Organisation of nerves in the thorax

Question 1

what is the CNS divided intoWhat do somatic spinal nerves provide somatic sensory innervation to?

Answer 1

Somatic (from Greek for body)
Skin and skeletal muscles

Autonomic or visceral (from Greek for guts)
Organs and parts of organs such as smooth muscle and glands

Question 2

What do somatic spinal nerves provide somatic sensory innervation to?

Answer 2

Body wall but NOT to viscera

Question 3

what does a dorsal root and a dorsal ramus contain/ ventral root and ventral ramus

Answer 3

Dorsal root: only has sensory fibres
Dorsal ramus: sensory and motor fibres.

Ventral root: motor fibres
Ventral ramus: motor and sensory neurons .

Anterior root: motor
Posterior root: sensory

Motor: skeletal muscle
Sensory: body wall

Grey matter contains cell bodies, while the white matter contains axons in spinal tracts
Sensory neurones come from the dorsal horn – these form posterior roots which are sensory
Motor neurones come form the ventral horn – these form anterior roots which are motor
The spinal nerves and rami contain both sensory and motor neurones

Question 4

What is a dermatome?

Answer 4

An area of skin that is supplied by a single spinal nerve on one side or from a single spinal cord level

Question 5

What is a myotome?

Answer 5

Part of a skeletal muscle that is supplied by a single spinal nerve on one side or from a single spinal cord level

Question 6

What landmark does dermatome of the nipples and the umbilicol cord bit lie?

Answer 6

T4= nipples
T10= umbilical cord

Question 7

How many intercostal nerves are there?

Answer 7

11 intercostal + 1 subcostal under the 12th rib

Question 8

What are the branches of the intercostal nerves?

Answer 8

There is a lateral cutaneous branch (anterior and posterior branches) and an anterior cutaneous branch (medial and lateral branches)

Question 9

What structures do the phrenic nerves provide sensory and motor innervation to?

Answer 9

Motor = supply skeletal muscle of the diaphragm
Sensory:
Central diaphragm
Mediastinal pleura
Pericardium
Peritoneum on inferior surface of central diaphragm

Question 10

Describe the phrenic nerve?

Answer 10

The phrenic nerve is a somatic nerve
The anterior rami of cervical nerves C3, C4, C5 combine to form two phrenic nerves (one on each side)
Course:
Left: over the aortic arch
Right: lateral to SVC
Function:
Sensory: diaphragm, mediastinal pleura, pericardium
Motor: diaphragm (‘C3,4,5 keeps the diaphragm alive’)

Question 11

what are the phrenic and vagus nerve part of?

Answer 11

They are part of the autonomic nervous system.

Phrenic- skeletal muscles of the diaphragm, so it is voluntary- can hold your breath.

Question 12

what do autonomic nerves supply?

Answer 12

Divided into sympathetic and parasympathetic
As oppose to somatic nerves, they are involved in supply to and from the viscera
Motor pathways: have preganglionic and postganglionic neurones
Sympathetic:
Arise from spinal nerves T1-L2
Parasympathetic:
Arise from craniosacral nerves (CN 3,7,9,10 and S2-s4)

Question 13

where is the parasympathetic originated from and sympathetic nerve?

Answer 13

Parasympathetic nerve originate from CRANIOSCARAL.
nuclei are contained within the brain or sacral part of the spine .

Sympathetic nerve originate from the thoracic-lumbar, only originates from the thoracic and lumbar region of the spinal cord.

Question 14

How does the sympathetic get to all parts of the body

Answer 14

It originates in the thoracic region, from T1.
-but it goes to all parts of the body.
-need to go into the structures which is sitting on either side of the chest.
-

Question 15

Where do sympathetic preganglionic neurones to the body wall synapse?

Answer 15

In the ganglia of the sympathetic trunk, where the sympathetic nerve can get out and go to the target e.g. skin of the hands

Question 16

Where are the pre ganglionic and post ganglionic in the parasympathetic and sympathetic

Answer 16

Parasympathetic:
In the brain and base of the spinal cord.

Sympathetic:
Is from T1- L2

Question 17

Where do sympathetic preganglionic neurons to the viscera synapse such as heart and lungs/organs?

Answer 17

In unpaired ganglia

Question 18

The sympathetic trunk receive which spinal nerves?

Answer 18

T1-L2

Question 19

What is the significance of sympathetic fibres in spinal nerves T5-T12?

Answer 19

These are the thoracic splanchnic nerves that carry sympathetic fibres to the abdomen.

Question 20

What are the five sets of nerves that contain parasympathetic fibres?

Answer 20

Occulomotor (III)-- Cranial nerves
Facial (VII) --cranial nerves
Glossopharyngeal (IX) --cranial nerves
Vagus (X) --- cranial nerves
Sacral spinal nerves (S2-S4)

Question 21

Which spinal nerves do sympathetic fibres to the heart and lungs come from?

Answer 21

T2-T4 passing through cervical and upper thoracic ganglia

Question 22

Where do many of these fibres synapse?

Answer 22

In ganglia of the pulmonary and cardiac plexuses rather than in the trunk ganglia

Question 23

What effect do sympathetic and parasympathetic nerves have on bronchioles?

Answer 23

Sympathetic - bronchodilation

Parasympathetic - bronchoconstriction

Question 24

What are the effect of sympathetic and parasympathetic efferents to the heart?

Answer 24

Sympathetic - increase heart rate and force of contraction (inotropic and chronotropic effect)
Parasympathetic - decrease heart rate and vasoconstrict coronary arteries

Question 25

what does the vagus nerve wrap around?

Answer 25

Vagus nerve- winds up the ligementum ateriosum

Question 26

What are the roles of sympathetic and parasympathetic afferents from the heart?

