* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 48nervous
Endocannabinoid system wikipedia , lookup
Haemodynamic response wikipedia , lookup
Node of Ranvier wikipedia , lookup
Brain Rules wikipedia , lookup
Aging brain wikipedia , lookup
Optogenetics wikipedia , lookup
History of neuroimaging wikipedia , lookup
Neuropsychology wikipedia , lookup
Cognitive neuroscience wikipedia , lookup
Neuroplasticity wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Electrophysiology wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Neurotransmitter wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Neural engineering wikipedia , lookup
Metastability in the brain wikipedia , lookup
Synaptogenesis wikipedia , lookup
Biological neuron model wikipedia , lookup
End-plate potential wikipedia , lookup
Neuroregeneration wikipedia , lookup
Circumventricular organs wikipedia , lookup
Development of the nervous system wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Synaptic gating wikipedia , lookup
Single-unit recording wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Chemical synapse wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Chapter 48 Nervous System 1. Nervous systems perform the three overlapping functions of sensory input, integration, and motor output Networks of neurons either intricate connections form nervous systems • Neuron Structure and Synapses. – The neuron is the structural and functional unit of the nervous system. • Nerve impulses are conducted along a neuron. – Dentrite cell body axon hillock axon – Some axons are insulated by a myelin sheath. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Axon endings are called synaptic terminals. – They contain neurotransmitters which conduct a signal across a synapse. • A synapse is the junction between a presynaptic and postsynaptic neuron. • Neurons differ in terms of both function and shape. Fig. 48.4 • Types of Nerve Circuits. – Single presynaptic neuron several postsynaptic neurons. – Several presynaptic neurons single postsynaptic neuron. – Circular paths. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Supporting Cells (Glia) • Glia are supporting cells – That are essential for the structural integrity of the nervous system and for the normal functioning of neurons • In the CNS, astrocytes Figure 48.7 50 µm – Provide structural support for neurons and regulate the extracellular concentrations of ions and neurotransmitters • Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) – Are glia that form the myelin sheaths around the axons of many vertebrate neurons Node of Ranvier Layers of myelin Axon Schwann cell Axon Figure 48.8 Myelin sheath Nodes of Ranvier Schwann cell Nucleus of Schwann cell 0.1 µm • A Simple Nerve Circuit – the Reflex Arc. – A reflex is an autonomic response. ANIMATION • A ganglion is a cluster of nerve cell bodies within the PNS. • A nucleus is a cluster of nerve cell bodies within the CNS. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The membrane potential of a cell can be measured APPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of neurons and other cells. TECHNIQUE A microelectrode is made from a glass capillary tube filled with an electrically conductive salt solution. One end of the tube tapers to an extremely fine tip (diameter < 1 µm). While looking through a microscope, the experimenter uses a micropositioner to insert the tip of the microelectrode into a cell. A voltage recorder (usually an oscilloscope or a computer-based system) measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell. Microelectrode –70 mV Voltage recorder Figure 48.9 Reference electrode • How a Cell Maintains a Membrane Potential. – Cations. • Na+ is the principal extracellular cation. • K+ the principal intracellular cation. – Anions. • Cl– is principal extracellular anion. • Proteins, amino acids, sulfate, and phosphate are the principal intracellular anions. -70 mV The Resting Potential • The resting potential – Is the membrane potential of a neuron that is not transmitting signals • In all neurons, the resting potential – Depends on the ionic gradients that exist across the plasma membrane EXTRACELLULAR FLUID CYTOSOL [Na+] 15 mM – + [Na+] 150 mM [K+] 150 mM – + [K+] 5 mM – + [Cl–] 10 mM – [Cl–] + 120 mM [A–] 100 mM – + Plasma membrane Figure 48.10 • The concentration of Na+ is higher in the extracellular fluid than in the cytosol – While the opposite is true for K+ • A neuron that is not transmitting signals – Contains many open K+ channels and fewer open Na+ channels in its plasma membrane • The diffusion of K+ and Na+ through these channels – Leads to a separation of charges across the membrane, producing the resting potential • Ungated ion channels allow ions to diffuse across the plasma membrane. – These channels are always open. • This diffusion does not achieve an equilibrium since sodium-potassium pump transports these ions against their concentration gradients. Fig. 48.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Changes in the membrane potential of a neuron give rise to nerve impulses • Excitable cells have the ability to generate large changes in their membrane potentials. – Gated ion channels open or close in response to stimuli. • The subsequent diffusion of ions leads to a change in the membrane potential. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Hyperpolarization. – Gated K+ channels open K+ diffuses out of the cell the membrane potential becomes more negative. Fig. 48.8a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Depolarization. – Gated Na+ channels open Na+ diffuses into the cell the membrane potential becomes less negative. Fig. 48.8b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The Action Potential: All or Nothing Depolarization. – If graded potentials sum to -55mV a threshold potential is achieved. • This triggers an action potential. – Axons only. Fig. 48.8c Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • In the resting state closed voltage-gated K+ channels open slowly in response to depolarization. • Voltage-gated Na+ channels have two gates. – Closed activation gates open rapidly in response to depolarization. – Open inactivation gates close slowly in response to depolarization. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Step 1: Resting State. Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Step 2: Threshold. Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Step 3: Depolarization phase of the action potential. Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Step 4: Repolarizing phase of the action potential. Fig. 48.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Animation 2 • Schwann cells are found within the PNS. – Form a myelin sheath by insulating axons. Fig. 48.5 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Saltatory conduction. – In myelinated neurons only unmyelinated regions of the axon depolarize. • Thus, the impulse moves faster than in unmyelinated neurons. Fig. 48.11 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Chemical or electrical communication between cells occurs at synapses • Electrical Synapses. – Action potentials travels directly from the presynaptic to the postsynaptic cells via gap junctions. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Chemical Synapses. – More common than electrical synapses. – Postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl-. • Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • In a chemical synapse, a presynaptic neuron – Releases chemical neurotransmitters, which are stored in the synaptic terminal Postsynaptic neuron 5 µm Synaptic terminal of presynaptic neurons Figure 48.16 Animation Animation 2 5. Neural integration occurs at the cellular level • Excitatory postsynaptic potentials (EPSP) depolarize the postsynaptic neuron. – The binding of neurotransmitter to postsynaptic receptors open gated channels that allow Na+ to diffuse into and K+ to diffuse out of the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Inhibitory postsynaptic potential (IPSP) hyperpolarize the postsynaptic neuron. – The binding of neurotransmitter to postsynaptic receptors open gated channels that allow K+ to diffuse out of the cell and/or Cl- to diffuse into the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron. Fig. 48.14 Inhibits pain Organization of Nervous Systems • The simplest animals with nervous systems, the cnidarians – Have neurons arranged in nerve nets Nerve net Figure 48.2a (a) Hydra (cnidarian) • Sea stars have a nerve net in each arm – Connected by radial nerves to a central nerve ring Radial nerve Nerve ring Figure 48.2b (b) Sea star (echinoderm) • In relatively simple cephalized animals, such as flatworms – A central nervous system (CNS) is evident Eyespot Brain Nerve cord Transverse nerve Figure 48.2c (c) Planarian (flatworm) • Annelids and arthropods – Have segmentally arranged clusters of neurons called ganglia • These ganglia connect to the CNS – And make up a peripheral nervous system (PNS) Brain Brain Ventral nerve cord Ventral nerve cord Segmental ganglia Segmental ganglion Figure 48.2d, e (d) Leech (annelid) (e) Insect (arthropod) • Nervous systems in molluscs – Correlate with the animals’ lifestyles • Sessile molluscs have simple systems – While more complex molluscs have more sophisticated systems Anterior nerve ring Ganglia Brain Longitudinal nerve cords Figure 48.2f, g Ganglia (f) Chiton (mollusc) (g) Squid (mollusc) • In vertebrates – The central nervous system consists of a brain and dorsal spinal cord – The PNS connects to the CNS Brain Spinal cord (dorsal nerve cord) Figure 48.2h Sensory ganglion (h) Salamander (chordate) Evolutionary Trends • Nervous systems become centralized - formation of longitudinal cords • Conduction along pathway becomes one way afferent and efferent fibers • pathways within CNS become more complex (interneurons) - more flexible behavior • More segregation and specialization • Formation of a Brain - Cephalization • More and complex organs 1. Vertebrate nervous systems have central and peripheral components • Central nervous system (CNS). – Brain and spinal cord. • Both contain fluid-filled spaces which contain cerebrospinal fluid (CSF). – The central canal of the spinal cord is continuous with the ventricles of the brain. – White matter is composed of bundles of myelinated axons – Gray matter consists of unmyelinated axons, nuclei, and dendrites. • Peripheral nervous system. – Everything outside the CNS. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The brain provides the integrative power – That underlies the complex behavior of vertebrates • The spinal cord integrates simple responses to certain kinds of stimuli – And conveys information to and from the brain • The central canal of the spinal cord and the four ventricles of the brain – Are hollow, since they are derived from the dorsal embryonic nerve cord Gray matter White matter Ventricles Figure 48.20 The divisions of the peripheral nervous system interact in maintaining homeostasis • Structural composition of the PNS. – Paired cranial nerves that originate in the brain and innervate the head and upper body. – Paired spinal nerves that originate in the spinal cord and innervate the entire body. – Ganglia associated with the cranial and spinal nerves. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The cranial nerves originate in the brain – And terminate mostly in organs of the head and upper body • The spinal nerves originate in the spinal cord – And extend to parts of the body below the head • The PNS can be divided into two functional components – The somatic nervous system and the autonomic nervous system Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Figure 48.21 Parasympathetic division Enteric division • A closer look at the (often antagonistic) divisions of the autonomic nervous system (ANS). Fig. 48.18 Embryonic development of the vertebrate brain reflects its evolution from three anterior bulges of the neural tube Fig. 48.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • As a human brain develops further – The most profound change occurs in the forebrain, which gives rise to the cerebrum Brain structures present in adult Cerebrum (cerebral hemispheres; 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: Cerebral hemisphere Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Pituitary gland Medulla oblongata Spinal cord Cerebellum Central canal Figure 48.23c (c) Adult 4. Evolutionary older structures of the vertebrate brain regulate essential autonomic and integrative functions • The Brainstem. – The “lower brain.” – Consists of the medulla oblongata, pons, and midbrain. – Derived from the embryonic hindbrain and midbrain. – Functions in homeostasis, coordination of movement, conduction of impulses to higher brain centers. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The Medulla and Pons. – Medulla oblongata. • Contains nuclei that control visceral (autonomic homeostatic) functions. – – – – – Breathing. Heart and blood vessel activity. Swallowing. Vomiting. Digestion. • Relays information to and from higher brain centers. • Sleep Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Pons. – Contains nuclei involved in the regulation of visceral activities such as breathing. – Relays information to and from higher brain centers. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The Midbrain. – Contains nuclei involved in the integration of sensory information. • Superior colliculi are involved in the regulation of visual reflexes. • Inferior colliculi are involved in the regulation of auditory reflexes. – Relays information to and from higher brain centers. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The Reticular System, Arousal, and Sleep. – The reticular activating system (RAS) of the reticular formation. • Regulates sleep and arousal. • Acts as a sensory filter. Fig. 48.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings – Sleep and wakefulness produces patterns of electrical activity in the brain that can be recorded as an electroencephalogram (EEG). • Most dreaming occurs during REM (rapid eye movement) sleep. Fig. 48.22b-d Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The Cerebellum • The cerebellum – Is important for coordination and error checking during motor, perceptual, and cognitive functions – The Cerebellum. • Develops from part of the metencephalon. • Functions to error-check and coordinate motor activities, and perceptual and cognitive factors. • Relays sensory information about joints, muscles, sight, and sound to the cerebrum. • Coordinates motor commands issued by the cerebrum. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The Diencephalon • The embryonic diencephalon develops into three adult brain regions – The epithalamus, thalamus, and hypothalamus – Epithalamus. • Includes a choroid plexus and the pineal gland. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings – Thalamus. • Relays all sensory information to the cerebrum. – Contains one nucleus for each type of sensory information. • Relays motor information from the cerebrum. • Receives input from the cerebrum. • Receives input from brain centers involved in the regulation of emotion and arousal. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings – Hypothalamus. • Regulates autonomic activity. – Contains nuclei involved in thermoregulation, hunger, thirst, sexual and mating behavior, etc. – Regulates the pituitary gland. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings – The Hypothalamus and Circadian Rhythms. • The biological clock is the internal timekeeper. – The clock’s rhythm usually does not exactly match environmental events. – Experiments in which humans have been deprived of external cues have shown that biological clock has a period of about 25 hours. • In mammals, the hypothalamic suprachiasmatic nuclei (SCN) function as a biological clock. – Produce proteins in response to light/dark cycles. • This, and other biological clocks, may be responsive to hormonal release, hunger, and various external stimuli. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Biological clocks usually require external cues – To remain synchronized with environmental cycles EXPERIMENT In the northern flying squirrel (Glaucomys sabrinus), activity normally begins with the onset of darkness and ends at dawn, which suggests that light is an important external cue for the squirrel. To test this idea, researchers monitored the activity of captive squirrels for 23 days under two sets of conditions: (a) a regular cycle of 12 hours of light and 12 hours of darkness and (b) constant darkness. The squirrels were given free access to an exercise wheel and a rest cage. A recorder automatically noted when the wheel was rotating and when it was still. (a) 12 hr light-12 hr dark cycle Light Dark Light Dark 1 Days of experiment RESULTS When the squirrels were exposed to a regular light/dark cycle, their wheel-turning activity (indicated by the dark bars) occurred at roughly the same time every day. However, when they were kept in constant darkness, their activity phase began about 21 minutes later each day. (b) Constant darkness 5 10 15 20 Figure 48.25 12 16 20 24 4 Time of day (hr) 8 12 12 16 20 24 4 Time of day (hr) CONCLUSION The northern flying squirrel’s internal clock can run in constant darkness, but it does so on its own cycle, which lasts about 24 hours and 21 minutes. External (light) cues keep the clock running on a 24-hour cycle. 