The Spinal Nerves

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The Spinal Nerves

• SHANDONG UNIVERSITY
• Liu Zhiyu

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General description

• 31 pairs spinal nerves
• Cervical nerves8 pairs (C1-C8)
• Thoracic nerves12 pairs (T1-T12)
• Lumbar nerves5 pairs (L1-L5)
• Sacral nerves5 pairs (S1-S5)
• Coccygeal nerves1 pair (Co1)

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General Description

• Formation each spinal nerve is formed by union
  of anterior and posterior roots at intervertebral
  foramen
• The anterior root-contains motor fibers for
  skeletal muscles. Those from T1 to L2 contain
  sympathetic fibers S2 to S4 also contain
  parasympathetic fibers.
• The posterior root-contains sensory fibers whose
  cell bodies are in the spinal ganglion.

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Functional Components of Spinal Nerves

• Somatic efferent nerve fibers (SE) fibers that
  transmit motor impulses from spinal cord to
  skeletal muscles.
• Visceral efferent nerve fibers (VE) fibers that
  transmit motor impulses from spinal cord to
  smooth muscles, cardiac muscle and glands.
• Somatic afferent nerve fibers (SA) fibers that
  transmit exteroceptive and proprioceptive
  impulses from body to spinal cord
• Visceral afferent nerve fibers (VA) fibers that
  transmit interoceptive impulses from the viscera
  to spinal cord

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Branches of spinal nerves

• Anterior branch
• Posterior branch
• Communicating branch
• Meningeal branch

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Cervical plexus

• Formation formed by anterior rami of C1-C4
  spinal nerves
• Position lies in front of the origin of levator
  scapulae and scalenus medius and deep to the
  superior part of the sternocleidomastoid

C1
C2
C3
C4
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Branches of Cervical Plexus

• Cutaneous branches
• Lesser occipital
• Great auricular
• Transverse nerve of neck
• Supraclavicular nerves
• Emerge around middle of posterior border of
  sternocleidomastoid, to supply skin of neck and
  scalp between auricle and external occipital
  protuberance

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Branches of Cervical Plexus

• Phrenic nerve
• Arises from anterior rami of C3-C5 (motor and
  sensory)
• Runs vertically downward across the front of the
  scalenus anterior
• Enters the thorax by passing betweem the
  subclavian a. and v.

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Branches of Cervical Plexus

• Phrenic nerve
• Accompanied by pericardiophrenic vessels and
  passes anterior to lung roots between mediastinal
  pleura and pericardium to supply motor and
  sensory innervation to diaphragm
• Sensory fibers supply to pleurae, pericardium and
  peritoneum of diaphragm usually right phrenic
  nerve may be distributed on live, gallbladder and
  biliary system.

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Brachial Plexus

• Formation
• Formed by anterior rami of C5-C8 and T1 spinal
  nerves
• Position
• Passes through the scalene fissure to
  posterosuperior of subclavian artery, then
  enters the axilla to form three cords

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Main branche of brachial plexus

• Lateral cord
• musculocutaneous n.
• lateral root of median n.
• Medial cord
• medial root of median n.
• ulnar n.
• Posterior cord
• radial n.
• axillary n.

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Main Branche of Brachial Plexus

• Musculocutaneous nerve
• Origin arises from the lateral cord of the
  brachial plexus.
• Distribution
• Biceps brachii
• Brachalis BBC nerve
• Coracobrachialis
• Skin on anterior aspect of forearm

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Main Branche of Brachial Plexus

• Median nerve
• Origin arises from the medial and lateral cord
  of the brachial plexus.
• Muscular branches
• Flexor of forearm except brachioradialis flexor
  carpi ulnaris and ulnar half of flexor digitorum
  profundus
• Thenar except adductor pollicis, first two
  lumbricals
• Cutaneous branches
• Skin of thenar, central part of palm,
• Palmar aspect of radial three and one-half
  fingers, including middle and distal fingers on
  dorsum
• Injury Apehand

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Main Branche of Brachial Plexus

• Ulnar nerve
• Origin arises from the medial cord of the
  brachial plexus.
• Muscular branches
• Flexor carpi ulnaris, ulnar half of flexor
  digitorum profundus, hypothenar muscles,
  interossei, 3rd and 4th lumbricals and adductor
  pollicis
• Cutaneous branches
• Skin of hypothenar, palmar surface of ulnar
  one and one-half fingers, ulnar half of dorsum of
  hand, posterior aspect of ulnar two and one-half
  fingers
• Injury clawhand

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Radial nerve

• Origin arise from the posterior cord of the
  brachial plexus
• Course Winds around the back of the arm in the
  spinal groove of the back of the humerus between
  the heads of the triceps. It pierces the lateral
  fascial septum above the elbow and divides into
  superficial and deep branches.

