Nerves of the Thorax Flashcards
What are the 2 main divisions of the nervous system?
Central Nervous System Peripheral Nervous System
What can the PNS be divided into?
- Somatic Nervous System 2. Autonomic Nervous System
What is the somatic NS?
- Voluntary - Controls external actions of skin and muscles (skeletal muscles) - Has both sensory and motor fibres
What is the autonomic NS?
- Involuntary - Innervating organs/viscera –> internal activities - Has parasympathetic (calming) and sympathetic (arousing) elements - Has both sensory and motor fibres
What are afferent fibres?
Sensory –> arriving at CNS back from body
What are efferent fibres?
Motor –> leaving CNS to body
What is effect of sympathetic motor fibres on heart?
Make it contract quicker and with more force
What is effect of parasympathetic motor fibres on heart?
Make it contract slower and with less force
What are the sensory fibres in the sympathetic system?
Pain fibres (go back to CNS)
What are the sensory fibres in the parasympathetic system?
Tell us about general condition of viscera (e.g. how full blood vessels are, how full/empty stomach is)
What is the spinal cord enclosed within?
The bony vertebral column
How many segments is the spinal cord divided into?
31 segments
What does each segment of the spinal cord give rise to?
A pair of spinal nerves (emerging from spinal cord): - 8 pairs of cervical spinal nerves - 12 pairs of thoracic spinal nerves - 5 pairs of lumbar spinal nerves - 5 pairs of sacral spinal nerves - 1 pair of coccygeal spinal nerves
Where do intercostal nerves arise from?
Thoracic spinal nerves
What do nerves contain?
Both motor (efferent) and sensory (afferent_ fibres within it
Segmental spinal nerve: What emerges from spinal cord?
A set of rootlets: - Dorsal rootlets - Ventral rootlets These project out laterally
What do dorsal rootlets contain?
Sensory (afferent) fibres
What do ventral rootlets contain?
Motor (efferent) fibres
What happens to these dorsal and ventral rootlets?
They come together to become a mixed spinal nerve (contains motor and sensory information)
What then happens to this mixed spinal nerve?
Has branches going towards dorsal and ventral aspects –> ventral and dorsal ramus
What is the ventral ramus?
Anterior division of a spinal nerve
What is the dorsal ramus?
Posterior division of a spinal nerve
What is a ganglion?
Cell body or nucleus outside of CNS
Autonomic (parasympathetic and parasympathetic) efferents. Describe neurne pathway:
2 neurone pathway:
- 1st neurone –> preganglionic neurone (cell body in CNS)
Leaves CNS and synapse with another neurone (cell body outside CNS –> ganglion)
- 2nd neurone –> postganglionic neurone
What is the main parasympathetic nerve of the trunk?
Vagus nerve
Where does the vagus nerve come from?
Brain stem (medulla)
Where do any fibres of parasympathetic nature emerge from?
Cranial or sacral (S2-S4) region
Describe 2 neurone pathway of parasympathetic nerves:
Really long preganglionic fibre and short postganglionic fibre
Where do all fibres of sympathetic nature emerge from?
Segmental spinal nerves T1-L2 only (thoracic and lumbar segments) (i.e. in between parasympathetic origins)
When sympathetic fibres leave spinal cord, what do they enter into?
Sympathetic chains (either side of vertebral column)
Describe 2 neurone pathway of sympathetic fibres
Preganglionic fibres are short and postganglionic fibers are longer
Where are the origins of all sympathetic fibres?
In segmental spinal nerves T1-L2 only
Where are the sympathetic chains?
Either side of vertebral column
Where do sympathetic fibres synapse?
In the sympathetic chain
What are branches from the spinal nerve to the sympathetic chain called?
White (myelinated) ramus communicans
Grey (non-myelinated) ramus communicans
Describe pathway of somatic (voluntary) nerve e.g. contracting bicep
Motor (efferent) fibre leaves spinal cord via ventral root (as is motor). Joins with sensory fibres to form spinal nerve. Doesn’t go into sympathetic chain. Travels to bicep.
Describe pathway of sympathetic motor fibres leaving CNS to target organ
Efferent (motor) fibre leaves spinal cord via ventral roots and joins with sensory fibres to form spinal nerve. Goes into sympathetic chain via the white ramus communicans. Synpases in sympathetic chain (cell body is outside CNS so is a ganglion). Then heads towards relevant organ via splanchnic nerve.
