Spinal Nerves

SPINAL NERVE SUPPLY

http://www.webmanmed.com/spinalnrv.html

There are 31 pair of spinal nerves. With the exception of C1 all nerves have a ventral and dorsal nerve root exiting through the intervertebral foramen. This division somewhat resembles the tongue of a snake as it is bifid. The ventral nerve root enters the anterior horn while the dorsal nerve root enters the posterior horn. C1 exits between the cranial occipital bone and 1st cervical vertebra, and frequently does not have a dorsal root. C2 exits between the axis and atlas (or between C1 & C2). C8 exits between the 7th cervical vertebra and the 1st thoracic vertebra. The first thoracic nerve exits between T1 & T2. Therefore in the cervical region the respective nerves exit above the referenced segment with the exception of C8, where there is not a corresponding vertebra. In the thoracic, lumbar and sacral regions the reference segmental nerve supply exits beneath the referenced vertebral segment.

The upper cervical nerves associate with cranial nerves as referenced in our cranial nerve section. Additionally they form the cervical plexus. Plexi are a network of nerves. The spine has five plexiwhich frequently overlap. The names of these plexi are: the cervical,brachial, lumbar, sacral and coccygeal. The thoracic spine for the most part is not involved in the plexi.

All spinal nerves consist of mixed fibers both sensory & motor. This allows for neurotransmission from the sensory receptors to the spinal cord or afferent transmission. The dorsal root is responsible for the conducting of sensory transmission. Efferent transmission is conducted from the spinal cord to the muscles for motor response as well as for the conducting of the sympathetic & parasympathetic pathways. This efferent transmission is predominantly conducted through the ventral root. The dorsal root merges with the posterior horn and the ventral root merges with the anterior horn. The spinal roots traverse laterally and merge slightly distal to the dorsal root ganglion to form a spinal nerve. At which time they traverse through the intervertebral foramen of their respective segment and form the rami. The rami can either divide or return back towards the spine to provide nerve supply to the meninges, vertebra and ligaments or move into the periphery to supply the skin, muscles and viscera.

The sympathetic chain consisting of 22 ganglia emerge from the ventral root and involve three cervical segments, eleven thoracic segments, four lumbar segments, and four sacral segments. And are responsible for elevated heart rate, increased electrical activity of the brain, deep and rapid breathing, and dilation of blood vessels, eyes and galvanic skin response. Or in other words, it is the system which conducts the “fight or flight” mechanism.

The parasympathetic or craniosacral division is more simplistic anatomically than the sympathetic division of the autonomic nervous system, due to its preganglionic neurons being located in the brain stem and the sacral region. Itspostganglionic neurons are located in close approximation to the organ to be supplied. While the parasympathetic division is considered to be a supportive system for the sympathetic, frequently they have an antagonistic relationship. This antagonistic relationship must be carefully balanced and regulated. The parasympathetic division is active during rest. This is when it provides digestion and the conservation of energy, however, should you eat a large meal and immediately jog, you have thrown these two divisions into direct opposition.

Hilton’s Law states: “a nerve trunk which supplies the muscles of any given joint also supplies the muscles which move the joint and the skin over the insertions of such muscles.”

Based upon this law and supporting EMG studies, we can assume that underlying dermatomes are residing myotomes and sclerotomes with resulting sensory and motor dysfunction. Should there be an organic or biomechanical encroachment or compression affecting the ventral nerve root you would anticipate autonomic impairment and subsequent viscerotomes. The most obvious evidence of a dermatome pattern is the lesions produced by herpes zoster. As this infection predominantly affects the dorsal root ganglia of the thoracic segments, dermatomal patterns are outlined by defined pain, hyperesthesia and pustules. However, it can occur at any level of the spine and following the active state of the lesions post-herpetic neuralgia may be experienced periodically for years, and is usually predicated by stress and a compromised autoimmune system. Radiculopathies also follow these pathways with resulting dysesthesia.

