Chapter 18 ( nervous regulation of the circulation and rapid control of arterial pressure) Flashcards
How is the sympathetic nervous system distributed?
thoracic nerves and first one or two lumbar nerves
how does the sympathetic nervous system enter circulatoin?
- via specific nerves that innervate vasculature of internal viscera and heart
- via peripheral portions of spinal nerves in peripheral areas
what is the only vessel that is not innervated by sympathetic NS?
capillaries
what does sympathetic stimulation do to small arteries and arterioles?
increase resistance which decreases blood flow to tissues.
what does sympathetic stimulation to large vessels like veins do?
these vessels decrease in volume which pumps more blood to the heart
parasympathetic innervation of heart
Vagus nerve which decreases heart rate and contractility
Where is the vasomotor center?
reticular substance in brain and lower 1/3 of pons
where is the vasodilator area ?
anterolateral part of lower medula. These project upward and inhibit the vasoconstrictor area
Where is the vasoconstricor area?
anterolateral part of upper medula
sympathetic vasoconstrictor tone
continuous firing of vasoconstrictors. ~1-2 per second. They maintain a partial state of contraction
vasomotor center affect on heart
lateral portion of vasomotor center on heart transmits excitatory impulses through sympathetic fibers to the heart and increases heart rate and contractility. Medial portion of vasomotor area sends signals to adjacent dorsal motor nuclei of vagus nerves which transmit parasympathetic impulses to slow the heart.
control of vasomotor center by higher nervous centers
reticular substance of pons, mesencephalon, and diencephalon can excite or inhibit vasomotor area. In general the neurons in the lateral and superior portions of the reticular substance cause excitation. The more medial and inferior cause inhibition.
hypothalamus role on vasomotor center
Causes both powerful excitatory or inhibitory effects on vasomotor center. The posterolateral portions cause excitation and the anterior portion causes mild excitation or inhibition
cerebral cortex role on vasomotor center
many parts can either excite or inhibit vasomotor center
Norepinephrine
secreted out of vasoconstrictor nerves which acts on alpha adrenergic receptors of vascular smooth muscle( in some tissues it causes vasodilation)
adrenal medullae- these secrete the epinephrine and norepinephrine into the blood.