Study guide for Exam 3
Study guide for Exam 3 Bil 268
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Date Created: 01/31/16
1 Lecture 16: Somatic Motor System: I. Muscles are divided into categories: a. Nonstriated: smooth, secretory, in charge of material movement through intestines, and the control of blood pressure and its flow. b. Striated: - Skeletal: bones around joints. Each skeletal muscle is enclosed in a connective tissue sheath that 100s of muscle fibers (cell of SM). A single axon branch from the CNS innervates each muscle fiber. - Cardiac: heart muscle, involuntary movement. Somatic motor system consists of motor neurons and innervating skeletal muscles. II. Lower Motor Neuron: - Only motor neurons directly command muscle contraction. a. Ventral horn Dorsal root receives sensory input. Where can you find the cell body of a sensory neuron? Ganglia. Ventral horn: body of motor neurons. b. Segmental organization: - Lower motor neurons bundle together from the ventral roots: each joins a dorsal root from the spinal cord to form a spinal nerve that exits the cord through notches between vertebrae. - Motor neurons that innervate distal and proximal musculature are found mainly in the cervical, and lumbarsacral segment, whereas those innervating axial are found at medial level. - The cells innervating the axial muscle are medial to those innervating the distal muscles, and the innervating flexors are dorsal to those innervating extensors. - Cell bodies are located in the left ventral horn showing the dark grey color. - Presynaptic cell innervates the neuron. Postsynaptic cell innervates the muscle fiber. - Each group in the spinal cord has 30 dermatomes. - Muscles are divided into: axial (trunk); distal (hands, feet); and proximal (shoulder, elbow). c. Alpha motor neurons: - For every muscle’s axons, there are different motor neuron pools. - Size principle: muscles fibers get excited from small to large; depends on excitation and path. Small alpha neurons are recruited first larger alpha neurons. - Directly trigger the generation of force by muscles. - Motor unit: one alpha neuron and all the muscles fibers that innervates. - Motor neuron pool: collection of alpha motor neurons that innervate ONE single muscle. - Inputs to alpha motor neurons: lower motor neurons are controlled by synaptic inputs in the ventral horn. 3 major sources of input: i. Dorsal root ganglion in charge of muscle length (sensory) ii. Upper motor neuron in the motor cortex and brain stem, in charge of voluntary movement. iii. Interneurons in the spinal cord, in charge of excitatory or inhibitory, motor programs in the spinal cord. - Types of motor neurons: a. Fast: rapidly fatiguing white fibers, have large diameter, and fast conducting axon. (Type II) b. Slow: slower fatiguing red/white fiber, small diameter, and slower conducting axons. (Type I) - Three input sources to alpha motor neurons: 1. Sensory input synapses to alpha motor neurons 2. SI synapses on interneuron 3. Upper motor neurons M1 is in the control from the brain. 2 - Examples: - Long distance runner slow muscle fiber - Body builder fast muscle fiber III. Excitationcontraction coupling: - Overview: muscle contraction is initiated by the release of Ach from the axon terminals. Ach produces a large ESP in the postsynaptic membrane due to the muscle cell activation of nicotinic Ach Receptors. Muscle cells contain voltagegated sodium channels, this ESPS is sufficient to evoke and action potential in the muscle fiber, which triggers the release of Ca2+, which leads to contraction of the fiber. Relaxation occurs when the Ca2+ levels are lowered by reuptake into the organelles. a. Muscle fibers structure: - Myofibrils: cylindrical structures, contract in response to an action potential sweeping down the sarcolemma. These make up the muscle fibers and contract in response to action potential. - T tubules: insideout axons; networks tunnels. It is linked to a calcium release channel in the SR; the arrival of an action potential causes a conformational change in the voltagesensitive tetrad of channel, leading Ca2+ flow through. (Contraction of myofibril) Connects the sarcoplasmic reticulum to the sarcolemma. - Sarcoplasmic reticulum: extensive intracellular sac that stores Ca2+ - Sarcolemma: cell membrane that encloses muscle fibers. o When the muscle is at rest, myosin cannot interact with actin because the myosin attachment sites on the actin molecule are covered by the protein “troponin.” Binding to it will expose the site where myosin binds to actin. b. Excitation: 1. Action potential occurs in the alpha neuron axon 2. Ach is released at the neuromuscular junction. 3. Nicotinic receptor channels open, and the sarcolemma depolarizes (ESPS) 4. Voltagegated Na+ channels open, and an action potential is generated in the muscle fiber. 5. Ca2+ release from the sarcoplasmic reticulum causes a depolarization on the T tubules. c. Contraction: 1. Ca2+ binds to troponin. 2. Myosin binding sites on the actin are exposed. 3. The cycle continues as long as Ca2+ and ATP are present. d. Relaxation: 1. The sarcolemma and T tubules return to their resting potentials. 2. Ca2+ is sequestered by the sarcoplasmic reticulum by an ATP drivepump. 3. Myosin binding sites on actin are covered by troponin. - Myofibrils are divided into disks (Z lines) - Muscle contraction occurs when thin and thick filaments slide along each other. - H band thick - I band thin (excitation occurs) - A band overlapping between H and I bands. IV. Spinal Control of motor units: i. Myotatic Reflex: function of the muscle spindle; stretch receptor and detector. Overview: when a muscle is pulled on, it tends to pull back (contract). In addition, the MR involves sensory feedback from the muscle; motor neurons must receive a continual synaptic input from the muscles. The discharge of Ia sensory axons is closely related to the length of the muscle. The stretching of the equatorial region of the spindle leads to depolarization of the Ia axon endings due to the opening of mechanosensitive 3 ion channels. The resulting increased action potential discharge of the Ia axons synaptically depolarizes the alpha motor neuron, which respond by increasing their action potential frequency. 