced following vigorous exercise, is related to the effects of inflammatory chemicals on the muscle fibers.
- Exercise schedules that alternate exercise with periods of rest, such as lifting weights every other day, provide time for the repair of muscle tissue.
Oxygen Deficit
- Oxygen deficit is the lag time between when a person begins to exercise and when they begin to breathe more heavily.
- Excess postexercise oxygen consumption is the lag time before breathing returns to its preexercise rate once exercise stops.
Smooth Muscle
- Smooth muscle cells are non-striated, small, spindle-shaped muscle cells, usually with one nucleus per cell.
- The myofilaments are not organized into sarcomeres.
- These cells comprise organs controlled involuntarily, except the heart.
- Neurotransmitter substances, hormones, and other factors can stimulate smooth muscle.
Cardiac Muscle
- Cardiac muscle cells are long, striated, and branching, with usually only one nucleus per cell.
- Cardiac muscle is striated as a result of the sarcomere arrangement.
- Cardiac muscle contraction is autorhythmic.
Skeletal Muscles
- Skeletal muscles are attached to bones and are responsible for movement.
- They are named based on their shape, location, size, number of origins, and their function.
Muscles of Mastication
- The muscles of mastication are responsible for chewing.
- These muscles include:
- Temporalis
- Masseter
- Pterygoids (two pairs)
Pelvic Diaphragm Muscles
- The muscles of the pelvic diaphragm support the pelvic organs and help to control urination and defecation.
- These muscles include:
- Levator ani
- Ischiocavernosus
- Bulbospongiosus
- Deep transverse perineal
- Superficial transverse perineal
Upper Scapular and Limb Muscles
- These muscles are involved in movement of the shoulder and upper limb.
- These muscles include:
- Trapezius: shoulders and upper back, extends neck and head
- Pectoralis major: chest, elevates ribs
- Serratus anterior: between ribs, elevates ribs
- Deltoid: shoulder, abductor of the upper limbs
Muscles of the Shoulder
- These muscle are located in the shoulder and play a role in shoulder joint movement.
- They include:
- Supraspinatus
- Infraspinatus
- Teres minor
- Subscapularis
Upper Limb Muscles
- These muscles are located in the upper limb and play a role in elbow and shoulder movement.
- They include:
- Triceps brachii: 3 heads, extends elbow
- Biceps brachii: “flexing muscle”, flexes elbow and shoulder
- Brachialis: flexes elbow
- Latissimus dorsi: lower back, extends shoulder
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Description
This quiz covers the intricate details of skeletal muscle structure, focusing on myofibrils and the vital role of sarcomeres. It explains how actin and myosin myofilaments are organized and their function in muscle contraction. Test your knowledge on the structural units that contribute to the striated appearance of skeletal muscle.
