Campbell's AP Biology Notes: Command And Control Center
Campbell’s AP Biology Notes
Chapter 48: Nervous Systems
Command and Control Center * The human brain contains an estimated 100 billion nerve cells, or neurons * Each neuron my communicate with thousands of other neurons * Functional magnetic resonance imaging (fMRI) is a technology that can reconstruct a 3-D map of brain activity * The results of brain imaging and other research methods reveal that groups of neurons function in specialized circuits dedicated to different tasks
48.1: Nervous Systems consist of circuits of neurons and supporting cells * All animals except sponges have some type of nervous system * What distinguishes the nervous systems of the different animal groups is how the neurons are organized …show more content…
into circuits * The simplest animals with nervous systems, the cnidarians have neurons arranged in nerve nets * Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring * In relatively simple cephalized animals, such as flatworms a central nervous system (CNS) is evident * 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) * Nervous systems in molluscs correlate with the animals’ lifestyles * Sessile molluscs have simple systems while more complex molluscs have more sophisticated systems * In vertebrates the central nervous system consists of a brain and dorsal spinal cord * The PNS connects to the CNS * Nervous systems process information in three stages: sensory input, integration, and motor output * Sensory neurons transmit information from sensors that detect external stimuli and internal conditions * Sensory information is sent to the CNS where interneurons integrate the information * Motor output leaves the CNS via motor neurons which communicate with effector cells * The three stages of information processing are illustrated in the knee-jerk reflex * Most of a neuron’s organelles are located in the cell body * Most neurons have dendrites, highly branched extensions that receive signals from other neurons * The axon is typically a much longer extension, that transmits signals to other cells at synapses and may be covered with a myelin sheath * Neurons have a wide variety of shapes that reflect their input and output interactions * 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 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
48.2: Ion pumps and ion channels maintain the resting potential of a neuron * Across its plasma membrane, every cell has a voltage called a membrane potential * The inside of a cell is negative relative to the outside * The membrane potential of a cell can be measured * 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 * The concentration of Na+ is higher in the extracellular fluid than in the cytosol while the opposite is true for K+ * By modeling a mammalian neuron with an artificial membrane we can gain a better understanding of the resting potential of a neuron * 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 * Gated ion channels open or close, in response to membrane stretch or the binding of a specific ligand and in response to a change in the membrane potential
48.3: Action potentials are the signals conducted by axons * If a cell has gated ion channels its membrane potential may change in response to stimuli that open or close those channels * Some stimuli trigger a hyperpolarization an increase in the magnitude of the membrane potential * Other stimuli trigger a depolarization a reduction in the magnitude of the membrane potential * Hyperpolarization and depolarization are both called graded potentials because the magnitude of the change in membrane potential varies with the strength of the stimulus * In most neurons, depolarizations are graded only up to a certain membrane voltage, called the threshold * A stimulus strong enough to produce a depolarization that reaches the threshold triggers a different type of response, called an action potential * An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane and is the type of signal that carries information along axons * Both voltage-gated Na+ channels and voltage-gated K+ channels are involved in the production of an action potential * When a stimulus depolarizes the membrane Na+ channels open, allowing Na+ to diffuse into the cell * As the action potential subsides K+ channels open, and K+ flows out of the cell * A refractory period follows the action potential during which a second action potential cannot be initiated * An action potential can travel long distances by regenerating itself along the axon * At the site where the action potential is generated, usually the axon hillock an electrical current depolarizes the neighboring region of the axon membrane * The speed of an action potential increases with the diameter of an axon * In vertebrates, axons are myelinated also causing the speed of an action potential to increase * Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction
