The Nervous System: The Spinal Cord and Spinal Nerves

Transcription

1 14 The Nervous System: The Spinal Cord and Spinal Nerves PowerPoint Lecture Presentations prepared by Steven Bassett Southeast Community College Lincoln, Nebraska

2 Introduction The Central Nervous System (CNS) consists of: The spinal cord Integrates and processes information Can function with the brain Can function independently of the brain The brain Integrates and processes information Can function with the spinal cord Can function independently of the spinal cord

3 Gross Anatomy of the Spinal Cord Features of the Spinal Cord 45 cm in length Passes through the foramen magnum Extends from the brain to L 1 Consists of: Cervical region Thoracic region Lumbar region Sacral region Coccygeal region

4 Gross Anatomy of the Spinal Cord Features of the Spinal Cord Consists of (continued): Cervical enlargement Lumbosacral enlargement Conus medullaris Cauda equina Filum terminale: becomes a component of the coccygeal ligament Posterior and anterior median sulci

5 Figure 14.1a Gross Anatomy of the Spinal Cord Cervical spinal s C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 Cervical enlargement T 7 Thoracic spinal s T 8 T 9 Posterior median sulcus T 10 T 11 T 12 Lumbosacral enlargement L 1 Conus medullaris L 2 Lumbar spinal s L 3 L 4 L 5 Inferior tip of spinal cord Cauda equina Sacral spinal s S 1 S 2 S 3 Coccygeal (Co 1 ) S 4 S 5 Filum terminale (in coccygeal ligament) Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal s and indicate where the roots leave the vertebral canal. The spinal cord, however, extends from the brain only to the level of vertebrae L 1 L 2.

6 Gross Anatomy of the Spinal Cord Features of the Spinal Cord Transverse view White matter Gray matter Central canal Dorsal root and ventral root: merge to form a spinal Dorsal root is sensory: axons extend from the soma within the dorsal root ganglion Ventral root is motor

7 Figure 14.1d Gross Anatomy of the Spinal Cord Dorsal root Dorsal root ganglion Posterior median sulcus White matter Central canal Gray matter Spinal Ventral root Anterior median fissure C 3 T 3 L 1 S 2 Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray and white matter

8 Gross Anatomy of the Spinal Cord Features of the Spinal Nerves Consist of: Sensory s (afferent s): transmit impulses toward the spinal cord Motor s (efferent s): transmit impulses away from the spinal cord

9 Figure 14.1d Gross Anatomy of the Spinal Cord Dorsal root Dorsal root ganglion Posterior median sulcus White matter Central canal Gray matter Spinal Ventral root Anterior median fissure C 3 T 3 L 1 S 2 Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray and white matter

10 Spinal Meninges Features of spinal meninges: Specialized membranes that provide protection, physical stability, and shock absorption Continuous with the cranial (cerebral) meninges Denticulate ligaments help anchor the spinal cord in position Made of three layers Dura mater: tough, fibrous outermost layer Arachnoid mater: middle layer Pia mater: innermost layer

11 Figure 14.2c The Spinal Cord and Spinal Meninges White matter Gray matter Ventral root Dorsal root Pia mater Spinal Dorsal root ganglion Arachnoid mater Dura mater Posterior view of the spinal cord showing the meningeal layers, superficial landmarks, and distribution of gray and white matter

12 Figure 14.2a The Spinal Cord and Spinal Meninges Spinal cord Anterior median fissure Pia mater Denticulate ligaments Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel Dorsal root of sixth cervical Ventral root of sixth cervical Anterior view of spinal cord showing meninges and spinal s. For this view, the dura and arachnoid membranes have been cut longitudinally and retracted (pulled aside); notice the blood vessels that run in the subarachnoid space, bound to the outer surface of the delicate pia mater.

