Pupillary diameter, or more precisely iris size, is controlled by two muscles, the sphincter pupillae, which is primarily under the control of the parasympathetic nervous system, and the dilator pupillae, which is primarily under the control of the sympathetic nervous system.
What branch of the nervous system controls pupillary response?
The parasympathetic nervous system is the main system responsible for pupil constriction in response to light. The integrated afferent input is transmitted along the axons of the retinal ganglion cells (RGC), which contribute to the optic nerve.
Is the pupillary light reflex sympathetic or parasympathetic?
The basic autonomic mechanism controlling the pupil is straightforward: pupil constriction is mediated via parasympathetic activation of the circular sphincter pupillae muscle, and dilation via sympathetic activation of the radial dilator pupillae muscle (1).
How are pupil responses regulated?
The size of the pupil is controlled by the activities of two muscles: the circumferential sphincter muscle found in the margin of the iris, innervated by the parasympathetic nervous system: and the iris dilator muscle, running radially from the iris root to the peripheral border of the sphincter.
Is pupillary reflex somatic or autonomic?
Pupillary Reflex Pathways. The pupil is under competing autonomic control in response to light levels hitting the retina. The sympathetic system will dilate the pupil when the retina is not receiving enough light, and the parasympathetic system will constrict the pupil when too much light hits the retina.
What nerve controls pupillary constriction or dilation?
The oculomotor nerve is responsible for the efferent limb of the pupillary reflex; it drives the iris muscles that constrict the pupil.
What is the function of pupillary response?
The pupillary light reflex allows the eye to adjust the amount of light reaching the retina and protects the photoreceptors from bright lights. The iris contains two sets of smooth muscles that control the size of the pupil (Figure 7.2).
Is increased heart rate sympathetic or parasympathetic?
Sympathetic stimulation of the heart increases heart rate (positive chronotropy), inotropy and conduction velocity (positive dromotropy), whereas parasympathetic stimulation of the heart has opposite effects.
Is bronchodilation sympathetic or parasympathetic?
Dilation and Constriction of Bronchioles
Parasympathetic stimulation causes bronchoconstriction while sympathetic stimulation causes bronchodilation. During an asthma attack, the muscles that encircle the airway tighten or constrict, limiting the flow of air to and from the lungs.
Is decreased heart rate sympathetic or parasympathetic?
The sympathetic nervous system (SNS) releases the hormones (catecholamines – epinephrine and norepinephrine) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate.
What does it mean when your pupils are non reactive?
– Non-reactive pupils may also be caused by local damage; – One dilated or fixed pupil may indicate an expanding/developing intracranial lesion, compressing the oculomotor nerve on the same side of the brain as the affected pupil.
What does pupil size indicate?
Muscles in the colored part of your eye, called the iris, control your pupil size. Your pupils get bigger or smaller, depending on the amount of light around you. In low light, your pupils open up, or dilate, to let in more light. When it’s bright, they get smaller, or constrict, to let in less light.
Why do both pupils constrict in response to light?
In the light reflex, the pupils constrict when light is shone on the retina. If one eye only is stimulated, both pupils constrict, the so-called consensual reflex. The afferents are optic nerve fibres which pass to both pretectal nuclei, crossing in the posterior commissure.
What could an abnormal pupillary reflex indicate?
Pupillary light reflex is used to assess the brain stem function. Abnormal pupillary light reflex can be found in optic nerve injury, oculomotor nerve damage, brain stem lesions, such as tumors, and medications like barbiturates.
Can the pupillary response be inhibited?
These results show that the anticipation of an electric shock can modify not only the startle reflex response but also the pupillary light reflex, suggesting that the inhibition of the light reflex by threat may be another suitable laboratory model of human anxiety.
Which of the following is a neurotransmitter used by the sympathetic nervous system?
Each division uses different neurotransmitters to perform their actions- for the sympathetic nervous system, norepinephrine and epinephrine are the neurotransmitters of choice, while the parasympathetic division uses acetylcholine to perform its duties.