Download Nervous System

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PT 2
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The nervous system has been compared with
a computer system, with the brain acting as
the central processing unit, relaying
messages by way of the spinal cord through
nerve fibers
◦ Nerves radiate to every structure in the body to
provide connection for input and output data
 Myelinated nerves – have a coat of white fatty material,
interrupted along the length of the nerve at regularly
spaced intervals -found mostly in the CNS
 Nonmyelinated nerves – have a thin coat of myelin –
found in the autonomic nervous system
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Normally, impulses pass in only one direction.
◦ Sensory neurons conduct impulses from the sense
organs to the spinal cord and brain
◦ Motor neurons conduct impulses from the brain and
spinal cord to muscles and glands
◦ Interneurons are responsible for delivering a signal from
one neuron to another
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The point at which an impulse is transmitted
from the axon of one neuron to the dendrite of
another is a microscopic space called a synapse.
 Myelinated nerves have a faster signal than nonmyelinated
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There is no physical contact of neurons in the
synapse.
◦ The electrical impulses from one neuron to the next
neuron do not directly jump the synapse but
instead cause release of a chemical at the synapse.
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Neurons are so specialized that they have lost
the power to produce new cells.
◦ When an axon is severed, that part distal to the cell
body dies.
 Once a connection is broken within the CNS, it is
broken forever.
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The CNS includes the brain and spinal cord
◦ Each are protected from injury by the skeletal
system
 Brain – skull
 Spinal Cord – vertebrae
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The CNS contains both white and grey matter
◦ White color is created by myelinated fibers formed
by the bundles of axons and dendrites
◦ Gray color is created by the masses of nerve cells
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The meninges are three membranes that
envelop the CNS, separating the brain and
spinal cord from the body cavities.
◦ Dura matter
 Outermost layer, hardest, toughest, most fibrous
◦ Arachnoid
 Middle membrane, less dense, web like in appearance
◦ Pia matter
 Innermost, thin, compact, very vascular
 Supplies blood for the CNS tissue
**Inflammation of the meninges is called
meningitis
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The brain contains about 100 billion neurons.
The brain in the dog and cat is a highly
evolved structure but is less well developed
than in more specialized mammals, such as
primates.
◦ The brain of a canine is more immature than the
human brain at birth, but maturation of cerebral
function proceeds at a higher rate.
 A 1 month old puppy has near adult development of
the CNS
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The brain is divided into
◦ Forebrain
 Motor area
 Controls gross, fine, and complicated muscle movements
 Collects, recognizes, and organizes sensations of pain,
temperature, touch, position, and movement
◦ Midbrain
 Located between the forebrain and hindbrain
 Contains auditory, visual, and muscle control centers and is
involved in body posture and equilibrium
◦ Hindbrain
 Reflex centers for controlling respiration and circulation
 Damage to this area instantly causes death