Flashcards in Chapter 18 ( nervous regulation of the circulation and rapid control of arterial pressure) Deck (33)
How is the sympathetic nervous system distributed?
thoracic nerves and first one or two lumbar nerves
how does the sympathetic nervous system enter circulatoin?
1. via specific nerves that innervate vasculature of internal viscera and heart
2. via peripheral portions of spinal nerves in peripheral areas
what is the only vessel that is not innervated by sympathetic NS?
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
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.
emotional fainting( vasovagal syncope)
vagus nerve slows heart and vasodilation occurs which causes the fainting.
3 ways to increase arterial pressure
arterioles are constricted, large vessels like veins constrict which causes the heart to pump harder, direct stimulation by autonomic nervous system
rapidity of arterial pressure
can increase pressure 2 times in 5- 10 seconds and decrease pressure by ½ in 10-40 seconds. It is the fastest way of controlling arterial pressure
Baroreceptor arterial pressure control system-
s initiated by stretch receptors called either baroreceptors or pressoreceptors which are located at specific points in walls of several large systemic arteries. A rise in arterial pressure causes them to stretch and send feedback signals through the ANS to reduce arterial pressure.
carotid baroreceptors pathway
via herings nerve, glossopharyngeal nerve, tractus solitarius in medulla
aortic baroreceptors pathway
via vagus nerve, tractus solitarius of medulla.
carotid sinus baroreceptors stimulation
get stimulated at 60 mm Hg and maximize at 180 mm Hg
what causes baroreceptors to respond quicker
a rising pressure
control of arterial pressure by carotid and aortic chemoreceptors
sensative to Oxygen lack, Co2 excess, and hydrogen excess. They excite nerve fibers along the baroreceptor fibers which pass through herings nerves and vagus nerves to vasomotor nerve. They decrease parasympathetic stimulation and increase sympathetic stimulation which increases heart rate and constricts the vessels. ( probably to try and get blood to the tissue thats lacking O2)
when are chemoreceptors most powerfull?
below 80 mm Hg
atrial and pulmonary reflexes
contain low pressure receptors that act like baroreceptors(if 300 ml was inserted into a dogs atria, the atria pressure rises only 15 mmHg. With the arterial baroreceptors removed it rises to 40 mm Hg and with the low pressure receptors removed in rises to 100 mm Hg)
atrial reflex that activates the kidney (volume reflex)
an increase in atrial pressure increases the heart rate as much as 75%. ( 15% from increase in atrial volume and 40-60 % from bainbridge reflex)
what is the bainbridge reflex?
when the atrial stretch receptors stretch and send a signal via vagus nerves to the medulla. Signals are sent back via vagus and sympathetic nerves to increase heart rate and strength of heart contraction
CNS ischemic response
most powerful of all activators of sympathetic vasoconstrictor response. It is only activated when arterial pressure is below 60 mmHg and works its best at 15-20 mm Hg. Its an emergency pressure control system that acts rapidly and very powerfully to prevent further decrease in arterial pressure whenever blood flow to the brain decreases dangerously close to lethal level. Often called the last ditch stand