Chap 5 - Nervous System IV PDF

Introduction to Human Physiology FHSC 203 Chap 5 – Nervous System IV Lara HADDAD Introduction  The central nervous system consists of the:  Encephalon or brain, contained within the cranium  Medulla spinalis or spinal Nervo...

Introduction to Human Physiology FHSC 203 Chap 5 – Nervous System IV Lara HADDAD Introduction  The central nervous system consists of the:  Encephalon or brain, contained within the cranium  Medulla spinalis or spinal Nervous System cord, lodged in the vertebral canal Central Nervous Peripheral System (CNS) Nervous System Brain Spinal cord Lara HADDAD Introduction  Cephalization  Elaboration of the anterior portion of the CNS  Increase in number of neurons in the head  Highest level has been reached in the human brain Lara HADDAD BRAIN  The average adult human brain weighs 1.6Kg in men and 1.45kg in women.  It is composed of wrinkled, pinkish gray tissue.  During the first 26 days of development:  Ectoderm thickens along dorsal midline to form the neural plate  The neural plate invaginates, forming a groove flanked by neural folds  The neural groove fuses dorsally and forms the neural tube Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN  Because the brain grows more rapidly than the membranous skull that contains it: 1. 2 major flexures develop:  The midbrain They move the forebrain toward the  The cervical brain stem Lara HADDAD BRAIN Lara HADDAD BRAIN 2. Cerebral hemispheres grow posteriorly and laterally and envelop the diencephalon and midbrain 3. Cerebral hemisphere surfaces crease and fold into convolutions Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD Basic Pattern of the CNS  Spinal Cord  Central cavity surrounded by a gray matter core  External to which is white matter composed of myelinated fiber tracts Lara HADDAD Basic Pattern of the CNS  Brain  Similar to spinal cord but with additional areas of gray matter  Cerebellum has gray matter in nuclei  Cerebrum has nuclei and additional gray matter in the cortex Lara HADDAD Basic Pattern of the CNS Lara HADDAD BRAIN  Ventricles of the brain  Arise from expansion of the lumen of the neural tube  Connected to one another and to the central canal of the spinal cord; hollow ventricular chambers are filled with cerebrospinal fluid and lined by ependymal cells Lara HADDAD BRAIN  The ventricles are:  The paired C-shaped lateral ventricles paired; one deep within each cerebral hemisphere; large C-shaped chambers that reflect the pattern of cerebral growth; each ventricle communicates with third ventricle  The third ventricle found in the diencephalon narrow; in the diencephalon; receives communication from lateral ventricles; continuous with fourth ventricle  The fourth ventricle found in the hindbrain dorsal to the pons continuous with third ventricle via cerebral aquaduct; lies in the hindbrain dorsal to the pons and superior medulla; continuous with the central canal of the spinal cord inferiorly Lara HADDAD BRAIN Lara HADDAD Protection of the brain  The brain is protected by:  Bone  Meninges  Cerebrospinal fluid  Harmful substances are shielded from the brain by the blood-brain barrier. Lara HADDAD Protection of the brain 1. Meninges  Three connective tissue membranes that lie external to the CNS organs.  The meninges:  cover and protect CNS  protect blood vessels and enclose venous sinuses  contain cerebrospinal fluid  form partitions in the skull Lara HADDAD Protection of the brain  The meninges from external to internal:  dura mater  arachnoid mater  pia mater Lara HADDAD Protection of the brain a. dura mater  strongest meninx  two layered sheet of fibrous connective tissue where it surrounds the brain and separate in certain areas & form dural sinuses Lara HADDAD Protection of the brain  Dural septa limit excessive movement of brain within the cranium including:  Falx Cerebri-large sickle shaped fold that dips into the longitudinal fissure between the cerebral hemispheres; attaches to crista galli anteriorly  Falx Cerebelli-small midline partition that runs along the vermis of cerebellum  Tentorium Cerebelli-resembles a tent over the cerebellum; nearly horizontal dural fold extends into transverse fissure between cerebral hemispheres and cerebellum Lara HADDAD Protection of the brain Lara HADDAD Protection of the brain b. arachnoid mater  midline meninx  forms loose brain covering  separated from dura mater by subdural space  Subarachnoid Space- beneath arachnoid membrane;filled with CSF and contains largest blood vessels serving brain  Arachnoid Villi-projections of arachnoid mater where CSF is absorbed into venous blood of sinus Lara HADDAD Protection of the brain c. pia mater  means gentle mother  composed of delicate connective tissue and is richly invested with tiny blood vessels  only meninx that clings tightly to brain Lara HADDAD BRAIN  Adult brain regions are:  Cerebral hemispheres  Diencephalon  Brain stem (midbrain, pons, and medulla)  Cerebellum Lara HADDAD BRAIN 1. Cerebral hemispheres  Form the superior part of the brain and make up 83% of its mass  Contain gyri: elevated ridges of tissue, and shallow grooves (sulci)  Contain deep grooves called fissures  Are separated by the longitudinal fissure  Have three basic regions:  Cortex  White matter  Basal nuclei Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN  Deep sulci divide the hemispheres into five lobes:  Frontal  Parietal  Temporal  Occipital  Insula (buried deep within the lateral sulcus and forms part of its floor; covered by portions of the temporal, parietal, and frontal lobes)  Central sulcus – separates the frontal and parietal lobes  Parieto-occipital sulcus – separates the parietal and occipital lobes  Lateral sulcus – separates the parietal and temporal lobes  The