The spinal nerves have overlapping supply thus serving as a protective mechanism against injury as it pertains to nerve innervation of a given structure or organ. Segmental supply as referenced below is derived from consistencies from Gray’s Anatomy, Correlative Neuroanatomy by Waxman & deGroot, Human Anatomy and Physiology by Dr. Marieb and various EMG studies. The reader should note that innervation can occur within a segment or two above or below our specific reference depending upon the individual.

Below are links to data tables containing information about spinal nerve segment, plexus, innervation of muscle and visceria, and dermatome pattern for each spinal region.

C1 through C8 – thecervical region

T1 through T12 – the thoracic region

L1 through L5 – the lumbar region

S1 through S5 + coccyx – the sacro-coccygeal region

SPINAL NERVE SEGMENT	PLEXUS	INNERVATION OF MUSCLE & VISCERIA	DERMATOME PATTERN
C1	CERVICAL	Anterior & Lateralis Rectus Capitis; Longus Capitis; Omohyoid; Thyrohyoid; Geniohyoid.	When present, referral is in the back of head covering occipital region.
C2	CERVICAL	Anterior & Lateralis Rectus Capitis; Omohyoid; Sternohyoid; Sternothyroid; Longus Capitis; Longus Colli	Posteriorly refers to the supraoccipital region; Laterally the zone refers from the superior aspect of the ear inferiorly to the posterior aspect of the ear.
C3	CERVICAL	Omohyoid; Sternohyoid; Sternothyroid; Longus Capitis; Longus Colli; Scalenes Medius: Scalenes Posterior; Levator scapulae; Rhomboids; Trapezius; Respiratory diaphragm.	Lateral and anterior aspect of the neck
C4	CERVICAL	Longus Capitis; Longus Colli; Scalenus Medius; Scalenes Posterior; Levator Scapulae; Trapezius; Rhomboids; Teres Minor; Supraspinatus; Infraspinatus; Deltoid; Respiratory Diaphragm	Superior posterior aspect of neck as well as anterior inferior aspect of neck
C5	CERVICAL AND BRACHIAL	Sometimes part of the Levator Scapulae; Rhomboids; Supraspinatus; Infraspinatus; Subscapularis; Deltoid; Biceps Brachii; Brachioradialis; Scalenes Anterior; Scalenes Posterior; Serratus Anterior; Pectoralis Major & Minor; Teres Major & Minor; Longus Colli; Respiratory Diaphragm	Posteriorly traverses from the superior aspect of the cervical thoracic junction to anteriorly slightly superior to or directly on top of the clavicle; additionally it traverses from the superior aspect of the CT junction superiorly and slightly posterior across the shoulder down the anterior medial aspect of the arm and forearm terminating slightly superior to the wrist.
C6	BRACHIAL	Sometimes Latissimus Dorsi; Scalene Anterior; Scalenes Posterior; Pectoralis Major & Minor; Serratus Anterior; Supraspinatus; Infraspinatus; Subscapularis; Teres Major & Minor; Deltoid; Biceps Brachii; Triceps; Brachioradialis; Pronator Teres; Longus Colli; Extensor Carpi radialis & Ulnaris; Extensor Digiti Quanti Proprius; Flexor Carpi Radialis	With a broad horizontal distribution it initiates from the inferior aspect of C6 traverses the posterior aspect of the upper back & shoulder, and distally down the lateral aspect of the arm, forearm, and into the thumb.
C7	BRACHIAL	Scalene Anterior; Scalenes Posterior; Pectoralis Major & Minor; Serratus Anterior; Subscapularis; Teres Major; Latissimus Dorsi; Triceps; Pronator Teres; Longus Colli; Extensor Carpi radialis & Ulnaris; Extensor Digitorum & Quanti Proprius; Flexor Carpi Radialis; Palmaris Longus	With a broad horizontal distribution it traverses inferior from the CT junction across the superior aspect of the upper back to the posterior aspect of the shoulder & distally down the posterior aspect of the arm, forearm, middle & index fingers.
C8	BRACHIAL	Scalene Anterior; Scalene Posterior; Pectoralis Major & Minor; Subscapularis; Teres Major; Latissimus Dorsi; Triceps; Sometimes Pronator Teres; Longus Colli; Extensor Carpi Radialis & Ulnaris; Extensor Digitorum & Quanti Proprius; Flexor Digitorum Superficialis & Profundus; Flexor Pollicis Longus & Brevis; Interossei; Lumbricales; Palmaris Longus	The referral initiates medial to the vertebral border of the scapulae traverses beneath the inferior angle and continues superior and laterally to the axilla at which time it traverses from the axilla distally down the medial aspect of the arm, forearm & into the ring and little finger.
