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 anotherHas cell body with cytoplasm Nucleus inside the cell bodyDendrites – 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 MatterBrain is composed of white and gray matter.White matter from the myelin sheath and gray matter is from the neuroglia cellsCerebral 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 Brain3 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 FluidSpace 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 cordIs 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 3rd, 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:HypertensionNot fully formed at birthExposures to microwavesRadiatonInfectionsTrauma, Ischemia, Inflammation

Functions of the CSF1. Protection – acts to cushion a blow to the head and lesson impact2. 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

MeningitisInflammation 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 PunctureAKA Spinal Tap is a diagnostic test for examination of CSF Removal of 5 to 20 ml of CSF from spinal canalNeedle puncture is between the 3rd and 4th lumbar vertebraeCSF is examined for color, blood cells, bacteria, malignant cells, and glucose

To Be Continued