Lecture 6.2: The Autonomic Nervous System

Question 1

ANS Function

Answer 1

Regulates essential non-voluntary, visceral functions

Its two divisions (sympathetic & parasympathetic)

These act in opposition to each other, constantly work to maintain homeostasis

The balance of their activities gives autonomic tone

Question 2

The Vertebral Column Structure

Answer 2

Cervical Vertebrae: The 7 vertebrae directly inferior to the skull
Thoracic Vertebrae: 12 vertebrae inferior to cervical (vertebrae 8-19)
Lumbar Vertebrae: 5 vertebrae inferior to thoracic (vertebrae 20-24)
Sacrum Vertebrae: The 5 (fused) vertebrae inferior to the lumbar
Coccyx: The fused vertebrae inferior to the sacrum

Question 3

Where does the sympathetic nervous system (SNS) emerge from?

Answer 3

Nerves emerge from T1–T12 and L1- L2
Hence known as the thoracolumbar division of ANS

Question 4

Where does the parasympathetic nervous system (PNS) emerge from?

Answer 4

Cranio-sacral anatomical origins

Question 5

Some general actions of the ANS

Answer 5

• Blood pressure
• Heart and breathing rates
• Body temperature
• Digestion
• Metabolism (thus affecting body weight)
• Water and electrolyte (such as sodium and calcium) balance
• Body fluid production (saliva, sweat, and tears)
• Urination
• Defecation
• Sexual responses

Question 6

What is special about the adrenal medulla and sweat glands?

Answer 6

Most organs have both sympathetic and and parasympathetic innervation

The adrenal medulla and sweat glands only have a sympathetic supply

Question 7

Autonomic pathways are made up of a two-neurone chain

Answer 7

Preganglionic neurone cells are located in the CNS (brainstem/ spinal chord):
• Do not supply effector organs directly
• Preganglionic neurons are myelinated

Postganglionic neuron cells are located in the peripheral nervous system
• Rely on pre-synaptic neuron for drive
• Terminates directly on effector organ
• Postganglionic neurons are unmyelinated

Question 8

Paravertebral Chain

Answer 8

Sympathetic Ganglia form a Paravertebral Chain

AKA the sympathetic trunk, with one chain on each side of the vertebral
column

They extend superiorly to the base of the skull and inferiorly to the coccyx, where the two chains fuse together

Question 9

Sympathetic Neurotransmission

Answer 9

Preganglionic neurone releases acetylcholine

This attaches to nictonic receptors on ganglion

Postganglionic neurone releases noradrenaline

This attaches to alpha/beta adrenoreceptors on the effector organ/muscle

Question 10

Some outcomes of sympathetic activation

Answer 10

• Increased flow of blood to skeletal muscles
• Increased energy expenditure
• Diversion of blood to heart
• Increase in heart rate
• Increase in blood pressure
• Reduced blood flow to GI tract and skin
• Stimulation of chromaffin cells of the adrenal medulla will release
catecholamines (adrenaline and noradrenaline) into the bloodstream

Question 11

Parasympathetic Neurotransmission

Answer 11

Preganglionic neurone releases acetylcholine

This attaches to nictonic receptors on ganglion

Postganglionic neurone releases acetylcholine

This attaches to muscarinic receptors on the effector organ/muscle

Question 12

Neuroreceptors in the ANS (3)

Answer 12

muscarinic
adrenergic
dopaminerig

Question 13

Cranial Nerves

Answer 13

• 12 Pairs
• Originate in different regions of the brain and brainstem
• Some are sensory only
• Some (voluntary) motor only
• Some are mixed
• Most have no autonomic component
• Four of the pairs have a parasympathetic component: III, VII, IX and X
• None have a sympathetic component

Question 14

What is Cranial Nerve 3?

Answer 14

Oculomotor Nerve

Question 15

What is Cranial Nerve 7?

Answer 15

Facial Nerve

Control facial movement and expression, also carries nerves that are involved in taste to the anterior 2/3 of the tongue and producing tears (lacrimal gland)

Question 16

What is Cranial Nerve 9?

Answer 16

Glossopharyngeal Nerve

Provides motor, parasympathetic and sensory information to your mouth and throat, helps raise part of your throat, enabling swallowing

Question 17

What is Cranial Nerve 10?

Answer 17

Vagus Nerve

Regulation of internal organ functions, such as digestion, heart rate, and respiratory rate, as well as vasomotor activity, and certain reflex actions, such as coughing, sneezing, swallowing, and vomiting

Question 18

Sacral Parasympathetic Nerves (S2-S4) [need to summarise this card more]

Answer 18

During bladder filling, parasympathetic contraction of the muscle of the bladder wall (detrusor) is suppressed and sympathetic action contracts the internal sphincter

During bladder filling, parasympathetic contraction ofthe muscle of the bladder wall (detrusor) is suppressedand sympathetic action contracts the internal sphincter.

Question 19

Autonomic Innervation of Organs

Answer 19

Most organs receive dual innervation by sympathetics and parasympathetics

Question 20

What is Vasovagal Syncope (Neurocardiogenicsyncope)?

Answer 20

Occurs when you faint because your body overreacts to certain triggers, such as the sight of blood, extreme emotional distress or also orthostatic causes, i.e. prolonged standing or when in crowded, hot places

Question 21

Why does Vasovagal Syncope occur?

Answer 21

An initial increase in sympathetic activity is subsequently reduced by a
feedback mechanism

This doesn’t balance an increase in parasympathetic activity, causing
vasodilatation, bradycardia and hypotension leading to fainting

Question 22

What is Raynaud Syndrome?

Answer 22

This results from spasm of the digital arteries, usually precipitated by cold and relieved by heat

Question 23

Symptoms of Raynaud Syndrome (6)

Answer 23

• Pallor, then cyanosis, then redness of digits
• Pain
• Numbness
• Paresthesia (tingling)
• Difficulty moving the affected area
• In chronic, severe disease, tissue infarction and
  finger loss can occur

Question 24

Treatment of Raynaud Syndrome

Answer 24

Peripheral sympathectomy (surgical interruption of peripheral sympathetic nerve pathways) can be performed in severe cases if staying out of the cold or vasodilators don’t work