What is a splanchnic nerve?
Paired visceral nerves that contribute to the innervation of internal organs. Carry fibres of ANS (effereent) as well as sensory fibres (afferent) from organs. I.e. how sympathetic fibres get to organ.
E.g. cardiac splanchnic nerve, pulmonary splanchnic nerve
Some sympathetic fibres are sent towards body wall, not just viscera (e.g. skin for sweating). Describe pathway of these fibres
Motor (efferent) fibres leave spinal cord via ventral roots and join with sensory fibres to form spinal nerve. They then jump into sympathetic chain where they synapse. They then head out towards the body wall as postganglionic jumps back onto spinal nerve and heads out towards the skin (or wherever)
Sketch 3
What are plexuses and where do they form?
Bundle of nerves (both sympathetic and parasympathetic input) that form once you get near organ
Where is the origin of the intercostal nerves?
Throacic segments T1-T11
What is the nerve at T12?
Subcostal nerve as no rib underneath (floating)
What do the intercostal nerves supply?
- Intercostal muscles
- Cervical and costal pleura
- Skin adjecent to intercostal space
What are the components of the intercostal nerves?
Autonomic –> Sympathetic
Somatic –> Motor and Sensory
Where is the origin of the vagus nerve?
Medulla (brain stem)
What does the vagus nerve supply?
Parallel to thoracic viscera
What are the components of the vagus nerve?
Somatic –> Motor and Sensory (Recurrent Laryngeal Nerve)
Autonomic –> Parasympathetic
What is the origin of the phrenic nerve?
Cervical segments C3-5
What does the phrenic nerve supply?
- Diaphragm
- Parietal pleura (diaphragm and mediastinum)
- Pericardium
Describe the components of the phrenic nerve
Somatic –> Motor and Sensory
Where is the origin of the recurrent laryngeal nerve?
Off vagus nerve
What does the recurrent laryngeal nerve supply?
- Muscles off larynx
- Intrinsic sensory from membranes below vocal fold
What are the components of the recurrent laryngeal?
Somatic –> motor and sensory
What are pain fibres?
Afferent/sensory fibres of the sympathetic system
How can referred pain occur?
Sensory nervous system gets confused
- Normally, spinal fibres carry sensory info from skin and body wall back to CNS
- Info about the heart also travels on spinal nerves to CNS
Sometimes, during an issue, CNS receives extra info from heart. Gets confused as can only detect which sensory level it is from
E.g. information from heart goes back to T1-T4 but so does information from skin –> pain from heart can get referred to skin
What is function of phrenic nerve?
Motor functions – innervates the diaphragm.
Sensory functions – innervates the central part of the diaphragm, the pericardium and the mediastinal part of the parietal pleura
What is function of vagus nerve (the 10th cranial nerve CN X)
Provides parasympathetic supply for all of the organs of the thorax and abdomen
Describe the course of the phrenic nerve
Originates C3-C5. It runs down on the front of the anterior scalene muscle, and passes in front of the subclavian artery, and behind the subclavian vein.
Here, the course of the right and left phrenic nerve becomes different.
Describe route of right phrenic nerve after this point
- Passes anteriorly over the lateral part of the right subclavian artery.
- Enters the thorax via the superior thoracic aperture
- Descends anteriorly along the right lung root
- Courses along the pericardium of the right atrium of the heart
- Pierces the diaphragm at the inferior vena cava opening
- Innervates the inferior surface of the diaphragm.
Describe the course of the left phrenic nerve after this point
- Passes anteriorly over the medial part of the left subclavian artery
- Enters the thorax via the superior thoracic aperture
- Descends anterior to the left lung root
- Crosses the aortic arch and bypasses the vagus nerve
- Courses along the pericardium of the left ventricle
- Pierces and innervates the inferior surface of the diaphragm.
What is the sensory function of the vagus nerve?
What is the motor function of the vagus nerve?
Provides motor innervation to the majority of the muscles of the pharynx, soft palate and larynx.
What is the parasympathetic function of the vagus nerve?
Innervates the smooth muscle of the trachea, bronchi and gastro-intestinal tract and regulates heart rhythm.
Where does vagus nerve originate?
Brainstem (medulla)
How does the vagus nerve exit the cranium?
