18. Autonomic Nervous System and Hypothalamus

 

[Also see Netters Atlas of Human Neuroscience p.116-7]

 

          ANS is entirely efferent (motor)

          involuntary

          has two neurons between CNS and end-organ (preganglionic, postganglionic)

          tissue types involved:

1.         cardiac muscle (includes SA and AV nodes),

2.         smooth muscle

3.         most glands

          organs/systems involved: digestive, respiratory, urogenital, endocrine, spleen, heart, liver, blood vessels, glands

 

 

Sympathetic Nervous System

Parasympathetic Nervous System

Spinal location

thoracolumbar

craniosacral

General function

emergency, catabolic fight or flight

homeostatic, anabolic rest and digest

Presynaptic cell bodies

ICL: intermediolateral cell column (T1-L2): lateral horns of gray matter

 

T1-T6: head and neck, chest, upper limb, GIdiaphragm

T7-T11: abdomen, wall of trunk, GIrectosigmoid junction

T12-L2: lower limb, pelvic viscera, rectum, anal canal

- gray matter of brainstem (III, VII, IX, X)

- S2-S4

Emerge

With thoracic and upper lumbar nerves

Travel with cranial nerves, sacral nerves

Length of fibers

short pre-ganglionic (to sympathetic chain via WRCs), long post-ganglionic

long pre, short post

Presynaptic neurotransmitter

ACh nicotinic receptors

ACh nicotinic receptors

Postsynaptic neurotransmitters

NE adrenergic receptors)

ACh (sweat glands only)

ACh muscarinic receptors

Function

- increase respiratory rate

- open airways

- increase heart rate and contractility

- dilates arteries of heart and skeletal muscle

- constricts blood vessels in GI tract

- constricts arteries in skin

- stimulates glycogen release by liver

- decreases peristalsis

- arrector pili muscles

- sweating

- dilates eyes

- decreases heart rate

- increases peristalsis

- increases digestive functions

- constricts pupils (near vision)

- decreases respiratory rate

Clinical correlations

Horners syndrome

 

 

The cervical spinal cord has neither sympathetic nor parasympathetic nuclei

 

WRC=white ramen communicans

1.         carry sympathetic pre-ganglionic fibers to sympathetic chain (paravertebral ganglions)

2.         carry non-ANS fibers from viscera to CNS)

 

Sympathetic Trunk

-     presynaptic fibers may terminate at first ganglion encountered, ascend, descend; exit via gray rami communicans

-     presynaptic fibers may go right through (terminating to innervate abdominopelvic viscera via splanchnic nerve)

 

Parasympathetic distribution

1.         Oculomotor (III): Edinger Westphal nucleus

a.         accommodation (via ciliary muscles lens)

b.         pupillary constriction

c.         convergence of eyes (via medial rectus)

2.         Facial Nerve (VII)

a.         superior salivatory nucleus pterygopalatine ganglion ( lacrimal gland) and submandibular ganglion ( submandibular/sublingual glands)

3.         Glossopharyngeal Nerve (IX)

a.         inferior salivatory nucleus otic ganglion ( parotid gland)

4.         Vagus Nerve (X)

a.         dorsal motor nucleus (floor of 4th ventricle) enteric ganglia ( heart, lungs, abdominal viscera)

5.         Sacral Outflow (S2-S4)

a.         ventral gray matter preganglionic cell bodies pelvic splanchnic nerves ( distal GI, ureter, genitals)

 

 

Hypothalamus (control and integrative center for ANS)

          Cortex influences ANS via hypothalamus through limbic system (visceral manifestations of drives and emotions: eating, sex, fear, rage, aggression)

          regions function

o          satiety (VMN)

o          hunger and thirst (LN)

o          circadian rhythms (SCN)

o          heat/sweating: (AN)

o          cold/shivering (PN)

o          parasympathetic (PVN)

Relevant anatomy

1.         Posterolateral portion (Posterior and lateral nuclei) sympathetic system

2.         Anteromedial portion (Anterior and paraventricular nuclei) parasympathetic system

3.         Medial: satiety (VMN) aphagia

4.         Lateral: hunger and thirst (LN) hyperphagia

Tracts

1.         hypothalamospinal tract (sympathetic)

2.         hypothalmomedullary tract (parasympathetic and sympathetic)

Examples of hypothalamic control (via ANS, pituitary, etc.)

1.         skeletal muscle contraction during fear response

2.         Circadian rhythms + Sleep

3.         Reproductive Behavior

4.         body temperature control (from lateral spinothalamic tract)

a.         input

                                                                i.      anterior hypothalamus (heat) sweating

                                                              ii.      posterior hypothalamus (cold) shivering

b.         output

                                                                i.      peripheral vasodilation, sweating, increased cardiac output ( lowering body temperature)

                                                              ii.      vasoconstriction, piloerection, shivering ( elevating body temperature; shivering mediated by hypothalamic dorsomedial nucleus)

 

Clinical Correlations: Hirschsprungs Disease (megacolon), Pure Autonomic Failure (PAF), Multiple System Atrophy (MSA), Heatstroke

 

ANS receptors

1.         Adrenergic (NE and epinephrine: sympathetic)

a.         alpha 1 receptors ( vasoconstriction of arterioles and veins, mydriasis)

                                                                i.      agonist: nasal decongestant

                                                              ii.      antagonist: treats hypertension

b.         alpha 2 receptors ( decreased sympathetic outflow (CNS); increased vasoconstriction (periphery)

                                                                i.      agonist: treats hypertension

                                                              ii.      antagonist: treats impotence

c.         beta receptors ( increased heart rate and contractility; bronchodilation, vasodilation)

                                                                i.      agonist: treats asthma

                                                              ii.      antagonist: beta blockers treats hypertension

2.         Muscarinic Receptors (ACh: parasympathetic): not so useful clinically