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Chapter 08 Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I. Structural Organization of the Brain A. Central Nervous System 1. Composed of the brain and spinal cord a. Receives input from sensory neurons and directs activity of motor neurons that innervate muscles and glands b. Association neurons integrate sensory information and help direct the appropriate response to maintain homeostasis and respond to the environment. Central Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gyrus Sulcus Corpus callosum Cerebrum Meninges Spinal cord Central canal Tentorium cerebelli Cerebellum B. Embryonic Development 1. From the ectoderm comes a groove that will become the neural tube around 20 days after conception. This will eventually become the CNS. 2. Between the neural tube and the developing epidermis, a neural crest forms. This will become PNS ganglia. Embryonic Development of the CNS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neural crest Neural groove Neural crest Cranial neuropore Neural canal Neural tube Caudal neuropore Neural crest Neural groove Neural groove Neural crest Waldrop Wall of yolk sac Embryonic Development, cont 3. By week 4 after conception, three distinct swellings are seen on the neural tube: a. Prosencephalon (forebrain) b. Mesencephalon (midbrain) c. Rhombencephalon (hindbrain) Embryonic Development, cont 4. By week 5, these regions differentiate into five regions. a. The forebrain divides into the telencephalon and diencephalon. b. The mesencephalon remains the midbrain c. The hindbrain divides into the metencephalon and myelencephalon. 5. These terms are still used to describe regions of the adult brain. Developmental Sequence of the Brain Weeks 4 and 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Three primary vesicles Wall Five secondary vesicles Adult derivatives of Walls Cavities Cavity Telencephalon Prosencephalon (forebrain) Mesencephalon (midbrain) Diencephalon Mesencephalon Cerebral hemisphere Thalamus Hypothalamus Lateral ventricles Midbrain Aqueduct Pons Rhombencephalon Metencephalon (hindbrain) Third ventricle Upper portion Cerebellum Myelencephalon Medulla oblongata Spinal cord of fourth ventricle Lower portion 6. Later development a. Telencephalon – get two cerebral hemispheres and the two lateral ventricles (remnant of the tube) b. Diencephalon – get the thalamus, hypothalamus, and the third ventricle c. Mesencephalon – get the midbrain and cerebral aqueduct d. Metencephalon – get the pons, cerebellum, and upper fourth ventricle e. Myelencephalon – get the medulla oblongata and lower fourth ventricle f. The posterior neural tube becomes the spinal cord C. Choroid plexuses and cerebrospinal fluid 1. Consists of simple cuboidal to columnar epithelium in close association with blood capillaries 2. Project into the roofs of the ventricles 3. Secrete cerebrospinal fluid (CSF) into the ventricles and central canal of the cord. 4. CSF is made from blood and is returned to blood Ventricle of the Brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral ventricle Interventricular foramen Lateral ventricle Third ventricle Third ventricle Interventricular foramen Mesencephalic aqueduct Mesencephalic aqueduct Fourth ventricle Fourth ventricle (a) To central canal of spinal cord (b) To central canal of spinal cord D. Brain statistics 1. Gray matter forms the cortex and deep nuclei; white matter is deep forming tracts 2. The adult brain has 100 billion neurons. 3. It weighs about 1.5 kg (3−3.5 pounds). 4. It receives 15% of the total blood flow to the body per minute. 5. Scientists have demonstrated neurogenesis (the formation of new brain cells from neural stem cells) in adult brains within the subgranular zone of the hippocampus and subventricular zone of the lateral ventricles II. The Cerebrum A. 1. 2. 3. 4. Introduction Derived from the telencephalon Largest portion of the brain - 80% of the mass Responsible for higher mental functions Consists of a right and left cerebral hemisphere connected internally by the corpus callosum B. Cerebral Cortex 1. The outer region of the cerebrum composed of 2−4 mm gray matter with underlying white matter. 