Spinal Cord and Spinal Nerves

Chapter 12

APR Enhanced Lecture Slides

See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes and animations.

12-1

12-2 Spinal Cord and Spinal Nerves

Spinal Nerves 31 pairs

Spinal cord 12.1 Spinal Cord

– Cervical Brain Level of foramen – Thoracic Cervical magnum enlargement Roots of spinal nerves – Lumbar Spinal nerves – Sacral Spinal cord • Gives rise to 31 pairs of spinal nerves • Not uniform in diameter throughout length – Cervical enlargement: supplies upper limbs Lumbosacral Conus enlargement – Lumbar enlargement: supplies lower limbs medullaris Level of second lumbar vertebra Cauda • Conus medullaris: tapered inferior end. equina

• Cauda equina: origins of spinal nerves extending Filum inferiorly from lumbosacral enlargement and terminale conus medullaris.

Posterior view 12-4 Spinal Cord Regions

Cervical Thoracic Lumbar Sacral Coccygeal Cervical & Lumbosacral Enlargements Medullary Cone & Cauda Equina Spinal Cord

Conus medullaris Filum terminale Cauda equina

8 Meninges of the Spinal Cord • Connective tissue membranes surrounding spinal cord and brain – Dura mater: continuous with epineurium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Duramater of the spinal nerves Subdural space – Arachnoid mater: thin and wispy Denticulate ligament Arachnoid mater – Pia mater: bound tightly to surface of Subarachnoid space brain and spinal cord. Forms the filum Pia mater Epineurium of terminale, which anchors spinal cord to spinal nerve coccyx and the denticulate ligaments that attach the spinal cord to the dura mater Dorsal root ganglion Spinal nerve

• Spaces Ventral root – Epidural: anesthesia injected. Contains blood vessels, areolar connective tissue and fat. (a) Anterolateral view – Subdural: serous fluid – Subarachnoid: CSF and blood vessels within web-like strands of arachnoid tissue 12-9 Meninges of Spinal Cord Meninges of the Spinal Cord

Spinous process of vertebra Transverse process of vertebra

Spinal cord Dorsal root Dorsal root ganglion Denticulate ligament Spinal nerve

Ventral root

Body of Pia mater vertebra

Subarachnoid Periosteum space

Arachnoid Epidural mater space filled with adipose tissue Subdural Dura space mater

Anterior 12-11 (b) Superior view Cross Section of Spinal Cord

Posterior median sulcus Central canal Dorsal root White matter Dorsal root ganglion Dorsal (posterior) column Central canal Ventral (anterior) column Lateral column Ventral root

Gray matter Posterior (dorsal) Spinal horn nerve Lateral horn Anterior (ventral) horn

Ventral root Gray commissure Rootlets White commissure Anterior median fissure (a) Anterolateral view

Ascending nerve tracts

Descending nerve tracts

Gray matter White matter Cross Section of Spinal Cord

• Anterior median fissure and posterior median sulcus: deep clefts partially separating left and right halves • White matter: myelinated axons forming tracts – Three columns (funiculi): ventral, dorsal, lateral • Each of these divided into tracts (fasciculi; pathways) • Gray matter: neuron, cell, cell bodies, dendrites, axons – Horns • Posterior (dorsal) • Anterior (ventral) • Lateral (associated with ANS)

12-14 Cross Section of Spinal Cord

Posterior median sulcus Central canal Dorsal root White matter Dorsal root ganglion White matter Dorsal (posterior) Dorsal (posterior) Central canal column column Ventral (anterior) Ventral (anterior) column column Lateral column Ventral root Lateral column

Gray matter Posterior (dorsal) Spinal horn Dorsal root nerve Lateral horn Anterior (ventral) horn

Ventral root Gray commissure Rootlets White commissure Dorsal root ganglion Anterior median fissure (a) Anterolateral view (b)

Ascending nerve tracts

Descending nerve tracts

Posterior median sulcus Central canal Dorsal root White matter Dorsal root ganglion • Commissures: connections Dorsal (posterior) column Central canal between left and right Ventral (anterior) column halves Lateral column Ventral root Gray matter Posterior (dorsal) – Gray with central canal in the Spinal horn nerve center Lateral horn Anterior (ventral) – White horn

