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The Central Nervous System The Brain The Brain looks pinkish grey, is wrinkly like a walnut, and has the consistency of oatmeal. It weighs on average 3.5 lbs for men and 3.2 pounds for women. Embryonic Development At three weeks old, the outer layer of the “brain” thickens and forms a line that runs down the center called a neural plate. That plate invaginates to form a neural fold. (That big line that runs down the center of the brain). As the Neural groove deepens… The superior edges of the neural grooves fuse and drop forming a neural tube. This neural tube deepens and extends forming the caudal (tail) end of the brain forming what will later be defined as the spinal cord. In week five of development, the Primary vesicles of the brain give rise to secondary vesicles, which will later form the major regions of the brain. Secondary structure Forms: Telencephalon Diencephalon Two cerebral hemispheres of brain Hypothalamus, thalamus, epithalamus, and retina of the eye Mesencephalon, metencephalon, Myencephalon. Midbrain, pons and cerebellum, and medulla oblongata Cerebral Hemispheres Cerebral Hemispheres The most superior part of the brain, makes up 83% of the brains body weight. The elevated ridges of the cerebral hemispheres are called gyri. They are separated by grooves called sulci. The deeper grooves are called fissures. Regions of the brain Lobes: Frontal Parietal Occipital Temporal Cerebellum Pons Medulla oblongata Brain stem Olfactoral stem Olfactoral tract Hypocampus hypothallumus Gyri and sulci Precentral gyrus Postcentral gyrus Central sulcus Parieto-occipital sulcus Gyri of insula (medial to temporal lobe) Fissures Longitudinal fissure Transverse cerebral fissure Thing to keep in “mind” about the cerebral cortex. No one area of the cerebral cortex acts alone, and all conscious behavior involves every area of the cerebral cortex in some way. The cerebral cortex Contains three function areas, motor areas, sensory areas, and association areas. Each hemisphere of the cerebral cortex is contralaterally concerned with the senses of the opposite side of the body. The cerebral cortex: motor areas Primary motor cortex: contains a type of nerve cell called pyramidal cells that allow us to consciously control precise voluntary movement. These pyramidal cells serve for function of only one area. For example, there are pyramidal cells that are specifically for foot movement, while there are other pyramidal cells that are designed for hand movement. Stroke Stroke is a very serious problem that develops when there is an interruption in the flow of blood to the brain. Also known as cerebrovascular accidents or "brain attacks." There are two main types of strokes. If a blood vessel is blocked by clots or other particles, it is called an ischemic stroke. If a blood vessel breaks and bleeds, it is called a hemorrhagic stroke. Signs of a stroke Symptoms of stroke: Sudden weakness or numbness in your face, body, arms or legs, especially if only one side is affected Sudden loss of vision or problems seeing in one or both eyes Sudden confusion, inability to speak or understand what others are saying Sudden dizziness, instability or inability to stand, walk or coordinate movement Sudden severe, unexplained headache Commonality of stroke Stroke is the third leading cause of death, after coronary heart disease and cancer. Each year there are about 600,000 strokes in the US, and strokes kill over 150,000 Americans each year. Over 15% of people who have had a stroke die within 30 days, and 15-30% of people who survive a stroke are permanently disabled. Who’s at risk Anyone can have a stroke but most people who have strokes are over the age of 55. Strokes affect both men and women. African Americans tend to be at highest risk, but people of all races and ethnicities suffer from strokes. How to prevent stroke There are many things you can do to reduce your risk of stroke: don't smoke keep your blood pressure under control stay physically active if you have diabetes, treat it eat a healthy diet that focuses on fruits, vegetables, and whole grains maintain a healthy weight keep your blood cholesterol under control avoid illegal drug use Who should be screened? People of all ages should be periodically screened for risk factors of stroke: diabetes high blood pressure poor blood cholesterol levels overweight/obesity motor areas continued Premotor cortex- In the frontal lobe of the brain, just anterior of the precentral gyrus. Responsible for learned motor skills and repetitious and patterned nature. motor areas continued Broca’s area- inferior to the anterior region of the premotor area. Present only on left side of the brain, directs muscles involved in speech production. motor areas continued Frontal eye field- superior to Broca’s area. Controls voluntary movements of the eyes. Sensory areas Sensory areas allow for the conscious awareness of sensation. Mostly in the parietal temporal and occipital lobes. Sensory areas continued Primary somatosensory cortex- posterior to the postcentral gyrus. Receives information from skin, muscles and tendons when stimulus is applied. It is not the size of the body part, but the number of sensors in that region that determines sensitivity. The face and fingertips are the most sensitive areas. Sensory areas continued Somatosensory association cortexposterior to primary somatosensory cortex. Integrates sensory inputs like temperature, pressure, etc. from past experience to judge a stimulus without the use of another sense like sight. Sensory areas continued Visual area- extreme posterior of occipital lobe. It creates a contralateral map of visual space. Auditory areas Primary auditory