NROB60 Chapter 7.doc

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University of Toronto St. George
Human Biology
Janelle Le Boutillier

NROB60 – Chapter 7 Introduction: - The human brain appears complicated because it is distorted as a result of the selective growth of some parts within the confines of the skull. Gross Organization of the Mammalian Nervous System: - The nervous system of all mammals has 2 divisions: o The central nervous system (CNS) o The peripheral nervous system (PNS) Anatomical References: - Using a rat’s example: o Anterior or rostral – the direction or anatomical reference, pointing towards the rat’s nose o Posterior or caudal – the direction pointing toward the rat’s tail o Doral – the direction pointing up o Ventral – the direction pointing down - The nervous system is divided into 2 equal halves: o Bilateral symmetry - the right side of the brain and spinal cord is the mirror image of the left side o Midline – the invisible line running down the middle of the nervous system  Medial – structures close to the midline  Lateral – structures farther away from the midline o Ipsilateral - 2 structures that are on the same side o Contralateral – 2 structures that are on the opposite sides of the midline - To view the internal structure of the brain, it is usually necessary to slice it up o Section – a slice (to slice is to section) - The standard approach to is to make cuts parallel to one of the 3 anatomical planes of section: o Midsagittal plane – the plane of the section resulting from splitting the brain into equal right and left halves  Sagittal plane – sections parallel to the midsagittal plane o Horizontal plane – perpendicular to the sagittal plane and is parallel to the ground  Horizontal sections splits the brain into dorsal and ventral parts o Coronal plane – perpendicular to the sagittal plane and to the ground  Coronal plane splits the brain into anterior and posterior parts The Central Nervous System: - The central nervous system consists of the parts of the nervous system that are encased in bone: o The brain and the spinal cord - The brain lies entirely within the skull, there are 3 parts that are common to all mammals o Cerebrum o Cerebellum o Brain stem The Cerebrum: - The rostral-most and largest part of the brain - It is split down the middle into 2 cerebral hemispheres, separated by the deep sagittal fissure o The right cerebral hemisphere – receives sensations from, and controls movements of the left side of the body o The left cerebral hemisphere – concerned with sensations and movements from the right side of the body The Cerebellum: - Lies behind the cerebrum and contains as many neurons as both cerebral hemispheres combined. - It is a movement control center that has extensive connections with the cerebrum and the spinal cord o In contrast to the cerebral hemispheres, the left side of the cerebellum is concerned with movements of the left side of the body. (right side same thing) The Brain Stem: - Forms the stalk from which the cerebral hemispheres and the cerebellum sprout - It is a complex nexus of fibers and cells that serves to relay information from the cerebrum to the spinal cord and cerebellum, and vice versa. - It is also the site where vital functions are regulated, such as breathing, consciousness and the control of body temperature. o Brian stem is the most important to life, damage to the brain stem means rapid death The Spinal Cord: - It is encased in the bony vertebral column and is attached to the brain stem - It is the major conduit of information from the skin, joints, and muscles of the body to the brain and vice versa. o A transection of the spinal cord results in anesthesia (lack of feeling) in the skin and paralysis of the muscles in parts of the body caudal to the cut.  Paralysis in this case, means that they cannot be controlled by the brain - The spinal cord communicates with the body via the spinal nerves, which are part of the peripheral nervous system. o Each spinal nerve attaches to the spinal cord by means of 2 branches  Dorsal root – contains axons bringing information into the spinal cord  Ventral root – contains axons carrying information away from the spinal cord The Peripheral Nervous System: - The PNS has 2 parts: o Somatic PNS o Visceral (Autonomtic) PNS The Somatic PNS: - All the spinal nerves that innervate the skin, joints, and muscles that are under voluntary control are part of the somatic PNS. o The somatic motor axons, which command muscle contraction, derive from motor neurons in the ventral spinal cord.  The cell bodies of the motor neurons lie within the CNS, but their axons are mostly in the PNS. o The somatic sensory axons, which innervate and collect information from the skin, muscles, and joints, enter the spinal cord via the dorsal roots.  The cell bodies of these neurons lie outside the spinal cord in clusters called dorsal root ganglia. The Visceral PNS: - Also called the involuntary, or autonomic nervous system, consists of the neurons that innervate the internal organs, blood vessels and glands. o Visceral sensory axons bring information about visceral function to the CNS  Such as the pressure and oxygen content of the blood in the arteries o Visceral motor fibers command the contraction and relaxation of muscles  Forming the walls of the intestines and the blood vessels (smooth muscles), the rate of cardiac muscle contraction, and the secretory function of various glands. Afferent and Efferent Axons: - Afferent (carry to) and efferent (carry from) indicate whether the axons are transporting information toward or away from a particular point o Afferents – the somatic or visceral sensory axons bringing information into the CNS o Efferents – the axons that emerge from the CNS to innervate the muscles and glands The Cr
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