48.4: Neurons communicate with other cells at synapses * In an electrical synapse electrical current flows directly from one cell to another via a gap junction * The vast majority of synapses are chemical synapses * In a chemical synapse, a presynaptic neuron releases chemical neurotransmitters, which are stored in the synaptic terminal * When an action potential reaches a terminal the final result is the release of neurotransmitters into the synaptic cleft * The process of direct synaptic transmission involves the binding of neurotransmitters to ligand-gated ion channels * Neurotransmitter binding causes the ion channels to open, generating a postsynaptic potential * Postsynaptic potentials fall into two categories: excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) * After its release, the neurotransmitter diffuses out of the synaptic cleft and may be taken up by surrounding cells and degraded by enzymes * Unlike action potentials postsynaptic potentials are graded and do not regenerate themselves * Since most neurons have many synapses on their dendrites and cell body a single EPSP is usually too small to trigger an action potential in a postsynaptic neuron * If two EPSPs are produced in rapid succession an effect called temporal summation occurs * In spatial summation EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together * Through summation an IPSP can counter the effect of an EPSP * In indirect synaptic transmission a neurotransmitter binds to a receptor that is not part of an ion channel * This binding activates a signal transduction pathway involving a second messenger in the postsynaptic cell, producing a slowly developing but long-lasting effect * The same neurotransmitter can produce different effects in different types of cells * Acetylcholine is one of the most common neurotransmitters in both vertebrates and invertebrates, can be inhibitory or excitatory * Biogenic amines include epinephrine, norepinephrine, dopamine, and serotonin and are active in the CNS and PNS * Various amino acids and peptides are active in the brain * Gases such as nitric oxide and carbon monoxide are local regulators in the PNS
48.5: The vertebrate nervous system is regionally specialized * In all vertebrates, the nervous system shows a high degree of cephalization and distinct CNS and PNS components * 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 * The PNS transmits information to and from the CNS and plays a large role in regulating a vertebrate’s movement and internal environment * 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 * The somatic nervous system carries signals to skeletal muscles * The autonomic nervous system regulates the internal environment, in an involuntary manner and is divided into the sympathetic, parasympathetic, and enteric divisions
* The sympathetic and parasympathetic divisions have antagonistic effects on target organs * The sympathetic division correlates with the “fight-or-flight” response * The parasympathetic division promotes a return to self-maintenance functions * The enteric division controls the activity of the digestive tract, pancreas, and gallbladder * In all vertebrates the brain develops from three embryonic regions: the forebrain, the midbrain, and the hindbrain * By the fifth week of human embryonic development five brain regions have formed from the three embryonic regions * As a human brain develops further the most profound change occurs in the forebrain, which gives rise to the cerebrum * The brainstem consists of three parts: the medulla oblongata, the pons, and the midbrain * The medulla oblongata contains centers that control several visceral functions * The pons also participates in visceral functions * The midbrain contains centers for the receipt and integration of several types of sensory information * A diffuse network of neurons called the reticular formation is present in the core of the brainstem * A part of the reticular formation, the reticular activating system (RAS) regulates sleep and
arousal * The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions * The cerebellum is also involved in learning and remembering motor skills * The embryonic diencephalon develops into three adult brain regions: the epithalamus, thalamus, and hypothalamus * The epithalamus: includes the pineal gland and the choroid plexus * The thalamus is the main input center for sensory information going 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 * The hypothalamus also regulates circadian rhythms such as the sleep/wake cycle * Animals usually have a biological clock which is a pair of suprachiasmatic nuclei (SCN) found in the hypothalamus * Biological clocks usually require external cues to remain synchronized with environmental cycles * The cerebrum develops from the embryonic telencephalon * The cerebrum has right and left cerebral hemispheres that each consist of cerebral cortex overlying white matter and basal nuclei * The basal nuclei are important centers for planning and learning movement sequences * In mammals the cerebral cortex has a convoluted surface called the neocortex * In humans, the largest and most complex part of the brain is the cerebral cortex, where sensory information is analyzed, motor commands are issued, and language is generated * A thick band of axons, the corpus callosum provides communication between the right and left cerebral cortices
