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SPINAL NERVES

JULIAN RIZALDY C. RACA JR., M.D.

DIPLOMATE

PHILIPPINE BOARD OF SURGERY

 

 


Spinal Cord

 

•          cylindrical,  grayish-white structure

 

•          begins above the foramen magnum where it continues with the medulla oblongata of the brain

 

•          in adults -  it terminates below at the level of the lower border of the  1st lumbar vertebra

 

•          in a young children -  it is relatively longer and ENDS at the upper border of the 3rd lumbar vertebra

 

•          in the cervical region -  it gives origin to the BRACHIAL PLEXUS

 

•          in the lower thoracic & lumbar regions -  it gives origin to the lumbosacral plexus

 

•          has a fusiform enlargement -   CERVICAL & LUMBAR enlargements

 

•          inferiorly it tapers off into the CONUS MEDULLARIS, from the apex of  which is a prolongation of PIA MATER  called the FILUM TERMINALE – descends to be attached to the BACK of  the coccyx

 

•          cord possesses in the midline anteriorly a deep longitudinal fissure -  ANTERIOR MEDIAN FISSURE and on the posterior surface, a shallow furrow -  POSTERIOR MEDIAN SULCUS

 

Spinal Nerves

 

•          31 pairs of spinal nerves

 

•          pass through INTERVERTEBRAL FORAMINA  in the  vertebral column as they leave the spinal cord

 

•          named according to vertebral column which they are associated

–         x8 CERVICAL

–         12 THORACIC

–         5  LUMBAR

–         5   SACRAL

–          1  COCCYGEAL

 

•          spinal cord grows slowly in length than the vertebral column

 

•          in the upper cervical region -  spinal nerve roots are short and run almost horizontally

 

•          roots of lumbar and sacral nerves below the level of termination of the cord form a ve

 

•          rtical bundle of nerves -  CAUDA EQUINA

 

•          Each  SPINAL NERVE is connected to the SPINAL CORD by  2 roots - ANTERIOR ROOT & POSTERIOR ROOT

 

 

•          ANTERIOR ROOT

 

–         consists of bundles of nerve fibers carrying nerve impulses  AWAY from the CNS

–         are called EFFERENT fibers

–         those that go to skeletal muscles cause them to contract MOTOR FIBERS

–         cells of origin lie in the ANTERIOR GRAY HORN of the SPINAL CORD

 

•          POSTERIOR ROOT

 

–         consists of bundles of nerve fibers carrying impulses to the CNS

–         are called  AFFERENT fibers

–         concerned with carrying information about sensations of  TOUCH,  PAIN,  TEMPERATURE,  & VIBRATION

–         called SENSORY fibers

–         cell bodies are situated in a swelling manner in the POSTERIOR root called  -  POSTERIOR ROOT GANGLION

 

•          At each INTERVERTEBRAL FORAMEN the ANTERIOR & POSTERIOR ROOTS unite to form SPINAL NERVES ( mixture of MOTOR & SENSORY FIBERS )

–         upon emerging from the foramen, it divides into a large ANTERIOR RAMUS & a small POSTERIOR RAMUS

 

•          ANTERIOR RAMUS – continues anteriorly to supply the uscles & skin of the ANTEROLATERAL BODY WALL & all muscles & skin of the LIMBS

 

•          POSTERIOR RAMUS – passes posteriorly around the vertebral column to supply muscles & skin of the BACK

 

•          spinal nerves also give off a small MENINGEAL BRANCH supplying the VERTEBRAE & COVERINGS OF THE SPINAL CORD

 

•          THORACIC SPINAL NERVES also give branches called RAMI COMMUNICANTES that are associated with the SYMPATHETIC portion of the AUTONOMIC NERVOUS SYSTEM

 

•          PLEXUSES

 

–         at the ROOT OF THE LIMBS, the anterior rami join one another to form complicated NERVE PLEXUSES

–         CERVICAL & BRACHIAL PLEXUSES – found at the root of the UPPER LIMBS

–         LUMBAR & SACRAL PLEXUSES – found at the root of the LOWER  LIMBS

 

•          DERMATOME – area of skin supplied by a single spinal nerve & therefore a single segment of the spinal cord

 

