 PT PT  PT 2 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