Via jugular foramen
In the neck, the vagus nerve passes into the carotid sheath, travelling inferiorly with the internal jugular vein and common carotid artery.
Where do right and left vagus nerves start to take different courses?
At the base of the neck, the right and left nerves have differing pathways
Describe course of left vagus nerve after base of neck
The left vagus nerve passes inferiorly between the left common carotid and left subclavian arteries, posterior to the sternoclavicular joint, entering the thorax.
Describe course of right vagus nerve after base of neck
The right vagus nerve passes anterior to the subclavian artery and posterior to the sternoclavicular joint, entering the thorax.
Which branches of the vagus nerve arise in the neck?
- Superior pharyngeal branches
- Superior laryngeal nerve
- Recurrent laryngeal nerve (right side only)
Describe course of right recurrent laryngeal nerve (RLN)
Hooks underneath the right subclavian artery, then ascends towards to the larynx. It innervates the majority of the intrinsic muscles of the larynx.
Describe course of left vagus nerve once it enters thorax
Left vagus nerve forms anterior vagal trunk
Describe course of right vagus nerve once it enters thorax
Right vagus nerve becomes posterior vagal trunk
How does vagus nerve contribute to innervating oesophagus?
Branches from the vagal trunks contribute to the formation of the oesophageal plexus, which innervates the smooth muscle of the oesophagus.
What branches of the vagus nerve arise in the thorax?
- Oesophageal
- Left recurrent laryngeal nerve
- Cardiac branches
Describe course of left RLN?
It hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx.
How do the vagal trunks enter the abdomen?
The vagal trunks enter the abdomen via the oesophageal hiatus of the diaphragm
How do the vagus nerves terminate?
In the abdomen, the vagal trunks terminate by dividing into branches that supply the oesophagus, stomach and the small and large bowel (up to the splenic flexure).
In the thorax and abdomen, the vagus nerve is the main parasympathetic outflow to the heart and gastro-intestinal organs.
What is parasympathetic effect of cardiac branches of vagus nerve on heart?
Reduction in resting heart rate (innervate SA and AV nodes of the heart)
What is parasympathetic effect of vagus nerve in GI?
The function of the vagus nerve is to stimulate smooth muscle contraction and glandular secretions in these organs. For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production.
What are the intercostal nerves continuations of?
Continuations of anterior rami of thoracic spinal neves from T1 to T11
The intercostal nerves are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. These nerves in addition to supplying the thoracic wall also supply the pleura and peritoneum.
What is function of intercostal nerves?
The intercostal nerves are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. They give motor innervation to the intercostal muscles, and sensory innervation to the chest wall.
What do the first 2 intercostal nerves (T1 and T2) supply?
In addition to supplying the thorax, also give branches to the brachial plexus
What do the typical T3-T6 intercostal nerves supply?
Only supply the thoracic wall
What do lowest five intercostal nerves (T7-T11) supply?
Supply thorax, abdomen and peritoneum
Describe course of T2-T6 intercostal nerves
The anterior divisions pass forward in the intercostal spaces below the intercostal vessels. At the back of the chest, they lie between the pleura and the posterior intercostal membranes.
Describe course of T7-T11 intercostal nerves
The anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves are continued anteriorly from the intercostal spaces into the abdominal wall hence they are also called thoracoabdominal nerves.
Supply rectus abdominis, intercostal musles, anterior abdominal wall musculature
What is the sympathetic chain?
Component of the autonomic nervous system and is composed of general visceral afferent and efferent axons that allow for involuntary control of bodily functions
Describe the location of the symathetic chain?
Paired, longitudinally arranged sympathetic ganglia forming the sympathetic chain
Run from base of skull to coccyx either side of vertebral column
Describe components of sympathetic chain
- Cervical: three discrete ganglia - superior, middle and inferior cervical sympathetic ganglia
- Thorax: T2 to T12 thoracic sympathetic ganglia adjacent to their respective vertebral bodies, located within the posterior mediastinum
- Abdomen: L1 to L5 lumbar sympathetic ganglia
- Pelvis: S1 to S5 sacral sympathetic ganglia. Located medial to the anterior S1-S4 sacral foramina
- Unpaired coccygeal ganglion
Does phrenic nerve pass posterior or anterior to root of lung?
Anterior
Does vagus nerve pass posterior or anterior to root of lung?
posterior
