Lecture 6.2: The Autonomic Nervous System Flashcards
ANS Function
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
The Vertebral Column Structure
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
Where does the sympathetic nervous system (SNS) emerge from?
Nerves emerge from T1–T12 and L1- L2
Hence known as the thoracolumbar division of ANS
Where does the parasympathetic nervous system (PNS) emerge from?
Cranio-sacral anatomical origins
Some general actions of the ANS
• 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
What is special about the adrenal medulla and sweat glands?
Most organs have both sympathetic and and parasympathetic innervation
The adrenal medulla and sweat glands only have a sympathetic supply
Autonomic pathways are made up of a two-neurone chain
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
Paravertebral Chain
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
Sympathetic Neurotransmission
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
Some outcomes of sympathetic activation
• 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
Parasympathetic Neurotransmission
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
Neuroreceptors in the ANS (3)
muscarinic
adrenergic
dopaminerig
Cranial Nerves
• 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
What is Cranial Nerve 3?
Oculomotor Nerve
What is Cranial Nerve 7?
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)
What is Cranial Nerve 9?
Glossopharyngeal Nerve
Provides motor, parasympathetic and sensory information to your mouth and throat, helps raise part of your throat, enabling swallowing
What is Cranial Nerve 10?
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
Sacral Parasympathetic Nerves (S2-S4) [need to summarise this card more]
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.
Autonomic Innervation of Organs
Most organs receive dual innervation by sympathetics and parasympathetics
What is Vasovagal Syncope (Neurocardiogenicsyncope)?
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
Why does Vasovagal Syncope occur?
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
What is Raynaud Syndrome?
This results from spasm of the digital arteries, usually precipitated by cold and relieved by heat
Symptoms of Raynaud Syndrome (6)
- 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
Treatment of Raynaud Syndrome
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
