The peripheral nervous system
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The Peripheral Nervous System. Chapter 14. The Peripheral Nervous System (PNS). The nervous system outside the brain and spinal cord (CNS) Provides vital links to the body and outside world Nerves allow the CNS to receive information and initiate action

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The Peripheral Nervous System

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The peripheral nervous system

The Peripheral Nervous System

Chapter 14


The peripheral nervous system pns

The Peripheral Nervous System (PNS)

  • The nervous system outside the brain and spinal cord (CNS)

    • Provides vital links to the body and outside world

    • Nerves allow the CNS to receive information and initiate action

  • Sensory inputs and motor outputs categorized as

    • Somatic or visceral

    • General or special

  • Autonomic nervous system (ANS): general visceral motor part of the PNS

    • Two divisions: parasympathetic and sympathetic


Functional organization of the pns

Central nervous system (CNS)

Peripheral nervous system (PNS)

Sensory (afferent) division

Motor (efferent) division

Somatic sensory

General: Touch, pain,

pressure, vibration,

temperature, and

proprioception in

skin, body wall, and

limbs

Visceral sensory

General: Stretch,

pain, temperature,

chemical changes,

and irritation in

viscera; nausea and

hunger

Somatic nervous

system

Autonomic

nervous system

(ANS)

Motor innervation of

all skeletal muscles

Motor innervation

of smooth muscle,

cardiac muscle,

and glands

Special: Hearing,

equilibrium, vision

Special: Taste, smell

Sympathetic

division

Parasympathetic

division

Functional Organization of the PNS

Figure 14.1


Basic structural components of the pns

Basic Structural Components of the PNS

  • Sensory receptors: pick up stimuli from inside or outside the body

  • Nerves: bundles of peripheral axons

  • Ganglia: clusters of peripheral neuronal cell bodies

  • Motor endings: axon terminals of motor neurons

    • Innervate effectors (muscle fibers and glands)


Peripheral sensory receptors

Peripheral Sensory Receptors

  • Structures that pick up sensory stimuli that initiate signals in sensory axons

  • General sensory receptors – widely distributed nerve endings of sensory neurons monitor:

    • Touch, Pressure, Vibration, Stretch, Pain, Temperature, Proprioception

  • Two main categories of sensory receptors

    • Free nerve endings of sensory neurons: monitor general sensory information

    • Complete receptor cells: specialized epithelial cells or small neurons that monitor most types of special sensory information

  • Sensory receptors also classified according to

    • Location, type of stimulus detected, and structure


  • Classification by location

    Classification by Location

    • Exteroceptors: sensitive to stimuli arising from outside the body

      • Located at or near body surfaces

      • Include receptors for touch, pressure, pain, and temperature

    • Interoceptorsreceive stimuli from internal viscera

      • Located in digestive tube, bladder, and lungs

      • Monitor a variety of stimuli: changes in chemical concentration, taste stimuli, stretching of tissues, temperature

    • Proprioceptors located in skeletal muscles, tendons, joints, and ligaments

      • Monitor degree of stretch

      • Send inputs on body movement to the CNS


    Classification by stimulus detected

    Classification by Stimulus Detected

    • Mechanoreceptors: respond to mechanical forces

      • Touch, pressure, stretch, vibration, and itch

      • Baroreceptors monitor blood pressure

    • Thermoreceptors: respond to temperature changes

    • Chemoreceptors: respond to chemicals in solution

    • Photoreceptors: respond to light, located in the eye

    • Nociceptors: respond to harmful stimuli that result in pain


    Classification by structure

    Classification by Structure

    • General sensory receptors divided into two groups:

      • Free nerve endings: abundant in epithelia and underlying connective tissue

        • Respond to pain and temperature

        • Monitor affective senses

      • Encapsulated nerve endings: consist of one or more end fibers of sensory neurons

        • Enclosed in connective tissue


    Structure of free and encapsulated general sensory receptors

    Structure of free and encapsulated general sensory receptors

    Tactile corpuscle

    (touch, light pressure)

    Epithelial tactile

    complexes (light touch)

    Free nerve

    endings

    (pain and

    temperature)

    Epidermis

    Dermis and

    hypodermis

    Lamellar

    corpuscle

    (deep pressure)

    Hair follicle receptor

    (hair movement)

