Describe the functions, characteristics, and attachments of skeletal muscles.

Here are the answers based on the objectives listed in the image:

a) The functions of muscles are:

• Movement: Skeletal muscles contract to move bones, allowing for locomotion and manipulation of objects. Cardiac muscle pumps blood, and smooth muscle moves substances through internal organs.
• Maintain Posture: Sustained contractions of skeletal muscles maintain body position against gravity.
• Joint Stability: Muscle tendons crossing joints contribute to their stability.
• Heat Production: Muscle contraction generates heat, which helps maintain body temperature.

b) The special features (characteristics) of skeletal muscles are:

• Excitability (Responsiveness): The ability to respond to stimuli by producing electrical signals (action potentials).
• Contractility: The ability to shorten forcefully when stimulated, generating tension.
• Extensibility: The ability to stretch or extend without being damaged.
• Elasticity: The ability to return to their original length and shape after contraction or extension.

c) The attachments of skeletal muscles involve:

• Tendons: Most skeletal muscles attach to bones via strong, cord-like structures made of dense regular connective tissue.
• Origin: The attachment of a muscle to the stationary bone or the less movable bone.
• Insertion: The attachment of a muscle to the movable bone. When the muscle contracts, the insertion is pulled towards the origin.

d) The different directions (arrangements) of skeletal muscle fibers (fascicles) include:

• Parallel: Fascicles are parallel to the longitudinal axis of the muscle (e.g., biceps brachii).
• Fusiform: A type of parallel muscle with a spindle shape, wider in the middle and tapering at the ends (e.g., biceps brachii).
• Pennate: Fascicles are short and attach obliquely to a central tendon (e.g., rectus femoris - bipennate, deltoid - multipennate).
• Convergent: Fascicles spread out from a broad origin and converge to a single tendon (e.g., pectoralis major).
• Circular: Fascicles are arranged in concentric rings, forming sphincters (e.g., orbicularis oculi).

e) The mode of action of skeletal muscles involves:

• Contraction: Muscle contraction occurs via the sliding filament model, where myosin heads pull on actin filaments, causing the sarcomeres to shorten.
• Agonist (Prime Mover): The muscle primarily responsible for a specific movement.
• Antagonist: The muscle that opposes the action of the agonist, relaxing as the agonist contracts.
• Synergist: Muscles that assist the agonist by adding force or reducing unwanted movements.
• Fixator: A type of synergist that stabilizes the origin of the agonist so that the agonist can act more efficiently.

f) Skeletal muscles are named based on several criteria, including:

• Location: (e.g., temporalis muscle near the temporal bone).
• Shape: (e.g., deltoid for triangular, trapezius for trapezoid).
• Size: (e.g., gluteus maximus for largest, gluteus minimus for smallest).
• Direction of Fibers: (e.g., rectus abdominis for straight, external oblique for angled).
• Number of Origins: (e.g., biceps brachii for two heads, triceps brachii for three heads).
• Location of Attachments: (e.g., sternocleidomastoid attaches to sternum, clavicle, and mastoid process).
• Action: (e.g., flexor digitorum for flexing digits, adductor longus for adduction).

g) The nerve supply of skeletal muscles:

• Skeletal muscles are voluntarily controlled and are innervated by somatic motor neurons.
• Each motor neuron extends from the central nervous system to a group of muscle fibers.
• The point of communication between a motor neuron and a muscle fiber is called the neuromuscular junction.
• At the neuromuscular junction, the motor neuron releases the neurotransmitter acetylcholine (ACh), which binds to receptors on the muscle fiber, initiating an action potential and muscle contraction.