Vagus and Sympathetic System of the Thorax Flashcards
Learning outcomes
- Describe the course and distribution of the right and left vagus nerves
- Describe the clinical importance of the anatomy of the left recurrent laryngeal nerve
- Describe the position and extent of the sympathetic trunks and ganglia
- Describe the pre- and post-ganglionic neural connections of the sympathetic trunks
- Describe the functions of the sympathetic trunks and their branches
- State the signs of Horner’s syndrome
- Describe the pre- and post-ganglionic neural connections of the parasympathetic system
- Contrast the functional anatomy of the sympathetic and parasympathetic systems
Nervous System flowchart
Nervous System flowchart
What is the Autonomic Nervous System (ANS) under the control of?
What is dual innervation?
- The Autonomic Nervous System (ANS) is the under the control of the hypothalamus
- Dual innervation is the mechanism in which an organ/tissue can receive fibres (also known as receiving innervation) from both the parasympathetic and sympathetic systems.
Which tissues have sympathetic innervation only?
- Sympathetic only tissues/organs:
1) Most blood vessels e.g coronary arteries
2) Erector pili muscle – makes hair follicles stand up to generate head when body is cold
3) Sweat glands
What effects do sympathetic and parasympathetic have in relation to each other?
- Sympathetic and parasympathetic functionally complement each other, and exert opposite effects to keep the body functioning normally
- One of the two is more active at any given time
What is the function of the ANS?
What 2 things does the ANS regulate?
- The function of the ANS is to provide a stable internal environment
- The ANS regulates visceral (organ) activity (circulation, respiration, digestion excretion, reproduction)
- supplies smooth muscle (walls of blood vessels, bronchi, intestines)
- regulates body temp
What does the ANS consist of?
What does the ANS produce a motor response to?
What do visceral pain and reflex afferents follow?
- The ANS consists of general visceral efferent (GVE) fibres that create a motor response to general visceral afferent (GVA) fibre stimulation.
- Autonomic fibres accompany GVA fibres
- Although GVA fibres are part of the ANS, they are not classified as part of the sympathetic or parasympathetic system.
- Visceral pain afferents tend to follow the path of sympathetic supply
- Visceral reflex afferents follow the path of parasympathetic supply
How do autonomic nerves reach their effectors?
1) 1st neuron
* The cell body of the 1st neuron (preganglionic neuron) is at the grey matter of the spinal cord or brainstem
* The axon of the pre-ganglionic neuron is myelinated, making it appear white
2) 2nd neuron
* The cell body of the 2nd neuron (post-ganglionic neuron) is at an autonomic ganglion
* The axon of the post-ganglionic neuron is unmyelinated, making it appear grey
What are 3 things the ANS supply?
- The ANS supplies:
1) Smooth muscles (walls of blood vessels)
2) Cardiac muscle
3) Glands
What is the role of the of the parasympathetic system?
What 5 changes does parasympathetic innervation cause?
- The role of the parasympathetic system is rest and digest (conserving energy)
- Changes parasympathetic innervation causes:
1) Slows breathing and heart rate, reducing cardiac output and BP
2) Stimulates digestion (secretion of digestive enzymes)
3) Opens sphincters (e.g intestines)
4) Secretomotor to glands (salivary glands – produces saliva, lacrimal glands in the eye)
5) Constricts pupils (accommodation for close focus)
What is the vagus nerve?
Where does it exit the CNS from?
What is the role of the vagus nerve?
- The vagus nerve is the 10th cranial nerve
- It exits the CNS from the brainstem
- The vagus nerve is the main parasympathetic innervation for thoracic organs and some abdominal organs (viscera)
Where does the vagus nerve leave the cranial cavity?
Where does the vagus nerve descend?
Where does it enter the thoracic cavity?
- The vagus nerve leaves the cranial cavity through the jugular foramen
- The vagus nerve descends through the jugular foramen between the internal jugular vein and internal carotid artery (common carotid further down) in the carotid sheathe
- It then passes through the superior thoracic aperture (thoracic inlet) into the thoracic cavity
Where does the right and left vagus nerve enter the thoracic cavity?
- The right vagus nerve entera the thoracic cavity between the right subclavian artery and right brachiocephalic vein
- left vagus nerve enters the thoracic cavity posterior to the left brachiocephalic vein between the subclavian and common carotid arteries
What branches do the right and left vagus give off?
Where do these branches wind around?
- The right vagus gives off the right recurrent (changing direction) laryngeal nerve, which winds around right subclavian artery
- Left vagus enters the thoracic cavity posterior to the left brachiocephalic vein, between the left subclavian artery and left common carotid artery
- The left vagus gives off the left recurrent laryngeal nerve, which goes through the aorticopulmonary window and winds around the aortic arch (at the junction between 4th and 6th aortic arch), just posterolateral to the ligamentum arteriosum
What is the aorticopulmonary window ?
What 2 things are in the aorticopulmonary window?
- The aorticopulmonary window is between the left pulmonary artery and aorta and contains both the left recurrent laryngeal nerve and the ligamentum arteriosum
What 3 things do the recurrent laryngeal nerves supply?
- The recurrent laryngeal nerves supply:
1) Intrinsic laryngeal muscles (except cricothyroid muscle) – allows pitch of voice to be changed
2) Middle and inferior pharyngeal constrictor muscles – propels bolus down the oesophagus
3) Sensory supply to the laryngeal cavity below the level of the vocal cords
What is the role of the sympathetic nervous system (SNS)?