    Bulbous corpuscle

    (pressure)


    Free nerve endings

    Free Nerve Endings

    • Two specialized types of free nerve endings

      • Epithelial tactile complexes (Merkel discs): consist of tactile epithelial cell innervated by sensory nerve ending

        • Slowly adapting receptors for light touch

      • Hair follicle receptors: wrap around hair follicles, rapidly adapting receptors


    Unencapsulated nerve endings

    Unencapsulated Nerve Endings

    Table 14.1 (1 of 4)


    Encapsulated nerve endings

    Encapsulated Nerve Endings

    • Mechanoreceptors include four main types

      • Tactile (Meissner’s) corpuscles

      • Lamellar (Pacinian) corpuscles

      • Bulbous corpuscles (Ruffini endings)

      • Proprioceptors


    Tactile corpuscles

    Tactile Corpuscles

    • Tactile (Meissner’s) corpuscles

      • Spiraling nerve ending surrounded by Schwann cells

      • Occur in the dermal papillae

      • Rapidly adapting receptors for discriminative touch

      • Occur in sensitive, hairless areas of the skin

    Table 14.1 (2 of 4)


    Encapsulated nerve endings1

    Encapsulated Nerve Endings

    • Lamellar Corpuscles: single nerve ending surrounded by layers of flattened Schwann cells

      • Occur in the hypodermis

      • Sensitive to deep pressure—rapidly adapting receptors

    • Bulbous Corpuscles: located in the dermis and respond to pressure

      • Monitor continuous pressure on the skin—adapt slowly

    • Proprioceptors: monitor stretch in locomotory organs

      • Three types of proprioceptors


    Lamellar corpuscles and bulbous corpuscles

    Lamellar Corpuscles and Bulbous Corpuscles

    Table 14.1 (3 of 4)


    Three types of proprioceptors

    Three Types of Proprioceptors

    • Muscle spindles: measure the changing length of a muscle

      • Imbedded in the perimysium between muscle fascicles

    • Golgi tendon organs: located near the muscle-tendon junction

      • Monitor tension within tendons

    • Joint kinesthetic receptors: sensory nerve endings within the joint capsules


    Structure of proprioceptors

    Secondary sensory

    endings (type II fiber)

     Efferent (motor)

    fiber to muscle spindle

     Efferent

    (motor) fiber

    to extrafusal

    muscle fibers

    Primary

    sensory

    endings

    (type Ia

    fiber)

    Extrafusal

    muscle

    fiber

    Muscle

    spindle

    Intrafusal

    muscle

    fibers

    Connective

    tissue capsule

    Sensory

    fiber

    Tendon

    organ

    Tendon

    Structure of Proprioceptors

    Figure 14.3


    Proprioceptors

    Proprioceptors

    Table 14.1 (4 of 4)


    Cranial nerves

    Cranial Nerves

    • Attach to the brain and pass through foramina of the skull

    • Numbered from I–XII

    • Cranial nerves I and II attach to the forebrain

      • All others attach to the brain stem

    • Primarily serve head and neck structures

      • The vagus nerve (X) is the only cranial nerve that extends into the abdomen


    The cranial nerves

    Filaments of

    olfactory nerve (I)

    Frontal lobe

    Olfactory bulb

    Olfactory tract

    Optic nerve (II)

    Temporal lobe

    Optic chiasma

    Optic tract

    Oculomotor

    nerve (III)

    Infundibulum

    Trochlear

    nerve (IV)

    Facial nerve (VII)

    Vestibulocochlear

    nerve (VIII)

    Trigeminal

    nerve (V)

    Abducens

    nerve (VI)

    Glossopharyngeal

    nerve (IX)

    Vagus nerve (X)

    Cerebellum

    Accessory nerve (XI)

    Medulla oblongata

    Hypoglossal nerve (XII)

    The Cranial Nerves

    Figure 14.4a


    The cranial nerves1

    Cranial nerves

    Sensory function

    Motor function

    Somatic

    sensory

    (SS)

    Visceral

    sensory

    (VS)

    Somatic

    motor

    (SM)

    Visceral motor:

    parasympathetic

    (VM)

    I

    Olfactory

    Smell

    II

    Optic

    Vision

    III

    Oculomotor

    SM

    VM

    IV

    Trochlear

    SM

    General

    V

    Trigeminal

    SM

    VI

    Abducens

    SM

    (b)

