Sensory aspects of respiratory disease

Question 1

Physiologic or pathologic stimulus leading to
conscious sensation diagram
(slide 5, lecture 10)

Answer 1

Conscious Sensation Production
1. The sensory stimulation (e.g. a cut) activates sensory
transducers which transmit the signal via excitation of
sensory nerves (afferent nerves into the CNS).
2. CNS creates a sensory impression – neurophysiology.
a. This impression leads to the perception of
information.
3. The brain interprets the information coming from
sensory nerves and evokes a ‘sensation’ – behavioural
psychology.

Question 2

Difference between symptom and sign

Answer 2

▪ Symptom – an abnormal or worrying SENSATION
that leads a person to seek medical attention.
▪ Sign – an OBSERVABLE feature on physical
examination.

Question 3

Prevalence of Respiratory Symptoms
Cough
Chest pain
Dyspnoea

Answer 3

▪ Cough:
o 3rd most common complaint in GP practice.
o 10-38% patients in respiratory outpatients
complain of a cough.

▪ Chest pain:
o Most common trigger for consultation (35%).

▪ Dyspnoea:
o 6-27% of general population, 3% A&E visits.

Question 4

Location of cough receptors

Answer 4

Cough Receptors – Rapidly adapting irritant receptors
Location:
▪ Within the epithelium and most numerous on the
posterior wall of the trachea.
▪ Main carina (and other branching points).
▪ Less numerous in the distal airways.
▪ Absent beyond the bronchioles.
▪ Also found in the diaphragm, pleura, pericardium
and stomach.

Question 5

Types of cough receptors

Stimuli of each type

Answer 5

Forms of Cough Receptor
Can be divided into three main types of receptor:
▪ Slow adapting stretch receptors.

▪ Rapidly adapting stretch receptors.

▪ C-fibre receptors.

Question 6

ALL sensory nerves from the airway pass through

Answer 6

the 10th cranial nerve, AKA the Vagus nerve.

Question 7

C-Fibre Receptors
Stimulator?
Structure?
Location?
Respond to? Examples?

Answer 7

Main stimulator =chemicals like capsaicin.

Structure= “free” nerve endings that are small and unmyelinated – conduction is therefore slow.

Located in the larynx, trachea, bronchi and lungs.

They respond to chemical stimuli and inflammatory mediators. Inflammatory mediators include:
o Substance P.
o Neurokinin A.
o Calcitonin Gene Related Peptide.

Question 8

Rapidly Adapting Stretch Receptors 
Type of receptor?
Stimulus?
Structure?
Located in?

Answer 8

mechanoreceptor.

Main stimulus is inflation. They respond to mechanical, chemical and inflammatory mediators’ stimuli.
o Hyperinflation (mechanical) stimulates a rapid response.

They are small myelinated fibres – conduction is therefore fast.

Located in the naso-pharynx, larynx, trachea and bronchi.

Question 9

Slowly Adapting Stretch Receptors 
Type of receptor?
Structure?
Located in?
Respond to?

Answer 9

a mechanoreceptor.

They are myelinated fibres – conduction is therefore fast.

Located in the airways smooth muscle (primarily trachea and main bronchi).

Main stimulus is inflation. They respond to mechanical, chemical and inflammatory mediators’ stimuli.
o Hyperinflation (mechanical) stimulates a slow response.

Question 10

2 types of receptor lead to a cough:

Activated by?

Answer 10

1) Mechanoreceptors.
o Activated by mechanical displacement and
citric acid.
o Look like a tree (picture on slide 15, lecture 10)

2) Nocireceptors.
o Activated by capsaicin, bradykinin, citric acid
and cinnamaldehyde.
o TRPV1, TRPA1 and B2 channels are present.

Question 11

Afferent neural pathways for cough

slide 17, lecture 10

Answer 11

Stimulation of irritant receptors (RARs)/ Or cough receptor by mechanical or chemical triggers
Goes down Vagus (X) nerve and Superior laryngeal nerve which combine to ‘cough centre’ in medulla which goes to cerebral cortex

Question 12

Efferent neural pathways for cough

slide 18, lecture 10

Answer 12

Cerebral cortex goes to “Cough Centre” in medulla
3 outputs to Glottis muscle, diaphragm, expiratory muscles
Cerebral cortex also goes directly to neurone from cough centre to glottis muscle

Question 13

Mechanics of cough draw graph
(slide 19, lecture 10)
Phases?