precentral and postcentral gyri border the central sulcus Lara HADDAD BRAIN 1.a. Cerebral Cortex  It enables us to be aware of ourselves and our sensations, to communicate, remember, and understand, and to initiate voluntary movements  It is composed of gray matter: neuron cells bodies, dendrites, associated glia and blood vessels  It is thin (2-4mm); 40% of the mass of the brain  Each hemisphere connects to contralateral side of body (controls the opposite side of the body)  Two hemispheres not entirely equal in functions Lara HADDAD BRAIN Lara HADDAD BRAIN 1.a. Cerebral Cortex  Three types of functional areas are:  Motor areas – control voluntary movement  Sensory areas – conscious awareness of sensation  Association areas – integrate diverse information Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.1. Cerebral Cortex motor areas 1.a.1.a. Primary Motor cortex  contain large neurons known as pyramidal cells in precentral gyri whose axons make up the corticospinal tracts  allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles Lara HADDAD BRAIN  Motor homunculus: caricature of relative amounts of cortical tissue devoted to each motor function Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.1. Cerebral Cortex motor areas 1.a.1.b. Premotor cortex  anterior to the precentral gyrus in the frontal lobe  controls learned motor skills of a repetitious or patterned nature  coordinates movement of several muscle groups simultaneously or sequentially  involved in planning of movements that depend on sensory feedback Lara HADDAD BRAIN Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.1. Cerebral Cortex motor areas 1.a.1.c. Broca’s Area  lies anterior to the inferior region of the premotor area  present in one hemisphere only (usually the left)  a motor speech area that directs muscles of the tongue  is active as one prepares to speak Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.1. Cerebral Cortex motor areas 1.a.1.a. Primary Motor cortex  contain large neurons known as pyramidal cells in precentral gyri whose axons make up the corticospinal tracts  allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.a. Primary somatosensory cortex  resides in the postcentral gyrus of the parietal lobe, just posterior to the primary motor cortex  receives information from the general (somatic) sensory receptors in the skin and in skeletal muscles, joints, and tendons  capable of spatial discrimination (identification of body region being stimulated) Lara HADDAD BRAIN Lara HADDAD BRAIN  Somatosensory homunculus – caricature of relative amounts of cortical tissue devoted to each sensory function Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.b. Somatosensory Association Cortex  lies posterior to primary somatosensory cortex  integrate sensory inputs (temperature, pressure…) to produce an understanding of an object being felt  determines size, texture, and relationships of parts of objects being felt Lara HADDAD BRAIN Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.c. Visual area  Primary visual cortex  Located on the extreme posterior tip of the occipital lobe  Receives visual information from the retinas  Visual association area  Surrounds the primary visual cortex  Interprets visual stimuli (e.g., color, form, and movement) Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.d. Auditory area  Primary auditory cortex  Located at the superior margin of the temporal lobe  interprets information from inner ear as pitch, loudness, and location  Auditory association area  Located posterior to the primary auditory cortex  Stores memories of sounds and permits perception of sounds and sound stimulus Lara HADDAD BRAIN Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.e. Olfactory area  lies on medial aspect of the temporal lobe in a small region called piriform lobe  part of the primitive rhinecephalon which includes all parts of cerebrum that receives olfactory signals (olfactory tracts and bulbs that extend to the nose)  region of conscious awareness of odors Lara HADDAD BRAIN Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.f. Gustatory area  region involved in perception of taste stimuli  located in insula deep to temporal lobe Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.g. Visceral Sensory Area  posterior to gustatory cortex  involved in conscious perception of visceral sensations (ex: upset stomach, full bladder) Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.2. Cerebral Cortex sensory areas 1.a.2.h. Vestibular Cortex  posterior part of the insula and adjacent parietal cortex  responsible for conscious awareness of balance (position of head in space) Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.3. Multimodal association areas  receive inputs from multiple sensory areas  send outputs to multiple areas, including the premotor cortex  allow us to give meaning to information received, store it as memory, compare it to pervious experience, and decide on action to take  each individual perception come together (hear, see, touch, feel, and smell) Lara HADDAD BRAIN  can be divided into 3 parts  anterior association area  posterior association area  limbic association area Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.3. Multimodal association areas 1.a.3.a. Anterior association areas  in frontal lobe, also called prefrontal cortex  the most complicated cortical region of all  involved with intellect, complex learning abilities, recall, and personality  contains working memory needed for judgment, reasoning, persistence, and conscience  development depends on feedback from social environment Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.3. Multimodal association areas 1.a.3.b. Posterior association areas  large region