Neural control of the lungs RT 3005/6005

Neural Control of the Respiratory System

• The autonomic nervous system (ANS) manages involuntary functions such as bronchial and arterial smooth muscle tone.
• The system comprises two subdivisions: sympathetic and parasympathetic.
• Sympathetic activation involves epinephrine and norepinephrine affecting beta (β2) and alpha (α) receptors.
• Parasympathetic control is mediated through acetylcholine.

Anatomy of the Lungs

• The apex is pointed and rises above the first rib; the base is broad and concave, extending to the 6th rib anteriorly and around the 11th rib posteriorly.
• The mediastinal border of the lungs curves to accommodate the heart, constituting the hilum where bronchi, vessels, and nerves enter.

Lung Structure

• The right lung is larger and heavier, divided into three lobes: upper, middle, and lower lobes; separated by horizontal and oblique fissures.
• The left lung consists of two lobes: upper and lower, separated by the oblique fissure.

Mediastinum

• The central cavity of the thoracic cage contains critical structures, including the trachea, heart, great vessels, nerves, portions of the esophagus, thymus gland, and lymph nodes.

Pleural Membranes

• Composed of visceral and parietal pleura, holding together via serous fluid, maintaining negative pressure that keeps lung tissue adhered to the thorax.
• The presence of air or fluid can equalize atmospheric pressure, causing separation.

Thoracic Structure

• The thorax protects the cardiopulmonary system, bordered by 12 thoracic vertebrae posteriorly, the sternum anteriorly, and 12 pairs of ribs laterally.
• Ribs are categorized: true ribs (1-7), false ribs (8-10), and floating ribs (11-12).
• Contains 11 intercostal spaces that house vascular bundles and nerves along their inferior borders.

Diaphragm

• The primary muscle of ventilation, shaped as a dome between the thorax and abdomen, merges into a central tendon.
• Features three orifices accommodating the esophagus, aorta, and inferior vena cava.
• Primarily innervated by the phrenic nerve; its downward movement during inspiration increases thoracic volume.

Inspiration Mechanics

• Scalene, sternocleidomastoid, pectoralis major, trapezius, and external intercostal muscles are involved in the inspiratory process.
• Scalene muscles elevate the first and second ribs, contributing to neck flexion.
• The sternocleidomastoid rotates the head and elevates the sternum, enhancing the anteroposterior (AP) diameter of the chest.
• Pectoralis major assists in the adduction of upper extremities and elevates the chest to increase lung volume.

Accessory Muscles of Expiration

• Utilized during increased resistance, these muscles include rectus abdominis, external oblique, internal oblique, transversus abdominis, and internal intercostal muscles.
• Their contraction raises intrathoracic pressure to counteract elevated airways resistance.

Internal Intercostal Muscles

• Positioned beneath the external intercostals, they contract during expiration to pull ribs downward and inward, aiding in airflow reduction.