G4iv: Describe the role of the vasomotor centre and the ANS in the regulation of CO & VR

  • Cardiovascular System is controlled by the CNS & integration of Afferent Information
  • Arterial BP is the 1° controlled variable
  • Centres of CNS influencing CV performance:
    • Medulla Premotor Sympathetic Cells
    • Medulla Premotor Parasympathetic Cells
    • Cerebral Cortex
    • Hypothalamus
    • Cerebellum
    • Periaqueductal Grey Matter (PAG)
  • The MEDULLA integrates all afferent info & alters ANS activity accordingly

Central Sympathetic Cells

  • Symp. control starts in neurons located in ROSTRAL VENTROLATERAL MEDULLA (RVLM)
  • RVLM neurons have spont AP activity
  • ∴Basal Symp. Tone
  • fibres from:
    • Medulla
    • NTS
    • Hypothalamus
    • Higher Centres
    • CVLM (caudal ventrolateral medulla)
  • Excited by excitatory α-acids, Vasopressin, Angiotension, ACh
  • Inhibited by GABA, Encephalins, Catecholamines

Central Parasympathetic Cells

  • fibres originate from DORSAL VAGAL NUCLEUS & NUCLEUS AMBIGUUS
  • Direct inhibition from Medulla Insp. Neurons = ↓firing = tachycardia of inspiration

Nucleus Tractus Solitarius

  • Where afferents (CN X & IX terminate)
  • Other 2° order afferents also terminate here
  • Via interneurons communicate with SC, Medulla, Hypothalamus, C. Cortex
  • NTS transmits info from BARORECEPTORS
  •  

↑BP →

NTS

Arrowdown3a

NUCLEUS AMBIGUUS → ↑Parasymp. Output

Arrowdown3a

CVLM activation → inhibits RVLM → ↓symp. output to Heart / vessels / kidney / medulla

  • NTS receives a lot of info
    • CV Afferents
    • Cortex
    • Hypothalamus
    • RVLM

Cerebellum

  • Controls posture & coordination of movement
  • Regulates CV system in response to muscle/joint activity

PAG

  • Produce defence reaction in response to nociception/threat
  • Supply specific cells of RVLM to induce specific ∆ in vascular beds

Hypothalamus

  • ‘Defence Area’
    • Inhibits BaroR reflex at NTS
    • Stimulates RVLM cells & inhibits Vagal Output 

Oppositely

  • ‘Depressor Area’
    • Enhances BaroR reflex

Limbic

  • Activates ‘Rage Behaviour’ → ↑HR, ↑BP, VD
  • Enhances ‘Playing Dead’ → severe ↓HR & HypoT

Cortex

  • Important for CV responses at onset of exercise
Cortex