Ventral root • Roots: spinal nerves arise as Gray commissure Rootlets White commissure rootlets then combine to Anterior median fissure form roots (a) Anterolateral view – Dorsal (posterior) root has a ganglion – Ventral (anterior) Ascending nerve tracts – Two roots merge laterally and Descending nerve tracts form the spinal nerve 12-16

Dorsal root Ventral root

Dorsal root Spinal nerve gangion Organization of Neurons in the Spinal Cord and Spinal Nerves • Dorsal root Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Posterior horn Dorsal root Dorsal root ganglion ganglion:

collections of Sensory neuron

cell bodies of Spinal nerve unipolar Interneuron sensory neurons forming dorsal Autonomic neuron Lateral horn Somatic motor neuron roots. Anterior horn Ventral root Superior view

• Motor neuron cell bodies are in anterior and lateral horns of spinal cord gray matter. – Multipolar somatic motor neurons in anterior (motor) horn – Autonomic neurons in lateral horn • Axons of motor neurons form ventral roots and pass into spinal nerves 12-18 12.2 Reflexes • Basic functional unit of nervous system and simplest portion capable of receiving a stimulus and producing a response • Automatic response to a stimulus that occurs without conscious thought. Homeostatic. • Components – Action potentials produced in sensory receptors transmitted to – Sensory neuron. To-Interneurons. To-Motor neuron. To- – Effector organ which responds with a reflex

12-19 Reflex Arc

Spinal cord Skin

4 Motor neuron Spinal nerve

Ventral root 5 Skeletal Effector organ muscle 1 A sensory receptor detects a stimulus. 2 A sensory neuron conducts action potentials through the nerve and dorsal root to the spinal cord. 3 In the spinal cord, the sensory neuron synapses with an interneuron. (An interneuron is not involved in a monosynaptic reflex arc.) 4 The interneuron synapses with a motor neuron.

5 A motor neuron axon conducts action potentials through the ventral 12-20 root and spinal nerve to an effector organ. Variety of Reflexes

• Some integrated within spinal cord; some within brain • Some involve excitatory neurons yielding a response; some involve inhibitory neurons that prevent an action • Higher brain centers can influence, suppress, or exaggerate reflex responses

12-21 Stretch Reflex • Muscles contract in response to a stretching force applied to them. Unique because no interneuron. • Muscle spindle: specialized muscle cells that respond to stretch. • Innervated by specific motor neurons: gamma motor neurons (small diameter neurons). Control sensitivity of muscle spindle. • Sensory neurons innervate the noncontractile centers of the muscle spindle cells. • These sensory neurons synapse with motor neurons of the spinal cord called alpha motor neurons which in turn innervate the muscle in which the muscle spindle is embedded. 12-22

Stretch Reflex

2 Sensory neurons conduct action potentials to the spinal cord.

3 Sensory neurons synapse directly with alpha motor neurons. Sensory neuron 3 4 Alpha motor neurons conduct action potentials to the muscle, causing it to contract and resist being stretched. 2 Note: The muscle that contracts is the muscle that is stretched. Alpha motor Quadriceps Muscle neuron femoris muscle spindle 4 (extensor) 1

Gamma motor neuron Patellar Sensory Sensory neuron tendon neuron endings Hammer Gamma motor tap neuron endings Patellar Hamstring ligament muscles (flexor) Muscle fiber of muscle spindle

Muscle fiber of muscle

Stretch reflex Str et c h

Muscle spindle 12-23 Golgi Tendon Reflex

• Prevents contracting muscles from applying excessive tension to tendons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Golgi tendon organ. Encapsulated Intense stretch of a skeletal muscle results in: To brain

nerve endings that have at their ends 1 Golgi tendon organs detect tension applied to a tendon.

