Muscular System Overview

This study guide covers concepts related to the muscular system, including muscle groups, fascicle arrangements, shapes, lever systems, and specific muscles of the body.

Muscle Concepts and Relationships

Origins and Insertions

• Biceps Brachii:
    - Origin: Scapula
    - Insertion: Radial tuberosity
• Triceps Brachii:
    - Origin: Scapula and humerus
    - Insertion: Olecranon process of ulna

Muscle Actions

• Flexion and Extension:
    - Flexion: Decreasing the angle between body parts, such as bending the arm at the elbow.
    - Extension: Increasing the angle, straightening the arm.

Muscle Groups and Functions

Classification of Muscles

1. Agonist (Prime Mover): A muscle that causes the desired action.
2. Antagonist: A muscle that opposes the action of the agonist.
3. Synergists: Muscles that assist the agonist in performing the desired action.
4. Fixators: Muscles that stabilize joints crossed by the prime mover to allow for effective movement.

Effects of Fascicle Arrangement

• Short Fascicles:
    - Contract quickly when stimulated.
    - Increased force generation, but limited range of motion.
• Long Fascicles:
    - Contract more slowly.
    - Decreased force generation but greater range of motion.

Muscle Shapes

• Parallel: Muscles arranged in parallel lines.
• Fusiform: A spindle-shaped muscle (e.g., biceps).
• Convergent: Broad origin and converges toward a single tendon (e.g., pectoralis major).
• Unipennate: Fascicles arranged on one side of the tendon (e.g., extensor digitorum).
• Bipennate: Fascicles on both sides of a central tendon (e.g., rectus femoris).
• Multipennate: Fascicles arranged in multiple directions around several tendons (e.g., deltoid).
• Circular: Muscles arranged in concentric rings (e.g., orbicularis oris).

Lever Systems

Muscles work within the body as part of lever systems:

• Parts of a lever system:
    - Lever: Rigid shaft (bone)
    - Fulcrum: Pivot point (joint)
    - Weight/Resistance: Force of gravity acting on the body part.
• Muscle contractions are always pulling forces.

Classes of Levers

1. Class I: Fulcrum is between the pull and the weight (e.g., seesaw, head movement at atlantooccipital joint).
2. Class II: Weight lies between the fulcrum and the pull (e.g., standing on toes, wheelbarrow).
3. Class III: Pull is between the fulcrum and the weight (most common lever in the body, e.g., biceps brachii with elbow as fulcrum).

Muscles Acting on the Face

Orbicularis Oculi

• Origin: Medial wall of the orbit
• Insertion: Medial wall of the orbit
• Action: Closes the eyelid
• Shape: Circular

Orbicularis Oris

• Origin: Opening of the mouth
• Insertion: Skin at the corners of the mouth
• Action: Closes the mouth
• Shape: Circular

Zygomaticus Major

• Origin: Zygomatic bone
• Insertion: Skin at the corners of the mouth and orbicularis oris
• Action: Elevates the corners of the mouth (smiling)
• Shape: Parallel

Depressor Anguli Oris

• Origin: Anterior 1/3 body of the mandible
• Insertion: Angle of the mouth
• Action: Depresses the corners of the mouth (frowning)
• Shape: Triangular

Muscles That Move the Head

Sternocleidomastoid

• Origin: Manubrium of the sternum and medial end of the clavicle
• Insertion: Mastoid process of the temporal bone
• Action: Flexion of cervical vertebrae and rotation of head to the opposite side
• Shape: Fusiform

Muscles Used in Breathing

Diaphragm

• Origin: Xiphoid process, costal cartilages of the last six ribs, and lumbar vertebrae
• Insertion: Central tendon of the diaphragm
• Action: Primarily responsible for respiration; contraction causes inspiration, relaxation allows expiration

External Intercostals

• Origin: Inferior border of the superior rib
• Insertion: Superior border of inferior rib
• Action: Elevation of the rib cage during inspiration
• Shape: Parallel

Internal Intercostals

• Origin: Superior border of the inferior rib
• Insertion: Inferior border of superior rib
• Action: Depression of the rib cage during expiration
• Shape: Parallel

Muscles of the Abdominal Wall

Rectus Abdominis

• Origin: Pubic crest and symphysis pubis
• Insertion: Costal cartilages of ribs 5, 6, and 7
• Action: Flexion of the vertebral column
• Shape: Parallel

External Obliques

• Origin: Last eight ribs
• Insertion: Iliac crest and linea alba
• Action: Flexion of the vertebral column; unilateral action causes lateral flexion
• Shape: Parallel