–         on the trunk, adjacent dermatomes overlap

–         on the limbs, it is more complicated because of embryonic changes that take place as the limbs grow out from the body wall

–         skeletal muscles also receive segmental innervation

–         most muscles are innervated by 2 or more spinal nerves & therefore by the same number of spinal cord segments

–         segmental innervation of the following muscles can be tested by eliciting simple muscle reflexes from the patient:

 

•          BICEPS BRACHII TENDON REFLEX (C5,6) – flexion of the elbow joint by tapping the BICEPS TENDON

•          TRICEPS TENDON REFLEX(C6,7,8) – extension of the elbow joint by tapping the TRICEPS TENDON

•          BRACHIORADIALIS TENDON REFLEX(C5,6,7) – supination of the radio-ulnar joint by tapping the insertion of the BRACHIORADIALIS TENDON

 

•          ABDOMINAL SUPERFICIAL REFLEXES – contraction of the underlying abdominal muscles by stroking the skin

 

–         Upper abdomen(T6,7)

–         Middle abdomen(T8,9)

–         Lower abdomen(T10-12)

–         PATELLAR TENDON REFLEX(L2,3,4) – “knee jerk”; extension of the knee joint by tapping the PATELLAR TENDON

–         ACHILLES TENDON REFLEX(S1,2) – “ankle jerk”; plantarflexion of the ankle joint by tapping the GASTROCNEMIUS TENDON

 

•          NERVE SUPPLY OF THE ANTERIOR ABDOMINAL WALL

 

–         cutaneous nerve supply is derived from the ANTERIOR RAMI of the lower 6 thoracic & 1st lumbar nerves

–         thoracic nerves are the lower 5 INTERCOSTAL & SUBCOSTAL nerves

–         the 1st lumbar nerve is reresented by the ILIOHYPOGASTRIC & ILIOINGUINAL NERVES, which are branches of the LUMBAR PLEXUS

–         dermatome of T6 – epigastrium; over the XIPHOID PROCESS

–         dermatome of T10 – UMBILICUS

–         dermatome of L1 – just above the INGUINAL LIGAMENT & SYMPHYSIS PUBIS

 

•          OBLIQUE & TRANSVERSE ABDOMINAL MUSCLES – lower 6 thoracic, ILIOHYPOGASTRIC & ILIOINGUINAL NERVES

 

•          RECTUS MUSCLE – lower 6 thoracic nerves

 

•          Pyramidalis – 12th thoracic nerve

 

•          PARIETAL PERITONEUM is supplied segmentally by intercostal & lumbar nerves, which also supply the overlying muscles & skin

 

•          NERVES OF THE POSTERIOR ABDOMINAL WALL

 

–         one of the main nervous pathways supplying the lower limb

–         is formed in the PSOAS MUSCLE from the ANTERIOR RAMI of the upper 4 LUMBAR NERVES

–         the anterior rami receive GRAY RAMI COMMUNICANTES from the SYMPATHETIC TRUNK

–         the upper two give off WHITE RAMI COMMUNICANTES to the SYMPATHETIC TRUNK

–         ILIOHYPOGASTRIC, ILIOINGUINAL, FEMORAL NERVES & LATERAL CUTANEOUS NERVE TO THE THIGH emerge from the lateral border of the PSOAS MUSCLE

–         ILIOHYPOGASTRIC & ILIOINGUINAL NERVES enter the lateral & anterior abdominal walls

–         ILIOHYPOGASTRIC NERVE – supplies the skin of the lower part of the ANTERIOR ABDOMINAL WALL

–         ILIOINGUINAL NERVE – supplies the skin of the groin & LABIA MAJORA & SCROTUM

–         LATERAL CUTANEOUS NERVE OF THE THIGH – enters the thigh behind the lateral end of the INGUINAL LIGAMENT; supplies the skin over the lateral surface of the thigh

–         FEMORAL NERVE(L2,3,4) – largest branch of the LUMBAR PLEXUS; enters the thigh behind the INGUINAL LIGAMENT & lateral to the femoral vessels & the FEMORAL SHEATH; it supplies the ILIACUS MUSCLE in the abdomen

–         OBTURATOR NERVE & 4th LUMBAR ROOT of  the LUMBOSACRAL TRUNK emerge from the medial border of the PSOAS MUSCLE at the brim of the pelvis

