Nursing Preparation Study Guide

Nursing Preparation Study Guide modifying the activities of motor centers in the brainstem. The second principal function is programming and fine-tuning movements controlled at the conscious and subconscious levels. The cerebellum refines learned movement patterns, which is performed indirectly by regulating activity along motor pathways at the basal nuclei, cerebral cortex, and motor centers in the brainstem. The cerebellum has a complex surface composed of neural tissue. The folia, or folds of the cerebellum surface, are less prominent than the folds in the surfaces of the cerebral hemispheres. The primary fissure separates the anterior and posterior lobes. Along the midline, a narrow band of cortex known as the vermis separates the cerebellar hemispheres. The slender flocculonodular lobe lies between the roof of the fourth ventricle and the cerebellar hemispheres, and the vermis. The cerebellum contains a superficial layer of neural cortex. The cerebellar cortex contains large, highly branched Purkinje cells. The extensive dendrites of each Purkinje cell receive input from up to 200,000 synapses. Internally, the white matter of the cerebellum forms a branching array that resembles a tree when viewed sectionally. Anatomists call it the arbor vitae, or “tree of life”. 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 damaged by a trauma or stroke, or temporarily affected by using alcohol or drugs. A disturbance in muscular coordination is called ataxia. In severe ataxia, the individual cannot sit or stand without assistance. The Mesencephalon The mesencephalon controls auditory and visual reflexes, as well as alertness in humans. The tectum, or roof of the mesencephalon, is the region posterior to the aqueduct of the midbrain. The mesencephalon contains two pairs of sensory nuclei known together as the corpora quadrigemina. These nuclei (the superior and inferior colliculi) are in charge of processing auditory and visual sensations. The area anterior to the aqueduct of the 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; these contain descending fibers that reach the cerebellum by way of the pons and carry voluntary motor commands issued by the cerebral hemispheres. The mesencephalon also contains the reticular activating system (RAS) that increases alertness and attentiveness when stimulated. 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.

©2018

Achieve Test Prep

Page 105

of 173