13 Sectional Anatomy of the Spinal Cord Gray matter Central canal Consists of somas (cell bodies) surrounding the central canal White matter Consists of axons Nerves are organized into tracts or columns Located outside the gray matter area

14 Sectional Anatomy of the Spinal Cord Organization of Gray Matter Somas are organized into groups called nuclei Sensory nuclei Motor nuclei Transverse view shows: Posterior gray horns Lateral gray horns Anterior gray horns Gray commissure

15 Sectional Anatomy of the Spinal Cord Organization of gray matter Posterior gray horns: somatic sensory and visceral nuclei Lateral gray horns: visceral motor nuclei Anterior gray horns: somatic motor nuclei Gray commissure Consists of axons crossing from one side to the other

16 Figure 14.4b Sectional Organization of the Spinal Cord Posterior gray horn Posterior median sulcus From dorsal root Posterior gray commissure Somatic Visceral Sensory nuclei Lateral gray horn Anterior gray horn Anterior gray commissure To ventral root Visceral Somatic Motor nuclei Anterior median fissure The left half of this sectional view shows important anatomical landmarks; the right half indicates the functional organization of the gray matter in the anterior, lateral, and posterior gray horns.

17 Sectional Anatomy of the Spinal Cord Organization of white matter Consists of columns of s (fascicles) Columns convey either: Sensory tracts (ascending tracts) Motor tracts (descending tracts)

18 Figure 14.4c Sectional Organization of the Spinal Cord Posterior white column (funiculus) Leg Hip Trunk Arm Lateral white column (funiculus) Flexors Extensors Hand Forearm Arm Shoulder Trunk Anterior white column (funiculus) Anterior white commissure The left half of this sectional view shows the major columns of white matter. The right half indicates the anatomical organization of sensory tracts in the posterior white column for comparison with the organization of motor nuclei in the anterior gray horn. Note that both sensory and motor components of the spinal cord have a definite regional organization.

19 Spinal Nerves There are 31 pairs of spinal s 8 cervical s 12 thoracic s 5 lumbar s 5 sacral s 1 coccygeal

20 Figure 14.1a Gross Anatomy of the Spinal Cord Cervical spinal s C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 Cervical enlargement T 7 Thoracic spinal s T 8 T 9 Posterior median sulcus T 10 T 11 T 12 Lumbosacral enlargement L 1 Conus medullaris L 2 Lumbar spinal s L 3 L 4 L 5 Inferior tip of spinal cord Cauda equina Sacral spinal s S 1 S 2 S 3 Coccygeal (Co 1 ) S 4 S 5 Filum terminale (in coccygeal ligament) Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal s and indicate where the roots leave the vertebral canal. The spinal cord, however, extends from the brain only to the level of vertebrae L 1 L 2.

21 Spinal Nerves Spinal s Each peripheral consists of: Epineurium: outer layer becomes continuous with the dura mater Perineurium: layer surrounding a fascicle a fascicle is a bundle of axons Endoneurium: layer surrounding a single axon

22 Figure 14.5a Anatomy of a Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering peripheral Perineurium (around one fascicle) Endoneurium Schwann cell A typical peripheral and its connective tissue wrappings Fascicle Myelinated axon

23 Spinal Nerves Peripheral Distribution of Spinal Nerves Four branches of the spinal s: White ramus Gray ramus White and gray ramus are collectively called rami communicantes Dorsal ramus Ventral ramus

24 Spinal Nerves Branches of the spinal s (details) Rami communicantes (white and gray ramus) Innervates smooth muscles, glands, and organs Motor impulses leave the spinal cord through the ventral root to the spinal s Dorsal ramus Innervates skeletal muscles of the neck and back Ventral ramus Innervates skeletal muscles of the limbs

25 Figure 14.6a Peripheral Distribution of Spinal Nerves Motor Commands Postganglionic fibers to smooth muscles, glands, etc., of back To skeletal muscles of back Dorsal root ganglion Dorsal root Visceral motor Somatic motor Dorsal ramus Ventral ramus To skeletal muscles of body wall, limbs Postganglionic fibers to smooth muscles, glands, etc., of body wall, limbs Ventral root Spinal Rami communicantes KEY Somatic motor commands Visceral motor commands Gray ramus (postganglionic) White ramus (preganglionic) Sympathetic Sympathetic ganglion Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity Preganglionic fibers to sympathetic ganglia innervating abdominopelvic viscera The distribution of motor neurons in the spinal cord and motor fibers within the spinal and its branches. Although the gray ramus is typically proximal to the white ramus, this simplified diagrammatic view makes it easier to follow the relationships between preganglionic and postganglionic fibers.

