Questions and Answers
During contraction, a skeletal muscle insertion moves toward the origin.
True
What is the attachment called for a muscle that moves an attached bone?
Which of the following is NOT one of the types of ordinary body movements?
What is flexion?
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What is the opposite of flexion?
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What is rotation in terms of muscle movement?
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What does abduction refer to?
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What does adduction refer to?
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What is circumduction?
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What is dorsiflexion?
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Which muscle is responsible for pulling the corners of the mouth downward?
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Which muscle is primarily used in blinking and squinting?
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What is a prime mover muscle?
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What is the function of the fixator muscle?
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What do we call the muscle that opposes or reverses a prime mover?
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What does adhesion mean in the context of muscle movements?
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What is the muscular system responsible for?
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What are the three basic muscle types of the body?
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What are two characteristics of muscles?
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The prefixes MYO and MYS refer to _____ and SARCO refers to _____ in muscle terminology.
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What is a key characteristic of skeletal muscle?
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What are the connective tissue wrappings of skeletal muscle?
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What type of attachments can skeletal muscles have?
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Where can skeletal muscles attach?
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Which statement about smooth muscle is correct?
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What characterizes cardiac muscle?
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What are four functions of skeletal muscle?
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What is the sarcolemma?
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What does the sliding filament theory describe?
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What are graded responses?
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What causes muscle fatigue?
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What are the two types of muscle contractions?
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What is muscle tone?
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How does exercise affect muscles?
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List the 5 golden rules of skeletal muscle activity.
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Study Notes
Muscular System Overview
- Muscles are essential for all types of bodily movement.
- There are three basic muscle types: skeletal, cardiac, and smooth.
Muscle Characteristics
- Skeletal and smooth muscle cells are elongated and known as muscle fibers.
- Muscle contraction results from the movement of microfilaments.
Muscle Terminology
- "MYO" and "MYS" prefixes relate to muscles.
- The prefix "SARCO" refers to flesh.
Skeletal Muscle Features
- Most skeletal muscles attach to bones via tendons.
- Skeletal muscle cells are multinucleate and striated, exhibiting visible banding.
- Skeletal muscles are under voluntary control.
Connective Tissue Wrappings
- Connective tissue surrounds and bundles skeletal muscle cells:
- Endomysium: surrounds individual muscle fibers.
- Perimysium: wraps around a fascicle (bundle) of fibers.
- Epimysium: covers the entire muscle.
- Fascia: outside of the epimysium.
Types of Skeletal Muscle Attachments
- Epimysium merges into tendons (cord-like) or aponeuroses (sheet-like) for attachment.
- Tendons are primarily made of collagen fibers and traverse joints.
- Aponeuroses attach muscles indirectly to bones, cartilages, or other tissues.
Smooth Muscle Characteristics
- Lacks striations and features spindle-shaped cells with a single nucleus.
- Involuntary and primarily located in the walls of hollow organs.
- Arranged in two layers, contracting alternately to change organ size and shape.
Cardiac Muscle Characteristics
- Striated, single-nucleus cells that branch and are interconnected at intercalated discs.
- Found exclusively in the heart and is involuntary.
- Cushioned by endomysium and arranged in spiral bundles.
Functions of Skeletal Muscle
- Responsible for movement, posture maintenance, joint stabilization, and heat generation.
Microscopic Anatomy of Skeletal Muscle
- Sarcolemma: specialized plasma membrane of muscle cells.
- Myofibrils: long organelles housed within muscle cells.
- Sarcoplasmic reticulum: smooth endoplasmic reticulum that stores and releases calcium.
- Sarcomere: contractile unit of muscle fibers with distinct light (I band) and dark (A band) regions.
Myofilament Arrangement
- Thick filaments are composed of myosin; thin filaments consist of actin.
- Myosin heads form cross bridges with actin during contraction.
- H zone: area where actin filaments do not overlap with myosin at rest.
Muscle Cell Stimulation and Contraction
- Excitability allows muscle cells to respond to stimuli.
- Contractility refers to the muscle's ability to shorten upon stimulation.
- Extensibility and elasticity permit stretching and recoil of muscle fibers.
Nerve Stimulation and Action Potential
- Motor neurons stimulate skeletal muscles to contract.
- A motor unit comprises one motor neuron and the skeletal muscle fibers it activates.
- Neuromuscular junctions facilitate communication between nerve impulses and muscle cells.
Muscle Contraction Mechanism
- Acetylcholine (ACh) is the key neurotransmitter that binds to sarcolemma receptors, initiating muscle contraction.
- Sodium ions enter the cell, generating an action potential that triggers contraction.
Sliding Filament Theory
- Myosin heads attach to actin and pull them towards the sarcomere's center, resulting in muscle shortening.
Graded Responses in Muscle Contraction
- Muscle contractions can vary depending on the frequency of stimulation and the number of stimulated fibers.
- Graded responses include twitch (brief), tetanus (sustained), unfused (incomplete), and fused (complete) tetanus.
Muscle Strength and Energy
- Muscle force correlates to the number of fibers stimulated.
- Muscles use stored ATP for initial contraction; glucose breakdown produces more ATP through various pathways.
Energy Pathways
- Direct phosphorylation of ADP by creatine phosphate resynthesizes ATP quickly (lasting ~15 seconds).
- Aerobic respiration through glucose metabolism generates ATP efficiently when oxygen is available.
- Anaerobic glycolysis can produce ATP rapidly without oxygen but leads to lactic acid and muscle fatigue.
