Pns 7-

SMS1084

Dr. Mohanad R. Alwan

Now that we’ve looked at spinal and cranial nerves, we can examine the divisions of the PNS.

The PNS is broken down into a sensory and a motor division.

We’ll concentrate on the motor division which contains the somatic nervous system and the autonomic nervous system.

Peripheral Nervous SystemPeripheral Nervous System

Nerves and ganglia outside the central nervous system

Nerve = bundle of neuron fibers

Neuron fibers are bundled by connective tissue

Structure of a NerveStructure of a Nerve

Endoneurium surrounds each fiber

Groups of fibers are bound into fascicles by perineurium

Fascicles are bound together by epineurium

Parasympathetic ganglion

Classification of NervesClassification of Nerves

Mixed nerves – both sensory and motor fibers

Afferent (sensory) nerves – carry impulses toward the CNS

Efferent (motor) nerves – carry impulses away from the CNS

Spinal NervesSpinal Nerves

There is a pair of spinal nerves at the level of each vertebrae.

Dorsal root ganglion – cell bodies of sensory neuronsDorsal root – axons of sensory neuronsVentral root – axons of motor neurons

31 pairs of spinal nerves

Spinal NervesSpinal Nerves

3 kinds of neurons connect CNS to the body◦ Sensory◦ Motor◦ Interneurons

Motor - CNS to muscles and organs

Sensory - sensory receptors to CNS

Interneurons: Connections Within CNS

SpinalCord

Brain

Nerves

12

13

Nervous SystemNervous System

Central Nervous System (CNS)

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

Peripheral Nervous System (PNS)

Autonomic Nervous System (ANS)(involuntary)

Autonomic Nervous System (ANS)(involuntary)

Somatic nervous System (voluntary)

Somatic nervous System (voluntary)

Sympathetic Nervous System

Sympathetic Nervous System

Parasympathetic Nervous System

Parasympathetic Nervous System

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

15

StimulusStimulus

Sensory System

CNS

Motor System (neurone)Somatic system

(voluntary)

Autonomic system

(involuntary)

Striated muscle Smooth muscle & glands

Effe ctor

ResponseResponse

(Brain / spinal cord)

(neurone)

Nerves to/from spinal cord◦ Control muscle

movements◦ Somatosensory inputs

Both Voluntary and reflex movements

Skeletal Reflexes◦ simplest is spinal reflex

arch

Muscle

MotorNeuron

InterneuronSkin receptors

SensoryNeuron

Brain

◦ Cell bodies of motor neurons reside in CNS (brain or spinal cord)

◦ Their axons (sheathed in spinal nerves) extend all the way to their skeletal muscles

Structure of spinal nerves: Somatic pathwaysStructure of spinal nerves: Somatic pathways

dorsal rootdorsal rootganglion

ventral root

spinalnerve

dorsalramus

ventralramus

dorsalhorn

ventralhorn

somaticsomaticsensorysensory

nervenerve(GSA)(GSA)

somaticsomaticmotormotornervenerve

(GSE)(GSE)

CNSinter-

neuron

CNSinter-

neuron

Mixed SpinalMixed SpinalNerveNerve

Mixed SpinalMixed SpinalNerveNerve

gray ramuscommunicans white ramus

communicans

sympatheticganglion

Autonomic Nervous SystemAutonomic Nervous System

The involuntary branch of the nervous system

Consists of only motor nerves

Divided into two divisions

Sympathetic division

Parasympathetic division

Two divisions: ◦ Sympathetic◦ Parasympatheitic

Control involuntary functions:◦ Heartbeat◦ Blood pressure◦ Respiration◦ Perspiration◦ Digestion

