Chapter 49 Nervous Systems

Overview: Command and Control Center The human brain contains about 100 billion neurons, organized into circuits more complex than the most powerful supercomputers A recent advance in brain exploration involves a method for expressing combinations of colored proteins in brain cells, a technique called “brainbow” This may allow researchers to develop detailed maps of information transfer between regions of the brain © 2011 Pearson Education, Inc.

Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells Each single-celled organism can respond to stimuli in its environment Animals are multicellular and most groups respond to stimuli using systems of neurons © 2011 Pearson Education, Inc.

A nerve net is a series of interconnected nerve 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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Spinal cord (dorsal nerve cord) Ventral nerve cord Brain Figure 49.2 Eyespot Brain Brain Radial nerve Nerve cords Ventral nerve cord Nerve ring Transverse nerve Nerve net Segmental ganglia (a) Hydra (cnidarian) (b) Sea star (echinoderm) (c) Planarian (flatworm) (d) Leech (annelid) Brain Ganglia Brain Anterior nerve ring Spinal cord (dorsal nerve cord) Ventral nerve cord Brain Sensory ganglia Figure 49.2 Nervous system organization. Longitudinal nerve cords Ganglia Segmental ganglia (e) Insect (arthropod) (f) Chiton (mollusc) (g) Squid (mollusc) (h) Salamander (vertebrate)

The CNS consists of a brain and longitudinal nerve cords Bilaterally symmetrical animals exhibit cephalization, 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 © 2011 Pearson Education, Inc.

Annelids and arthropods have segmentally arranged clusters of neurons called ganglia © 2011 Pearson Education, Inc.

Nervous system organization usually correlates with lifestyle Sessile molluscs (for example, clams and chitons) have simple systems, whereas more complex molluscs (for example, octopuses and squids) have more sophisticated systems © 2011 Pearson Education, Inc.

In vertebrates The CNS is composed of the brain and spinal cord The peripheral nervous system (PNS) is composed of nerves and ganglia © 2011 Pearson Education, Inc.

Organization of the Vertebrate Nervous System The spinal cord conveys information from and to the brain 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 © 2011 Pearson Education, Inc.

Cell body of sensory neuron in dorsal root ganglion Gray matter Figure 49.3 Cell body of sensory neuron in dorsal root ganglion Gray matter Quadriceps muscle White matter Hamstring muscle Figure 49.3 The knee-jerk reflex. Spinal cord (cross section) Sensory neuron Motor neuron Interneuron

The spinal cord and brain develop from the embryonic nerve cord 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 The nerve cord gives rise to the central canal and ventricles of the brain © 2011 Pearson Education, Inc.

Central nervous system (CNS) Peripheral nervous system (PNS) Figure 49.4 Central nervous system (CNS) Peripheral nervous system (PNS) Brain Cranial nerves Spinal cord Ganglia outside CNS Spinal nerves Figure 49.4 The vertebrate nervous system.

Gray matter White matter Ventricles Figure 49.5 Figure 49.5 Ventricles, gray matter, and white matter.

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 as well as to provide nutrients and remove wastes © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Glia Glia have numerous functions to nourish, support, and regulate neurons Embryonic radial glia form tracks along which newly formed neurons migrate Astrocytes induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier and restricting the entry of most substances into the brain © 2011 Pearson Education, Inc.

CNS PNS VENTRICLE Neuron Astrocyte Cilia Oligodendrocyte Schwann cell Figure 49.6 CNS PNS VENTRICLE Neuron Astrocyte Cilia Oligodendrocyte Schwann cell Microglial cell Capillary Ependymal cell Figure 49.6 Glia in the vertebrate nervous system. 50 m LM

The Peripheral Nervous System The PNS transmits information to and from the CNS and regulates movement and the internal environment In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS © 2011 Pearson Education, Inc.

The motor system carries signals to skeletal muscles and is voluntary The PNS has two efferent components: the motor system and the autonomic nervous system The motor system carries signals to skeletal muscles and is voluntary The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary © 2011 Pearson Education, Inc.

