Resp 9 - sensory aspect of respiratory symptoms

Question 1

Describe the pathway from stimulus to evoked sensation? What are the names for the two main parts of this?

Answer 1

sensory stimulus -> transducer (sensor) -> excitation of sensory nerves -> integration of CNS -> sensory impression
This is NEUROPHYSIOLOGY
Sensory impression -> perception -> evoked sensation
This is BEHAVIOURAL PSYCHOLOGY

Question 2

Describe the distribution of rapidly adapting irritant receptors within the airway epithelium.

Answer 2

They are most numerous on the posterior wall of the trachea and in the main carina.
Well placed to sense external environment.
They decrease in number as you go down the airways and they are absent in the bronchioles.
They are commonly found at the branch points of large airways.

Question 3

What are the three main types of sensory receptors in the lungs and airways?

Answer 3

C-fibre receptor - unmyelinated
Slowly adapting stretch receptors - myelinated
Rapidly adapting stretch receptors - myelinated

Question 4

Which nerve do all the sensory receptors in the lungs and airways pass through?

Answer 4

Vagus nerve (10th cranial nerve)

Question 5

What is used as a stimulus for the C-fibres?

Answer 5

Caspaicin - only C fibres respond

Question 6

What stimulates C-fibres?

Answer 6

Chemicals

Question 7

What do the rapidly and slowly adapting stretch receptors respond to?

Answer 7

Inflation (increase in tracheal pressure)

Rapidly adapting stretch receptors stop firing whereas slow adapting stretch receptors are stimulated to fire.

Question 8

Describe the differences between the three types of sensory receptor.

Answer 8

C-fibres are unmyelinated whereas the other two are myelinated.
C-fibres are found in the larynx, trachea, bronchi and lungs
Rapidly adapting stretch receptors are found in the naso-pharynx, larynx, trachea and bronchi
Slowly adapting stretch receptors are located on airway smooth muscle, mainly in the trachea and main bronchi

Question 9

What are the two broad types of sensory receptor in the airways that will lead to cough?

Answer 9

Mechanoreceptors

Nociceptors

Question 10

Other than mechanical displacement, what else activates the mechanoreceptors?

Answer 10

Citric acid

Question 11

What is the collection of neurons in the cough centre called?

Answer 11

Nucleus tractus solitarius

Question 12

Where are cough receptors found?

Answer 12

Mainly in the proximal airways
Can also be found in larynx pharyx, external auditory meatus
Also stomach, diaphragm, pleura, pericardium

Question 13

What are nociceptors activated by?

Answer 13

• Caspaicin
• Bradykinin
• Citric acid
• Cinnamaldehyde

Question 14

What is this collection of neurons connected to?

Answer 14

Medullary cough pattern generator

Question 15

What is the role of the cerebral cortex in the complete cough pathway?

Answer 15

The cerebral cortex is needed to generate a cough and generate the urge to cough. When asleep, this component of the complete cough pathway is inhibited so a certain degree of wakefulness is needed to cough. General anaesthetic also inhibits this.

Question 16

What are the three phases of cough?

Answer 16

Inspiratory phase
Glottic closure
Expiratory phase

Question 17

What is acute cough and what is it usually caused by?

Answer 17

Cough that lasts less than 3 weeks

It is commonly caused by rhinovirus

Question 18

What are the causes of chronic cough?

Answer 18

Asthma
Gastrooesophageal reflux
Rhinosinusitis
Chronic bronchitis
Bronchiectasis

Question 19

What is another name for chronic cough? How can the sensitivity be tested?

Answer 19

Cough Hypersensitivity Syndrome

Sensitivity can be measured using Capsaicin

Question 20

What drugs can inhibit the cortical control of the cough reflex?

Answer 20

Central action: Opiates: codeine, etc.

Peripheral: Moguisteine, levodopropizine

Question 21

Sensory perception from the nose and the pharynx goes through which nerves?

Answer 21

Nose - Trigeminal (V)
Pharynx - Glossopharyngeal (IX)
Vagus (X)

Question 22

How do you get hypersensitivity?

Answer 22

• increased excitability of the afferent nerves
• increase in receptor number
• increase in neurotransmitters
• increase in inflammatory mediators - changes reactivity of nerves

Question 23

Describe the anatomical pathways of touch and pain.

Answer 23

Main difference between the two = level at which the pathways cross through to the contralateral side.

Touch travels via Aalpha and Abeta fibres via the dorsal horn
Pain travels via Adelta and C fibres via the dorsal horn
Touch goes to the contralateral side at the level of the caudal medulla (brainstem)
Pain crosses at the same anatomical level - crosses right away

Both touch and pain end up in the primary somato-sensory cortex

Question 24

What is the clinical significance of this?

Answer 24

Brown-Sequard Syndrome - hemisection of the spinal cord
If you have a hemisection on the left side of the spinal cord, the touch sensation will be fine on the opposite side but the pain sensation on the other side will be affected

Question 25

What’s the difference between somatic and visceral pain?

Answer 25

Visceral pain comes from organs - difficult to localise, diffuse in character and referred to somatic structures
Somatic comes from skin - very localised

Question 26

What scale is used to grade dyspnoea?

Answer 26

Modified Borg Scale

Question 27

What are the three types of dyspnoea?

Answer 27

Air Hunger
Tightness
Work/Effort of breathing