Autonomic Nervous System

What does the ANS do

Regulates homeostasis and reproduction
Innervates secretory glands
Innervates heart and blood vessels to control BP and flow
Innervates the bronchi of lungs
Regulates digestive and metabolic functions
Regulates function of kidney, bladder, large intestine, and rectum
Sexual responses

Why care about ANS

Regulates cardiovascular and respiratory system’s response
Drugs that effect ANS will also effect your patient’s response to exercise

Afferent (GVA)

Information from spinal cord (T1-L2 and S2-4) and cranial nerves VII, IX, X

Efferent (GVE)

Sympathetic division (T1-L2)
Parasympathetic division (cranial nerve III, VII, IX, X, and S2-4)

GSA

Sensory skin, bones, muscles, etc.

GSE

Motor to skeletal muscle

GVA

Sensory of organs, glands, blood vessels

GVE

Motor to organs, glands, blood vessels

SVA

Taste, smell

SVE

Pharyngeal muscles

SSA

Vision, hearing, vestibular

Sensory receptors

Mechanoreceptors
Chemoreceptors
Nocioceptors
Thermoreceptors

Mechanoreceptors

Atria
Ventricles
Carotid sinus
Bladder
Intestines

Chemoreceptors

Carotid and aortic bodies respond to O2 level, medulla (hydrogen and CO2 concentration), hypothalamus (glucose, electrolytes)

Cranial nerves: VII, IX, X

Taste and swallowing (VII, IX, X)
Visceral information (IX, X)

Spinal cord: T1-L2

Carry information from viscera and trunk

Spinal cord (S2-S4): via anterior roots

Carry information from pelvic structures, bladder, genitals, lower colon

Central regulation of ANS

Cerebral cortex
Limbic system
Thalamus
Hypothalamus
Midbrain
Pons
Medulla
Spinal cord

Cerebral cortex

Conscious control of micturition, defecation, breathing

Limbic system

Emotional influence on ANS

Thalamus

Relays afferent information to limbic system and cortex

Hypothalamus

Master regulator of ANS
Receives information from reticulohypothalamic tracts
Regulates cardiorespiratory, metabolic, water re-absorption, digestive activity, reproduction
Exerts its control through pituitary gland (hormonal) descending pathways (dorsal longitudinal fasiculus) to brainstem centers and spinal cord

Midbrain

PAG relay to micturition center
Edinger-Westphal nucleus in PAG (CN III)

Pons

Primarily involved in respiration (pneumotaxic center)
Micturition center

Medulla

Heart rate, respiration, swallowing, coughing, chewing, vomiting
Solitary nucleus (afferent structure)

Solitary nucleus

Visceral function of cranial nerves IX, X
Relays information (reticulohypothalamic tract) to hypothalamus and other brainstem centers

Spinal cord

Autonomic reflexes
Pathways for afferent and efferent control of ANS

What neurotransmitters are used by the AES

Cholinergic: acetylcholine
Adrenergic: norepinephrine or epinephrine

Cholinergic neurons

All preganglionic neurons in the ANS are cholinergic neurons
Postganglionic neurons of the parasympathetic system
Sympathetic postganglionic neurons that innervate sweat glands and some sympathetic postganglionic neurons that innervate vessels in skeletal muscle

What are the two groups of cholinergic receptors

Nicotinic: fast ESPS
Muscarinic: G-protein mediated response and EPSP or IPSP

What do most sympathetic post-ganglionic neurons release

Norepinephrine

What does the adrenal medulla release

Epinepherine and norepinepherine

What are the two groups of adrenergic receptors

α1, α2
β1, β2

Sympathetic efferent neurons: cell bodies of pre-ganglionic neurons

Lateral horn spinal cord T1-L2

Sympathetic efferent neurons: exits

Ventral root goes through white ramus

Sympathetic efferent neurons: synapes

In the paravertebral ganglia or ascends/descends in the sympathetic trunk or goes straight through to synapse in ganglia closer to target tissue (celiac/mesenteric ganglia)

Sympathetic efferent neurons: post-ganglionic nerve

Passes through gray ramus and into ventral or dorsal ramus of peripheral nerve

Primary role of SNS

Maintain optimum blood supply to organs

Other functions of SNS

Generally maintains some background vasoconstriction
Stimulation of certain sympathetic efferents causes vasoconstriction (standing up)
Stimulation of different sympathetic efferents can cause vasodilation to skeletal muscle (during exercise)

SNS: regulation of body temperature

Release of epinephrine by adrenal medulla raise body metabolism
Controls blood flow to skin capillaries, sweat glands

SNS: regulation of blood flow to skeletal muscle

Skeletal muscle arterioles contain α and β2 andrenergic receptors and muscarinic cholinergic receptors

Vasoconstriction =

Norepinephrine + α
Background and position changes, skin

Vasodilation =

Epinephrine + β2 (exercise)
ACh + muscarinic receptor (exercise)

SNS: sympathetic control in head

Identical to effects on rest of body
Dilates pupil
Innervates smooth muscle portion of levator palpebrae superioris muscle
Salivary glands
Sweat glands

What does salivary glands produce

Thick saliva

SNS: regulation of viscera

Increases heart rate and contractility β1
Dilation of bronchial tree stim of β2

SNS: sexual function

Ejaculation

Parasympathetic nervous system: cell bodies

In brainstem or spinal cord (S2-4) or specific cranial nerve nuclei

Parasympathetic nervous system: ganglia

Are separate and nearer the effector organ

Parasympathetic nervous system: craniosacral

Division of ANS

Parasympathetic nervous system: cranial nerves

III, VII, IX, X
75% of fibers carried in X

Parasympathetic nervous system: sacral outflow

Cell bodies in lateral horn of gray matter S2-4, colon, bladder, genitalia

Parasympathetic nervous system: primary function

Energy conservation and storage

Parasympathetic nervous system: other functions

Decreased heart rate and contractility
Bronchoconstriction
Increased digestive activity, glycogen synthesis in liver, glandular secretions
Constriction of pupil, increased convexity of lens
Voiding of bowel and bladder
Erection of sexual organs

What happens when the ANS gets damaged

With denervation initial loss of all sympathetic tone
Eventually body compensates to achieve near normal basal levels
Basal secretion of epinephrine and norepinephrine play major role

Damage to peripheral nerves

Loss of sympathetic efferents cause loss of vascular control, temperature regulation, sweating in affected area
Loss leads trophic changes in skin (dry, flaking, red)

Damage to spinal cord

Autonomic dysreflexia (lesions above T6)
Temperature regulation
Orthostatic hypertension

Damage to brainstem

Interference with heart rate, respiratory rate, blood pressure, cranial nerves, thoracic and abdominal viscera

Damage to cerebrum

Especially hypothalamus
Homeostasis, metabolic disorders, obesity, anorexia, temperature regulation

Tests and measures

Heart rate
BP
BP and heart rate spine and standing (30 mm Hg systolic drop or 15 mm Hg diastolic drop abnormal)
Respiratory rate
Skin inspection