Midbrain the highest portion of the brain stem the

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Midbrain. The highest portion of the brain stem, the midbrain is involved in such functions as controlling eyeball movement and pupil size. The reflexive response of turning your head when you hear an unexpected loud noise is also initiated by the midbrain. Thalamus. The thalamus is an important relay center for incoming sensory impulses. Nerve cells within the thalamus brain stem cerebellum 403 Lesson 4 The Nervous System How do scientists learn about the brain? Recent advances in tech- nology have enabled scientists to “see” inside a living brain. Brain imaging techniques help scientists understand the functions of the brain, locate areas affected by neurological disorders, and develop new strategies to treat brain disorders. These techniques include: CT, or “CAT” scans, in which a series of X rays are beamed through the head, producing an image that shows the structure of the brain. PET scans, in which a machine detects and images radioactive material that is either injected into or inhaled by the patient. This type of scan provides information on brain function. MRI, which uses radio waves and magnetic fields to produce an anatomical view of the brain.
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receive information from different sense organs such as the eyes and ears. Through the spine the thalamus also receives information from touch and pressure receptors in the skin. Hypothalamus. The hypothalamus controls and balances various body processes to regulate body temperature, stimu- late appetite for food and drink, and regulate sleep. The hypothalamus also controls secretions from the pituitary gland that control metabolism, sexual development, and emotional responses. The Peripheral Nervous System he peripheral nervous system (PNS) consists of all of the T nerves that are not part of the CNS. The PNS carries messages between the CNS and the rest of the body. The PNS can be divided into two categories, the autonomic nervous system and the somatic nervous system. The Autonomic Nervous System The autonomic nervous system (ANS) controls such involuntary functions as digestion and heart rate. The ANS consists of a network of nerves divided into two smaller networks: the sympathetic ner- vous system and the parasympathetic nervous system. THE SYMPATHETIC NERVOUS SYSTEM You may have felt the effects of the sympathetic nervous system the last time you were startled. Messages from the sympathetic ner- vous system cause your heart rate to increase and the blood vessels leading to your muscles to dilate, allowing greater blood flow. This is the “fight or flight” response that prepares your body to react to what may be a dangerous situation. You also have experienced a a spontaneous response of the body to a stimulus, as when a doctor tests the knee-jerk reflex by tapping the ligament below the knee. Figure 15.5 on page 405 shows the steps of a reflex action.
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