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					                No. 31
1. Anterior Branches of Thoracic Nerves
2. Lumbar Plexus
3. Sacral Plexus
       Ⅲ. The Anterior Branches of
            Thoracic Nerves
   They are twelve in number on each side.
   The upper eleven lie between the ribs and are
    called the intercostal nerves.
   The twelfth lies below the last rib, so it is called
    the subcostal nerve.
   A typical intercostal nerve runs, at first, outside
    the pleura, across the internal surface of the
    intercostal membrane. Close to the costal angle,
    the nerve enters the fascial space between the
    intercostales interni and the intercostales intimi
    and continues forward along the costal groove,
    where it accompanies the intercostal vessels and
    lies below them.
   The upper six nerves run toward the sternum and
    terminate as the anterior cutaneous branches
    that pierce the intercostal muscles and the
    pectoralis major near the sternum.
   The lower five intercostal nerves and the
    subcostal nerve cross the costal arch and
    continue their course anteriorly between the
    obliquus internus abdominis and transversus
    abdominis. Then they pierce the sheath of rectus,
    penetrate the rectus abdominis and terminate as
    anterior cutaneous branches near the linea alba.
   Muscular branches of these nerves supply the
    intercostales and the anterolateral abdominal
    muscles. The cutaneous branches are distributed
    to the skin of the thoracic and abdominal wall.
   The distribution of the anterior branches
    of the thoracic nerves is segmental. On
    the anterior surface of the trunk, they
    present about the level of:
   T2-the sternal angle,
   T4-the nipple,
   T6-the xiphoid process ,
   T8-the costal arch,
   T10-the umbilicus,
   T12-the anterior superior iliac spine.
      Ⅳ. The Lumbar Plexus
 Ⅰ) The formation of lumbar plexus
 It is formed by the anterior branches of
  the first three lumbar nerves (L1-3), a
  part of the anterior branches of the last
  thoracic nerve (T12)and the fourth lumbar
  nerve (L4).
 Ⅱ) Location of lumbar plexus
 It is located anterior to the psoas major
  and the transverse processes of the
  lumbar vertebrae.
    Ⅲ) The branches of lumbar plexus
    1. The iliohypogastric nerve (T12, L1)
   Its cutaneous branch supplies the skin of the
    hypogastric region and inguinal region.
   Its muscular branch supplies the muscles of the
    lower part of the abdominal wall.
    2. The ilioinguinal nerve (L1)
   It supplies the skin of scrotum (or the greater lip
    of pudendum), and the muscles of lower
    abdominal wall.
    3. The lateral femoral cutaneous nerve (L2-3)
   It supplies the skin over the anterior and lateral
    parts of the thigh.
    4. The femoral nerve (L2-4)
   It descends between the psoas major and the
    iliacus, then passes down beneath the inguinal
    ligament into the femoral triangle, where it is
    “broken up” into several terminal branches.
   Its muscular branches supply the anterior group
    of muscles of the thigh---the quadriceps femoris,
    sartorius and pectineus.
   Its cutaneous branches to the thigh are the
    anterior cutaneous branches which are
    distributed to the anterior and anteromedial side
    of the skin of the thigh.
   Saphenous nerve:
   The longest one of its cutaneous branches
    is the saphenous nerve. It accompanies
    the femoral artery and descends through
    most of the length of the adductor canal,
    becomes subcutaneous at the medial side
    of the knee by emerging behind the
    sartorius. Then it runs downward with the
    great saphenous vein along the medial
    side of leg as far as the medial side of the
    foot. This nerve is distributed to the skin
    of the medial side of the leg and foot.
   Injury of the femoral nerve results in
    impaired flexion of the hip joint. Because
    the quadriceps femoris muscle is
    paralyzed. It is impossible to extend knee
    and the knee jerk reflex disappears. There
    would also be a loss of sensation in the
    skin of the anterior area of the thigh and
    the medial side of the leg and foot.
    5. The obturator nerve (L2-4)
   It emerges from the medial border of the psoas
    major, whence it passes along the lateral pelvic
    wall and through the obturator canal to the
    medial part of the thigh.
   The muscular branches of the nerve supply the
    medial group of muscles of the thigh, the
    cutaneous branches are distributed to the skin of
    the medial side of the thigh.
   Injury to the obturator nerve results in impaired
    adduction of the thigh and a loss of sensation in
    the skin of the medial aspect of the thigh.
    6. The genitofemoral nerve (L1-2)
   It supplies the skin over the scrotum (or
    the greater lip of pudendum), and the
    cremaster.
   The iliohypogastric, ilioinguinal and
    genitofemoral nerves must be protected
    carefully in the operation of the inguinal
    hernia.
       Ⅴ. The Sacral Plexus
 Ⅰ) The formation of sacral plexus
 This plexus is formed by the lumbosacral

  trunk (a part of L4 and L5), the anterior
  branches of the sacral and coccygeal
  nerves (S1-5, Co1).
 Ⅱ) The location of sacral plexus
 It is located in the pelvis, where it is

  closely related to the anterior surface of
  the piriformis.
 Ⅲ) The branches of sacral plexus
 1. The superior gluteal nerve (L4-5)
 It leaves the pelvis via the greater sciatic