Muscle Fatigue and Oxygen Debt
- Fatigued muscles cannot contract despite stimuli; oxygen debt must be repaid to remove lactic acid.
- Low ATP levels and increased acidity contribute to reduced muscle contraction efficiency.
Types of Muscle Contractions
- Isotonic contractions allow movement as myofilaments slide past each other.
- Isometric contractions increase muscle tension without shortening or movement.
Muscle Tone
- Muscle tone is maintained through partial contraction of some fibers even at rest, providing stability.
Effects of Exercise on Muscles
- Regular exercise enhances muscle size, strength, and endurance.
- Aerobic exercise promotes flexibility, more effective metabolism, and improves organ efficiency.
- Resistance exercise increases muscle size due to hypertrophy of individual muscle cells.
Golden Rules of Skeletal Muscle Activity
- Most skeletal muscles cross at least one joint.
- The bulk of skeletal muscle lies proximal to the joint crossed.
- Skeletal muscles have at least two attachments: origin and insertion.
- Muscles can only pull, never push.### Muscle Contraction
- During contraction, skeletal muscle insertion moves toward the origin.
Muscle Attachments
- Muscles attach to at least two points, including an immoveable bone (origin) and a moveable bone (insertion).
Types of Ordinary Body Movements
- Flexion: Decreases the angle of the joint, bringing bones closer.
- Extension: Increases the angle between bones; hyperextension occurs beyond 180 degrees.
- Rotation: Movement around a bone's longitudinal axis, common in ball-and-socket joints.
- Abduction: Moving a limb away from the midline.
- Adduction: Moving a limb toward the midline.
- Circumduction: A circular motion combining flexion, extension, abduction, and adduction.
Special Movements
- Dorsiflexion: Lifting foot so toes approach the shin.
- Plantar Flexion: Pointing toes downward (depressing the foot).
- Inversion: Turning the sole of the foot medially.
- Eversion: Turning the sole of the foot laterally.
- Supination: Forearm rotation laterally, making radius and ulna parallel (palm faces anteriorly).
- Pronation: Forearm rotation medially, bringing the radius across the ulna (palm faces posteriorly).
- Opposition: Moving the thumb to touch other fingers.
Types of Muscles
- Prime Mover (Agonist): Major muscle responsible for a movement.
- Antagonist: Muscle opposing a prime mover; stretched and relaxed when the agonist acts.
- Synergist: Helper muscle that aids prime movers and prevents unwanted movements.
- Fixator: Stabilizes the origin of a prime mover.
Naming Skeletal Muscles
- Based on direction of fibers (e.g., "rectus" for straight).
- Relative size (e.g., "maximus" for largest).
- Location (e.g., "temporalis" for temporal bone).
- Number of origins (e.g., "triceps" for three heads).
- Origin and insertion locations (e.g., "sterno" for sternum).
- Muscle shape (e.g., "deltoid" for triangular).
- Action (e.g., "flexor" for flexing a bone).
Fascicle Arrangements
- Circular: Concentric rings, like sphincters (e.g., orbicularis).
- Convergent: Fascicles converge toward a single tendon (e.g., pectoralis major).
- Parallel: Length runs parallel to the muscle (straplike muscles).
- Fusiform: Spindle-shaped with an expanded belly (e.g., biceps brachii).
- Pennate: Fascicles attach obliquely to a central tendon, can be unipennate, bipennate, or multipennate.
Head and Neck Muscles
- Facial Muscles: Frontalis, orbicularis oculi, orbicularis oris, buccinator, zygomaticus.
- Chewing Muscles: Masseter, temporalis.
- Neck Muscles: Platysma, sternocleidomastoid.
Specific Muscles and Their Functions
- Frontalis: Raises eyebrows.
- Orbicularis Oculi: Closes eyes, squints, blinks.
- Orbicularis Oris: Closes mouth, protrudes lips.
- Masseter: Closes jaw, elevates mandible.
- Buccinator: Flattens cheek, assists in chewing.
- Sternocleidomastoid: Flexes neck, rotates head.
Muscles of the Trunk, Shoulder, and Arm
- Anterior Muscles: Pectoralis major, intercostals (external and internal).
- Abdominal Muscles: Rectus abdominis, external and internal obliques, transversus abdominis.
- Posterior Muscles: Trapezius, latissimus dorsi, erector spinae, quadratus lumborum, deltoid.
Muscles of the Upper Limb
- Biceps Brachii: Supinates forearm, flexes elbow.
- Triceps Brachii: Extends elbow (antagonist to biceps).
- Flexor and Extensor Muscles: Flexor carpi radialis, ulnaris, extensor carpi radialis, and digitorum.
Muscles of the Lower Limb
- Gluteus Maximus: Hip extension.
- Gluteus Medius: Hip abduction.
- Iliopsoas: Hip flexion; stabilizes upper body.
- Quadriceps Group: Extend knee; some also flex hip.
- Hamstring Muscles: Flex knee, extend hip.
- Gastrocnemius and Soleus: Plantar flex foot.
Fun Facts
- Zygomaticus: Used to grin.
- Buccinator: Important for playing saxophone.
- Orbicularis Oculi: Involved in blinking and squinting.
- Platysma: Contributes to expressions like the "sad clown."
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Explore the muscular system through this set of flashcards covering key concepts such as the types of muscles and their characteristics. This quiz is designed to reinforce your understanding of muscle function and structure in the human body.
