Transcript Chapter 13
Central Nervous System Chapter 13 – Lecture Notes to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora 1 Chapter Overview 13.1 Central Nervous System 13.2 Protection and Nourishment of the CNS 13.3 Cerebrum 13.4 Limbic System 13.5 Signal Processing in the Cerebrum 13.6 Diencephalon 13.7 Brain Stem 13.8 Cerebellum 13.9 Spinal Cord 13.10 Propagation of Impulses 2 Essential Terms Central Nervous System (CNS) brain and spinal cord control center for thoughts emotions creativity wisdom memories activities behaviors Tract bundle of axons 3 Introduction CNS made up of ~100 billion neurons Adult brain mass of ~1300g (3 lbs) Spinal cord mediates rapid reactions reflexes pathway for sensory nerve impulses to brain pathway for motor nerve impulses from brain 4 Concept 13.1 Central Nervous System 5 CNS Brain cerebrum 1. – 2. 3. 4. cerebral hemispheres diencephalon brain stem cerebellum Spinal Cord medulla oblongata to superior edge of L2 Protection of CNS two types of connective tissues bony skull cranial and spinal meninges cushion of cerebrospinal fluid 6 Figure 13.1a 7 Figure 13.1c 8 Figure 13.2 9 Skeletal Protection Brain is located in cranial cavity of skull Spinal cord is located within vertebral canal of vertebral column vertebral foramina of vertebrae stacked one on top of one another form the vertebral canal 10 Meninges three connective tissue coverings that encircle brain and spinal cord cranial meninges spinal meninges superficial to deep dura mater arachnoid mater pia mater 11 Figure 13.3a 12 Figure 13.4a 13 Dura Mater of Brain most superficial adheres to periosteum of cranial bones strongest menix extensions separate portions of brain falx cerebri two hemispheres of cerebrum falx cerebelli two hemispheres of cerebellum tentorium cerebelli separates cerebrum from cerebellum 14 Dura Mater of Spinal Cord between dura mater and all of vertebral canal epidural space cushion of fat dura mater tissue sinuses that act as collection points for interstitial fluid and blood leaving brain return interstitial fluid and blood to internal jugular veins of neck 15 Arachnoid Mater avascular collagen fibers some elastic fibers surrounds both brain and spinal cord subdural space thin space between dura mater and arachnoid matter contains interstitial fluid 16 Pia Mater innermost membrane tightly adheres to surface of CNS interlacing bundles of collagen fibers some fine elastic fibers surrounds both brain and spinal cord subarachnoid space thin space between arachnoid mater and pia matter contains cerebrospinal fluid also covers surface blood vessels of CNS 17 Meninges and Spinal Nerves All three cover spinal nerves up to point of exit from spinal column through intervertebral foramina 18 Denticulate Ligaments suspend spinal cord in middle of dural sheath membranous extensions of pia mater project laterally and fuse with arachnoid mater and inner surface of dura mater between anterior and posterior nerve roots of spinal nerves on either side protect spinal cord against shock and sudden displacement 19 Concept 13.2 Nourishment and Protection 20 Blood Flow to CNS to brain via internal carotid and vertebral arteries flows into dural sinuses empties into internal jugular veins to spinal cord via posterior intercostal and lumbar arteries empties into posterior intercostal and lumbar veins 21 Figure 20.20c 22 Figure 20.20d 23 Blood Flow to Brain Brain at rest uses 20% of oxygen and glucose even though only 2% of mass of adult Neurons synthesize ATP almost exclusively from glucose when activity increases in a particular region, blood flow to that area also increases 24 Blood Flow to Brain decreased blood flow to brain short time can cause unconsciousness 1 to 2 minutes impairs neuronal function 4 minutes causes permanent injury virtually no glucose stored in the brain low blood glucose to brain can cause mental confusion dizziness convulsions loss of consciousness 25 Blood Flow to Brain Blocked blood flow to brain arterial blockage can damage brain CVA cerebrovascular accident stroke most common brain disorder affect 500,000 people per year in US 1/3 leading cause of death 26 Blood Brain Barrier Physiology protects CNS from harmful substances pathogens prevents passage from blood into interstitial fluid of neural tissue water soluble substances