26 Spinal Nerves Sensory impulses associated with the spinal s Sensory impulses travel in the spinal through the dorsal root to the spinal cord

27 Figure 14.6b Peripheral Distribution of Spinal Nerves Sensory Information From interoceptors of back From exteroceptors, proprioceptors of back Dorsal root Somatic sensory Visceral sensory Dorsal ramus Ventral ramus From exteroceptors, proprioceptors of body wall, limbs From interoceptors of body wall, limbs Dorsal root ganglion Rami communicantes KEY Ventral root Somatic sensations Visceral sensations From interoceptors of visceral organs A comparable view detailing the distribution of sensory neurons and sensory fibers

28 Spinal Nerves Dermatomes Each pair of spinal s monitors specific surface areas These are clinically important areas regarding surgery

29 Figure 14.7 Dermatomes C 2 C 3 NV C 2 C 3 C 2 C 3 C 3 C 4 C 5 T 1 T 2 T 3 T 4 T 2 T 3 T 4 T 5 T 6 T 7 C 4 C 5 T 5 T 8 T 6 T 9 T 2 T 2 C 6 T 7 T 8 T 9 T 10 T 11 T 12 T 10 T 11 T 12 L 1 L 2 L L 4 3 L 5 C 6 C 7 T 1 L 1 C 8 L 2 S 2 S S 4 3 C 7 T 1 L 3 L 1 S 5 C 8 L 4 L 2 S 2 S 1 L 5 L 5 L 3 S 1 L 4 ANTERIOR POSTERIOR

30 Nerve Plexuses There are four plexuses Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Sometimes the lumbar and sacral are combined to form the lumbosacral plexus

31 Figure 14.8 Peripheral Nerves and Nerve Plexuses Cervical plexus Brachial plexus C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 Lesser occipital Great auricular Transverse cervical Supraclavicular Phrenic Axillary Musculocutaneous Thoracic s T 11 Lumbar plexus Sacral plexus T 12 L 1 L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Iliohypogastric Ilioinguinal Genitofemoral Femoral Obturator Superior Inferior Gluteal s Radial Ulnar Median Pudendal Sciatic Lateral femoral cutaneous Saphenous Common fibular Tibial Medial sural cutaneous

32 Nerve Plexuses The Cervical Plexus (C 1 C 5 ) Consists of cutaneous and muscular branches Cutaneous branch innervates: Head Neck Chest

33 Nerve Plexus The Cervical Plexus Consists of cutaneous and muscular branches Muscular branch innervates: Omohyoid, sternohyoid, geniohyoid, thyrohyoid Sternothyroid Scalenes Sternocleidomastoid Levator scapulae Trapezius Diaphragm (controlled by the phrenic of the cervical plexus)

34 Figure 14.9 The Cervical Plexus Cranial s Accessory (N XI) Hypoglossal (N XII) Lesser occipital Great auricular Nerve roots of cervical plexus Supraclavicular s Clavicle C 1 C 2 C 3 C 4 C 5 Geniohyoid muscle Transverse cervical Thyrohyoid muscle Ansa cervicalis Omohyoid muscle Phrenic Sternohyoid muscle Sternothyroid muscle

35 Nerve Plexus The Brachial Plexus (C 4 T 1 ) The immediate s emerging from C 5 to T 1 are the: Superior trunk Middle trunk Inferior trunk These trunks all merge to form the lateral cord

