Muscle Anatomy: Thenar Muscles

Muscle Anatomy

• Location: Thenar muscles are located at the base of the thumb on the palm side of the hand.
• Muscles Included:
  1. Abductor Pollicis Brevis: Abducts the thumb.
  2. Flexor Pollicis Brevis: Flexes the thumb. Has two heads:
     • Superficial head
     • Deep head
  3. Opponens Pollicis: Allows opposition of the thumb (bringing the thumb across the palm).
  4. Adductor Pollicis: Adducts the thumb. Not technically a thenar muscle but closely related in function.

Nerve Innervation

• Median Nerve:
  • Supplies the abductor pollicis brevis, flexor pollicis brevis (superficial head), and opponens pollicis.
• Ulnar Nerve:
  • Supplies the flexor pollicis brevis (deep head) and adductor pollicis.

Functional Movements

• Abduction: Moving the thumb away from the palm (abductor pollicis brevis).
• Flexion: Bending the thumb towards the palm (flexor pollicis brevis).
• Opposition: Thumb movement to touch other fingers (opponens pollicis).
• Adduction: Moving the thumb back towards the index finger (adductor pollicis).

Muscle Relations

• Superficial Relationships: The thenar muscles are situated beneath the skin and superficial fascia of the palm.
• Deep Relationships:
  • Proximity to the carpal bones of the wrist.
  • The opponens pollicis lies deep to the abductor and flexor pollicis brevis.
• Functional Interactions: Work synergistically with other intrinsic muscles of the hand (like the hypothenar muscles) to facilitate precise hand movements.

Muscle Anatomy

• Thenar muscles are situated at the base of the thumb on the palm side.
• Abductor Pollicis Brevis: Responsible for abducting the thumb away from the palm.
• Flexor Pollicis Brevis:
  • Flexes the thumb toward the palm.
  • Composed of two heads: superficial head and deep head.
• Opponens Pollicis: Facilitates opposition, allowing the thumb to touch other fingers across the palm.
• Adductor Pollicis: Adducts the thumb; while not a true thenar muscle, it plays a significant role in hand function.

Nerve Innervation

• Median Nerve:
  • Innervates the abductor pollicis brevis, superficial head of the flexor pollicis brevis, and opponens pollicis.
• Ulnar Nerve:
  • Innervates the deep head of the flexor pollicis brevis and adductor pollicis.

Functional Movements

• Abduction: Moving the thumb away from the palm, primarily by abductor pollicis brevis.
• Flexion: Bending the thumb towards the palm, primarily by flexor pollicis brevis.
• Opposition: The thumb moves to touch other fingers, mainly through opponens pollicis.
• Adduction: Moving the thumb back towards the index finger, facilitated by adductor pollicis.

Muscle Relations

• Superficial Relationships: The thenar muscles lie deep to the skin and superficial fascia of the palm.
• Deep Relationships:
  • Positioned near the wrist's carpal bones.
  • Opponens pollicis is located deep to both abductor and flexor pollicis brevis.
• Functional Interactions: Work in coordination with other intrinsic hand muscles, including hypothenar muscles, to enable intricate hand movements.

Hypothenar Muscles

• Located on the ulnar side of the hand; comprised of three muscles.
• Abductor Digiti Minimi:
  • Originates from the pisiform bone.
  • Inserts at the ulnar side of the proximal phalanx of the little finger.
• Flexor Digiti Minimi Brevis:
  • Originates from the hook of the hamate bone and the flexor retinaculum.
  • Inserts at the ulnar side of the proximal phalanx of the little finger.
• Opponens Digiti Minimi:
  • Originates from the hook of the hamate bone and the flexor retinaculum.
  • Inserts at the ulnar margin of the 5th metacarpal bone.

Muscle Functions

• Abductor Digiti Minimi: Responsible for abducting the little finger from the ring finger.
• Flexor Digiti Minimi Brevis: Flexes the proximal phalanx of the little finger.
• Opponens Digiti Minimi: Facilitates opposition of the little finger by bringing it across the palm towards the thumb.

Nerve Supply

• All hypothenar muscles are innervated by the ulnar nerve, spanning C8 to T1.
• The deep branch of the ulnar nerve specifically innervates these muscles.

Muscle Insertions

• Intrinsic muscles are located entirely within a specific body region, such as the hand or foot.
• In the hand, lumbricals insert on the extensor expansions of the fingers.
• In the foot, interossei muscles insert on the proximal phalanges.

