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By the end of this section, you will be able to:
  • Describe the role of higher centers of the brain in autonomic regulation
  • Explain the connection of the hypothalamus to homeostasis
  • Describe the regions of the CNS that link the autonomic system with emotion
  • Describe the pathways important to descending control of the autonomic system

The pupillary light reflex ( [link] ) begins when light hits the retina and causes a signal to travel along the optic nerve. This is visual sensation, because the afferent branch of this reflex is simply sharing the special sense pathway. Bright light hitting the retina leads to the parasympathetic response, through the oculomotor nerve, followed by the postganglionic fiber from the ciliary ganglion, which stimulates the circular fibers of the iris to contract and constrict the pupil. When light hits the retina in one eye, both pupils contract. When that light is removed, both pupils dilate again back to the resting position. When the stimulus is unilateral (presented to only one eye), the response is bilateral (both eyes). The same is not true for somatic reflexes. If you touch a hot radiator, you only pull that arm back, not both. Central control of autonomic reflexes is different than for somatic reflexes. The hypothalamus, along with other CNS locations, controls the autonomic system.

Pupillary reflex pathways

This diagram shows the connections between the different nerves and pathways in the eyes. A hand is shown shining a light on the right eye, and arrows and text callouts indicate the different pathways that are activated.
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.

Forebrain structures

Autonomic control is based on the visceral reflexes, composed of the afferent and efferent branches. These homeostatic mechanisms are based on the balance between the two divisions of the autonomic system, which results in tone for various organs that is based on the predominant input from the sympathetic or parasympathetic systems. Coordinating that balance requires integration that begins with forebrain structures like the hypothalamus and continues into the brain stem and spinal cord.

The hypothalamus

The hypothalamus is the control center for many homeostatic mechanisms. It regulates both autonomic function and endocrine function. The roles it plays in the pupillary reflexes demonstrates the importance of this control center. The optic nerve projects primarily to the thalamus, which is the necessary relay to the occipital cortex for conscious visual perception. Another projection of the optic nerve, however, goes to the hypothalamus.

The hypothalamus then uses this visual system input to drive the pupillary reflexes. If the retina is activated by high levels of light, the hypothalamus stimulates the parasympathetic response. If the optic nerve message shows that low levels of light are falling on the retina, the hypothalamus activates the sympathetic response. Output from the hypothalamus follows two main tracts, the dorsal longitudinal fasciculus    and the medial forebrain bundle    ( [link] ). Along these two tracts, the hypothalamus can influence the Eddinger–Westphal nucleus of the oculomotor complex or the lateral horns of the thoracic spinal cord.

Questions & Answers

Explain how different foods can affect metabolism
Abraham Reply
what is Endocrine system?
Islam Reply
which secrete hormones and other products direct into the blood
Cell is basic, structural and functional unit of life
Kabuja Reply
The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life." Some organisms, such as bacteria, are unicellular, consisting of a single cell.
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what is the basic function of the lymphatic system
The other main function is that of defense in the immune system. Lymph is very similar to blood plasma: it contains lymphocytes. It also contains waste products and cellular debris together with bacteria and proteins. Associated organs composed of lymphoid tissue are the sites of lymphocyte producti
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lymphatic systems main function is to transport lymph
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Which of the following accurately describe external respirations
Robin Reply
different between anatomy and physiology
Samwel Reply
anatomy is the study of STRUCTURE of the body while physiology is the study of the function of the part of the body
Anatomy deals with the structure and parts of the body while physiology is the function of the the body parts
not understanding what is a cell
Kesa Reply
its the fundamental unit of life or its the primary step in which two or more cell combine to form a tissue .
Is the smallest structural and functional unit of life
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what is osteomalàcia
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what is hydroxyapitate
Hydroxyapatite, also called hydroxylapatite, is a naturally occurring mineral form of calcium apatite with the formula Ca₅(PO₄)₃, but it is usually written Ca₁₀(PO₄)₆(OH)₂ to denote that the crystal unit cell comprises two entities. Hydroxyapatite is the hydroxyl endmember of the complex apatite gro
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wat work does anatomy do in the hospital and can they get work fast after finishing
SULE Reply
what is the meaning of suture?
praba Reply
it is a protective layer of brain
it is a kind of non movable joint present between skull bones
suture is an example of fibrous joint and is synatrosys(is not movable)
a junction between the sclerites of an imsect's body
c organ,organ system, organism
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reproductive sytstem
describe structure and functions of spleen
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why calcium does not prodecessed by biological process?
James Reply
when calcium isn't processed that becomes Calcium Homeostasis
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What are the functions of batholine glan
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what is pathogen
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an organism who invades the susceptible host
what tenderness chord
Tenderness A She tried to show me how to love D I bit her lips and bruised ...
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Pathogens are decease causing agents.... it can be a viral infection or fungai infection... thank u
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What is nosocomial
hospital accused infection.
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How do we measure power in skeletal muscles....
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