encompassing parts of temporal, parietal, and occipital lobes  play role in recognizing patterns and faces, localizing us and our surroundings in space, and binding different sensory inputs into a coherent whole  involved in understanding written and spoken language Lara HADDAD BRAIN 1.a. Cerebral Cortex 1.a.3. Multimodal association areas 1.a.3.c. Limbic association areas  part of limbic system  provides emotional impact that makes a scene important to us  hippocampus establishes memories that allow us to remember incidents Lara HADDAD BRAIN 1.a. Cerebral Cortex: lateralization of cortical funtioning  Lateralization of Cortical Function - Each hemisphere of the brain has unique abilities not shared by its partner  Cerebral Dominance - designates the hemisphere that is dominant for language Lara HADDAD BRAIN  Left hemisphere – controls language, math, and logic  Right hemisphere – controls visual-spatial skills, emotion, and artistic skills (free spirit) and far better in recognizing faces Lara HADDAD BRAIN 1.b. Cerebral White matter  second of three basic regions of each cerebral hemisphere  responsible for communication between cerebral areas and between cerebral cortex and lower CNS centers  consists mainly of myelinated fibers bundled into large tracts Lara HADDAD BRAIN  Types include  Commissures – connect corresponding gray areas of the two hemispheres enabling them to function as a coordinated whole; largest commissure is the corpus callosum; run horizontally  Association fibers – connect different parts of the same hemisphere; short fibers connect adjacent gyri; long fibers connect different cortical lobes; run horizontally  Projection fibers – enter cerebral cortex from lower brain or spinal cord centers or descend from cortex to lower area; motor output leaves through these fibers from cerebral cortex; tie the cortex to rest of nervous system and to body's receptors and effectors; run vertically Lara HADDAD BRAIN Lara HADDAD BRAIN 1.c. Basal nuclei  deep within cerebral white matter  third basic region of each hemisphere  recieve input from entire cerebral cortex, as well as from other subcortical nuclei and each other  The corpus striatum is composed of three parts  Caudate nucleus  Lentiform nucleus – composed of the putamen and the globus pallidus  Fibers of internal capsule running between and through caudate and lentiform nuclei Lara HADDAD BRAIN Lara HADDAD BRAIN Lara HADDAD BRAIN  Though somewhat elusive, the following are thought to be functions of basal nuclei  Influence muscular activity  Regulate attention and cognition  Regulate intensity of slow or stereotyped movements  Inhibit antagonistic and unnecessary movement Lara HADDAD BRAIN 2. Diencephalon  It is located between the cerebral hemispheres and above the midbrain Lara HADDAD BRAIN  Consists of three paired structures  Thalamus  Hypothalamus  Epithalamus  Encloses the third ventricle Lara HADDAD BRAIN 2.a. Thalamus  It is a large, dual lobed mass of grey matter cells located at the top of the brainstem, superior to the hypothalamus  The bilateral egg shaped nuclei in the thalamus form the superolateral walls of the third ventricle  It’s a well hidden brain region that makes up 80% of diancephalon Lara HADDAD BRAIN Third ventricle Thalamus Lara HADDAD BRAIN  Afferent impulses from all senses converge and synapse in the thalamus  Impulses of similar function are ―sorted out,‖ edited, and relayed as a group  All inputs ascending to the cerebral cortex pass through the thalamus  Plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory Lara HADDAD BRAIN 2.b. Hypothalamus  Located below the thalamus, it caps the brain stem and forms the inferolateral walls of the third ventricle  Mammillary bodies  Small, paired nuclei bulging anteriorly from the hypothalamus  Relay station for olfactory pathways Lara HADDAD BRAIN  Infundibulum – stalk of the hypothalamus; connects to the pituitary gland  Main visceral control center of the body Lara HADDAD BRAIN  It is the main visceral control center of the body and is vitally important to overall by homeostasis:  Autonomic Control Center (influence on blood pressure , rate and force of heartbeat, digestive tract motility..)  Center for emotional response (perception of pleasure, fear, and rage)  Body Temperature Regulation  Regulation of food intake (feelings of hunger and satiety )  Regulation of water balance and thirst Lara HADDAD BRAIN  Regulation of sleep wake cycles  Control of endocrine system functioning: Releasing hormones control secretion of hormones by the anterior pituitary The supraoptic and paraventricular nuclei produce ADH and oxytocin Lara HADDAD BRAIN 2.c. Epithalamus  Most dorsal portion of the diencephalon; forms roof of the third ventricle  Pineal gland – extends from the posterior border and secretes melatonin  Melatonin – a hormone involved with sleep regulation, sleep-wake cycles, and mood  Choroid plexus – a structure that secretes cerebrospinal fluid (CSF) Lara HADDAD BRAIN 3. Brain stem  Consists of three regions:  Midbrain  Pons  medulla oblongota  accounts for only 2.5% of brain mass Lara HADDAD BRAIN Lara HADDAD BRAIN  Similar to spinal cord but contains embedded nuclei in the white matter  Controls automatic behaviors necessary for survival  Provides the pathway for tracts between higher and lower brain centers  Associated with 10 of the 12 pairs of cranial nerves Lara HADDAD BRAIN 3. Brain stem 3.a. Midbrain  Located between the diencephalon and the pons  Midbrain structures include  Cerebral peduncles – two bulging structures that contain descending pyramidal motor tracts and form vertical pillars that seem to hold up the cerebrum  Cerebral aqueduct – hollow tube that connects the third and fourth ventricles Lara HADDAD BRAIN Lara