2 Sensory neurons conduct action potentials to the spinal cord. numerous terminal branches with 3 3 Sensory neurons synapse with inhibitory interneurons Sensory that synapse with alpha motor neurons. neuron small swellings associated with 4 Inhibition of the alpha motor neurons causes muscle relaxation, 2 relieving the tension applied to the tendon. Note: The muscle that 4 Inhibitory bundles of collagen fibers in tendon. relaxes is attached to the tendon to which tension is applied. Alpha motor interneuron neuron Muscle contraction Located in tendon near muscle increases tension applied to tendons. In response, action 1 potentials are conducted • Prevent damage to tendons that could to the spinal cord. Sensory neuron Hamstring be caused by excessive tension muscles Golgi (fexor) tendon • Produces sudden relaxation of the organ

Golgi muscles Tendon Muscle tendon refex

– Example: weight lifter suddenly Golgi tendon organ drops heavy weight. Sudden movements of “clean and jerk” put so much tension on tendons like Achilles, they could break.

12-24 Withdrawal Reflex

• Function is to remove a body limb or other part from a painful stimulus. • Reciprocal innervation: causes relaxation of extensor muscle when flexor muscle contracts. – Also involved in stretch reflex. • Crossed extensor reflex: when a withdrawal reflex is initiated in one lower limb, the crossed extensor reflex causes extension of opposite lower limb.

12-25 Withdrawal Reflex

Stimulation of pain receptors results in: To brain

1 Pain receptors detect a painful stimulus. Sensory neuron 2 2 Sensory neurons conduct action potentials Quadriceps to the spinal cord. femoris 3 muscle 3 Sensory neurons synapse with excitatory (extensor) Interneurons that synapse with alpha motor neurons. Excitatory 4 Excitation of the alpha motor neurons 4 interneuron results in contraction of the flexor muscles and withdrawal of the limb from the painful stimulus. Alpha motor neuron Hamstring muscles (fexor)

Sensory neuron

Stimulus Pain receptor

Withdrawal reflex 12-26 Withdrawal Reflex with Reciprocal Innervation

Collateral branch Reciprocal innervation Reciprocal innervation from sensory Inhibitory neuron 1 During the withdrawal reflex, Quadriceps femoris interneuron sensory neurons conduct action muscle (extensor) potentials from pain receptors to the spinal cord. 4 3 2 Sensory neurons synapse with excitatory interneurons that are part of the withdrawal 1 reflex.

Hamstring Sensory 3 Collateral branches of the sensory neurons also synapse with inhibitory muscles neuron To brain interneurons that are part of (flexor) reciprocal innervation.

The inhibitory interneurons 2 4 synapse with alpha motor neurons supplying the extensor muscles, causing them to relax and not oppose the flexor muscles of the withdrawal reflex, Alpha motor which are contracting. neuron Excitatory Withdrawal reflex interneuron

1 During the withdrawal reflex, sensory neurons from pain receptors conduct action potentials to the spinal cord.

2 Sensory neurons synapse with excitatory interneurons that are part of the withdrawal reflex.

3 The excitatory interneurons that are part of the withdrawal reflex stimulate alpha motor neurons that innervate flexor muscles, causing withdrawal of the limb from the painful stimulus.

4 Collateral branches of the sensory neurons Quadriceps also synapse with excitatory interneurons femoris that cross to the opposite side of the spinal muscle cord as part of the crossed extensor reflex. (extensor)

5 The excitatory interneurons that cross the Sensory spinal cord stimulate alpha motor neurons neuron supplying extensor muscles in the opposite limb, causing them to contract and support To brain body weight during the withdrawal reflex. 1

5 2 4

Alpha motor 3 neuron

Hamstring muscles (flexor) Alpha motor Excitatory neuron interneuron

Withdrawal Crossed reflex extensor reflex 12-28 Interactions with Spinal Cord Reflexes

To From brain brain • Sensory information Sensory Ascending Descending receptor axon axon goes to brain; e.g., Site of Descending divergence Ascending tract tract Sensory neuron pain.

Site of • Descending tracts convergence Skin from brain carry info Motor neuron Interneuron to reflexes.

Effector organ Skeletal muscle • Neurotransmitters produce either EPSPs or IPSPs modifying the reflex.

