Central Nervous System Notes
Central Nervous System Notes BIOL 214
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Date Created: 01/25/16
Central Nervous System Embrvonic Develoloment of the Brain 1 Earliest phase of development starts in the threeweekold embryo ectoderm thickens along the dorsal midline axis to form the neural plate 2 Neural plate invaginates forming a groove flanked by neural folds neural groove is CNS neural folds are PNS 3 Neural fold cells migrate to form the neural crest which will form much of the PNS and many other structures 4 Neural groove deepens and superior edges fuse forming the neural tube which will detach from the surface ectoderm and sink into a deeper position 5 As soon as the neural tube forms constrictions appear to mark off the three primary brain vesicles prosencephalon forebrain mesencephalon midbrain and rhombencephalon hindbrain 6 ln week 5 primary vesicles create secondary vesicles 1 Forebrain divides into the telencephalon endbrain and diencephalon interbrain 2 Hindbrain constricts to form the metencephalon afterbrain and the myelencephalon spinal brain 7 Telencephalon sprouts two lateral swellings that will become the two cerebral hemispheres 8 Diencephalon specializes to form the hypothalamus thalamus epithalamus and retina 9 Mesencephalon metencephalon and myelencephalon transform into the midbrain pons and cerebellum and the medulla oblongata 10 Cerebrum becomes lateral ventricles diencephalon becomes third ventricle brain stem becomes cerebral aqueduct hindbrain becomes fourth ventricle and spinal cord becomes central canal Regions and Organization Basic pattern consists of a central cavity surrounded by gray matter neuron cell bodies external to which is white matter myelinated fiber tracts Both the cerebral hemispheres and the cerebellum are covered in an outer bark of gray matter called the cortex 0 Cortex is not found in the brain stem mostly covered in white matter Ventricles Ventricles arise from expansions of the lumen cavity of the embryonic neural tube Hollow ventricular chambers are filled with cerebrospinal fluid and lined by ependymal cells Paired lateral ventricles are large Cshaped chambers that reflect the pattern of cerebral growth 0 Anteriorly they lie close together separated by a thin membrane known as the septum pellucidum Third ventricle is located in the diencephalon and communicates with the lateral ventricles via the interventricular foramen Fourth ventricle is continuous with the third ventricle via the cerebral aqueduct that moves through the midbrain 0 Three openings mark the walls of the fourth ventricle paired lateral apertures and a median aperture I These apertures connect the ventricles to the subarachnoid space a fluidfilled space surrounding the brain Cerebral Hemisoheres Form the superior part of the brain and account for 83 of total brain mass and are the most conspicuous parts of an intact brain Entire surface is marked by elevated ridges known as gyri and shallow grooves known as sulci o Deeper grooves are known as fissures and separate large regions of the brain I Longitudinal fissure separates the cerebral hemispheres I Transverse cerebral fissure separates the cerebral hemispheres from the cerebellum 0 Sulci divide each hemisphere into five lobes frontal parietal temporal occipital and insula I Central sulcus separates frontal from parietal I Bordering the central sulcus are the precentral gyrus and the postcentral gyrus I Parietooccipital sulcus separates parietal from occipital I Lateral sulcus separates parietal from frontal and outlines the flaplike temporal lobe I lnsula buried deep within the lateral sulcus and forms part of its floor Each cerebral hemisphere contains three basic regions 0 Superficial cortex of gray matter 0 Internal white matter 0 Basal nuclei islands of gray matter situated deep within the white matter Cerebral Cortex Known as the executive suite of the nervous system where our conscious mind is found Enables us to be aware of ourselves and our sensations to communicate remember and understand and to initiate voluntary movements Modern imaging techniques allow us to see the brain in action 1 PET scans show maximal metabolic activity in the brain 2 Functional MRI reveals blood flow Generalizations of the cerebral cortex include 1 Contains three kinds of functional areas motor sensory and association 2 Each hemisphere is chiefly concerned with sensory and motor functions of the opposite contralateral side of the body 3 The two hemispheres are not equal in function 1 Lateralization of cortical functions 4 No functional area of the cortex acts alone and conscious behavior involves the entire cortex in one way or another Motor Areas control voluntary movement 0 Primary motor cortex located in the precentral gyrus I Allows us to consciously control the precise or skilled voluntary movements of our skeletal muscles I Long axons form motor tracts known as pyramidal or corticospinal tracts I Somatotopy mapping of the body in CNS structures 0 Premotor cortex anterior to the precentral gyrus I Controls learned motor skills of a repetitious or patterned nature I Coordinates the movement of several muscle groups and is involved in planning movements 0 Broca s area lies anterior to the inferior region of the premotor area I Present in one hemisphere only I Motor speech area that directs the muscles involved in speech production 0 Frontal eye field superior to Broca s area I Controls voluntary movement of the eyes Sensory Areas concerned with conscious awareness of sensation 0 Primary somatosensory cortex resides in the postcentral gyrus I Neurons receive information from the general sensory receptors in the skin and proprioceptors in skeletal muscles joints and tendons I