DEVELOPMENTAL ANATOMY & ORGANIZATION OF THE NERVOUS SYSTEMEXEQUIEL P. DIMAANO, MD

NERVOUS SYSTEM

• Structurally

• Central nervous system (CNS)

• Peripheral nervous system (PNS)

• Functionally

• Somatic

• Visceral

STRUCTURAL DIVISIONS OF THE NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEMSTRUCTURAL DIVISION OF THE NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM - BRAIN

• Cerebral hemispheres

• outer portion or the gray matter - cell bodies

• an inner portion or the white matter – axons

• Ventricles- filled with cerebrospinal fluid (CSF)

• Cerebellum

• two lateral lobes - hemispsheres

• midline portion - vermis

CENTRAL NERVOUS SYSTEM - BRAIN

• Brainstem

• Diencephalon – hypothalamus & thalamus

• Midbrain

• Pons

• Medulla

CENTRAL NERVOUS SYSTEM - SPINAL CORD

• the superior two-thirds of the vertebral canal

• circular to oval in cross-section with a central canal

• from the foramen magnum to approximately the level of the disc between vertebrae LI and LII in adult

(LIII in neonates)

CENTRAL NERVOUS SYSTEM - SPINAL CORD• 2 major enlargements

• Cervical enlargement - origins of spinal nerves C5 to T1 – Brachial Plexus

• Lumbosacral enlargement – origins of spinal nerves L1 to S3 – Lumbosacral Plexus

• distal end of the cord - conus medullaris

• the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris

CENTRAL NERVOUS SYSTEM - SPINAL CORD• Externally

• Anterior median fissure

• Posterior median sulcus

• Posterolateral sulcus - where the posterior rootlets of spinal nerves enter the cord

• Internally

• small Central canal, surrounded by

• Gray matter – rich in cell bodies

• White matter – rich in nerve cell processes

SPINAL CORD - ARTERIAL SUPPLY

• Longitudinally oriented vessels

• 1 Anterior spinal artery

• 2 Posterior spinal arteries

• Feeder arteries or segmental spinal arteries

• from the vertebral and deep cervical arteries in the neck,

• the posterior intercostal arteries in the thorax and

• the lumbar arteries in the abdomen.

• 1 Anterior spinal artery

• originates within the cranial cavity as the union of two vessels that arise from the vertebral arteries

• 2 Posterior spinal arteries

• originate in the cranial cavity, usually arising directly from a terminal branch of each vertebral artery (the posterior inferior cerebellar artery)

Reinforced along their length by 8-10 segmental medullary arteries

The largest of these is the arteria radicularis magna or the artery of Adamkiewicz

SPINAL CORD - ARTERIAL SUPPLY

• Segmental Spinal Arteries

• give rise to anterior and posterior radicular arteries

• follow, and supply, the anterior and posterior roots

SPINAL CORD - VENOUS DRAINAGE

• two pairs of veins on each side bracket the connections of the posterior and anterior roots to the cord;

• one midline channel parallels the anterior median fissure;

• one midline channel passes along the posterior median sulcus

• drain into an extensive internal vertebral plexus in the extradural (epidural) space of the vertebral canal

SPINAL CORD - MENINGES

• the dura mater is the thickest and most external of the coverings;

• the arachnoid mater is against the internal surface of the dura mater;

• the pia mater is adherent to the brain and spinal cord.

VERTEBRAL CANAL• The vertebral canal is bordered:

• anteriorly -bodies of the vertebrae, intervertebral discs, and posterior longitudinal ligament;

• Laterally - pedicles and intervertebral foramina;

• posteriorly - laminae and ligamenta flava, and in the median plane the roots of the interspinous ligaments and vertebral spinous processes

PERIPHERAL NERVOUS SYSTEMSTRUCTURAL DIVISION OF THE NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM

• Cranial Nerves

• Spinal Nerves

• Visceral Plexuses (Pre-vertebral, Cardiac, etc)

• Somatic Plexuses (Cervical, Brachial, Lumbo-Sacral)

• Enteric Plexus

PERIPHERAL NERVOUS SYSTEM- SPINAL NERVES

• posterior root - contains the processes of sensory neurons;

• the cell bodies of the sensory neurons, which are derived embryologically from neural crest cells, are clustered in a spinal ganglion;

• the anterior root contains motor nerve fibers

• the cell bodies of the primary motor neurons are in anterior regions of the spinal cord

• All major somatic plexuses (cervical, brachial, lumbar, and sacral) are formed by anterior rami

NOMENCLATURE OF SPINAL NERVES

• 8 cervical nerves-C1 to C8;

• 12 thoracic nerves-T1 to T12;

• 5 lumbar nerves-L1 to L5;

• 5 sacral nerves-S1 to S5;

• 1 coccygeal nerve (Co).

