Transcript brain
Brain Structure and Function 1 “If the human brain were so simple that we could understand it, we would be so simple that we couldn’t” -Emerson Pugh, The Biological Origin of Human Values (1977) 2 Phineas Gage • September 13th, 1848 • Phineas 25 years old • Rutland & Burlington Railroad, Cavendish, VT • Paving the way for new RR tracks • “Tamping Iron” – 1.25in x 3ft 3 Neuroscience and Phineas Gage 4 Phineas Gage • Accident – Quick Recovery • Months later: “No longer Gage” – Before: capable, efficient, best foreman, well-balanced mind – After: extravagant, anti-social, liar, grossly profane • Stint with P.T Barnum • Died 12 years later 5 Overview: Command and Control Center • The circuits in the brain are more complex than the most powerful computers • Functional magnetic resonance imaging (MRI) can be used to construct a 3-D map of brain activity • The vertebrate brain is organized into regions with different functions 6 • Each single-celled organism can respond to stimuli in its environment • Animals are multicellular and most groups respond to stimuli using systems of neurons 7 Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells • The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets • A nerve net is a series of interconnected nerve cells • More complex animals have nerves 8 • Nerves are bundles that consist of the axons of multiple nerve cells • Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring 9 Fig. 49-2 Eyespot Brain Radial nerve Nerve cords Nerve ring Transverse nerve Nerve net Brain Ventral nerve cord Segmental ganglia (a) Hydra (cnidarian) (b) Sea star (echinoderm) (c) Planarian (flatworm) (d) Leech (annelid) Brain Brain Ventral nerve cord Anterior nerve ring Ganglia Brain Longitudinal nerve cords Ganglia (f) Chiton (mollusc) (g) Squid (mollusc) Spinal cord (dorsal nerve cord) Sensory ganglia Segmental ganglia (e) Insect (arthropod) (h) Salamander (vertebrate) 10 Bilaterally symmetrical animals exhibit cephalization Cephalization is the clustering of sensory organs at the front end of the body Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS) The CNS consists of a brain and longitudinal nerve cords 11 Fig. 49-2b Eyespot Brain Nerve cords Transverse nerve Brain Ventral nerve cord Segmental ganglia (c) Planarian (flatworm) (d) Leech (annelid) 12 Fig. 49-2c Brain Ventral nerve cord Anterior nerve ring Ganglia Longitudinal nerve cords Segmental ganglia (e) Insect (arthropod) (f) Chiton (mollusc) 13 • Nervous system organization usually correlates with lifestyle • Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex molluscs (e.g., octopuses and squids) have more sophisticated systems 14 Fig. 49-2d Brain Brain Ganglia (g) Squid (mollusc) Spinal cord (dorsal nerve cord) Sensory ganglia (h) Salamander (vertebrate) 15 • In vertebrates – The CNS is composed of the brain and spinal cord – The peripheral nervous system (PNS) is composed of nerves and ganglia 16 Organization of the Vertebrate Nervous System • The spinal cord conveys information from the brain to the PNS • The spinal cord also produces reflexes independently of the brain • A reflex is the body’s automatic response to a stimulus – For example, a doctor uses a mallet to trigger a knee-jerk reflex – Science 360 reflexes-reaction-time 17 Fig. 49-3 Quadriceps muscle 2. Sensors detect The sudden movement Cell body of sensory neuron in dorsal root ganglion Sensory neurons Conveys the information to the brain Gray matter White matter Hamstring muscle Spinal cord section) Sensory neuron and (cross Motor neurons relay The message to the quad To cause it to contract; They also communicate with interneurons That inhibit the hamstring from contracting Sensory neuron Motor neuron Interneuron 18 • Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord • The spinal cord and brain develop from the embryonic nerve cord 19 Fig. 49-4 Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Cranial nerves Ganglia outside CNS Spinal nerves 20 Fig. 49-5 Gray matter Consisting mainly of Neuron cell bodies, Dendrites and Unmyelinated axons White matter Consists of bundled Axons with myelin sheaths Ventricles 21 • The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid • The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord 22 • The brain and spinal cord contain – Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons – White matter, which consists of bundles of myelinated axons In general, men have approximately 6.5 times the amount of gray matter related to general intelligence than women, and women have nearly 10 times the amount of white matter related to intelligence than men. Gray matter represents information processing centers in the brain, and white matter represents the networking of – or connections between – these processing centers. 23 • may help to explain why men tend to excel in tasks requiring more local processing (like mathematics), • while women tend to excel at integrating and assimilating information from distributed graymatter regions in the brain, such as required for language facility. • These two very different neurological pathways and activity centers, however, result in equivalent overall performance on broad measures of cognitive ability, such as those found on intelligence tests. 