1. Muscle spindle: are specialized structures located deep within most skeletal muscle. The spindles are associated Ia axons, specialized for the detection of changes in muscle length (stretch), are examples of “propioceptors. ” Ia axons enter the spinal cord via dorsal roots, branch repeatedly, and form excitatory synapses upon both interneurons and alpha motor neurons of the ventral horns. 2. Kneejerk reflex: when your doctor ta the tendon beneath your kneecap, it stretches the quadriceps muscles, which then reflexively contracts and causes your leg to extend. (monosynaptic reflex one synapse separates sensory input from motor neuron). 3. Types of muscle fibers: i. Intrafusal fiber: muscle fibers that are located within its fibrous capsule. Receive motor innervation by gamma motor neuron ii. Extrafusal fiber: lie outside the spindle and form the bulk of the muscles. Innervated by the alpha motor neuron. Review: Weight on muscle muscle lengthens spindles are stretched depolarization of an alpha motor neuron muscle contracts. iii. Gamma Motor Neuron: regulates muscle spindle responses. 1. Functions of gamma MN: i. Activation of alpha motor neurons causes the Extrafusal muscle fiber to shorten. ii. If the muscle spindle becomes slack, it goes “off the air” and no longer reports the length of muscle. iii. Activation of gamma MN causes the poles of the spindle to contract, keeping it “on the air” 2. Gamma loop: alpha activation alone decreases Ia activity, while gamma activation alone increases Ia activity. Feedback loop - Gamma MN> intrafusal muscle fiber> Ia Afferent axon> alpha motor neuron> Extrafusal muscle fiber. - Gamma MN controls the Myotatic reflex loop, sets desired muscle length, and it is compensated by alpha MN. - Reverse Myotatic reflex: fine motor. Polysynaptic reflex. Golgi tendon organ: source of propio receptive inputs from muscle and muscle force of contraction. PRESSURE RECEPTOR. They are located at the junction of the muscle and the tendon, are innervated by a group of Ib sensory axons, which are smaller that Ia axons. Ib activity from the Golgi tendon organs encodes muscle tension information. Ia activity from the spindles encodes muscle length. Reverse Myotatic reflex protects the muscle from being overload. Its normal function is to regulate muscle tension within an optimal rate. a. Decreased alpha motor neurons is increased muscle contraction. Tension receptor: causes relaxation and reverse myotactic reflex. - Reciprocal inhibition: the contraction of one set of muscles accompanied by the relaxation if the antagonist muscle. Spinal interneurons: polysynaptic all mediated by innervating spinal interneurons; spinal interneurons receive synaptic input from primary sensory axons, descending axon from the brain, and collaterals of lower motor neuron axons. i . Crossedextensor reflex: Activation of the extensor muscles and the inhibition of the flexors of the opposite side. Reciprocal inhibition, but in this case, activation of the flexors on one side of the spinal cord is accompanied by the inhibition of the flexors on the opposite side. ii . Locomotion: Central pattern generators: circuits that give rise to rhythmic motor activity. Electrical stimulation of the stumps of axons descending from the brain can generate alternating rhythmic activity in the spinal cord, mimicking that which occurs during swimming. Activation of the NMDA receptors on spinal interneurons was sufficient to generate locomotor activity. iii . Circuit for rhythmic Alternating activity: 4 1. The membrane depolarizes 2. Na2+ and Ca2+ flow into the cell through the NMDA receptors 3. Ca2+ activates potassium channels 4. K+ flows out of the cell 5. The membrane hyperpolarizes. 6. CA2+ stops flowing into the cell. 7. K+ channels close. 8. Membrane depolarizes, and cycle repeats. 1 Lecture 17: Brain Control of Movement Descending Control: - Overview: the central motor system is arranged as a hierarchy of control levels, with the forebrain at the top and the spinal cord at the bottom. - Hierarchy control: highest level represented by the association areas of neocortex and basal ganglia of the forebrain is connected with strategy: the goal of the movement. Middle level is represented by the motor cortex and cerebellum, is concerned with tactics: sequences of muscle contractions. Lowest level is represented by brain stem and spinal cord, is in charged of the execution: activation of the motor neuron and interneuron pools that generate the goaldirected movement and make any necessary adjustments of posture. I.Descending Pathways: a. The descending tracts of the spinal cord: - The lateral pathways consisting of the corticospinal and rubroespinal tracts, control voluntary movement of the distal musculature. (Direct cortical control) - The ventromedial pathway, consisting of the reticulospinal, vestibulospinal, and tectospinal tracts, control postural muscle and locomotion. (Brain stem control) b. Lateral Pathway: voluntary movement. 1. Two thirds of the axons in the tract originate in areas 4 and 6 of the frontal lobe, collectively called motor cortex. Also, somatosensory area of the parietal lobe serves to regulate the flow of somatosensory information to the brain. Controls movements of arms and hands. 2. Voluntary movement originates in the cortex. 3. Components: i. Pyramidal Tract (corticospinal tract): Axons from the cortex pass through the internal capsule bridging the telencephalon and thalamus, course through the base of the cerebral peduncle (large connection of axons) in the midbrain; then, pass through the pons, and collect to from a tract at the base of the medulla, which is called the medulla pyramid, running down the ventral surface of the medulla. LONGEST pathway. ii. Rubroespinal tract: originates in the red nucleus of the midbrain. Axons from the red nucleus decussate in the pons, almost immediately, and join those in the corticospinal tract in the lateral column of the spinal cord. - A major source of input to the red nucleus is the very region of the frontal cortex. 