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PT PT 2 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 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 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 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. 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. The CNS includes the brain and spinal cord ◦ Each are protected from injury by the skeletal system Brain – skull Spinal Cord – vertebrae 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 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 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 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