Can be influenced by thought and emotion

2 divisions:◦ Sympathetic

“Fight or flight” “E” division

Exercise, excitement, emergency, and embarrassment

◦Parasympathetic “Rest and digest” “D” division

Digestion and diuresis

“ Fight or flight” response Release adrenaline and

noradrenaline Increases heart rate and

blood pressure Increases blood flow to

skeletal muscles Inhibits digestive functions

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

SYMPATHETIC

Dilates pupil

Stimulates salivation

Relaxes bronchi

Accelerates heartbeat

Inhibits activity

Stimulates glucose

Secretion of adrenaline,nonadrenaline

Relaxes bladder

Stimulates ejaculationin male

Sympatheticganglia

Salivaryglands

Lungs

Heart

Stomach

Pancreas

Liver

Adrenalgland

Kidney

Basic organization◦ Issues from T1-L2

◦ Preganglionic fibers form the lateral gray horn◦ Supplies visceral organs and structures of superficial

body regions◦ Contains more ganglia than the parasympathetic division

“ Rest and digest ” system

Calms body to conserve and maintain energy

Lowers heartbeat, breathing rate, blood pressure

CENTRAL NERVOUS SYSTEMBrain

PARASYMPATHETIC

Spinalcord

Stimulates salivation

Constricts bronchi

Slows heartbeat

Stimulates activity

Contracts bladder

Stimulates erectionof sex organs

Stimulates gallbladder

Gallbladder

Contracts pupil

Summary of autonomic differencesAutonomic nervous system controls physiological arousal

Sympatheticdivision (arousing)

Parasympatheticdivision (calming)

Pupils dilate EYES Pupils contract

Decreases SALVATION Increases

Perspires SKIN Dries

Increases RESPERATION Decreases

Accelerates HEART Slows

Inhibits DIGESTION Activates

Secrete stresshormones

ADRENALGLANDS

Decrease secretionof stress hormones

Voluntary Skeletal muscle Single efferent neuron Axon terminals release

acetylcholine Always excitatory Controlled by the cerebrum

Involuntary Smooth, cardiac muscle;

glands Multiple efferent neurons Axon terminals release

acetylcholine or norepinephrine

Can be excitatory or inhibitory

Controlled by the homeostatic centers in the brain – pons, hypothalamus, medulla oblongata

Most internal organs are innervated by both branches of the ANS which exhibit antagonistic control

A great example is heart rate. An increase in sympathetic stimulation causes HR to increase whereas an increase in parasympathetic stimulation causes HR to decrease

Exception to the dual innervation rule:Sweat glands and blood vessel smooth muscle are only innervated by symp and rely strictly on up-down control.

Exception to the antagonism rule:Symp and parasymp work cooperatively to achieve male sexual function. Parasymp is responsible for erection while symp is responsible to ejaculation. There’s similar ANS cooperation in the female sexual response.

Both ANS divisions share the same general structure. ◦ Autonomic pathways always

consist of 2 neurons in series.◦ They synapse in an autonomic

ganglion – would this be outside the CNS

◦ The 1st neuron in the autonomic pathway is the preganglionic neuron, Cell body in CNS, myelinated, and

projects to the autonomic ganglion.

◦ While the 2nd neuron is the postganglionic neuron. Cell body in autonomic ganglion,

unmyelinated, and projects to the effector or organ.

Sympathetic

CNS ganglion

short preganglionicneuron

long postganglionicneuron

target

Parasympathetic

CNS ganglion

long preganglionicneuron

target

short postganglionicneuron

Overview of the Autonomic Nervous SystemOverview of the Autonomic Nervous SystemDifferences between Sympathetic & ParasympatheticDifferences between Sympathetic & Parasympathetic

Relative Lengths of Neurons

Parasympathetic

Overview of the Autonomic Nervous SystemOverview of the Autonomic Nervous SystemDifferences between Sympathetic & ParasympatheticDifferences between Sympathetic & Parasympathetic

Neurotransmitters

ACh, +

NE (ACh at sweat glands),+ / -, α & ß receptors

ACh, + / -muscarinic receptors

• All preganglionics release acetylcholine (ACh) & are excitatory (+)

• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)

• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)

Sympathetic

• Excitation or inhibition is a receptor-dependent & receptor-mediated response

Potential for pharmacologicmodulation of autonomic responses

Potential for pharmacologicmodulation of autonomic responses

ACh, +

Point of CNS OriginPoint of CNS Origin T1 L2

(thoracolumbar)

Brainstem,

S2 S4

(craniosacral)