24 Evolution of the Brain crash course nervous system Reptilian Paleomammalian Neomammalian 25 Reptilian Brain • The oldest of the distinct brains • Vital functions such as heart rate, breathing, body temperature and balance – Brain stem and the cerebellum Cerebellum:: voluntary muscle control 26 Paleomammalian • Emerged in the first mammals • A.K.A the limbic system – Records memories of behaviours – Basically emotions – Hippocampus (memories), the amygdala (anxiety, fear, anger) and the hypothalamus – The seat of value judgements 27 Neomammalia n Brain • a.k.a the neocortex • Became important in primates and culminated with humans – Human language, abstract thought, imagination, consciousness – Flexible with almost infinite learning 28 abilities Fig. 49-9ab Telencephalon Forebrain Diencephalon Mesencephalon Midbrain Metencephalon Hindbrain Myelencephalon Mesencephalon Metencephalon Midbrain Hindbrain Forebrain (a) Embryo at 1 month Diencephalon Myelencephalon Spinal cord Telencephalon (b) Embryo at 5 weeks 29 Fig. 49-9c Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) Diencephalon: Cerebrum Hypothalamus Thalamus Pineal gland (part of epithalamus) Neocortex Aka Neomammalian brain Limbic system Aka paleomammalian brain Brainstem: Midbrain Pons Pituitary gland Medulla oblongata Spinal cord Reptilian brain Cerebellum Central canal (c) Adult 30 The Cerebral Cortex • Cerebral Cortex –the body’s ultimate control and information processing center –The top layer of the cerebrum 31 Thought to be present in only the superior mammals! the “newest” part of the brain possessed by more phylogenetically advanced species 32 The lobes of the cerebral hemispheres 33 The lobes of the cerebral hemispheres Planning, decision making speech Sensory Auditory Vision 34 The Cerebral Cortex • Frontal Lobes – involved in speaking and muscle movements and in making plans and judgments – the “executive” • Parietal Lobes – include the sensory cortex – Integrates sensory information 35 The Cerebral Cortex • Occipital Lobes – include the visual areas, which receive visual information from the opposite visual field • Temporal Lobes – include the auditory areas, each of which receives auditory information primarily from the opposite ear 36 The Cerebral Cortex • • • • Frontal (Forehead to top) Motor Cortex Parietal (Top to rear) Sensory Cortex Occipital (Back) Visual Cortex Temporal (Above ears) Auditory Cortex 37 • Contralateral- one side controls the other side • Homunculus- visual representation of the “body within the brain” • Unequal representation- the “body part” is proportional to the amount of cerebral cortex or tissue devoted to it Motor/Sensory Cortex 38 39 Sensory Areas – Sensory Homunculus 40 Figure 13.10 The Cerebral Cortex Aphasia impairment of language, usually caused by left hemisphere damage either to Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding) Broca’s Area an area of the left frontal lobe that directs the muscle movements involved in speech Wernicke’s Area an area of the left temporal lobe involved in language comprehension and expression 41 Language Areas • Broca Expression • Wernicke Comprehension and reception • Aphasias LEFT HEMISPHERE 42 The Cerebrum • The cerebrum develops from the embryonic telencephalon • The cerebrum has right and left cerebral hemispheres • Each cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nuclei • In humans, the cerebral cortex is the largest and most complex part of the brain • The basal nuclei are important centers for planning and learning movement sequences 43 Fig. 49-UN4 44 • A thick band of axons called the corpus callosum provides communication between the right and left cerebral cortices • The right half of the cerebral cortex controls the left side of the body, and vice versa 45 Fig. 49-13 Left cerebral hemisphere Right cerebral hemisphere Corpus callosum Thalamus Cerebral cortex Basal nuclei 46 The Brain • Brainstem – responsible for automatic survival functions; homeostasis, coordination of movement • Medulla –controls heartbeat and breathing 47 The Brainstem • The brainstem coordinates and conducts information between brain centers • The brainstem has three parts: the midbrain, the pons, and the medulla oblongata • Also called the reptilian brain, the oldest part of the brain that was present in the common ancestor before mammals and reptiles 48 • The midbrain contains centers for receipt and integration of sensory information • The pons regulates breathing centers in the medulla • The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion 49 Parts of the Brain THALAMUS Relays messages amygdala hippocampus pituitary CEREBELLUM Coordination and balance BRAINSTEM Heart rate and breathing 50 The Brain (more) • Thalamus – the brain’s sensory switchboard, located on top of the brainstem – it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla 51 Arousal and Sleep • The brainstem and cerebrum control arousal and sleep • this regulates the amount and type of information that reaches the cerebral cortex and affects alertness • The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles 52 Fig. 49-10 Eye Reticular formation Input from touch, pain, and temperature receptors Input from nerves of ears 53 • Sleep is essential and may play a role in the consolidation of learning and memory • Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep” 54 Fig. 49-11 Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Location Time: 0 hours Time: 1 hour Left hemisphere Right hemisphere 55 Reticular Formation •Widespread connections of neurons in the core of the brainstem • Arousal of the brain as a whole •Reticular activating system (RAS) •Maintains consciousness and alertness •Functions in sleep and arousal from sleep 56 The Cerebellum –helps coordinate voluntary movement and balance; nonverbal learning and memory 57 The Diencephalon • The diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamus • The epithalamus includes the pineal gland and generates cerebrospinal fluid from blood • The thalamus is the main input center for sensory information to the cerebrum and the main output center for motor information leaving the cerebrum • The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing 58 Fig. 49-UN3 59 60 The Limbic System a.k.a paleomammalian brain • Hypothalamus, pituitary, amygdala, and hippocampus all deal with basic drives, emotions, and memory – Hippocampus Memory processing – Amygdala Aggression (fight) and fear (flight) – Hypothalamus Hunger, thirst, body temperature, pleasure; regulates pituitary gland (hormones) 61 Forms the inner border of the cortex controls emotion, motivation, learning and memory The intermediate mammalian braincorresponds to the brain of inferior mammals new neurons 62 The Limbic System Hypothalamus neural structure lying below (hypo) the thalamus; directs several maintenance activities eating drinking body temperature helps govern the endocrine system via the pituitary gland linked to emotion 63 A mouse. A Laser beam. A manipulated memory. 64 Biological Clock Regulation by the Hypothalamus • The hypothalamus also regulates circadian rhythms such as the sleep/wake cycle – Mammals usually have a pair of suprachiasmatic nuclei (SCN) in the hypothalamus that function as a biological clock • Biological clocks usually require external cues to remain synchronized with environmental cycles 65 Biological clocks Directs gene expression and cellular activity Usually synchronized to dark and light cycles Usually a 24 hour cycle Importance of sleep for the brain 66 Fig. 49-12 RESULTS Wild-type hamster hamster Wild-type hamster with SCN from hamster hamster with SCN from wild-type hamster Circadian cycle period (hours) 24 Normal hamster Normal scn that works 23 22 21 20 Normal hamster Transplanted with Mutant SCN 19 Before procedures After surgery and transplant 67 The Limbic System Motivation: self-stimulation in rats brain mechanisms of pleasure and addiction 68 The Limbic System • Amygdala – two almond-shaped neural clusters that are components of the limbic system and are linked to emotion and fear – Social processing – attention 69 August 1st, 1966 Charles Whitman 70 Paul Broca [1800s] Tumor of Broca's area • Suggested localization after studying the Brain of “Tan” post mortem 71 Found that the left frontal lobe controlled speech Techniques to examine functions of the brain 1. Remove part of the brain & see what effect it has on behavior 2. Examine humans who have suffered brain damage 72 3. Stimulate the brain 4. Record brain activity 73 74 Brain Lateralization 75 Our Divided Brains • Corpus collosum – large bundle of neural fibers (myelinated axons, or white matter) connecting the two hemispheres • Largest white matter area of the brain, and females have more of it! (scientists are still researching this) 76 Other correlations Bigger: -Musicians -Left handed and ambidextrous -Verbal memory capacity and semantic coding testing -nondyslexic -women (?) smaller • Nonmusicians • Right handers • Dyslexics • Men (?) 77 Hemispheric Specialization (lateralization) LEFT RIGHT Symbolic thinking (Language) Detail Literal meaning Spatial perception Overall picture Context, metaphor 78 Contra-lateral division of labor • Right hemisphere controls left side of body and visual field • Left hemisphere controls right side of body and visual field 79 Split Brain Patients • Epileptic patients had corpus callosum cut to reduce seizures in the brain • Lives largely unaffected, seizures reduced • Affected abilities related to naming objects in the left visual field 80 Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions • Each side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal • Each lobe contains primary sensory areas and association areas where information is integrated 81 Fig. 49-15 Frontal lobe Parietal lobe Speech Frontal association