Anatomy of the Autonomic Nervous System Flashcards
Function of ANS?
Involuntary control of the viscera
3 divisions of the ANS?
Sympathetic
Parasympathetic
Enteric
Pathway of the ANS? (fibres/ganglia)
Consists of a pre-ganglionic neurone, a ganglion, and a post-ganglionic fibre
Locations of sympathetic and parasympathetic ganglia?
Sympathetic - Paravertebral ganglia in the sympathetic trunk. Found closer to spinal cord than viscera being innervated
Parasympathetic - Ganglia found close to or in the viscera they innervate
The two types of nerves involved and their functions?
Afferent - carries sensory impulses from all parts of the body to the CNS
Efferent - carries “messages/instructions” from brain to muscles/organs of the body
Which spinal nerves do preganglionic efferent fibres originate from in sympathetic NS?
Thoracic nerves
Upper lumbar nerves (L1-L3)
Known as the THORACOLUMBAR outflow
Pathway of preganglionic neurones to ganglion?
Emerge from spinal cord via ventral root of grey matter in spinal cord
Pass through ventral ramus to white rami communicates to ganglion
Structural components of sympathetic nervous system?
Sympathetic trunks (2)
Nerve plexuses
Subsidiary ganglia
Viscera innervated by SNS?
Sweat glands Arrector muscles of hair Smooth muscle in vessels Heart Lungs Abdominal/pelvic viscera
What happens to preganglionic neurone after it has entered ganglion?
Synapses within the ganglion or sends fibres up and down to other ganglia
Postganglionic fibres travel via dorsal or ventral rami to effector organ via grey rami communicantes
What is the sympathetic trunk and why is it necessary?
A chain of ganglia and connecting fibres which lie next to the vertebra for the entire length of the vertebral column.
Allows dispersion of the sympathetic outflow from a relatively small region of the spinal cord (T1-L3) to peripheral regions via all spinal nerves
What is a plexus regarding the sympathetic nervous system?
A network of nerve fibres originating from different levels associated with an organ
What are the different sympathetic plexuses?
Cervical - Plexus around pharynx - Cardiac plexus - Thyroid plexus - Pulmonary plexus Thoracic - Plexus around thoracic aorta - Splanchnic nerves
4 divisions of splanchnic nerves and point of entry to abdomen plexus
Greater (T5-T9), pierce diaphragm and enter abdomen plexus around great blood vessels supplying gut
Lesser (T10-T11), pierce diaphragm and enters abdomen plexus around aorta
Least (T12), pierce diaphragm and enters abdomen plexus and around gut
Lumbar, below diaphragm and take part in all plexuses of sympathetic nerves in abdominal/pelvic regions
Parasympathetic efferent fibres arise from?
Cranial nerves
Sacral nerves
Known as the CRANIO-SACRAL OUTFLOW
How is the sacral outflow arranged?
Leaves via the anterior rami of S2-4
Visceral branches pass directly to pelvic viscera as pelvic splanchnic nerves
There are minute ganglia in wall of viscera giving rise to postganglionic fibres
5 fibre types of pelvic splanchnic nerves and viscera they terminate at/in?
Motor fibres to rectum
Motor fibres to bladder wall
Inhibitory fibres to bladder sphincter (relaxation)
Vasodilator fibres to penis/clitoris (erection)
Visceromotor fibres to large part of the gut (superior to most of abdominal/pelvic viscera)
What are the 4 cranial nerves comprising cranial outflow?
Oculomotor nerve (CN III) Facial nerve (CN VII) Glossopharyngeal nerve (CN IX) Vagus nerve (CN X)
Where is the enteric system?
The walls of the alimentary tract
What two plexuses are involved in the enteric system?
Myenteric plexus (found between smooth muscle layers) Submucosal plexus (found in submucosal layer of gut wall)
Functions of enteric system?
Sensory - monitoring mechanical, chemical, and hormonal activity of the gut
Motor - gut motility, secretion, vessel tone
