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Functions Of The Brain

FUNCTIONAL ANATOMY OF THE BRAIN

I. HIND BRAIN

A. Brain stem: A bundle of nervous tissue that connects the cerebrum to the spinal cord. It consists of numerous tracts if nerve fibers and several nuclei. The parts of the brain stem include the midbrain, pons, and medulla oblongata.

1. Medulla oblongata (medulla): Extends from the pons to the foramen magnum of the skull. Its dorsal surface flattens to form the floor of the 4th ventricle and its ventral surface is marked by the corticospinal tracts, most of whose fibers cross over at this level. All nerve fibers connecting the brain and spinal cord must go through the medulla oblongata.

a. cardiac center: Impulses originating in the cardiac center are transmitted to the heart on peripheral nerves, altering heart rate.

b. vasomotor center: Certain cells of the vasomotor center initiate impulses that travel to smooth muscles in the walls of certain blood vessels (vasoconstriction), elevating blood pressure. Other cells of the vasomotor center produce the opposite effect, dilating blood vessels (vasodilatation) and consequently dropping blood pressure.

c. respiratory center: The respiratory center acts with centers in the pons to regulate the rate, rhythm and depth of breathing.

2. Reticular formation: A complex network of nerve fibers associated with tiny islands of gray matter. Extends from the upper spinal cord into the diencephalon. Its nerve fibers join centers of the hypothalamus, basal nuclei, cerebellum, and cerebrum with fibers in all the major ascending and descending tracts.

When the sensory impulses reach the reticular formation, it responds by activating the cerebral cortex into a state of wakefulness. without this arousal, the cortex remains unaware of stimulation and cannot interpret sensory Information or carry on thought processes. Thus, decreased activity in the reticular formation results in sleep. If the reticular formation is injured so that it cannot function,...