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Baroreceptors and Chemoreceptors

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Topic updated on 03/07/14 10:04am

Baroreceptors
  • Baroreceptors
    • Overview
      • baroreceptors aka mechanoreceptors sense changes in arterial pressure
        • "pressure sensors" located in walls of carotid sinus and aortic arch
          • respond to stretching
    • Carotid Sinus
      • baroreceptors that respond to ↑ AND ↓ in arterial pressure (aka BP)
        • transmit to brainstem via carotid sinus nerve
          • carotid sinus nerve joins with glossopharyngeal nerve (CN IX)
            • CN IX synapses in nucleus tractus solitarius of medulla
    • Aortic Arch
      • baroreceptors that respond ONLY to ↑ in arterial pressure (aka BP)
        • transmit to brainstem via vagus nerve (CN X)
          • CN X synapses in nucleus tractus solitarius of medulla
  • Baroreceptor Reflex
    • Overview
      • a fast, neurally mediated reflex that attempts to keep arterial pressure constant via changes in output of sympathetic and parasympathetic nervous systems to heart and blood vessels
    • e.g., Hypotension and Hemorrhage (↓ Arterial Pressure)
      • ↓ Arterial Pressure → ↓ Stretch → ↓ Afferent Baroreceptor Firing → ↑ Efferent Sympathetic Firing & ↓ Efferent Parasympathetic Firing →
        • (1) Vasoconstriction
        • (2) ↑ HR
        • (3) ↑ Contractility
        • (4) BP
      • Description
        • (1) ↓ in blood pressure is sensed by baroreceptors in carotid sinus
          • decrease in blood pressure = decrease in stretch
        • (2) ↓ in stretch causes ↓ firing of afferent nerves
          • carotid sinus nerve (glossopharyngeal nerve, CN IX)
          • vagus nerve (CN X)
        • (3) glossopharyngeal n. and vagus n. synapse in nucleus tractus solutarius
          • nerves relay ↓ in blood pressure to brain
        • (4) nucleus tractus solutarius directs a series of coordinated responses using medullary cardiovascular centers that increases blood pressure
    • e.g., Carotid Massage
      • ↑ Pressure on Carotid Artery → ↑ Stretch → ↑ Afferent Baroreceptor Firing → HR   
    • Cushing Reaction
      • Mechanism
        • increase in intracranial pressure constricts cerebral arteries
          • causes cerebral ischemia
        • cerebral ischemia induces hypertension (sympathetic response)
          • causes reflex bradycardia
      • Cushing Triad
        • (1) hypertension; (2) bradycardia; (3) respiratory depression
Chemoreceptors
  • Chemoreceptors
    • Peripheral Chemoreceptors
      • receptors in carotid sinus and aortic arch sense ↓ PO2, ↑ PCO2, ↓ pH
        • ↓ PO2 aka < 60 mmHg
      • carotid bodies
        • aka chemoreceptors in carotid sinus
        • transmit to brainstem via carotid sinus nerve
          • carotid sinus nerve joins with glossopharyngeal nerve (CN IX)
            • CN IX synapses in nucleus tractus solitarius of medulla
      • aortic bodies
        • aka chemoreceptors in aortic arch
        • transmit to brainstem via vagus nerve (CN X)
          • CN X synapses in nucleus tractus solitarius of medulla
    • Central Chemoreceptors
      • receptors in medulla sense ↑/↓ PCO2, ↑/↓ pH (NOT ↑/↓ PO2) in brain fluid
        • PCO2, pH influenced by arterial CO2
 


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Qbank (1 Questions)

TAG
0) (M1.CV.27) Paramedics respond to a call regarding an 18-year-old male with severe sudden-onset heart palpitations. The patient reports symptoms of chest pain, fatigue, and dizziness. Upon examination, his heart rate is 175/min and regular. His blood pressure is 110/75 mm Hg. Gentle massage below the level of the left mandible elicits an immediate improvement in the patient, as his heart rate returns to 70/min. What was the mechanism of action of this maneuver? Topic Review Topic

1. Increasing the refractory period in ventricular myocytes
2. Increasing sympathetic tone in systemic arteries
3. Decreasing the length of phase 4 of the SA node myocytes
4. Impairing conduction in the AV node
5. Decreasing the firing rate of carotid baroreceptors

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