  foramen superior to the piriformis in
  company with the superior gluteal vessels,
  and passes between the gluteus medius
  and gluteus minimus.
 It supplies the gluteus medius and gluteus

  minimus and the tensor fasciae latae.
    2. The inferior glutea nerve (L5-S2)
   It leaves the pelvis through the greater
    sciatic foramen inferior to the piriformis in
    company with the inferior gluteal vessels.
   It supplies the gluteus maximus and the
    skin over the lower part of the gluteal
    region.
    3. The pudendal nerve (S2-4)
   It emerges from the pelvis via the greater
    sciatic foramen below the piriformis in
    company with the internal pudendal
    vessels. It crosses the dorsum of the
    sacrospinous ligament to enter the
    perineum through the lesser sciatic
    foramen. Then it traverses the lateral wall
    of the ischiorectal fossa and gives off
    branches to innervate the muscles and
    skin of the perineum and the external
    genital organs:
    1) The anal nerve
   It is distributed to the sphincter ani externus and
    skin of the anus.
    2) The perineal nerve
   It is distributed to the muscles of the perineum
    and the skin of the scrotum or the greater lip of
    pudendum.
    3) The dorsal nerve of penis or clitoris
   It passes to the dorsum of the penis (or clitoris).
   It supplies the skin of the penis (or clitoris),
    prepuce and the glans penis (or glans of clitoris).
    4. The posterior femoral cutaneous
    nerve (S1-3)
   It descends in company with the sciatic
    nerve and is distributed to the skin of the
    posterior part of the thigh.
    5. The sciatic nerve (L4-S3)
   It is the largest nerve in the body.
   The nerve leaves the pelvis through the greater
    sciatic foramen inferior to the piriformis along
    with the inferior gluteal nerve. Then it runs
    inferolaterally deep to the gluteus maximus, and
    descends between the ischial tuberosity and the
    greater trochanter of femur to enter the posterior
    compartment of the thigh. Here, it passes
    downward between the biceps femoris and the
    semimembranosus, semitendinosus to enter the
    popliteal fossa, and terminates by dividing into
    the tibial and common peroneal nerves.
   The branches of the sciatic nerve supply
    the muscles of the foot, leg and the
    posterior compartment of the thigh. It also
    supplies the skin of the leg and foot.
   The level of division of the sciatic nerve is
    variable. It is usually at the superior angle
    of the popliteal fossa but these two nerves
    may be separated even at their origins in
    the pelvis.
    1) The tibial nerve (L4-S3)
   It is the large one of the two terminal branches of
    the sciatic nerve.
   At first the nerve descends through the center of
    the popliteal fossa in company with the politeal
    vessels and posterior to the popliteal vein, it then
    passes deep to the triceps surae and posterior to
    the medial malleolus, where the tibial nerve is
    divided into the medial and lateral plantar
    nerves to supply the plantar muscles and the
    skin over the sole of the foot.
   In the popliteal fossa, the tibial nerve gives off
    branches to all the muscles of the posterior
    compartment of the leg. It also gives off a
    cutaneous branch, the medial sural cutaneous
    nerve, which descends in company with the
    small saphenous vein.
   At the lower part of the leg, the medial sural
    cutaneous nerve usually joins the lateral sural
    cutaneous nerve, coming from the common
    peroneal nerve, to form the sural nerve which is
    distributed to the skin of the posterior and lateral
    surface of the leg and over the lateral border of
    the dorsum of the foot.
    2) The common peroneal nerve (L4-S2)
   It begins at the superior angle of the
    popliteal fossa and passes lateroinferiorly
    along the medial border of the biceps
    femoris and its tendon. It leaves the fossa
    by passing superficially to the lateral head
    of the gastrocnemius. The nerve then
    passes around the posterolateral surface
    of the neck of fibula to enter deep to the
    superior part of the peroneus longus.
   The common peroneal nerve is palpable
    where it winds around the neck of fibula,
    and is divided into the superficial and deep
    peroneal nerves.
   The common peroneal nerve supplies the
    muscles of the anterior and lateral
    compartments of the leg. It also gives off
    branches of the skin over lateral surface of
    the leg and dorsum of the foot.
    ① The superficial peroneal nerve
   It descends between the peroneus longus
    and brevis and pierces the deep fascia to
    become superficial in the distal one third
    of the leg. The branches of this nerve
    supply the peroneal muscles and the skin
    on the distal part of the anterior surface of
    the leg, the dorsum of the foot and toes.
    ② The deep peroneal nerve
   It is in company with the anterior tibial artery. At
    first it lies between the extensor digitorum longus
    and the tibialis anterior and then between the
    extensor hallucis longus and the tibialis anterior.
   It supplies the anterior group of muscles of the
    leg and a small area of the skin between the first
    and second toes.
   Functional disturbances in the case of the
    common peroneal nerve injuries include impaired
    dorsiflex of the foot, reduced or lost eversion of
    the foot. This condition causes the foot to hang
    down and is known as “foot-drop” or “talipes
    equinovarus”. There is also a variable loss of
    sensation of the anterolateral aspect of the leg
    and the dorsum of the foot.

				
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