anatomy 5.8 ans_javier

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Anatomy 5.8 January 17, 2012

ANSDr. Javier

Group 6 | Bautista A., Bautista B., Bautista C., Bautista V., Bello C., Bello H., Bernardo, Biag E. of 6

OUTLINE

I. Functional components of peripheral nerves

II. Overview of ANS

III. Spinal Cord, Roots & Nerves

IV. Sympathetic Nervous System

V. Parasympathetic Nervous System

VI. ANS Control by the Brain

VII. Visceral Afferents

Objectives:

To describe the general organization of the Autonomic Nervous System,

its functions and principle divisions

To describe the origin and general distribution of each of the principle

divisions

To differentiate the principle divisions by anatomic features, the involved

neurotransmitters and their systemic effects

To describe the higher control of ANS

To briefly touch the Visceral Afferent Pathways

I. FUNCTIONAL COMPONENTS OF PERIPHERAL NERVES

Motor system (general visceral efferent, GVE) which provides for

the innervations of the smooth muscle, cardiac muscle andglandular tissue of the body.

GVE fibers are found in:

1. Body wall structure – Blood vessels of skeletal muscles and skin,

arrector pili muscles and glands of the skin

2.

Internal organs – Blood vessels and glands of these organs

Nervous impulses are conveyed along two-neuron chains from

CNS to target structure

o Preganglionic neurons

Located in the brainstem or the spinal cord

Their axons constitute preganglionic fibers

o Postganglionic neurons

Located in autonomic ganglia (outside CNS)

Their axons constitute post ganglionic fibers

Functional Components

Each nerve can be differentiated according to:

1. Afferent vs Efferent

2. Somatic vs Visceral

3. General vs Special

4. Somatic vs Autonomic

A. AFFERENT VERSUS EFFERENT

Afferent

o Stimulus from the periphery towards the CNS

o Example: Pseudounipolar neurons conducting impulses from

sensory origin to CNS

Efferent

o From CNS (ex. multipolar neurons, muscles and glands

o Located at the ventral horn

o Motor nerve fibers

B. SOMATIC VS. VISCERAL

Attribute Somatic System Visceral System

Embryological

origin of tissue

Derived from the body

wall

Related to somatic

(parietal) mesoderm

o dermatome (skin)

o myotome (muscles)

Derived from

splanchnic (visceral)

mesoderm,

endoderm

Examples of adult

tissues

Dermis of the skin,

skeletal muscles,

connective tissues

Glands, cardiac

muscle, smooth

muscle of GIT and

blood vesselsPerception Conscious, voluntary Unconscious,

involuntary

C. GENERAL VS. SPECIAL

Sensory/Motor + Somatic/Visceral

Somatic Visceral

Sensory

(afferent)

Somatic sensory

General Somatic

Afferent (GSA)

Visceral sensory

General Visceral

Afferent (GVA)

Motor

(efferent)

Somatic motor

General Somatic

Efferent (GSE)

Visceral motor

General Visceral

Efferent (GVE)

Somatic nerves – Somatic Nervous System

Visceral nerves – Autonomic Nervous System

D. SOMATIC VS. AUTONOMIC

Somatic nervous system

o Only one neuron from the ventral horn cells to effector organ

(Skeletal ms) Release of ACh

Autonomic nervous system

o Preganglionic and postganglionic neuron synapse at the

ganglion

o Postganglionic neuron has the nerve cell bodies in the ganglion

o “Location” of neuron is in the nerve cell body of the neuron

o

Preganglionic fiber is myelinated but the postganglionic fibe

is unmyelinated

o Innervated organs: Smooth muscle, cardiac muscle, glands

(myoepithelial cells)



Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez of 6

II. OVERVIEW OF THE ANS

Table 1. Differences between sympathetic and parasympathetic

Location of

preganglionic cell

bodies

Sympathetic Parasympathetic

Neurotransmitters

(potential for

pharmacologic

modulation

responses)

*excitation or inhibition

is a receptor-

dependent andreceptor- mediatedresponse

Preganglionic

neurons – release

Ach and are

excitatory (+)

