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Questions and Answers
What structure descends through the inguinal canals into the scrotum during development?
What structure descends through the inguinal canals into the scrotum during development?
Which muscle is NOT involved in forming the pelvic floor?
Which muscle is NOT involved in forming the pelvic floor?
Why are hernias more common in men than in women?
Why are hernias more common in men than in women?
What function do the ischiocavernosus and bulbospongiosus muscles serve?
What function do the ischiocavernosus and bulbospongiosus muscles serve?
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Which structures pierce the pelvic diaphragm?
Which structures pierce the pelvic diaphragm?
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Which muscle is the largest and forms the bulk of the buttock?
Which muscle is the largest and forms the bulk of the buttock?
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What is the primary function of the diaphragm during contraction?
What is the primary function of the diaphragm during contraction?
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What is a function of the abdominal muscles?
What is a function of the abdominal muscles?
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What does the term 'hiatus' refer to in relation to the diaphragm?
What does the term 'hiatus' refer to in relation to the diaphragm?
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Which of the following correctly describes the gluteus minimus?
Which of the following correctly describes the gluteus minimus?
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Which characteristic of muscles refers to their ability to respond to stimuli?
Which characteristic of muscles refers to their ability to respond to stimuli?
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What type of muscle tissue is characterized by being striated and voluntary?
What type of muscle tissue is characterized by being striated and voluntary?
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Which type of muscle is responsible for the contraction of the heart?
Which type of muscle is responsible for the contraction of the heart?
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What is the main function of skeletal muscles in maintaining posture?
What is the main function of skeletal muscles in maintaining posture?
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In addition to movement, what is another major function of muscles?
In addition to movement, what is another major function of muscles?
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How are muscle fibers primarily characterized?
How are muscle fibers primarily characterized?
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What defines a muscle as an organ?
What defines a muscle as an organ?
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Which characteristic allows muscle fibers to return to their resting length after being stretched?
Which characteristic allows muscle fibers to return to their resting length after being stretched?
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What is the primary structural difference between actin and myosin within myofibrils?
What is the primary structural difference between actin and myosin within myofibrils?
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What triggers the muscle contraction process involving ca ions?
What triggers the muscle contraction process involving ca ions?
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Which of the following best describes the role of acetylcholine in muscle movement?
Which of the following best describes the role of acetylcholine in muscle movement?
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What is the function of the Ca pump during muscle relaxation?
What is the function of the Ca pump during muscle relaxation?
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How does the all-or-none principle apply to muscle fiber contractions?
How does the all-or-none principle apply to muscle fiber contractions?
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What is the term for the minimal strength required to cause a muscle contraction?
What is the term for the minimal strength required to cause a muscle contraction?
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What happens to a muscle fiber that does not receive a threshold stimulus?
What happens to a muscle fiber that does not receive a threshold stimulus?
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Which statement accurately describes the contraction response of a muscle fiber to a threshold stimulus?
Which statement accurately describes the contraction response of a muscle fiber to a threshold stimulus?
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What characterizes a motor unit in relation to muscle fibers?
What characterizes a motor unit in relation to muscle fibers?
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What is the primary effect of exercise on muscle tissue?
What is the primary effect of exercise on muscle tissue?
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Which of the following muscles is located in the upper extremities?
Which of the following muscles is located in the upper extremities?
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In terms of motor control, which muscles have smaller motor units?
In terms of motor control, which muscles have smaller motor units?
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What is one consequence of stimulation of a single motor unit within a muscle?
What is one consequence of stimulation of a single motor unit within a muscle?
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Study Notes
Muscle Characteristics
- Excitability: Muscles respond to stimuli, such as nerve impulses.
- Extensibility: Muscle fibers can stretch beyond their resting length.
- Elasticity: Muscles recoil to their original length after being stretched.
- Contractility: Muscle fibers can shorten when stimulated.
Types of Muscle Tissue
- Skeletal Muscle: Voluntary muscle attached to bones, responsible for movement.
- Smooth Muscle: Involuntary muscle found in the walls of hollow organs, controlling internal movements.
- Cardiac Muscle: Involuntary muscle found in the heart, responsible for heart contractions.
Muscle Appearance
- Skeletal Muscle: Long, thread-like cells with striations and multiple nuclei.
- Smooth Muscle: Spindle-shaped cells without striations, containing a single centrally located nucleus.
- Cardiac Muscle: Striated, branching cells with a single nucleus, connected by intercalated disks.
Muscle Functions
- Movement: Muscle contraction allows all body movement, including locomotion, manipulation of objects, and circulation of blood.