BRACHIAL PLEXUS

• is formed by the anterior rami of cervical spinal nerves C5 to C8, and T1

• The major spinal cord level associated with innervation of the diaphragm, C4, is immediately above the spinal cord levels associated with the upper limb

BRACHIAL PLEXUS SENSORY TEST - AUTONOMOUS AREAS

• the upper lateral region of the arm for spinal cord level C5;

• the palmar pad of the thumb for spinal cord level C6;

• the pad of the index finger for spinal cord level C7;

• the pad of the little finger for spinal cord level C8;

• skin on the medial aspect of the elbow for spinal cord level T1

BRACHIAL PLEXUS MUSCLE TESTING

• flexion of the forearm at the elbow joint is controlled primarily by C6;

• extension of the forearm at the elbow joint is controlled mainly by C7;

• flexion of the fingers is controlled mainly by C8;

• abduction and adduction of the index, middle and ring fingers is controlled predominantly by T1

BRACHIAL PLEXUS REFLEXES

• a 'tap' on the tendon of the biceps in the cubital fossa tests mainly for spinal cord level C6;

• a tap on the tendon of the triceps posterior to the elbow tests mainly for C7.

UPPER LIMB MUSCLES - PERIPHERAL NERVES

• anterior compartment of the arm - musculocutaneous nerve;

• anterior compartment of the forearm - median nerve,

• two exceptions- one flexor of the wrist (the flexor carpi ulnaris muscle) and part of one flexor of the fingers (the medial half of the flexor digitorum profundus muscle) are innervated by the ulnar nerve;

UPPER LIMB MUSCLES - PERIPHERAL NERVES

• most intrinsic muscles of the hand are innervated by the ulnar nerve,

• except for the thenar muscles and two lateral lumbrical muscles, which are innervated by the median nerve

• all muscles in the posterior compartments of the arm and forearm - radial nerve

UPPER LIMB SOMATIC SENSORY – PERIPHERAL NERVES

• the musculocutaneous nerve innervates skin on the anterolateral side of the forearm;

• the median nerve innervates the palmar surface of the lateral three and one-half digits, and the ulnar nerve innervates the medial one and one-half digits;

• the radial nerve supplies skin on the posterior surface of the forearm and the dorsolateral surface of the hand.

LUMBOSACRAL PLEXUS

• spinal cord levels L1 to S3

• anterior rami of L1 to L3 and most of L4 (lumbar plexus)

• L4 to S5 (sacral plexus).

SENSORY TESTING - AUTONOMOS AREAS

• over the inguinal ligament-L1;

• lateral side of the thigh-L2;

• lower medial side of the thigh-L3;

• meidal side of the great toe (digit 1)-L4;

• medial side of digit 2-L5;

• little toe (digit 5)-S1;

• back of the thigh-S2;

• skin over the gluteal fold-S3

MUSCLE TESTING• flexion of the hip is controlled

primarily by L1 and L2;

• extension of the knee is controlled mainly by L3 and L4;

• knee flexion is controlled mainly by L5 to S2;

• plantarflexion of the foot is controlled predominantly by S1 and S2;

• adduction of the digits is controlled by S2 and S3.

LUMBOSACRAL PLEXUS - REFLEXES

• a 'tap' on the patellar ligament at the knee tests predominantly L3 and L4;

• a tendon tap on the calcaneal tendon posterior to the ankle (tendon of gastrocnemius and soleus) tests S1 and S2.

LOWER LIMB MUSCLES - PERIPHERAL NERVES• large muscles in the gluteal region are

innervated by the superior and inferior gluteal nerves;

• most muscles in the anterior compartment of the thigh are innervated by the femoral nerve

• except the tensor fasciae latae, which is innervated by the superior gluteal nerve

• most muscles in the medial compartment are innervated mainly by the obturator nerve

• except the pectineus, which is innervated by the femoral nerve, and part of the adductor magnus, which are innervated by the tibial division of the sciatic nerve

LOWER LIMB MUSCLES - PERIPHERAL NERVES• most muscles in the posterior

compartment of the thigh and the leg and in the sole of the foot are innervated by the tibial part of the sciatic nerve

• except the short head of the biceps femoris in the posterior thigh, which are innervated by the common fibular division of the sciatic nerve;

• the anterior and lateral compartments of the leg and muscles associated with the dorsal surface of the foot are innervated by the common fibular part of the sciatic nerve

UPPER LIMB SOMATIC SENSORY – PERIPHERAL NERVES

• the femoral nerve innervates skin on the anterior thigh, medial side of the leg, and medial side of the ankle;

• the obturator nerve innervates the medial side of the thigh;

• the tibial part of the sciatic nerve innervates the lateral side of the ankle and foot;

• the common fibular nerve innervates the lateral side of the leg and the dorsum of the foot.

