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PSYB64H3 (197)
Chapter 2

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University of Toronto Scarborough
Janelle Leboutillier

2 | The Anatomy and Evolution of the Nervous System Anatomical Directions and Planes of Section - rostral/anterior: toward the head end of the animal - caudal/posterior: located toward the tail end of the animal - ventral/inferior: located toward the belly side - dorsal/superior: located toward the back - anatomical terms relative to another place e.g., dogs ears caudal to its nose but rostral to its shoulders - figure 2.1, p. 28 anatomical direction differ in ppl vs. animals on four legs neuraxis: imaginary line that runs length of spinal cord to front of the brain four legged animal = parallel to the floor (straight neuraxis), dorsal parts of the brain same as dorsal parts of the spinal cord two stance = 90 degree angle on neuraxis at the brain, making dorsal parts of the brain at a 90 degree angle to the dorsal parts of the spinal cord - midline: imaginary line that divides us into approximately equal halves - ipsilateral: structures are on same side of the midline - contralateral: if structures are opposite sides of midline - medial: structures close to midline - lateral: structures to side of midline - proximal: close to the centre - distal: far away from the centre - proximal and distal usually use to refer to limbs - figure 2.2, p. 29 1. coronal sections (aka frontal sections): divide brain from front to back 2. sagittal sections: parallel to midline, showing side view of brain structures section that divides brain into two approximately equal halves midsagittal section 3. horizontal (aka axial) section: divides brain from top to bottom Protecting and Supplying the Nervous System Meninges - layers of membranes covering central nervous system and peripheral nerves - figure 2.3, p. 30 three layers of meninges dura mater (hard mother in latin): outermost layer; both in central and peripheral nervous system arachnoid layer: below dura mater, more delicate layer; named because of spiders web structure pia mater: inner most layer; nearly transparent, sticks to outside of brain between pia and arachnoid layer subarachnoid space - meningitis: when meninges become infected - meningiomas: tumor arises in tissue of meninges Cerebrospinal Fluid - CSF: secreted w/in hollow spaces in brain known as ventricles - w/in lining of ventricles choroid plexus = converts material from nearby blood supply into CSF - similar composition to clear plasma of blood - floats brain into the skull provides cushion to soften blow to the brain if you bump your head neurons respond to appropriate input, not pressure on brain pressure often causes them to fire in maladaptive ways (i.e., tumour pressing on part of the brain = seizures) floating brain = prevents neurons from responding to pressure and false info from it - circulates through central canal of spinal cord and our ventricles in brain figure 2.5, p. 31 two lateral ventricles in each hemisphere third and fourth in brainstem fourth is continuous w/ central canal of spinal cord below fourth, small opening allows CSF to flow into subarachnoid space and spinal cord - new CSF made constantly, about three times a day - old CSF reabsorbed into blood supply at top of head - figure 2.6, p. 32 hydrocephalus = water in the brain, blockage in the circulation system - CSF has completely self-contained, separate circulation system no direct contact w/ blood supply Blood Supply - receives nutrients through carotid arteries (either side of neck) and through vertebral arteries (Travel up through back of skull) - figure 2.7, p.32 branch to form anterior, middle, and posterior cerebral arteries - brain unable to store energy = interruption of blood supply = damage quickly other structures not affected quickly life support for other organs can continue indefinitely The Central Nervous System - (CNS): includes brain and spinal cord tissue encased in bone covered by three layers of membranes cerebrospinal fluid circulates w/in layers covering CNS, not PNS damage = considered permanent - peripheral nervous system (PNS): contains all nerves that exit brain and spinal cord carries sensory and motor mssgs to and from other parts of body tissue isnt encased in bone cover by two layers of membrane damage = recovery can occur - figure 2.8, p. 33 general organization of CNS and PNS The Spinal Cord- long cylinder of nervous tissue; extends from medulla to fist lumbar vertebra (or vertebral column: bones of spinal column that protect and enclose spinal cord) - neurons making up spinal cord found in upper two third of vertebral column - shorter than vertebral column (stops growing before bones in vertebral column) - centre of spinal cord central canal - figure 2.9, p. 34 spinal cords exit between bones bones cushioned from one another by disks 31 segments (based on point of exit of nerve) 8 cervical nerves: head, neck, and arms 12 thoracic nerves: most of torso 5 lumbar nerves: lower back and legs 5 sacral nerves: back of legs and genitals 1 coccygeal nerve: *discussed in ch7 - white matter: made up of axons (parts of neurons that carry signals to other neurons) white because of myelin that covers axons responsible of carrying info to and from the brain sensory neurons travel up dorsal parts of spinal cord motor neurons travel up ventral parts of spinal cord - gray matter: consists areas primarily of cell bodies gray because cells absorb chemicals that preserve the tissue = staining the
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