pulmonary stretch receptors

Examples of pulmonary stretch receptors in the following topics:

• Proprioceptor Regulation of Breathing

  • These stretch receptors are mechanoreceptors, which are a type of sensory receptor that specifically detects mechanical pressure, distortion, and stretch, and are found in many parts of the human body, especially the lungs, stomach, and skin.
  • When the lungs are inflated to their maximum volume during inspiration, the pulmonary stretch receptors send an action potential signal to the medulla and pons in the brain through the vagus nerve.
  • Additionally, people with emphysema have an impaired Hering–Bauer reflex due to a loss of pulmonary stretch receptors from the destruction of lung tissue, so their lungs can over-inflate as well as collapse, which contributes to shortness of breath.
  • The heart rate returns to normal during expiration when the stretch receptors are deactivated.
  • The vagus nerve is the neural pathway for stretch receptor regulation of breathing.

• Local Regulation of Blood Flow

  • Local responses to stretch, carbon dioxide, pH, and oxygen also influence smooth muscle tone and thus vasoconstriction and vasodilation.
  • Generally, norepinephrine and epinephrine (hormones secreted by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive acting on alpha-1-adrenergic receptors.
  • However, the arterioles of skeletal muscle, cardiac muscle, and the pulmonary circulation vasodilate in response to these hormones acting on beta-adrenergic receptors.
  • Generally, stretch and high oxygen tension increase tone, and carbon dioxide and low pH promote vasodilation.
  • Pulmonary arterioles are a noteworthy exception as they vasodilate in high oxygen.

• Neural Mechanisms (Respiratory Center)

  • It controls the intensity of breathing and is inhibited by the stretch receptors of the pulmonary muscles at maximum depth of inspiration, or by signals from the pnuemotaxic center.

• Classification of Receptors by Stimulus

  • Sensory receptors can be classified by the type of stimulus that generates a response in the receptor.
  • Sensory receptors perform countless functions in our bodies.
  • Cutaneous receptors are sensory receptors found in the dermis or epidermis.
  • Encapsulated receptors consist of the remaining types of cutaneous receptors.
  • A tonic receptor is a sensory receptor that adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that adapts rapidly to a stimulus.

• Classification of Receptors by Location

  • Some sensory receptors can be classified by the physical location of the receptor.
  • Sensory receptors code four aspects of a stimulus:
  • Receptors are sensitive to discrete stimuli and are often classified by both the systemic function and the location of the receptor.
  • While the cutaneous touch receptors found in the dermis and epidermis of our skin and the muscle spindles that detect stretch in skeletal muscle are both mechanoreceptors, they serve discrete functions.
  • The spindle is a stretch receptor with its own motor supply consisting of several intrafusal muscle fibers.

• Great Vessels of the Heart

  • This expansion, or stretching of the aorta, provides potential energy to help maintain blood pressure during diastole, when the aorta passively contracts.
  • Blood first passes through the pulmonary valve as it is ejected into the pulmonary arteries.
  • Four pulmonary veins enter the left atrium.
  • The pulmonary arteries and veins are both considered to be part of pulmonary circulation.
  • Diagram of pulmonary circulation.

• Hypotonia and Hypertonia

  • Hypertonia is the reduced ability of muscles to stretch due to increased muscle tension; hypotonia, due to chronic reduced muscle tension.
  • Hypertonia is a reduction in the ability of a muscle to stretch due to increased muscle tension; it is caused by lesions to upper motor neurons.
  • Dystonic hypertonia is the resistance to passive stretching in muscles, and the return of limbs to fixed positions after contraction.
  • The disruption of input from stretch receptors leads to decreased muscle innervation sensitivity, causing hypotonia.
  • Hypotonia is thought to be associated with the disruption of afferent input from stretch receptors and/or lack of the cerebellum's facilitatory efferent influence on the fusimotor system (the system that innervates intrafusal muscle fibers thereby controlling muscle spindle sensitivity ).

• Spinal Reflexes

  • The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle.
  • Although the tendon reflex is less sensitive than the stretch reflex, it can override the stretch reflex when tension is great, making you drop a very heavy weight, for example.
  • Like the stretch reflex, the tendon reflex is ipsilateral.
  • The sensory receptors for this reflex are called Golgi tendon receptors, and lie within a tendon near its junction with a muscle.
  • The tendon organ is a stretch receptor that signals the amount of force on the muscle and protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load.

• Muscle Tone

  • Muscle tone is a measure of a muscle's resistance to stretching while in a passive resting state.
  • Muscle tone is controlled by neuronal impulses and influenced by receptors found in the muscle and tendons.
  • If tone decreases and the muscle stretches the spindle, an impulse results in a muscle contraction.
  • With this contraction, the spindle is no longer stretched.
  • Distinct stretch receptors called golgi tendon organs assess the level of stretch within the tendon.

• Cutaneous Sensation

  • The somatosensory system is composed of the receptors and processing centers to produce the sensory modalities, such as touch and pain.
  • Mechanoreceptors are sensory receptors that respond to pressure and vibration.
  • The receptive field—the region in which a receptor can sense an effect—can vary from small to large.
  • The Merkel receptor is a disk-shaped receptor located near the border between the epidermis and dermis.
  • It demonstrates a slow response and has a large receptive field; it is good for detecting steady pressure or stretching, such as during the movement of a joint.