2. Characterized by raised folds called gyri separated by depressed grooves called sulci; together called convolutions 3. Each hemisphere is divided by deep sulci or fissures into 5 lobes - Frontal , Parietal, Temporal, Occipital, Insula Lobes of the Cerebrum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Precentral gyrus Superior frontal gyrus Superior frontal sulcus Frontal poles Central sulcus Superior frontal gyrus Postcentral gyrus Parietal lobe Central sulcus Frontal lobe Lateral sulcus Superior frontal sulcus Longitudinal fissure Occipital lobe Temporal lobe Parietal lobe Cerebellar hemisphere Occipital poles (a) (b) 4. Frontal and Parietal Lobes a. Separated by the central sulcus b. The precentral gyrus is located in the frontal lobe and is responsible for motor control; neurons called upper motor neurons c. The postcentral gyrus is in the parietal lobe and is responsible for somatesthetic sensation (coming from receptors in the skin, muscles, tendons, and joints); called the somatosensory cortex Maps of the Precentral and Postcentral Gyri Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central sulcus Somatosensory cortex Motor cortex Thumb, fingers, and hand Lower arm Facial expression Upper arm Upper leg Trunk Lower leg Pelvis Pelvis Trunk Neck Upper arm Lower arm Hand, fingers, and thumb Upper leg Salivation Vocalization Mastication Lower leg Foot and toes Foot and toes Genitals Upper face Lips Teeth and gums Swallowing Tongue and pharynx Longitudinal fissure Insula Insula Parietal lobes Central sulcus Motor cortex Somatosensory cortex Frontal lobes (a) (b) 5. Temporal, Occipital, and Insula Lobes a. Temporal lobe: auditory centers b. Occipital lobe: vision and coordination of eye movements c. Insula: encoding of memory and integration of sensory information with visceral responses; receives olfactory, gustatory, auditory, and pain information Functional Regions of the Cerebrum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central sulcus Primary motor cortex involved with the control of voluntary muscles Somatosensory cortex for cutaneous and proprioceptive senses Frontal lobe Parietal lobe Motor speech area (Broca’s area) General interpretive area Auditory area Lateral sulcus Occipital lobe Interpretation of sensory experiences, memory of visual and auditory patterns Combining visual images, visual recognition of objects Cerebellum Temporal lobe Brain stem Functions of the Cerebral Lobes 6. Mirror Neurons a. Found in frontal and parietal lobes to integrate sensory and motor neural activity b. Connected through the insula and cingulate gyrus to emotion centers in the brain c. May be involved in the ability to learn social skills and language d. Have been implicated in autism (autism spectrum disorder) 7. Visualizing the Brain a. X-ray computed tomography (CT): looks at soft tissue absorption of X-rays b. Positron emission tomography (PET): radioactively labeled fluoro-deoxyglucose injected into the blood; emits gamma rays in active tissues 1) Used to monitor cancer 2) Used to study brain metabolism, drug distribution in the brain, and changes in blood flow following activity Visualizing the Brain, cont c. Magnetic resonance imaging (MRI): Protons in tissues are aligned by powerful magnets. The chemical composition of different tissues results in differences in proton alignment. 1) Can be amplified using MRI contrast agents injected before imaging 2) Shows clear definition between gray matter, white matter, and cerebrospinal fluid Visualizing the Brain: MRI Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral ventricle Third ventricle White matter of cerebrum Gray matter of cerebrum Courtesy of Dr. Llinas, New York University Medical Center Visualizing the Brain, cont d. Functional magnetic resonance imaging (fMRI): visualizes increased neuronal activity in different brain regions indirectly by looking at blood flow 1) Release of the neurotransmitter glutamate increases vasodilation of blood vessels in the area. 2) Active brain regions receive more oxyhemoglobin; called the BOLD response for blood oxygenation level dependent contrast Visualizing the brain, cont e. Magnetoencephalogram (MEG) 1) Based on magnetic fields produced by postsynaptic currents 2) Sensors are SQUIDS – superconducting quantum interference devices 3) More accurate than EEGs Visualizing the Brain, cont f. Electroencephalogram (EEG): Electrodes on the scalp detect synaptic potentials produced by cell bodies and dendrites in the cerebral cortex. 