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Chapter 2

Chapter 2. The Nervous System. Overview. The human nervous system is an extremely complex entity that performs a multitude of functions, in much the same way as a dynamic network of interconnected computers. ANATOMY. Nervous system.

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Chapter 2

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  1. Chapter 2 The Nervous System

  2. Overview • The human nervous system is an extremely complex entity that performs a multitude of functions, in much the same way as a dynamic network of interconnected computers

  3. ANATOMY

  4. Nervous system • The nervous system can be divided into two anatomical divisions, each with their own subdivisions: • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Cranial nerves • Spinal nerves

  5. Nerve • The nerve cell, or neuron, is the functional unit of the nervous system • There are four functional parts to each nerve: • Dendrite • Axon • Cell body • Axon terminal

  6. Central Nervous System • Spinal cord - participates directly with the control of body movements, the processing and transmission of sensory information from the trunk and limbs, and the regulation of visceral functions • Brain – central processor

  7. Meninges • Three membranes, or meninges, envelop the structures of the CNS: • The dura. The outermost and strongest of the layers • The arachnoid. A thin and delicate avascular layer • The pia. Conveys the blood vessels that supply the spinal cord, and has a series of lateral specializations, the denticulate (dentate) ligaments

  8. Peripheral Nervous System • Somatic Nerves • Consists of the cranial nerves and the spinal nerves

  9. Cranial Nerves • The cranial nerves (CN) are typically described as comprising 12 pairs, which are referred to by the Roman numerals I through XII • CN I (olfactory) and II (optic) are not true nerves but are fiber tracts of the brain

  10. Cranial nerves • CN I – Olfactory. The olfactory nerve is responsible for the sense of smell • CN II – Optic. The optic nerve is responsible for vision

  11. Cranial nerves • CN III – Oculomotor • The somatic portion supplies the levator palpabrae superioris muscle, the superior, medial and inferior rectus muscles, and the inferior oblique muscles. These muscles are responsible for some eye movements. • The visceral efferent portion of this nerve innervates two smooth intraocular muscles: the ciliary and the constrictor pupillae. These muscles are responsible for papillary constriction.

  12. Cranial nerves • CN IV – Trochlear. Supplies the superior oblique muscle • CN VI – Abducens. Supplies the lateral rectus muscle

  13. Cranial nerves • CN V – Trigeminal. Maxillary, ophthalmic and mandibular branches. Ophthalmic and maxillary are exclusively sensory, the latter supplying the soft and hard palate, maxillary sinuses, upper teeth and upper lip and the mucous membrane of the pharynx. The mandibular branch carries sensory information but also represents the motor component of the nerve, supplying the muscles of mastication, both pterygoids, the anterior belly of digastric, tensor tympani, tensor veli palatini and mylohyoid.

  14. Cranial nerves • CN VII – Facial. Comprised of a sensory (intermediate) root, which conveys taste, and a motor root, the facial nerve proper, which supplies the muscles of facial expression, the platysma muscle, and the stapedius muscle of the inner ear

  15. Cranial nerves • CN VIII – Vestibulocochlear. Subserves two different senses – balance and hearing • CN IX – Glossopharyngeal. Contains somatic motor, visceral efferent, visceral sensory, and somatic sensory fibers

  16. Cranial nerves • CN X – Vagus. Contains somatic motor, visceral efferent, visceral sensory, and somatic sensory fibers • CN XI – Accessory. Cranial and spinal component • CN XII – Hypoglossal. The motor nerve of the tongue

  17. The Spinal Nerves • A total of 31 symmetrically arranged pairs • Divided topographically into 8 cervical pairs (C 1-8), 12 thoracic pairs (T 1-12), 5 lumbar pairs (L 1-5), 5 sacral pairs (S 1-5), and a coccygeal pair • Peripheral nerves are enclosed in three layers of tissue of differing character. From the inside outward, these are the endoneurium, perineurium, and epineurium

  18. Cervical Nerves • The 8 pairs of cervical nerves are derived from cord segments between the level of the foramen magnum and the middle of the seventh cervical vertebra • Divide into a larger ventral ramus, and a smaller dorsal ramus

  19. Cervical Plexus • Sensory branches • The small occipital nerve (C 2, 3) • The great auricular nerve (C 2, 3) • The cervical cutaneous nerve (cutaneous coli) (C 2, 3) • Supraclavicular branches (C 3, 4) • Communication branches • Ansa cervicalis • Muscular branches

  20. Brachial Plexus • Arises from the anterior primary divisions of the fifth cervical through the first thoracic nerve roots, with occasional contributions from the fourth cervical and second thoracic roots

  21. Plexus Roots • The roots of the plexus, which consist of C 5 and C 6, join to form the upper trunk, C 7 becomes the middle trunk, and C 8 and T 1 join to form the lower trunks • Each of the trunks divides into anterior and posterior divisions, which then form cords

  22. Plexus Branches • The branches give rise to the peripheral nerves: • Musculocutaneous (lateral cord) • Axillary • Radial (posterior cord) • Ulnar (medial cord) • Median (medial and lateral cords)

  23. Nerves from the Roots • The dorsal scapular nerve (C 5) • Supplies the rhomboids and levator scapulae muscles • The long thoracic nerve (C 5-7) • Supplies the serratus anterior muscle

  24. Nerves from the Trunks • Subclavius • Suprascapular nerve. Motor supply to the supraspinatus and infraspinatus muscles, and sensory innervation to the shoulder joint

  25. Nerves from the Cords • The medial and lateral pectoral nerves. • Supply the pectoralis major and pectoralis minor muscles • Subscapular nerve • Supplies the subscapularis muscle • Thoracodorsal nerve • Supplies the latissimus dorsi muscle • Medial antebrachial cutaneous nerve • Medial brachial cutaneous nerve

