SPINAL CORD, NERVES, PLEXUSES AND DERMATOMES -2 Dr. Sangeeta S Kotrannavar Assistant Professor Dept. of Anatomy USM-KLE IMP, Belagavi Objectives • Spinal nerves • Describe the organization of spinal nerves and their functional component • Define nerve plexus • State the different nerve plexuses • Dermatomes • Define & describe the dermatomes and map out the dermatomes of the body & applied anatomy of dermatomes Spinal cord Structure of typical spinal nerve Arise from spinal cord by 2 roots • Ventral root – contains motor fibers • Dorsal root – contains sensory fibers Both roots joined to form spinal nerve, which is mixed nerve Spinal nerve • Spinal nerve divides into ventral (ant.) & dorsal (post.) rami (branch) • Ventral ramus supplies body wall & viscera • Dorsal ramus supplies the intrinsic muscles of the back and the skin covering them. • Dorsal primary ramus divides into medial and lateral branches Motor Spinal nerve Sensory Sympathetic To skeletal M & skin of back To skeletal M. & skin of body wall & limbs To smooth M. & glands of visceral organs Ventral root-motor Dorsal root-sensory Spinal ganglion-(sensory ganglion / dorsal root ganglion)- Before joining, dorsal root shows ganglion which is seen in intervertebral foramen. Ganglion is made up of unipolar neurons. Two processes- 1) Peripheral 2) Central. Applied Anatomy • The dorsal nerve root ganglia (and the sensory ganglia of cranial nerves) can be infected with a virus condition called as herpes zoster. • Vesicles appear on the skin over the area of distribution of the nerve. • The condition is highly painful Exit of spinal nerves • Upper 7 cervical nerves leave the intervertebral foramen above the respective vertebra, • 8th cervical nerve below 7th cervical vertebra. • All thoracic, lumbar and sacral nerves emerge below respective vertebrae. Reflex arc Spinal Nerves “Nerves attached to spinal cord” • 31 pairs of spinal nerves • C1-C8 • T1-T12 • L1-L5 • S1-S5 • Co-1 Nerve Plexuses • Ventral rami (branches) of various spinal nerves blend together to form an interwoven network of nerves, called “nerve plexus” • Ventral primary rami are the only sources for the formation of all plexuses. • Plexuses: • Cervical • Brachial • Lumbar • Sacral • Coccygeal Cervical plexus • The cervical plexus is a network of nerve fibres that supplies innervation to some of the structures in the neck and trunk. • Location - in the posterior triangle of the neck, halfway up the sternocleidomastoid muscle, and within the prevertebral layer of cervical fascia. Cervical plexus …… • Formation - The plexus is formed by the ventral rami (divisions) of cervical spinal nerves C1-C4. • Communicates with accessory nerve and hypoglossal nerve. Muscular innervation of cervical plexus Cervical plexus Branches • Cutaneous branches • Muscular Branches • They supply some of the muscles of the neck • Ansa cervicalis (goose’s neck) is a loop of nerves, formed by nerve roots C1-C3. It supplies infrahyoid muscles (except thyrohyoid by C1+XII) • Phrenic nerve - arises from the anterior rami of C3-C5. It provides motor &sensory innervation to diaphragm. Cutaneous innervation of cervical plexus Branches of cervical plexus • Cutaneous (4 branches): • Lesser occipital nerve - innervates lateral part of occipital region (C2 ONLY) • Great auricular nerve - innervates skin near concha auricle and external acoustic meatus (C2&C3) • Transverse cervical nerve - innervates anterior region of neck (C2&C3) • Supraclavicular nerves - innervate region of supraspinatus, shoulder, and upper thoracic region (C3,C4) • Muscular • Ansa cervicalis (loop formed from C1-C3) – supplies sternothyroid, sternohyoid, omohyoid • Phrenic (C3-C5)-innervates diaphragm and pericardium • Scalene muscles • Sternocleidomastoid & trapezius muscle Brachial plexus • Formation: by ventral rami of C5,C6,C7,C8 and T1 (with contribution from C4 &T2) • Location: posterior triangle & axilla • Supplies upper limb (brachium) • Consists of roots, trunks, divisions and cords. Branches of brachial plexus Like tree L M L U Upper &lower L T R A M 4 U Ulnar Nerve Brachial plexus…… Brachial plexus summary…… Brachial plexus summary…… APPLIED ASPECT Erb’s paralysis • Site is UPPER TRUNK. • Cause-birth injury/fall on shoulder. • Deformity—Policeman’s tip. Klumpke’s paralysis • Site LOWER TRUNK • Deformity—Claw hand APPLIED ASPECT OF RADIAL NERVE Saturday night palsy • In spiral groove injury due to #/intramuscular injections. • Wrist drop—flexion at wrist. • Injury due to cruches pressure Lumbosacral plexus Lumbar plexus • Provides motor and sensory nerves for the anterior & medial compartment of thigh • Location: on posterior abdominal wall deep to psoas major, in front of transverse processes of lumbar vertebrae Lumbar plexus • Formation - by the ventral divisions of the first four lumbar nerves (L1-L4) & from contributions of subcostal nerve (T12) Lumbar plexus branches • Iliohypogastric nerve- supplies Transversus abdominis & abdominal internal oblique • Femoral nerve – supplies extensor comportment muscles • Obturator nerve - supplies adductor comportment muscles Lumbar plexus-summary Nerve Segment Innervated muscles Cutaneous branches Iliohypogastric T12-L1 • Anterior cutaneous ramus • Transversus abdominis • Lateral cutaneous ramus • Abdominal internal Ilioinguinal L1 • Anterior scrotal nerves in males oblique • Anterior labial nerves in females • Cremaster in males • Femoral ramus Genitofemoral L1, L2 labia major in female • Genital ramus Lateral femoral L2, L3 • Lateral femoral cutaneous cutaneous • Obturator externus • Adductor longus • Adductor brevis Obturator L2-L4 • Cutaneous ramus • Gracilis • Pectineus • Adductor magnus • Iliopsoas • Pectineus • Anterior cutaneous branches Femoral L2-L4 • Sartorius • Saphenous • Quadriceps femoris Sacral plexus • Provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis. • Location - Lies in front of piriformis muscle deep to pelvic fascia and behind internal iliac vessels & ureter. Sacral plexus …. Formation – • lumbosacral trunk (L4&L5) • Ventral division of S 1- 3 nerves Sacral plexus branches • Sciatic nerve (L4-S3 both div.) which splits on the back of the thigh into tibial nerve & common fibular nerve – supplies post. compartment of thigh & leg • Pudendal nerve – (S2-3 ventral div.) supplies skin, external genital organs & muscles of perineum. Sacral plexus branches Nerves of the lower extremity Coccygeal plexus • Formation • ventral rami of S5-Co1 • Location • on plevic surface of coccygeus • Branches – • Anococcygeal nerve – supplies skin of coccygeal area Applied • Disc prolapse at cervical & lumbar regions is very common as it is leads to nerve root compression & irritation Dermatome • Areas of skin supplied by individual spinal nerves are called dermatomes. • To understand the arrangement of dermatomes it is necessary to know some facts about the development of the limbs. • C1-No dermatome. Development of limbs • Upper limbs (UL) undergoes 90 degrees lateral rotation, while lower limb (LL) turns medially • Pre-axial border lies along thumb & big toe • Post-axial border lies along little finger and toe • Ant.surface – Flexor surface in UL, while extensor in LL • Post. Surface - Extensor surface in UL, while flexor in LL Dermatomes of upper limb Dermatomes of upper limb Dermatomes of lower limb & thorax Applied • Testing of dermatomes able to identifying sensory impairment &level of spinal cord involvement in neurological disorder MTF •Regarding spinal nerves T A They form nerve plexus F B There are 33 pairs of spinal nerves F C Dorsal root contain efferent fibres T D Spinal nerves is mixed nerve T E Central canal contains CSF OSPE Practical • Identify external and internal features of spinal cord • Identify the spinal nerves .