Postganglionic

neurons – NE and

are excitatory* (+) orinhibitory* (-); Ach at

eccrine sweat

glands; nicotinic α

and β receptors

Preganglionic

neurons —release

Ach and are (+)

Postganglionic

neurons – Ach and

are (+)/(-);muscarinic

receptors

Branching of axons

Preganglionic

neurons –More

ganglia from the

same axon

Postganglionic

neurons – Branched

(greater

distribution/

diffused; prolonged

effect)

Preganglionic

neurons – 1 axon

Postganglionic

neurons – Branched

but not as extensive

as in sympathetic n

(more localized

effect)

Target tissues Organs of head,

neck, trunk and

external genitalia

Adrenal medulla

Sweat glands in skin

Arrector muscles of

hair

ALL vascular smooth

muscle

Distributed to

essentially alltissues because of

vascular smooth

muscle

Organs of head,

neck, trunk and

external genitalia

Never reaches

limbs or body wall

except for external

genitalia

Functional

differences

“Fight or flight”

Catabolic (expend

energy)

“Feed and breed”,

“rest and digest”

Maintain

homeostasis

Similarities between Sympathetic and Parasympathetic

o Both are efferent (motor) systems: “Visceromotor”

o Both involve regulation of the internal environment generally

outside of our conscious control: Autonomous

o Both involve 2 neurons that synapse in a peripheral ganglion

o Innervate glands, smooth muscles, cardiac muscles

Differences between Sympathetic and Parasympathetic

o Neurotransmitters and their receptors: basis for pharmacologica

modification (medication or anesthetics)

o Dual innervations of many organs- having a break and an

accelerator provides more control

o Predominance of one over the other




Dual innervation of organs

o having a “break and an accelerator” provides more control

o

Interplay of opposing/antagonistic effects

Exemption to the dual innervations rule:

o Sweat glands and blood vessel smooth muscle are only

innervated by sympathetic

o Rely strictly on up- down control

Higher frequency of stimulation, increased smooth muscle

contraction or increased sweat secretion

Exemption to the antagonism rule:

o Sympathetic and parasympathetic work cooperatively to

achieve male sexual function.

o

Parasympathetic is responsible for erection while sympathetic

is responsible for ejaculation.

o

There’s a similar ANS cooperation in the female sexual

response.

III. SPINAL CORD, ROOTS AND NERVES

Figure 1. Arrangement of spinal cord, spinal nerve and

sympathetic chain ganglion.

Efferent fibers branch out to ventral root, exit IV canal , join with

dorsal root to form the spinal nerve

2 ventral branches of rami communicantes merge to form the

sympathetic chain ganglion

ventral root + dorsal root= spinal nerve → rami communicantes →

sympathetic chain ganglion

Spinal Nerve & Sympathetic Trunk

o Ganglia (pairs)

3 cervical

11-12 thoracic

2-4 lumbar

4 sacral

1 coccygeal (Located at midline, anterior to the vertebral

body of the coccyx; a.k.a. ganglion impar )

o

14 pairs white rami communicantes (T1-L2)

o 31 pairs gray rami communicantes

Note:

Ventral root + dorsal root= Spinal nerve

White matter - More lateral

Gray matter - Medial

For each spinal nerve, there is a gray ramus

Preganglion - Myelinated - White

Postganglion - Unmyelinated - Gray

Somatic Pathways

o Interneuron between GSA and GSE

o

Mixed spinal nerves

Sympathetic pathway

o Nerve cell bodies at intermedial gray column/ lateral horn

IV. SYMPATHETIC NERVOUS SYSTEM

Fight or flight

Afferent fibers will come from the ventral root and then exit the

intervertebral canal and join the dorsal root to form the spina

nerve

Ventrally located branches (rami communicantes; sing

Communicans) join sympathetic chain ganglion

Group of SCG ->becomes sympathetic trunk (both sides of the

vertebral column) -> becomes paravertebral ganglia

Ganglion impar (fuses at midline)

