Resp 9 - sensory aspect of respiratory symptoms Flashcards
Describe the pathway from stimulus to evoked sensation? What are the names for the two main parts of this?
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
Describe the distribution of rapidly adapting irritant receptors within the airway epithelium.
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.
What are the three main types of sensory receptors in the lungs and airways?
C-fibre receptor - unmyelinated
Slowly adapting stretch receptors - myelinated
Rapidly adapting stretch receptors - myelinated
Which nerve do all the sensory receptors in the lungs and airways pass through?
Vagus nerve (10th cranial nerve)
What is used as a stimulus for the C-fibres?
Caspaicin - only C fibres respond
What stimulates C-fibres?
Chemicals
What do the rapidly and slowly adapting stretch receptors respond to?
Inflation (increase in tracheal pressure)
Rapidly adapting stretch receptors stop firing whereas slow adapting stretch receptors are stimulated to fire.
Describe the differences between the three types of sensory receptor.
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
What are the two broad types of sensory receptor in the airways that will lead to cough?
Mechanoreceptors
Nociceptors
Other than mechanical displacement, what else activates the mechanoreceptors?
Citric acid
What is the collection of neurons in the cough centre called?
Nucleus tractus solitarius
Where are cough receptors found?
Mainly in the proximal airways
Can also be found in larynx pharyx, external auditory meatus
Also stomach, diaphragm, pleura, pericardium
What are nociceptors activated by?
- Caspaicin
- Bradykinin
- Citric acid
- Cinnamaldehyde
What is this collection of neurons connected to?
Medullary cough pattern generator
What is the role of the cerebral cortex in the complete cough pathway?
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.
What are the three phases of cough?
Inspiratory phase
Glottic closure
Expiratory phase
What is acute cough and what is it usually caused by?
Cough that lasts less than 3 weeks
It is commonly caused by rhinovirus
What are the causes of chronic cough?
Asthma Gastrooesophageal reflux Rhinosinusitis Chronic bronchitis Bronchiectasis
What is another name for chronic cough? How can the sensitivity be tested?
Cough Hypersensitivity Syndrome
Sensitivity can be measured using Capsaicin
What drugs can inhibit the cortical control of the cough reflex?
Central action: Opiates: codeine, etc.
Peripheral: Moguisteine, levodopropizine
Sensory perception from the nose and the pharynx goes through which nerves?
Nose - Trigeminal (V)
Pharynx - Glossopharyngeal (IX)
Vagus (X)
How do you get hypersensitivity?
- increased excitability of the afferent nerves
- increase in receptor number
- increase in neurotransmitters
- increase in inflammatory mediators - changes reactivity of nerves
Describe the anatomical pathways of touch and pain.
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
What is the clinical significance of this?
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
What’s the difference between somatic and visceral pain?
Visceral pain comes from organs - difficult to localise, diffuse in character and referred to somatic structures
Somatic comes from skin - very localised
What scale is used to grade dyspnoea?
Modified Borg Scale
What are the three types of dyspnoea?
Air Hunger
Tightness
Work/Effort of breathing