Muscle Actions

• Intrinsic muscles facilitate fine motor control and maintain postural stability.
• Lumbricals flex fingers at the metacarpophalangeal joints while extending them at the interphalangeal joints.
• Interossei muscles enable abduction (dorsal) and adduction (palmar) of the fingers.

Innervation and Nerve Roots

• Lumbricals in the hand are innervated by the median nerve (1st and 2nd lumbricals) and the ulnar nerve (3rd and 4th lumbricals); origins are from C8-T1 nerve roots.
• Interossei muscles in the hand are solely innervated by the ulnar nerve, also associated with C8-T1 roots.
• Foot intrinsic muscles are primarily innervated by the lateral and medial plantar nerves, linked to S1-S2 nerve roots.

Muscle Origins

• Lumbricals in the hand originate from the tendons of the flexor digitorum profundus muscle.
• Interossei muscles originate from the sides of the metacarpals.
• In the foot, the abductor hallucis muscle originates from the calcaneus, as well as the flexor digitorum brevis muscle.

Functional Anatomy of Muscles

• Intrinsic muscles stabilize and control digit movements and allow for adaptable grip strength.
• They work synergistically with extrinsic muscles for precise and coordinated actions.
• Essential for tasks requiring dexterity, such as writing and gripping objects.
• Intrinsic muscles also maintain the arches of the foot and hand during various activities, supporting posture.

Muscle Origins

• Pectoralis Major: Has two heads; the clavicular head originates from the medial half of the clavicle, while the sternocostal head arises from the sternum and the first six ribs.
• Rectus Abdominis: Originates from the pubic symphysis and the pubic crest, providing support for the abdominal wall.
• Serratus Anterior: Arises from the upper eight or nine ribs, playing a crucial role in scapular movement.
• Deltoid: Composed of three parts with origins at the lateral third of the clavicle, acromion, and spine of scapula, facilitating shoulder movements.
• Biceps Brachii: Short head originates from the coracoid process of the scapula, while the long head comes from the supraglenoid tubercle, contributing to upper arm flexion.

Muscle Insertions

• Pectoralis Major: Inserts at the lateral lip of the intertubercular groove of the humerus, crucial for arm movement.
• Rectus Abdominis: Inserts at the costal cartilages of ribs 5-7 and the xiphoid process, aiding in trunk flexion.
• Serratus Anterior: Inserts on the medial border of the scapula, essential for scapular positioning.
• Deltoid: Inserts at the deltoid tuberosity of the humerus, allowing for diverse shoulder actions.
• Biceps Brachii: Inserts at the radial tuberosity and through the bicipital aponeurosis, facilitating elbow flexion and forearm supination.

Muscle Actions

• Pectoralis Major: Functions to adduct, medially rotate, and flex the arm at the shoulder joint.
• Rectus Abdominis: Primarily flexes the lumbar spine and compresses abdominal contents for stability.
• Serratus Anterior: Protracts and rotates the scapula, ensuring its stability against the thoracic wall during arm movements.
• Deltoid: Responsible for abducting, flexing, and extending the arm, important for shoulder mobility.
• Biceps Brachii: Flexes the elbow and supinates the forearm; also contributes weakly to shoulder flexion.

Nerve Root Functions

• Pectoralis Major: Innervated by both medial and lateral pectoral nerves, originating from spinal roots C5-T1, supporting arm movements.
• Rectus Abdominis: Innervated by the thoracoabdominal nerves (T7-T11), involved in abdominal and trunk motions.
• Serratus Anterior: Innervated by the long thoracic nerve (C5-C7), crucial for scapular function and stability.
• Deltoid: Innervated by the axillary nerve (C5-C6), vital for shoulder joint movement and stability.
• Biceps Brachii: Innervated by the musculocutaneous nerve (C5-C7), essential for flexing the elbow and forearm movements.

Muscle Origins

• Trapezius originates from the occipital bone, nuchal ligament, and spinous processes of C7 to T12.
• Latissimus Dorsi arises from the spinous processes of T7 to L5, iliac crest, and thoracolumbar fascia.
• Rhomboid Major starts from the spinous processes of T2 to T5.
• Rhomboid Minor originates from the spinous processes of C7 to T1.
• Levator Scapulae is derived from the transverse processes of C1 to C4.
• Serratus Posterior Superior originates from the spinous processes of C7 to T3.
• Serratus Posterior Inferior comes from the spinous processes of T11 to L2.

