The Nervous System

The Brain

• Brain-the complex organ that serves as the command center for the entire body, regulating every process from involuntary breathing to high-level thought

  • Cerebrum-the larges and most rostral part of the brain

    • It is responsible for learning and intelligence, for receiving and interpreting sensory information, and it is where the conscious mind resides

      • Longitudinal Fissure-separates the cerebrum into left and right cerebral hemispheres

      • Olfactory Bulbs-receive information from the olfactory nerves, then send the impulses to the cerebrum via the olfactory tracts

      • Gyri-the hills or ridges on the surface of the cerebrum

      • Sulci-the shallow depressions in the surface of the cerebrum between the gyri

  • Cerebellum-caudal to the cerebrum

    • It coordinates movement, balance, posture, and complex reflexes

    • There is no longitudinal fissure, but the right and left sides are described as the right and left cerebellar hemispheres

    • The gyri and sulci are small and tight, giving a wrinkled appearance to the surface of the cerebellum

  • Diencephalon-serves as a passageway between the brainstem and the cerebrum

    • It is more of an area than a distinctly visible thing

      • Pituitary Gland-the only externally visible part of the diencephalon

        • It is called the master endocrine gland because it regulates the production and release of other hormones throughout the body

          • Optic Chiasm-an X-shaped structure located at the base of the brain where the two optic nerves meet and partially cross

        • It is often removed from preserved sheep brain specimens when the dura mater is removed

      • Thalamus-a relay station for regulating sensory inputs to the cerebrum

        • It is a circular structure ventral to the corpus callosum

      • Hypothalamus-a bridge between the nervous system and the endocrine system

        • It is an area of the diencephalon rather than a distinct structure and is located between the thalamus and pituitary gland

      • The pineal body is a small, bean shaped structure located caudal to the thalamus

  • Brainstem-the most primitive part of the brain

    • It contains centers that control basic body functions, such as breathing, cardiac function, and digestive tract function, and it connects the rest of the brain with the spinal cord

      • Medulla Oblongata-the area of the brainstem that connects with the spinal cord

      • Pons-located just rostral to the medulla oblongata

        • It is separated from the medulla oblongata by a horizonal groove

      • Midbrain-located between the pons and the cerebrum

  • The cranial nerves are the 12 pairs of nerves that originate directly from the brain

    • All other nerves are spinal nerves-they originate from the spinal cord

    • Cranial nerves are generally identified by the Roman numerals I through XII, although they have specific names as well

    • The cranial nerves have a variety of functions, some of which occur outside the head region

  • Corpus Callosum-made up of nerve fibers that connect the right and left cerebral hemispheres

    • It looks like a whitish ear inside the cerebrum

  • The locations of the gray and white matter in the cerebrum and cerebellum are obvious grossly when a cut surface is examined

  • Gray matter and white matter are name based on their gross appearance on cut sections of brain tissue

    • Gray Matter-contains most of the neuron cell bodies and it is where many nerve impulses are imitated

      • Gray matter is found in the cortex of the cerebrum and cerebellum

    • White Matter-consists mainly of myelinated nerve fibers-it is the wiring that carries impulses in and out of the gray matter

      • White matter is found in the medulla of the cerebrum and cerebellum

    • In the diencephalon and brainstem, gray matter and white matter switch places from their positions in the cerebrum and cerebellum to their opposite positions in the spinal cord