HADDAD BRAIN  Various nuclei  Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)  Corpora quadrigemina – four domelike protrusions of the dorsal midbrain Superior colliculi – visual reflex centers Inferior colliculi – auditory relay centers Lara HADDAD BRAIN  Substantia nigra – located deep to the cerebral peduncle; its dark color reflects a high content of melanin pigment; linked to basal nuclei;  Red nucleus – largest nucleus of the reticular formation (a system of small nuclei scattered through the core of the brain stem); red nuclei are relay nuclei for some descending motor pathways Lara HADDAD BRAIN 3. Brain stem 3.b. Pons  Bulging brain stem region between the midbrain and the medulla oblongata  Forms part of the anterior wall of the fourth ventricle Lara HADDAD BRAIN  Fibers of the pons:  Connect higher brain centers and the spinal cord  Relay impulses between the motor cortex and the cerebellum (pontine nuclei)  Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)  Contains nuclei of the reticular formation Lara HADDAD BRAIN 3. Brain stem 3.c. Medulla oblongata  It is located inferior to the pons and anterior to the cerebellum  Pyramids are two longitudinal ridges flanking the midline of medulla's ventral aspect; formed by large pyramidal tracts descending from motor cortex Lara HADDAD BRAIN  The decussation of the pyramids is just above the medulla - spinal cord junction, where most of the fibers in/from medulla cross over to opposite side before continuing into spinal cord  The nuclei of the medulla relay sensory information on the state of stretch of muscles and joints to the cerebellum  olivary nuclei  vestibular nuclei; mediate responses that maintain equilibrium  the nucleus gracilis and nucleus cuneatus; relay nuclei in a pathway by which somatic sensory information ascends from the spinal cord to the somatosensory cortex Lara HADDAD BRAIN Lara HADDAD BRAIN  It contains:  Cardiovascular Center  Respiratory Centers  Various other centers; these centers carry out visceral functions from the hypothalamus which relays its instructions through medullary reticular centers Lara HADDAD BRAIN 4. Cerebellum  Located dorsal to the pons & medulla  Protrudes under the occipital lobes of cerebrum  Makes up 11% of brain’s mass Lara HADDAD BRAIN  Provides precise timing & appropriate patterns of skeletal muscle contraction to produce smooth movement and agility needed for our daily living  Process inputs received from the cerebral motor cortex, various brain stem nuclei, and sensory receptors Lara HADDAD BRAIN  Two bilaterally symmetrical hemispheres, each with 3 lobes  anterior & posterior lobes coordinate body movements & flocculonodular lobes adjust posture to maintain balance  Neural arrangement – gray matter cortex, internal white matter, scattered nuclei  Arbor vitae – distinctive treelike pattern of cerebellar white matter  Cerebellar peduncles - 3 paired fiber tracts connect cerebellum to brain stem Lara HADDAD BRAIN Lara HADDAD BRAIN  Cerebellar Processing  motor areas of cerebral cortex, via relay nuclei in brain stem, notify cerebellum of their intent to initiate voluntary muscle contractions  cerebellum receives information from proprioreceptors throughout the body and from visual and equilibrium pathways; this info enables cerebellum to evaluate body position and momentum Lara HADDAD BRAIN  cerebellar cortex calculates best way to coordinate force, direction, and extent of muscle contraction to prevent overshoot, maintain posture and ensure smooth coordinated movements  via superior peduncles, cerebellum dispatches to the cerebral motor cortex its blueprint for coordinating movement; cerebellar fibers send info to brain stem nuclei The cerebellum continually compares the body's performance with the higher brains intention and sends messages to initiate the appropriate corrective measures Lara HADDAD BRAIN Lara HADDAD Functional brain systems  Networks of neurons working together & spanning wide areas of the brain which include 2 systems: 1. Limbic system 2. Reticular formation Lara HADDAD Functional brain systems 1. Limbic system  Group of structures located on the medial aspect of each cerebral hemisphere and diencephalon;  Included are:  parts of rhinencephalon (septal nuclei, cingulate gyrus, parahippocampal gyrus, dentate gyrus, and C-shaped hippocampus)  the amygdala Lara HADDAD Functional brain systems Lara HADDAD Functional brain systems  The main limbic structures in the diencephalon are the hypothalamus and the anterior thalamic nuclei  The fornix link limbic system regions of diencephalon and cerebral hemispheres together Lara HADDAD Functional brain systems  The two parts of the limbic system that are important in emotions are:  Amygdala: an almond shaped nucleus that sits on the tail of the caudate nucleus; recognizes angry or fearful facial expressions, asseses danger, and elicits the fear response  Cingulate Gyrus: plays a role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated Lara HADDAD Functional brain systems Lara HADDAD Functional brain systems 2. Reticular formation  Composed of loosely clustered neurons that form three broad columns along the length of the brain stem:  raphe nuclei  medial group (large)  lateral group of nuclei (small)  Has far flung axonal connections; ideal for governing the arousal of the brain as a whole Lara HADDAD Functional brain systems Lara HADDAD Functional brain systems  Reticular Activating System (RAS) is the arm of reticular formation where reticular neurons send a continuous stream of impulses to the cerebral cortex, keeping the cortex alert and conscious and enhancing its excitability Lara HADDAD Functional brain systems  RAS:  act like a filter for flood of sensory inputs; Repetitive, familiar, or weak signals are filtered out, but unusual, significant, or strong impulses do reach consciousness  Severe injury results in permanent unconsciousness (coma)  Motor function – Helps control coarse motor movements – Autonomic centers regulate visceral motor functions – e.g., vasomotor, cardiac, and respiratory centers Lara HADDAD Higher Mental Functions  Normal brain function involves continuous electrical activity of the neurons. A. Electroencephalogram (EEG) records some aspects of neuron activity in brain; made by placing electrodes to an apparatus that measures electrical potential differences between various cortical areas. Lara HADDAD Higher Mental Functions  Patterns of neuronal electrical activity recorded; generated by synaptic activity at the surface of the cortex.  