A. PREGANGLIONIC CELL BODIES

Exit spinal cord via ventral root -> spinal nerve -> white ramus

communicans -> synapse at ganglion within sympathetic trunk ->

axon of the ganglion of the post-ganglionic fiber leave the

sympathetic trunk -> spinal nerve via gray ramus communicans

Thoracolumbar area

Preganglionic cell bodies in intermediolateral cell column

(Lamina VII)

Spinal cord level: T1- L2/L3

Somatotrophic organization

Clinical significance:

Dysfunction due to cord injury - Spinal nerve impingement

Referred pain




Figure 1: Sympathetic Pathways

B. POSTGANGLIONIC CELL BODIES

For coccygeal to cervical

1. Paravertebral ganglia

Located just beside the vertebrae

United by preganglionic into sympathetic trunk

Preganglionic neurons are thoracolumbar but postganglionic

neurons span from the cervical area down to coccyx

Some preganglionic fibers ascend or descend in trunk

o Synapse at same level

o Ascend to synapse at higher ganglion

o Descend to synapse at lower ganglion

2. Prevertebral (preaortic) ganglia

Located anterior to abdominal aorta in plexuses surrounding its

major branches Example: Celiac ganglion, superior and inferior mesenteric ganglia

Preganglionic fibers reach prevertebral ganglia via

abdominopelvicsplanchnic nerves

3. Adrenal Medulla

Certain splanchnic nerves synapse on hormone-producing cells of

the adrenal medulla (modified postganglionic neurons)

Cells of the adrenal medulla are derived from the neural crest

Norepinephrine and epinephrine are released to the blood stream

to reach their target organs

C. Sympathetic System: Preganglionic Pathways

1. Synapse at same level2. Synapse above or below spinal level within sympathetic chain

3. Exit through splanchnic nerves to synapse to collateral ganglion or

to adrenal medulla

SUMMARY: SNS

Thoracolumbar preganglionic cell bodies (intermediolateral gray)

Short preganglionic fiber releasing ACh

Ganglia with nicotinic receptors at sympathetic trunk

prevertebral ganglia, adrenal medulla

Long postganglionic fiber releasing NE (+ Epi at adrenal medulla

Ach in sweat glands)

Diffuse and prolonged effect on target organs with α/β receptors

Lansang Notes:

Inferior cervical ganglion + 1st

thoracic ganglion = stellate ganglion

Thoracic splanchnic nerves (greater, lesser, and least; T5 –T12)

o Carry preganglionic fibers (T5-T12) through sympathetic trunk

to postganglionic prevertebral ganglia

preganglionic fibers

o

T5-T9: greater splanchnic nerve

o T10-T11: lesser splanchnic nerve

o

T12: least

postganglionic fiber – reach abdominal viscera

lumbar splanchnic nerves

carry preganglionic fiber from upper lumbar spinal cord (L1-L2)

reach lower abdomen and pelvis

distribution of sympathetic outflow

T1 to T5 – head and neck

T1 to T2 – eye

T2 to T6 – heart and lungs

T6 to L2 – abdominal viscera

L1 to L2 – urinary, genital

Superior cervical ganglion (postganglionic fiber) – form carotid

plexus which innervates head

V. PARASYMPATHETIC NERVOUS SYSTEM

A. CRANIAL OUTFLOW

CN III, VII, IX, X

Four ganglia in head Vagus nerve (CN X) - major preganglionic parasympathetic supply

to thorax and abdomen

synapse in ganglia within wall of target organs (e.g. enteric plexus

B. SACRAL FLOW

S2-S4 via pelvic splanchnic

Hindgut/pelvic viscera distal to the left colonic (colic) flexure, and

external genitalia

As with SNS, have preganglionic bodies located in gray areas o

spinal cord (analogous to lateral horn/IMLC)




C. PARASYMPATHETIC CRANIAL OUTFLOW

CN III Oculomotor

o Nucleus: Edinger-Westphal

o preganglionic fibers: oculomotor nerve

o ganglion: ciliary ganglion

o postganglionic fibers: short ciliary nn

o

target organs:

ciliary muscle - relaxes zonal fibers, making lens more convex

sphincter papillae - constricts pupils (myosis)