    The Cranial Nerves

    Figure 14.4b (1 of 2)


    The cranial nerves2

    Cranial nerves

    Sensory function

    Motor function

    Somatic

    sensory

    (SS)

    Visceral

    sensory

    (VS)

    Somatic

    motor

    (SM)

    Visceral motor:

    parasympathetic

    (VM)

    VII

    Facial

    General

    General;

    taste

    SM

    VM

    VIII

    Vestibulocochlear

    Hearing;

    equilibrium

    Some

    IX

    Glossopharyngeal

    General

    General;

    taste

    SM

    VM

    X

    Vagus

    General

    General;

    taste

    SM

    VM

    XI

    Accessory

    SM

    XII

    Hypoglossal

    SM

    (b)

    The Cranial Nerves

    Figure 14.4b (2 of 2)


    Olfactory nerves

    Olfactory Nerves

    • Sensory nerves of smell

    Table 14.2 (1 of 12)


    Ii the optic nerves

    II The Optic Nerves

    • Sensory nerve of vision

    Table 14.2 (2 of 12)


    Iii the oculomotor nerves

    III The Oculomotor Nerves

    • Innervates four of the extrinsic eye muscles

    Table 14.2 (3 of 12)


    Iv the trochlear nerves

    IV The Trochlear Nerves

    • Innervates the superior oblique muscle (an extrinsic eye muscle)

    Table 14.2 (4 of 12)


    V the trigeminal nerves

    V The Trigeminal Nerves

    Table 14.2 (5 of 12)


    The trigeminal nerves

    The Trigeminal Nerves

    • Largest of the cranial nerves has three divisions

      • Ophthalmic division (V1)

      • Maxillary division (V2)

      • Mandibular division (V3)

    • Cell bodies of sensory neurons located in the trigeminal ganglion

    • Mandibular division contains motor fibers that innervate the chewing muscles


    Vi the abducens nerves

    VI The Abducens Nerves

    • Abducts the eyeball—innervates lateral rectus muscle

    Table 14.2 (6 of 12)


    Vii the facial nerves

    VII The Facial Nerves

    • Innervates muscles of facial expression

    Table 14.2 (7 of 12)


    Viii the vestibulocochlear nerves

    VIII The Vestibulocochlear Nerves

    • Sensory nerve of hearing and balance

    Table 14.2 (8 of 12)


    Ix the glossopharyngeal nerves

    IX The Glossopharyngeal Nerves

    • Innervates structures of the tongue and pharynx

    Table 14.2 (9 of 12)


    X the vagus nerves

    X The Vagus Nerves

    • A mixed sensory and motor nerve

      • “Wanders” into thorax and abdomen

      • Parasympathetic innervation of organs

    Table 14.2 (10 of 12)


    Xi the accessory nerves

    XI The Accessory Nerves

    • Unique among cranial nerves

    • Accessory nerves are formed from ventral rootlets of the spinal cord

    • Do not arise from the brainstem

    Table 14.2 (11 of 12)


    Xii the hypoglossal nerves

    XII The Hypoglossal Nerves

    • Runs inferior to the tongue innervates the tongue muscles

    Table 14.2 (12 of 12)


    Spinal nerves

    Spinal Nerves

    • 31 pairs—contain thousands of nerve fibers

    • Connect to the spinal cord

    • Named for point of issue from the spinal cord

      • 8 pairs of cervical nerves (C1–C8)

      • 12 pairs of thoracic nerves (T1–T12)

      • 5 pairs of lumbar nerves (L1–L5)

      • 5 pairs of sacral nerves (S1–S5)

      • 1 pair of coccygeal nerves (Co1)