SPINAL NERVE SEGMENT	PLEXUS	INNERVATION OF MUSCLE & VISCERIA	DERMATOME PATTERN
T1	BRACHIAL	Intercostals of Respective Level; Levatores Costarum; Serratus Posterior & Superior; Semispinalis Thoracis; Pectoralis Major & Minor; Transversus Thoracis; Sometimes Pronator Teres; Flexor Digitorum Superficalis & Profundus; Interossei, Lumbricales; Flexor Pollicis Longus & Brevis; Opponens Pollicis; Abductor Pollicis Brevis; Thyroid; Heart	Posteriorly from about the level of T1 the pattern traverses inferiorly across the spine of the scapula around and under the axilla anteriorly to the sternum at approximately the level of the 2nd and 3rd rib; Additionally it traverses from the sternum at the level of the 2nd or 3rd rib laterally to the anterior aspect of the shoulder and down the anterior medial aspect of the arm, forearm and terminates at the base of the thenar eminence.
T2	BRACHIAL	Transversus Thoracis; Intercostals of Respective Level; Levatores Costarum; Serratus Posterior Superior; Semispinalis Thoracis; Intrinsic Back Muscles; Heart, Heart Valves; Coronary Arteries	Posteriorly it traverses from T2 inferiorly beneath the inferior angle of the scapula at which time it ascends superiorly to the axilla and anteriorly above the nipple line to the sternum.
T3	NONE	Transversus Thoracis; Intercostals of Respective Level; Levatores Costarum; Serratus Posterior Superior; Semispinalis Thoracis; Intrinsic Back Muscles; Heart; Chest; Pleura; Bronchial Tubes; Lungs	Traverses from approximately the level of T3 inferiorly and lateral to the inferior angle of the scapula at which time it traverses superiorly and laterally around the thorax and terminates at the sternum just superior to the nipple line.
T4	NONE	Transversus Thoracis; Intercostals of Respective Level; Levatores Costarum; Semispinalis Thoracis; Intrinsic Back Muscles; Gall Bladder; Common Bile Duct;	Traverses from the level of T4 well beneath the scapula at approximately the level of the 7th rib; anteriorly it sweeps superiorly under the axilla and across the nipple line.
T5	NONE	Transversus Thoracis; Intercostals of Respective Level; Levatores Costarum; Semispinalis Thoracis; Stomach; Liver; Solar Plexus;	T5 traverses in a pattern slightly inferior to that referenced at T4 with its anterior translation across the inferior aspect of the breast and mastic cleft and terminating at the sternum.
T6	NONE	Transversus Thoracis: Intercostals of Respective Level: Levatores Costarum; Semispinalis Thoracis; Stomach; Pancreas	T6 traverses from the 6th segment posteriorly along the course of the 6th or 7th rib anteriorly and terminates at the xiphoid process.
T7	NONE	Intercostals of Respective Levels; Levatores Costarum; Intrinsic Back Muscles; Transverse Abdominis; Rectus Abdominis; Pancreas; Spleen; Duodenum	The dermatome pain referral for the T7 spinal nervetraverses from the 7th segment, anteriorly along the 7th & 8th rib and terminates slightly inferior of the xiphoid process.
T8	NONE	Intercostals of Respective Levels; Levatores Costarum; Intrinsic Back Muscles; External Obliques; Internal Obliques; Transverse Abdominis; Rectus Abdominis; Spleen	Traverses posteriorly from T8 to anteriorly at the mid epigastrium.
T9	NONE	Intercostals of Respective Levels; Levatores Costarum; Intrinsic Back Muscles; External Obliques; Internal Obliques; Transverse Abdominis; Rectus Abdominis; Adrenal Glands	Traverses posteriorly from T9 to anteriorly slightly above the umbilicus.
T10	NONE	Intercostals of Respective Levels: Levatores Costarum; Serratus Posterior Inferior; Intrinsic Back Muscles; External Obliques; Internal Obliques; Transverse Abdominis; Rectus Abdominis; Kidneys; Adrenal Glands	Traverses posteriorly from T10 to anteriorly through the umbilicus.
T11	NONE	Intercostals of Respective Levels; Levatores Costarum; Serratus Posterior Inferior; Intrinsic Back Muscles; External Obliques; Internal Obliques; Transverse Abdominis; Rectus Abdominis; Kidneys; Ureters	Traverses posteriorly from T11 to anteriorly slightly beneath the umbilicus.
T12	LUMBAR	Intercostals of Respective Levels; Levatores Costarum; Serratus Posterior Inferior; Intrinsic Back Muscles; External Obliques; Internal Obliques; Transverse Abdominis; Rectus Abdominis; Pyramidalis; Small Intestine; Kidneys	Traverses posteriorly from T12 to anteriorly slightly above the pubis.

