The Spinal Cord and Spinal Nerves

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14 The Nervous System: The Spinal Cord and Spinal Nerves

PowerPoint® Lecture Presentations prepared by Steven Bassett Southeast Community College Lincoln, Nebraska

• 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

• Features of the Spinal Cord • 45 cm in length • Passes through the foramen magnum

• Extends from the brain to L1 • Consists of: • Cervical region • Thoracic region • Lumbar region • Sacral region • Coccygeal region

• 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

C1 C2 Cervical spinal C3 nerves C4 C5 C 6 Cervical C 7 enlargement C8

T1 T2 T3 T4

Thoracic T8 spinal Posterior nerves T9 median sulcus

T10

Lumbosacral T11 enlargement

T12

L Conus 1 medullaris

Lumbar L3 Inferior spinal tip of nerves spinal cord L4 Cauda equina

S1 Sacral spinal S nerves 2 S3

S4 S5

Coccygeal Filum terminale

nerve (Co1) (in coccygeal ligament)

Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The spinal cord, however,

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

Dorsal root White matter ganglion

Central Gray canal matter

Spinal Ventral nerve root Anterior median fissure

• Features of the Spinal Nerves • Consist of: • Sensory nerves (afferent nerves): transmit impulses toward the spinal cord • Motor nerves (efferent nerves): transmit impulses away from the spinal cord

Dorsal root White matter ganglion

Central Gray canal matter

Spinal Ventral nerve root Anterior median fissure

• 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

Ventral root Spinal nerve

Dorsal root Dorsal root Pia mater ganglion

Arachnoid mater

Dura mater

Posterior view of the spinal cord showing the meningeal layers, superficial landmarks, and distribution of gray and white matter © 2012 Pearson Education, Inc. 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 nerve Ventral root of sixth cervical nerve

Anterior view of spinal cord showing meninges and spinal nerves. 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. © 2012 Pearson Education, Inc. 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

• 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

• 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

Posterior median sulcus From dorsal root Posterior gray horn Posterior gray commissure Somatic Sensory Visceral nuclei

Lateral Visceral gray horn Motor nuclei Anterior Somatic gray horn To ventral Anterior gray root commissure

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.

• Organization of white matter • Consists of columns of nerves (fascicles) • Columns convey either: • Sensory tracts (ascending tracts) • Motor tracts (descending tracts)

Posterior white Leg column (funiculus) Hip Trunk Arm

Lateral white column (funiculus) Flexors Extensors Hand Forearm Arm Shoulder Trunk

Anterior white Anterior white column (funiculus) 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.

• There are 31 pairs of spinal nerves • 8 cervical nerves • 12 thoracic nerves • 5 lumbar nerves • 5 sacral nerves • 1 coccygeal nerve

C1 C2 Cervical spinal C3 nerves C4 C5 C 6 Cervical C 7 enlargement C8

T1 T2 T3 T4

Thoracic T8 spinal Posterior nerves T9 median sulcus

T10

Lumbosacral T11 enlargement

T12

L Conus 1 medullaris

Lumbar L3 Inferior spinal tip of nerves spinal cord L4 Cauda equina

S1 Sacral spinal S nerves 2 S3

S4 S5

Coccygeal Filum terminale

nerve (Co1) (in coccygeal ligament)

• Spinal nerves • Each peripheral nerve 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

Blood vessels

Connective Tissue Layers

Epineurium covering peripheral nerve Perineurium (around one fascicle)

Endoneurium

Schwann cell

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

• Branches of the spinal nerves (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 nerves • Dorsal ramus • Innervates skeletal muscles of the neck and back • Ventral ramus • Innervates skeletal muscles of the limbs

Postganglionic fibers To skeletal to smooth muscles, muscles of back glands, etc., of back Dorsal Visceral Somatic Dorsal root ganglion root motor motor

Dorsal ramus

Ventral ramus

To skeletal muscles of body wall, limbs Ventral root

Postganglionic fibers to smooth muscles, glands, etc., of body wall, limbs Spinal nerve

Gray ramus Sympathetic ganglion (postganglionic) Rami communicantes White ramus Postganglionic fibers (preganglionic) to smooth muscles, glands, visceral organs Sympathetic nerve in thoracic cavity

