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CENTRAL NERVOUS SYSTEM CH. 8 Central Nervous System -- consists of brain and spinal cord -- covered by meninges, bathed in CSF -- Cerebral cortex – higher center -- consists of gyri and sulci -- four lobes: frontal, parietal, temporal, occipital -- higher level thinking, interpretation -- two hemispheres held together by the corpus callosum -- Diencephalon – thalamus, hypothalamus, pituitary, epithalamus (pineal gland) -- Brainstem: --midbrain – between diencephalon and pons --hindbrain – pons, medulla oblongata -- Cerebellum: “little brain” All of these parts have their origins during embryogenesis STRUCTURAL ORGANIZATION OF THE BRAIN The brain begins as a hollow tube, and remains hollow. 5 Regions of the brain are formed during development. The cavities of the brain are the ventricles. Ventricles of the Brain Ventricles are chambers that are filled with cerebrospinal fluid. They are connected with the central canal that runs through the spinal cord. CEREBRUM Outer part of cerebrum, the cerebral cortex, consists of gray matter. Underneath is white matter, except for the gray basal nuclei. Fig. 8.5 Shows the four lobes, precentral & postcentral gyri, central sulcus Techniques for Visualizing the Brain --MRI (Magnetic Resonance Imaging) -- uses a magnetic field to make pictures of structures inside the body. --can see CSF, gray and white matter --shows structural abnormalIties. E.g. brain tumors, nerve injury, damage caused by stroke, bleeding, an aneurism Techniques for Visualizing the Brain --EEG (electroencephalogram) -- electrodes on the scalp detect synaptic potentials produced by cerebral cortex - Four types of wave patterns - E.g Different waves happen at different stages of sleep - Deviations from normal patterns are used to diagnose - Epilepsy - Confirm brain death in someone with persistent coma Techniques for Visualizing the Brain --MRI AND EEG -- Figure 8.8 Shows an MRI image of the brain, revealing the sensory cortex. -- the combination of the two techniques allows scientists to map the parts of the brain that correspond with functional areas of the body Techniques for Visualizing the Brain --Functional MRI visualizes increased neuronal activity in the brain indirectly, by the increased blood flow. --brain regions with the highest metabolic activity receive the most blood flow -- e.g. the colors indicated in the picture indicate increased blood flow to the brain areas stimulated when the subject views a screen displaying images that change at 30 second intervals. Can be used to look at growth of a tumor, Determine how well the brain is functioning after a stroke, learn where seizures are located, diagnose Alzheimer’s Techniques for Visualizing the Brain --PET (Positron Emission Tomography); positrons are injected into the blood; (electrons collide with positrons to release gamma rays, which can be detected) -- used to determine stages of cancer and patient responses to cancer treatments -- may detect early onset -- used to study brain metabolism, and drug distribution in the brain --CT (Computed Tomography) -- Xray tissues at different depth -- generates a 3D image tissues Maps of the Precentral and Postcentral Gyri Basal Nuclei Masses of gray matter located deep in the white matter of the cerebrum; they relay motor impulses from cortex to brainstem Allows intended movements – CLICK HERE Inhibits unintended movements – CLICK HERE INJURY TO BASAL NUCLEI • • • • Tremors (while resting, not while moving) Hypertonia – muscle rigidity (muscles will not stretch) Delay in initiating movements Clinical Examples: two neurodegenerative disorders: – Parkinson’s Disease – exhibit shaking and lack of normal facial expressions • Due to deficiency of dopamine • Dopamine activates other neurons in the basal ganglia that release other inhibitory neurotransmitters • Treatment: administering L-dopa (synthetic dopamine precursor) – Huntington’s Disease (autosomal dominant) • Degeneration of caudate nucleus • Rapid involuntary movements of the limbs (writhing movements) CEREBRAL CORTEX • Cerebral dominance – (cerebral lateralization) - one side of the brain complements the other (is not really dominant) – Studies with people who had their corpus