12-29 12.3 Spinal Nerves

– Schwann cells Adipose tissue – Connective tissue Epineurium • Endoneurium: Perineurium surrounds individual neurons • Perineurium:

surrounds axon groups Artery Endoneurium and vein to form fascicles Loose connective tissue Schwann Fascicle • Epineurium: surrounds cell the entire nerve Axon

12-30 31 Pair of Spinal Nerves Posterior (Dorsal) & Anterior (Ventral) Roots Posterior (Dorsal) Root Ganglia Posterior (Dorsal) and Anterior (Ventral) Rootlets Posterior Spinal root nerves ganglia

Posterior Anterior rami rami Organization of Spinal Nerves

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Thirty-one pairs of spinal C1 Cervical 2 plexus nerves 3 (C1–C4) Cervical 4 nerves 5 6 7 Brachial • First pair exit vertebral column 8 plexus T1 (C5–T1) between skull and atlas 2 3 4 • Last four pair exit via the 5 Thoracic 6 nerves 7 Duramater sacral foramina 8 9 • Others exit through 10 11 12 intervertebral foramina Cauda equina L1 2 Lumbar • Eight pair cervical, twelve pair Lumbar plexus nerves 3 (L1–L4) Lumbo- 4 sacral 5 thoracic, five pair lumbar, five plexus Sacral (L1–S4) S1 plexus pair sacral, one pair coccygeal Sacral S2 (L4–S4) S3 nerves S4 S5 Coccygeal Coccygeal nerves Co plexus (S5–Co) Posterior view 12-36 Dermatomal Map

• Spinal nerves indicated by capital letter and number • Dermatomal map: skin area supplied with sensory innervation by spinal nerves

C2 C1 Head movement 2 Diaphragm C3 3 movement Cervical 4 C2 C4 nerves Neck and shoulder C3 5 C4 T3 6 movement T4 7 C4 T5 Upper limb T2 T6 8 T3 C6 movement T7 C7 T1 T4 C5 C8 C5 T2 T8 T5 T2 C5 2 T1 T6 T1 T9 T10 T7 T1 3 T 11 T8 C6 C6 T1 T12 4 C6 T9 L1 C7 T10 5 C7 T1 S2 T1 T 11 6 Rib movement T12 Thoracic C8 S5 inbreathing, C8 L2 Co nerves 7 L1 S3 vertebral column C6 S4 8 movement, and S3 C8 S4 9 tone in postural L2 L2 back muscles S3 L2 10 C7 11 L3 L3 L3 12 S2 S2 Hip movement L1

L4 L4 Lumbar 2 L4 L4 L5 nerves 3 4 Lower limb S1 S1 5 L5 movement S1 L5 L5 S1 L5 S1 Sacral nerves

Coccygeal 12-37 nerves (a) Posterior view Branches of Spinal Nerves •Dorsal Ramus: innervate deep muscles of the trunk responsible for movements of the vertebral column and the C.T. and skin near the midline of the back. •Ventral Ramus: what they innervate depends upon which part of the spinal cord is considered. –Thoracic region: form intercostal nerves that innervate the intercostal muscles and the skin over the thorax –Remaining spinal nerve ventral rami (roots of the plexus): form five plexuses (intermingling of nerves). • Ventral rami of C1-C4= cervical plexus • Ventral rami of C5-T1= brachial plexus • Ventral rami of L1-L4= lumbar plexus • Ventral rami of L4-S4= sacral plexus • Ventral rami of S4 and S5= coccygeal plexus • Communicating Rami: communicate with sympathetic chain of ganglia.

Dorsal root of Rootlets spinal nerve Ventral root of spinal nerve Communicating rami

Dorsal root (spinal) ganglion Ganglion of Spinal nerve sympathetic chain

Dorsal ramus of spinal nerve Ventral ramus of spinal nerve (intercostal nerve)

Roots of Splanchnic nerve

(a) Anterolateral view

Dorsal rootlets

Intervertebral foramen

Dorsal root ganglion Spinal nerve Transverse process of vertebra (cut) 12-39 (b) Posterior view b: © McGraw-Hill Higher Education, Inc./Rebecca Gray, photographer/Don Kincaid, dissections Posterior ramus Anterior ramus Rami