    Spinal nerves posterior view

    Cervical plexus

    Cervical

    nerves

    C1 – C8

    Brachial plexus

    Cervical

    enlargement

    Thoracic

    nerves

    T1 – T12

    Intercostal

    nerves

    Lumbar

    enlargement

    Lumbar

    nerves

    L1 – L5

    Lumbar plexus

    Sacral

    nerves

    S1 – S5

    Sacral plexus

    Coccygeal

    nerve

    Co1

    Cauda equina

    Spinal Nerves Posterior View

    Figure 14.5


    Spinal nerves1

    Spinal Nerves

    • Connect to the spinal cord by the dorsal root and ventral root

      • Dorsal root—contains sensory fibers

        • Cell bodies—located in the dorsal root ganglion

      • Ventral root—contains motor fibers arising from anterior gray column

    • Branch into dorsal ramus and ventral ramus

      • Dorsal and ventral rami contain sensory and motor fibers

      • Dorsal rami innervate back muscles follow a neat, segmented pattern

        • Innervate a horizontal strip of muscle and skin n iline with emergence point from the vertebral column

    • Rami communicantes connect to the base of the ventral ramus leading to the sympathetic chain ganglia


    Spinal nerves2

    Sensory axon

    and cell body

    Dorsal root

    ganglion

    Dorsal root

    Dorsal

    ramus

    Nerves

    Spinal

    nerve

    Ventral

    ramus

    Ventral

    root

    Axon of

    motor

    neuron

    Neuromuscular

    junction

    Sensory receptors in

    skin (e.g., free nerve

    endings of sensory

    neuron)

    Spinal Nerves

    Figure 14.6


    Spinal nerves3

    Spinal Nerves

    White matter

    Gray matter

    Ventral root

    Dorsal and ventral

    rootlets of spinal

    nerve

    Dorsal root

    Dorsal root

    ganglion

    Dorsal ramus

    of spinal nerve

    Ventral ramus

    of spinal nerve

    Spinal nerve

    Rami communicantes

    Sympathetic trunk

    ganglion

    (a) Anterior view showing spinal cord, associated nerves, and vertebrae.

    The dorsal and ventral roots arise medially as rootlets and join laterally

    to form the spinal nerve.

    Figure 14.7a


    Innervation of the back

    Dorsal ramus

    Ventral ramus

    Spinal nerve

    Rami communicantes

    Intercostal nerve

    Sympathetic trunk

    ganglion

    Dorsal root ganglion

    Dorsal root

    Ventral root

    Branches of intercostal nerve

    Lateral cutaneous

    Anterior

    cutaneous

    Sternum

    (b) Cross section of thorax showing the main roots and branches of a spinal nerve.

    Innervation of the Back


    Innervation of the anterior thoracic and abdominal wall

    Innervation of the Anterior Thoracic and Abdominal Wall

    • Thoracic region

      • Ventral rami arranged in simple, segmented pattern

      • Intercostal nerves—supply intercostal muscles, skin, and abdominal wall

        • Each gives off lateral and anterior cutaneous branches


    Introduction to nerve plexuses

    Introduction to Nerve Plexuses

    • Nerve plexus—a network of nerves

    • Ventral rami (except T2–T12)

      • Branch and join with one another

      • Form nerve plexuses

        • In cervical, brachial, lumbar, and sacral regions

      • Primarily serve the limbs

      • Fibers from ventral rami crisscross


    The cervical plexus

    Ventral rami

    Segmental

    branches

    Hypoglossal

    nerve (XII)

    Ventral

    rami:

    Lesser occipital

    nerve

    C1

    Greater auricular

    nerve

    C2

    Transverse

    cervical nerve

    C3

    Ansa cervicalis

    C4

    Accessory nerve (XI)

    C5

    Phrenic nerve

    Supraclavicular

    nerves

    The Cervical Plexus

    • Buried deep in the neck under the sternocleidomastoid muscle

    • Formed by ventral rami of first four cervical nerves (cn 1–4)

    • Most are cutaneous nerves

    • Some innervate muscles of the anterior neck

    • Phrenic nerve—the most important nerve of the cervical plexus

    Figure 14.8


    The brachial plexus and innervation of the upper limb

    Major terminal

    branches

    (peripheral nerves)

    Roots

    (ventral

    rami)

    Cords

    Divisions

    Trunks

    Anterior

    Musculocutaneous

    C5

    Upper

    Lateral

    Posterior

    Median

    C6

    Medial

    Anterior

    Ulnar

    C7

    Middle

    Posterior

    Radial

    C8

    Posterior

    Anterior

    Lower

    Axillary

    T1

    Posterior

    (c) Flowchart summarizing relationships within the brachial plexus

    The Brachial Plexus and Innervation of the Upper Limb

    • Brachial plexus lies in the neck and axilla

    • Formed by ventral rami of C5–C8

    • Cords give rise to main nerves of the upper limb

    Figure 14.9c


    Nerves from the lateral and medial cords

    Axillary nerve

    Humerus

    Radial nerve

    Musculocutaneous nerve

    Ulna

    Radius

    Ulnar nerve

    Median nerve

    Radial nerve (superficial branch)