–         OBTURATOR NERVE(L2,3,4) – leaves the pelvis through the OBTURATOR FORAMEN into the thigh

–         4th LUMBAR ROOT of the LUMBOSACRAL TRUNK takes part in the formation of the SACRAL PLEXUS; on reaching the OBTURATOR CANAL, it splits into the ANTERIOR & POSTERIOR DIVISIONS which pass through the canal to enter the ADDUCTOR REGION of the thigh

–         GENITOFEMORAL NERVE(L1,2) – runs down the anterior surface of the PSOAS MUSCLE & divides into the:

–         GENITAL branch – enters the SPERMATIC CORD to supply the CREMASTER MUSCLE; and

–         FEMORAL branch – supplies a small area of the skin of the thigh; part of the neuronal pathway involved in the CREMASTERIC REFLEX

 

•          SACRAL PLEXUS

 

–         lies in the posterior pelvic wall, in front of the PYRIFORMIS MUSCLE

–         formed from the ANTERIOR RAMI of the 4th & 5th LUMBAR NERVES & ANTERIOR RAMI of the 1st to 4th SACRAL NERVES

–         branches to the lower limb, which leave the pelvis through the GREATER SCIATIC FORAMEN:

•          SCIATIC NERVE(L4,5; S1,2,3) – the largest nerve in the body

•          SUPERIOR GLUTEAL NERVE – supplies the GLUTEUS MEDIUS & MINIMUS MUSCLES & the TENSOR FASCIA LATA MUSCLE

•          INFERIOR GLUTEAL NERVE – supplies the GLUTEUS MAXIMUS MUSCLE

•          NERVE TO THE QUADRATUS FEMORIS, which also supplies the GEMELLUS INFERIOR MUSCLE

•          NERVE TO THE OBTURATOR INTERNUS, which also supplies the GEMELLUS SUPERIOR MUSCLE

•          POSTERIOR CUTANEOUS NERVE OF THE THIGH – supplies the skin of the buttocks & back of the thighs

 

–         branches to the pelvic muscles, pelvic viscera & perineum:

•          PUDENDAL NERVE(S2,3,,4) – leaves through the GREATER SCIATIC FORAMEN & enters the perineum through the LESSER SCIATIC FORAMEN

•          NERVE TO THE PIRIFORMIS MUSCLE

•          PELVIC SPLANCHNIC NERVE(S2,3,4) – constitute the sacral part of the PARASYMPATHETIC SYSTEM

 

–         PERFORATING CUTANEOUS – supplies the skin of the lower medial part of the buttocks

 

•          LUMBOSACRAL TRUNK

 

–         formed by the ANTERIOR RAMUS of the 4th LUMBAR NERVE, which joins the ANTERIOR RAMUS of the 5th LUMBAR NERVE

–         passes down into the pelvis & joins the SACRAL NERVES as they emerge from the ANTERIOR SACRAL FORAMINA

 

•          PUDENDAL NERVE – passes forward in the PUDENDAL CANAL & supplies the EXTERNAL ANAL SPHINCTER & muscles & skin of the PERINEUM

 

–         branches:

•          INFERIOR RECTAL NERVE – supplies the EXTERNAL ANAL SPHINCTER, the mucous membranes of the lower half of the anal canal & the perianal skin

•          DORSAL NERVE OF THE PENIS( or CLITORIS)

•          PERINEAL NERVE – supplies the muscles  in the UROGENITAL TRIANGLE & skin of the posterior surface of the SCROTUM ( or LABIA MAJORA )

 

•          The Brachial Plexus       

 

–         at the root of the neck,  the nerves that are about to enter the upper limb come together to form a complicated plexus

–         formed in the posterior triangle of the neck by the union of the anterior rami of the  5th,  6th,  7th,  & 8th cervical  &  1st thoracic spinal nerves

–         arranged and distributed efficiently in different nerve trunks to the various parts

–          of the upper limb

–         it provides the upper limb the ff. important functions:

•          sensory innervation to the skin and deep structures such as JOINTS

•          motor innervation to the muscles

•          influence the diameters of the blood vessels supplied by the sympathetic vasomotor nerves;  and

•          sympathetic secretomotor supply to the sweat glands  

 