Answer 26

Sympathetic - relay pain sensations from the heart

Parasympathetic - relay blood pressure and chemical information from the heart

Question 27

Where does the vagus nerve arise and where does it leave the skull?

Answer 27

Vagus nerves arise in the medulla and it leaves the skull via the jugular foramina

Question 28

Describe the path of descent of the vagus nerve.

Answer 28

The two vagus nerves pass postero-laterally to the common carotid arteries.
Right vagus passes posterior to the right lung root
Left vagus nerve crosses over anterior to the aortic arch and then posterior to the left main bronchus

Question 29

What are roles of sympathetic and parasympathetic efferents from the oesophageal plexus?

Answer 29

Sympathetic - relays pain sensation from the oesophagus

Parasympathetic - senses normal physiological information from the oesophagus

Question 30

Branches of the vagus provide sensory content from…?

Answer 30

Gut and lungs

REMEMBER: branches of the vagus provide NO AUTONOMIC SUPPLY to the body wall.

Question 31

State a feature of the left recurrent laryngeal nerve. What does it innervate?

Answer 31

It is NOT parasympathetic

It innervates most of the skeletal muscle of the larynx

Question 32

How do the vagi in the posterior and anterior mediastinum differ?

Answer 32

In the posterior part of the oesophagus, you form the posterior oesophageal nerve which mainly takes right vagal fibres through the diaphragm to the abdominal viscera.
The left vagus provides fibres to the oesophageal plexus and then continutes as the anterior oesophageal nerve.

Question 33

Label this diagram

Answer 33

o Remember you are above the plane of the arch of the aorta so you will NOT see the aorta
o You will see the right and left brachiocephalic vein but not its branches
o Vagus is posterior to phrenic nerves

Question 34

what are the right and left main branches?

Answer 34

Right main branches:
Sino-atrial nodal artery: supplying the SAN

Right marginal artery:
Posterior descending artery: posterior and inferior part of the heart

right coronary artery supplies: right atrium, right ventricle, SAN, AVN, posteroinferior 1/3rd of interventricular septum and some of the posterior part of left ventricle

Left main branches:
Circumflex artery: The circumflex mainly supplies the left atrium and the posterolateral part of the left ventricle

Left anterior descending (LAD): anterior interventricular septum and the left ventricle

left coronary artery supplies: most of the left atrium, left ventricle, atrioventricular branches and bundles

Question 35

what are the variation in the arteries?

Answer 35

Right dominant – posterior descending comes off right coronary, therefore right coronary artery supplies large portion of posterior wall of left ventricle. Sino-atrial nodal branch also comes off right coronary artery.
Left dominant – posterior descending comes off large left circumflex artery, supplying most of the posterior wall of left ventricle. This time, sino-atrial nodal branch comes off left coronary artery

Question 36

what are the 2 types of sulci and what do they separate?

Answer 36

Coronary sulcus – separating atria from ventricles

Atrioventricular sulcus – separating the ventricles from each other

Question 37

what does the severity of the disease depend on?

Answer 37

Size and location of artery
Size of blockage
Whether there are collateral blood vessels

Question 38

what does the white and grey ramus contain?

Answer 38

White ramus communicans contains myelinated preganglionic sympathetic fibres
Grey ramus communicans contains unmyelinated postganglionic sympathetic fibres

Question 39

Course of the vagus nerves

Answer 39

Parasympathetic nerve to: heart, bronchi, stomach, intestines

-Arises from the medulla of the brainstem as cranial nerve 10 (CN X)
-Descends down the neck posterolateral to the common carotids
-Left vagus: crosses anterior to aortic arch and then posterior to left lung root
-Right vagus: passes posterior to right lung root
-Both vagus nerves form a plexus around the oesophagus and then turn into oesophageal/gastric nerves
-Left recurrent laryngeal nerve:
-Passes inferior and under the aortic arch and travels in a groove between the oesophagus and trachea to the neck
-Right recurrent laryngeal nerve:
Passes under the right subclavian artery and travels upwards to the neck

Question 40

what is the cardiac plexus made from and what is its course?

Answer 40

The cardiac plexus is formed of small mixed nerves – containing both sympathetic and parasympathetic nerves
Parasympathetic:
Preganglionic parasympathetic fibres reach the heart via cardiac branches from the right and left vagal nerves, they synapse at ganglia either at the plexus or in the walls of the atria
Vagal afferents sense cardiac reflexes – changes in blood pressure and blood chemistry
Sympathetic:
Sympathetic nerves reach the cardiac plexus through cardiac nerves from the sympathetic trunk. Preganglionic = fibres from T1-T5 enter and move through the sympathetic trunk to synapse at cervical or upper thoracic ganglia. The postganglionic fibres then travel to the cardiac plexus from both sides of the spinal cord
Pain sensation can be referred to cutaneous regions supplied by the same spinal roots as the nerve transmitting the impulse

Question 41

Describe the cardiac veins and the pathways they follow

Answer 41

The coronary sinus empties into the right atrium by the opening of the inferior vena cava
Great cardiac vein: drains from the apex, up the anterior interventricular sulcus, then along the coronary sulcus, it eventually enlarges to form the coronary sinus. The great cardiac vein’s path is related to the LAD and circumflex artery
Middle cardiac vein: drains from the apex, up the posterior interventricular sulcus into the coronary sinus. It’s path is related to the posterior descending artery
Small cardiac vein: drains from the lower anterior end of the coronary sulcus, it then travels along the base of the heart to drain into the atrial end of the coronary sinus. It is a companion of the right coronary artery
Posterior cardiac vein: drains from the posterior surface of left ventricle, it either drains directly into the coronary sinus or via the great cardiac vein