    Dorsal branch of ulnar nerve

    Superficial branch of ulnar nerve

    Digital branch of ulnar nerve

    Muscular branch

    Median nerve

    (a) The major nerves

    of the upper limb

    Digital branch

    Nerves from the Lateral and Medial Cords

    • Musculocutaneous—main branch of the lateral cord

      • Innervates the biceps brachii and brachialis

    • Median—originates from both lateral and medial cords

      • Innervates anterior forearm muscles and lateral palm

    • Ulnar—branches from the medial cord

      • Innervates intrinsic hand muscles and skin of the medial hand

    Figure 14.9a


    Nerves from the lateral and medial cords1

    Roots (ventral rami)

    Anterior

    divisions

    C4

    Dorsal scapular

    Posterior

    divisions

    C5

    Nerve to

    subclavius

    Trunks

    C6

    Suprascapular

    Roots

    Upper

    C7

    Posterior

    divisions

    Trunks

    Middle

    C8

    Lateral

    Lower

    T1

    Cords

    Posterior

    Long thoracic

    Medial pectoral

    Medial

    Lateral pectoral

    Axillary

    Upper

    subscapular

    Musculo-

    cutaneous

    Lower

    subscapular

    Radial

    Thoracodorsal

    Median

    Medial cutaneous

    nerves of the arm

    and forearm

    Ulnar

    (b) Roots (rami C5–T1), trunks, divisions, and cords

    Nerves from the Lateral and Medial Cords

    Figure 14.9b


    Nerves from the lateral and medial cords2

    Nerves from the Lateral and Medial Cords

    Major terminal

    branches

    (peripheral nerves)

    Roots

    (ventral

    rami)

    Cords

    Divisions

    Trunks

    Anterior

    Musculocutaneous

    C5

    Upper

    Lateral

    Posterior

    Median

    C6

    Medial

    Anterior

    Ulnar

    C7

    Middle

    Posterior

    Radial

    C8

    Posterior

    Anterior

    Lower

    Axillary

    T1

    Posterior

    (c) Flowchart summarizing relationships within the brachial plexus

    Figure 14.9c


    Nerves from the posterior cord

    Musculocutaneous nerve

    Axillary nerve

    Branches of axillary nerve

    Radial nerve

    Ulnar nerve (cut)

    Median nerve (cut)

    Posterior cutaneous nerve

    Deep radial nerve

    Superficial branch of radial nerve

    Anterior

    divisions

    Posterior

    divisions

    Nerves from the Posterior Cord

    • Radial—continuation of the posterior cord

      • Largest branch of the brachial plexus

      • Innervates muscles of the posterior upper limb

    • Axillary innervates the deltoid and teres minor

    Figure 14.12


    Axillary and radial nerves

    Muscular innervation

    Cutaneous innervation

    Musculocutaneous

    nerve

    Median nerve

    Ulnar nerve

    C5

    C5

    C6

    C6

    C7

    C7

    C8

    C8

    T1

    T1

    Anterior view

    Posterior view

    Coraco-

    brachialis

    Biceps brachii

    Brachialis

    Medial cutaneous

    nerves off

    medial cord

    Pronator teres

    Flexor carpi radialis

    Flexor

    carpi

    ulnaris

    Palmaris longus

    Flexor digitorum

    superficialis

    Flexor pollicis

    longus

    Musculocutaneous

    nerve

    Flexor digitorum

    profundus

    Pronator

    quadratus

    Adductor

    pollicis

    3 Thenar muscles

    Ulnar nerve

    3 Hypothenar

    muscles

    7 Interossei

    Lumbricals to

    digits 2,3

    Lumbricals to

    digits 4,5

    Median nerve

    Indicates variable contribution

    Axillary and Radial Nerves

    Figure 14.10


    Axillary and radial nerves1

    Muscular innervation

    Cutaneous innervation

    Radial nerve

    Axillary nerve

    C5

    C5

    C6

    C6

    C7

    C8

    Anterior view

    Posterior view

    T1

    Teres minor

    Deltoid

    Axillary

    nerve

    Axillary

    nerve

    Triceps brachii

    (long head)

