Muscular System-II

Muscular System Overview

Course Information

• MCB 244 Anatomy and Physiology, Fall 2024

• Instructor: Dr. Bharathi Aravamudan

• Focus: Muscular System Part II

Learning Outcomes

At the conclusion of this lecture, students should be able to:

• Compare and contrast proximal and distal muscle attachments.

• Describe organizational patterns in muscle fascicles.

• Differentiate between agonists, antagonists, and synergists.

• Understand characteristics of muscles that inform their names with examples.

• Identify muscles involved in facial expression, extrinsic eye movements, mastication, tongue movements, neck actions, vertebral column movements, respiration, and abdominal wall organization.

Axial and Appendicular Muscles

Axial Muscles

• Origins and insertions are on the axial skeleton.

• Functions: support and move head/vertebral column, contribute to facial expression, breathing, chewing, swallowing, and protect abdominal/pelvic organs.

Appendicular Muscles

• Control movements of upper/lower limbs and pectoral/pelvic girdles.

• Organized by location.

Organizational Patterns of Muscle Fibers

• Parallel Muscles: Fascicles run parallel to muscle’s long axis; high endurance.

• Circular Muscles: Fascicles arranged concentrically; control passage through openings.

• Convergent Muscles: Fascicles merge at a common site; pull in various directions.

• Pennate Muscles: Fascicles organized like a feather for more tension but less distance; variants include unipennate, bipennate, and multipennate.

Actions of Skeletal Muscles

• Agonist: Prime mover (e.g., triceps brachii in forearm extension).

• Antagonist: Opposes the agonist (e.g., biceps brachii in forearm extension).

• Synergist: Assists the agonist (e.g., biceps brachii and brachialis in elbow flexion).

Naming of Skeletal Muscles

Muscles are named based on:

• Muscle Action: e.g., flexor digitorum (flexes digits).

• Body Regions: e.g., rectus femoris (near femur).

• Attachments: e.g., sternocleidomastoid (originates on sternum/clavicle).

• Orientation: e.g., rectus abdominis (vertical fibers).

• Shape: e.g., deltoid (triangular).

• Size: e.g., gluteus maximus (largest buttock muscle).

• Number of Heads: e.g., triceps brachii (three heads).

Muscles of Facial Expression

• Generally attach to subcutaneous layer beneath the skin.

• Responsible for various facial expressions and primarily innervated by the facial nerve (CN VII).

Specific Muscles

• Forehead & Eyebrows: Occipitofrontalis (raises eyebrows).

• Eyelids: Orbicularis oculi (closes eye).

• Nose: Nasalis (flared nostrils).

• Mouth: Orbicularis oris (closes lips).

Clinical View: Face and Eye

• Bell Palsy: Unilateral facial paralysis due to facial nerve issues, leading to asymmetry.

• Extrinsic Eye Muscles: Six muscles control eye movement; innervated primarily by oculomotor (CN III) and abducens (CN VI).

Muscles of Mastication & Tongue

• Muscles that move the mandible are primarily innervated by the trigeminal nerve (CN V). Main muscles include temporalis and masseter.

• Tongue movements are performed by intrinsic muscles and several extrinsic muscles like genioglossus and hyoglossus, mainly innervated by the hypoglossal nerve (CN XII).

Neck Muscles

• Suprahyoid Muscles: Elevate hyoid during swallowing.

• Infrahyoid Muscles: Depress hyoid or thyroid cartilage.

• Major Movement Muscles: Sternocleidomastoid and scalene muscles flex or rotate neck.

Muscles of Respiration

• The diaphragm is the primary muscle during breathing, expanding the thoracic cavity.

• Intercostal Muscles: Elevate ribs for inhalation and depress ribs for exhalation.

Muscles of the Abdominal Wall

• Comprise external oblique, internal oblique, transversus abdominis, and rectus abdominis. They stabilize and compress abdominal organs as well as flex the vertebral column.

Clinical View: Hernias

• Hernias occur when parts of abdominal organs protrude through weak points, often in the inguinal region, requiring medical attention.