36 Figure 14.10b The Brachial Plexus Dorsal scapular BRACHIAL PLEXUS Suprascapular Superior trunk Middle trunk Inferior trunk C 4 C 5 C 6 C 7 C 8 T 1 Musculocutaneous Median Lateral antebrachial cutaneous Ulnar Radial Superficial branch of radial Deep radial Ulnar Median Anterior interosseous Deep branch of ulnar Superficial branch of ulnar Palmar digital s Anterior view of the brachial plexus and upper limb showing the peripheral distribution of major s Anterior Radial Ulnar Median Distribution of cutaneous s

37 Nerve Plexus The cords of the brachial plexus Lateral cord: merging of the trunks Medial cord: an extension of the inferior trunk Posterior cord: an extension of the middle trunk

38 Figure 14.10a The Brachial Plexus KEY Roots (ventral rami) Trunks Divisions Cords Peripheral s Dorsal scapular Nerve to subclavius muscle SUPERIOR TRUNK Suprascapular C 5 C 6 Lateral cord MIDDLE TRUNK C 7 BRACHIAL PLEXUS Posterior cord Lateral pectoral C 8 Medial pectoral Subscapular s Medial cord Musculocutaneous Medial antebrachial cutaneous Median Axillary Thoracodorsal Ulnar First rib INFERIOR TRUNK Long thoracic T 1 Posterior brachial cutaneous Radial The trunks and cords of the brachial plexus

39 Nerve Plexus The cords of the brachial plexus (details) Lateral cord: extends to form the musculocutaneous The lateral cord and medial cord extend to form the median Medial cord extends to form the ulnar Posterior cord: branches to form the radial and axillary

40 Figure 14.10a The Brachial Plexus KEY Roots (ventral rami) Trunks Divisions Cords Peripheral s Dorsal scapular Nerve to subclavius muscle SUPERIOR TRUNK Suprascapular C 5 C 6 Lateral cord MIDDLE TRUNK C 7 BRACHIAL PLEXUS Posterior cord Lateral pectoral C 8 Medial pectoral Subscapular s Medial cord Musculocutaneous Medial antebrachial cutaneous Median Axillary Thoracodorsal Ulnar First rib INFERIOR TRUNK Long thoracic T 1 Posterior brachial cutaneous Radial The trunks and cords of the brachial plexus

41 Figure 14.10b The Brachial Plexus Dorsal scapular BRACHIAL PLEXUS Suprascapular Superior trunk Middle trunk Inferior trunk C 4 C 5 C 6 C 7 C 8 T 1 Musculocutaneous Median Lateral antebrachial cutaneous Ulnar Radial Superficial branch of radial Deep radial Ulnar Median Anterior interosseous Deep branch of ulnar Superficial branch of ulnar Palmar digital s Anterior view of the brachial plexus and upper limb showing the peripheral distribution of major s Anterior Radial Ulnar Median Distribution of cutaneous s

42 Figure 14.10c The Brachial Plexus Musculocutaneous Axillary Branches of axillary Radial Ulnar Median Posterior antebrachial cutaneous Deep branch of radial Radial Ulnar Superficial branch of radial Dorsal digital s Median Posterior Distribution of cutaneous s Posterior view of the brachial plexus and the innervation of the upper limb

43 Figure The Cervical and Brachial Plexuses Median Radial Ulnar Right brachial artery Clavicle, cut and removed Deltoid muscle Musculocutaneous Right axillary artery over axillary Biceps brachii, long and short heads Coracobrachialis muscle Skin Median Cervical plexus Right common carotid artery Brachial plexus (C 5 T 1 ) Sternocleidomastoid muscle, sternal head Sternocleidomastoid muscle, clavicular head Right subclavian artery Retractor holding pectoralis major muscle (cut and reflected)

44 Table 14.2 The Brachial Plexus

45 Nerve Plexus The Lumbar and Sacral Plexuses (T 12 S 4 ) Also called the lumbosacral plexus Lumbar plexus s Genitofemoral Lateral femoral cutaneous Femoral Sacral plexus s Sciatic (branches to form the common fibular and the tibial ) Pudendal