48.6: The cerebral cortex controls voluntary movement and cognitive functions * Each side of the cerebral cortex has four lobes: frontal, parietal, temporal, and occipital * Each of the lobes contains primary sensory areas and association areas * 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 * In the somatosensory cortex and motor cortex neurons are distributed according to the part of the body that generates sensory input or receives motor input * During brain development, in a process called lateralization, competing functions segregate and displace each other in the cortex of the left and right cerebral hemispheres * The left hemisphere becomes more adept at language, math, logical operations, and the processing of serial sequences * The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing * Studies of brain activity have mapped specific areas of the brain responsible for language and speech * Portions of the frontal lobe, Broca’s area and Wernicke’s area are essential for the generation and understanding of language * The limbic system is a ring of structures around the brainstem * This limbic system includes three parts of the cerebral cortex: the amygdala, hippocampus, and olfactory bulb * These structures interact with the neocortex to mediate primary emotions and attach emotional “feelings” to survival-related functions * Structures of the limbic system form in early development and provide a foundation for emotional memory, associating emotions with particular events or experiences * The frontal lobes are a site of short-term memory and interact with the hippocampus and amygdala to consolidate long-term memory * Many sensory and motor association areas of the cerebral cortex are involved in storing and retrieving words and images * Experiments on invertebrates have revealed the cellular basis of some types of learning * In the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmission * Modern brain-imaging techniques suggest that consciousness may be an emergent property of the brain that is based on activity in many areas of the cortex
48.7: CNS injuries and diseases are the focus of much research * Unlike the PNS, the mammalian CNS cannot repair itself when damaged or assaulted by disease * Current research on nerve cell development and stem cells may one day make it possible for physicians to repair or replace damaged neurons * Signal molecules direct an axon’s growth by binding to receptors on the plasma membrane of the growth cone * This receptor binding triggers a signal transduction pathway which may cause an axon to grow toward or away from the source of the signal * The genes and basic events involved in axon guidance are similar in invertebrates and vertebrates * Knowledge of these events may be applied one day to stimulate axonal regrowth following CNS damage * The adult human brain contains stem cells that can differentiate into mature neurons * The induction of stem cell differentiation and the transplantation of cultured stem cells are potential methods for replacing neurons lost to trauma or disease * 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 * 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 * 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 (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 * A successful treatment for AD in humans may hinge on early detection of senile plaques * Parkinson’s disease is a motor disorder caused by the death of dopamine-secreting neurons in the substantia nigra and is 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
Chapter 48: Nervous Systems
Command and Control Center * The human brain contains an estimated 100 billion nerve cells, or neurons * Each neuron my communicate with thousands of other neurons * Functional magnetic resonance imaging (fMRI) is a technology that can reconstruct a 3-D map of brain activity * The results of brain imaging and other research methods reveal that groups of neurons function in specialized circuits dedicated to different tasks
48.1: Nervous Systems consist of circuits of neurons and supporting cells * All animals except sponges have some type of nervous system * What distinguishes the nervous systems of the different animal groups is how the neurons are organized …show more content…
into circuits * The simplest animals with nervous systems, the cnidarians have neurons arranged in nerve nets * Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring * In relatively simple cephalized animals, such as flatworms a central nervous system (CNS) is evident * 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) * Nervous systems in molluscs correlate with the animals’ lifestyles * Sessile molluscs have simple systems while more complex molluscs have more sophisticated systems * In vertebrates the central nervous system consists of a brain and dorsal spinal cord * The PNS connects to the CNS * Nervous systems process information in three stages: sensory input, integration, and motor output * Sensory neurons transmit information from sensors that detect external stimuli and internal conditions * Sensory information is sent to the CNS where interneurons integrate the information * Motor output leaves the CNS via motor neurons which communicate with effector cells * The three stages of information processing are illustrated in the knee-jerk reflex * Most of a neuron’s organelles are located in the cell body * Most neurons have dendrites, highly branched extensions that receive signals from other neurons * The axon is typically a much longer extension, that transmits signals to other cells at synapses and may be covered with a myelin sheath * Neurons have a wide variety of shapes that reflect their input and output interactions * 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 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
48.2: Ion pumps and ion channels maintain the resting potential of a neuron * Across its plasma membrane, every cell has a voltage called a membrane potential * The inside of a cell is negative relative to the outside * The membrane potential of a cell can be measured * 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 * The concentration of Na+ is higher in the extracellular fluid than in the cytosol while the opposite is true for K+ * By modeling a mammalian neuron with an artificial membrane we can gain a better understanding of the resting potential of a neuron * 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 * Gated ion channels open or close, in response to membrane stretch or the binding of a specific ligand and in response to a change in the membrane potential