4. Decussation: crosses, which means that the right motor cortex directly commands the movements of the left side of the body, and the left motor cortex controls the muscles of the right side of the body. This is the junction between medulla and spinal cord. 5. Corticospinal lesions: - Lesion of the area could cause a movement deficit as severe as that observe after lesion in the lateral columns. - Fractionated movement of arms and hands - Recovery if rubroespinal tract intact, which means that over time, partially compensates the loss of the corticospinal tract input. c. Ventromedial Pathways: - Overview: Contains four different tracts that originates in the brain stem and terminate among the spinal interneurons controlling proximal and axial muscles. This controls balance, vision, and body position. 1. Vestibulospinal tract: - Ipsilateral - Originates in the vestibular nuclei of the medulla, and is in charge of the sensory information. 2 - It projects bilaterally down the spinal cord and activates the cervical spinal circuits that control the neck and back muscles, and thus guide head movement. 2. Tectospinal tract: - Originates in the superior colliculus of the midbrain, which receives direct input from the retina. From this input, the superior colliculus constructs a map of the world around us. Stimulation at one site in this map leads to an operating response that directs the head and eyes to move so that the appropriate point of space is imaged on the fovea. 3. The pointe and medullary Reticulospinal tract: - Arises from the reticular formation of the brain stem, which runs the length if the brain stem and its core, just under the cerebral aqueduct and fourth ventricle. - Receives input from many sources and participates in the control posture of the trunk and the antigravity muscles of the limbs. - Reticulospinal Pontine tract: enhances the antigravity reflexes of the spinal cord. The activity of ventral horn neurons maintains, rather than changes, muscle length and tension. - Medullary reticulospinal tract: liberates antigravity muscles from reflex. In charge of maintaining posture and certain reflexes. II. Motor Cortex: 1. Area 4 is referred to as Primary Motor cortex (M1), which is specialized for skilled voluntary movement. Higher motor area in humans shows that electrical stimulation of area could evoke complex movement. 2. Premotor area PMAproximal 3. Supplementary motor area (SMA) distal 4. Coding of Movement in M1: - Occurs before and during a voluntary movement; consists of direction and force vectors. - Direction vector: points in direction that is best for the cell ( the length of this vector represents how active a cell was during a particular movement) - Population vector: average of cell’s direction vector for each direction of movement. - There is a strong correlation between population vector and M1. - Studies have suggested the existence of a finegrained movement map in M1, the discovery that the movement direction tuning of individual M1 neurons is rather broad. - The M1 cells fire most vigorously during movement in one direction (180*), but also discharged during movements that varies more or less 45* from the preferred direction. - Georgopoulus: hypothesized that movement direction was encoded instead by the collective activity of a population of neurons. a. Direction & magnitude vectors: i. The activity of each cell was represented as a direction vector pointing in the direction that was best for the cell. ii. The length of the vector represented how active (magnitude) that cell had been during a particular movement. iii. Population vector: represent the activity of the entire population of M1 cells, and the actual direction of movement. III. Basal Ganglia: participates in memory, cognitive and motor functions. - Overview: major subcortical input to area 6 arises in the ventral lateral nucleus. The input to this part of VL arises from the basal ganglia buried deep within the telencephalon. The basal ganglia, in turn, are targets of the cerebral cortex, particularly the frontal, prefrontal, and parietal cortex. VL input called VLo - Selection and initiation of willed movements 3 a. Structure of basal ganglia: - Caudate nucleus - Putamen - Globus Pallidus: source of the output of the thalamus - Subthalamic nucleus - Substantia nigra - Striatum: target of cortical input to the basal ganglia. (Caudate + putamen) o Pathway: Cortex> Striatum> Globus Pallidus > VLo> Cortex (SMA) b. Motor loop: positive feedback loop. - The thalamocortical connection (from VLo to SMA) is excitatory and facilitates the discharge of movementrelated cells in the SMA - At rest, neurons in the globus pallidus are spontaneously active and therefore inhibit VL. Cortical activation (1) excites putamen neurons, which (2) inhibit globus pallidus neurons, which (3) release the cells in VLo from inhibition, allowing them to become active. The activity in VLo boosts the activity of the SMA; this part of the circuit acts as a positive feedback loop that may serve to focus, or funnel, the activation of widespread cortical areas onto the SMA c. Basal ganglia disorders: - Overview: increased inhibition of the thalamus by the basal ganglia underlies hypokinesia, a paucity of movement. Whereas, decreased basal ganglia output lead to hyperkinesia, and excess of movement. - Parkinson’s Disease: high activity in the thalamus and low dopamine in the sustancia nigra. In result, the patients have low sensory motor activity. - Huntington’s Disease: loss of neurons in the caudate, putamen and globus pallidus. IV. Cerebellum: a. Anatomy: 1. Folia: shallow ridges from side to side of the cerebellum. 2. Lobules: increase the surface area of the cerebellum and contains 50% of neurons. 