Wave frequency is expressed in hertz (Hz); its the number of peaks in one second; a frequency of 1 Hz means that one peak occurs each second. Lara HADDAD Higher Mental Functions 1. Alpha waves: (8-13 Hz) regular and rhythmic, low amplitude, synchronous waves; they indicate a brain is idling - calm, relaxed state of wakefulness 2. Beta waves: (14-30 Hz) rhythmic waves but are not as regular as alpha waves and have a higher frequency; occur when we are mentally alert Lara HADDAD Higher Mental Functions 3. Theta waves: (4-7 Hz) more irregular; common in children; uncommon in adults but may appear when concentrating 4. Delta waves: (4Hz or less) high amplitude waves seen during sleep and when reticular activity system is damped, such as anesthesia Lara HADDAD Higher Mental Functions  Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body.  EEG can be used for diagnosis of:  Epilepsy  Sleep disorders  Brain functions  Tumors…. Lara HADDAD Higher Mental Functions  Interference with cerebral functions is suggested when the frequency of brain waves is too high or too low.  Spontaneous waves are always present even during coma, their absence- called a “flat EEG”- is clinical evidence of brain death. Lara HADDAD Higher Mental Functions B. Consciousness  Encompasses conscious perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (memory, logic, judgment, perseverance, and so on). Lara HADDAD Higher Mental Functions  Unconsciousness is always a signal that brain function is impaired:  Brief: Fainting or syncope  Extended: coma Lara HADDAD Higher Mental Functions  It is a continuum that grades behavior in response to stimuli as 1. Alertness 2. drowsiness or lethargy (which proceeds to sleep) 3. Stupor 4. coma Lara HADDAD Higher Mental Functions  Consciousness  involves simultaneous activity of large areas of the cerebral cortex  is superimposed on other types of neural activity  is holistic and totally interconnected Lara HADDAD Higher Mental Functions C. Sleep and Sleep-wake cycles  Sleep – state of partial unconsciousness from which a person can be aroused, & has 2 major types 1. Non-rapid eye movement (NREM) – a person passes through 4 stages of NREM during 1st 30-45 minutes of sleep 2. Rapid eye movement (REM) – occurs after the 4th NREM stage has been achieved Lara HADDAD Higher Mental Functions 1. Non-rapid eye movement (NREM) – first major type of sleep  defined in terms of EEG patterns  during first 30 to 45 of sleep cycle we pass through first 2 stages of NREM and into NREM stages 3 and 4, slow wave sleep  frequency of EEG waves decline as we pass through deeper and deeper sleep Lara HADDAD Higher Mental Functions Lara HADDAD Higher Mental Functions 2. Rapid eye movement (REM) –  after 90 minutes of NREM sleep EEG pattern change abruptly  we go to REM sleep  alpha waves; increase in heart rate, respiratory rate, and blood pressure; oxygen in brain is tremendous in this stage Lara HADDAD Higher Mental Functions  Circadian/24 hours cycle reflects the alternating cycles of sleep and wakefulness.  The brain is actively guided into sleep.  Sleep patterns change throughout life and are regulated by the hypothalamus. Lara HADDAD Higher Mental Functions  A typical sleep pattern alternates between REM and NREM sleep.  REM recurs about every 90min with each REM period getting longer  Dreams occur at the end of the sleep period  Just before we wake, hypothalamic neurons release peptides called orexins, the wake up chemicals  Certain neurons of the reticular formation fire at a maximal rates arousing the sleepy cortex Lara HADDAD Higher Mental Functions  The slow wave sleep are presumed to be restorative.  A person deprived of sleep become moody and depressed, and exhibits various personality disorders.  REM sleep gives the brain an opportunity to analyze the day's events.  Daily sleep requirements decline with age. Lara HADDAD Higher Mental Functions  Sleep disorders:  Narcolepsy- when people lapse abruptly into REM sleep from the awake state  these sleep episodes last about 15 minutes and occur without warning  triggered by a pleasurable event  brains of people with this have fewer cells in the hypothalamus that secrete orexins Lara HADDAD Higher Mental Functions  Insomnia- a chronic inability to obtain the amount or quality of sleep needed to function adequately during the day  Sleep Apnea- temporary cessation of breathing during sleep; victim awakes abruptly due to hypoxia Lara HADDAD Higher Mental Functions D. Language  Language is the function that involves practically all of the association cortex.  Language implementation system analyzes incoming and produces outgoing word sounds and grammatical structures:  Broca’s area  Wenicke’s area  Basal nuclei Lara HADDAD Higher Mental Functions  Corresponding areas on the right side are involved with nonverbal language components. Lara HADDAD Higher Mental Functions  What do patients with lesions in Broca's Areas suffer from?  can understand language but have difficulty speaking  What do patients with lesions involving Wernicke's area suffer?  