reflex syncope

Examples of reflex syncope in the following topics:

• Syncope

  • Syncope, the medical term for fainting, is a transient loss of consciousness.
  • There are two broad categories of syncope, cardiogenic or reflex, which underlie most forms of syncope.
  • Variants of reflex syncope often have characteristic histories, including precipitants and time course which are made evident by skilled history taking.
  • Other types include postural syncope (caused by a change in body posture), cardiac syncope (due to heart-related conditions), and neurological syncope (due to neurological conditions).
  • Recurrent syncope with complex associated symptoms called neurally mediated syncope.

• Carotid Sinus Syncope and Massage

  • Massage of the carotid sinus, or carotid sinus massage, is used to diagnose carotid sinus syncope.
  • This condition is called carotid sinus syncope, and results in dramatic changes in heart rate or blood pressure.
  • Carotid sinus syncope sometimes accompanies convulsive seizures because of the intensity of the carotid sinus reflex when pressure builds in one or both carotid sinuses.

• Reflexes and Diagnosis

  • A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.
  • Scientific use of the term "reflex" refers to a behavior that is mediated via the reflex arc; this does not apply to casual uses of the term "reflex".
  • Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.
  • While the reflexes above are stimulated mechanically, the term H-reflex refers to the analogous reflex stimulated electrically, and Tonic vibration reflex for those stimulated to vibration.
  • While 2+ is considered normal, some healthy individuals are hypo-reflexive and register all reflexes at 1+, while others are hyper-reflexive and register all reflexes at 3+.

• Vagus (X) Nerve

  • Afferent vagus nerve fibers that innervate the pharynx and back of the throat are responsible for the gag reflex.
  • Excessive activation of the vagal nerve during emotional stress can also cause vasovagal syncope due to a sudden drop in cardiac output, causing cerebral hypoperfusion.

• Gastrointestinal Reflex Pathways

  • The digestive system functions via a system of long reflexes, short reflexes, and extrinsic reflexes from gastrointestinal (GI) peptides working together.
  • In addition, there are three overarching reflexes that control the movement, digestion, and defecation of food and food waste: the enterogastric reflex, the gastrocolic reflex, and the gastroileal reflex.
  • When this occurs, it is called a short reflex.
  • The gastrocolic reflex is the physiological reflex controlling the motility, or peristalsis, of the gastrointestinal tract.
  • The gastroileal reflex is a third type of gastrointestinal reflex.

• Components of a Reflex Arc

  • A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
  • The path taken by the nerve impulses in a reflex is called a reflex arc.
  • There are two types of reflex arcs:the  autonomic reflex arc, affecting inner organs, and the somatic reflex arc, affecting muscles.
  • For example, the withdrawal reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli.
  • The path taken by the nerve impulses in a reflex is called a reflex arc.

• Spinal Reflexes

  • Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex.
  • Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex.
  • This reflex has the shortest latency of all spinal reflexes.
  • Like the stretch reflex, the tendon reflex is ipsilateral.
  • The crossed extensor reflex is a withdrawal reflex.

• Autonomic Reflexes

  • Autonomic reflexes are unconscious motor reflexes relayed from organs and glands to the CNS through visceral afferent signaling.
  • An example of referred pain from an autonomic reflex arc occurs when the bowel is suddenly distended.
  • The medulla's major ANS functions include respiration (the respiratory control centre, or "rcc"), cardiac regulation (the cardiac control centre, or "ccc"), vasomotor activity (the vasomotor centre or "vmc"), and certain reflex actions (such as coughing, sneezing, vomiting and swallowing).
  • General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS (see for a depiction of a typical nerve fiber, including general visceral afferent fibers).
  • While the unconscious reflex arcs are normally undetectable, in certain instances, they may send pain sensations to the CNS masked as referred pain.

• Proprioceptive Sensations

  • An unconscious reaction is seen in the human proprioceptive reflex, or Law of Righting.
  • It provides the sensory component of the Golgi tendon reflex.
  • The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system.
  • In a Golgi tendon reflex, skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax.
  • This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex.

• Optic (II) Nerve

  • Most of the axons of the optic nerve terminate in the lateral geniculate nucleus (where information is relayed to the visual cortex), while other axons terminate in the pretectal nucleus and are involved in reflexive eye movements.
  • It also conducts the visual impulses that are responsible for two important neurological reflexes: the light reflex and the accommodation reflex.
  • The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye; the accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object, as in reading.