Chap14_2401 - 1 THE BRAIN AND CRANIAL NERVES Chapter 14...

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Unformatted text preview: 1 THE BRAIN AND CRANIAL NERVES Chapter 14 Anatomy and Physiology Lecture 2 THE BRAIN AND THE CRANIAL NERVES I. BRAIN A. PRINCIPAL PARTS-Brain is made up of about 100 billion neurons. -Is one of the largest organ in the body, weighing about 1300g. (3lb) -Brain is Mushroom-shaped , and divided into four principal parts: a . Brain stem- Midbrain, Pons, & Medulla Oblongata b . Diencephalon- Thalamus & Hypothalamus c. Cerebrum- Right and left halves called cerebral hemispheres d . Cerebellum (Little brain) Brain's many functions : - the center for registering sensations; - correlating sensations with one another and stored information - making decisions - taking action - center for intellect - emotions - behavior - memory - directs our behavior towards others 3 BRAINSTEM Medulla Oblongata Brain Stem { Pons Midbrain Connects the Spinal cord to the remainder of the brain and is responsible for many essential functions. Damage to brainstem area often causes death. MEDULLA OBLONGATA (Medulla) Is a continuation of the upper portion of the spinal cord and forms the inferior part of the brain stem. Lies just superior to the level of the foramen magnum and extends upward to the inferior portion on the Pons. *Measures 3cm (about 1 inch ) in length. Function : 1. Conduction Pathway for Motor and Sensory Impulses-Contains all ascending and descending tracts that communicate between the spinal cord and various parts of the brain. (These tracts constitute the white matter of the medulla.) -* Pyramids are two roughly triangular structure on the ventral side of the medulla. -Are composed of the largest motor tracts that pass from the outer region of the cerebrum (cerebral cortex) to the spinal cord. -*Just about the junction of the medulla with the spinal cord, most 4 of the fibers in, the left pyramid cross to the right side, and most of the fibers in the right pyramid cross to the left. Note- this crossing is called the Decussation of Pyramids . ( Decussation explains why motor areas of one side of the cerebral cortex control muscular movements on the opposite side of the body.) 2. Reticular Formation- area of dispersed gray matter containing some white fibers. -Functions in consciousness and arousal from sleep. Unconsciousness (The most common knockout blow is one that makes contact with the mandible. Such a blow twists and distorts the brain stem and overwhelms the reticular activating system (RAS) of the reticular formation by sending a sudden volley of nerve impulses to the brain, resulting in unconsciousness.) - Think of blowing of fuse; - Think of a "breaker" if current is over-loaded. 3. Three vital reflex centers of the reticular system (Regions within Medulla) a. Cardiovascular Center- regulates the rate and force of heartbeat and the diameter of blood vessels....
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Chap14_2401 - 1 THE BRAIN AND CRANIAL NERVES Chapter 14...

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