1) Four patterns are usually seen: a) Alpha waves: active, relaxed brain. Seen most in frontal and parietal lobes b) Beta waves: produced with visual stimulation and mental activity. Seen most in frontal lobe EEG, cont c) Theta waves: seen during sleep; most from occipital and temporal lobes d) Delta waves: also seen in sleep, from all over the cerebrum EEG Wave Patterns Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alpha Beta Theta Delta 1 sec Techniques for Visualizing Brain Function 8. Sleep a. May be genetically controlled, although sleep is affected by environmental factors b. Neurotransmitters involved 1) Histamine – wakefulness 2) Adenosine & GABA – sleep 3) Serotonin – induces REM sleep and stimulates non-REM sleep Sleep, cont c. Two recognized categories: 1) REM: rapid eye movement; state when dreams occur. Theta waves are seen here. 2) Non-REM: also called resting sleep; divided into four stages, determined by EEG waves seen. Stages 3 and 4 are often called slowwave sleep, characterized by delta waves. d. Sleep pattern 1) When people first fall asleep, they enter non-REM sleep and progress through the four stages. 2) Next, a person ascends back up the stages of nonREM sleep to REM sleep. 3) This cycle repeats every 90 minutes, and most people go through five per night. 4) If allowed to awaken naturally, people usually do so during REM sleep. 5) Slow-wave is prominent in the first part of sleep, while REM is prominent in the second half e. REM Sleep 1) Some brain regions are more active during REM sleep than during the waking state. 2) The limbic system (involved in emotion) is very active during REM sleep. 3) Breathing and heart rate may be very irregular. 4) Benefits consolidation of nondeclarative memories f. Non-REM Sleep 1) As you fall asleep, neurons decrease their firing rates, decreasing blood flow and energy metabolism. 2) Breathing and heart rate are very regular. 3) Non-REM sleep may allow repair of metabolic damage done to cells by free radicals and allows time for the neuroplasticity mechanisms needed to store memories. 4) Benefits consolidation of spatial and declarative memories C. Basal Nuclei 1. Masses of gray matter located deep in the white matter of the cerebrum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor cerebral cortex Thalamus Claustrum Putamen Basal nuclei Lentiform nucleus Globus pallidus Corpus striatum Caudate nucleus Cerebellum Spinal cord Basal Nuclei, cont 2. Most prominent is the corpus striatum; composed of: a. Caudate nucleus b. Lentiform nucleus; made up of the putamen and the globus pallidus 3. Also includes subthalamic nucleus of the diencephalon and substantia nigra of the midbrain 4. Degeneration of dopaminergic neurons from the substantia nigra to the corpus striatum causes Parkinson’s disease 5. Motor circuit a. The neurons from motor regions of the frontal lobe release glutamate (stimulatory) in the putamen. The putamen then releases GABA (inhibitory) to other regions of the basal nuclei. b. The globus pallidus sends GABA-releasing (inhibitory) neurons to the thalamus, which sends excitatory axons to the motor cortex of the cerebrum. c. This completes a motor circuit. This circuit stimulates appropriate movements and inhibits unwanted movement. The Motor Circuit Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glutamate neurotransmitter (excitatory) Caudate Dopamine neurotransmitter (excitatory) Putamen GABA neurotransmitter (inhibitory) Thalamus Globus pallidus Subthalamic nucleus Substantia nigra D. Cerebral Lateralization (Dominance) 1. Each side of the precentral gyrus controls movements on the contralateral (opposite) side of the body due to decussation of fibers. 2. Somatesthetic sensation from each side of the body projects to contralateral sides of the postcentral gyrus. 3. Communication between the sides occurs through the corpus callosum; this is severed in severe forms of epilepsy. Cerebral Lateralization, cont 4. Some tasks seem to be performed better by one side of the brain than the other. a. Right hemisphere: visuospatial tasks, recognizing faces, composing music, arranging blocks, reading maps b. Left hemisphere: Language, speech, writing, calculations, understand music Cerebral Lateralization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Olfaction Olfaction Speech, writing Left ear Right ear Simple language comprehension Main language center Spatial concepts Calculation Left visual half field Right visual half field Split brain E. Language 1. Most of the knowledge of how the brain controls language has come from studying people with speech problems called aphasias. 