    Triceps brachii

    (lateral head)

    Radial

    nerve

    Radial

    nerve

    Triceps brachii

    (medial head)

    Brachioradialis*

    Extensor carpi radialis longus

    Anconeus

    Extensor carpi radialis brevis

    Extensor digitorum

    Extensor digiti minimi

    Supinator

    Extensor carpi ulnaris

    Abductor pollicis longus

    Extensor pollicis brevis

    Extensor pollicis longus

    Extensor indicis

    Radial

    nerve

    Indicates variable contribution

    *Functionally brachioradialis acts as a

    flexor of the forearm. It develops from

    the posterior compartment and thus is

    innervated by a posterior division nerve.

    Axillary and Radial Nerves

    Figure 14.10 (continued)


    The lumbar plexus and innervation of the lower limb

    The Lumbar Plexus and Innervation of the Lower Limb

    • Lumbar plexus arises from L1– L4

      • Smaller branches innervate the posterior abdominal wall and psoas muscle

      • Main branches innervate the anterior thigh

        • Femoral nerve—innervates anterior thigh muscles

        • Obturator nerve—innervates adductor muscles


    The lumbar plexus

    Kidney

    L3 vertebra

    Ilioinguinal

    nerve

    Ureter

    Iliohypogastric

    Lateral femoral

    cutaneous nerve

    Ilioinguinal

    Psoas major

    Femoral

    External iliac

    artery

    Lateral femoral

    cutaneous

    Femoral

    nerve

    Obturator

    Urinary

    bladder

    Anterior femoral

    cutaneous

    Femoral

    artery

    Saphenous

    (b) Nerves of the lumbar plexus, anterior view

    (c) Distribution of the

    major nerves from

    the lumbar plexus

    to the lower limb

    The Lumbar Plexus

    Ventral rami:

    Ventral rami

    L

    1

    Anterior division

    Posterior

    division

    L

    2

    Iliohypogastric

    Ilioinguinal

    L

    3

    Genitofemoral

    Lateral femoral

    cutaneous

    L

    4

    Obturator

    L

    5

    Femoral

    Lumbosacral

    trunk

    (a) Ventral rami and major branches of the

    lumbar plexus

    Figure 14.13


    The sacral plexus

    The Sacral Plexus

    • Arises from spinal nerves L4–S4 caudal to the lumbar plexus

    • Often considered with the lumbar plexus: Lumbosacral plexus

    • Sciatic nerve—the largest nerve of the sacral plexus

      • Actually two nerves in one sheath: tibial nerve—innervates most of the posterior lower limb and common fibular (peroneal) nerve—innervates muscles of the anterolateral leg

    • Superior and inferior gluteal nerves innervate the gluteal muscles

    • Pudendal nerve innervates muscles of the perineum


    The sacral plexus1

    Ventral rami:

    Ventral rami

    L4

    Anterior division

    Posterior division

    Superior

    gluteal

    L5

    Lumbosacral

    trunk

    S1

    Inferior

    gluteal

    S2

    Common

    fibular

    Tibial

    S3

    Posterior

    femoral

    cutaneous

    (a) Ventral rami and major branches of the sacral plexus

    S4

    Pudendal

    S5

    Sciatic

    Co1

    Gluteus maximus

    (medial portion

    removed)

    Piriformis

    Inferior gluteal

    nerve

    Pudendal nerve

    Greater trochanter

    of femur

    Common fibular

    nerve

    Tibial nerve

    Posterior femoral

    cutaneous nerve

    (b) Dissection of the gluteal region, posterior view

    Sciatic nerve

    Ischial tuberosity

    The Sacral Plexus

    Superior gluteal

    Inferior gluteal

    Pudendal

    Sciatic

    Posterior femoral

    cutaneous

    Common fibular

    Tibial

    Sural (cut)