are able to speak but produce a type of nonsense often referred to as a word salad; difficulty understanding language Lara HADDAD Higher Mental Functions E. Memory  The storage and retrieval of information.  Essential for learning and incorporating our experiences into behavior and are part of our experiences. Lara HADDAD Higher Mental Functions  Memory storage involve 2 distinct stages:  short term memory (STM): working memory; capacity is limited to seven or eight chunks of information  long term memory (LTM): limitless capacity; can be forgotten with time; STM gets sent here when we want to remember something really good Lara HADDAD Higher Mental Functions  The transfer of information from STM to LTM is affected by:  Emotional state: we learn best when we are alert, motivated, and aroused  Rehearsal: repeating or rehearsing material enhances memory Lara HADDAD Higher Mental Functions  Association: associating new information with old memories in LTM enhances memory  Automatic memory: subconscious information stored in LTM Lara HADDAD Higher Mental Functions  Memory consolidation involves fitting new facts into the various categories of knowledge already stored in cerebral cortex:  Declarative (fact) Memory:  entails learning explicit information, such as names, faces, words, and dates  related to our conscious thoughts and our ability to manipulate symbols and language  when fact memories are committed to LTM, they are usually filed along with context in which they were learned (ex: when you think of your new acquaintance, you probably picture him at the basketball game where you met him) Lara HADDAD Higher Mental Functions  Nondeclarative (Skill) Memory:  less conscious or even unconscious learning  categories include: procedural (skills) memory (piano playing) motor memory (riding a bike) emotional memory Lara HADDAD Higher Mental Functions  acquired through experience and repetition do not have to think through how to do something you just do it once learned hard to unlearn Lara HADDAD Higher Mental Functions  new memories for declarative memory: 1. sensory input is processed in the association cortices, which then causes cortical neurons to dispatch impulses to medial temporal lobe (includes hippocampus and surrounding temporal cortical areas 2. Temporal lobe areas play major role in memory consolidation and memory access ( by communicating with thalamus and prefrontal cortex) Lara HADDAD Higher Mental Functions 3. prefrontal cortex and medial temporal lobe receive input from acetylcholine - releasing neurons in basal forebrain 4. sprinkling of acetylcholine onto these structures allow formation of memories Lara HADDAD Higher Mental Functions  The loss of ACh input seems to disrupt the formation of new memories and retrieval of old ones  Memories are retrieved when the same sets of neurons that were initially involved in memory formation are stimulated Lara HADDAD Higher Mental Functions Lara HADDAD Higher Mental Functions  Molecular mechanism for learning: 1. neuronal RNA content is altered and newly synthesized mRNAs are delivered to axons and dendrites 2. dendritic spines change shape 3. unique extracellular proteins are deposited at synapses involved in LTM 4. the number and size of presynaptic terminals may increase 5. more neurotransmitter is released by the presynaptic neurons Lara HADDAD Higher Mental Functions  Molecular mechanism for learning:  persistent increase in synaptic strength that has been shown to be crucial for memory formation is long term potentiation LTP NMDA receptors are kind of glutamate receptor that can act as a calcium channel and initiate the cellular changes that bring about LTP; are blocked preventing calcium entry when postsynaptic terminal is depolarized by binding of glutamate to different receptors, NMDA block is removed and calcium flows into the postsynaptic cell Lara HADDAD Higher Mental Functions calcium influx triggers activation of enzymes that carry out two main tasks: 1. They modify the proteins in the postsyaptic terminal, and also in the presynaptic terminal via retrograde messengers such as oxide and endocannabinoids 2. They cause the activation of genes in the postynaptic neurons nucleus, which leads to synthesis of synaptic proteins in the presence of CREB (cAMP response-element binding protein), the molecular messenger that brings news to the nucleus that more protein is needed BDNF (brain-derived neurotrophic factor) Lara HADDAD Higher Mental Functions Lara HADDAD Protection of the brain  The brain is protected by:  Bone  Meninges  Cerebrospinal fluid  Harmful substances are shielded from the brain by the blood-brain barrier. Lara HADDAD Protection of the brain 2. Cerebrospinal fluid (CSF)  A watery broth similar to composition of blood plasma; contains less protein than plasma and its ion concentrations are different.  Found in and around the brain and spinal cord. Lara HADDAD Protection of the brain  Forms liquid cushion that:  gives buoyancy to CNS structures  reduces brain weight by 97% and prevents the brain from crushing under its own weight  protects the brain and spinal cord from blows and other trauma  helps nourish the brain and carries chemical signals throughout it Lara HADDAD Protection of the brain  Choroid Plexuses-clusters of capillaries that:  form tissue fluid filters, which hang from the roof of each ventricle  forms CSF  help cleanse CSF by removing wastes  ependymal cells of the choroid plexuses are joined by tight junctions, and they have ion pumps that allow them to modify this filtrate by actively transporting only certain ions across their membrane into the CSF Lara HADDAD Protection of the brain Lara HADDAD Protection of the brain Lara HADDAD Protection of the brain 3. Blood brain barrier  A protective mechanism that helps maintain a stable environment for the brain.  