The Nervous System PDF

The Nervous system is: The organized network of nerve tissue in the body. It includes the central nervous system (the brain and spinal cord), the peripheral nervous system (nerves that extend from the spinal cord to the rest of the body), and other nerve tissue.  FOUR PRIMARY FUNCTIONS OF...

The Nervous system is: The organized network of nerve tissue in the body. It includes the central nervous system (the brain and spinal cord), the peripheral nervous system (nerves that extend from the spinal cord to the rest of the body), and other nerve tissue.  FOUR PRIMARY FUNCTIONS OF NERVOUS SYSTEM 1. Sensing the world  Vision, Hearing, Smell, Taste, Touch 2. Transmitting information 3. Processing information 4. Producing a response  The functional unit of the nervous system is the nerve cell ”NEURON”  Theysend electrochemical messages around the body  Glialcells provide support and protection for neurons Parts of a neuron Nerve Cell  Parts of nerve cell  Dendrites: receive chemical signals from neighboring cells.  Cell Body: contains the nucleus & organelles  Axon: long extension that carries electrical messages away from the body to the terminal axons  Terminal Axons: passes the signal to the next cell.  Myelin sheath: Protective covering for axon  Types of Neurons 3 main types of neurons: Sensory neuron = detect stimuli Interneurons = relay sensory signals to the brain and then return messages back to motor neurons. Motor neuron = pass message from the brain to rest of body for muscle response  Reflex “ what happens when you step on a nail”?  Reflexes are automatic  The Stimulus (nail ) is received by the sensory neurons in the foot  This info travels to the spine, where the interneuron is triggered  The interneuron transmits the signal to the brain (through the spinal cord)and carries the message back and stimulates the motor neuron, to move the foot  Nervous System Has two main divisions 1. Central Nervous System ( CNS) brain, spinal cord 2. Peripheral Nervous System ( PNS) all other nerves  2 MAIN DIVISIONS: Central Nervous System (CNS) Receives, interprets, and sends signals to the Peripheral Nervous System (PNS) Has 2 main parts:  Brain – main control center  Spinal Cord – connects and relays nerve impulses to the brain  PERIPHERAL NERVOUS SYSTEM (PNS)  Connects Central Nervous System (CNS) to all organ systems  Made up of:  Sensory Neurons: detect stimuli  Motor Neurons: carry signal to stimulate response  2 major subsystems:  Somatic – voluntary movement (balance, movement)  Autonomic – involuntary movement (digestion, fight or flight)  Parts of the Nervous System  Central  Peripheral Nervous  Autonomic System Sympathetic  Brain  Fight or Flight Cerebrum Parasympathetic Cerebellum  Relaxation Brain Stem and  Somatic Pons Sensory and Motor Lobes (4) Nerves  Spinal Cord Reflex Arc “information superhighway”  Smaller part of the brain ,towards the back FUNCTIONS: Coordinates all movement Helps maintain posture, muscle control, and balance  Large front part of the brain FUNCTIONS:  Voluntary activity  Memory  Language  Receives and responds to sensory signals  Controls motor functions  Top layer of the brain Stores: experiences and/or learning  PONS BRAIN STEM  Breathing  swallowing, coughing,  Heart rate sneezing, and  Internal Organs vomiting  Includesthe Medulla Oblongata Damage in this area will usually kill you. Medulla  “controls: emotions and memories” Damage to these areas can lead to amnesia or emotional disturbances Which explains why a central cord injury affects the upper extremities more than the lower extremities  Intersegmental tracts: These tracts communicate the spinal cord parts together: 1- dorso-lateral tract lies between the tip of the posterior horn and the surface of the spinal cord. 2-Fasciculus proprius is around the gray matter of the spinal cord. ** A complete spinal cord injury causes permanent damage to the area of the spinal cord that is affected. Paraplegia or tetraplegia is the result of complete spinal cord injuries. ** An incomplete spinal cord injury refers to partial damage to the spinal cord.  