48.3: Action potentials are the signals conducted by axons * If a cell has gated ion channels its membrane potential may change in response to stimuli that open or close those channels * Some stimuli trigger a hyperpolarization an increase in the magnitude of the membrane potential * Other stimuli trigger a depolarization a reduction in the magnitude of the membrane potential * Hyperpolarization and depolarization are both called graded potentials because the magnitude of the change in membrane potential varies with the strength of the stimulus * In most neurons, depolarizations are graded only up to a certain membrane voltage, called the threshold * A stimulus strong enough to produce a depolarization that reaches the threshold triggers a different type of response, called an action potential * An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane and is the type of signal that carries information along axons * Both voltage-gated Na+ channels and voltage-gated K+ channels are involved in the production of an action potential * When a stimulus depolarizes the membrane Na+ channels open, allowing Na+ to diffuse into the cell * As the action potential subsides K+ channels open, and K+ flows out of the cell * A refractory period follows the action potential during which a second action potential cannot be initiated * An action potential can travel long distances by regenerating itself along the axon * At the site where the action potential is generated, usually the axon hillock an electrical current depolarizes the neighboring region of the axon membrane * The speed of an action potential increases with the diameter of an axon * In vertebrates, axons are myelinated also causing the speed of an action potential to increase * Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction
48.4: Neurons communicate with other cells at synapses * In an electrical synapse electrical current flows directly from one cell to another via a gap junction * The vast majority of synapses are chemical synapses * In a chemical synapse, a presynaptic neuron releases chemical neurotransmitters, which are stored in the synaptic terminal * When an action potential reaches a terminal the final result is the release of neurotransmitters into the synaptic cleft * The process of direct synaptic transmission involves the binding of neurotransmitters to ligand-gated ion channels * Neurotransmitter binding causes the ion channels to open, generating a postsynaptic potential * Postsynaptic potentials fall into two categories: excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) * After its release, the neurotransmitter diffuses out of the synaptic cleft and may be taken up by surrounding cells and degraded by enzymes * Unlike action potentials postsynaptic potentials are graded and do not regenerate themselves * Since most neurons have many synapses on their dendrites and cell body a single EPSP is usually too small to trigger an action potential in a postsynaptic neuron * If two EPSPs are produced in rapid succession an effect called temporal summation occurs * In spatial summation EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together * Through summation an IPSP can counter the effect of an EPSP * In indirect synaptic transmission a neurotransmitter binds to a receptor that is not part of an ion channel * This binding activates a signal transduction pathway involving a second messenger in the postsynaptic cell, producing a slowly developing but long-lasting effect * The same neurotransmitter can produce different effects in different types of cells * Acetylcholine is one of the most common neurotransmitters in both vertebrates and invertebrates, can be inhibitory or excitatory * Biogenic amines include epinephrine, norepinephrine, dopamine, and serotonin and are active in the CNS and PNS * Various amino acids and peptides are active in the brain * Gases such as nitric oxide and carbon monoxide are local regulators in the PNS
48.5: The vertebrate nervous system is regionally specialized * In all vertebrates, the nervous system shows a high degree of cephalization and distinct CNS and PNS components * 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 * The PNS transmits information to and from the CNS and plays a large role in regulating a vertebrate’s movement and internal environment * 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 * The somatic nervous system carries signals to skeletal muscles * The autonomic nervous system regulates the internal environment, in an involuntary manner and is divided into the sympathetic, parasympathetic, and enteric divisions