46 Figure 14.12a The Lumbar and Sacral Plexuses, Part I T 12 T 12 subcostal L 1 Iliohypogastric Branches of genitofemoral Ilioinguinal Genitofemoral Lateral femoral cutaneous Femoral branch Genital branch Femoral Obturator L 2 L 3 L 4 L 5 The lumbar plexus, anterior view LUMBAR PLEXUS Lumbosacral trunk

47 Figure 14.12b The Lumbar and Sacral Plexuses, Part I L 5 Lumbosacral trunk Superior gluteal Inferior gluteal S 1 S 2 S 3 SACRAL PLEXUS Sciatic S 4 S 5 Posterior femoral cutaneous Pudendal Co 1 The sacral plexus, anterior view

48 Figure 14.12c The Lumbar and Sacral Plexuses, Part I Subcostal Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Femoral Superior gluteal Inferior gluteal Pudendal Posterior femoral cutaneous (cut) Obturator Sciatic Saphenous Saphenous Sural Fibular Common fibular Superficial fibular Deep fibular Sural Tibial Saphenous Saphenous Sural The lumbar and sacral plexuses, anterior view Tibial Fibular

49 Table 14.3 The Lumbar and Sacral Plexuses

50 Figure 14.12d The Lumbar and Sacral Plexuses, Part I Superior gluteal Inferior gluteal Pudendal Posterior femoral cutaneous Sciatic Saphenous Sural Fibular Tibial Common fibular Medial sural cutaneous Tibial Lateral sural cutaneous Sural Saphenous Sural Saphenous Sural Medial plantar Tibial Fibular Lateral plantar The sacral plexus, posterior view

51 Figure 14.13c The Lumbar and Sacral Plexuses, Part II (Part 1 of 2) Gluteus maximus (cut) Inferior gluteal Pudendal Perineal branch Hemorrhoidal branch Gluteus medius (cut) Gluteus minimus Superior gluteal Piriformis Posterior femoral cutaneous Perineal branches Sciatic Descending cutaneous branch Semitendinosus Biceps femoris (cut) A diagrammatic posterior view of the right hip and lower limb detailing the distribution of peripheral s

52 Figure 14.13c The Lumbar and Sacral Plexuses, Part II (Part 2 of 2) Tibial Popliteal artery and vein Medial sural cutaneous Gastrocnemius Common fibular Lateral sural cutaneous Small saphenous vein Sural Calcaneal tendon Tibial (medial calcaneal branch) A diagrammatic posterior view of the right hip and lower limb detailing the distribution of peripheral s

53 Figure 14.13a The Lumbar and Sacral Plexuses, Part II Gluteus maximus Superior gluteal Inferior gluteal Gluteus medius Gluteus minimus Internal pudendal artery Pudendal Nerve to gemellus and obturator internus Tibial branch Common fibular branch Greater trochanter of femur Posterior femoral cutaneous Gluteus maximus Components of sciatic A dissection of the right gluteal region

54 Figure 14.13b The Lumbar and Sacral Plexuses, Part II Sartorius Gracilis Semimembranosus Popliteal artery Semitendinosus Nerve to medial head of gastrocnemius Gastrocnemius, medial head Biceps femoris Tibial Lateral sural cutaneous Common fibular Plantaris Nerve to lateral head of gastrocnemius Gastrocnemius, lateral head Medial sural cutaneous A dissection of the popliteal fossa

55 Nerve Plexus Summary of the spinal s Cervical spinal s emerge from C 1 C 8 Thoracic spinal s emerge from T 1 T 12 Lumbar spinal s emerge from L 1 L 5 Sacral spinal s emerge from S 1 S 5 Coccygeal spinal s emerge from Co 1

56 Nerve Plexus Summary of the plexuses Cervical plexus s emerge from C 1 C 5 Brachial plexus s emerge from C 5 T 1 There is not a thoracic plexus Lumbar plexus s emerge from T 12 L 4 Sacral plexus s emerge from L 4 S 4 There is not a coccygeal plexus

