Muscle Anatomy Notes

Key Structures in Muscle Anatomy

• M Line

  • Dark area indicating the thick filaments in a myofibril.

• C Disc (Z line)

  • Area found in the thin part of the sarcomere; serves as the boundary between sarcomeres.

Muscle Types

• Active Muscle
  • Muscles that are engaged, such as the M line visible in a muscle contraction.
• I-line
  • Refers to the thin filaments in a muscle structure.

Muscle Structures and Coverings

• Myofibers
  • Bundles of myocytes, indicating a collection of muscle fibers.
• Endomysium
  • Connective tissue surrounding individual muscle fibers.

Tendons and Extrinsic vs Intrinsic Muscles

• Superior Oblique Muscle
  • Identified by its tendon passing across the medial area of the eye, important for eye movement.
• Extrinsic Muscles
  • Muscles originating outside of the target area but move the target. E.g., muscles of the eye and hand.
• Intrinsic Muscles
  • Muscles that originate and insert within the target area. E.g., the iris muscles of the eye and muscles in the hand.

Major Muscle Groups in Human Anatomy

Torso Muscles

• Trapezius
  • Major muscle around the neck and shoulders.
• Latissimus Dorsi
  • Sweeping muscle in the lower back area, involved in shoulder movement and rotation.
• Serratus Anterior
  • Located on the side, assists in the movement of the shoulder.
• Erector Spinae
  • Group of muscles responsible for maintaining an erect posture.
  • Divided into:
  • Iliocostalis
  • Longissimus
  • Spinalis

Abdominal Muscles

• Rectus Abdominis
  • Forms the front of the abdomen, contributes to flexion of the spine.
• Linea Alba
  • Connective tissue running down the middle of the abdomen, important in structuring the abdomen.
• Diaphragm
  • Critical muscle for respiration.
• Psoas
  • Provides support for sitting posture and spine stability.

Arm Muscles

• Biceps Brachii
  • Muscle with two heads, important for elbow flexion.
• Brachialis
  • Positioned under the biceps, contributes to elbow flexion.
• Triceps Brachii
  • Muscle with three heads, responsible for elbow extension.
• Brachioradialis
  • Muscle of the forearm, helps flex the elbow.

Leg Muscles

• Sartorius
  • Long muscle of the thigh, assists in crossing legs.
• Quadriceps
  • Group of four muscles that extend the knee:
  • Rectus Femoris
  • Vastus Lateralis
  • Vastus Medialis
  • Vastus Intermedius
• Hamstrings
  • Group of three muscles located at the back of the thigh, responsible for knee flexion:
  • Biceps Femoris
  • Semitendinosus
  • Semimembranosus

Calf Muscles

• Gastrocnemius
  • Major calf muscle involved in plantarflexion of the foot.
• Soleus
  • Underneath gastrocnemius; together they form the Achilles tendon.

Important Notes for Exam

• Use full names for muscles (e.g., Biceps Brachii, Triceps Brachii) in exams.
• Distinguish between intrinsic and extrinsic muscles, as it is critical for understanding muscle function in anatomy.