- Posture Maintenance: Skeletal muscles continuously contract and relax to maintain posture, known as muscle tone.
- Joint Stability: Muscles pull on bones, stabilizing joints and providing extra stability for certain joints like the shoulder.
- Heat Generation: Muscle contractions produce heat, essential for maintaining normal body temperature.
- Guarding Entrances/Exits: Muscles guard openings in the urinary and digestive systems, providing voluntary control over processes like swallowing, urination, and defecation.
Muscle as an Organ
- Muscles are organs composed of different tissues working together.
- Muscle cells contain myofibrils, composed of actin (thin) and myosin (thick) filaments.
- Myosin cross-bridges link with actin filaments, generating force for muscle contraction.
- Muscle contraction requires calcium ions and ATP.
- Acetylcholine is a neurotransmitter that stimulates muscle fibers, triggering a muscle impulse and calcium release.
- The calcium pump actively removes calcium, breaking the actin-myosin links and causing muscle relaxation.
- Cholinesterase breaks down acetylcholine, preventing continued muscle stimulation.
Calcium in Muscle Contraction
- Calcium initiates muscle contraction by facilitating the interaction between actin and myosin filaments.
Threshold Stimulus and All-or-None Principle
- The threshold stimulus is the minimum strength needed to cause a muscle contraction.
- Muscle fibers follow the all-or-none principle: a muscle fiber will contract fully or not at all in response to a threshold stimulus.
- A motor unit consists of a motor neuron and all the muscle fibers it innervates.
- Stimulation of a motor unit causes all its muscle fibers to contract.
- Muscles with fine motor control have smaller motor units, while larger muscles have larger motor units.
Exercise and Muscle Tissue
- Atrophy: Decrease in muscle size and strength due to lack of use.
- Hypertrophy: Increase in muscle size and strength due to exercise and stress.
Major Muscle Locations
- Head and Neck: Masseter, temporalis, trapezius, sternocleidomastoid.
- Trunk: Abdominals, pectoralis major.
- Upper Extremities: Biceps, triceps, deltoid, lattisimus dorsi.
- Lower Extremities: Iliopsoas, gluteus maximus, adductors, hamstrings, quadriceps, calcaneal tendon.
Muscles of the Jaw, Neck, Shoulder, Elbow, Wrist, Hip, Knee, and Ankle
- Gluteus Maximus:*
- Longest and most superficial buttock muscle.
- Involved in thigh extension.
- Gluteus Medius:*
- Large, thick muscle located beneath the gluteus maximus.
- Responsible for thigh abduction.
- Gluteus Minimus:*
- Smallest and deepest buttock muscle.
- All three gluteal muscles work together to strengthen the buttock area.
Diaphragm Structure and Function
- The diaphragm is a sheet-like muscle separating the thoracic and abdominal cavities.
- It contracts involuntarily, controlled by the phrenic nerve.
- Contraction pulls the diaphragm down, increasing the size of the thoracic cavity, which aids in inspiration (breathing in).
- Relaxation allows the diaphragm to spring back up, decreasing the size of the thoracic cavity, which aids in expiration (breathing out).
Hiatus
- Hiatus refers to an opening.
- The esophageal hiatus allows the esophagus, vena cava, and aorta to pass through the diaphragm.
Abdominal Muscle Organization
- Abdominal muscles are flat and layered, connecting to the ribs, vertebral column, and linea alba.
- Contraction of these muscles decreases the abdominal cavity size, increasing internal pressure.
- This helps with functions like:
- Expiration
- Defecation
- Urination
- Vomiting
- Childbirth
Inguinal Canals
- Bilateral structures in the groin.
- Formed during fetal development.
- Allow the testes to descend into the scrotum in males.
- Contain nerves, blood vessels, and the round ligament of the uterus in females.
- Contribute to the strength of the abdominal wall, but can be a site for hernias.
Pelvic Floor Muscles
- Muscles supporting pelvic viscera, including:
- Levator ani
- Superficial transverse perineus
- Bulbospongiosus
- Ischiocavernosus
- Levator ani forms the pelvic diaphragm, supporting pelvic organs and aiding in increasing abdominal pressure.
- The pelvic floor is pierced by the rectum, urethra, and vagina (in females).
- Ischiocavernosus and bulbospongiosus muscles contribute to erection of the penis and clitoris.
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Description
Test your knowledge on muscle characteristics and the different types of muscle tissue. This quiz covers the essential features, functions, and appearances of skeletal, smooth, and cardiac muscles. Dive in to see how well you understand the muscular system!
