Nervous System (Part A-3) Module 8 -Chapter 14 Overview Susie Turner, M.D. 1/9/13 Cellular structure of the nervous system Neurons Neuroglia Nervous System Divisions Central nervous system Peripheral nervous system Pathway or highway for impulses between the brain & spinal cord. Called Primary Brain Because responsible for the beginning & end of life. 3 Divisions Midbrain Pons Medulla Oblongata Brain Stem 1
Brain Stem Structures Midbrain Also called the Mesencephalon Middle Brain Connects cerebrum with brain stem Pons Name means Bridge Myelinated axons Connect midbrain to medulla Looks like a Big Butt Assists with breathing Brain Stem-Structures Medulla Oblongata Controls Vital Signs Respiratory rate, blood pressure, & heart rate Except temperature Contains Involuntary centers Cough, sneeze, etc Look like Little Butt Attaches to spinal cord Medulla Oblongata 2
Decussation of Pyramids at Medulla Motor Neurons of Primary Motor Cortex Called Pyramidal Cells Decussation Fibers Crossover to opposite side Cerebellum Name means little brain All functions involve movement Coordinates skeletal muscle activity Motor Activity Begins in Cerebrum Assist in balance & equilibrium 3
Spinal Cord 2 Major Functions 1. Highway for ascending & descending nerve impulses Transmits sensory impulses from body to brain Ascending Tracts Transmits motor impulses from brain to muscles & organs of body Descending Tracts 2. Center for Spinal Reflexes Spinal Cord Reflexes Rapid, automatic responses to stimuli Protective Sensory CNS Motor Response 1. Stimulus arrives at receptor 2. Activates Sensory Neuron 3. Information processing in CNS 4. Activates Motor Neuron 5. Response by Effector 4
Spinal Cord Located in spinal cavity of the vertebral column For protection Internal Anatomy Gray Matter H-shaped in cross section Inner gray matter composed of cell bodies & their dendrites White Matter Outer white matter composed of myelinated ascending & descending axons 5
Peripheral Nervous System Anatomical Division 1. Cranial Nerves Nerves exit directly from brain Innervate muscles of head & neck. 2. Spinal Nerves Nerves exit from spinal cord Innervate muscles from neck down Spinal Nerves Spinal nerves exit between the intervertebral spaces Total of 31 pairs Named for the region where they exit from (C1 nerve, C2 nerve etc) Form Plexuses 6
Plexuses Complex network of nerves Sensory & Motor Fibers Go to Skin & Muscles Move the Limbs Major Anterior Trunk Muscles Named for areas they serve Cervical, brachial, & lumbosacral Numbered consecutively as they exit Usually named after structures they innervate. Most are mixed nerves Cranial Nerves 7
Cranial Nerves Twelve pairs Primarily serve the head & neck Except Cranial Nerve X Vagus Nerve Vagus Nerve Roman Numeral X Wanderer" Because it is the "lost vagus" Parasympathetic motor fibers Extend into thoracic & abdominal cavities 8
2 Major Anatomical Divisions Divided into; 1. Somatic Nervous System Voluntary 2. Autonomic Nervous System Involuntary Somatic Nervous System Associated with voluntary movement Operates through conscious control Somat/o means body Walking, talking etc 1. Transmits sensory information to the brain & spinal cord and 2. Transmits motor information from brain & spinal cord to skeletal muscles 9
Autonomic Nervous System Associated with involuntary movement Automatic Operates without conscious control Examples are digestion, heart contraction, vasoconstriction, & gland secretion 1. Transmits sensory information to the brain & spinal cord 2. Transmits motor information from brain & spinal cord to glands, and smooth & cardiac muscle tissue 2 Efferent (Motor) Divisions Somatic Motor Division Innervates Skeletal muscles Autonomic Motor Division Innervates Smooth & cardiac muscles, glands Sympathetic Parasympathetic 10
Somatic Motor Neurons 2 locations 1. Primary or Upper Motor Neurons (UMN) Are in the brain 2. Secondary or Lower Motor Neurons (LMN) Are in the spinal cord. *In order to reach the muscles, motor commands generated in the CNS must travel on upper motor neurons and synapse with lower motor neurons UMN LMN Functional Differences Tend to oppose each other. Sympathetic Acute Stress Situations Flight, fight, fright Parasympathetic Normal Bodily Functions Like Resting & Eating Digest, Rest, & Nest 11
Effects of ANS Summary 12