–         the plexus can be divided into  ROOTS,  TRUNKS,  DIVISIONS,  and CORDS

–         the roots of  C5 and C6 unite to form the UPPER TRUNK

–         the root of  C7 continues as the MIDDLE TRUNK

–         the roots of  C8  &  L1 unite to form the UPPER TRUNK

–         each trunk then divides into  ANTERIOR  &  POSTERIOR DIVISION

–         the anterior divisions of the upper & middle trunks unite to form the LATERAL CORD

–         the anterior division of the lower trunk continues as the MEDIAL CORD

–         the posterior division of all  3 trunks join to form the POSTERIOR CORD

–         the cords are arranged around the axillary artery in the axilla and are enclosed by a sheath of fascia called the  AXILLARY SHEATH together with the axillary vein

 

–         Cords of the Brachial Plexus

–         all  3 cords of the brachial plexus lie above and lateral to the 1st part of  the axillary artery

–         names  ( L, M, P ) according to their relationship to the  2nd part of the AXILLARY ARTERY

–         MEDIAL CORD crosses behind the artery to reach the MEDIAL side

–         POSTERIOR CORD lies BEHIND the artery

–         LATERAL CORD lies on the LATERAL side of the artery

 

Branches of the Different Parts of the Brachial Plexus

 

•          Roots

 

–         Dorsal Scapular Nerve ( C5 )

–         Long Thoracic Nerve ( C5,  6,  7 )

 

•          Upper Trunk

 

–         Nerve to Subclavius ( C5 & 6 )

–         Suprascapular Nerve ( supplies the supraspinatus & infreaspinatus muscles)

 

•          Lateral Cord

 

–         Lateral Pectoral Nerve

–         Musculocutaneous Nerve

–         Lateral Root of Median Nerve

 

•          Medial Cord

 

–         Medial Pectoral Nerve

–         Medial Cutaneous Nerve of the Arm

–         Medial Cutaneous Nerve of the Forearm

–         Ulnar Nerve

–         Medial Root of the Median Nerve

 

•          Posterior Cord

 

–         Upper & Lower Subscapular Nerve

–         Thoracodorsal Nerve

–         Axillary Nerve

–         Radial Nerve

 

Branches of the Brachial Plexus found in the Axilla

 

•          Nerve to Subclavius ( C5 & 6 )

 

–         supplies Subclavius muscle

–         may give contribution ( C5 )to the Phrenic Nerve

–         ACCESSORY PHRENIC NERVE

 

•          Long Thoracic Nerve ( C5,  6,  7 )

 

–         from the roots of the brachial plexus in the neck

–         enters the axilla by passing down over the lateral border of the  1st rib BEHIND the axillary vessels and brachial plexus

 

•          Lateral Pectoral Nerve

 

–         from the lateral cord of the brachial plexus

–         supplies the PECTORALIS MAJOR muscle

Musculocutaneous Nerve

–         from the lateral cord of the brachial plexus

–         supplies the CORACOBRACHIALIS muscle

 

•          Lateral Root of Median Nerve

 

–         direct continuation of  the lateral cord of the brachial plexus

–         joined by the median root to form the MEDIAN NERVE TRUNK

–         passes downward on the lateral side of the axillary artery

–         gives no branches in the axilla

 

•          Medial Cutaneous Nerve of the Arm( T1 )

 

–         from the medial cord of the brachial plexus

–         joined by the in tercostobrachial nerve (lateral cutaneous branch of the 2nd intercostal nerve )

–         supplies the skin in the medial side of the arm

 

•          Medial Cutaneous Nerve of the Forearm

 

–         from the medial cord of the brachial plexus

–         descends in front of the axillary artery

 

•          Ulnar Nerve

 

–         from the medial cord of the brachial plexus

–         descends in the interval between  the axillary artery & vein

 

•          Medial Root of the Median Nerve

 

–         from the medial cord of the brachial plexus

–         crosses in front of the  3rd part of the axillary artery to join the lateral root of the median nerve

 

 

 

 

•          Upper & Lower Subscapular Nerve

 

–         from the posterior cord of the brachial plexus

–         supply the upper and lower parts of the subscapularis muscle

 

•          Thoracodorsal Nerve

 

–         from the posterior cord of the brachial plexus

–         runs downward to supply the LATISSIMUS DORSI MUSCLE

 

