Nervous System (Part A-1) 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 Nervous System Most complicated system of body Senses physical and chemical changes in the internal and external environments Coordinates, regulates and integrates voluntary & involuntary activities 1
Nerve Impulses Also called action potentials Convey information from cell to cell. Charges change across plasma membrane Because of flow of Na & K ions Provide Instantaneous response. Nervous System 2 Major Divisions Central nervous system Brain Spinal cord Peripheral nervous system Nerves Cranial Spinal Sensory Receptors Actually nerve endings 2
Homeostatic Regulation Adjustments in the body s physiological systems To maintain its stable internal environment. When environmental change occurs Called a stimulus Homeostatic Mechanisms 3 NECESSARY COMPONENTS 1. Receptor Receives the stimulus Transmits stimulus to control center 2. Control Center Directs or controls Receives and processes the information supplied by the receptor Also called the Integration Center 3. Effector Bodily response Causes an effect to happen that opposes the change In certain situations can enhance the change Receptor (Nerve Endings) Control Center (Brain) Effector (Muscle) 3
Effectors Cells that produce an action Do Something upon nerve stimulation a. Muscle Cells Skeletal Cardiac Smooth b. Glandular Cells Homeostatic Regulation Teacher asks a question in class Ears are receptors Brain is control center Effectors are muscles that control mouth & pharynx Action is muscle contraction to answer question. 4
Cellular Structure of the Nervous System 2 Principal Types of Cells Neurons Transmit nerve impulses Neuroglia Support Cells Neuron Classification Identified by direction the impulse travels Sensory (Afferent) Bring impulses in to CNS Motor (Efferent) Take impulses out of CNS 5
Neuroglia Nerve Glue Functions Support Neurons & Bind them to other tissues Supply nutrients & O2 to neurons Assists when neurons injured Different types in CNS vs PNS Neuroglial Cells in CNS 4 Types Astrocytes Astro means star "Blood Brain Barrier" Oligodendrocytes Oligo means few Dendro tree-like Myelinate "insulate" neuron cytoplasm extensions. Microglia Phagocytes Help fight infection Ependymal cells Assist with CSF circulation 6
Neuroglial Cells in PNS Schwann cells Myelinate the cytoplasm extensions Many Schwann cells per nerve fiber Neuron 3 Major Structures Cell Body Enlarged area Contains nucleus, organelles, part of cytoplasm Dendrites Receive & transmit impulses to cell body Dendron = Many tiny branches Axons (Nerve Fiber) Generate & transmit nerve impulse away from cell body To muscles, glands & other neurons Only one process End is called axon terminal 7
Myelin Sheath Lipid-like covering of some axons. Functions to; Insulate fibers Speeds nerve impulse transmission Axons appear white because sheath is made of Fat. Formed by Plasma Membrane of some neuroglia Schwann Cell wraps around axon to form 2 layers. Jelly Roll Wrap 1. Inner layer is myelin sheath Mainly plasma membrane 2. Outer layer is Neurilemma Squeezed plasma membrane & nucleus of the Schwann cell. Assists in healing of peripheral nerves Myelin Sheath of PNS 8
CNS Myelin Sheath Oligodendrocytes One cell wraps many fibers Do not have neurilemma effect Do not help in healing of injured axons Nodes of Ranvier Nodes of Ranvier Gaps or indentations between Schwann cells. Impulse jumps or leaps across nodes. Speeds transmission of impulse. 9
Synapse Small fluid-filled space between 2 neurons or between a neuron & its target Effector cell Nerve impulse must travel across this space. Neurotransmitters Chemical messenger released at synapse for communication Electrical events trigger its release from synaptic vesicles. Chemical crosses synapse & binds to certain receptor sites. To generate next electrical impulse 10
Meninges of Brain & Spinal Cord 3 Connective Tissue Membranes Cover & protect brain & spinal cord Dural Mater Arachnoid Mater Pia Mater Meninges 11
Meninges of Brain & Spinal Cord Dura Mater Outer layer Fibrous Connective Tissue Hard or Tough mother Arachnoid Mater Middle layer Delicate & spider-web like Spider mother Spinal fluid circulates in space below Subarachnoid Space Meninges of Brain & Spinal Cord Pia Mater Innermost delicate layer Little or Tender Mother Clings tightly to surface of brain & spinal cord Contains blood vessels & lymphatics Nourish outer brain Leptomeninges Term for arachnoid & pia mater Due to thinness & delicacy 12
Cerebrospinal Fluid (CSF) Colorless fluid Contains proteins, glucose, urea, salts, & some WBCs Circulates around spinal cord & through ventricles of brain Provides nutritive substances to the CNS & cushions it Ventricles of the Brain Total of 4 Ventricles Contain CSF Connect with each other thru canals & foramens 2 Lateral Ventricles Ram horn shaped 3 rd Ventricle 4 th Ventricle 13