Anatomy: Skeletal Muscles (Locations & Functions) Flashcards
Sarcolemma
Function: Encloses the muscle fiber and conducts action potentials.
Origin: Derived from the plasma membrane of muscle cells.
Location: Surrounds each muscle fiber (cell).
Sarcoplasm
Function: Site of metabolic processes and contains organelles and myofibrils.
Origin: The cytoplasm of muscle cells.
Location: Inside the muscle fiber.
Mitochondrion
Function: Produces ATP through aerobic respiration.
Origin: Organelle found in eukaryotic cells.
Location: Scattered throughout the sarcoplasm of muscle fibers.
Sarcoplasmic Reticulum
Function: Stores and releases calcium ions (Ca²⁺) during muscle contraction.
Origin: Specialized form of endoplasmic reticulum in muscle cells.
Location: Surrounds myofibrils within the muscle fiber.
Myofibril
Function: Contains the contractile elements (sarcomeres) responsible for muscle contraction.
Origin: Composed of myofilaments (actin and myosin).
Location: Runs parallel within the muscle fiber.
Nucleus
Function: Contains genetic material and regulates cellular activities, including protein synthesis.
Origin: Found in all eukaryotic cells.
Location: Typically located at the periphery of the muscle fiber.
Striation
Function: Indicates the organized arrangement of muscle fibers and contractile proteins.
Origin: Result of alternating thick (myosin) and thin (actin) filaments.
Location: Visible across myofibrils and muscle fibers under a microscope.
Triad
Function: Facilitates rapid transmission of action potentials and calcium release.
Origin: Formed by two terminal cisternae and one transverse tubule.
Location: At the junction of the A and I bands in the myofibrils.
Terminal Cisternae
Function: Stores calcium ions and releases them during muscle contraction.
Origin: Extensions of the sarcoplasmic reticulum.
Location: Flank the T-tubules in the triad structure.
Transverse Tubule (T-tubule)
Function: Transmits action potentials deep into the muscle fiber.
Origin: Extensions of the sarcolemma.
Location: Penetrates into the muscle fiber at the junction of the A and I bands.
Endomysium
Function: Surrounds and supports individual muscle fibers.
Origin: Layer of connective tissue.
Location: Within a muscle, surrounding each muscle fiber.
Perimysium
Function: Surrounds and organizes bundles of muscle fibers (fascicles).
Origin: Connective tissue layer.
Location: Between individual fascicles within a muscle.
Epimysium
Function: Surrounds the entire muscle, providing support and protection.
Origin: Outer layer of connective tissue.
Location: Envelops the entire muscle.
Fascicle
Function: A bundle of muscle fibers that allows for organized structure and efficient force generation.
Origin: Group of muscle fibers surrounded by perimysium.
Location: Found within a muscle, grouped together to form the muscle.
Synergist
Function/Action: Assists the prime mover (agonist) by providing additional force or by reducing undesirable movements.
Definition: A muscle that works together with another muscle to enhance its effect.
Example: The brachialis acts as a synergist to the biceps brachii during elbow flexion.
Fixator
Function/Action: Stabilizes the origin of the agonist so that it can act more efficiently.
Definition: A muscle that prevents unwanted movement at a joint.
Example: The rotator cuff muscles stabilize the shoulder during arm movements.
Antagonist
Function/Action: Opposes or reverses a particular movement of the agonist.
Definition: A muscle that acts in opposition to the agonist.
Example: The triceps brachii is an antagonist to the biceps brachii during elbow flexion
Agonist (Prime Mover)
Function/Action: The main muscle responsible for a specific movement.
Definition: A muscle that is primarily responsible for movement.
Example: The biceps brachii is the agonist during elbow flexion.
Epicranius (Occipitofrontalis)
Function/Action: Raises eyebrows and wrinkles the forehead.
Temporalis
Function/Action: Elevates and retracts the mandible (closes the jaw).
Origin: Temporal fossa.
Insertion: Coronoid process of the mandible.
Masseter
Function/Action: Elevates the mandible (primary muscle for jaw closure).
Origin: Zygomatic arch and maxilla.
Insertion: Angle and ramus of the mandible.
Frontalis (Frontal Belly of the epicranius)
Action: Elevates eyebrows, pullls scalp forward
Origin: Top of the forehead or forehead area. (cranial aponeurosis).
Insertion: Skin of eyebrows and root of the nose.
Orbicularis Oculi
Function/Action: Closes eyelids; enables blinking and squinting.
Origin: Frontal and maxillary bones.
Insertion: Skin of the eyelid.
Occipitalis (Occipital Belly)
Function: Pulls scalp backwards (raises eyebrows)
Origin: Occipital bone
Insertion: epicranial neurosis
Orbicularis Oris
Function/Action: Closes and protrudes lips (kissing muscle).
Origin: Indirectly from maxilla and mandible.
Insertion: Encircles mouth; inserts into the muscle and skin at the angles of the mouth.
Zygomaticus
Function/Action: Raises lateral corners of the mouth (smiling).
Origin: Zygomatic bone.
Insertion: Skin and muscle at the corner of the mouth.
Levator Anguli Oris
Function/Action: Elevates the angle of the mouth (smiling).
Origin: Maxilla.
Insertion: Lips
Buccinator
Function/Action: Compresses the cheek (as in whistling or sucking).
Origin: Molar region of maxilla and mandible.
Insertion: Cheeks
Risorius
Function/Action: Draws the corner of the lip laterally.
Origin: Fascia of masseter muscle.
Insertion: Skin at the corner of the mouth.
Depressor Labii Inferioris
Function/Action: Lowers the lower lip.
Origin: Mandible.
Insertion: Skin of lower lip.
Depressor Anguli Oris
Function/Action: Draws the corners of the mouth downward (frowning).
Origin: Mandible.
Insertion: Skin and muscle at the angle of the mouth.
Mentalis
Function/Action: Protrudes the lower lip and wrinkles the chin.
Origin: Mandible.
Insertion: Skin of the chin.
Thyrohyoid
Function/Action: Swallowing
Origin: Thyroid cartilage of the larynx.
Insertion: Hyoid bone.
Mylohyoid
Function/Action: Aids in swallowing, elevates the tongue, speech
Origin: Mylohyoid line of the mandible.
Insertion: Hyoid bone.