57 Figure 14.3 Posterior View of Vertebral Column and Spinal Nerves Occipital bone Spinal cord emerging from foramen magnum Cervical plexus (C 1 C 5 ) Cervical spinal s (C 1 C 8 ) Brachial plexus (C 5 T 1 ) Thoracic spinal s (T 1 T 12 ) Lumbar spinal s (L 1 L 5 ) Lumbar plexus (T 12 L 4 ) Sacral plexus (L 4 S 4 ) Sciatic Coccygeal s (Co 1 ) Sacral spinal s (S 1 S 5 ) emerging from sacral foramina

58 Reflexes Reflex An immediate involuntary response Reflex arc The neural wiring of a single reflex Begins at a sensory receptor and ends at a peripheral receptor

59 Reflexes Reflexes are classified according to: Their development Innate or acquired The site where information is processed Spinal or cranial (cerebral) The nature of the resulting motor response Somatic, visceral, or autonomic The complexity of the neural circuit Monosynaptic or polysynaptic

60 Reflexes Pathway of a reflex arc 1. Activation of a sensory receptor 2. Relay of information to the CNS 3. Information processing 4. Activation of a motor neuron 5. Response by the effector ANIMATION Components of a Reflex Arc

61 Figure A Reflex Arc Arrival of stimulus and activation of receptor Activation of a sensory neuron Dorsal root Sensation relayed to the brain by collateral Stimulus Receptor REFLEX ARC Effector Ventral root Information processing in CNS Response by effector Activation of a motor neuron KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

62 Figure The Classification of Reflexes Reflexes can be classified by development response complexity of circuit processing site Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes Genetically determined Control skeletal muscle contractions Include superficial and stretch reflexes One synapse Processing in the spinal cord Acquired Reflexes Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes Learned Control actions of smooth and cardiac muscles, glands Multiple synapses (two to several hundred) Processing in the brain

63 Reflexes Spinal reflexes can be: Monosynaptic Involves a single segment of the spinal cord Polysynaptic Integrates motor output from several spinal segments

64 Figure Neural Organization and Simple Reflexes Sensory receptor Ganglion Sensory neuron CENTRAL NERVOUS SYSTEM Ganglion Sensory neuron CENTRAL NERVOUS SYSTEM Motor neuron Circuit 2 Interneurons Circuit 1 Motor neurons Sensory receptor (muscle spindle) Skeletal muscle 1 Skeletal muscle A monosynaptic reflex circuit involves a peripheral sensory neuron and a central motor neuron. In this example, stimulation of the receptor will lead to a reflexive contraction in a skeletal muscle. Skeletal muscle 2 A polysynaptic reflex circuit involves a sensory neuron, interneurons, and motor neurons. In this example, the stimulation of the receptor leads to the coordinated contractions of two different skeletal muscles.

65 Reflexes Stretch reflex 1. Stimulus stretches a muscle 2. Activates a sensory neuron 3. Information is processed in the spinal cord 4. Motor neurons are activated 5. Muscle (effector) contracts

66 Figure 14.17a Stretch Reflexes Stimulus. Stretching of muscle stimulates muscle spindles Activation of a sensory neuron Information processing at motor neuron Response. Contraction of muscle Steps 1 5 are common to all stretch reflexes. Activation of motor neuron KEY Sensory neuron (stimulated) Motor neuron (stimulated)

67 Figure 14.17b Stretch Reflexes Stretch Receptor (muscle spindle) Spinal cord Stimulus REFLEX ARC Contraction Effector KEY Sensory neuron (stimulated) Motor neuron (stimulated) Response The patellar reflex is controlled by muscle spindles in the quadriceps group. The stimulus is a reflex hammer striking the muscle tendon, stretching the spindle fibers. This results in a sudden increase in the activity of the sensory neurons, which synapse on spinal motor neurons. The response occurs upon the activation of motor units in the quadriceps group, which produces an immediate increase in muscle tone and a reflexive kick.