•          Axillary Nerve

 

–         one of the terminal branches of the posterior cord of the brachial plexus

–         it turns backward and passes through the quadrangular space

 

•          Radial Nerve

 

–         largest branch of the brachial plexus

–         lies behind the axillary artery

–         gives off branches to the long & medial heads of the triceps muscle & the posterior cutaneous nerve of the arm which is distributed to the skin in the idle of the back of the arm

 

Cervical Plexus

 

•          formed by the anterior rami of the  1st 4 cervical nerves

•          rami are joined by connecting branches which form lines that lie in front of the origins of the levator scapulae and scalene medius muscle

•          plexus is covered in front by the prevertebral layer of  deep cervical fascia

•          related to the internal jugular vein within the carotid sheath

•          Branches

•          Cutaneous

•          Lesser Occipital

•          Greater Auricular

•          Transverse Cutaneos

•          Supraclavicular

 

•          Muscular Branches to the Neck muscles

–         Prevertebral Muscles

–         Sternocleidomastoid (proprioceptive,  C2&3)

–         Levator Scapulae ( C3&4 )

–         Trapezium ( proprioceptive,  C3&4 ) 

–         A branch From C1,  joins the HYPOGLOSSAL NERVE;  some fibers leave the  Hypoglossal Nerve as a descending branch which unites with the         descending Cranial Nerve,  C2&3,  to form the ANSA CERVICALIS

–         The 1st,  2nd,  3rd,  cervical nerve faphragibers within  ANSA CERVICALIS supply the   OMOHYOID,  STERNOHYOID,  STERNOTHYROID

–         These C1 fibers within the Thyroglossal Nerve leave it as the nerve to the             THYROHYOID & GENOHYOID

 

 

 

 

 

Nerve Supply to the DIAPHRAGM-PHRENIC NERVE

 

•          PHRENIC NERVE

 

–         only motor nerve supply to the diaphragm

–         contains sensory fibers & sympathetic fibers

–         some sensory fibers are PROPRIOCEPTIVE fibers for the muscle of the diaphragm

–         most supply the pleura and peritoneum covering the upper and lower surfaces of the central part of the diaphragm

–         other sensory fibers supply the MEDIASTINAL PLEURA & the PERICARDIUM

–         Runs vertically downward across the front of SCALENUS ANTERIOR behind the PREVERTEBRAL LAYER of deep fascia

–         enters the fascia by passing in front of the subclavian artery and behind the beginning of the brachiocephalic vein

 

Relations in the Neck

 

–         ANTERIORLY

–         Prevertebral layer of deep fascia

–         Internal jugular vein

–         Superficial Cervical & Suprscapular Arteries

–         In the Left side – Thoracic Duct, beginning of the brachiocephalic vein

 

–         POSTERIORLY

•          Scalenus Anterior

•          Subclavian Artery

•          Cervical Dome of the Diaphragm

 

–         Right Phrenic Nerve passes through the caval opening of the Diaphragm, in the right side of the INFERIOR VENA CAVA, to supply the central part of the peritoneum on its underaspect

 

–         Leftt Phrenic Nerve pierces the muscle of the diaphragm to supply the central part of the peritoneum on its under aspect

 

–         Phrenic Nerve possess  Afferent & Efferent Fibers

–         Efferent Fibers  -  sole nerve supply to the muscle of the Diaphragm

–         Afferent Fibers  -  carry sensation to the CENTRAL NERVOUS SYSTEM from

•          the peritoneum crossing the central region of the undersurface of the Diaphragm

•          pleura crossing the central region of the upppersurface of the Diaphragm

•          Pericardium & Mediastinal Parietal Pleura

 

 

–         Nerves of the Lower Limb

–         Nerves entering the lower limb provide the following important functions:

•          sensory innervation to the skin

•          motor innervation to the muscle

•          sympathetic vasomotor nerves that influence the diameters of the blood vessels 

•          sympathetic secrretomotor supply to the sweat glands

 

–         The nerves that innervate the lower limb originates from the

•          LU MBAR PLEXUS  -  abdomen

•          SACRAL PLEXUS   -  pelvis

 

–         These plexuses permit nerve fibers from the different segments of the spinal cord to be arranged and distributed efficiently in different nerve trunks to the various parts of the lower limb