area Somatosensory association area Taste Reading Speech Hearing Smell Auditory association area Visual association area Vision Temporal lobe Occipital lobe 82 Information Processing in the Cerebral Cortex • The cerebral cortex receives input from sensory organs and somatosensory receptors 83 Sensory Organs • Those that are associated with the 5 senses – -ears – Tongue – Eyes – Skin – nose 84 Somatosensory system • Those that detect: – Temperature – Body position – Pain – Touch – Sensory receptors are all over! – How the brain determines the bodies position 85 • Specific types of sensory input enter the primary sensory areas of the brain lobes – example: visual input reaches the occipital lobes, auditory input reaches the temporal lobe • Adjacent areas process features in the sensory input and integrate information from different sensory areas • In the somatosensory and motor cortices, neurons are distributed according to the body part that generates sensory input or receives motor input 86 Fig. 49-16 Parietal lobe Frontal lobe Leg Genitals Toes Jaw Primary motor cortex Abdominal organs Primary somatosensory cortex 87 Fig. 49-17 Max Hearing words Seeing words Min Speaking words Generating words 88 Emotions • Involves the limbic system: the amygdala, the thalamus and the hippocampus (the paleomammalian brain) – Emotion, motivation, olfaction, behavior and memory – Can involve sensory areas of the cerebrum (the neomammalian brain) 89 Emotions • Can be stored as memories – Recall of events is centered someplace differently than the emotions that go along with those events • The emotions can be stored in the amygdala or prefrontal cortex 90 Consciousness • Sense of awareness of surrounding, of oneself, our perceptions and internal thoughts 91 Consciousness • Modern brain-imaging techniques suggest that consciousness is an emergent property of the brain based on activity in many areas of the cortex • MRI can compare conscious and unconscious sensory activity but cannot determine a “consciousness center” in the brain 92 Concept 49.4 Changes in synaptic connections underlie memory and learning • Two processes dominate embryonic development of the nervous system – Neurons compete for growth-supporting factors in order to survive, they have many synapses – Only half the synapses that form during embryo development survive into adulthood (because they aren’t needed for proper function) 93 Changes • The number of neurons that are able to survive is determined by the competition for – Growth supporting factors The number of synapses can also change: the lower the activity, fewer synapses that survive 94 Brain Plasticity • The ability of the brain to reorganize neural pathways based on new experiences • Persistent functional changes in the brain represent new knowledge • Age dependent component • Brain injuries 95 • http://www.youtube.com/watch?v=VaDlLD 97CLM • The Story of Jodi and Brain Plasticitiy 96 Environmental influences on neuroplasticity Impoverished environment Enriched environment 97 Fig. 49-19 N1 N1 N2 N2 (a) Synapses are strengthened or weakened in response to activity. (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses. 98 Memory and Learning • Learning can occur when neurons make new connections or when the strength of existing neural connections changes • Short-term memory is accessed via the hippocampus (temporary links) • The hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortex 99 Repetition reinforces long term memory storage! The neurons make more/new connections 100 Long Term Potentiation • In the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmission • LTP involves glutamate receptors • If the presynaptic and postsynaptic neurons are stimulated at the same time, the set of receptors present on the postsynaptic membranes changes 101 Fig. 49-20a Ca2+ Na+ Glutamate NMDA receptor (open) NMDA receptor is open but Blocked by Mg Mg2+ Stored AMPA receptor NMDA receptor (closed) (a) Synapse prior to long-term potentiation (LTP) 102 Fig. 49-20b 1 3 2 A long term AMPA receptor then Replaces a NMDA receptor; the more AMPA vs NMDA receptors found the more Likely the memory is long term! (b) Establishing LTP A nearby synapse Depolarizes, causing the Mg To be released; The receptor now responds to glutamate 103 Fig. 49-20c 3 4 1 2 (c) Synapse exhibiting LTP 104 Concept 49.5: Nervous system disorders can be explained in molecular terms • Disorders of the nervous system include schizophrenia, depression, Alzheimer’s disease, and Parkinson’s disease • Genetic and environmental factors contribute to diseases of the nervous system 105 Schizophrenia • About 1% of the world’s population suffers from schizophrenia • Schizophrenia is characterized by hallucinations, delusions, blunted emotions, and other symptoms • Available treatments focus on brain pathways that use dopamine as a neurotransmitter 106 Fig. 49-21 50 Genes shared with relatives of person with schizophrenia 12.5% (3rd-degree relative) 25% (2nd-degree relative) 50% (1st-degree relative) 100% 40 