3. Vermis: splits the cerebellum into two hemispheres; sends output to the brainstem. Function: sequence of muscle contractions. - In charge of sequence of muscle contraction. b. Cerebellar lesions: - Ataxia movements to become uncoordinated and inaccurate. - Dysynergia: synergistic multijoint movement. Move in sequence instead of all at once. - Dysmetric: finger movement will come up short of the nose or shoot past it, when poking themselves in the face. V. Remarks: Neocortex is fully engaged and active as he looks at the catcher for the hand signal that instructs the type of pitch. At the same time, the ventromedial pathways are working to maintain his standing posture. Although his body is still, the neurons of the ventral horns of the spinal cord are firing madly under the influence of the ventromedial pathways, keeping the extensors of the lower leg activated. Regions of the cortex ad area 6, begin planning the movement strategy. The basal ganglia activity increases, triggering the initiation of the pitch. In response, to this input, SMA activity increases, followed immediately by the activation of M1 axons of the lateral pathways. The cerebellum, activated by the corticopontocerebellar inputs, uses these instructions to coordinate the timing of the descending activity so the proper sequence of muscles contractions can occur. Cortical input to the reticular information leads to the release of the antigravity muscles from reflex control. Finally, lateral pathway signals engage the motor neurons and interneurons of the spinal cord, which cause the muscles to contract. 4 1 Lecture 18: Chemical Control of Brain and Behavior: I. Overview: The secretory hypothalamus, by secreting chemical directly into the blood stream, the secretory hypothalamus can influence functions throughout both the brain and the body. Also, the Autonomic Nervous System (ANS) controls the responses of many internal organs, blood vessels and glands. Finally, the CNS consists of several related cell groups that differ with respect to the neurotransmitter they use. II. Components of the NS that operate over long distance and time: Secretory hypothalamus Autonomic nervous system Diffuse modulatory system (axonal projections that determine arousal and mood) Hypothalamus: Overview: Location: adjacent to dorsal Thalamus; pituitary hangs off. Function: integrates somatic and visceral responses in accordance with the need of the brain. Homeostasis. Structure: each side of the hypothalamus has three functional zones: lateral, medial, and periventricular. The lateral and medial zones have extensive connections with the brain stem and the telencephalon and regulate certain types of behavior. The periventricular zone is in charge to synchronize circadian rhythms with daily lightdark cycle. Three functional zones inside the hypothalamus: Lateral and Medial connections with brainstem and telencephalon. Periventricular Suprachiasmatic (region of the biological clock) Functions to synchronize circadian rhythm Control of the ANS Neurosecretory Pathways to the Pituitary Hypothalamic control of the posterior pituitary magnocells neurohormone bloodstream (e.g. oxytocin and vasopressin) Hypothalamic control of the anterior pituitary is controlled by parvocells. Parvo cells hypophysiotropic hormone release blood hormone secreting cells hormones blood action of various organs Hormones released by the anterior pituitary: (FLAT PEG) III. Follicle stimulating hormone (FSH) IV. Lutenizing hormone (LH) V. Adrenocorticotropic hormone (ACTH) VI. Thyroid stimulating hormone (TSH) VII. Prolactin (PRL) VIII. Endorphins (E) IX. Growth hormone (GH) Adenohypophysis: another name for anterior glandular lobe of the pituitary gland and its production and secretion of hormones. Example of hormone secretion scenario (getting sick): Stress hypothalamus secretes corticotropin secreted into the blood and received by H secretory cells ACTH is released by H secretory cells adrenal gland secretes cortisol to the blood immune system suppression Autonomic Nervous Systems: ANS (disynaptic pathway) X. Part of the PNS, which innervates internal organs, blood vessels, and glands. 2 XI. ANS is part of the PNS. XII. Central control: hypothalamus and solitary nucleus XIII. ANS preganglion cell sympathetic or parasympathetic systems post ganglion cell XIV. ANS sensory input solitary nucleus hypothalamus preganglionic neurons XV. Sympathetic system: high heart rate, high blood pressure XVI. Parasympathetic system: lowers high rate, lowers blood pressure ANS is divided into two systems: Parasympathetic system: brain stem and sacral, normal conditions, LONG preganglionic fibers, releases Ach. (Axonal length is closer to the target structure) Sympathetic system: thoracic and lumbar, fight or flight, short preganglionic fibers, Ach and norepinephrine (axons are far away from target). This system consists of pre and postganglionic neurons. This system is not always involved with excitation. The exceptions are the kidneys and the eyes. The kidney’s adrenal medulla releases cortisol but also releases norepinephrine. The eye has the ability to relax and contract. Study the CNS and PNS diagram in power point. Diffuse modulatory systems: Anatomy and functions: XVII. The core of each system has a small set of neurons XVIII. Neurons of the diffused systems arise from the central core of the brain, most of them from brain stem. XIX. Each neuron can influence many other, because each one has and axon that may contact more than 100,00 postsynaptic neurons spread widely across the brain. XX. The synapses made by many of these systems release transmitter molecules into extracellular fluid, so they can diffuse to many neurons rather than be confined to the vicinity of the synaptic cleft. Norepinephrine system: Main location is the locus coeruleus in the pons Functions of sleep, learning, emotion, and pain, etc. Serotonin system: XXI. Main location is the raphe nucleus in the brainstem Control of the sleep wake cycle, mood, and emotion 4 pairs of Raphe nuclei affect the serotonin system Example: LSD (acid); when a person feels high on acid, the person is has a high serotonin level. Dopamine system: Main location is substancia nigra and ventral tegmental area in the midbrain. Initiation of motor response and pleasurable sensation Example of Parkinson’s disease: motor control is very