usually pass by active transport others pass slowly lipid soluble substances pass readily 27 Blood Brain Barrier Anatomy cerebral arteries divide quickly into capillaries tight junctions seal together endothelial cells of CNS capillaries capillaries also surrounded by thick basement membrane astrocyte processes press against capillaries selectively pass some substances and inhibit others 28 Cerebrospinal Fluid (CSF) 80-150 ml volume clear colorless liquid protects and nourishes brain & spinal cord protects nourishes by carrying against chemical and physical injuries acting as shock absorber on which brain floats oxygen glucose other chemicals continuously circulates through cavities in and around CNS in subarachnoid space 29 Cerebrospinal Fluid (CSF) Contributes to homeostasis in three ways: 1. mechanical protection 1. 2. 3. shock absorber chemical protection circulation 30 Figure 13.5a 31 Formation of CSF CSF fills ventricles lateral ventricles located in each hemisphere of cerebrum separated by septum pellucidum third ventricle fourth ventricle CSF produced in choroid plexuses capillaries in walls of ventricles covered by ependymal cells that form CSF from blood plasma by filtration and secretion 32 Circulation of CSF Cilia on ependymal cells assist with flow from lateral ventricles through interventricular foramina to third ventricle then through cerebral aqueduct into fourth ventricle enters subarachnoid space through median aperture pair of lateral apertures reabsorbed into blood arachnoid villi 33 Figure 13.6a 34 Figure 13.3a 35 Figure 13.6c 36 Concept 13.3 Cerebrum 37 Cerebrum Seat of intelligence interprets sensory impulses controls muscular movements functions in emotional and intellectual processes Cerebral Cortex gray matter on outside White matter on inside receives & integrates incoming & outgoing information white is myelination Gray matter nuclei deep within white matter 38 Cerebral Cortex enlarges faster during embryonic development than white matter rolls and folds forming gyri (singular = gyrus) bulges or folds fissures deep grooves longitudinal fissure separates cerebrum into left and right hemispheres connected internally by corpus callosum sulci (singular = sulcus) shallow fissures 39 Figure 13.7a 40 Figure 13.7b 41 Figure 13.7c 42 Cerebral White Matter has tracts myelinated and unmyelinated axons communicate between regions of CNS three types association tracts 1. • between gyri in same hemisphere commissural tracts 2. • from gyri in one hemisphere to corresponding gyri in other hemisphere projection tracts 3. • from cerebrum to lower parts of CNS 43 Basal Nuclei mass of cell bodies two are side by side just lateral to thalamus globus pallidus and putamen third is caudate nucleus large “head” connected to smaller “tail” by long comma-shaped “body” receive input from cerebral cortex provide output to motor portions control subconscious contractions of skeletal muscles 44 Table 13.2 part 1 45 Table 13.2 part 2 46 Table 13.2 part 3 47 Table 13.2 part 4 48 Table 13.2 part 5 49 Concept 13.4 Limbic System 50 Limbic System controls emotion, behavior, and memory encircles upper part of brain stem and corpus callosum ring of structures on inner border of cerebrum and floor of diencephalon controls most involuntary aspects of behavior related to survival intense pain extreme pleasure anger/rage affection recognition of fear 51 Concept 13.5 Functional Areas of Cerebrum 52 Functional Areas of Cerebrum Sensory areas receive sensory impulses Motor areas initiate movements Association areas complex integrative functions memory emotions reasoning will judgment personality traits intelligence 53 Figure 13.10 54 Sensory Areas Posterior half of both hemispheres behind central sulci most direct connections with peripheral sensory receptors primary somatosensory area receives impulses for touch, proprioception, pain, itching, tickle, thermal sensations localize exactly the points where sensations originate primary visual area receives impulses for vision eye to thalamus to primary visual area shape, color, movement of visual stimuli 55 Sensory Areas primary auditory area receives impulses for basic characteristics of sound pitch and rhythm primary gustatory area receives impulses for taste primary olfactory area receives impulses for smell 56