30 The closer The relation The more likely To inherit 20 10 First cousin Individual, general population 0 Relationship to person with schizophrenia 107 Possible pathways • 1st: “speed” stimulates dopamine release causing symptoms of schizophrenia • 2nd: drugs that block dopamine receptors inhibit the symptoms • 3rd: might alter glutamate signaling since PCP blocks glutamate receptors and induces schizophrenia like symptoms 108 Depression • Two broad forms of depressive illness are known: major depressive disorder and bipolar disorder • In major depressive disorder, patients have a persistent lack of interest or pleasure in most activities • Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases • Treatments for these types of depression include drugs such as Prozac and lithium 109 Drug Addiction and the Brain Reward System • The brain’s reward system rewards motivation with pleasure • Some drugs are addictive because they increase activity of the brain’s reward system • These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco • Drug addiction is characterized by compulsive consumption and an inability to control intake 110 • Addictive drugs enhance the activity of the dopamine pathway • Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug 111 Fig. 49-22 Nicotine stimulates dopaminereleasing VTA neuron. Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine. Cerebral neuron of reward pathway Reward system response 112 Alzheimer’s Disease • Alzheimer’s disease is a mental deterioration characterized by confusion, memory loss, and other symptoms • Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain • A successful treatment in humans may hinge on early detection of amyloid plaques • There is no cure for this disease though some drugs are effective at relieving symptoms 113 Fig. 49-23 Amyloid plaque Neurofibrillary tangle 20 µm 114 Parkinson's disease • Parkinson’s disease is a motor disorder caused by death of dopamine-secreting neurons in the midbrain • It is characterized by difficulty in initiating movements, muscle tremors, slowness of movement, and rigidity • There is no cure, although drugs and various other approaches are used to manage symptoms 115 Stem Cell–Based Therapy • Unlike the PNS, the CNS cannot fully repair itself • However, it was recently discovered that the adult human brain contains stem cells that can differentiate into mature neurons • Induction of stem cell differentiation and transplantation of cultured stem cells are potential methods for replacing neurons lost to trauma or disease 116 Fig. 49-24 117 Sensation and Perception 118 Sensation • The process by which the central nervous system receives input from the environment via sensory neurons • Bottom up processing 119 Perception • The process by which the brain interprets and organizes sensory information • Top-down processing – Where knowledge and expectations guide the processing or Bottom up processing: use the data to arrive at the big picture 120 The psychophysics of sensation • Absolute threshold the minimum stimulation needed to detect a stimulus with 50% accuracy • Subliminal stimulation below the absolute threshold for conscious awareness – May affect behavior without conscious awareness • Sensory adaptation/habituation diminished sensitivity to an unchanging stimulus 121 The five major senses • Vision – electromagnetic – Occipital lobe • Hearing – mechanical – Temporal lobe • Touch – mechanical – Sensory cortex • Taste – chemical – Gustatory insular cortex • Smell – chemical – Olfactory bulb – Orbitofrontal cortex – Vomeronasal organ? 122 The sixth sense And the seventh…and eighth…and ninth… • Vestibular balance and motion – Inner ear • Proprioceptive relative position of body parts – Parietal lobe • Temperature heat – Thermoreceptors throughout the body, sensory cortex • Nociception pain – Nociceptors throughout the body, sensory cortex 123 Thresholds of the five major senses 124 The Retina Human Vision: Eyes and Brain The retina at the back of the eye is actually part of the brain! Rods – brightness Cones – color 125 You should now be able to: 1. Compare and contrast the nervous systems of: hydra, sea star, planarian, nematode, clam, squid, and vertebrate 2. Distinguish between the following pairs of terms: central nervous system, peripheral nervous system; white matter, gray matter; bipolar disorder and major depression 3. List the types of glia and their functions 4. Compare the three divisions of the autonomic nervous system 126 5. Describe the structures and functions of the following brain regions: medulla oblongata, pons, midbrain, cerebellum, thalamus, epithalamus, hypothalamus, and cerebrum 6. Describe the specific functions of the brain regions associated with language, speech, emotions, memory, and learning 7. Explain the possible role of long-term potentiation in memory storage and learning 127 8. Describe the symptoms and causes of schizophrenia, Alzheimer’s disease, and Parkinson’s disease 9. Explain how drug addiction affects the brain reward system 128