KEY Somatic motor Preganglionic fibers to commands sympathetic ganglia innervating abdomino- Visceral motor commands pelvic viscera

The distribution of motor neurons in the spinal cord and motor fibers within the spinal nerve 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. © 2012 Pearson Education, Inc. Spinal Nerves

• Sensory impulses associated with the spinal nerves • Sensory impulses travel in the spinal nerve through the dorsal root to the spinal cord

From interoceptors From exteroceptors, of back proprioceptors of back Dorsal Somatic Visceral root sensory sensory

Dorsal ramus Ventral ramus

From exteroceptors, proprioceptors of body wall, limbs Dorsal root ganglion From interoceptors of body wall, limbs

Rami communicantes Ventral KEY root Somatic sensations From interoceptors Visceral sensations of visceral organs

• Dermatomes • Each pair of spinal nerves monitors specific surface areas • These are clinically important areas regarding surgery

C2–C3

C2 C 3 C3

C4 T2 C4 C5 T3 T1 T4 T2 T5 C5 T3 T T 6 4 T7 T5 T8 T T6 T9 2 T T2 T7 10 T11 T8 T12 T9 C6 L1 T10 L2 T T L L3 1 11 4 C C6 L 7 T12 5 L1 S S L 4 3 2 S2 C8 C L 8 T1 3 L1 S C7 5 S1 L5 L4 S2 L2

L5 L3

• There are four nerve plexuses • Cervical plexus • Brachial plexus • Lumbar plexus • Sacral plexus • Sometimes the lumbar and sacral are combined to form the lumbosacral plexus

C1 Lesser occipital nerve C2 Great auricular nerve Cervical C 3 Transverse cervical nerve plexus C4 C5 Supraclavicular nerve C 6 Phrenic nerve Brachial C7 plexus C8 T1 T2 T3 Axillary nerve T4 T5 T6 T7 Musculocutaneous nerve T8

T9 Thoracic nerves

T10

T11

T12

L1 Radial nerve Lumbar L2 plexus Ulnar nerve

L3 Median nerve L4

L5 S1 Iliohypogastric Sacral nerve plexus S2 S3 Ilioinguinal S4 nerve S5 Co1 Genitofemoral nerve Femoral nerve Obturator nerve Superior Gluteal Inferior nerves

Pudendal nerve

Sciatic nerve Lateral femoral cutaneous nerve

Saphenous nerve

Common fibular nerve

Tibial nerve

• The Cervical Plexus (C1–C5) • Consists of cutaneous and muscular branches • Cutaneous branch innervates: • Head • Neck • Chest

• 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 nerve of the cervical plexus)

Accessory nerve (N XI) Cranial Hypoglossal nerves nerve (N XII) Great auricular nerve Lesser occipital nerve

Nerve roots of C3 Geniohyoid muscle cervical plexus Transverse C 4 cervical nerve C5 Thyrohyoid muscle Ansa cervicalis

Omohyoid muscle Supraclavicular Phrenic nerve nerves Clavicle Sternohyoid muscle

Sternothyroid muscle

• The Brachial Plexus (C4–T1)

• The immediate nerves emerging from C5 to T1 are the: • Superior trunk • Middle trunk • Inferior trunk • These trunks all merge to form the lateral cord

Musculocutaneous nerve

Median nerve

Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve

Deep radial nerve Superficial branch of radial nerve Ulnar nerve Median nerve Anterior interosseous nerve Radial nerve Deep branch of ulnar nerve Ulnar nerve Superficial branch of ulnar nerve Palmar digital nerves Median nerve

• 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

KEY Dorsal scapular Roots (ventral rami) nerve Nerve to Trunks C5 subclavius muscle Divisions Cords SUPERIOR TRUNK

Peripheral nerves C6 Suprascapular nerve

MIDDLE Lateral cord TRUNK C7 BRACHIAL PLEXUS Posterior cord

Lateral pectoral nerve C8 Medial pectoral nerve Subscapular nerves T1 Axillary nerve Medial cord INFERIOR TRUNK Musculocutaneous First nerve rib Long thoracic Medial antebrachial nerve cutaneous nerve Thoracodorsal nerve Median nerve Ulnar nerve

Posterior brachial Radial nerve The trunks and cords of the brachial cutaneous nerve plexus