callosum cut showed that different sides of the brain have specializations – Majority of people are right-handed (>90% of people). They use the left side of the brain. – Left-handed people – most of them only write with their left hand, but some do everything; they use the right side • • • THE DOMINANT HEMISPHERE (left) Controls voluntary movement using the dominant hand (right) controlled by the primary motor area Senses are sent to the right side of the brain (primary sensory area) Stereognosis using the dominant hand (right) – Mental construct through touch: being able to tell the difference between the feel of a nickel and the feel of a dime. This is the way blind people feel Braille. • Wernicke’s Language Comprehension area – located only in the dominant hemisphere (left): this is how we convert writing we see into understanding what the writing means; converting heard words into language we understand • Broca’s Speech Center – performance of speech (frontal lobe under the primary motor area); injury from stroke (CVA) causes people to be unable to speak, called aphasia CLICK HERE FOR • Mathematical Calculations. 3 + 5 x 4 = ? BROCA’S APHASIA • Learned reflexes and behaviors, e.g. driving a car CLICK HERE TO SEE SOMEONE WITH WERNICKE’S APHASIA THE SUBORDINATE HEMISPHERE • Right side in 90% of the population • Controls– Voluntary movement using the weaker hand – Stereognosis using the weaker hand – Spatial relations and patterns (e.g. what image do you see in the picture) Recognizing patters (foreground/background) – Musical ability (playing an instrument; perfect pitch) – Body sense (being coordinated; gymnasts, surgeons) – Artistic/intuitive FUNCTIONS NOT ASSOCIATED WITH A PARTICULAR HEMISPHERE: Consciousness: – Awareness of the environment (wakefulness), sensations, perceptions, and self-cognition (humans) “Aware that you are aware.” e.g. your dog is aware, but not ‘aware he’s aware.’ – Social behaviors, moral and ethical reasoning I’m aware that I’m aware I’m aware it’s time to eat Regions implicated as centers for emotion: • Limbic system: aggregations of neuron cell bodies (green) Aggression Fear Feeding Sex Goal-directed behavior Exists in a circuit with the hypothalamus. • Studies have shown that electro-shock of limbic system can function as a reward. • • • • • • Brain Regions Involved in Emotion a) Yellow – orbitofrontal area of prefrontal cortex; blue-green: cingulate gyrus of limbic system; b) insula is purple; anterior cingulate gyrus of limbic system is blue-green, amygdala is red EMOTION AND MEMORY: THE Prefrontal Cortex • Phineas Gage (1823 - 1860) worked on the Vermont railroad • He drilled a hole through his head. Walked to the doctor’s office; underwent serious personality changes • Here’s the video. Click HERE. Memory: Hippocampus • Required to take in memories and put them into permanent storage in the cortex • Removal of temporal lobe (which includes the hippocampus) results in not being able to form a new memory. Click here for video on H.M. who had his hippocampus removed Alzheimer’s Disease • The most common form of dementia • Loss of brain weight/volume • Loss of areas of the hippocampus and cerebral cortex, of synapses • Accumulation of “plaques” of proteins SYNAPTIC CHANGES IN MEMORY Glutamate binding to NMDA receptors causes Ca2+ to diffuse into the cell, binds to calmodulin and activates a 2nd messenger system. LTP: long-term potentiation is induced, genes are activated by transcription factors. DISORDERS OF THE CEREBRAL CORTEX • VIRAL Encephalitis – a virus damages a particular area • Cerebral palsy – damage to a motor area often due to cerebral ischemia; symptoms: loss of control of skeletal muscle • Dyslexia – inability to properly read and write words - skipping over a word while reading – – – – Mistaking b for d Writing ‘was’ instead of ‘saw’ 15% of children. More common in males Hypothesis: lack of cerebral dominance OR injury OR congenital (from birth) DISORDERS OF THE CEREBRAL CORTEX Cerebral Vascular Accident – – Insufficient O2 to the brain (4 arteries to brain) – Brain cells die – cerebral infarction (stroke) • Could be due to cerebral thrombosis (blood clot) • Could be due to cerebral hemorrhage (bleeding) due to –High blood pressure OR –Aneurysm (a bulging weak spot in a blood vessel) – Symptoms: depend on which cells die • Aphasia OR paralysis OR death – Sometimes functions can be regained (neuroplasticity) DISORDERS OF THE CEREBRAL CORTEX • Epilepsy – – Increased electrical activity of the brain leads to an altered state of consciousness – Seizure – your consciousness has been seized – Causes: metabolic/congenital; uremia (elevated urea in blood) • Cretinism – A deficiency of thyroxin from birth – Blood tests are now required in newborns – Hypothyroid babies are put on synthroid (synthetic thyroxin) so they don’t become mentally retarded DIENCEPHALON The diencephalon with the telencephalon (cerebrum) constitute the forebrain, which is surrounded by the cerebral hemispheres. Thalamus – contains 3rd ventricle, a relay center Epithalamus – contains the pineal gland which secretes melatonin Thalamus: The Waking Center (RAS: Reticular Activating System) • The thalamus consists of masses of gray matter in the center of the cerebral hemispheres; • All sensory information from the body travels to the thalamus before going to the cerebral cortex, except for olfactory senses (smell). Smell goes directly to the cerebral cortex. • Lets us tune out unimportant stuff, and tune in important stuff. It’s a “sensory filter.” It alerts the cerebral cortex to relevant info. (E.g. a mother is not awakened by noise except if it is her baby’s cry). Thalamus (cont.) • Regulates levels of alertness and consciousness – Sleep/wake states are controlled by opposing neurotransmitters in the RAS – Coma – we can’t be awakened or aroused at all – Stimulated level of alertness – excited – Hallucinations – we are in an extreme excited state Thalamus (cont.) • Drugs: – CNS stimulants – increase alertness of the RAS (epinephrine, caffeine, (which raises cAMP levels in the cell), amphetamines (mimic epi) – Hallucinogens (LSD, psilocybin) overstimulate the RAS, alter the ability of the RAS to filter sensory information into the cerebral cortex – CNS depressants – slow down the RAS: alcohol, sedatives, inhibit neuronal activity. Combining these coma; injury of thalamus interferes with the ability of information to get up to the cerebral cortex • The limbic system is connected with the thalamus – E.g. depression due to life events (which effect the limbic system) sends signals to the thalamus and we may sleep a lot – E.g. exciting news – may cause people to lose sleep Thalamus (cont.) • Student activity: propose a mechanism for narcolepsy, the condition in which a person inappropriately falls asleep during the day despite having enough sleep. HYPOTHALAMUS is linked to the limbic system • It’s linked to the pituitary gland by nerve fibers and blood vessels (hypothalamic/pituitary portal system) • Visceral Reflex Centers: – Regulates temperature (thermoregulatory reflex center) – Appetite/satiety reflex center: Regulates blood sugar level (normal - 100mg/dL) “ – Osmoregulatory reflex center (regulates salt and water balance: tonicity should be 300 mOsm) HYPOTHALAMUS (cont) • Modulates the activity of visceral reflex centers in the medulla oblongata: cardiovascular reflex center AND vomiting reflex center • Modulates the activity of the micturition reflex center and a defacation reflex center. These are located in the spinal cord. HYPOTHALAMUS (cont) • HOMEOSTASIS: It adjusts the activity of the various visceral organs to match the physical activity and energy requirements of the person (via descending autonomic fiber tracts, and the autonomic motor neurons) • It also secretes two hormones: ADH and oxytocin – These are neurotransmitter/hormones Midbrain and Hindbrain (brain stem) MIDBRAIN – between pons and diencephalon 1) Nigrostriatal system – dopamine sent from substantia nigra to basal nuclei (control of skeletal muscles; degeneration results in Parkinson’s) 2) Mesolimbic system – dopamine sent from Ventral tegmental area to nucleus accumbens (emotional reward) The Midbrain • Contains Visceral Reflex Centers: – Salivation Reflex Center – initiates salivation – Tearing Reflex Center – controls tearing, incl. when we get something in our eyes – Oculomotor reflex center – regulates pupil size; regulates tracking and focusing of our eyes. When we change from near to