C1 Roots (ventral rami): C1, C2, C3, C4 Branches C4 • C1-C4 Other nerves (not part of cervical plexus) • Innervates superficial

C1 neck structures, skin

Hypoglossal nerve (XII) of neck, posterior Accessory nerve (XI) C2 Lesser occipital nerve portion of head

Greater auricular nerve Nerve to • Ansa cervicalis: loop C3 sternocleidomastoid muscle Superior root of between C1 and C3 ansa cervicalis

Branch to infrahyoid muscles C4 • Phrenic nerve Transverse cervical nerve

Ansa cervicalis – From C3-C5 (cervical Nerve to trapezius muscle C5 and brachial plexuses) Branches to infrahyoid muscles Inferior root – Innervate diaphragm of ansa cervicalis

Supraclavicular nerves Phrenic nerve 12-41

Anterior view Cervical Plexus – Phrenic Nerve Phrenic Nerve Brachial Plexus

• C4 from cervical plus C5-T1 Roots (ventral rami): C5, C6, C7, C8, T1

Trunks: upper, middle, lower Anterior divisions • Five ventral rami form three Posterior divisions C5 Cords: posterior, lateral, medial trunks that separate into six

Major branches: T1 Axillary nerve divisions then form cords that Radial nerve Musculocutaneous nerve Median nerve Ulnar nerve give rise to: C5 • Branches/nerves Upper Dorsal scapular nerve trunk Sub clavian nerve – Axillary C6

Thoracodorsal nerve Upper and lower – Radial subscapular nerves Middle trunk Suprascapular nerve Posterior cord C7 – Musculocutaneous Axillary nerve Lateral cord Radial nerve – Ulnar Long Musculo- thoracic cutaneous nerve nerve C8 – Median Medial and lateral pectoral nerves Lower Medial cord – Smaller nerves such as trunk Median Medial brachial nerve cutaneous nerve T1 pectoral, long thoracic, Ulnar nerve Medial antebrachial cutaneous nerve Anterior view thoracodorsal, subscapular, suprascapular 12-44 Brachial Plexus Axillary n.

Brachial Plexus Median n.

Musculocutaneous n.

Superior, Middle, and Inferior Radial n. Trunks of Brachial Plexus

Ulnar n. Axillary Nerve

Axillary Nerve Axillary nerve

Origin Posterior cord of brachial plexus, C5–C6 Posterior cord Movements/Muscles Innervated Lateral cord Teres minor Laterally rotates arm Teres minor Medial cord • Deltoid Abducts arm • Deltoid Cutaneous (Sensory) Innervation Inferior lateral shoulder

12-47

Posterior views Axillary Nerve

Radial Nerve Posterior cord Origin Lateral cord Radial nerve Posterior cord of brachial plexus, C5–T1 Medial cord Movements/Muscles Innervated Extends elbow • Triceps brachii • Anconeus Long head of Lateral head of Flexes elbow triceps brachii triceps brachii • Brachialis (part; sensory only) • Brachioradialis Extends and abducts wrist • Extensor carpi radialis longus Medial head of Brachioradialis • Extensor carpi radialis brevis triceps brachii Supinates forearm and hand Extensor carpi • Supinator radialis longus Extends fingers Extensor carpi • Extensor digitorum • Extensor digiti minimi Anconeus radialisbrevis • Extensor indicis Supinator Extends and adducts wrist • Extensor carpi ulnaris Extensor digitorum

Abducts thumb Extensor digiti minimi Adductor pollicis • Abductor pollicis longus Extensor carpi ulnaris longus Extends thumb Extensor pollicis • Extensor pollicis longus Extensor indicis • Extensor pollicis brevis brevis and longus Cutaneous (Sensory) Innervation Posterior surface of arm and forearm, lateral two-thirds of dorsum of hand

Posterior view

12-49

Posterior view Anterior view Radial Nerve

12-50 Musculocutaneous Nerve

Musculocutaneous Nerve

Origin Lateral cord of brachial plexus, C5–C7 Posterior cord Movements/Muscles Innervated Lateral cord Musculocutaneous nerve Flexes shoulder Medial cord • Biceps brachii • Coracobrachialis Flexes elbow and supinates forearm and hand Biceps brachii Coracobrachialis • Biceps brachii Flexes elbow • Brachialis (also small amount of innervation from radial nerve) Brachialis Cutaneous (Sensory) Innervation Lateral surface of forearm

