Anatomy of Coughing Flashcards
What are 2 steps of a cough reflex?
1) Stimulation of sensory receptors in the airway mucosa
2) CNS response
What are the 2 components of the cough reflex?
* Sensory component
* Motor component
Explain the first, sensory stage of the cough reflex
Stimulation of sensory receptors in the mucosa of the:-
* Oropharynx
* Laryngopharynx
* Larynx
* Respiratory tree (trachea to bronchioles)
Explain the second, motor stage of the cough reflex
The CNS responds to sensory stimulation by rapidly coordinating the following:
* a DEEP inspiration using the diaphragm (phrenic nerves), intercostal muscles (intercostal nerves) & “accessory muscles of inspiration”
* adduction of the vocal cords to close the rima glottidis (vagus nerves)
* contraction of the anterolateral abdominal wall muscles (intercostal nerves) to build up intra-abdominal pressure - pushes the diaphragm superiorly and builds up pressure in the chest/respiratory tree inferior to the adducted vocal cords
* the vocal cords suddenly abduct to open the rima glottides (vagus nerves)
* the soft palate tenses (CN V) and elevates (vagus nerves) to close off the entrance into the nasopharynx and direct the stream of air (at ~100mph!!) through the oral cavity as a cough rather than through the nasal cavity as a sneeze!
What sensory receptors are stimulated in sneezing?
* CN V
* CN IX
What sensory receptors are stimulated in coughing?
* CN IX
* CN X
Name cranial nerves labelled A-D
A - CN V1 (trigeminal)
B - CN V2 (trigenimal)
C - CN IX (glossopharyngeal)
D - CN X (vagus nerve)
What are carotid sheaths?
Protective “tubes” of cervical (neck) deep fascia
Where to carotid sheaths start and end?
* Attaches superiorly to the bones of the base of the skull
* Blends inferiorly with the fascia of the mediastinum
What do the carotid sheaths contain?
* the vagus nerve
* the internal carotid artery
* the common carotid artery
* the internal jugular vein
What does the internal jugular vein do?
It drains blood from the brain and cranium to the heart
How do visceral pleura and respiratory tree visceral afferents connect with the CNS? (stimulation of lower respiratory tract’s respiratory mucosa)
* The pulmonary visceral afferents travel from visceral pleura & respiratory tree to the pulmonary plexus then follow the vagus nerve to the medulla of the brainstem
What is contained within the pulmonary plexus of the vagus nerve?
* sympathetic axons
* parasympathetic axons
* visceral afferents
How do motor nerves supply mucous glands and bronchial smooth muscles?
They travel from the tracheal bifurcation (pulmonary plexus) along the branches of the respiratory tree to supply all mucous glands and bronchiolar smooth muscles
Are sympathetic and parasympathetic axons sensory?
No, they are both motor (efferent)
Explain the mechanics of inspiration
* Diaphragm contracts abd descends (increases vertical chest dimension)
* Intercostal muscles contract elevating ribs (increases A-P and lateral chest dimensions)
* The chest walls pull the lungs outwards with them due to pleura (Air flows into the lungs due to -ve pressure)
What is the main muscle of quiet respiration?
Diaphragm
What nerves supply the diaphragm?
Phrenic nerves - anterior rami of C3, 4, 5 cervical spinal nerves
Where are phrenic nerves found in the neck?
Anterior surface of scalenus anterior muscle
Where are phrenic nerves found in the chest (thorax)?
Descending over the lateral aspects of the fibrous pericardium anterior to the lung root (hilum)
What is the function of phrenic nerves?
Supplies somatic sensory and sympathetic axons to the diaphragm & fibrous pericardium
How do phrenic nerves generate a deep, forced inspiration?
Generate greater outflow of action potentials of longer duration causing the diaphragm to flatten then descend maximally
What are the 3 layers of intercostal muscles?
* external intercostal muscles
* internal intercostal muscles
* innermost intercostal muscles
What are intercostal nerves?
Anterior rami of spinal nerves T1-T11 - pass through costal grooves of ribs
What happens in deep (forced) inspiration?
* The external intercostal muscles contract forcefully and raise the ribs maximally
what are the accessory muscles of deep (forced) inspiration?
* Pectoralis major and minor
* Scalenus anterior, medius and posterior
* Sternocleidomastoid
Where does pectoralis major attach?
Attaches between sternum/ribs & humerus
What is the function of the pectoralis major?
Adducts and medially rotates humerus
Why do patients with COPD often hold onto the arm of a chair or the thigh to breathe?
Allows pectoralis major (accessory muscle of inspiration) to pull the ribs upwards/outwards
What is recruitment of accessory muscles an important clinical sign of?
Dyspnoea
How does pectoralis minor aid in forced inspiration?
Can pull ribs 3-5 superiorly towards the coracoid process of the scapula
Where does the sternocleidomastoid attach?
Attaches between sternum/clavicle & mastoid process of temporal bone
Where does scalenus anterior, medius and posterior attach?
Attach between cervical vertebrae and ribs 1 & 2
How does sternocleidomastoid aid in forced inspiration?
Increases A-P diameter
How is the rima glottidis closed?
The vocal cords approximate in the midline, closing the rim glottidis
What class of muscle are the intrinsic muscles of the larynx?
All skeletal (voluntary) muscles
What causes the movement of the vocal cords?
Intrinsic muscles of the larynx
How do intrinsic muscles of the larynx cause movement of the vocal cords?
They attach between the cartilages, move the cartilages resulting in the movement of the vocal cords
What nerves supply the intrinsic muscles of the larynx?