2. Two areas are identified as important : a. Broca’s area b. Wernicke’s area 3. Broca’s Area a. Located in left inferior frontal gyrus b. Broca’s aphasia involves slow, poorly articulated speech. There is no impairment in understanding. 1) Interestingly, other actions of the tongue, lips, and larynx are not affected; only the production of speech is affected. c. Controls motor aspects of speech 4. Wernicke’s Area a. Located in left superior temporal gyrus b. Wernicke’s aphasia involves production of rapid speech with no meaning, called “word salad.” Language (spoken and written) comprehension is destroyed. c. Controls understanding of words. d. Information about written words is sent by the occipital lobe (visual cortex). 5. Speech a. To speak, word comprehension originates in Wernicke’s area and is sent to Broca’s area along the arcuate fasciculus. b. Broca’s area sends information to the motor cortex to direct movement of appropriate muscles. Speech Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor cortex (precentral gyrus) Motor speech area (Broca’s area) Wernicke’s area 6. Angular Gyrus a. Located at the junction between the parietal, occipital, and temporal lobes b. Center for integration of sensory information c. Damage here also produces aphasias involved in reading and writing F. The Limbic System 1. Group of brain regions responsible for emotional drives a. Areas of the cerebrum included: cingulate gyrus, amygdala, hippocampus, septal nuclei, anterior insula b. The hypothalamus and thalamus (in the diencephalon) are also part of this system The Limbic System, cont 2. Papez circuit a. The fornix connects the hippocampus to the mammillary bodies of the hypothalamus, which sends neurons to the thalamus. b. The thalamus sends neurons to the cingulate gyrus, which sends neurons to the hippocampus, completing the circuit. The Limbic System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Corpus callosum Thalamus Cingulate gyrus Fornix Mammillary body Septal nucleus Amygdala Preoptic nucleus Hippocampus Olfactory bulb Olfactory tract Cortex of right hemisphere Hypothalamus Limbic System, cont 3. Once called the rhinencephalon, or “smell brain,” because it deals with olfaction. 4. There are few synaptic connections between the limbic system and the cerebral cortex, which is why it is hard to control your emotions. Limbic System, cont 5. Emotions controlled by the limbic system: a. Aggression: areas in the amygdala and hypothalamus b. Fear: amygdala and hypothalamus c. Hunger/satiety: hypothalamus d. Sex drive: the whole system e. Goal-directed behaviors: hypothalamus and other regions G. Memory 1. Brain areas a. Studies of people with amnesia reveal that areas of the temporal lobe, hippocampus, caudate nucleus, and dorsomedial thalamus are involved in memory. b. The amygdala is important in learning fear responses. c. The prefrontal cortex may be involved in complex problem solving and working memory– very short-term memory. d. Left inferior frontal lobe – mathematical calculations Brain areas, cont e. Hippocampus is the critical component 1) Acquire new information 2) Consolidation of short-term memory to longterm memory f. Inferior temporal lobe – storage of long-term visual memories 2. Types of Memory a. Short-term memory: recent events; transferred to long-term memory through process of memory consolidation 1) Memory consolidation occurs in the medial temporal lobe, hippocampus, and amygdala. 2) Sleep is needed for optimum memory consolidation. b. Long-term memory 1) Requires actual structural change - Activation of genes, synthesis of mRNA, production of proteins, and formation of new synapses 2) Long-term memory can be classified into: a) Nondeclarative (implicit): memory of simple skills, how to do things b) Declarative (explicit): memory of things that can be verbalized. People with amnesia have impaired declarative memory; further broken into: 1) Semantic: facts 2) Episodic: events Categories of Memory 3. Alzheimer’s Disease a. Most common form of dementia b. Characteristics 1) Loss of cholinergic fibers in hippocampus and cerebral cortex 2) Accumulation of extracellular proteins called senile plaques 3) Accumulation of intracellular proteins forming neurofibrillary tangles Alzheimer’s Disease, cont c. Amyloid precursor protein (APP) is broken down into peptides called amyloid beta (Aβ) 1) Aβ forms dimers and oligomers that join to form the fibers in the β-pleated sheet structure that forms the amyloid senile plaques 2) Soluble dimers and oligomers of the 42-amino