SPINAL NERVE SEGMENT	PLEXUS	INNERVATION OF MUSCLE & VISCERIA	DERMATOME PATTERN
L1	LUMBAR	External Obliques; Internal Obliques; Transverse Abdominis; Cremaster; Rectus Abdominis; Quadratus Lumborum; Iliopsoas; Iliacus; Ileocecal Valve; Large Intestine	Traverses posteriorly & inferiorly from L1 to affect the pubic, medial thigh and groin regions.
L2	LUMBAR	External Obliques; Internal Obliques; Transverse Abdominis; Cremaster; Rectus Abdominis; Quadratus Lumborum; Iliacus; Psoas Major & Minor; Sartorius; Rectus Femoris; Vastus Lateralis; Vastus Intermedius; Vastus Medialis; Adductor Longus & Brevis; Pectineus; Gracilis; Female Reproductive System; Appendix	Traverses posteriorly from L2 above the buttocks inferiorly down the lateral aspect of the mid-thigh at which time it traverses anteriorly & inferiorly to the medial aspect of the mid-thigh.
L3	LUMBAR	Transverse Abdominis; Cremaster; Rectus Abdominis; Quadratus Lumborum; Iliacus; Psoas Major & Minor; Sartorius; Rectus Femoris; Vastus Lateralis; Vastus Intermedius; Vastus Medialis; Pectineus; Adductor Longus & Brevis; Adductor magnus; Gracilis; Obturator Externus; Urinary Bladder; Female & Male Reproductive System	Traverses posteriorly from L3 across the superior aspect of the buttocks & inferiorly down the lateral & distal aspect of the thigh, at which time it traverses anteriorly & inferiorly to the medial aspect of the distal thigh at the knee.
L4	LUMBAR-SACRAL	Transverse Abdominis; Cremaster; Rectus Abdominis; Obturator Externus; Gluteus Maximus, Medius & Minimus; Superior & Inferior Gemelli; Adductor Brevis; Adductor Magnus; Gracilis; Tensor Fasciae Latae; Rectus Femoris; Vastus Lateralis; Vastus Intermedius; Vastus Medialis; Biceps Femoris; Semimembranosus; Semitendinosus; Tibialis Anterior; Peroneus Tertius; Extensor Digitorum Longus & Brevis; Extensor Hallucis Longus; Prostate Gland	Traverses posteriorly from L4 through the buttocks and the entire length of the lateral aspect of the thigh; at which time it traverses anteriorly and slightly inferiorly beneath the patella to the medial aspect of the leg whereby it traverses inferiorly through the medial malleolus and into the great toe as well as the plantar surface of the great toe.
L5	SACRAL	Gluteus Maximus, Medius & Minimus; Tensor Fasciae Latae; Obturator Internus; Superior & Inferior Gemelli; Rectus Femoris; Vastus Lateralis; Vastus Intermedius; Vastus Medialis; Biceps Femoris; Semitendinosus; Semimembranosus; Tibialis Anterior; Extensor Hallucis Longus; Extensor Digitorum Longus & Brevis; Peroneus Tertius; Peroneus Longus & Brevis; Gastrocnemius; Soleus; Plantaris; Popliteus; Flexor Hallucis Longus & Brevis; Flexor Digitorum Longus & Brevis; Tibialis Posterior; Dorsal Interossei; Plantar Interossei; Perineum	Traverses posteriorly from L5 into the buttocks & inferiorly down the posterior lateral aspect of the thigh & proximal leg at which time it traverses anteriorly & inferiorly down the anterior aspect of the leg & medial dorsum of the foot.

