Circle of Willis The circle of Willis is an anastomotic system of arteries at the base of the brain that encircles the pituitary gland. An anastomotic system of arteries is a network of separate blood vessels that come together to form a structure, in this case the circle of Willis. The anterior portion of the circle of Willis is formed from the division of the internal carotid artery into the anterior cerebral artery and middle cerebral artery. The left and right anterior cerebral arteries are connected by the anterior communicating artery. In the posterior section of the circle of Willis, the left and right vertebral arteries form the bas lar artery, which branches into the left and right posterior cerebral arteries. The circle of Willis is completed by the posterior cerebral arteries joining the internal carotid system via the posterior communicating arteries. The circle of Willis is an important connection between the blood supply of the forebrain and hindbrain. However, a complete and well-developed circle of Willis is present in less than half the population; for the majority, there are anatomical differences in the diameter and presence of arteries that make up the system 2. 7. 6. 5. 4. 9. 11. Brain and Circle of Willis- ventra! view
Anatomy and Physiology of Special Sensory Organs
Sensory organs can be labeled as special sensory structures that permit sight, hearing, odor, and flavor. Sensory structures permitting proprioception, touch, thermal, and pain perception can be classified as more advanced sensory organs. The sensory neurons are trained to find out modifications in the external and internal conditions so that a person's body can react to that change. A stimulus is the first signal that is recognized by any sensory receptor of the body. Stimulus is an impulse generated when there is a change in the surroundings of a person. For example, a heated environment will alert the brain through the thermal sensory organs and generate a reflex accordingly.
Sensory Receptors
The human sensory system is one of the most complex and highly evolved structures, which processes a myriad of incoming messages. This well-coordinated system helps an organism or individual to respond to external stimuli, appropriately. The sensory receptors are an important part of the sensory system. These receptors are specialized epidermal cells that respond to external environmental stimuli. These receptors consist of structural and support cells that form the peripheral unit of the receptor and the neural dendrites which receive and detect the external stimuli.
1) Anterior cerebral artery
2) Middle cerebral artery
3) Posterior inferior cerebellar artery
4) Vertebral artery
5) Anterior inferior cerebellar artery
6) Basilar artery
7) Internal carotid artery
8) Anterior cerebral artery ( precommunicating part segment A1)
9) Posterior cerebral artery
10) posterior cerebral artery ( postcommunicating part segment P2)
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