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Radial nerve

• Distribution
• Extensor muscles of arm and forearm,
  brachioradialis
• skin on back of arm, forearm, and radial side of
  dorsum of hand and radial two and one-half
  fingers
• Injury wristdrop

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Main Branche of Brachial Plexus

• Axillary
• Origin arises from the posterior cord of the
  brachial plexus.
• Distribution Deltoid and teres minor muscle
  skin over deltoid and upper posterior aspect of
  arm
• Injury result in deltoid andteres minor
  paralysis (loss of shoulser abdution and weel
  external rotation) with loss of sensation over
  the deltoid

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Anterior branches of thoracic nerves

• Intercostal nerves (anterior rami of T1- T11)
• Subcostal nerve (anterior ramus of T12)
• Distribution distributed to intercostales and
  anterolateral abdominal muscles, skin of thoracic
  and abdominal wall, parietal pleura and peritoneum

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Segmental Innervation of Skin

• Adjacent dermatomes overlap considerably, so that
  to produce a region of complete anesthesia at
  least three contiguous spinal nerves have to be
  sectioned.

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Segmental Innervation of Skin

• Dermatome the area of skin supplied by a single
  nerve, and, therefore, a single segment of the
  spinal cord. On the trunk the dermatomes extend
  round the body from the posterior to the anterior
  median plane.
• T2 Sternal angle
• T4 Nipple
• T6 Xiphoid process
• T8 Costal arch
• T10 Umbilicus
• T12 Midpoint between umbilicus and symphysis
  pubis

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Lumbar plexus

• Formation formed by anterior rami of L1-L3, a
  part of anterior rami of T12and L4

L1 L2 L3 L4
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Main branche of lumbar plexus

• Position lies within substance of psoas major
• Branches
• Iliohypogastric
• Ilioinguinal
• Lateral femoral cutaneous
• Femoral
• Obturator
• Genitofemoral

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Branches of Lumbar Plexus

• Femoral nerve
• passes deep to inguinal ligament supplies
  anterior thigh muscles (quadriceps, sartorius and
  pectineus), hip and knee joint, and skin on
  anteromedial side of thigh, saphenous nerve is
  distributed to skin of medial side of leg and
  foot
• Obturator nerve
• Enters thigh through obturator foramen
  supplies medial group of muscles of thigh,
  obturator externus, and skin of medial side of
  thigh

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Sacral Plexus
L4

• Formation formed by anterior rami of L4 and L5
  spinal nerves (the lumbrosacral trunk) and
  anterior rami of sacral and coccygeal nerves
• Position lies in pelvic cavity, anterior to
  sacrum and piriformis

L5
S1
S2
S3
S4
S5
Co
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Main branches of sacral plexus

• Superior gluteal n.
• Inferior gluteal n.
• Pudendal n.
• Posterior femoral cutaneou n.
• Sciatic n.

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Branches of Sacral Plexus

• Sciatic nerve
• Leaves pelvis through infrapiriform foramen
  to enter gluteal region, runs inferiorly
  laterally deep to gluteus maximus, passing midway
  between the greater trochanter of femur and
  ischial tuberosity to back of thigh, lying deep
  to long head of biceps femoris, normally divided
  into tibial and common peroneal nerves just above
  popliteal fossa innervates semitendinosus,
  semimembranosus and biceps femoris and has
  articular branches to hip and knee joints

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Branches of Sacral Plexus

• Tibial nerve
• Decends through popliteal fossa and lies on
  popliteus then runs inferiorly with posterior
  tibial vessels and terminates beneath flexor
  retinaculum by dividing into medial and lateral
  plantar nerves supplies posterior muscles of leg
  and knee joint

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Branches of Sacral Plexus

• Common peroneal nerve
• Arises at apex of popliteal fossa and
  follows medial border of biceps femoris and its
  tendon passes over posterior aspect of head of
  fibula and then winds around neck of fibula, deep
  to peroneus longus, where it divides into deep
  and superficial peroneal nerves

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Branches of Sacral Plexus

• Deep peroneal nerve
• Arises between peroneus longus and neck of
  fibula descends on interosseous membrane and
  enters dorsum of foot
• Supplies anterior muscles of leg, and skin of
  first interdigital cleft
• Superficial peroneal nerve
• Arises between peroneus longus and neck of fibula
  and descends in lateral compartment of leg
• Supplies peroneus longus and brevis and skin on
  anterior surface of leg and dorsum of foot