SPINAL CORD, , 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 • 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 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 -(sensory ganglion / dorsal root ganglion)- Before joining, dorsal root shows ganglion which is seen in . Ganglion is made up of unipolar neurons.

Two processes- 1) Peripheral 2) Central.

Applied Anatomy

• The dorsal ganglia (and the sensory ganglia of ) 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 , • 8th cervical nerve below 7th cervical vertebra. • All thoracic, lumbar and sacral nerves emerge below respective vertebrae. 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 “”

• Ventral primary rami are the only sources for the formation of all plexuses.

• Plexuses: • Cervical • Brachial • Lumbar • Sacral • Coccygeal

Cervical plexus

• The is a network of nerve fibres that supplies innervation to some of the structures in the 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 and .

Muscular innervation of cervical plexus

Cervical plexus Branches

• Cutaneous branches • Muscular Branches • They supply some of the muscles of the neck

• (goose’s neck) is a loop of nerves, formed by nerve roots C1-C3. It supplies (except thyrohyoid by C1+XII)

• - 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): • - innervates lateral part of occipital region (C2 ONLY) • Great auricular nerve - innervates skin near concha and external acoustic meatus (C2&C3) • Transverse cervical nerve - innervates anterior region of neck (C2&C3) • - innervate region of supraspinatus, , 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 • • Sternocleidomastoid & muscle

Brachial plexus

• Formation: by ventral rami of C5,C6,C7,C8 and T1 (with contribution from C4 &T2) • Location: posterior triangle & • Supplies (brachium) • Consists of roots, trunks, divisions and cords.

Branches of Like tree

L M L

U Upper &lower L T R A

M 4 U 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

Saturday night palsy • In spiral groove injury due to #/intramuscular injections. • Wrist drop—flexion at wrist. • Injury due to cruches pressure

• Provides motor and sensory nerves for the anterior & medial compartment of

• Location: on posterior deep to psoas major, in front of transverse processes of

Lumbar plexus • Formation - by the ventral divisions of the first four (L1-L4) & from contributions of (T12) Lumbar plexus branches

• - supplies Transversus abdominis & abdominal internal oblique

• – supplies extensor comportment muscles

• - 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 • • Pectineus • Anterior cutaneous branches Femoral L2-L4 • Sartorius • Saphenous • Quadriceps femoris

• Provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire , and part of the .

• Location - Lies in front of deep to pelvic fascia and behind internal iliac vessels & . Sacral plexus ….

Formation – • (L4&L5) • Ventral division of S 1- 3 nerves

Sacral plexus branches • (L4-S3 both div.) which splits on the back of the thigh into & common fibular nerve – supplies post. compartment of thigh & leg • – (S2-3 ventral div.) supplies skin, external genital organs & muscles of . 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 . Development of limbs

• Upper limbs (UL) undergoes 90 degrees lateral rotation, while lower limb (LL) turns medially • Pre-axial border lies along & big toe • Post-axial border lies along 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 & 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