Blood Vessels There are three main types of blood vessels:  Arteries  Veins  Capillaries  Arteries  Carry blood away from the heart  Thick muscular walls  Lots of elastic tissue in the wall  Relatively small lumen  Blood under high pressure  Blood flow rapid  Blood flows in pulses  No valves Veins  Carry blood back to the heart  Thin muscular walls  Little elastic tissue in the wall  Relatively large lumen  Blood under low pressure  Blood flow is slow  No pulse  Valves prevent backflow of blood  Capillaries  Link up arteries and veins in the tissues  No muscle  Wall made up of one cell thick endothelium  Pressure falls as blood passes along capillary  Blood flowing is slowing down  No pulse  No valves Small  lumen - just large enough for a red blood cell to squeeze through  Role of the kidney in regulating blood pressure: Healthy kidneys respond to a hormone called aldosterone which is produced in the adrenal glands, to help the body regulate blood pressure. Kidney damage and uncontrolled high blood pressure contribute to a negative spiral. As more arteries become blocked and stop functioning, the kidneys eventually fail. Blood is fluid that transports oxygen and nutrients to the cells and carries away carbon dioxide and other waste products, consisting of plasma, and The formed elements (blood cells, and platelets). Technically, blood is a transport liquid pumped by the heart to all body parts, after which it is returned to the heart to repeat the process.  Is specialized fluid of connective tissue Contains cells suspended in a fluid matrix  Functions of Blood 1. Transport of dissolved substances 2. Regulation of pH and ions 3. Restriction of fluid losses at injury sites 4. Defense against toxins and pathogens 5. Stabilization of body temperature  Physical Characteristics of Blood  Color range : - Oxygen-rich blood is scarlet red - Oxygen-poor blood is dull red  pH must remain between 7.35–7.45 ( Slightly alkaline )  Blood temperature is slightly higher than body temperature  5-6 Liters or about 6 quarts /body  Blood Plasma Composed of approximately 90 percent water Includes many dissolved substances –Nutrients, Salts (metal ions) –Respiratory gases –Hormones –Proteins, Waste products  Plasma Proteins Albumin – regulates osmotic pressure Clotting proteins – help to stem blood loss when a blood vessel is injured Albumins (60%) Globulins (35%) Antibodies –protect the body from antigens Fibrinogen (4%)  The formed elements The three classes of formed elements are the erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).  Erythrocytes (Red Blood Cells) The main function is to carry oxygen Anatomy of circulating erythrocytes Biconcave disks Essentially bags of hemoglobin Anucleate (no nucleus) Contain very few organelles  Hemoglo bin Iron-containing protein Binds strongly, but reversibly, to oxygen Each hemoglobin molecule has four oxygen binding sites Each erythrocyte has 250 million hemoglobin molecules  Leukocytes (White blood cells) Crucial in the body’s defense against disease These are complete cells, with a nucleus and organelles Able to move into and out of blood vessels (diapedesis) Can respond to chemicals released by damaged tissues.  Leukocyte Levels in the Blood Normal levels =4,000 to 11,000 cells/ml Abnormal leukocyte levels Leukocytosis Above 11,000 leukocytes/ml Generally indicates an infection Leukopenia Abnormally low leukocyte levels Commonly caused by certain drugs  Types of Leukocytes Granulocytes  Granules in their cytoplasm can be stained  Include neutrophils, eosinophils, and basophils  Granulocytes  Neutrophils  Multilobed nucleus with fine granules Basophils Act as phagocytes at active sites of infection Have histamine-containing gran  Initiate inflammation Eosinophils Large brick-red cytoplasmic granules Found in response to allergies and parasitic worms  Agranulocy tes Lymphocytes The nucleus fills most of the cell Play an important role in the immune response Monocytes The largest of the white blood cells Function as macrophages Important in fighting chronic infection  Hematopoiesis – Blood Cell Formation Occurs in red bone marrow All blood cells are derived from a common stem cell (hemocytoblast)