What 6 changes does SNS innervation bring about?
- The role of the sympathetic nervous system (SNS) is preparing the body for fight or flight (uses energy)
- Changes the SNS innervation brings about:
1) Increases heart rate and strength of heart beat
2) Dilates coronary arteries (indirectly, by local metabolic factors)
3) Constricts peripheral arteries (raises BP)
4) Relaxes bronchial smooth muscles (Increases respiratory efficiency)
5) Closes sphincters
6) Controls body temperature (blood vessels, sweat glands)
What is the outflow of the SNS?
Where are the pre-ganglionic cells bodies of sympathetic neurons located?
- The SNS has thoracolumbar outflow
- Pre-ganglionic cells bodies of sympathetic neurons are located in the intermediolateral horn of T1-L2 spinal cord segments (lateral horns only in thoracic, upper lumbar and sacral regions)
SNS diagrams
SNS diagrams
Where does each sympathetic trunk extend between?
Where does each trunk fuse?
- Each sympathetic trunk extends between the atlas (C1) and the coccyx
- Each trunk fuses with each other in the single ganglion impar, which is opposite to the coccyx
What are the 4 options in what a pre-ganglionic sympathetic neuron does when it leaves the CNS?
- Options in what a pre-ganglionic sympathetic neuron does:
1) Go up and synapse
* The pre-ganglionic neuron (myelinated) can leave the CNS and enter the sympathetic chain via white rami communicans (WRC)
* It can then ascend to the sympathetic chain towards the cervical ganglia
* In cervical region, it can synapse and become a post-ganglionic neuron (unmyelinated)
* The post-ganglionic neuron then leaves the sympathetic trunk via grey ramus communicans (GRC)
2) Synapse at the same level
* A pre-synaptic neuron (myelinated) can leave the CNS and go into the synaptic chain and synapse at the level it comes out
* E.g Comes out in T2 of the spinal cord and synapses in T2 ganglion, and the post-synaptic neuron (unmyelinated) will pass back into the spinal nerve, then off into its distribution of T2 (around the upper thorax and armpit)
* T1-T5 goes to the heart
3) Go down and synapse
* Enters the synaptic chain, and instead of synapsing, we descend to a lower level and synapse in lumbar/sacral ganglion
* E.g coming out of T12, descending through the sympathetic chain to synapse in sympathetic ganglion around L4, then traveling back out of the L4 ganglion to supply sweat glands
4) Pass through without synapsing
* Pre-synaptic neuron leaves the CNS, and enters the sympathetic chain, but doesn’t synapse
* Instead, we pass straight out of the front of the sympathetic ganglion in a thoracic splanchnic nerve
* We then come down to the abdomen, where we synapse onto a preaortic/ prevertebral ganglion
* The post-ganglionic neurons then go to supply the abdominal viscera e.x the gut tube
Routes of pre-ganglionic neurons
Routes of pre-ganglionic neurons
What is unique about the pre-ganglionic neurons that supply the adrenal medulla?
- The pre-ganglionic neurons that innervate the adrenal medulla pass through the paravertebral chain without synapsing and go straight to the adrenal glands.
- The adrenal glands then act as a ganglion
How are thoracic splanchnic nerves formed?
Where do they pass out of sympathetic ganglion?
- Thoracic splanchnic nerves form when pre-synaptic neuron leaves the CNS, and enters the sympathetic chain, but don’t synapse
- Instead, they pass straight out of the front of the sympathetic ganglion in a thoracic splanchnic nerve
4) What segments supply the sympathetics for the:
* Head
* Upper limb
* Thoracic and abdominal wall
* Lower limb
- Segments for Sympathetic supply for the:
- Head – T1-T3 segments
- Upper limb – T4-T6 segments
- Thoracic and abdominal wall – T1-T12 segments
- Lower limb – T12 to L2 segments
Where is the cardiac plexus located?
What 4 structures does the cardiac plexus consist of?
- The cardiac plexus is located anterior to the bifurcation of the trachea and posterior to the ascending aorta
- Structures of the cardiac plexus:
1) Sympathetic pre-ganglionic neurone from T1-T5
2) Ganglia of T1-T5
3) Inferior (C7-C8) and middle (C5-C6) cervical ganglia
4) Parasympathetics from vagus
What 3 structures make up the pulmonary plexus?
- Structures that make up the pulmonary plexus (more info post msa):
1) Sympathetics pre-ganglionic neutrons from T2-T4
2) T2-T4 ganglia
3) Parasympathetics from vagus
What roots does the phrenic nerve originate from?
What is the phrenic the sole motor supply of?
What might occur is the phrenic nerve is severed?
- The phrenic nerve originates from roots C3-C5
- The phrenic nerve is the sole motor supply of the diaphragm
- If the phrenic nerve is severed, the person can still live, but can’t exercise
What are intercostal nerves formed by?
Do intercostal nerves have motor or sensory fibres?
- Intercostal nerves are formed by anterior (ventral) rami of thoracic spinal nerves
- Intercostal nerves have both motor and sensory fibres (mixed fibres), with sensory branches supplying the skin, and motor branches supplying the intercostal and abdominal wall muscles
What is Pancoasts tumour?
What might it affect?
- Pancoasts tumour is a tumour at the apex of the lungs
- It may affect the sympathetic trunk or the stellate ganglion, compromising sympathetic supply to the head and neck on the same side
