2-Batiz-Neuroanatomia-SNP

Prof. Luis Federico Bátiz

SNP

• Nervous structures outside the brain and spinal cord

• Nerves allow the CNS to receive information and take action

• Functional components of the PNS• Sensory inputs and motor outputs

• Categorized as somatic or visceral• Sensory inputs also classified as general or special

Functional Organization of the PNS

Basic Structural Components of the PNS

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

• Motor endings – axon terminals of motor neurons• Innervate effectors (muscle fibers and glands)

• Nerves and ganglia • Nerves – bundles of peripheral axons• Ganglia – clusters of peripheral neuronal cell

bodies

Structural Organization of PNS in Region of a Spinal Nerve

Peripheral endings• Afferent: Sensory Receptors• Efferent: Motor Somatic / Vegetative

Peripheral Sensory Receptors

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

• Two main categories of sensory receptors• Special nerve endings of sensory neurons

• Monitor general sensory information• Independent receptor cells – specialized epithelial cells or

small neurons• Monitor most types of special sensory information

• Sensory receptors also classified according to: • Location• Type of stimulus detected• Structure

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

• Interoceptors – (visceroceptors) receive stimuli from internal viscera• Monitor a variety of stimuli

• Proprioceptors – monitor degree of stretch• Located in musculoskeletal organs

Classification by Modality

• Mechanoreceptors – respond to mechanical forces

• Thermoreceptors – respond to temperature changes

• Chemoreceptors – respond to chemicals in solution

• Photoreceptors – respond to light – located in the eye

• Nociceptors – respond to harmful stimuli (pain)

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Structure

• General sensory receptors• Widely distributed • Nerve endings of sensory neurons monitor:

• Touch, pressure, vibration, stretch• Pain, temperature, proprioception

• Divided into two groups• Free nerve endings• Encapsulated nerve endings


Free Nerve Endings

• Abundant in epithelia and underlying connective tissue

• Respond to pain and temperature

• Two specialized types of free nerve endings • Merkel discs – lie in the epidermis

• Slowly adapting receptors for light touch• Hair follicle receptors – wrap around hair follicles

• Rapidly adapting receptors


Unencapsulated Nerve Endings

Encapsulated Nerve Endings

• Consist of one or more end fibers of sensory neurons• Enclosed in connective tissue• Mechanoreceptors

• Include four main types

• Meissner’s corpuscles • Pacinian corpuscles• Ruffini’s corpuscles• Proprioceptors


Encapsulated Receptors

Proprioceptors

• Monitor stretch in locomotory organs

• 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

Proprioceptors


Structure of Receptors in Skin

Somatic efferent: Innervation of Skeletal Muscle

• Motor axons innervate skeletal muscles• Neuromuscular junctions (motor end plates)

• Similar to synapses between neurons

• Acetylcholine diffuses across the synaptic cleft• Binds with molecules (receptors) on the sarcolemma

• Motor axons branch to innervate muscle fibers

The Neuromuscular Junction

Motor Unit

• A motor neuron and all the muscle fibers it innervates

Vegetative efferent: Innervation of Visceral Muscle / Glands

• Simpler than neuromuscular junctions of skeletal muscle

• Near the smooth muscle or gland it innervates • Visceral motor axon swells into a row of

varicosities• Visceral motor responses

• Slower than somatic motor reflexes

Innervation of Smooth Muscle

Nerves

• Cranial Nerves• 12 pairs

• Spinal Nerves• 31 pairs

Functional components of nerves

• General somatic afferent fibers (GSA): transmit exteroceptive and proprioceptive impulses from head and face to somatic sensory nuclei

• Special somatic afferent fibers (SSA): transmit sensory impulses from special sense organs of vision, equilibrium and hearing to the brain

• General visceral afferent fibers (GVA): transmit interoceptive impulses from the viscera to the visceral sensory nuclei

• Special visceral afferent fibers (SVA): transmit sensory impulses from special sense organs of smell and taste to the brain

• General somatic efferent fibers (GSE): innervate skeletal muscles of eye and tongue

• Special visceral efferent fibers (SVE): transmit motor impulses from the brain to skeletal muscles derived from brachial (gill) arches of embryo. These include the muscles of mastication, facial expression and swallowing

• General visceral efferent fibers (GVE): transmit motor impulses from the general visceral motor nuclei and relayed in parasympathetic ganglions. The postganglionic fibers supply cardiac muscles，smooth muscles and glands

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) extends into the abdomen

http://info.med.yale.edu/caim/cnerves/cn1/cn1_1.html

The 12 Pairs of Cranial Nerves

Classification of cranial nerves

• Sensory cranial nerves: contain only afferent (sensory) fibers• ⅠOlfactory nerve • ⅡOptic nerve• Ⅷ Vestibulocochlear nerve

• Motor cranial nerves: contain only efferent (motor) fibers• Ⅲ Oculomotor nerve • Ⅳ Trochlear nerve • ⅥAbducent nerve • Ⅺ Accessory nerv • Ⅻ Hypoglossal nerve

• Mixed nerves: contain both sensory and motor fibers---• ⅤTrigeminal nerve, • Ⅶ Facial nerve,• ⅨGlossopharyngeal nerve• ⅩVagus nerve