acid form of Aβ causes Alzheimer’s 3) Forms 1% of early onset Alzheimer’s have a mutation in the APP gene or the presentlin gene; most have “sporadic” form with environmental and genetic interactions Alzheimer’s Disease, cont d. Tau protein 1) Normal tau proteins bind to and stabilize microtubules in axons 2) In Alzheimer’s, they aggregate and become insoluble forming the neurofibrillary tangles 3) Soluble, intermediate tau proteins are more toxic e. Toxic changes in Alzheimer’s Disease 1) Loss of synapses and dendritic spines 2) Reduced LTP 3) Reduced excitotoxicity leading to neuron apoptosis 4) Mitochondrial release of reactive oxygen species causing oxidative stress and apoptosis f. People with APOe4 gene have an increased chance of developing Alzheimer’s g. 1) 2) 3) 4) Current treatments Acetylcholinesterase inhibitors Antagonists of glutamate Drugs for depression Many others are in clinical trials 4. Synaptic Changes in Memory a. Short-term memory involves a recurrent circuit (reverberating circuit) where neurons synapse on each other in a circle. 1) Interruption of the circuit destroys the memory because there was no structural change. b. Long-term memory requires a relatively permanent change in neuron chemical structure and synapses. Synaptic Changes in Memory, cont c. Long-term potentiation (LTP) in the hippocampus is a good example. 1) Synapses that are stimulated at a high frequency exhibit increased excitability. 2) In these synapses, glutamate is secreted by the presynaptic neuron. 3) The postsynaptic neuron has both AMPA and NMDA receptors for glutamate. 4) Glutamate binds to AMPA receptor, allowing Na+ in. Long-term potentiation, cont 5) This depolarizes the cell and activates NMDA receptor channels (which were inactive due to a Mg+ blocking the pore). 6) NMDA allows Ca2+ and Na+ in. 7) The Ca2+ binds to a protein called calmodulin, which in turn activates an enzyme called CaMKII. 8) CaMKII causes more AMPA receptors to fuse to the plasma membrane. This alone strengthens the synapse–it becomes more sensitive to glutamate release (EPSP). Long-term potentiation, cont 9) Rise in Ca2+ also causes long-term changes in postsynaptic neurons a) Ca2+ enters the nucleus and binds to calmodulin b) Activates protein kinase that activates a transcription factor called CREB (cyclic AMP response element binding protein c) Activates genes to produce mRNA and proteins, including dendritic spines with AMPA receptors inserted. Synaptic Changes in Memory Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) (both): Reprinted from Esther A. Nimchinsky, Bernardo L. Sabatini, and Karel Svoboda, “Structure and Function of Dendritic Spines,” Annual Review of Physiology, Volume 64: 313–353 © 2002 by Annual Reviews, www.annualreviews.org Synaptic Changes in Memory, cont d. A retrograde messenger (likely NO) is released into the synapse, and the presynaptic axon is changed so that more glutamate can be released and increase LTP e. Endocannabinoids may lift inhibition from GABAreleasing neurons on the synapse, further strengthening it. Synaptic Changes in Memory Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Presynaptic axon Glutamate 4. Increased release of glutamate from presynaptic axon AMPA receptor Na+ Na+ Ca2+ 3. Increased Na+ diffusion through more AMPA receptors 1. Glutamate binds to AMPA and NMDA receptors NMDA receptor Postsynaptic membrane of dendrite CaMKII Nitric LTP Ca2+ oxide induction as retrograde messenger 2. Ca2+ goes through NMDA receptors into cytoplasm, activates CaMKII 5. Neural Stem Cells in Learning a. Neural stem cells have been found in the hippocampus, and scientists suspect that neurogenesis is part of learning. b. In mice, physical activity and an enriched environment promote neurogenesis. c. Aging and stress reduce neurogenesis. H. Emotions and Memory 1. Emotions sometimes strengthen and other times weaken memory formation. a. If the memory has an emotional component, the amygdala is involved in memory formation. b. Stress impairs memory consolidation in the hippocampus and working memory function of the prefrontal cortex. c. Posttraumatic stress disorder may result in hippocampal atrophy. d. Memories are stored but retrieval is hindered Emotions and Memory, cont 2. The amygdala and hippocampus have receptors for stress hormones, such as cortisol. a. It is thought that cortisol may strengthen emotional memory formation via the amygdala but weaken hippocampal memory formation and