Skeletal Muscle Functions and Tissue Organization

Functions of Skeletal Muscle

• Skeletal muscles are responsible for movement.
• Skeletal muscles contribute to heat production.
• Skeletal muscles aid in joint stability.
• Skeletal muscles also regulate blood sugar and control body openings and passages.
• Vitamin D synthesis is carried out by the skin, liver, and kidneys, not skeletal muscle.

Muscle Tissue Organization

• Endomysium is the loose connective tissue layer that surrounds each individual muscle cell (muscle fiber).
• The fascia separates groups of muscles from each other and subcutaneous tissue.
• Perimysium bundles muscle fibers into fascicles.
• Epimysium covers the entire muscle.

Tendons

• Tendons are connective tissue structures that attach muscle to bone.

Muscle Roles

• Agonist (or prime mover) is a muscle that produces most of the force during a particular joint action.
• Antagonists oppose the action of the prime mover.
• Fixators hold a bone still during a particular action.
• A synergist aids the prime mover.

Muscle Terminology

• "Brevis" means short in the name of a muscle.

Facial Muscles

• The zygomaticus major and minor elevate the angle of the mouth.
• The temporalis, masseter, and medial pterygoid elevate the mandible.
• The orbicularis oculi closes the eye.
• The buccinator compresses the cheek.

Neck Muscles

• The sternocleidomastoid is a muscle in the neck.
• Contraction of the right sternocleidomastoid turns the head toward the left, which is contralateral movement.
• Simultaneous contraction of the right and left sternocleidomastoids draws the head straight forward and down, which is bilateral movement.
• Contraction of the left scalene muscles tilts the head toward the left shoulder, which is ipsilateral movement.
• The trapezius muscle also stabilizes the scapula during arm movements and has an attachment to the external occipital protuberance.

Trunk Muscles

• The diaphragm forms a dome between the thoracic and abdominal cavities.
• The rectus abdominis, transverse abdominal, and abdominal obliques are located in the anterior abdominal wall.
• Erector spinae is a deep muscle of the back that runs vertically from the cranium to the sacrum, and is used to straighten the back after bending.

Upper Limb Muscles

• The brachialis is the prime mover in flexing the elbow.
• The triceps brachii is the prime mover of elbow extension and is a three-headed muscle on the posterior side of the humerus.
• The brachioradialis is located on the lateral side of the forearm and it flexes the elbow.
• The deltoid is a prominent scapular muscle that can move the arm in many different ways; its actions include medially rotating the arm, abducting the arm, flexing the arm, and laterally rotating the arm.
• The extensor digitorum extends the digits and also extends the wrist and fingers.
• The biceps brachii supinates the forearm and acts as a synergist in elbow flexion. The triceps brachii extends the elbow. The palmaris longus anchors the skin and fascia of the palmar region.

Rotator Cuff Muscles

• Tendons of the subscapularis, teres minor, supraspinatus and infraspinatus muscles help form the rotator cuff.

Lower Limb Muscles

• The quadriceps femoris is located in the anterior thigh and its action is the extension of the knee.
• Vastus medialis, rectus femoris, vastus lateralis, and vastus intermedius all insert on the tibial tuberosity.
• The flexors of the knee are found in the posterior compartment of the thigh.
• The adductor muscles of the thigh are found in the medial compartment.
• Gracilis flexes and medially rotates the tibia at the knee.
• Gluteus maximus is the largest of the gluteal muscles and it extends and abducts the thigh at the hip. It is active in stair climbing, running, and elevation of the trunk after stooping, and is a large posterior thigh muscle.
• Soleus is a broad, flat calf muscle located deep to the gastrocnemius, and is located in the posterior leg.
• Gastrocnemius actions include plantar flexion of the foot and flexion of the knee.

Knee Joint

• The patellar ligament connects the kneecap to the tibial tuberosity.