Transcript THE_NERVOUS_SYSTEM_(Part_I)

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 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:
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 3rd and 4th
lumbar vertebrae
CSF is examined for color,
blood cells, bacteria,
malignant cells, and
glucose
To Be Continued