Muscle Insertions

• Trapezius inserts into the clavicle, acromion, and spine of the scapula.
• Latissimus Dorsi attaches to the intertubercular groove of the humerus.
• Rhomboid Major connects to the medial border of the scapula.
• Rhomboid Minor also attaches to the medial border of the scapula, positioned above the major.
• Levator Scapulae inserts at the superior angle of the scapula.
• Serratus Posterior Superior connects to ribs 2-5.
• Serratus Posterior Inferior attaches to ribs 9-12.

Muscle Actions

• Trapezius elevates, retracts, and rotates the scapula; extends the neck.
• Latissimus Dorsi extends, adducts, and medially rotates the arm.
• Rhomboid Major and Minor work together to retract and elevate the scapula.
• Levator Scapulae elevates the scapula and assists in downward rotation.
• Serratus Posterior Superior elevates upper ribs, aiding in inspiration.
• Serratus Posterior Inferior depresses lower ribs, facilitating expiration.

Innervation

• Trapezius innervated by the accessory nerve (CN XI).
• Latissimus Dorsi receives innervation from the thoracodorsal nerve.
• Rhomboid Major and Minor are innervated by the dorsal scapular nerve.
• Levator Scapulae is innervated by the dorsal scapular nerve and cervical nerves (C3-C4).
• Serratus Posterior Superior is innervated by intercostal nerves (T2-T5).
• Serratus Posterior Inferior is innervated by intercostal nerves (T9-T12).

Nerve Roots

• Trapezius is influenced by nerve roots C3 and C4 (proprioception) and CN XI.
• Latissimus Dorsi is associated with nerve roots C6, C7, and C8.
• Rhomboid Major and Minor connect to nerve roots C4 and C5.
• Levator Scapulae is tied to nerve roots C3, C4, and C5.
• Serratus Posterior Superior associates with nerve roots T1-T4.
• Serratus Posterior Inferior connects to nerve roots T9-T12.

Muscle Origins

• Gluteus Maximus: Originates from the posterior iliac crest, sacrum, coccyx, and sacrotuberous ligament, contributing to its function in hip extension and lateral rotation.
• Gluteus Medius: Arises from the external surface of the ilium, positioned between the anterior and posterior gluteal lines, playing a crucial role in hip stabilization during walking.
• Gluteus Minimus: Also originates from the external surface of the ilium but is situated between the anterior and inferior gluteal lines, assisting in hip abduction and medial rotation.

Muscle Insertions

• Gluteus Maximus: Inserts onto the iliotibial tract and the gluteal tuberosity of the femur, facilitating movements like climbing and running.
• Gluteus Medius: Attaches to the lateral surface of the greater trochanter of the femur, essential for maintaining the pelvis level during locomotion.
• Gluteus Minimus: Inserts into the anterior surface of the greater trochanter of the femur, supporting hip abduction and stabilization.

Innervation

• Gluteus Maximus: Innervated by the inferior gluteal nerve, which is crucial for its powerful extension and external rotation of the hip.
• Gluteus Medius and Gluteus Minimus: Both receive innervation from the superior gluteal nerve, vital for hip abduction and medial rotation.

Nerve Root Segments

• Gluteus Maximus: Governed by nerve root segments L5, S1, and S2, linking it to the lumbosacral plexus for movement coordination.
• Gluteus Medius and Gluteus Minimus: Both associated with nerve root segments L4, L5, and S1, which are critical for efficient lower limb function and stability during various activities.

Muscle Anatomy

• Deep gluteal muscles are located beneath the gluteus maximus, contributing to hip stability and movement.
• Piriformis:
  • Originates from the anterior surface of the sacrum and inserts at the greater trochanter of the femur.
  • Function: Primarily laterally rotates the hip, crucial for rotational movements.
• Gemellus Superior:
  • Originates from the ischial spine and also inserts at the greater trochanter (with obturator internus).
  • Function: Assists in lateral rotation and hip abduction.
• Obturator Internus:
  • Originates from the pelvic surface of the obturator membrane and surrounding bones, inserting at the greater trochanter.
  • Function: Laterally rotates the thigh and stabilizes the hip joint.
• Gemellus Inferior:
  • Originates from the ischial tuberosity and inserts with obturator internus at the greater trochanter.
  • Function: Aids in lateral rotation of the hip.
• Quadratus Femoris:
  • Originates from the ischial tuberosity, inserting at the intertrochanteric crest of the femur.
  • Function: Laterally rotates the hip and stabilizes the femur during movement.