* The sympathetic and parasympathetic divisions have antagonistic effects on target organs * The sympathetic division correlates with the “fight-or-flight” response * The parasympathetic division promotes a return to self-maintenance functions * The enteric division controls the activity of the digestive tract, pancreas, and gallbladder * In all vertebrates the brain develops from three embryonic regions: the forebrain, the midbrain, and the hindbrain * By the fifth week of human embryonic development five brain regions have formed from the three embryonic regions * As a human brain develops further the most profound change occurs in the forebrain, which gives rise to the cerebrum * The brainstem consists of three parts: the medulla oblongata, the pons, and the midbrain * The medulla oblongata contains centers that control several visceral functions * The pons also participates in visceral functions * The midbrain contains centers for the receipt and integration of several types of sensory information * A diffuse network of neurons called the reticular formation is present in the core of the brainstem * A part of the reticular formation, the reticular activating system (RAS) regulates sleep and
arousal * The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions * The cerebellum is also involved in learning and remembering motor skills * The embryonic diencephalon develops into three adult brain regions: the epithalamus, thalamus, and hypothalamus * The epithalamus: includes the pineal gland and the choroid plexus * The thalamus is the main input center for sensory information going 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 * The hypothalamus also regulates circadian rhythms such as the sleep/wake cycle * Animals usually have a biological clock which is a pair of suprachiasmatic nuclei (SCN) found in the hypothalamus * Biological clocks usually require external cues to remain synchronized with environmental cycles * The cerebrum develops from the embryonic telencephalon * The cerebrum has right and left cerebral hemispheres that each consist of cerebral cortex overlying white matter and basal nuclei * The basal nuclei are important centers for planning and learning movement sequences * In mammals the cerebral cortex has a convoluted surface called the neocortex * In humans, the largest and most complex part of the brain is the cerebral cortex, where sensory information is analyzed, motor commands are issued, and language is generated * A thick band of axons, the corpus callosum provides communication between the right and left cerebral cortices
48.6: The cerebral cortex controls voluntary movement and cognitive functions * Each side of the cerebral cortex has four lobes: frontal, parietal, temporal, and occipital * Each of the lobes contains primary sensory areas and association areas * 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 * In the somatosensory cortex and motor cortex neurons are distributed according to the part of the body that generates sensory input or receives motor input * During brain development, in a process called lateralization, competing functions segregate and displace each other in the cortex of the left and right cerebral hemispheres * The left hemisphere becomes more adept at language, math, logical operations, and the processing of serial sequences * The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing * Studies of brain activity have mapped specific areas of the brain responsible for language and speech * Portions of the frontal lobe, Broca’s area and Wernicke’s area are essential for the generation and understanding of language * The limbic system is a ring of structures around the brainstem * This limbic system includes three parts of the cerebral cortex: the amygdala, hippocampus, and olfactory bulb * These structures interact with the neocortex to mediate primary emotions and attach emotional “feelings” to survival-related functions * Structures of the limbic system form in early development and provide a foundation for emotional memory, associating emotions with particular events or experiences * The frontal lobes are a site of short-term memory and interact with the hippocampus and amygdala to consolidate long-term memory * Many sensory and motor association areas of the cerebral cortex are involved in storing and retrieving words and images * Experiments on invertebrates have revealed the cellular basis of some types of learning * In the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmission * Modern brain-imaging techniques suggest that consciousness may be an emergent property of the brain that is based on activity in many areas of the cortex
48.7: CNS injuries and diseases are the focus of much research * Unlike the PNS, the mammalian CNS cannot repair itself when damaged or assaulted by disease * Current research on nerve cell development and stem cells may one day make it possible for physicians to repair or replace damaged neurons * Signal molecules direct an axon’s growth by binding to receptors on the plasma membrane of the growth cone * This receptor binding triggers a signal transduction pathway which may cause an axon to grow toward or away from the source of the signal * The genes and basic events involved in axon guidance are similar in invertebrates and vertebrates * Knowledge of these events may be applied one day to stimulate axonal regrowth following CNS damage * The adult human brain contains stem cells that can differentiate into mature neurons * The induction of stem cell differentiation and the transplantation of cultured stem cells are potential methods for replacing neurons lost to trauma or disease * 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 * 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 * 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 (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 * A successful treatment for AD in humans may hinge on early detection of senile plaques * Parkinson’s disease is a motor disorder caused by the death of dopamine-secreting neurons in the substantia nigra and is 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