Neurons identify the body region being stimulated known as spatial discrimination 0 Somatosensory association cortex lies posterior to the primary somatosensory cortex I Major function is to integrate sensory inputs temperature pressure etc to produce an understanding of an object being felt 0 Primary visual cortex seen on the extreme posterior tip of the occipital lobe but most of it is buried deep within the calcarine sulcus I Receives visual information that originates on the retina of the eye 0 Visual association area surrounds the primary visual cortex and covers much of the occipital lobe I Uses past visual experiences to interpret visual stimuli I Helps with recognition and appreciation 0 Primary auditory cortex located in the superior margin of the temporal lobe I Sound energy exciting the hearing receptors of the inner ear causes impulses to be transmitted where they are interpreted as pitch loudnessandloca on o Auditory association area posterior to the primary auditory cortex I Permits the perception of the sound stimulus I Memories of sounds heard in the past are stored here for reference 0 Olfactory cortex lies on the medial aspect of the temporal lobe I Conscious awareness of different odors o Rhinencephalon primitive brain I Includes all parts of the cerebrum that receive olfactory signals 0 Gustatory cortex located in the insula I Region involved in the perception of taste stimuli o Visceral sensory area cortex of the insula I Conscious perception of visceral sensations o Vestibular equilibrium cortex I Conscious awareness of balance Multimodal Association Areas 0 Areas that receive inputs from multiple senses and sent outputs to multiple areas I Anterior association area known as the prefrontal cortex I Most complicated region I Involved with intellect complex learning abilities cognition recall and personality I Contains working memory which is necessary for the production of abstract ideas judgment reasoning persistence and planning I Posterior association area large region encompassing parts of the temporal parietal and occipital lobes I Plays a role in recognizing patterns and faces localizing us and our surroundings in space and binding sensory outputs I Many parts are involved in understanding written and spokenlanguage I Limbic association area includes the cingulate gyrus parahippocampal gyrus and the hippocampus I Part of the limbic system I Provides the emotional impact that makes a scene important to us Cerebral White Matter 0 White matter deep to the cortical gray matter is responsible for communication between cerebral areas and between the cerebral cortex and lower CNS centers 0 Consists largely of myelinated fibers bundled into large tracts I Commissures connect corresponding gray areas of the two hemispheres enabling them to function as a coordinated whole I Largest commissure is the corpus callosum I Association fibers connect different parts of the same hemisphere I Projection fibers either enter the cerebral cortex from lower brain or cord centers or descend from one cortex to lower areas I Internal capsule a compact band of projection fibers at the top of the brain stem that passes between the thalamus and some of the basal nuclei I Corona radiata distinctive arrangement of projection tract fibers in a fan shape Basal Nuclei 0 Located deep within the cerebral white matter 0 Also known as basal ganglia 0 Made up of caudate nucleus putamen and globus pallidus I Putamen and globus pallidus form lentiform nucleus I Collectively the lentiform and caudate nuclei are called the corpus striatum because of their striped appearance Diencephalon Consists largely of three structures thalamus hypothalamus and epithalamus o Thalamus consists of bilateral eggshaped nuclei which form the superolateral walls of the third ventricle I Nuclei are connected at the midline by an interthalamic adhesion I Makes up 80 of the diencephalon I Relay station for information coming into the cerebral cortex I Information is sorted out and edited and relayed to the appropriate area of the sensory cortex as well as to specific cortical association areas 0 Hypothalamus caps the brain stem and forms the inferolateral walls of the third ventricle I Extends from the optic chiasm to the posterior margin of the mammillary bodies I Mammillary bodies paired pealike nuclei that bulge anteriorly from the hypothalamus I Relay stations in the olfactory pathways I lnfundibulum located between optic chiasm and mammillary bodies I Stalk of hypothalamic tissue that connects the pituitary gland to the base of the hypothalamus I Main visceral control center of the body and is vital to homeostasis I Regulates the autonomic nervous system by controlling the activity centers of the brain stem and spinal cord to influence blood pressure rate and force of heartbeat digestive tract motility and eye pupil size I Lies in the heart of the limbic system and contains nuclei involved in the perception of pleasure tear rage and biological rhythms I Main thermostat of the body and initiates sweating and shivering I Regulates hunger I Regulates water balance and thirst I Regulates sleepwake cycles I Controls the endocrine system by releasing and inhibiting hormones o Epithalamus most dorsal portion of the diencephalon and forms the roof of the third ventricle I Pineal gland secretes melatonin a sleepinducing signal and antioxidant Brain Stem Produces the rigidly programmed automatic behaviors necessary for survival Associated with 10 out of 12 of the cranial nerves Regions include the midbrain pons and medulla oblongata o Midbrain located between the diencephalon and the pons I Contains two bulging cerebral peduncles that form pillars to hold up the cerebrum I Nuclei scattered throughout the surrounding