Anterior views 12-51 Posterior view Musculocutaneous Nerve

12-52 Ulnar Nerve

Ulnar Nerve

Origin Medial cord of brachial plexus, C8–T1 Posterior cord Movements/Muscles Innervated Lateral cord Flexes and adducts wrist Medial cord • Flexor carpi ulnaris Flexes fingers • Part of the flexor digitorum profundus controlling the distal phalanges of little and ring fingers Ulnar nerve Adducts thumb • Adductor pollicis Controls hypothenar muscles Anterior view • Flexor digiti minimi brevis • Abductor digiti minimi • Opponens digiti minimi Flexes metacarpophalangeal joints and extends interphalangeal joints Posterior view • Two medial (ulnar) lumbricales Flexor carpi ulnaris Abducts and adducts fingers Flex or digitorum • Interossei profundus Cutaneous (Sensory) Innervation Medial third of hand, little finger, and medial half of ring finger Adductor pollicis

Hypothenar muscles All dorsal and palmar interossei The two medial (ulnar) lumbricales

12-53

Anterior view Ulnar Nerve

Median Nerve

Origin Posterior cord Medial and lateral cords of brachial Lateral cord plexus, C5–T1 Medial cord Movements/Muscles Innervated Pronates forearm and hand • Pronator teres • Pronator quadratus Median nerve Flexes and abducts wrist • Flexor carpiradialis Flexes wrist • Palmaris longus Flexes fingers • Part of flexor digitorum profundus Anterior view controlling the distal phalanx of the middle and index fingers • Flexor digitorum superficialis Palmaris longus Controls thumb muscle Pronator teres • Flexor pollicis longus Posterior view Controls thenar muscles Flexor carpi radialis • Abductor pollicis brevis • Opponens pollicis Flexor digitorum profundus Flexor digitorum superficialis • Flexor pollicis brevis Flexor pollicis longus Flexes metacarpophalangeal joints and extends interphalangeal joints Pronator quadratus • Two lateral (radial) lumbricales Thenar muscles Cutaneous (Sensory) Innervation Lateral two-thirds of palm of hand, Carpal tunnel deep thumb, index and middle fingers, The two lateral to flexor retinaculum and the lateral half of ring finger (radial) lumbricales and dorsal tips of the same fingers

12-55

Anterior view Brachial Plexus - Median Nerve Other Nerves of the Brachial Plexus

• Small nerves that innervate muscles acting on scapula and arm – Pectoral – Long thoracic – Thoracodorsal – Subscapular – Suprascapular • Innervate the skin of the medial arm and forearm

L4 Roots ( ventral rami) Posterior divisions S4 Anterior divisions • Lumbar plexus: ventral Nerves rami of L1-L4 L1

• Sacral plexus: ventral rami L2 of L4-S4 Iliohypogastric Ilioinguinal L3

• Usually considered Lateral femoral cutaneous L4 together because of their Genitofemoral

Femoral close relationship L5 Obturator Lumbosacral • Four major nerves exit and trunk Superior gluteal S1

enter lower limb Inferior gluteal Common – Obturator fibular S2 (peroneal)

Sciatic – Femoral Tibial S3 – Tibial S4 Posterior femoral cutaneous – Common fibular (peroneal) S5

Pudendal 12-58 Anterior view Lumbar Plexus

Femoral n.

Obturator n.

Lumbosacral trunk Common Sciatic n. Tibial n. Fibular n. Sacral Plexus

Superficial Deep Fibular n. Fibular n.