8 12 The cerebrum is the most highly evolved structure of the mammalian brain • The cerebrum is derived from the embryonic telencephalon. Fig. 48.24a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The cerebrum is divided into left and right cerebrum hemispheres. – The corpus callosum is the major connection between the two hemispheres. – The left hemisphere is primarily responsible for the right side of the body. – The right hemisphere is primarily responsible for the left side of the body. • Cerebral cortex: outer covering of gray matter. – Neocortex: region unique to mammals. • The more convoluted the surface of the neocortex the more surface area the more neurons. • Basal nuclei: internal clusters of nuclei. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 6. Regions of the cerebrum are specialized for different functions • The cerebrum is divided into frontal, temporal, occipital, and parietal lobes. Fig. 48.24b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Frontal lobe. – Contains the primary motor cortex. • Parietal lobe. – Contains the primary somatosensory cortex. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Information Processing in the Cerebral Cortex • Specific types of sensory input – Enter the primary sensory areas • Adjacent association areas – Process particular features in the sensory input and integrate information from different sensory areas Connects right and left hemispheres Major input center for sensory info going to cerebrum also main output center for motor info leaving cerebrum Coordination of movement and balance Homeostasis regulation: thermostat, hunger, thirst, sex, fight or flight Superchiasmatic nuclei acts as a biological clock Controls visceral functions: breathing, heart, blood vessel, swallowing, vomiting, digestion Link to Probe da Brain • Integrative Function of the Association Areas. – Much of the cerebrum is given over to association areas. • Areas where sensory information is integrated and assessed and motor responses are planned. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The brain exhibits plasticity of function. – For example, infants with intractable epilepsy may have an entire cerebral hemisphere removed. • The remaining hemisphere can provide the function normally provided by both hemispheres. • Lateralization of Brain Function. – The left hemisphere. • Specializes in language, math, logic operations, and the processing of serial sequences of information, and visual and auditory details. • Specializes in detailed activities required for motor control. – The right hemisphere. • Specializes in pattern recognition, spatial relationships, nonverbal ideation, emotional processing, and the parallel processing of information. • Language and Speech. – Broca’s area. • Usually located in the left hemisphere’s frontal lobe • Responsible for speech production. – Wernicke’s area. • Usually located in the right hemisphere’s temporal lobe • Responsible for the comprehension of speech. – Other speech areas are involved generating verbs to match nouns, grouping together related words, etc. Grammatical refinement of words – speech production Linguistic meaning determined on left side comprehension Higher frequency sounds sent to right area of brain for emotional overtones Written words translated into sounds • Emotions. – In mammals, the limbic system is composed of the hippocampus, olfactory cortex, inner portions of the cortex’s lobes, and parts of the thalamus and hypothalamus. • Mediates basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory – For example, the amygdala is involved in recognizing the emotional content of facial expression. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 48.27 Connects higher brain involved in complex learning, reasoning and personality and emotion Center of convergence for sensory data and a major organizer of emotional information-may act as a memory filter - tying info to an event or emotion • Memory and Learning. – Short-term memory stored in the frontal lobes. – The establishment of long-term memory involves the hippocampus. • The transfer of information from short-term to longterm memory. – Is enhanced by repetition (remember that when you are preparing for an exam). – Influenced by emotional states mediated by the amygdala. – Influenced by association with previously stored information. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings – Different types of long-term memories are stored in different regions of the brain. – Memorization-type memory can be rapid. • Primarily involves changes in the strength of existing nerve connections. – Learning of skills and procedures is slower. • Appears to involves cellular mechanisms similar to those involved in brain growth and development. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cellular Mechanisms of Learning • Experiments on invertebrates – Have revealed the cellular basis of some types of learning Siphon (a) Touching the siphon triggers a reflex that causes the gill to withdraw. If the tail is shocked just before the siphon is touched, the withdrawal reflex is stronger. This strengthening of the reflex is a simple form of learning called sensitization. Mantle Gill Tail Head Figure 48.31a, b (b) Sensitization involves interneurons that make synapses on the synaptic terminals of the siphon sensory neurons. When the tail is shocked, the interneurons release serotonin, which activates a signal transduction pathway that closes K+ channels in the synaptic terminals of the siphon sensory neurons. As a result, action potentials in the siphon sensory neurons produce a prolonged depolarization of the terminals. That allows more Ca2+ to diffuse into the terminals, which causes the terminals to release more of their excitatory neurotransmitter onto the gill motor neurons. In response, the motor neurons generate action potentials at a higher frequency, producing a more forceful gill withdrawal. Gill withdrawal pathway Touching the siphon Siphon sensory neuron Gill motor neuron Gill Sensitization pathway Interneuron Shocking the tail Tail sensory neuron EPSPs • In the vertebrate brain, a form of learning called long-term potentiation (LTP) – Involves an increase in the strength of synaptic transmission 1 The presynaptic neuron releases glutamate. Glutamate binds to AMPA receptors, opening the AMPAreceptor channel and depolarizing the postsynaptic membrane. 2 PRESYNAPTIC NEURON 7 NO diffuses into the presynaptic neuron, causing it to release more glutamate. NO NMDA receptor 6 Ca2+ stimulates the postsynaptic neuron to produce nitric oxide (NO). 5 Ca2+ initiates the phosphorylation of AMPA receptors, making them more responsive. Ca2+ also causes more AMPA receptors to appear in the postsynaptic membrane. Figure 48.32 Glutamate AMPA receptor NO P Glutamate also binds to NMDA receptors. If the postsynaptic membrane is simultaneously depolarized, the NMDA-receptor channel opens. 3 Ca2+ Signal transduction pathways POSTSYNAPTIC NEURON Ca2+ diffuses into the postsynaptic neuron. 4 • Functional changes in synapses in synapses of the hippocampus and amygdala are related to memory storage and emotional conditioning. – Long-term depression (LTD) occurs when a postsynaptic neuron displays decreased responsiveness to action potentials. • Induced by repeated, weak stimulation. – Long-term potentiation (LTP) occurs when a postsynaptic neuron displays increased responsiveness to stimuli. • Induced by brief, repeated action potentials that strongly depolarize the postsynaptic membrane. • May be associated with memory storage and learning. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Human Consciousness. – Brain imaging can show neural activity associated with: • Conscious perceptual choice • Unconscious processing • Memory retrieval • Working memory. – Consciousness appears to be a whole-brain phenomenon. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 7. Research on neuron development and neural stem cells may lead to new approaches for treating CNS injuries and diseases • The mammalian PNS has the ability to repair itself, the CNS does not. – Research on nerve cell development and neural stem cells may be the future of treatment for damage to the CNS. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Cell Development • Signal molecules direct an axon’s growth – By binding to receptors on the plasma membrane of the growth cone • Nerve Cell Development. Fig. 48.28 • Neural Stem Cells. – The adult human brain does produce new nerve cells. • New nerve cells have been found in the hippocampus. • Since mature human brain cells cannot undergo cell division the new cells must have arisen from stem cells. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Neural Stem Cells • The adult human brain – Contains stem cells that can differentiate into mature neurons Figure 48.34 • The induction of stem cell differentiation and the transplantation of cultured stem cells – Are potential methods for replacing neurons lost to trauma or disease Diseases and Disorders of the Nervous System • Mental illnesses and neurological disorders – Take an enormous toll on society, in both the patient’s loss of a productive life and the high cost of long-term health care Schizophrenia • About 1% of the world’s population – Suffers from schizophrenia • Schizophrenia is characterized by – Hallucinations, delusions, blunted emotions, and many other symptoms • Available treatments have focused on – Brain pathways that use dopamine as a neurotransmitter Depression • Two broad forms of depressive illness are known – Bipolar disorder and major depression • Bipolar disorder is characterized by – Manic (high-mood) and depressive (low-mood) phases • In major depression – Patients have a persistent low mood • Treatments for these types of depression include – A variety of drugs such as Prozac and lithium Alzheimer’s Disease • Alzheimer’s disease (AD) – Is a mental deterioration characterized by confusion, memory loss, and other symptoms • AD is caused by the formation of – Neurofibrillary tangles and senile plaques in the brain Senile plaque Neurofibrillary tangle 20 m Figure 48.35 • A successful treatment for AD in humans – May hinge on early detection of senile plaques Parkinson’s Disease • Parkinson’s disease is a motor disorder – Caused by the death of dopamine-secreting neurons in the substantia nigra – Characterized by difficulty in initiating movements, slowness of movement, and rigidity • There is no cure for Parkinson’s disease – Although various approaches are used to manage the symptoms