Introduction to the PNS

Peripheral Nervous System

Brian J. Piper, Ph.D., M.S.

The Nervous System

-------------------------------Enteric (digestive)

Goals

• Anatomy & Physiology of:– Somatic Nervous System– Autonomic Nervous System

4

Meninges of the Spinal Cord

Spinal cord

Spinal cord

Pia mater

Arachnoid mater

Dura mater

Dorsal root

Dorsal root

Spinal nerve

Epidural space

(a) (b)

Ventral root

Dorsal rootganglion

Thoracicvertebra

Spinalnerve

Dorsal rootganglion

Subarachnoidspace

Dorsal branch(dorsal ramus)

Ventral branch(ventral ramus)

Ventral root

Epiduralspace

Body ofvertebra

Refresher I• Afferent: towards center (brain), ≈sensory• Efferent: away from center (brain), ≈motor• Ganglia: mass of cell bodies• Plexus: network of neurons

Refresher II

• Nicotinic: subtype of Acetycholine receptor

1530-1600

• Muscarinic: subtype of Acetycholine receptor

Jean Nicot Nicotiana tobaccum

Amanita muscaria

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Peripheral Nervous System

• Cranial nerves arising from the brain• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

• Spinal nerves arising from the spinal cord• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

12 Cranial Nerves

• On Old Olympic Towering Tops A Finn And German Viewed Some Hops

• Once One Openly Told Tourists About FightingVampires Gobling Various Antelope Herds

• Oh Once One Takes The Anatomy Final Very Good Vacations Are Heavenly

http://en.wikipedia.org/wiki/List_of_mnemonics_for_the_cranial_nerves

CN I: Olfactory

• Connect nasal cavity to temporal cortex• Substantial individual differences• Forms new neurons throughout life!

CN II: Optic

• Connects retina to thalamus (lateral geniculate nucleus)

• Partial decussation

CN VIII: Vestibulocochlear (Auditory)

• Connects cochlea to brainstem• Responsible for balance & hearing

Somatic Nervous System

• Voluntary Nervous System– Motor cell bodies in ventral horn– Send axons to muscle– Use Acetylcholine to stimulate

Autonomic NS: Two Neurons

ACh

Howland & Mycek (2006). Lippincott’s Illustrated Reviews: Pharmacology. p. 36.

ACh: Acetylcholine

Autonomic Nervous System• Autonomous “automatic”• Functions: blood pressure, heart rate, sleep, bladder

& bowel function• Sympathetic NS: “fight or flight”

• Parasympathetic NS: “rest & maintain”

Medulla: EpinephrineCortex: Cortisol

Walter Cannon

Automobile Analogy

Functional Consequences of Normal ANS Function

Sympathetic Parasympathetic

Heart Rate Increased Decreased

Blood pressure Increased Decreased

Bowel motility Decreased Increased

Lung Bronchodilation Bronchoconstriction

Pupils Dilation Constriction

Adrenal glands Catecholamine release -

Sexual function (males) Orgasm Erection

Bladder Increased sphincter tone Decreased sphincter tone

Parotid gland - Salivation

Low & Engstrom (2012). Disorders of the ANS. In Harrison’s VII, Ch 375, p. 3352.

Unbalanced

Sympathetic Parasympathetic

Heart Rate Increased < DecreasedBlood pressure Increased > decreased (mildly)

Bowel motility Decreased Increased

Lung Bronchodilation Bronchoconstriction

Pupils Dilation Constriction

Adrenal glands Catecholamine release -

Sexual function (males) Orgasm Erection

Bladder Increased sphincter tone < Decreased sphincter tone

Parotid gland - Salivation

Low & Engstrom (2012). Disorders of the ANS. In Harrison’s VII, Ch 375, p. 3352.

Sympathetic & Parasympathetic Innervation I

• Central components “accident” example

• All at once (Sym) versus individual components (PS)

Sympathetic versus Parasympathetic

Preganlionic projection: short long

ComparisonSympathetic Parasympathetic

Origin T1 to T12, L1, L2 CN III, VII, IX, X, S2, S3

Target organs Diffuse Localized

Transmitter Adrenergic Muscarinic

Amplification Yes (1:20) No (1:1)

Comparison of Somatic and Autonomic Nervous Systems

Somatic Sympathetic ParaSymp

# neurons 1 >1 2Myelinated Yes Pre-Gang Pre-Gang

Neuro-transmitter

ACh Pre: AChPost: NE, Ep

Pre: AChPost: ACh

Receptor Nicotinic Pre: NicPost: Adren

Pre: NicPost: mus

Light Reading

O:15 to 3:58: http://www.youtube.com/watch?v=sPS7GnromGo

ANS (Stress) & Health

• Top Causes of Death (2009):– 1) Heart Disease– 2) Cancer– 3) Chronic respiratory diseases– 4) Stroke– 5) Accidents– 6) Alzheimer’s – 7) Diabetes– 8) Influenza & pneumonia– 9) Kidney disease– 10) Suicide

http://www.cdc.gov/nchs/data/nvsr/nvsr59/nvsr59_04.pdf