3 layers in the brain capillaries:  endothelium of capillary wall  thick basal lamina surrounding external face of each capillary  bulbous feet of the astrocytes clinging to the capillaries Lara HADDAD Protection of the brain Lara HADDAD Protection of the brain  The blood brain barrier is selective  It allows water, respiratory gases, nutrients, & fat-soluble molecules to enter neural tissues  It prevents entry of water-soluble, potentially harmful substances  Bloodborne metabolic wastes are denied entry to brain tissue (proteins, certain toxins, and most drugs) Lara HADDAD Protection of the brain  Brain injuries:  Concussion-an alteration in brain function; usually temporary, following a blow to the head; victim may be dizzy or lose consciousness  Contusion-more serious concussion; individual may remain conscious, but severe brain stem contusions always cause coma Lara HADDAD Protection of the brain  Subdural/Subarachnoid Hemorrhage-bleeding from ruptured into those spaces; accumulation of blood in skull; increases pressure and compresses brain tissue  Cerebral Edema-swelling of the brain Lara HADDAD Protection of the brain  Cerebrovascular Accidents (CVAs)-strokes-  Occur when blood circulation to brain area is blocked and brain tissue dies; results in hemiplegia, sensory deficits, or speech impairments  Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia  Tissue plasminogen activator (tPA) is the only approved treatment for stroke Lara HADDAD Protection of the brain  Degenerative brain disorders  Alzheimer's Disease (AD)-results in slow, progressive loss of memory and motor control and increasing dementia  Parkinson's (substansia nigra) and Huntington's Disease (basal nuclei and cerebral cortex)-both involve abnormalities of the neurotransmitter dopamine (too little or too much secreted) and are characterized by abnormal movements Lara HADDAD Spinal cord  Central cavity surrounded by gray matter (mostly neuron cell bodies); external white matter composed of myelinated fiber tracts.  It is connected to the brain and is about the diameter of a human finger.  From the brain the spinal cord descends down the middle of the back and is surrounded and protected by the bony vertebral column. Lara HADDAD Embryonic development  Develops from caudal portion of neural tube.  By week 6, there are two clusters of neuroblasts:  Alar plate – will become interneurons- Axons form white matter  Basal plate – will become motor neurons  Neural crest cells form the dorsal root ganglia Lara HADDAD Embryonic development Lara HADDAD Spinal cord  CNS tissue is enclosed within the vertebral column from the foramen magnum to L1.  Provides two-way communication to and from the brain.  Protected by bone, meninges, and CSF. Lara HADDAD Spinal cord  Epidural space - space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins.  Conus medullaris - terminal portion of the spinal cord. Lara HADDAD Spinal cord  Filum terminale - fibrous extension of the pia mater; anchors the spinal cord to the coccyx.  Denticulate ligaments - delicate shelves of pia mater; attach the spinal cord to the vertebrae. Lara HADDAD Spinal cord Lara HADDAD Spinal cord  Spinal nerves – 31 pairs attach to the cord by paired roots. 1. Cervical Nerves "C" : (nerves in the neck) supply movement and feeling to the arms, neck and upper trunk 2. Thoracic Nerves "T" : (nerves in the upper back) supply the trunk and abdomen Lara HADDAD Spinal cord 3. Lumbar Nerves "L" : (nerves in the lower back) 4. Sacral Nerves "S" : (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs  Cauda equina – collection of nerve roots at the inferior end of the vertebral canal Lara HADDAD Spinal cord Lara HADDAD Spinal cord  C1-C7 spinal nerves project ABOVE C1-C7 vertebrae  C8 spinal nerve projects below C7 vertebra  T1-S5 spinal nerves project BELOW T1-S5 vertebrae Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  2 grooves partially divide spinal cord into 2 halves:  anterior (Ventral) median fissures  posterior (Dorsal) median fissures Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Gray Matter and Spinal Roots  Gray matter - consists of soma, unmyelinated processes, & neuroglia (support cells)  Gray commissure – connects masses of gray matter; encloses central canal Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Dorsal horns – extend posteriorly – interneurons  Ventral horns – extend anteriorly - interneurons & somatic motor neurons  Lateral horns – contain sympathetic nerve fibers  In 3-D, these horns form columns of gray matter that run the entire length of the spinal cord Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Axons of neurons of lateral & ventral horns emerge from spinal cord via ventral roots: motor roots  Axons of sensory neurons (with cell bodies located in dorsal root ganglion) enter posterior aspect of cord & form dorsal roots: sensory roots  Ventral & dorsal roots combine to form spinal nerves Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Four zones are evident within the gray matter:  somatic sensory (SS): Interneurons receiving input from somatic sensory neurons  visceral sensory (VS): Interneurons receiving input from visceral sensory neurons  visceral motor (VM): Visceral motor (autonomic) neurons  somatic motor (SM): Somatic motor neurons Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  White Matter  It is composed of myelinated & unmyelinated nerve fibers that allow  Communication between different parts of the spinal cord & between the cord & the brain Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Fibers run in three