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PSYB64H3 (201)
Chapter 2

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Zachariah Campbell

PSYB64Chapter 2 The Anatomy and Evolution of the Nervous System Anatomical Directions and Planes of SectionThe following are for 4 legged animals the neuraxis forms a straight line running parallel to the groundrostral or anteriorstructures that are located toward the head end of the animal o ex Head of the dog is rostral to its shoulderscaudal or posteriorstructures located toward the tail end of the animal o ex The dogs ears are caudal to its nose and its hips are caudal to its shouldersinferior or ventralstructures located toward the belly sidesuperior of dorsalstructures towards the backthe dorsal parts of the animals brain are in line with the dorsal parts of the spinal cord for people the directions are different because our 2 legged stance puts a 90 degree bend in the neuraxis an imaginary line that runs the length of the spinal cord through the brainin humans the dorsal parts of our brain form a 90 degree angle with the dorsal parts of the spinal cordmidlinean imaginary line that divides us into approximately equal havesipsilateralstructures are both on the same side of the midline ex Left arm and left leg are ipsilateralcontralateralstructures are on opposite sides of the midline ex Left arm and right leg are contralateralmedialstructures close to the midline ex Heart is medial to armslateralstructures to the side of the midline ex Ears are lateral to noseproximalclose to the center ex Shoulders are proximal relative to elbowsdistalfar from the center ex Toes are distal relative to knees there are 3 major planes of sectiono coronalfrontal sections divide nervous system from front to back ex Looking at brain in the faceo sagittalparallel to the midline allow us to see a side view of the brain structures o horizontal or axialdivides the brain from top to bottomProtecting and Supplyingthe bony skull protects from all but the most serious blowsthe skull bones are not fully mature in infants they are born with skull bones that can overlap each other somewhat like the tectonic plates of the Earth o this aids the movement of the babys head through the birth canal o takes about 18 months for the human skull to fuse completelyMeningesthese are layers of membranes that surround the nervous system and aid in protectionthe 3 layers are o dura materhard mother outermost layer composed of leather like tissue that follows the outlines of the skull bones o arachnoid layerbelow the dura mater delicate layer that looks like a spiders web o pia materpious mother nearly transparent membrane that sticks closely to outside of brainbetween arachnoid and pia mater layers is the subarachnoid spaceall 3 layers cover the brain and spinal cord BUT ONLY DURA MATER AND PIA MATER COVER NERVES THAT EXIT THE BRAIN peripheral nervous systemmeningitiscondition in which the meninges get infected o it could be lifethreateningwhen tumors arise in the tissue of the meninges they are referred to as meningiomasCerebrospinal Fluid CSFCSF is secreted within hollow spaces in the brain called ventriclesWithin the lining of the ventricles the choroid plexus coverts material from the nearby blood supply into CSFCSF is similar in composition to blood plasma and because of its weight and composition it essential floats in the brain within the skull This has advantages o If you bump your head the fluid acts like a cushion to soften the blow o Neurons respond to appropriate input not to pressure on the brain Pressure can often cause neurons to fire in maladaptive ways such as when a tumor causes seizures by pressing down on a part of the brain o The CSF prevents neurons from responding to pressure and providing false infoCSF circulates through the central canal of the spinal cord and the 4 ventricles in the brain two rdthlateral one in each hemisphere and 3 and 4 in the brain stem th The 4 ventricle is continuous with the central canal of the spinal cord which runs the length of the cord at its midline th Below the 4 ventricle there is a small opening that allows the CSF to flow into the subarachnoid space that surrounds both the brain and the spinal cordNew CSF is made constantly with the entire supply being turned over about 3 times per day and the old CSF is reabsorbed into the blood supply at the top of the headBlockages can occur in the narrow sections of the circulation system of CSF and this is known and hydrocephalusHydrocephalus means water on the brainLeft untreated it can cause mental retardation as the large amount of CSF prevents the normal growth of the brainIt can be treated by installing a shunt to drain off excess fluid and surgery can be used to repair the obstruction in the baby when it is olderCSF is a separate circulation system that NEVER HAS direct contact with the blood supplyIn a spinal tap procedure the physician withdraws some fluid from the subarachnoid space through a needle because the composition of CSF is important for diagnosing some diseasesBlood SupplyBrain receives its nutrients from the carotid arteries on either side of the neck and through the vertebral arteries that travel up through the back of the skullonce inside the skull these major arteries brain to form the anterior middle and posterior cerebral arteries which serve most the brainany interruption of blood supply produces damage very quickly because the brain doesnt store energy
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