Answer 13

There are THREE main phases:
o Inspiratory phase.
o Glottic closure.
o Expiratory phase.

▪ High brain activity when you have the need to cough.

Question 14

Causes of cough

Answer 14

▪ Acute infection – e.g. bronchopneumonia, rhinovirus.
▪ Chronic infection – e.g. CF or TB.
▪ Airways disease – e.g. Asthma.
▪ Parenchymal disease – e.g. Emphysema.
▪ Tumours.
▪ Foreign bodies.
▪ Cardiovascular problems – e.g. Left ventricular failure.
▪ Other disease – e.g. Recurrent aspiration, GERD.
▪ Drugs – e.g. ACE inhibitors.

Question 15

Causes of chronic cough (>3 weeks)
Most common?
Second most common?
Other cause?

Answer 15

1) Most common= Asthma and eosinophilic-associated (25%)
2) Second= acid reflux (25%)
In gastro-oesophageal reflux, protons from the stomach can activate cough receptors.

3) Other cause= drugs such as ACE inhibitors only contribute ~1% of the cause.

Question 16

Cough hypersensitivity syndrome=?
Triggers?
Sensitivity measured with? Mechanism?
Possible causes of condition?

Answer 16

Increased sensitivity of the cough receptors.

Triggers=deep breathing, laughing, talking, exercise etc.

Sensitivity is measured using capsaicin with increasing dosages of capsaicin. Capsaicin activates nocireceptors through the TRPV1 receptors.

Possible causes?
▪ Increased excitability of the afferent nerves by chemical mediators (e.g. prostaglandin E2).
▪ Increase in receptor number (e.g. TRPV1).
▪ Increase in NT in the brainstem (e.g. neurokinins).

Question 17

Treatment
General name for all drugs?
Symptomatic suppressant therapy?
Disease-specific therapy:

Answer 17

Antitussives

Symptomatic suppressant therapy:
o Narcotics:
Codeine, dihydrocodiene, pholcodiene.
Morphine, diamorphine, methadone.
o Non-narcotics:
Dextromethorphan (derivative of morphine), levopropoxyphene.

Disease specific therapy:
Eosinophil-associated – e.g. corticosteroids.
GERD – e.g. Proton pump inhibitors.
Post-nasal drip – e.g. antihistamines or topical steroids.
Bronchiectasis – e.g. antibiotics.

Question 18

Which nerve contributes to sensory input from nose?

Answer 18

Trigeminal (V)

Question 19

Which nerve contributes to sensory input from pharynx?

Answer 19

Glossopharyngeal (IX)

Vagus (X)

Question 20

Which nerve contributes to sensory input from larynx?

Answer 20

Vagus (X)

Question 21

Which nerve contributes to sensory input from lungs?

Answer 21

Vagus (X)

Question 22

Which nerve contributes to sensory input from chest wall?

Answer 22

Spinal nerves

Question 23

Chest pain can be felt in:

Answer 23

o Chest wall.
o Skin.
o Pleural pain.
o Deep-seated, poorly-localised.
o Nerve root pain.
o Referred pain (pain that occurs at a different site from where the issue is)

Question 24

Difference between touch and pain pathways

Answer 24

The main difference is at which level the pathways
cross to the contra-lateral side:
o Touch – crosses at the caudal medulla.
o Pain – crosses at the same anatomical level, i.e. straight away

Question 25

Brown-Sequard Syndrome

Answer 25

hemisection of the left side of the spinal cord means touch will be fine but pain will be felt on the other side of the body.

Question 26

3 types of pain:

Answer 26

Somatic, visceral and neuropathic.
o Somatic is localised while visceral is from the
organs and isn’t very specific

Question 27

Causes of chest Pain from RESPIRATORY Disease

Answer 27

▪ Pleuropulmonary Disorders.
▪ Tracheobronchitis.
▪ Inflammation or trauma.
▪ Referred pain (shoulder-tip pain).

Question 28

Causes of chest Pain from NON-RESPIRATORY Disease

Answer 28

▪ Cardiovascular disorders – e.g. MI or pericarditis.
▪ Gastrointestinal disorders – e.g. GERD.
▪ Psychiatric disorders – e.g. panic disorder.

Question 29

Dyspnoea meaning

Answer 29

troublesome shortness of breath

Question 30

Treatment of Dyspnoea

Therapeutic options?

Answer 30

Treat the cause.
Therapeutic options (difficult) include: bronchodilators, lung resections, pulmonary rehabilitation.