Nerve Supply

• Piriformis: Innervated by the nerve to piriformis (S1, S2), essential for muscle function.
• Gemelli and Obturator Internus: Received innervation from the nerve to obturator internus (L5, S1).
• Quadratus Femoris: Innervated by the nerve to quadratus femoris (L5, S1).
• Importance of nerve supply lies in facilitating muscle function and coordination during movement.

Functional Movements

• Deep gluteal muscles play a crucial role in stabilizing the hip joint during dynamic activities like walking and running.
• These muscles engage primarily in laterally rotating the femur, which is vital for various physical activities.
• Assist with hip abduction, important for movements like side leg raises and lateral movements.
• Proper functioning of deep gluteal muscles is essential for a balanced gait, preventing excessive pelvic drop on the opposite side during walking.
• Common activities involving these muscles include sports with rotational movements (tennis, golf) and those requiring lateral movements (dancing, martial arts).

Medial Thigh Muscles

Muscle Anatomy

• The medial thigh primarily comprises five key muscles:
  • Adductor Longus
  • Adductor Brevis
  • Adductor Magnus
  • Gracilis
  • Obturator Externus

Origin Points

• Adductor Longus originates from the pubis near the pubic symphysis.
• Adductor Brevis starts from the inferior pubic ramus.
• Adductor Magnus has dual origin points:
  • Ischial tuberosity for the hamstring part
  • Inferior pubic ramus and ischial ramus for the adductor part.
• Gracilis is derived from the inferior pubic ramus.
• Obturator Externus arises from the outer surface of the obturator membrane and surrounding bone.

Insertion Sites

• Adductor Longus inserts on the middle third of the femur's linea aspera.
• Adductor Brevis attaches to the pectineal line and proximal part of the linea aspera.
• Adductor Magnus connects to the entire length of the linea aspera and the adductor tubercle for its hamstring part.
• Gracilis inserts on the medial surface of the tibia, contributing to the pes anserinus.
• Obturator Externus attaches to the trochanteric fossa of the femur.

Muscle Actions

• Adductor Longus functions in hip adduction, flexion, and medial rotation.
• Adductor Brevis mainly aids in hip adduction and flexion.
• Adductor Magnus performs dual roles:
  • Adductor part: hip adduction and flexion
  • Hamstring part: hip extension.
• Gracilis is involved in hip adduction, knee flexion, and medial rotation of the leg.
• Obturator Externus specializes in lateral rotation of the hip.

Innervation and Nerve Roots

• Adductor Longus and Adductor Brevis are innervated by the obturator nerve with roots at L2 and L3.
• Adductor Magnus receives innervation from two sources:
  • Adductor part: obturator nerve (L2, L3)
  • Hamstring part: tibial nerve (L4).
• Gracilis is also innervated by the obturator nerve (L2, L3).
• Obturator Externus has innervation from the obturator nerve with nerve roots L3 and L4.

Muscle Origins

• Iliopsoas:
  • Comprises Psoas Major from lumbar vertebrae (T12-L5) and Iliacus from the iliac fossa.
• Rectus Femoris:
  • Originates from the anterior inferior iliac spine (AIIS) and the superior margin of the acetabulum.
• Sartorius:
  • Starts at the anterior superior iliac spine (ASIS).

Muscle Insertions

• Iliopsoas:
  • Inserts at the lesser trochanter of the femur.
• Rectus Femoris:
  • Connects to the tibial tuberosity via the patellar ligament.
• Sartorius:
  • Attaches to the medial aspect of the proximal tibia at the pes anserinus.

Muscle Actions

• Iliopsoas:
  • Responsible for hip flexion and assists with lateral rotation of the thigh.
• Rectus Femoris:
  • Facilitates hip flexion and knee extension.
• Sartorius:
  • Engages in hip flexion, abduction, lateral rotation, and assists in knee flexion.

Nerve Innervation

• Iliopsoas:
  • Psoas Major is innervated by the lumbar plexus (L2-L3); Iliacus is innervated by the femoral nerve (L2-L4).
• Rectus Femoris:
  • Innervated by the femoral nerve (L2-L4).
• Sartorius:
  • Also innervated by the femoral nerve (L2-L4).

Nerve Root Contributions

• Iliopsoas:
  • Primarily L2-L3 for Psoas Major; L2-L4 for Iliacus.
• Rectus Femoris:
  • Contributes from L2-L4.
• Sartorius:
  • Involved nerve roots are L2-L4.