Review Sheet 13 Gross Anatomy Of The Muscular System

Review Sheet 13: Gross Anatomy of the Muscular System

This comprehensive review sheet covers the gross anatomy of the muscular system, providing a detailed overview of major muscle groups, their origins, insertions, actions, and innervation. Understanding this intricate system is crucial for anyone studying anatomy, physiology, or related fields. We'll explore the muscles systematically, focusing on key features and clinically relevant information. Remember, this is a review sheet—it assumes prior exposure to the material. Use it to consolidate your knowledge and identify areas needing further study.

Head and Neck Muscles

The muscles of the head and neck are complex, responsible for facial expression, mastication (chewing), and head movement.

Facial Expression Muscles

These muscles are innervated by the facial nerve (CN VII) and are responsible for a wide range of expressions. Key examples include:

• Orbicularis oculi: Closes the eyelids.
• Orbicularis oris: Compresses and puckers the lips.
• Zygomaticus major: Elevates the corner of the mouth (smiling).
• Buccinator: Compresses the cheeks (blowing, whistling).
• Frontalis: Raises the eyebrows (surprise).

Mastication Muscles

These muscles are involved in chewing and are primarily innervated by the mandibular division of the trigeminal nerve (CN V3).

• Masseter: Powerful elevator of the mandible.
• Temporalis: Elevates and retracts the mandible.
• Medial pterygoid: Elevates and protracts the mandible.
• Lateral pterygoid: Protracts and depresses the mandible, also contributes to lateral movement.

Neck Muscles

These muscles are involved in head movement and stabilization. Innervation varies depending on the muscle.

• Sternocleidomastoid: Flexes the neck, rotates the head to the opposite side. Innervated by spinal accessory nerve (CN XI) and C2-C3.
• Trapezius: Elevates, depresses, retracts, and rotates the scapula. Innervated by spinal accessory nerve (CN XI) and C3-C4.

Muscles of the Upper Limb

The upper limb muscles are categorized into those of the shoulder, arm, forearm, and hand. They facilitate a wide range of movements, from gross motions like lifting to fine motor skills like writing.

Shoulder Muscles

These muscles control the movement of the scapula and humerus. Innervation varies.

• Deltoid: Abducts, flexes, and extends the humerus. Innervated by axillary nerve (C5-C6).
• Rotator cuff muscles (SITS): Supraspinatus (abduction), infraspinatus (external rotation), teres minor (external rotation), subscapularis (internal rotation). Innervated by suprascapular, axillary, and subscapular nerves.
• Pectoralis major: Flexes, adducts, and medially rotates the humerus. Innervated by medial and lateral pectoral nerves (C5-T1).
• Latissimus dorsi: Extends, adducts, and medially rotates the humerus. Innervated by thoracodorsal nerve (C6-C8).

Arm Muscles

These muscles primarily act on the elbow and forearm.

• Biceps brachii: Flexes the elbow and supinates the forearm. Innervated by musculocutaneous nerve (C5-C7).
• Brachialis: Flexes the elbow. Innervated by musculocutaneous nerve (C5-C7).
• Brachioradialis: Flexes the elbow. Innervated by radial nerve (C5-C6).
• Triceps brachii: Extends the elbow. Innervated by radial nerve (C7-C8).

Forearm Muscles

The forearm muscles are divided into anterior (flexor) and posterior (extensor) compartments. They control wrist, hand, and finger movements. Innervation is primarily by the radial, median, and ulnar nerves. Detailed study of individual forearm muscles is crucial, and involves understanding their specific actions and innervation. This requires careful examination of anatomical texts and potentially atlases.

Hand Muscles

The intrinsic muscles of the hand are responsible for fine motor control of the fingers and thumb. These are innervated by the median and ulnar nerves. Understanding the complex interplay of these muscles is critical for comprehending hand function.

Muscles of the Lower Limb

The lower limb muscles are responsible for locomotion, balance, and support. They are grouped into muscles of the hip, thigh, leg, and foot.

Hip Muscles

These muscles control movement at the hip joint.

• Gluteus maximus: Extends and laterally rotates the thigh. Innervated by inferior gluteal nerve (L5-S2).
• Gluteus medius: Abducts and medially rotates the thigh. Innervated by superior gluteal nerve (L4-S1).
• Gluteus minimus: Abducts and medially rotates the thigh. Innervated by superior gluteal nerve (L4-S1).
• Iliopsoas: Flexes the hip. Innervated by branches of lumbar plexus (L1-L3).
• Adductor group: Adducts the thigh. Innervated by obturator nerve (L2-L4).

Thigh Muscles

The thigh muscles are divided into anterior (extensor), medial (adductor), and posterior (flexor) compartments.

• Quadriceps femoris (anterior): Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius. Extends the knee. Innervated by femoral nerve (L2-L4).
• Hamstrings (posterior): Biceps femoris, semitendinosus, semimembranosus. Flexes the knee and extends the hip. Innervated by sciatic nerve (L4-S3).
• Adductor group (medial): Adducts the thigh. Innervated by obturator nerve (L2-L4).

Leg Muscles

The leg muscles are similarly divided into anterior (dorsiflexors), lateral (eversion), and posterior (plantarflexors) compartments. These muscles control ankle and toe movements. They are innervated by the tibial and common fibular nerves.

Foot Muscles

The intrinsic muscles of the foot are responsible for fine control of toe movement. These are innervated by the tibial and deep fibular nerves. Understanding the actions of these muscles requires careful attention to anatomical details.

Clinical Correlations

Understanding the muscular system is essential for diagnosing and treating a variety of clinical conditions. Examples include:

• Rotator cuff tears: Injuries to the rotator cuff muscles are common in athletes and can lead to shoulder pain and weakness.
• Carpal tunnel syndrome: Compression of the median nerve in the carpal tunnel can cause pain, numbness, and tingling in the hand.
• Muscle strains: Overstretching or tearing of muscle fibers can occur during physical activity.
• Muscular dystrophy: A group of inherited diseases that cause progressive muscle weakness and degeneration.
• Myasthenia gravis: An autoimmune disease that causes muscle weakness and fatigue.

Further Study and Resources

This review sheet provides a foundation for understanding the gross anatomy of the muscular system. For a deeper understanding, refer to:

• Detailed anatomical textbooks: These provide comprehensive descriptions of individual muscles, their origins, insertions, actions, and innervation.
• Anatomical atlases: These offer visual representations of the muscular system, facilitating better comprehension of muscle relationships and spatial arrangements.
• Online resources: Several reputable websites and online anatomical databases offer interactive models and quizzes.

Remember that consistent review and active recall are vital for mastering this complex subject. Use this sheet as a springboard for further exploration and reinforce your understanding through practice and application. This rigorous approach will strengthen your knowledge and prepare you for any assessments.