CN VII Facial

o

2 sets of nuclei, ganglia, and target organ(s)

o Tears:

nucleus: lacrimal/lacrimatory

preganglionic fibers: nervus intermedius greater petrosal

n. nerve of pterygoid canal

ganglion: pterygopalatine

postganglionic fibers: maxillary n. zygomaticotemporal n.

lacrimal n.

target organ:

lacrimal gland

mucosa of nasal cavity, paranasal sinuses, palate, pharynx

CN IX Glossopharyngeal

o

nucleus: inferior salivatory

o preganglionic fibers: tympanic branch of CN IX lesser

petrosal n.

o ganglion: otic ganglion

o

postganglionic fibers: auriculotemporal nerveo target organ: parotid gland

CN X Vagus

o nucleus: dorsal motor nucleus of CN X

o preganglionic fibers: vagal nerve trunks and branches

o ganglia: on plexuses near or within walls of target organ

o postganglionic fibers: short direct fibers

o

target organ:

cardiac muscle

bronchial smooth muscle

pulmonary blood vessels and glands

stomach and intestines until left colic (splenic) flexure

gallbladder and biliary ducts

kidneys

SUMMARY: PNS

Craniosacral preganglionic cell bodies (cranial nerve nuclei and

sacral gray matter)

Long preganglionic fiber releasing Ach Ganglia with nicotinic receptors near or in walls of target organs

Short postganglionic fibers releasing Ach

In contrast to SNS, has localized and short-lived effect on the

target organ

VI. ANS CONTROL BY THE BRAIN

The hypothalamus is the boss!

Anterior, Medial regions-control Parasympathetic Nervous System

Posterior, Lateral Regions-control Sympathetic Nervous System

These fibers exert direct control via nuclei in the reticular

formations

o Ex: There are respiratory and cardiovascular centers in the

Medulla Oblongata

The Brain controls the ANS by:

1)

Subconscious cerebral input via the limbic lobe connections

influences hypothalamic function

Mediates our “fight or flight” response to emotiona

situations

The relationship between the hypothalamus and the

periaqueductal gray matter and amygdale allow us to

respond to fear

2) Other controls come from the cerebral cortex, reticular

formation and the spinal cord

VII. VISCERAL AFFERENTS

Visceral Sensory Nerves (GVA)

o

Run with sympathetic and parasympathetic nerves

o Cell bodies in dorsal root ganglion (pseudo-unipolar)

o

Nerve ending in viscera

Somatic Sensation

o Conscious, sharp, well-localized

o Touch, pain, temperature, pressure, proprioception




Visceral Sensation

o Often unconscious. If conscious: it is dull, poorly localized

o

Distension, cramping, blood gas, blood pressure, irritants

Visceral pain is carried almost exclusively by the sensory

component of the SNS

Visceral pressure and movement sensation is carried almost

exclusively by the sensory component of the PNS

S

A. VISCERAL REFLEX ARC

Rectal or Defecation Reflex

1) Sensory stretch receptors in rectum sense distension

2) Stimulus sent to spinal cord segments S2-S4

3) Integrate with pre-ganglionic cell bodies

4) Efferent signal travels to pelvic splanchnic nerves

5)

Contraction of muscles defecation

Micturition Reflex

1) Distension in the bladder

2)

Stimulus sent to spinal cord segments S2-S4

3) Integrate with pre-ganglionic cell bodies

4) Efferent signal travels to pelvic splanchnic nerves

5)

Contraction of Detrusor muscle micturition

B. VISCERAL AFFERENTS AND REFERRED PAIN

C. REFERRED PAIN

Pain originating in a visceral structure perceived as being from an

area of skin innervated by the same segmental level as the

visceral afferent

Results from convergence of somatic and visceral afferents on the

same segmental level of the spinal cord

o Ex: Pain originating in the chest can also radiate down the left

side of the arm

“cross talk” in the dorsal horn

convergence &

“cross-talk” somatic afferent

anatomy 5.8 ans_javier

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