high; and very high dopamine levels. Example of cocaine and amphetamine: the person gets high because these drugs block the uptake and more dopamine accumulates in the brain. For Parkinson’s disease, the patient is treated with dopamine. Acetylcholine system: Main location is the basal forebrain complex in the telencephalon (learning and memory) Pontomesencephalotegmental complex region that regulates excitability Main difference between this system and others is that this is the ONLY system that travels through the basal nucleus of Meynert. Meynert’s area is related to Alzheimer’s Disease – degeneration of Ach neurons Remarks: All the systems discussed above maintain brain homeostasis. They regulate different processes within a certain pathological range. The ANS regulates blood pressure within a range that is appropriate. Blood 3 pressure variations optimize an animal’s performance under different conditions. In a similar way, the noradrenergic locus coeruleus and serotonergic raphe nuclei regulates levels of consciousness and mood. Lecture 19: Emotion Emotion: I. Overview: emotions are feeling we all experience at one time or another. Theories: The JamesLange theory: proposed that we experience emotion in response to physiological changes in our body. CannonBard theory: completely opposite from the JamesLange theory. He proposed that emotional experience could occur independently of emotional expression. II. He believed that emotions could be experienced even if physiological change cannot be sensed. III. He offered cases of animals he and others studied after transection of the spinal cord. Such surgery removed body sensation below the level of the cut, but it did not appear to abolish emotion. IV. He also observed that fear for example is accompanied by increased heart rate, inhibited digestion, and increased sweating. However, these same physiological changes accompany other emotions, such as, anger, illness, etc. Comparison of both theories: in the JamesLange theory, the man perceives the threatening animal and reacts. As a consequence of his body’s response to the situation, he becomes afraid. In the CannonBard theory, the threatening stimulus first causes the feeling of fear; and the man’s reaction follows. iii. Research has also shown that, to some extent, we can be aware of our body’s autonomic function (interoceptive awareness), a key component in JamesLange theory. Another interesting challenge to CannonBard theory, demonstrated by later studies, is that emotion is sometimes affected by damage to the spinal cord. Some evidence indicates that forcing oneself to express an emotionsuch as smiling in order to feel happysometimes work. Unconscious Emotion: experience or expression of emotion in the absence of conscious awareness of the stimulus that evoked the emotion. Broca’s limbic lobe: V. They form a ring or border around the bran stem. VI. The limbic lobe consists of the cortex around the corpus callosum, mainly in the cingulate gyrus, and the cortex on the medial surface of the temporal lobe, including the hippocampus. The Papez circuit: James Papez proposed that there is an “emotion system”, lying on the medial wall of the brain, which links the cortex with the hypothalamus. VII. Papez believed that the experience of emotion was determined by activity in the cingulate cortex and, less directly, other cortical areas. Emotional expression was thought to be governed by the hypothalamus. The cingulate cortex projects to the hippocampus, and the hippocampus projects to the hypothalamus by way of the bundle of axons called the fornix. Hypothalamic effects reach the cortex via a relay in the anterior thalamic nuclei. VIII. Pathway: Neocortex (emotional coloring) cingulate cortex (emotional experience) hippocampus (fornix) Hypothalamus (emotional expression) anterior nuclei of thalamus cingulate cortex. Limbic System: Paul MacLean IX. According to him, the evolution of a limbic system enabled animals to experience and express their emotions and freed them from the stereotypical behavior dictated by their brain. X. Difficulties with the single emotion system concept: given the diversity of emotion we experience, there is no compelling reason to think that the only one system (rather than several) is involved. Fear: KlüverBucy Syndrome: XI. Klüver and Bucy found that bilateral removal of the temporal lobes, or temporal lobectomy, in rhesus monkeys has a dramatic effect on the animal’s aggressive tendencies and responses to fearful situations. The surgery produces several behavioral abnormalities. XII. Decreased vocalization and facial expressions XIII. When done in humans it flattened emotions. XIV. Probably related to the destruction of the amygdala. Amygdala: The amygdala is a complex of nuclei that are commonly divided into three groups: basolateral nuclei, corticomedial nuclei (inhibits aggression), and the central nucleus. The information from all the sensory systems feeds into the amygdala, particularly the basolateral nuclei. Each sensory system has a different projection pattern to the amygdala nuclei, and interconnections within the amygdala allow the integration of information from different sensory modalities. Ventral amygdalofugal pathway Stria terminalis S. M case: (amygdala and fear) XV. Numerous studies on human have examined the effect of lesions that include the amygdala on the ability to recognize facial expressions. Two lesions are rarely alike, and they typically include damage to other brain structures in addition to amygdala. XVI. S. M was women that had bilateral destruction of the amygdala resulting from Urbach Wiethe disease, a rare disorder characterized by the thickening of skin, mucous membranes, and certain internal organs. She had difficulty recognizing certain emotions expressed by people on a photograph. She could not recognize angry or a fearful face. XVII. Functional MRI, demonstrates that neural activity in the amygdala is consistent with a role in processing emotions, especially fear. Neural Circuit for Learned Fear: XVIII. Through training, a sound tone becomes associated