memory retrieval. Brain Regions Involved in Emotion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (b) (both): Reprinted Figure 2 (1st and 3rd panels) with permission from RJ Dolan, “Emotion, Cognition, and Behavior” Science 298: 1191–1194. Copyright 2002 AAAS a. Yellow = prefrontal cortex; mint green = cingulate gyrus b. Purple = insula; mint green = cingulate gyrus; red = amygdala 3. Prefrontal Cortex a. Orbitofrontal region: ability to consciously experience pleasure and reward; receives input from all the senses and the limbic system 1) Damage here results in severe impulsive behavior. b. Lateral prefrontal area: motivation, sexual desire, and cognitive functions III. Diencephalon A. Introduction 1. Part of the forebrain that includes the epithalamus, thalamus, hypothalamus, part of the pituitary gland, and the third ventricle 2. Surrounded by the cerebral hemispheres Diencephalon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermediate mass Corpus callosum Choroid plexus of third ventricle Septum pellucidum Genu of corpus callosum Splenium of corpus callosum Thalamus Pineal body Anterior commissure Corpora quadrigemina Hypothalamus Cortex of cerebellum Optic chiasma Infundibulum Arbor vitae of cerebellum Pituitary gland Medulla oblongata Mammillary body (a) Pons Telencephalon Forebrain Diencephalon Midbrain Hindbrain (b) b: © The McGraw-Hill Company, Inc./Karl Rubin, Photographer B. Thalamus and Epithalamus 1. Thalamus a. Paired masses of gray matter b. Relay center through which all sensory information, except smell, is passed to the cerebrum c. Intralaminar nuclei promote a state of arousal from sleep and alertness 2. Epithalamus a. Contains the choroid plexus over the third ventricle where cerebrospinal fluid is produced b. Also contains the pineal gland, which secretes the hormone melatonin that helps regulate circadian rhythms C. Hypothalamus and Pituitary Gland 1. Hypothalamus a. Very important for maintaining homeostasis and regulating the autonomic system. Contains centers for: 1) Hunger/satiety and thirst 2) Regulation of body temperature 3) Regulation of sleep and wakefulness 4) Sexual arousal and performance 5) Emotions of fear, anger, pain, and pleasure 6) Control of the endocrine system 7) Controls hormone secretion from the pituitary gland b. Regions of the Hypothalamus & Functions 1) Lateral region: hunger 2) Medial region: satiety 3) Preoptic-anterior: shivering, hyperventilation, vasodilation, sweating 4) Supraoptic: produces antidiuretic hormone, which helps control urine formation 5) Paraventricular: produces the hormone oxytocin, which stimulates childbirth Regions of the Hypothalamus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Paraventricular nucleus Dorsomedial nucleus Posterior nucleus Anterior nucleus Ventromedial nucleus Preoptic area Mammillary body Suprachiasmatic nucleus Supraoptic nucleus Median eminence Optic chiasma Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis) Pituitary gland c. Regulation of the Pituitary Gland 1) ADH and oxytocin are transported along the hypothalamo-hypophyseal tract to the posterior pituitary gland, where they are stored until needed. 2) The hypothalamus also produces releasing hormones and inhibiting hormones that are transported along the adenohypophysis to the anterior pituitary to regulate the secretion of pituitary hormones. d. Regulation of Circadian Rhythms 1) Suprachiasmatic nuclei (SCN): contain about 20,000 “clock cells” with activity that oscillates every 24 hours – main control of circadian rhythms 2) Entrained by information about day length via tracts from retinal ganglion cells with the photopigment melanopsin by way of retinohypothalamic tracts 3) Controls the secretion of melatonin from the pineal gland which is the major regulator of circadian rhythms; secreted mainly at night Regulation of Circadian Rhythms, cont 4) Circadian clock genes are found in cells of the SCN, other brain areas, heart, liver, kidneys, skeletal muscle, adipose tissue, and other organs IV. Midbrain and Hindbrain A. Midbrain 1. Also called the mesencephalon. Includes: a. Corpora quadrigemina 1) Superior colliculi: visual reflexes 2) Inferior colliculi: auditory reflexes b. Cerebral peduncles: ascending and descending tracts c. Red nucleus: connects the cerebrum and cerebellum; involved in motor coordination Midbrain, cont d. Substantia nigra: important part of the motor circuit; part of the dopaminergic nigrostriatal system 1) Ventral