Internal Obliques

• Origin: Iliac crest, inguinal ligament, thoracolumbar fascia
• Insertion: Costal cartilages of last four ribs and linea alba
• Action: Flexion of the vertebral column; unilateral action causes lateral flexion

Pectoral Girdle Muscles (Anterior & Posterior)

Pectoralis Minor

• Origin: Ribs 3 through 5
• Insertion: Coracoid process of the scapula
• Action: Protraction of the scapula
• Shape: Triangular

Trapezius (Posterior)

• Origin: Occipital bone and spinous processes of C7 through T12
• Insertion: Lateral 1/3 of the clavicle, acromion, and spine of the scapula
• Action: Stabilizes scapula, elevation, retraction, and depression of the scapula

Shoulder Joint Muscles

Subscapularis

• Origin: Subscapular fossa of the scapula
• Insertion: Lesser tubercle of the humerus
• Action: Medial rotation of the humerus
• Shape: Triangular

Supraspinatus

• Origin: Supraspinous fossa of the scapula
• Insertion: Greater tubercle of the humerus
• Action: Weak ABduction of the shoulder joint
• Shape: Triangular

Elbow Joint Muscles (Anterior)

Biceps Brachii

• Origin:
    - Long head: Supraglenoid tubercle
    - Short head: Coracoid process of scapula
• Insertion: Radial tuberosity of the radius
• Action: Flexion of the elbow joint
• Shape: Fusiform

Triceps Brachii

• Origin:
    - Long head: Infraglenoid tubercle
    - Lateral head: Lateral, posterior surface of the humerus
    - Medial head: Posterior surface of the humerus
• Insertion: Olecranon of the ulna
• Action: Extension of the elbow joint
• Shape: Fusiform

Hip Joint Muscles

Iliopsoas

• Iliacus:
    - Origin: Iliac fossa and sacrum
    - Insertion: Lesser trochanter of the femur
    - Action: Flexion of the hip joint
    - Shape: Triangular
• Psoas Major:
    - Origin: Transverse processes and bodies of L1 to L5
    - Insertion: Lesser trochanter of the femur
    - Action: Flexion of the hip joint
    - Shape: Triangular

Gluteus Maximus

• Origin: Iliac crest, sacrum, and coccyx
• Insertion: Gluteal tuberosity of the femur
• Action: Extension of the hip joint
• Shape: Triangular

Knee Joint Muscles

Quadriceps Femoris

• Musculature: Composed of four muscles:
    1. Rectus Femoris:
       - Origin: Anterior inferior iliac spine (AIIS)
       - Insertion: Tibial tuberosity via patellar ligament
       - Action: Extension of the knee joint
       - Shape: Fusiform
    2. Vastus Lateralis:
       - Origin: Greater trochanter and linea aspera of the femur
       - Insertion: Tibial tuberosity via patellar ligament
       - Action: Extension of the knee joint
    3. Vastus Medialis:
       - Origin: Linea aspera of the femur
       - Insertion: Tibial tuberosity via patellar ligament
       - Action: Extension of the knee joint
       - Shape: Fusiform
    4. Vastus Intermedius:
       - Origin: Anterior and lateral surfaces of shaft of femur
       - Insertion: Tibial tuberosity via patellar ligament
       - Action: Extension of the knee joint

Hamstrings

• Biceps Femoris:
    - Origin:
       - Long head: Ischial tuberosity
       - Short head: Linea aspera of the femur
    - Insertion: Lateral condyle of tibia and head of fibula
    - Action: Flexion of the knee joint
    - Shape: Fusiform
• Semitendinosus:
    - Origin: Ischial tuberosity
    - Insertion: Medial surface of proximal shaft of tibia
    - Action: Flexion of the knee joint
    - Shape: Fusiform
• Semimembranosus:
    - Origin: Ischial tuberosity
    - Insertion: Medial condyle of tibia
    - Action: Flexion of the knee joint
    - Shape: Fusiform

Ankle and Toes Muscles

Tibialis Anterior

• Origin: Lateral condyle and shaft of the tibia
• Insertion: First metatarsal and medial cuneiform
• Action: Dorsiflexion of the ankle joint
• Shape: Unipennate

Gastrocnemius

• Origin: Medial and lateral condyles of the femur
• Insertion: Calcaneus by way of the Achilles tendon
• Action: Plantar flexion of the ankle joint
• Shape: Bipennate

Soleus

• Origin: Head of the fibula and medial shaft of the tibia
• Insertion: Calcaneus by way of the Achilles tendon
• Action: Plantar flexion of the ankle joint
• Shape: Unipennate

This comprehensive study guide captures the essential details and concepts related to the muscular system as covered in the lecture. Use it to deepen your understanding of muscular anatomy, function, and mechanics.