THE NERVOUS SYSTEM (Part 1)

Central Nervous System Communication and coordination system of the body Seat of intellect and reasoning Consists of the brain, spinal cord, and nerves

Neurons (Nerve Cell) Transmits a message from one cell to another Has cell body with cytoplasm Nucleus inside the cell body Dendrites – nerve cell process that carry impulse to cell body (may be one or many)

Neurons (continued) Axons carry impulses away from cell body Only one axon on each neuron

Neurilemma (Myelin Sheath) Covering that speeds up the nerve impulse along the axon Myelin is a fatty substance that protects the axon Myelin is called white matter

Multiple Sclerosis (MS) Immune cells attack myelin sheath of axon – myelin sheath destroyed, leaving scar tissue on nerve cells. Transmission of nerve impulses blocked Cause – unknown

Neuroglia Nerve tissue made up of neurons and neuroglia Neuroglia (nerve glue) – both myelinated and unmyelinated Make up about half of the bulk of the brain

Neuroglia Cells that insulate, support, and protect the neurons Glioma – one of the most common types of brain tumor

White and Gray Matter Brain is composed of white and gray matter. White matter from the myelin sheath and gray matter is from the neuroglia cells Cerebral cortex (outer layer) is gray, highest center of reasoning and intellect

Types of Neurons Afferent (Sensory) neurons emerge from the skin or sense organs and carry messages from all parts of the body to the brain and spinal cord Efferent (Motor) neurons carry messages from the brain and spinal cord to muscles and glands

Types of Neurons (continued) Interneurons (Associative) - carry impulses from sensory neurons to motor neurons Synapse – space between neurons, messages go from one cell to the next

Divisions of the Nervous System Central Nervous System (CNS) – consists of brain and spinal cord Peripheral Nervous System (PNS) – cranial and spinal nerves

Divisions of Nervous System (continued) Autonomic Nervous System - includes peripheral nerves and ganglia, supplies heart muscle, smooth muscle and secretory glands – controls involuntary body functions

The Brain 3 pounds mass of soft nervous tissue 100 billion neurons Composed of white and gray matter Adequate blood supply is needed, brain tissue will die in 4-8 minutes without oxygen

Coverings of the Brain Protected by the skull, cerebrospinal fluid, and three membranes called meninges. DURA MATER – outer brain covering, lines the inside of the skull, tough dense fibrous connective tissue

Coverings of the Brain (continued) ARACHNOID – middle layer of meninges that resembles fine cobweb. PIA MATER – covers the brain’s surface, comprised of blood vessels held together by connective tissue “The meninges PAD the brain” Pia; Arachnoid; Dura

Cerebrospinal Fluid Space between arachnoid and pia mater is filled with CEREBROSPINAL FLUID (CSF) Acts as a shock absorber and source of nutrients for the brain and spinal cord Is a clear, colorless fluid

Ventricles of the Brain Brain has 4 cavities filled with CSF called CEREBRAL VENTRICLE 1. Have right and left ventricle 2. Third ventricle – behind and below the lateral ventricle 3. Fourth ventricle is below the 3 rd, in front of the cerebellum and behind the pons and medulla oblongata.

Ventricle of the Brain (continued) CSF is produced by a structure called the CHOROID PLEXUS. Choroid Plexus is a network of blood vessels lining the ventricles which helps in the formation of CSF

Blood-Brain Barrier (BBB) Choroid plexus capillaries prevent substances (like drugs) from penetrating brain tissues Blood born immune cells such as lymphocytes, monocytes, etc. can’t penetrate the barrier Makes infections, like meningitis, difficult to cure

Blood Brain Barrier (continued) BBB can be broken down by: Hypertension Not fully formed at birth Exposures to microwaves Radiaton Infections Trauma, Ischemia, Inflammation

Functions of the CSF 1. Protection – acts to cushion a blow to the head and lesson impact 2. Buoyancy – because brain is in fluid its net weight is reduced and pressure at the base of the brain is reduced 3. Excretion of waste products – one way flow to the blood takes potentially harmful drugs and other substances away from the brain. 4. Endocrine Medium – transports hormones to other parts of the brain.

Hydrocephalus CSF builds up within the ventricles May result from: 1. Overproduction of CSF 2. Obstruction within the ventricular system 3. Problems with CSF absorption

Meningitis Infection or inflammation of the meninges Caused by both bacteria and viral infections Symptoms – severe headache and stiff neck with pain Need to seek immediate medical attention

Meningitis Inflammation of cranial meninges spreads to spinal meninges, which leads to excess production of CSF, causing HA, reduced pulse, slow breathing, and partial or total unconsciousness

Lumbar Puncture AKA Spinal Tap is a diagnostic test for examination of CSF Removal of 5 to 20 ml of CSF from spinal canal Needle puncture is between the 3 rd and 4 th lumbar vertebrae CSF is examined for color, blood cells, bacteria, malignant cells, and glucose

To Be Continued