  26. The Musculocutaneous Nerve (C 5-6) • Motor - supplies the coracobrachialis, biceps brachii and brachialis muscles • Sensory - lateral antebrachial cutaneous nerve

  27. Axillary Nerve (C5–6) • Motor - Teres minor, deltoid muscle • Sensory - Superior lateral brachial cutaneous nerve

  28. The Radial Nerve (C 6-8, T 1) • Motor • In the arm - supplies the triceps, anconeus, and the upper portion of the extensor-supinator group of forearm muscles • In the forearm, the posterior interosseous nerve innervates all of the muscles of the six extensor compartments of the wrist, with the exception of the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL)

  29. The Radial Nerve (C 6-8, T 1) • Sensory • The posterior brachial cutaneous nerve: the dorsal aspect of the arm • The posterior antebrachial cutaneous nerve: the dorsal surface of the forearm • The superficial radial nerve: the dorsal aspect of the radial half of the hand

  30. The Median Nerve (C 5-T 1) • Motor (anterior interosseous nerve) • Innervation to flexor pollicis longus (FPL), and to the pronator quadratus (PQ) • May supply all or none of the flexor digitorum profundus and part of the flexor digitorum superficialis • Sensory - supplies the skin of the palmar aspect of the thumb and the lateral 2 ½ fingers, and the distal ends of the same fingers

  31. The Ulnar Nerve (C 8, T 1) • Motor – supplies the flexor carpi ulnaris, the ulnar head of the flexor digitorum profundus, and all of the small muscles deep and medial to the long flexor tendon of the thumb, except the first 2 lumbricales • Sensory - supplies the ulnar side of the dorsum of the hand, the dorsal aspect of the fifth finger and the ulnar half of the forefinger

  32. The Thoracic Nerves • Dorsal rami • Ventral rami

  33. The Lumbar Plexus • Formed from the ventral nerve roots of the second, third, and fourth lumbar nerves (in approximately 50% of cases, the plexus also receives a contribution from the last thoracic nerve)

  34. Branches • L 1, L 2, and L 4 divide into upper and lower branches. • The upper branch of L 1 forms the iliohypogastric and ilioinguinal nerves • The lower branch of L 1 joins the upper branch of L 2 to form the genitofemoral nerve • The lower branch of L 4 joins L 5 to form the lumbosacral trunk

  35. Femoral Nerve (L2-4) • The motor component supplies the iliopsoas muscle, while in the thigh it supplies the sartorius, pectineus, and quadriceps femoris muscles

  36. Femoral Nerve (L2-4) • The sensory distribution of the femoral nerve includes the anterior and medial surfaces of the thigh via the anterior femoral cutaneous nerve, and the medial aspect of the knee, the proximal leg and articular branches to the knee, via the saphenous nerve

  37. Obturator Nerve (L2-4) • The anterior division - supplies muscular branches to the adductors longus, brevis and the gracilis, and rarely to the pectineus • The posterior division - supplies the obturator externus, and the adductors magnus and brevis

  38. Lateral Femoral Cutaneous Nerve • A purely sensory nerve that is derived primarily from the second and third lumbar nerve roots, with occasional contributions from the first lumbar nerve root • Associated with meralgia paresthetica

  39. The Sacral Plexus • The sacral plexus is formed by the ventral rami of the L4‑5 and the S1‑4 nerves • The upper 3 nerves of the plexus divide into 2 sets of branches; the medial branches, which are distributed to the multifidi muscles, and the lateral branches, which become the medial cluneal nerves

  40. Superior Gluteal Nerve • The roots of the superior gluteal nerve (L4, L5, S1) arise within the pelvis from the sacral plexus • Supplies the gluteus medius and gluteus minimus

  41. Inferior Gluteal Nerve • Supplies the gluteus maximus

  42. Sciatic Nerve • The largest nerve in the body • Arises from the L 4, L 5 and S 1-3 nerve roots as a continuation of the lumbosacral plexus • Composed of the independent tibial (medial) and common peroneal (lateral) divisions

  43. Common Peroneal Nerve • Formed by the upper 4 posterior divisions (L 4, 5 and S 1, 2) of the sacral plexus • Three terminal rami: the recurrent articular, the superficial peroneal, and deep peroneal

  44. The Superficial Peroneal • Motor supply to the peroneus longus and brevis muscles • Sensory distribution to the lower front of the leg, to the dorsum of the foot, part of the big toe, and adjacent sides of the second to fifth toes up to the second phalanges

  45. The Deep Peroneal • Supplies the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius muscles • Divides into a medial and lateral branches

  46. The Pudendal Plexus • Supplies the coccygeus, levator ani, and sphincter ani externus muscles

  47. Coccygeal Plexus • Small sensory anococcygeal nerves derived from the last three segments (S 4, 5, C)

  48. The Tibial Nerve • Formed from all 5 anterior divisions (L 4, 5 and S 1, 2, 3) • Supplies the gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus pedis, and flexor hallucis longus muscles • The portion of the tibial trunk below the popliteal space is often called the posterior tibial nerve

  49. Sural nerve • A sensory branch of the tibial nerve • Formed by the lateral sural cutaneous nerve from the common peroneal nerve and the medial calcaneal nerve from the tibial nerve

  50. Proprioception • A specialized variation of the sensory modality of touch, which plays an important role in coordinating muscle activity, involves the integration of sensory input concerning static joint position (joint position sensibility), joint movement (kinesthetic sensibility), velocity of movement, and force of muscular contraction, from the skin, muscles, and joints

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