FUNCTIONAL DIVISIONS OF THE NERVOUS SYSTEM

SOMATIC PARTFUNCTIONAL DIVISION OF THE NERVOUS SYSTEM

SOMATIC NERVES• Arise segmentally along the developing

CNS in association with somites

• Part of each somite (the dermatomyotome) gives rise to skeletal muscle and the dermis of the skin

• Cells that migrate anteriorly give rise to muscles of the limbs and trunk (hypaxial muscles) and to the associated dermis;

• Cells that migrate posteriorly give rise to the intrinsic muscles of the back (epaxial muscles) and the associated dermis

SOMATIC PART

• Somatic motor fibers carry information away from the CNS to skeletal muscles and are also called somatic motor efferents or general somatic efferents (GSEs)

• Somatic sensory neurons carry information from the periphery into the CNS and are also called somatic sensory afferents or general somatic afferents (GSAs)

DERMATOMES

• dermatome is that area of skin supplied by a single spinal cord level, or on one side, by a single spinal nerve.

MYOTOMES

• myotome is that portion of a skeletal muscle innervated by a single spinal cord level or, on one side, by a single spinal nerve

VISCERAL PART • Visceral sensory neurons

• from neural crest cells

• general visceral afferent fibers (GVAs)

• primarily with chemoreception, mechanoreception, and stretch reception

• Visceral motor neurons • from cells in lateral regions of the

neural tube

• general visceral efferent fibers (GVEs),

• synapse with other cells, usually other visceral motor neurons, that develop outside the CNS from neural crest cells

AUTONOMIC NERVOUS SYSTEM

• In spinal levels T1 to L2 are termed sympathetic

• innervates structures in peripheral regions of the body and viscera

• In cranial and sacral regions are termed parasympathetic

• more restricted to innervation of the viscera only

SYMPATHETIC SYSTEM

• Fight or flight

• on each side, a paravertebral sympathetic trunk

• extends from the base of the skull to the inferior end of the vertebral column where the two trunks converge anteriorly to the coccyx at the ganglion impar

SYMPATHETIC NERVES

•White ramus communicans

• connects anterior rami of T1 to L2 to the sympathetic trunk or to a ganglion

• carry preganglionic sympathetic fibers

• contains are myelinated

• Gray ramus communicans

• connects the sympathetic trunk or a ganglion to the anterior ramus

• contains the postganglionic sympathetic fibers

• nonmyelinated

SYMPATHETIC NERVES

• Fibers T1 to T5 pass superiorly

• Fibers from T5 to L2 pass inferiorly

• All sympathetics passing into the head have preganglionic fibers that emerge from spinal cord level T1 and ascend in the sympathetic trunks to the highest ganglion in the neck (the superior cervical ganglion), where they synapse.

THORACIC & VISCERAL SYMPATHETICS

• Preganglionic sympathetic fibers may synapse with postganglionic motor neurons in ganglia and then leave the ganglia medially to innervate thoracic or cervical viscera

ABDOMINO-PELVIC SYMPATHETICS

• Preganglionic sympathetic fibers may pass through the sympathetic trunk and paravertebral ganglia without synapsing and, together with similar fibers from other levels, form splanchnic nerves (greater, lesser, least, lumbar, and sacral

PARASYMPATHETIC SYSTEM

• Breed and Feed

• Cranial nerves III, VII, IX - parasympathetics to structures within the head and neck only

• Cranial X - innervates thoracic and most abdominal viscera

• Spinal nerves S2 to S4 - innervate inferior abdominal viscera, pelvic viscera, and the arteries associated with erectile tissues of the perineum

ENTERIC SYSTEM

• form two interconnected plexuses, the myenteric (Auerbach) and submucous (Meissner) nerve plexuses

• derived from neural crest cells

• reflex activity within and between parts of the gastrointestinal system

REFERRED PAIN

• occurs when sensory information comes to the spinal cord from one location, but is interpreted by the CNS as coming from another location innervated by the same spinal cord level

• Usually happens when the pain information comes from a region, such as the gut, which has a low amount of sensory output

• neurons at the same spinal cord level that receive information from the skin, which is an area with a high amount of sensory output

THANK YOU FOR LISTENING!