tegmental area (VTA): Part of the dopaminergic mesolimbic system that sends neurons to the limbic system and nucleus accumbens in the forebrain 2) Involved in the behavioral reward system and has been implicated in addiction and psychiatric disturbances Dopaminergic Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Caudate nucleus (tail) Corpus callosum Putamen Ventral tegmental area Substantia nigra Caudate nucleus (head) Locus ceruleus Fourth ventricle Nucleus accumbens Corpus striatum Mesolimbic dopamine system Nigrostriatal dopamine system Prefrontal cortex Cerebellum Medial forebrain bundle Pons B. Hindbrain 1. Introduction a. Also called the rhombencephalon b. Composed of the metencephalon and myelencephalon 2. Metencephalon a. Composed of the pons and cerebellum b. The pons houses sensory and motor tracts heading from/to the spinal cord. 1) The trigeminal, abducens, facial, and vestibulocochlear nerves arise from the pons 2) Two respiratory control centers are found here: a) Apneustic b) Pneumotaxic 3) Surface fibers connect to the cerebellum c. Cerebellum 1) Second largest brain structure; gray matter outside, white matter inside 2) Receives input from proprioceptors in joints, tendons, and muscles 3) Works with the basal nuclei and motor cortex to coordinate movement a) Fibers from the cerebellum pass through the red nucleus to the thalamus and then to the motor cortex Cerebellum, cont 4) The cerebellum is needed for motor learning and the proper timing and force required to move limbs in a specific task. 5) The cerebellum influences motor coordination through inhibition on the motor cortex from Purkinje cells. 6) May have roles in acquisition of sensory data, memory, emotion, and other higher functions 3. Myelencephalon a) Made up of the medulla oblongata b) All ascending and descending tracts between the brain and spinal cord pass through the medulla. 1) Tracts cross sides in the pyramids. 2) Cranial nerves VIII, IX, X, XI, and XII come off the medulla. Medulla Oblongata, cont c) Contains nuclei required for regulation of breathing and cardiovascular response = vital centers 1) Vasomotor center controls blood vessel diameter. 2) Cardiac control center controls heart rate. 3) Respiratory center works with areas in the pons to control breathing. Respiratory Control Centers in the Brain Stem Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Midbrain Pons Brain stem respiratory centers Pneumotaxic area Apneustic area Rhythmicity area Reticular formation Medulla oblongata C. Reticular Activating System 1. To fall asleep, we must tune out sensory stimuli. When awake, we are alert to sensory stimuli. 2. This depends on the activation and inhibition of the reticular activating system (RAS). a. Includes the pons and reticular formation of the midbrain Structures of the RAS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thalamus Hypothalamus Pons Medulla Cerebellum Brainstem Reticular Activating System, cont 3. Arousal from sleep and alertness: a. Neurons from the pons release ACh on the thalamus. This enhances passing of sensory information to the cerebral cortex. b. Neurons from the hypothalamus and basal forebrain release monoamines onto the cerebrum, further enhancing alertness. c. Neurons from the lateral hypothalamic area release arousing polypeptide hormones, orexin and hypocretin-1 1) Loss of these neurons leads to narcolepsy. Reticular Activating System, cont 4. Sleep a. Neurons from the ventrolateral preoptic nucleus (VLPO) of the hypothalamus release GABA into other areas of the RAS. b. This inhibits the RAS and allows sleep. c. This activity is increased with depth of sleep. 5. Many drugs act on the RAS to promote either sleep or wakefulness V. Spinal Cord Tracts A. Introduction 1. The spinal cord is composed of white matter surrounding a gray matter core a. The gray matter is arranged with a left and right dorsal horn and a left and right ventral horn. Introduction, cont 2. The white matter is composed of ascending and descending fiber tracts. a. Arranged into six columns called funiculi b. Ascending tracts carry sensory impulses and are given the prefix spino- with a suffix that indicates the brain region it synapses on; ex – lateral spinothalamic tract c. Descending tracts carry motor impulses and are given the suffix -spinal, and the prefix indicates the brain region they come from; ex – anterior corticospinal tract B. Ascending Tracts 1. Convey sensory information from receptors