with pain. The presumed fear response is mediated by the amygdala. The emotional stimulus reaches basolateral nuclei for the amygdala by way of the auditory cortex, and the signal is released to the central nucleus. Efferents from the amygdala project to the brain stem periaqueductal gray matter, causing the behavioral reaction to the stimulus, and to the hypothalamus, resulting in the autonomic response. The experience of emotion presumably involves projections to the cerebral cortex. Aggression: Types of aggression: XIX. Predatory aggression: involves attacks made against a member of a different species for the purpose of obtaining food. It is not associated with high levels of activity in the sympathetic division of ANS. XX. Affective aggression: is for show rather than to kill and, it is highly associated with the ANS. Hypothalamus and aggression: XXI. Researches discover that one of the brain structures that is highly involves in the aggressive behavior is the hypothalamus; they studied cats and dogs. When the cerebral hemisphere was reduced, the animal expressed a remarkable behavioral transformation. XXII. Sham rage: an emotional stage where the animal would show or express behaviors as of rage but in a situation that normally would not cause anger. Midbrain and aggression: XXIII. 2 major pathways involving autonomic function to the brain stem: Medial forebrain bundle axons from the lateral hypothalamus make up part of the medial forebrain bundle, and these projects to the ventral tegmental area in midbrain. (Predator like behavior). Dorsal longitudinal: Medial hypothalamus sends axons to the periaqueductal gray matter (PAG) of the midbrain. (Affective aggression). Lecture 20: Brain Rhythms Electroencephalogram EEG Brain activity recorded from scalp I. Auditory Evoked Potential (slide not posted) detects less than 1 microvolt. II. Repeat recoding many times and you obtain an average. By reducing the background noise, you increase the signal. EEG results from synaptic excitation in the cerebral cortex: EEG signals are large; average is not calculated. (1020 microvolts) Noninvasive recording. Synchronous activity of many pyramidal neurons: This is the sum of response of many neurons; excitation and inhibition are locked together. III. Two pairs of electrodes detecting potential difference. IV. Synchronous activity must be present for EEG. V. Electrode is far away from neurons. One or two cells are too small for the EEG to detect. VI. Pyramidal cells have greater potential to detect. VII. In the irregular, the neurons are irregular and the sum is irregular too. VIII. Blink – mechanical artifact recorded in the EEG. What is the real signal compared to background noise? How are synchronous EEG waves generated? Pacemaker Mutual excitation and inhibition IX. Types of neural network: One neuron is a leader Neurons are working together X. Right rhythm XI. Cells receive excitatory input The E cell will excite I cell and will inhibit (locomotion behavior alternating pattern of excitation) XII. Where can you find an oscillator? You can find in the thalamus sensory gateway. Inside the thalamus, you find two cells. EEG waves XIII. Based on frequency and amplitude. Beta wave activated cortex you can record when you are awake and sleep state. Sleep state can detect brain activity not necessarily passive. XIV. Beta: fastest (> 14 Hz), activated cortex XV. Alpha: 813 Hz, waking states XVI. Theta: 47 Hz, sleep states XVII. Delta: < 4 Hz, deep sleep, large amplitude Functions of brain rhythms Disconnect the cortex from sensory input Coordinate activity between regions of NS No function Functions of the brain waves hypotheses Take a rest disconnecting from sensory input For any task, you need to have so many neurons in your brain to wok together. Recruiting neurons to work together between regions. Not important to brain function Seizures and epilepsy Seizures result from extremely synchronous brain activity Generalized/partial seizure Epilepsy: repeated seizures What happens when your brain waves go wrong? Seizures and epilepsy Periodic seizures– become epilepsy Why is this bad to the brain? This is over excitation exitoxicity from too much neuron activity and will kill postsynaptic neurons and produce brain damage. Generalized seizure covers the whole brain Sleep Universal among higher vertebrates Sleep deprivation, devastating. Onethird of lives in sleep state Defined: “Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment.” Do fish sleep? How to tell that fish is asleep? Sleep deprivation by electrical shock and constant light Hypocretin (orexin), hypothalamus, narcolepsy Zebra fish sleep is quite similar to mammalian sleep How to tell fish is asleep? Stop swimming, immobilized at bottom or on the surface, increased threshold for electric shock Sleep deprivation by electrical shockà sleep more after that Constant light almost suppress zf sleep completely (different from humans) and no compensatory increase in sleep. This might result from light suppression of melatonin Both humans and zf have hypocretin, one of the most important sleepregulating molecules. In Humans death of hypocretinproducing neurons or mutation of hypocretin receptors à narcolepsy (excessive sleep during the day). But mutation of hypocretin receptors in zf à no increase in sleep during the day. Human hypocretinproducing neurons project to DA and 5HT neurons while zf HPNs project to GABA neurons. Insomnia: cannot fall in asleep at night. Article from Mike Locher: Orexin, a neuropeptide that stimulates eating and regulates wakefulness, also fosters animal’s seeking and craving (intense or abnormal desire) responses. It promotes drugseeking and craving in rats. Two states of sleep Dreams – REM Somnambulism – NonREM What’s PET imaging? Positron emission tomography Inject radioactively labeled 2DG called FDG, fludeoxyglocose with radioactive isotope fluorine18 ( F) Neurons pick up FDG à correlation between neural activity and amount of FDG taken by neurons Red (+4) means more activity in REM, green and dark blue (between +1 and 1) mean similar activity, white (4) means less activity in REM! The sleep cycle: Stage 1: nonREM, Theta Stage 2: nonREM, spindle & K complex Stage 3: nonREM, Delta Stage 4: nonREM, Delta Stage 5: REM, Beta Repeat every 90 min Why do we sleep? Restoration Adaptation Synaptic homeostasis hypothesis: Sleeping to reset overstimulated synapses. “One major function of sleep is to reduce synaptic connection in the brain.” (Sci. 2009 324:109) “Synaptic communication can grow stronger during sleep.” Mechanisms of sleep Sleep is an active process DMS à thalamus à control EEG & block sensory input REMon cells: ACh in pons REMoff cells: NE and serotonin in locus coeruleus and raphe nuclei Circadian Rhythms Chronobiology: Ultradian rhythms: < 24 h, sleep cycle, heartbeat Circadian rhythms: 24 h, sleepwake cycle Infradian rhythms: > 24 h, menstrual cycle Circadian rhythms: rhythms with a period of one day Zeitgebers: environmental time cues Primary zeitgeber: lightdark cycle Internal biological clocks Suprachiasmatic nuclei (SCN): luminance NT: GABA BlockerTTX does not disrupt their rhythmicity Lesions of SCN disrupt the clock Light sensors (retinal GCs)à clocks à output Benson and colleagues: Discovered specialized type of ganglion cell in retina Photoreceptor, but not rod or cone cell Contains melanopsin, slowly excited by light Synapses directly onto SCN neurons Molecular clocks similar in humans, mice, flies, mold Clock genes: Period (Per), Timeless (Tim), Clock Takahashi: Regulation of transcription and translation, negative feedback loop Drosophila per à mRNA à PER protein tim à mRNA à TIM protein Increase in [PER/TIM dimers] à dissociated à PER transported into nucleus à PER binding to CLK/CYC transcription factor à removal of CLK/CYC from promoter of per & Lecture 21: Language and Attention Language Definition: Simplest use of communication. Ex: frogs vocalization male attracting females Fish conducts sounds to attract females. Language areas in the brain Left cerebral hemisphere Broca’s area: Frontal lobe Wernicke’s area: Temporal lobe Gene: FoxP2 Looking at the genes of ancestors between primates and chimpanzees, and humans. Comparing genetics, humans only have two different genome sequences compared to chimpanzees. Left cerebral cortexà dominant roleà Broca’s area (frontal lobe) – close to motor cortex and probably has to do with motor processing, speech. Wernicke’s area: temporal lobeà near the primary auditory cortex The Discovery of Specialized Language Areas in the Brain Wada Procedure: Used to determine hemisphere dominant for speech Brodmann areas Korbinian Brodmann: 1 to 52 Brodmann area is divided into 52 areas. Broca’s: 42 and 45 Wernicke’s area: 22, 39, 40 Primary motor cortex: 4 Primary somatocortex: 1,2,3 V1: 17 Broca’s area: 44 & 45 Wernicke’s area: 22, 39, 40 How did scientist found out left side is dominant? Left side and right side are supplied by different blood vessels. If you inject CNS suppressants, and carried out the left side of the hemisphere and then compared language processing. Aphasia Definition: inability to produce or understand speech. Broca’s aphasia (expressive/motor): anomia, agrammatism, paraphasic errors Wernicke’s aphasia (fluent/sensory) If the patient has damage to one of the language areas, they will have aphasia, lack of language communication due to illness or physical trauma. Broca’s aphasia motor part is defected. They can understand they cannot express. Bad grammar? Substitute incorrect words. Wernicke aphasia fluent aphasia the patient can talk sensory aphasia problem is comprehension they don’t understand the question. Ex: movie clips shown in class Broca’s aphasia doctor has conversation with patient Patient used to be a dentist. Has trouble communicating with the woman. Conduction aphasia: speech is fluent, comprehension remains good, major impairment in repetition, paraphasic errors, Arcuate fasciculus Fiber tract that connects these two areas: arcuate fasciculus. If the fiber is damaged, the areas will be affected. Hypotheses of language processing WernickeGeschwind model Spoken word Written word Ex: spoken words begins in the A1, then Wernicke’s area Broca’s area yellow area (angular gyrus) M1 is last. Ex: written word first you begin with V1Angular gyrusWernicke’s areaBroca’s area. **The difference is where these two situations begin. Splitbrain studies Corpus callosum: major connection b/w two parts of the brain Visual stimulation of one hemisphere The stimulation can only reach one side of the brain. One side registers the image. Asymmetrical Language Processing in the Cerebral Hemispheres SplitBrain Studies: people can be born with it or needed to remove it because of seizures. Roger Sperry (1950s): NOBEL Splitbrain procedure Sever axons making up the corpus callosum No major deficits With proper experiments, animals behaved as if they had 2 brains Left Hemisphere Language Dominance Right visual field, repeated easily Left visual field, difficulty verbalizing Image only in left visual field, object in left hand, unable to describe UNABLE TO DESCRIBE ANYTHING TO LEFT OF VISUAL FIXATION POINT If the image is from the right side and received from the left side, no problem. If the image is from the left side, and received from the right side, ask patient what did you see? The patient will say nothing. Movie professor at Chicago showing connection between hemispheres. Language function of the right hemisphere: Functions of right hemisphere: Read and understand numbers, letters, and short words (nonverbal response) Baynes, Gazzaniga, and colleagues: Right hemisphere able to write, cannot speak Left hemisphere: Language Asymmetry in the brain: Planum temporale in the temporal lobe 65% left side is larger than the right side of 100 autopsy 10% right side if larger than left of 100 autopsies Others are the same. Three techniques Electrical stimulation: how stimulus affects the language processing. Positron emission tomography (PET): neuron can pick up the radioactive level and the image displays neuronal activity Magnetic resonance imaging (MRI): related to neurons oxygen level of O is high or low is