distant vision, there’s a change in the size of the pupils. They’re constricted when we look at something close; wide when we’re looking far away HINDBRAIN 1) pons: contains respiratory control centers; relay center 2) cerebellum: motor coordination 3) medulla oblongata, which contains visceral control centers Medulla Oblongata Reflex centers – Cardiovascular reflex center regulates blood pressure – Respiratory reflex center regulates CO2 and O2 levels and pH • Whenever CO2 accumulates, it can combine with water • CO2 + H2O H2CO3 (carbonic acid. Therefore a buildup of CO2 causes respiratory acidosis) - Coughing reflex center (a rapid forced exhalation) - Sneezing reflex center (a forced exhalation out the nose) - Swallowing reflex center (deglutition) - Vomiting reflex center. (anti-emetic drugs suppress electrical activity of the vomiting reflex center Medulla Oblongata (cont) -- Vestibular reflex center – receives information from the v.c. nerve from the cochlea and otolith organs -- receives visual information from the eyes, tracking of eyes when spinning -- receives info about spatial orientation, balance, equilibrium -- receives info from peripheral proprioceptors (e.g. stretch receptors w/in muscle spindles). --sends out messages to through somatic motor neurons to contract skeletal muscles, effects posture -- sends out messages to the oculomotor reflex center in the midbrain (which controls the size of the pupils; controls eyeball movement by controlling the extrinsic eye muscles while we spin or rotate. This causes our eyes to move in the direction we’re spinning in (tracking or nystagmus). These signals also go to the vomiting reflex center, causing motion sickness. Clinical Issues • Vertigo – a person experiences spinning even though they’re not spinning. A clinical problem if the person is not really spinning. • Motion sickness – requires drugs that slow down electrical activity in the vestibular reflex center/vomiting reflex center • Nystagmus – eyes drift in direction of spinning with a rapid return in the opposite direction. This is a clinical problem if the person is not really spinning. • The medulla oblongata is the region of the brain least affected by general anesthesia. Thankfully. CEREBELLUM • Means “small brain”/ unconsciously coordinates voluntary motor activity. • It receives sensory information from the vestibular apparatus • It receives sensory information from peripheral proprioceptors (in joints and tendons) and stretch receptors • It activates signals along the extra-pyramidal tract to activate somatic motor neurons to control skeletal muscles. • The cerebrum wants to move a body part the cerebellum deals with the details of how to move the body part. Injuries to the CEREBELLUM • Cerebellar Ataxia – a loss of coordination; • Intention tremors – tremors during movement • Dysarthria – hesitant and slurred speech; it Seems like the person is drunk. • Decomposition of voluntary movements INTENTION TREMOR CONTROL OF SKELETAL MUSCLE ACTIVITY • BASAL nuclei (inhibit) MIDBRAIN • CEREBELLUM (excitatory) MIDBRAIN • CEREBRAL CORTEX MIDBRAIN INVOLUNTARY (extrapyramidal tract) SOMATIC MOTOR NEURONS SKELETAL MUSCLE CEREBRAL CORTEX (PRIMARY MOTOR AREA) VOLUNTARY PATHWAY, PYRAMIDAL TRACTS SOMATIC MOTOR NEURONS (Excitatory or inhibitory); needed for fine motor control ASCENDING/DESCENDING SPINAL CORD TRACTS - Carry information from sensory organs up the spinal cord to the brain - Naming: Ascending start with spino- and end with the name of the brain region where they end. Descending begin with the brain region and end with spinal. - Ascending – carry sensory information - Descending – corticospinal, pyramidal tracts(motor), extrapyramidal motor tracts CRANIAL NERVES (PNS) See table 8.6 12 pairs designated by Roman Numerals most are ‘mixed’ (sensory and motor) Those associated with sensory are sensory only. Their cell bodies are located in ganglia near the sensory organ SPINAL NERVES 31 pairs 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal these are mixed REFLEX ARC Does not directly involve the brain A sensory neuron synapses with a motor neuron. Or, a sensory neuron synapses with an association neuron and then a motor neuron. An easy way to study nervous system function.