in the skin, muscles, joints, and organs 2. Crossover of tracts (decussation) may occur in the spinal cord or in the medulla. This means that the origin of the input and the brain area are contralateral. Ascending Tracts Ascending Tracts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Postcentral gyrus Axons of third-order neurons Thalamus Cerebral cortex Medial lemniscal tract (axons of second-order neurons) Medulla oblongata Fasciculus cuneatus (axons of first-order sensory neurons) Lateral spinothalamic tract (axons of second-order neurons) Joint stretch receptor (proprioceptor) Pain receptor Spinal cord Axons of first-order neurons (not part of spinothalamic tract) Fasciculus gracilis (axons of first-order sensory neurons) Temperature receptor (a) Touch receptor (b) C. Descending Tracts 1. Two major groups: a. Corticospinal or pyramidal: descend directly without synaptic interruption from the cerebral cortex to the spinal cord 1) Cell bodies of these neurons are located in the precentral gyrus (Primary motor cortex) and superior frontal gyrus (Supplementary motor complex). 2) 80−90% cross in the medulla pyramids and descend as lateral corticospinal tracts. 3) Those that do not cross in the medulla, descend as anterior corticospinal tracts and cross in the spinal cord at the level that the nerves leave the cord. Descending Motor Tracts Descending Pyramidal Tracts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Primary motor area of cerebral cortex Internal capsule Thalamus Medulla oblongata Pyramid Anterior corticospinal tract Lateral corticospinal tract Cervical spinal cord Lumbar spinal cord Skeletal muscle Descending Tracts, cont b. Extrapyramidal tracts: originate in the brain stem and are controlled by the motor circuits of the corpus striatum, substantia nigra, and thalamus 1) Symptoms of Parkinson disease reveal the importance of these tracts for initiating body movements, maintaining posture, and controlling facial expression. Extrapyramidal Tracts, cont 2) Reticulospinal tracts are the major descending extrapyramidal tracts. 3) These originate in the reticular formation of the brain stem. This area is stimulated or inhibited by neurons from the cerebellum, basal nuclei, and cerebrum. 4) Vestibulospinal tracts arise from the vestibular nuclei in the medulla oblongata 5) Rubrospinal tracts arise from the red nuclei. Higher Motor Neuron Control of Skeletal Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cerebral cortex Cerebellum Red nucleus Vestibular nucleus Lower motor neurons Vestibulospinal tract Brain stem reticular formation Rubrospinal tract Basal nuclei Reticulospinal tract Pyramidal (corticospinal) tracts Thalamus VI. Cranial and Spinal Nerves A. 1. 2. 3. 4. Cranial Nerves Part of the PNS Nerves that arise directly from nuclei in the brain Twelve pairs Most are mixed nerves with both sensory and motor neurons (somatic and parasympathetic) 5. Those associated with vision, olfaction, and hearing are sensory only and have their cell bodies in ganglia located near the sensory organ. Cranial Nerves B. Spinal Nerves 1. Part of the PNS 2. Nerves that arise directly from the spinal cord 3. 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal 4. All are mixed nerves that separate near the spinal cord into a dorsal root carrying sensory fibers and a ventral root carrying motor fibers. a. The dorsal root ganglion houses the sensory neuron cell bodies. b. Motor neuron cell bodies are in the ventral gray horns Distribution of Spinal Nerves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cranial nerves (12 pairs) Cervical plexus Brachial plexus Cervical (8 pairs) Thoracic (12 pairs) Spinal nerves Lumbar plexus Sacral plexus Some peripheral nerves: Ulnar Median Radial Femoral Lateral femoral cutaneous Sciatic Lumbar (5 pairs) Sacral (5 pairs) Coccygeal (1 pair) C. Reflex arc 1. Unconscious motor response to a sensory stimulus 2. Parts of an arc a. Sensory receptor b. Sensory neuron c. Association neuron in CNS d. Motor neuron e. Effector – muscle or gland that responds 3. Types of arcs a. Somatic reflex – effectors are skeletal muscles b. Autonomic reflex – effectors are smooth muscle, cardiac muscle, or glands Reflex Arc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Upper motor neuron (association neuron in brain) Dorsal root ganglion Cell body of neuron Dorsal root Sensory neuron Somatic motor neuron Spinal nerve Association neuron Spinal cord Ventral root Skeletal muscle