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Chapter 13-14.docx

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University of Toronto Scarborough
Biological Sciences
Ted Petit

Chapter 13/14 The Brain and Cranial Nerves • Major Parts of the Brain - Cerebrum 1. two cerebral hemispheres - Diencephalon 1. thalamus 2. hypothalamus 3. epithalamus - Brain stem 1. midbrain 2. pons 3. medulla oblongata - Cerebellum 1. two cerebellar hemispheres • Protection and Coverings - Cranial meninges 1. continuous with the spinal meninges, same basic parts a. dura mater 1) tough outer layer 2) dense irregular CT 3) forms sac from foramen magnum to second sacral vertebra b. arachnoid mater 1) middle layer 2) collagen and elastin fibers 3) subdural space is between dura mater and arachnoid mater, contains a little fluid c. pia mater 1) inner layer 2) delicate CT covering spinal cord 3) subarachnoid space is between arachnoid mater and pia mater, contains cerebrospinal fluid 4) extended thickened portions called denticulate ligaments fuse with arachnoid mater and dura mater to hold cord in place 2. dura mater has 2 layers in cranial meninges a. periosteal layer (outer) 1) periosteum of cranial bones b. meningeal layer (inner) 1) corresponds to spinal dura mater c. between layers are dural sinuses d. extensions of dura mater separate parts of the brain 1) falx cerebri- between cerebral hemispheres 2) falx cerebelli- between cerebellar hemispheres 3) tentorium cerebelli- between cerebrum and cerebellum - Cerebrospinal fluid (CSF) 1. similar to plasma 2. circulates through subarachnoid space 3. functions a. cushions CNS b. maintained at optimal chemical levels (ions, nutrients, etc.) 4. the ventricles are cavities within the brain that contain CSF a. all ventricles are interconnected to one another, the subarachnoid space, and the central canal of the spinal cord b. lined with ependymal cells c. four ventricles 1) two lateral- each within a cerebral hemisphere, separated by a thin membrane called septum pellucidum 2) third ventricle- between the lateral ventricles, connected to lateral ventricles by interventricular foramina (foramina of Monro) 3) fourth ventricle- between brain stem and cerebellum, connected to third ventricle by cerebral aqueduct 5. CSF formed at choroid plexuses a. capillaries covered by ependymal cells, in all ventricles 6. CSF reabsorbed into venous circulation a. through arachnoid villi (extensions of arachnoid mater projecting into dural sinuses) 7. circulation of CSF - Blood-brain barrier 1. brain capillary cells are joined by tight junctions 2. only things that can get through the lipid bilayer of capillary cells can pass easily (e.g.2 O , CO 2, and some things are specially transported (glucose, amino acids) 3. protects brain from harmful substances • Cerebrum - Gyri are the ridges - Sulci are the grooves (deepest grooves called fissures) - Paired lobes (frontal, parietal, temporal, occipital) - Made up of... 1. gray matter (cortex) a. allows us to perceive, understand, communicate, remember, do voluntary movements b. divided into many "functional areas" (but there is lots of overlap, and no one area acts alone) c. three major kinds of functional areas 1) motor areas- control voluntary motor function 2) sensory areas- conscious awareness of sensation 3) association areas- integrate diverse information d. each hemisphere specializes in functions on the opposite side of the body (contralateral) e. hemispheres not equal in function 1) left side generally more involved in logical, analytical tasks like language and math 2) right side generally more involved in spatial perception, art, music 2. white matter a. provides for communication between all areas of CNS and PNS b. three main types of fibers 1) association fibers- transmit signals between gyri in the same hemisphere 2) commissural fibers- transmit signals from gyri in one hemisphere to the corresponding gyri in the other hemisphere (corpus callosum, anterior and posterior commissures) 3) projection fibers- form ascending and descending tracts, transmit signals from cerebrum and other parts of brain to and from spinal cord 3. basal nuclei (basal ganglia) a. groups of gray matter embedded in white matter
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