    Deep fibular

    Superficial fibular

    Plantar branches

    (c) Distribution of the major nerves from

    the sacral plexus to the lower limb

    Figure 14.14


    The sacral plexus2

    Muscular innervation

    of medial thigh

    Muscular innervation

    of anterior thigh

    Cutaneous innervation

    Femoral nerve

    Obturator nerve

    Anterior view

    Posterior view

    L2

    L2

    L3

    L3

    L4

    L4

    Iliacus

    Sartorius

    Obturator

    externus

    Pectineus

    Rectus femoris

    Adductor brevis

    Vastus

    intermedius

    Vastus lateralis

    Adductor

    longus

    Vastus

    medialis

    Lateral

    femoral

    cutaneous

    nerve

    Obturator

    nerve

    Adductor

    magnus

    Gracilis

    Femoral

    nerve

    The Sacral Plexus

    Figure 14.15


    The sacral plexus3

    Muscular innervation of

    posterior thigh and leg

    Muscular innervation of

    lateral and anterior leg

    Cutaneous innervation

    Anterior view

    Tibial nerve

    Common fibular nerve

    Posterior view

    L4

    L5

    S1

    S2

    S3

    Sciatic nerve*

    Biceps femoris

    (long head)

    Biceps femoris

    (short head)

    Semitendinosus

    Posterior

    femoral

    cutaneous

    nerve

    Adductor magnus

    Semimembranosus

    Plantaris

    Gastrocnemius

    Common

    fibular

    nerve

    Gastrocnemius

    Popliteus

    Soleus

    Tibialis

    anterior

    Fibularis

    longus

    Tibialis

    posterior

    Flexor

    digitorum

    longus

    Extensor

    hallucis

    longus

    Extensor

    digitorum

    longus

    Flexor

    hallucis

    longus

    Fibularis

    brevis

    Tibial

    nerve

    Fibularis tertius

    Abductor hallucis

    Flexor digitorum brevis

    Extensor

    digitorum

    brevis

    Flexor hallucis brevis

    All other muscles

    of the sole

    Lumbricals

    *Sciatic nerve formed by tibial and common

    fibular nerves wrapped by common sheath.

    The Sacral Plexus

    Figure 14.15 (continued)


    Innervation of the skin dermatomes

    C2

    C3

    C4

    C5

    T1

    T2

    T3

    T4

    T2

    T2

    T5

    T6

    T7

    T8

    C6

    C6

    T9

    T10

    C5

    C5

    T11

    T12

    L1

    L1

    C6

    C6

    S2

    C7

    C7

    C8

    S3

    C8

    L2

    L2

    L3

    L3

    L4

    L4

    L5

    L5

    S1

    S1

    (a) Anterior

    view

    Innervation of the Skin: Dermatomes

    • Dermatome: an area of skin innervated by cutaneous branches of a single spinal nerve

    • Upper limb: skin supplied by nerves of the brachial plexus

    • Lower limb

      • Lumbar nerves—anterior surface

      • Sacral nerves—posterior surface


    Map of dermatomes posterior view

    C2

    C3

    C4

    C5

    C6

    C7

    C8

    T1

    T2

    T3

    T4

    T5

    T6

    T7

    T8

    T9

    T10

    C6

    C6

    T11

    T12

    C7

    C7

    L1

    S1

    L2

    C8

    C8

    L3

    S2

    L5

    L4

    S3

    S4

    S5

    S1

    S2

    S2

    S1

    L1

    L2

    L5

    L5

    L3

    L4

    (b) Posterior

    view

    L4

    L4

    L5

    L5

    S1

    Map of Dermatomes—Posterior View

    Figure 14.16b


    Disorders of the pns

    Disorders of the PNS

    • Shingles (herpes zoster): viral infection stems from childhood chicken pox

      • Often brought on by stress mostly experienced by those over 50

    • Migraine headache relates to sensory innervation of cerebral arteries

      • Arteries dilate and compresses and irritate sensory nerve endings

    • Myasthenia gravis progressive weakening of the skeletal muscles

      • An autoimmune disorder

      • Antibodies destroy acetylcholine receptors


    The pns throughout life

    The PNS Throughout Life

    • Spinal nerves form late in week 4

    • Each of the 31 pairs of spinal nerves:

      • Sends motor fibers to an individual myotome

      • Sends sensory fibers to the overlying band of skin

    • During week 5, nerves reach the organs they innervate

    • Embryonic muscles migrate to new locations

      • Some skin dermatomes become displaced

      • Muscles and skin always retain their original nerve supply


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