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

KEY Dorsal scapular Roots (ventral rami) nerve Nerve to Trunks C5 subclavius muscle Divisions Cords SUPERIOR TRUNK

Peripheral nerves C6 Suprascapular nerve

MIDDLE Lateral cord TRUNK C7 BRACHIAL PLEXUS Posterior cord

Posterior brachial Radial nerve The trunks and cords of the brachial cutaneous nerve plexus

Musculocutaneous nerve

Median nerve

Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve

Anterior Anterior view of the brachial plexus and upper limb Distribution of showing the peripheral distribution of major nerves cutaneous nerves © 2012 Pearson Education, Inc. Figure 14.10c The Brachial Plexus Musculocutaneous nerve Axillary nerve

Branches of axillary nerve

Radial nerve

Ulnar nerve Median nerve Posterior antebrachial cutaneous nerve

Deep branch of radial nerve

Superficial branch Radial of radial nerve nerve

Ulnar Dorsal digital nerves nerve

Median nerve Posterior Distribution of cutaneous nerves

Right common Cervical carotid artery Clavicle, cut plexus and removed Brachial plexus

Deltoid muscle (C5–T1)

Musculocutaneous Sternocleido- nerve mastoid muscle, sternal head Right axillary artery over axillary nerve Sternocleido- Median nerve mastoid muscle, Radial nerve clavicular head Biceps brachii, long and short heads Right subclavian artery Ulnar nerve

Coracobrachialis Retractor holding muscle pectoralis major muscle (cut and Skin reflected) Right brachial artery

• The Lumbar and Sacral Plexuses (T12–S4) • Also called the lumbosacral plexus • Lumbar plexus nerves • Genitofemoral nerve • Lateral femoral cutaneous nerve • Femoral nerve • Sacral plexus nerves • Sciatic nerve (branches to form the common fibular nerve and the tibial nerve) • Pudendal nerve

T12

T12 subcostal nerve

Iliohypogastric nerve L2 LUMBAR PLEXUS Ilioinguinal nerve

L3 Genitofemoral nerve Lateral femoral cutaneous nerve L4 Branches of Femoral branch genitofemoral nerve Genital branch L Femoral nerve 5 Obturator nerve Lumbosacral trunk The lumbar plexus, anterior view

Lumbosacral trunk

S 1 SACRAL Superior gluteal nerve PLEXUS S2 Inferior gluteal nerve S3

Sciatic nerve S5

Posterior femoral Co1 cutaneous nerve Pudendal nerve

The sacral plexus, anterior view

Iliohypogastric nerve

Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve

Superior gluteal nerve Inferior gluteal nerve

Pudendal nerve Posterior femoral cutaneous nerve (cut) Obturator nerve

Sciatic nerve

Saphenous nerve

Sural Saphenous nerve nerve Fibular nerve

Common fibular nerve

Superficial fibular Tibial nerve nerve Saphenous Deep fibular Sural nerve nerve nerve

Saphenous Sural nerve nerve

Superior gluteal nerve Inferior gluteal nerve

Posterior femoral Pudendal cutaneous nerve nerve

Sciatic nerve

Saphenous nerve

Sural nerve Fibular Tibial nerve nerve Common fibular nerve

Medial sural cutaneous nerve

Lateral sural Tibial cutaneous nerve nerve Saphenous Sural nerve nerve Sural nerve

Saphenous Sural nerve nerve Medial plantar nerve Lateral plantar Fibular Tibial nerve The sacral plexus, nerve nerve posterior view © 2012 Pearson Education, Inc. Figure 14.13c The Lumbar and Sacral Plexuses, Part II (Part 1 of 2)

Gluteus maximus (cut) Gluteus medius (cut)

Inferior gluteal Gluteus minimus nerve Pudendal nerve Superior gluteal nerve Perineal branch Hemorrhoidal Piriformis branch

Posterior femoral cutaneous nerve

Perineal branches Sciatic nerve

Descending cutaneous branch

Semitendinosus Biceps femoris (cut) A diagrammatic posterior view of the right hip and lower limb detailing the distribution of peripheral nerves © 2012 Pearson Education, Inc. Figure 14.13c The Lumbar and Sacral Plexuses, Part II (Part 2 of 2) Tibial nerve Common fibular Popliteal artery nerve and vein

