Autonomic Reflexes Flashcards
How is the baroreceptor reflex stimulated?
Changed arterial blood pressure changes stretch of baroreceptors in carotid sinus and aortic arch which signal the medulla in the brain
How does the baroreceptor reflex respond to increased arterial BP?
Increased blood pressure increases stretch of baroreceptors
There is increased afferent nerve activity to the brain
This leads to increased inhibition of sympathetic nervous system
Sympathetic effects on heart, vessels and catecholamine release are reduced
Overall effect is a lowering of the blood pressure
How does the baroreceptor reflex respond to decreased arterial BP?
Decreased blood pressure decreases stretch of baroreceptors
There is decreased afferent nerve activity to the brain
This leads to increased stimulation of the sympathetic nervous system
Sympathetic effects on heart, vessels and catecholamine are increased
Overall effect is increasing the blood pressure
4 sympathetic effects on blood pressure altered in the baroreceptor reflex?
Vasomotor tone
Heart rate
Heart force of contraction
Catecholamine release
How does vasomotor tone affect blood pressure?
Increased vasomotor tone (vasoconstriction) increases total peripheral resistance
This increases blood pressure and vice versa
How do heart rate and force of contraction affect blood pressure?
Increase in both increases overall cardiac output
This increases blood pressure and vice versa
How does catecholamine release affect blood pressure?
They have generic effects which increase vasoconstriction etc which increases blood pressure
Hence increased release leads to increased blood pressure
What CVS effects does standing up have and how does it stimulate the baroreceptor reflex?
Increased pooling of blood in lower limbs
Reduced venous return leads to reduced force of contraction leads to reduced cardiac output decreasing blood pressure which reduces firing of baroreceptors to brain - increased sympathetic effects to increase BP again
What is postural hypotension?
Arterial blood pressure is not maintained on standing leading to decreased cerebral blood flow and fainting
How does postural hypotension arise?
Impaired sympathetic response to baroreceptor reflex leading to little change in cardiac output and no increase in total peripheral resistance
What is the consensual reflex and where does it occur?
Occurs in the eye
In response to light the iris elongates to constrict the pupil (gap between iris components)
What are the sympathetic and parasympathetic effects on iris?
Sympathetic - Iris contracts, pupil dilates
Parasympathetic - Iris elongates, pupil contracts
What two molecules stimulate sympathetic and parasympathetic stimulation of iris?
Atropine - stimulates sympathetic effects
Pilocarpine - stimulates parasympathetic effects
Which cells detect light in the consensual reflex?
Photosensitive photoganglion cells
How and where is the signal then transmitted to brain?
Sensory input carried by OPTIC NERVE to the PRETECTAL NUCLEUS in the brain