Tibial n. Fibular n.60 Obturator Nerve

Obturator Nerve L2 L3 Origin L4 Lumbosacral plexus, L2–L4 Movements/Muscles Innervated Rotates thigh laterally • Obturator externus Adducts thigh Obturator nerve • Adductor magnus (adductor part) • Adductor longus • Adductor brevis Adducts thigh and flexes knee Obturator externus • Gracilis Cutaneous (Sensory) Innervation Superior medial side of thigh Adductor magnus

Adductor brevis

Adductor longus

Gracilis

12-61 Medial view Anterior view Obturator Nerve

Femoral Nerve L2 L3 Origin L4 Lumbosacral plexus, L2–L4 Psoas major Movements/Muscles Innervated Flexes hip • Psoas major Iliacus • Iliacus • Pectineus Femoral nerve Flexes hip and flexes knee • Sartorius Sartorius Extends knee Pectineus • Vastus lateralis Vastus • Vastus intermedius lateralis • Vastus medialis Extends knee and flexes hip • Rectus femoris Rectus femoris Cutaneous (Sensory) Innervation Anterior and lateral branches supply the anterior and lateral thigh; saphenous Vastus branch supplies the medial leg intermedius Vastus medialis and foot

12-63

Anterior view Medial view Anterior view Femoral Nerve

12-64 Tibial and Common Fibular Nerves

• The two nerves together referred to as the sciatic (ischiadic) nerve

12-65 Sciatic Nerve

Tibial Nerve Origin L4 Lumbosacral plexus, L4–S3 L5 Movements/Muscles Innervated S1 S2 Extends hip and flexes knee Tibial nerve • Biceps femoris (long head) S3 • Semitendinosus • Semimembranosus Extends hip and adducts thigh • Adductor magnus (hamstring part) Biceps femoris long head Adductor Plantar flexes foot magnus • Plantaris Semimembranosus • Gastrocnemius Semitendinosus • Soleus • Tibialis posterior Flexes knee • Popliteus Flexes toes • Flexor digitorum longus • Flexor hallucis longus Cutaneous (Sensory) Innervation Gastrocnemius None

Popliteus Soleus Medial and Lateral Plantar Nerves Flexor digitorum Origin longus Tibial nerve Movements/Muscles Innervated Flexor hallucis Flex and adduct toes longus • Plantar muscles of foot Tibialis posterior Cutaneous (Sensory) Innervation Sole of foot

Sural Nerve (Not Shown) Origin Tibial nerve Movements/Muscles Innervated None Medial plantar nerve to plantar muscles Lateral plantar nerve Cutaneous (Sensory) Innervation to plantar muscles Lateral and posterior one-third of leg and lateral side of foot 12-67 Anterior view Posterior view Posterior view Tibial Nerve

L4 Common Fibular L5 (Peroneal) Nerve S1 S2 Origin Lumbosacral plexus, L4–S2 Movements/Muscles Innervated Extends hip and flexes knee • Biceps femoris (short head) Cutaneous (Sensory) Innervation Common fibular Lateral surface of knee (peroneal) nerve

Deep Fibular Biceps femoris (Peroneal) Nerve short head

Origin Common fibular (peroneal) nerve Movements/Muscles Innervated Dorsiflexes foot • Tibialis anterior • Fibularis tertius Tibialis anterior Fibularis Extends toes longus • Extensor digitorum longus Extensor digitorum • Extensor hallucis longus longus • Extensor digitorum brevis Fibularis brevis Cutaneous (Sensory) Innervation Extensor hallucis Great and second toe longus

Superficial Deep fibular Superficial Fibular fibular (peroneal) (peroneal) nerve (Peroneal) Nerve nerve Fibularis Origin tertius Common fibular (peroneal) nerve Extensor Movements/Muscles Innervated digitorum Plantar flexes and everts foot brevis • Fibularis longus • Fibularis brevis Cutaneous (Sensory) Innervation 12-69 Dorsal anterior third of leg and dorsum of foot Anterior view Lateral view Anterior view Common Fibular Nerve

12-70 Other Lumbosacral Plexus Nerves

• Nerves that innervate the skin of the suprapubic area, external genitalia, superior medial thigh, posterior thigh – Gluteal nerves – Pudendal nerve – Iliohypogastric nerve – Ilioingual nerve – Genitofemoral nerve – Cutaneous femoral

12-71 Coccygeal Plexus

• S5; coccygeal nerve • Muscles of pelvic floor • Sensory information from skin over coccyx

12-72