directions – ascending, descending, and transversely  Divided into three funiculi (columns) – posterior, lateral, and anterior  Each funiculus contains several fiber tracks  Fiber tract names reveal their origin and destination  Fiber tracts are composed of axons with similar functions Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 1. Ascending pathways – conduct sensory impulses upward through a chain of 3 neurons Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 1. Ascending pathway:  The central processes of first-order neurons branch diffusely as they enter the spinal cord and medulla  These branches take part in spinal cord reflexes  Conducts impulses from cutaneous receptors and proprioceptors  Synapses with second-order neuron Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Others synapse with second-order neurons in the cord and medullary nuclei  Fibers from touch and pressure receptors form collateral synapses with interneurons in the dorsal horns  Third-order neurons with their cell body in thalamus  Interneuron  Axon extends to somatosensory cortex Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 1. Nonspecific ascending pathways – receive input from many different types of sensory receptors, and make multiple synapses in the brain  Nonspecific pathway for pain, temperature, and crude touch within the lateral spinothalamic tract Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 2. Specific ascending pathways – mediate precise, straight-through transmission of inputs from a single type (or a few related types) of sensory receptor that can be localized precisely on the body surface, such as discriminative touch & vibrations  Specific ascending pathways within the fasciculus gracilis and fasciculus cuneatus tracts, and their continuation in the medial lemniscal tracts (medulla to thalamus) Lara HADDAD Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 3. Spinocerebellar tracts – convey information about muscle or tendon stretch to the cerebellum, which uses this information to coordinate skeletal muscle activity Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord 2. Descending pathway:  Descending tracts deliver efferent impulses from the brain to the spinal cord, and are divided into two groups:  Direct pathways equivalent to the pyramidal tracts: regulates fast, finely controlled, or skilled movements  Indirect pathways essentially all others: regulates muscles that maintain posture & balance, control coarse limb movements, & head, neck, & eye movements involved in tracking visual objects  Motor pathways involve two neurons (upper and lower) Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord a. Direct pathway:  Direct pathways originate with the pyramidal neurons in the precentral gyri Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Impulses are sent through the corticospinal tracts and synapse in the anterior horn  Stimulation of anterior horn neurons activates skeletal muscles  Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord b. Indirect (extrapyramidal) pathway:  Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system  This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  These motor pathways are complex and multisynaptic, and regulate:  Axial muscles that maintain balance and posture  Muscles controlling coarse movements of the proximal portions of limbs  Head, neck, and eye movement Lara HADDAD Cross-Sectional Anatomy of the Spinal Cord  Reticular nuclei – maintain balance  Vestibular nuclei – receive input from the equilibrium apparatus of the ear and cerebellum  Vestibulospinal tracts – control the segmental apparatus during standing  Red nuclei – control flexor muscles  Superior colliculi and tectospinal tracts mediate head movements Lara HADDAD Spinal cord trauma  Paraesthesias – loss of sensory function.  Paralysis – loss of motor function. Lara HADDAD Spinal cord trauma  Flaccid paralysis – severe damage to the ventral root or anterior horn cells.  Lower motor neurons are damaged and impulses do not reach muscles  There is no voluntary or involuntary control of muscles  Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged  Spinal neurons remain in tact and muscles are stimulated irregularly  There is no voluntary control of muscles Lara HADDAD Spinal cord trauma  Transection – Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut  Paraplegia – transection between T1 and L1  Quadriplegia – transection in the cervical region Lara HADDAD Spinal cord trauma  Poliomyelitis – Destruction of the anterior horn motor neurons by the poliovirus  Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes  Vaccines are available and can prevent infection Lara HADDAD Spinal cord trauma  Amyotrophic Lateral Sclerosis (ALS)  Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract  Symptoms – loss of the ability to speak, swallow, and breathe  Death occurs within five years  Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase Lara HADDAD Developmental aspect of the CNS  CNS is established during the first month of development.  Gender-specific areas appear in response to testosterone (or lack thereof).  Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the fetus’ developing CNS. Lara HADDAD Developmental aspect of the CNS  Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage.  The hypothalamus is one of the last areas of the CNS to develop.  Visual cortex develops slowly over the first 11 weeks. Lara HADDAD Developmental aspect of the CNS  Growth and maturation of the nervous system occurs throughout childhood and reflects progressive myelination.  Age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s.  Excessive use of alcohol causes signs of senility unrelated to the aging process. Lara HADDAD