Medial sural cutaneous Lateral sural nerve cutaneous nerve Gastrocnemius

Small saphenous vein

Sural nerve

Calcaneal tendon

Tibial nerve (medial calcaneal branch)

A diagrammatic posterior view of the right hip and lower limb detailing the distribution of peripheral nerves © 2012 Pearson Education, Inc. Figure 14.13a The Lumbar and Sacral Plexuses, Part II Gluteus maximus

Superior gluteal nerve

Inferior gluteal nerve

Gluteus medius Gluteus minimus Tibial branch Internal pudendal Common fibular Components of artery branch sciatic nerve Greater trochanter of femur Pudendal nerve Posterior femoral cutaneous nerve Nerve to gemellus and obturator internus Gluteus maximus

A dissection of the right gluteal region

© 2012 Pearson Education, Inc. Figure 14.13b The Lumbar and Sacral Plexuses, Part II Biceps femoris Tibial nerve Sartorius Gracilis Lateral sural cutaneous nerve Semimembranosus Common fibular Popliteal artery nerve

Semitendinosus Plantaris

Nerve to Nerve to lateral head medial head of gastrocnemius of gastrocnemius Gastrocnemius, Gastrocnemius, lateral head medial head

Medial sural cutaneous nerve

• Summary of the spinal nerves

• Cervical spinal nerves emerge from C1–C8

• Thoracic spinal nerves emerge from T1–T12

• Lumbar spinal nerves emerge from L1–L5

• Sacral spinal nerves emerge from S1–S5

• Coccygeal spinal nerves emerge from Co1

• Summary of the nerve plexuses

• Cervical plexus nerves emerge from C1–C5

• Brachial plexus nerves emerge from C5–T1

• There is not a thoracic plexus

• Lumbar plexus nerves emerge from T12–L4

• Sacral plexus nerves emerge from L4–S4 • There is not a coccygeal plexus

Occipital bone

Spinal cord emerging from foramen magnum

Cervical plexus (C1–C5) Cervical spinal nerves (C1–C8 )

Brachial plexus (C5–T1)

Thoracic spinal nerves (T1–T12)

Lumbar plexus Lumbar (T –L ) spinal 12 4 nerves (L1–L5)

Sciatic Sacral nerve plexus (L4–S4)

• 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

• 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

• 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

Arrival of stimulus and Activation of a Dorsal Sensation activation of receptor sensory neuron root relayed to the brain by collateral

REFLEX ARC Receptor Stimulus

Effector Ventral Information processing root in CNS

Response by effector Activation of a KEY motor neuron Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

Reflexes

can be classified by

development response complexity of circuit processing site

Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes

• Genetically • Control skeletal muscle contractions • One synapse • Processing in determined • Include superficial and stretch reflexes the spinal cord

Acquired Reflexes Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes

• Learned • Control actions of smooth and • Multiple synapses • Processing in cardiac muscles, glands (two to several hundred) the brain

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

Sensory CENTRAL receptor Ganglion NERVOUS SYSTEM Sensory neuron

CENTRAL Ganglion NERVOUS Interneurons Sensory SYSTEM neuron Motor Circuit 2 neuron

Circuit 1 Motor neurons

Sensory receptor (muscle spindle) Skeletal muscle 1

Skeletal muscle Skeletal muscle 2

A monosynaptic reflex circuit involves a peripheral A polysynaptic reflex circuit involves a sensory neuron, sensory neuron and a central motor neuron. In this interneurons, and motor neurons. In this example, the example, stimulation of the receptor will lead to a stimulation of the receptor leads to the coordinated reflexive contraction in a skeletal muscle. contractions of two different skeletal muscles.

• 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

Stimulus. Stretching of muscle Activation of a stimulates muscle spindles sensory neuron

Information processing at motor neuron

Response. Contraction Activation of of muscle motor neuron KEY Sensory neuron (stimulated) Steps 1–5 are common to all stretch reflexes. Motor neuron (stimulated)

Receptor (muscle spindle) Spinal cord Stretch REFLEX ARC Stimulus

Effector KEY Sensory neuron (stimulated) Contraction Motor neuron (stimulated)

The patellar reflex is controlled by muscle spindles in the quadriceps group. The Response 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.