Somatic motor branches of the vagus nerve (CN X)
What is the function of the intrinsic muscles of the larynx in the cough reflex?
Adduct the vocal cords during cough reflex
What is the rim glottidis?
Not a structure - it is a space that gets larger depending on the abduction/adduction of vocal cords
What are right and left vagus nerves?
Mixed cranial nerves
Where do the vagus nerves connect with the CNS?
At the medulla (oblongata) of the brainstem
What part of skull does vagus nerve pass through?
Jugular foramen
How do vagus nerves descend through the neck?
Within the carotid sheath
Why is the vagus nerve important in the cough reflex?
Supply somatic sensor and motor axons to the larynx
Which parts of the larynx are supplied with somatic sensory and somatic motor neurones?
* Sensory to the mucosa lining the larynx
* Motor to the intrinsic muscles of the larynx
How do vagus nerves descend through the chest?
Posterior to the lung root (unlike phrenic nerves which descend anterior to the lung root)
What do the vagus nerves supply the chest organs with?
Parasympathetic axons
How do the vagus nerves supply parasympathetic axons to the chest organs (including the lungs)?
Via the pulmonary plexus
How do the vagus nerves pass through the diaphragm?
With the oesophagus
What happens once vagus nerves reach the stomach?
Divide into many parasympathetic branches for the foregut & midgut organs
Explain the mechanics of expiration
* Diaphragm relaxes and rises (decreases vertical thoracic dimension - increases intra-thoracic pressure)
* Intercostal muscles relax lowering ribs (decreases A-P and lateral chest dimensions)
* Elastic tissue of lungs recoils (air flows out of lungs)
What are the accessory muscles of active expiration?
* Abdominal wall muscles
* Internal intercostal muscles
Explain the process of deep, forced expiration in cough reflex
* The right & left anterolateral abdominal wall muscles contract forcefully increasing intra-abdominal pressure
* The diaphragm is forced superiorly by the compressed abdominal contents
* Intra-thoracic pressure increases, increasing the pressure within the respiratory tree inferior to the vocal cords
Label the anterolateral abdominal wall muscles labelled A-H (pic)
A - left rectus abdominus
B - left external oblique
C - left internal oblique
D - left transverses abdominus
E - right transverses abdominus
F - right internal oblique
G - right external oblique
H - right rectus abdominus
Where are axial sections viewed from?
The foot of the patient
What should abdominal muscles not be confused with?
Intercostal muscles
What is a useful way for remembering the direction in which the abdominal wall muscles run?
* External oblique - hands in pockets
* Internal oblique - hands on chest
* Transversus abdominus - perpindicular to midline
* Rectus abdominus - straight up and down
Which direction does the external oblique run in?
Fibre direction the same as the external intercostal muscle (hands in pockets)
What is an aponeurosis?
Flattened tendon
Which of the abdominal muscles has an aponeurosis?
* External obliques * Internal obliques * Transversus abdominus
Where does the aponeurosis of the right external oblique blend with the aponeurosis of the left external oblique?
At the midline (linea alba)
Where do the external obliques attach?
Superiorly - the superficial aspects of the lower ribs Inferiorly - the anterior part of the iliac crest and the pubic tubercle
What is the linea semilunaris?
Where the muscle fibres end and the aponeurosis begins
Where does the aponeurosis of the right internal oblique blend with the aponeurosis of the left internal oblique?
The midline linea alba
Where do the internal obliques attach?
* Superiorly - inferior border of the lower ribs * Inferiorly - the iliac crest and thoracolumbar fascia of the lower back
What direction do the internal obliques run in?
* Opposite direction to the external obliques * Fibre direction the same as the internal intercostal muscle (hands on chest)
Where does the aponeurosis of the right transversus abdominus blend with the aponeurosis of the left transversus abdominus?
At the linea alba
Where does the transverses abdominus attach?
* Superiorly - deep aspects of lower ribs * Inferiorly - iliac crest and thoracolumbar fascia of the lower back
What special features does the rectus abdominus have?
* Right and left rectus sheaths * Tendinous intersections
What are the rectus sheaths composed of?
The aponeuroses of the other 3 muscles
Which abdominal muscle group does not have an aponeurosis?
Rectus abdominus
What do the tendinous intersections do?
Divide each of the 2 long flat muscles into 3 or 4 smaller quadrate muscles (“6-pack” or “8-pack”)
What is the effect of the tendinous intersections in contraction of the abdominal muscles?
During contraction, allows for curved anterior aspect of the abdomen rather than completely straight
What are the somatic motor, somatic sensory and sympathetic nerve fibres supplying the structures of the abnormal wall conveyed within?
The thoracoabdominal nerves
How are the thoracoabdominal nerves formed?
The 7th to the 11th intercostal nerves travel anteriorly then their terminal branches leave the intercostal spaces, in the plane between the internal oblique & the transversus abdominus as the thoracoabdominal nerves
What is the T12 anterior ramus?
The subcostal nerve
What is the L1 anterior ramus?
* Half of the L1 anterior ramsus is Iliohypogastric nerve * Other half is ilioinguinal nerve
What are the functions of the abdominal wall muscles?
* tonic (continuous low level) contractions maintain posture * tonic (continuous low level) contractions support the vertebral column * contractions produce movements of the vertebral column (spine): flexion, lateral flexion, rotations * “guarding” contractions protect the abdominal viscera * contractions increase intra-abdominal pressure to assist: defecation, micturition, labour * Contractions aid forced expiration
Why can mechanical back pain sometimes be improved by abdominal muscle exercises?
Tonic contractions of the abdominal muscles support the vertebral column
