Anatomy & Physiology

Anatomy & Physiology Study Guide The cerebellum receives proprioceptive information from the spinal cord and monitors all proprioceptive, visual, tactile, balance, and auditory sensations received by the brain. The cerebellum can be permanently destroyed by trauma or stroke or temporarily impacted by drugs such as alcohol. The result in a disturbance in muscular coordination is called ataxia . In severe ataxia, the individual cannot sit or stand without assistance. The Me enceph lon Auditory and visual reflexes are controlled by the mesencephalon. It also controls alertness in humans. The tectum , or roof of the mesencephalon, is the region posterior to the aqueduct of midbrain. It contains two sets of sensory nuclei known collectively as the corpora quadrigemina . These nuclei (the superior and inferior colliculi) process visual and auditory sensations. The area anterior to the aqueduct of midbrain is called the tegmentum . On each side, the tegmentum contains a red nucleus and the substantia nigra. This nucleus, which receives information from the cerebrum and cerebellum, issues subconscious motor commands that affect upper limb position and background muscle tone. The cerebral peduncles are the nerve fiber bundles on the ventrolateral surfaces of the mesencephalon. They contain descending fibers that go to the cerebellum by way of the pons, and other fibers carry voluntary motor commands issued by the cerebral hemispheres. The mesencephalon also contains the reticular activating system (RAS) that when stimulated increases alertness and attentiveness. The Diencephalon At the subconscious level, the diencephalon integrates sensory information with motor output. The epithalamus, thalamus, and hypothalamus are the divisions of the diencephalon. The epithalamus is the roof of the diencephalon superior to the third ventricle. The anterior portion of the epithalamus contains an extensive area of choroid plexus. The pineal gland is located in the posterior portion of the epithalamus, and this endocrine structure secretes the hormone melatonin . Melatonin regulates the day–night cycles and controls the internal sleep-wake signals. It also regulates reproductive functions. Most of the neural tissue in the diencephalon is concentrated in the left thalamus and right thalamus , which form the lateral walls, and the hypothalamus, which forms the floor. Ascending sensory information from the spinal cord and cranial nerves synapses in a nucleus in the left or right thalamus before reaching the cerebral cortex and our conscious awareness. The hypothalamus has centers whose functions involve emotions and visceral processes that affect the cerebrum, as well as regions of the brain stem. It also is the link between the endocrine and nervous systems and controls many autonomic functions. On each side of the diencephalon, the thalamus is the final relay point for ascending sensory information that will be projected to the primary sensory cortex. It filters information and only passes on small amounts of arriving sensory information. The thalamus also coordinates the activities of the basal nuclei and the cerebral cortex by relaying information between them. The Hypothalamus The hypothalamus extends from the optic chiasm to the posterior margins of the mamillary bodies. The mamillary bodies process sensory information, including olfactory sensations. They also contain motor nuclei that control reflex movements associated with eating, such as chewing, licking, and Achieve Page 133 of 368 ©2018