Site of Peripheral Site of Peripheral GangliaGanglia

Paravertebral – in sympathetic chain

On or near target tissue

Length of Length of preganglionic fiberpreganglionic fiber

Short Long

Length of Length of postganglionic fiberpostganglionic fiber

Long Short

NT at Target NT at Target SynapseSynapse

Norepinephrine

(adrenergic neurons)

Acetylcholine

(cholinergic neurons)

Type of NT Type of NT Receptors at Receptors at Target SynapseTarget Synapse

Alpha and Beta

( and )

Muscarinic

NT at GanglionNT at Ganglion Acetylcholine Acetylcholine

Receptor at Receptor at GanglionGanglion

Nicotinic Nicotinic

In the following tables, note the effects of the sympathetic and parasympathetic nervous systems on various body organs.

Target OrganTarget Organ Parasympathetic Parasympathetic EffectsEffects

Sympathetic Sympathetic EffectsEffects

Eye (Iris)Eye (Iris) Stimulates constrictor muscles. Pupil constriction.

Stimulates dilator muscles. Pupil dilates.

Eye (Ciliary Eye (Ciliary muscle)muscle)

Stimulates. Lens accommodates – allows for close vision.

No innervation.

Salivary GlandsSalivary Glands Watery secretion. Mucous secretion.

Sweat GlandsSweat Glands No innervation. Stimulates sweating in large amounts. (Cholinergic)

GallbladderGallbladder Stimulates smooth muscle to contract and expel bile.

Inhibits gallbladder smooth muscle.

Arrector PiliArrector Pili No innervation Stimulates contraction. Piloerection (Goosebumps)



Cardiac MuscleCardiac Muscle Decreases HR. Increases HR and force of contraction.

Coronary Blood Coronary Blood VesselsVessels

Constricts. Dilates

Urinary Bladder; Urinary Bladder; UrethraUrethra

Contracts bladder smooth muscle; relaxes urethral sphincter.

Relaxes bladder smooth muscle; contracts urethral sphincter.

LungsLungs Contracts bronchiole (small air passage) smooth muscle.

Dilates bronchioles.

Digestive OrgansDigestive Organs Increases peristalsis and enzyme/mucus secretion.

Decreases glandular and muscular activity.

Liver Liver No innervations No innervation (indirect effect).



KidneyKidney No innervation. Releases the enzyme renin which acts to increase BP.

PenisPenis Vasodilates penile arteries. Erection.

Smooth muscle contraction. Ejaculation.

Vagina; ClitorisVagina; Clitoris Vasodilation. Erection. Vaginal reverse peristalsis.

Blood CoagulationBlood Coagulation No effect. Increases coagulation rate.

Cellular Cellular MetabolismMetabolism

No effect. Increases metabolic rate.

Adipose TissueAdipose Tissue No effect. Stimulates fat breakdown.



Mental ActivityMental Activity No innervation. Increases alertness.

Blood VesselsBlood Vessels Little effect. Constricts most blood vessels and increases BP. Exception – dilates blood vessels serving skeletal muscle fibers (cholinergic).

UterusUterus Depends on stage of the cycle.

Depends on stage of the cycle.

Endocrine Endocrine PancreasPancreas

Stimulates insulin secretion.

Inhibits insulin secretion.

Preganglionic fibers have their somat in the lateral horns of the thoracic and lumbar spinal cord.

Preganglionic fibers leave the cord via the ventral root and enter a white ramus communicans to enter a chain ganglion – which is part of the sympathetic trunk.

Let’s look at a picture!

Certain splanchnic nerves synapse on hormone-producing cells of the adrenal medulla – the interior of the adrenal glands which sit upon the kidneys.

How does this contribute to the “diffuseness” of sympathetic activity?

The Hypothalamus is the Boss:

◦ Its anterior and medial regions direct parasympathetic function while its posterior and lateral regions direct sympathetic function

◦ These centers exert control directly and via nuclei in the reticular formation (e.g., the cardiovascular centers in the MO, respiratory centers in MO and pons, etc.)

◦ The connection of the limbic system to the hypothalamus mediates our “flight or flight” response to emotional situations.

I will open ur mouth like my

toy

Health & Medicine

Pns 7-