cortex: located in superior portion of the temporal lobe. Involved in interpreting pitch, loudness, and sound. Auditory association area: Posterior to the primary motor cortex. It interprets and perceives a sound stimulus. Olfactory cortex: Medial area of temporal lobe. Used to interpret impulses from smell receptors in the nasal cavity. Gustatory cortex Gustatory (taste) cortex: Located deep in the temporal lobe. It’s involved in the perception of tastes. EWW That tastes disgusting! Visceral Sensory areas Just posterior to the gustatory complex, the visceral sensory area is responsible for the perception of visceral sensation. (i.e. full bladder, upset stomach, feeling like your lungs will explode if you hold your breath too long.) Vestibular cortex Responsible for the conscious awareness of balance. Multimodal association areas Multimodal association areas • Multimodal association areas are responsible for collecting a large amount of information and processing it on multiple levels. Multimodal association areas: prefrontal cortex Encompasses most of the cerebrum. Is involved in the process of memory formation, intellect, complex learning abilities, recall, and personality. The ability of the prefrontal cortex varies greatly from the use of positive and negative feedback. Multimodal association areas: Posterior association areas Encompasses the parietal, temporal and occipital lobes. Allows one to pay attention to the space around them, also plays a role in written and spoken language. Multimodal association areas: Limbic association areas Cingulate gyrus, parahippocampal gyrus, and the hippocampus. Provides the emotional impact of a scene, which allows for the proper response to a stimulus. Cerebral White Matter Responsible for communication between hemispheres of the brain. Commissures (made of commissural fibers) connect the grey areas of the hemispheres. The largest fissure is called the corpus callosum. Cerebral White Matter continued Association fibers- connects different parts of the same hemisphere. Projection fibers- motor output from the cerebral cortex to the rest of the body. Projection fibers run vertically in the brain, while association fibers and commissure fibers run horizontally. Basal Nuclei Receives input from the entire cerebral cortex as well as from other subcortical nuclei and each other. The true function of the Basal nuclei is unclear due to many parts of the cerebral cortex having overlapping functions. Diencephalon Contains the: Thalamus Hypothalamus epithalamus. Diencephalon: Thalamus The thalamus contains a pair of egg shaped nuclei. The thalamus acts as the relay station for all information that enters the cerebral cortex. Diencephalon: hypothalamus Hypothalamus (below the thalamus) is the main visceral control center of the brain and is in charge of homeostasis in the body. It is responsible for: autonomic control emotional response body temperature regulation Regulation of food intake regulation of water balance and thirst regulation of sleep/wake cycle control of endocrine system functions Diencephalon: epithalamus Contains the pineal gland, which secretes melatonin. This is a major part of the sleep/wake cycle. Brain stem Contains the: pons midbrain medulla oblongata Brain stem: midbrain b/w the diencephalon and the pons. Contains the: corpora quadragemina: forms four bumps on the mid brain which themselves hold: superior colliculi-visual reflex center inferior colliculi-Allows for the reflex response to sound. Brain stem: Pons Wedged between the midbrain and the medulla oblongata. Composed mostly of conduction tracts. The pons relays signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Brain stem: medulla oblongata Most inferior part of the brain stem. The medulla oblongata controls autonomic functions, and relays nerve signals between the brain and spinal cord. It is also responsible for controlling several major points and autonomic functions of the body: respiration– chemoreceptors cardiac center – sympathetic, parasympathetic system vasomotor center – baroreceptors reflex centers of vomiting, coughing, sneezing, and swallowing The Cerebellum The cerebellum Located posteriorly, and is inferior to the occipital lobe of the cerebrum. Has two cerebellar hemispheres . Special purkinji cells are located in the cerebellum, which send signals through the white matter to synapse the central nuclei of the cerebellum. Cerebellar processing The cerebellum processes information in the following way: 1. motor areas of the cerebral cortex notify the cerebellum that it will trigger a voluntary muscle movement. 2. At the same time, the cerebellum receives information from the body (muscle tension, tendons, etc…). This allows the cerebellum to evaluate body position and momentum. 3. Cerebellar cortex calculates the best way to handle force, direction, and extent of muscle contraction to prevent overshoot, maintain posture, and ensure smooth coordinated movements. 