SPINAL NERVE SEGMENT	PLEXUS	INNERVATION OF MUSCLE & VISCERA	DERMATOME PATTERN
S1	SACRAL	Gluteus Maximus, Medius & Minimus; Piriformis; Superior & Inferior Gemelli; Obturator Internus; Rectus Femoris; Vastus Lateralis; Vastus intermedius; Vastus Medialis; Biceps Femoris; Semitendinosus; Semimembranosus; Tibialis Posterior; Peroneus Tertius; Extensor Digitorum Longus & Brevis; Extensor Hallucis Longus; Peroneus Longus & Brevis; Gastrocnemius; Soleus; Plantaris; Popliteus; Flexor Digitorum Longus & Brevis; Flexor Hallucis Longus & Brevis; Abductor Hallucis; Abductor Digiti Minimi; Quadratus Plantae; Flexor Digiti Minimi Brevis; Dorsal Interossei; Plantar Interossei	Traverses posteriorly from S1 into the buttocks, posterior aspect of thigh, leg & heel also involving the area of the lateral aspect of the heel, foot & little toe.
S2	SACRAL	Levator Ani; Coccygeus; Transversus Perinei Superficialis; Bulbocavernosus; Ischiocavernosus; Transverse Perinei Profundus; Sphincter Urethra; Sphincter Ani Externus; Piriformis; Gluteus Maximus; Biceps Femoris; Gastrocnemius; Soleus; Plantaris; Popliteus: Flexor Digitorum Longus; Flexor Hallucis Longus & Brevis; Abductor Hallucis; Abductor Digiti Minimi; Quadratus Plantae; Flexor Digiti Minimi Brevis; Dorsal Interossei; Plantar Interossei	Traverses posteriorly from S2 through the gluteal cleavage sweeping slightly medial beneath the gluteal cleft at which time it traverses inferiorly down the medial aspect of the thigh, leg, ankle, and heel & terminates in the arch of the foot. Anteriorly, in males, the root of the penis as well as approximately 2/3 of the proximal shaft. In females, external genitalia.
S3	SACRAL	Levator Ani; Coccygeus; Transversus Perineai Superficialis; Bulbocavernosus; Ischiocavernosus; Transversus Perinei Profundus; Sphincter Ani Externus	Posteriorly affects the perianal region, anteriorly in males the distal 1/3 of the shaft, glands penis and urethral meatus. In females, the internal genitalia are innervated.
S4	SACRAL AND COCCYGEAL	Levator Ani; Coccygeus; Transversus Perineai Superficialis; Bulbocavernosus; Ischiocavernosus; Transversus Perineai Profundus; Sphincter Urethra; Sphincter Ani	Seems to be limited to the anal region
S5	COCCYGEAL	Levator Ani; Coccygeus; Transversus Perinei Superficialis; Bulbocavernosus; Ischiocavernosus; Transversus Perineai Profundus; Sphincter Urethra; Sphincter Ani;	Appears to be limited to the anus & rectum.
COCCYX	COCCYGEAL	Levator Ani; Coccygeus; Transversus Perineai Superficialis; Bulbocavernosus; Ischiocavernosus; Transversus Perineai Profundus; Sphincter Urethra; Sphincter Ani	Appears to be limited to the anus & rectum.