white matter I Corpora quadrigemina raise four domelike protrusions on the dorsal midbrain surface I Superior colliculi visual reflex centers that coordinate head and eye movements I lnferior colliculi part of the auditory relay from the hearing receptors of the ear to the sensory cortex I Substantia nigra dark color reflects a high content of melanin a precursor of the neurotransmitter dopamine I Red nucleus reddish hue due to its rich blood supply and to the presence of iron pigment in its neurons 0 Pons bulging brain stem region wedged between the midbrain and the medulla oblongata that forms part of the anterior wall of the fourth ventricle I Chiefly composed of conduction tracts I Contains pontine nuclei that act as relays for conversations between the motor cortex and the cerebellum I Trigeminal abducens and facial nerves issue from the pontine nuclei I Part of the reticular formation and help the medulla maintain the normal rhythm of breathing o Medulla oblongata most inferior part of the brain stem I Contains the pyramids which are longitudinal ridges formed by the large pyramidal tracts descending from the motor cortex I Decussation of the pyramids crossover point of the pyramids that explains why one side of the brain controls the opposite side of the body I lmportant visceral motor nuclei include the following I Cardiac center that adjusts the force and rate of heart contraction to meet the body s needs as well as the vasomotor center which changes blood vessel diameter to regulate blood pressure I Respiratory centers to generate respiratory rhythm I Centers that regulate vomiting hiccuping swallowing coughing and sneezing Cerebellum Located dorsal to the pons and medulla Provides the precise timing and appropriate patterns of skeletal muscle contraction for smooth coordinated movements and agility needed for our daily lives Cerebellar activity occurs subconsciously Contains two applesized cerebellar hemispheres connected by a wormlike vermIs Folia pleatlike gyri on the surface of the cerebellum Arbor vitae distinctive pattern of white matter in the cerebellum that resembles a branching tree Functional Brain Svstems Limbic system a group of structures located on the medial aspect of each cerebral hemisphere and diencephalon 0 Includes parts of the rhinencephalon septal nuclei cingulate gyrus parahippocampal gyrus dentate gyrus and Cshaped hippocampus and the amygdala o Emotionalaffective brain I Cingulate gyrus plays a role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated I Amygdala recognizes angry or fearful facial expressions assesses danger and elicits the fear response 0 Most limbic system output is relayed through the hypothalamus I Psychosomatic illnesses emotioninduced illnesses Reticular formation extends through the central core of the medulla oblongata pons and midbrain o Reticular activating system RAS send a continuous stream of impulses to the cerebral cortex keeping the cortex alert and conscious and enhancing its excitability I Also acts like a filter for floods of sensory inputs I Inhibited by sleep centers located in the hypothalamus and is depressed by alcohol sleepinducing drugs and tranquilizers I Severe damage to this system could result in permanent unconsciousness Brain Wave Patterns and the EEG Electroencephalogram records the continuous electrical activity of neurons 0 Made by placing electrodes on the scalp and then connecting the electrodes to an apparatus that measures electrical differences Brain waves patterns of neuronal electrical activity generated by synaptic activity 0 Alpha waves 813 Hz relatively regular and rhythmic lowamplitude synchronous waves I Indicate a brain is calm and awake 0 Beta waves 1430 Hz rhythmic but not as regular as alpha waves and also have a higher frequency I Occur when we are mentally alert and concentrating o Theta waves 47 Hz irregular waves that can appear when concentrating I Common in children but uncommon in awake adults 0 Delta waves 4 Hz or less highamplitude waves seen during deep sleep such as during anesthesia I In awake adults indicate brain damage 0 A flat EEG indicates brain death Epileptic seizures reflect a torrent of electrical discharges of groups of brain neurons 0 Petit mal mild forms of seizures in which the expression goes blank while consciousness disappears o Tonicclonicgrand mal person loses consciousness bones can be broken due to extreme convulsions loss of bowel and bladder control and severe biting of the tongue are common I Can be controlled by anticonvulsive drugs or a vagus nerve stimulator Consciousness Encompasses conscious perception of sensations voluntary initiation and control of movement and capabilities associated with higher mental processing memory logic judgment perseverance o Alertness o Drowsiness or lethargy 0 Stupor 0 Coma Suppositions about consciousness include o It involves simultaneou activity of large areas of the cerebral cortex o It is superimposed on other types of neural activity o It it holistic and totally interconnected Syncope a brief loss in consciousness Coma total unresponsiveness to sensory stimuli for an extended period Sleep and SleepWake Cvcles Defined as a state of partial unconsciousness from which a person can be aroused by stimulation Types of sleep include o Nonrapid eye movement NREM sleep I Most nightmares occur during NREM sleep 0 Rapid eye movement REM sleep I Most dreaming occurs during REM sleep Circadian rhythm 24hour cycle of sleep and wakefulness Narcolepsy the abrupt lapse into REM sleep from the awake state Insomnia the chronic inability to obtain the amount or quality of sleep needed to function adequately Sleep apnea a temporary cessation of breathing during sleep
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