4. Then the cerebellum dispatches it’s information for coordinated movement. The cerebellum’s role in cognition The cerebellum is responsible for recognizes and predicts sequences of events so that it can adjust for the multiple movements exerted on a limb involving several joints. Functional Brain Systems A function brain system is a system that spans far distances in the brain but still works closely together. Examples: Limbic system Reticular formation The Limbic system A group of structures located in the medial aspect of the cerebral hemisphere and diencephalon. This system is the main emotional, or affective area of the brain. The Limbic System The reticular formation Extends through the central core of the medulla oblongata, pons, and midbrain. maintains tone, balance, and posture-especially during body movements. Acts as a filter for the massive amounts of information from sensory input. Higher Mental Functions Higher mental functions Brain wave patterns and EEG: The EEG is a tool that records aspects of brain activity. These activities are electrically recorded as brain waves. Wave Types Alpha Waves: regular, rhythmic and low amplitude. Indicator of calm and awake brain. Beta waves: rhythmic but not as regular as alpha waves. Occurs when focusing on a problem or stimulus. Theta waves: less common than beta waves. Uncommon in awake adults, but may appear when concentrating. Delta waves: seen during sleep. In an awake adult, this indicates brain damage. Brain Waves What does it mean to be clinically conscious? These criteria are the suppositions about being conscious: Consciousness involves stimulus of large areas of the brain. It is superimposed on other types of neural activity (like cognition and motor control). It is holistic and totally interconnected. Information about thought can be collected by different areas of the brain simultaneously. Sleep and Sleep-wake cycles NREM sleep- The first two stages of sleep, where we do not dream. (Takes 30-45 minutes) In the 3rd and 4th stages we enter slow wave sleep where brain wave frequency slows and wave amplitude increases. After stages four of NREM sleep is achieved, EEG are changed abruptly. (90 minutes) Sleep and Sleep-wake cycles REM sleep-After stage four of NREM, the EEG will change back and forth to all various types of wavelengths. Increases, heart rate and breathing rate and other sympathetic responses. Oxygen rates skyrocket higher than when awake. A temporary paralysis occurs in the skeletal muscles. NOTE that most nightmare occur in NREM sleep stages three and four. Also, REM is associated with sexual arousal, thus “morning wood.” Language Broca’s area: the region of the brain responsible for language and language interpretation. Wernicke’s area: the area responsible for speech production. Damaging Wernicke’s area will cause people to speak incoherent gibberish. Memory Involves the storage and retrieval of information. Short term memory involves the immediate retrieval of information and application of that information. Short term memory lasts for only up to 15 seconds. memory Long term memory involves the storage of information for any time after 15 seconds. As sensory information bombards the cerebral cortex, information we do not even think of consciously is stored in our minds. Emotional state: When norepinephrine is present in the brain, emotional information we receive is almost instantaneous. Rehearsal: repeating a process or speech over and over again. This is why studying your notes repeatedly helps you do well on a test. Association: Association of new memories is easier to remember if it can be associated with old memories. Automatic memory: Automatic memory occurs when you are receiving input and store other information while receiving said input. Categories of memory Declarative memory: Learning explicit information like names and faces. Procedural memory: (Skill) Learning a process like playing the piano. Motor memory: doing a motor function like riding a bike. Emotional memory: remembering something that changing your emotional state. Protecting the Brain The meninges is the covering that protects the brain. It reduces the damage from impact and prevents the brain from rubbing against the skull. The meninges formed by three layers: Dura mater Arachnoid mater Pia mater The meninges formed by three layers Dura mater- Strongest layer; the dura veinous sinuses are located here, which drain blood back to the neck. Arachnoid mater- separated from the dura mater by a space called subdural space. Never enters the sulci of the brain. Pia mater- Clings tightly to the brain like a cellophane hat. Cerebrospinal Fluid Cushion that surrounds the brain and spinal cord. Looks kind of like blood plasma. About 500 ml of CSF is produced daily. About 150 ml of CSF is covering the brain and spine at any one time. Blood-Brain Barrier The blood-brain barrier is the end-all-beall of maintaining homeostasis of the brain. The blood-brain barrier prevents fluxuations in the brain’s balance of nutrients and minerals from causing the neurons of the brain to fire uncontrollably. The Spinal Cord The Spinal Cord The spinal cord provides a two way conduction path for information to enter and leave the brain. The spinal cord is the major reflex center in your body. The spinal dura mater is a meningx that protects the spine from trauma with the CSF. Drawing CSF for testing The procedure known as a Lumbar puncture is the process of drawing CSF to screen for pathogens and drugs. Typically done below the L3 vertebrae, due to there being a low chance of damaging the spinal cord. For the majority of the spinal cord It is about the width of your thumb for the majority of your body with the exception of the cervical enlargement and the lumbar enlargement, which are larger bulbs in the spinal cord that act as nexus’ for spinal nerves. Ascending pathways to the brain First order neurons: cell bodies that lie in a ganglion (bundle of related sensory neurons) which conduct impulses from cutaneous layers of the skin. Second order neurons: Reside in dorsal portion of the spinal cord. They transmit impulses to the thalamus or to the cerebellum where they synapse. Third order neurons: They relay impulses to the somatosensory cortex of the cerebrum. Developmental aspects of the CNS During prenatal development, there are certain areas of the brain that develop specific to each gender. Exposure to drugs and alcohol during pregnancy can cause mental defects in the fetus, if not death.