dependent on hemoglobin. Without O the signal will be very high. Bloodoxygenlevel dependent (BLOD) contrast Attention Consequences of attention Enhances detection Shortens reaction time When you pay attention, you will drive all your brain into the stimulus, causing to miss other things in the surroundings. Neglect syndrome: an attentional disorder Definition: patients that had a stroke in the right side hemisphere will ignore everything on their left visual field; however, after a couple of month they might recover an 80%. Attentionenhanced neural responses: Monkey experiment. Electrode recorded. Lecture 22: Wiring the Brain Genesis of Neurons: 3 steps: cell proliferation, migration, & differentiation Cell proliferation Ventricular and marginal zones Five positions: A cell in the ventricular zone extends a process that reaches upward the pia. The nucleus of the cell migrates upward from the ventricular surface toward the pial surface; the cell’s DNA is copied The nucleus, containing two complete copies of genetic instructions, settles back to the ventricular surface. The cell retracts its arm from the pial surface. The cell divides into two. The newly daughter cells is cleaved vertically during division. After, the vertical cleavage, bot daughter cells remain in the ventricular zone to divide again and again. Later in development to expand the population of neuronal precursors, horizontal cleavage is the rule. In this case, the daughter cell lying farthest away from the ventricular surface migrates away to take up its position in the cortex. They will repeat the patterns until all the neurons and glia of the cortex have been generated. Stem cells à different cell types Birth time à neuronal fate The adult ventricular zone retains some capacity to generate new neurons. The factor that makes one cell different from another is the specific genes that generate mRNA and, ultimately protein. The cell fate is regulated by differences in the gene expression during development. If transcription factors, or the “upstream” molecules that regulate them, are unevenly distributed within a cell, then the cleavage plane can determine which factors are passed in to daughter cells. Mature cortical cells can be classified as glia or neurons, and the neurons can be further classified according to the layer in which they reside, this are called neural stem cells. The ultimate fate of the migrating daughter cell is determined by many factors, such as the age of the precursor cell, its position within the ventricular zone, and its environment at the time of division. The first cells to migrate away from the dorsal ventricular zone are destined to reside in a layer called subplate, which eventually disappears as development proceeds. The next cells to divide become layer VI neurons, followed by layers V, IV, III, and II. Cell Migration Pyramidal cells and astrocytes migrate vertically from ventricular zone by moving along thin radial glial fibers (provide the scaffold on which the cortex is built) towards the pia. Inhibitory interneurons and oligodendroglia generate from a different site and migrate laterally Neuroblasts (immature neurons) and radial glial cells Neuroblasts destined to become subplate cells are among the first to migrate away from ventricular zone. Neuroblasts destined to become the adult cortex migrate next. They cross the cortical plate and subplate Insideout Cell differentiation Cell takes on the appearance and characteristics of a neuron called differentiation, a consequence of a specific spatiotemporal pattern of gene expression. It occurs in the cortical plate Neuronal differentiation occurs first, followed by astrocyte differentiation that peaks at about the time of birth. Oligodendrocytes are the last cells to differentiate. Programmed Environmental factors Genesis of connections Three phases: Overview: imaging you lead a growing retinal ganglion cell axon to the correct location in the LGN. First, you travel down the optic stalk down the brain, and must decide which fork in the road to take. The correct path depends on the location in the retina of your ganglion (pathway selection). Having forged your way into the dorsal thalamus, you are now confronted with the choice of which thalamic nucleus to innervate. The correct choice is the lateral geniculate nucleus (target selection). Finally, you must now find the correct layer of the LGN (address selection). Pathway formation Growing axon: Axonal growth – growth cone: growing tip of a neurite; which is specialized to identify an appropriate path for a neurite elongation. The leading edge of the growth cone consists of flat sheets of membrane called lamellipodia that undulate in rhythmic waves. Extending from the lamellipodia are thin spikes called filopodia, which constantly probe the environment, moving in and out of the lamellipodia. Growth of the neurite occurs when the filopodium takes hold of the substrate (surface) and pulls the advancing growth cone forward Extracellular matrix (fibrous glycoproteins laminin) Cell surface molecules (integrin) Fasciculation (cell adhesion molecules – CAMs): mechanism that causes the axon growing together to stick together. Fasciculation is due to the expression of specific surface molecules (CAMs). Axon Guidance: Axons conclude a segment when they arrive at an intermediate target. Guidance Cues: interactions of these cell surface molecules with guidance cues in the environment determine the direction and amount of growth. Guidance can be attractive or repulsive. Chemoattractant (e.g., netrin): is a diffusible molecule that acts over a distance to attract growing axons towards their target. For example, netrin is secreted by neurons in the ventral midline of the spinal cord. The gradient of netrin attracts the axons of the dorsal horn neurons that will cross the midline to form the spinothalamic tract. Chemorepellent (e.g., slit): a diffusible molecule that chases the axons away. For example, slit enables the escape the powerful siren song of netrin. In order for slit to ex
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