Sensory cranial nerves

N. Location of cell body and axon categories

Cranial exit

Terminal nuclei

Main action

Ⅰ Olfactory cells (SVA)

Cribrifomforamina

Olfactory bulb

Smell

Ⅱ Ganglion cells (SSA)

Optic canal

Lateral geniculate body

Vision

Ⅷ Vestibular ganglion(SSA)

Internal acoustic meatus

Vestibular nuclei

Equilibrium

Cochlear ganglion (SSA)

Cochlear nuclei

Hearing

CN I: Olfactory Nerves

• Sensory nerves of smell

CN II: Optic Nerve

• Sensory nerve of vision

Table 14.2

CN VIII: Vestibulocochlear Nerve

• Sensory nerve of hearing and balance

Table 14.2

Motor cranial nerves

N. Nucleus of origin and axon categories

Cranial exit Main action

Ⅲ Nucleus of oculomotor (GSE)

Superior orbital fissure

Motot to superior, inferior and medial recti; inferior obliquus; levator palpebrae superioris

Accessory nucleus of oculomotor (GVE)

Parasympathetic to sphincter pupillea and ciliary muscl

Ⅳ Nucleus of trochlear nerve (GSE)


Motor to superior obliquus

Ⅵ Nucleus of abducent nerve (GSE)


Motor to lateral rectus

Ⅺ Nucleus of accessory nerve (SVE)

Jugular foramen Motor to sternocleidomastoid and trapezius

Ⅻ Nucleus of hypoglossal nerve( GSE)

Hypoglossal canal Motot to muscles of tongue

Motor cranial nerves

IIIIVVI

XI

XII


CN III: Oculomotor Nerve

• Innervates four of the extrinsic eye muscles

Table 14.2


CN IV: Trochlear Nerve

• Innervates an extrinsic eye muscle

Table 14.2

CN VI: Abducens Nerve

• Abducts the eyeball

Abducent nerve injury

Mixed Nerves

VVIIIXX

CN V: Trigeminal Nerve

• Provides sensory innervation to the face• Motor innervation to chewing muscles

CN VII: Facial Nerve

• Innervates muscles of facial expression• Sensory innervation of face• Taste

CN IX: Glossopharyngeal Nerve

• Sensory and motor innervation of structures of the tongue and pharynx

• Taste

CN X: Vagus Nerve

• A mixed sensory and motor nerve

• Main parasympathetic nerve• “Wanders” into thorax

and abdomen

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

• 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 (cell bodies in gray matter of spinal cord – no ganglia)

Spinal Nerves

• Branch into dorsal ramus and ventral ramus• Both contain sensory and motor fibers

• Rami communicantes connect to the base of the ventral ramus• Lead to the sympathetic chain ganglia (gray and white ramus)

Innervation of the Skin: Dermatomes

• Dermatome – an area of skin • Innervated by cutaneous branches of a single spinal

nerve• Upper limb – skin is supplied by nerves of the

brachial plexus• Lower limb

• Lumbar nerves – anterior surface• Sacral nerves – posterior surface

Map of Dermatomes

Spinal nerve pathways

Cervical plexus

• Formed by ventral rami of C1–C4

• Innervates skin and muscles of the neck, ear, back of head, and shoulders

• Phrenic nerve• Major motor and

sensory nerve of the diaphragm (receives fibers from C3–C5)

Brachial plexus

• Formed by ventral rami of C5–C8 and T1 (and often C4and T2)

• It gives rise to the nerves that innervate the upper limb

• Major branches of this plexus: • Roots—five ventral rami

(C5–T1)• Trunks—upper, middle,

and lower• Divisions—anterior and

posterior • Cords—lateral, medial,

and posterior

Upper

Middle Trunks

Lower

Roots (ventral rami):

Upper subscapularLower subscapularThoracodorsalMedial cutaneousnerves of the armand forearm

Long thoracicMedial pectoralLateral pectoral

Nerve tosubclaviusSuprascapular

Dorsal scapular

Posteriordivisions

Anteriordivisions

Lateral

PosteriorCords

Medial

AxillaryMusculo-cutaneousRadialMedianUlnar

Posteriordivisions

Trunks Roots

C4

C5

C6

C7

C8

T1

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

Lumbar plexus

• Arises from L1–L4

• Innervates the thigh, abdominal wall, and psoas muscle• Femoral nerve—innervates quadriceps and skin of anterior thigh

and medial surface of leg• Obturator nerve—passes through obturator foramen to innervate

adductor muscles

Sacral plexus• Arises from L4–S4

• Serves the buttock, lower limb, pelvic structures, and perineum• Sciatic nerve

• Longest and thickest nerve of the body• Innervates the hamstring muscles, adductor magnus, and most

muscles in the leg and foot• Composed of two nerves: tibial and common fibular

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

Disorders of the PNS: Myasthenia Gravis

• Myasthenia gravis • Progressive weakening of the skeletal muscles• An autoimmune disorder• Antibodies destroy acetylcholine receptors

Ptosis due to weakness of eyelid muscles

• www.intelligencetest.com/reflex/index.htm

http://www.intelligencetest.com/reflex/index.htm�

2-Batiz-Neuroanatomia-SNP

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