Central Nervous System (information processing) Figure 49.7 Central Nervous System (information processing) Peripheral Nervous System Afferent neurons Efferent neurons Autonomic nervous system Motor system Sensory receptors Control of skeletal muscle Figure 49.7 Functional hierarchy of the vertebrate peripheral nervous system. Internal and external stimuli Sympathetic division Parasympathetic division Enteric division Control of smooth muscles, cardiac muscles, glands

The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions The sympathetic division regulates arousal and energy generation (“fight-or-flight” response) The parasympathetic division has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions © 2011 Pearson Education, Inc.

The enteric division controls activity of the digestive tract, pancreas, and gallbladder © 2011 Pearson Education, Inc.

Parasympathetic division Sympathetic division Figure 49.8 Parasympathetic division Sympathetic division Action on target organs: Action on target organs: Constricts pupil of eye Dilates pupil of eye Inhibits salivary gland secretion Stimulates salivary gland secretion Sympathetic ganglia Constricts bronchi in lungs Relaxes bronchi in lungs Cervical Slows heart Accelerates heart Stimulates activity of stomach and intestines Inhibits activity of stomach and intestines Thoracic Stimulates activity of pancreas Inhibits activity of pancreas Stimulates gallbladder Stimulates glucose release from liver; inhibits gallbladder Figure 49.8 The parasympathetic and sympathetic divisions of the autonomic nervous system. Lumbar Stimulates adrenal medulla Promotes emptying of bladder Inhibits emptying of bladder Promotes erection of genitalia Sacral Promotes ejaculation and vaginal contractions Synapse

Concept 49.2: The vertebrate brain is regionally specialized Specific brain structures are particularly specialized for diverse functions These structures arise during embryonic development © 2011 Pearson Education, Inc.

Figure 49.9a Figure 49.9 Exploring: The Organization of the Human Brain

Embryonic brain regions Brain structures in child and adult Figure 49.9b Embryonic brain regions Brain structures in child and adult Cerebrum (includes cerebral cortex, white matter, basal nuclei) Telencephalon Forebrain Diencephalon (thalamus, hypothalamus, epithalamus) Diencephalon Midbrain Mesencephalon Midbrain (part of brainstem) Metencephalon Pons (part of brainstem), cerebellum Hindbrain Myelencephalon Medulla oblongata (part of brainstem) Mesencephalon Cerebrum Diencephalon Metencephalon Midbrain Midbrain Diencephalon Myelencephalon Hindbrain Figure 49.9 Exploring: The Organization of the Human Brain Pons Medulla oblongata Spinal cord Forebrain Telencephalon Cerebellum Spinal cord Embryo at 1 month Embryo at 5 weeks Child

Left cerebral hemisphere Right cerebral hemisphere Figure 49.9c Left cerebral hemisphere Right cerebral hemisphere Cerebral cortex Corpus callosum Cerebrum Basal nuclei Figure 49.9 Exploring: The Organization of the Human Brain Cerebellum Adult brain viewed from the rear

Diencephalon Thalamus Pineal gland Brainstem Hypothalamus Midbrain Figure 49.9d Diencephalon Thalamus Pineal gland Brainstem Hypothalamus Midbrain Pituitary gland Pons Figure 49.9 Exploring: The Organization of the Human Brain Medulla oblongata Spinal cord

Arousal and Sleep The brainstem and cerebrum control arousal and sleep The core of the brainstem has a diffuse network of neurons called the reticular formation 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 © 2011 Pearson Education, Inc.

Input from nerves of ears Figure 49.10 Eye Input from nerves of ears Figure 49.10 The reticular formation. Reticular formation Input from touch, pain, and temperature receptors

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” © 2011 Pearson Education, Inc.

Low-frequency waves characteristic of sleep Figure 49.11 Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Location Time: 0 hours Time: 1 hour Left hemisphere Figure 49.11 Dolphins can be asleep and awake at the same time. Right hemisphere

Biological Clock Regulation Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity Mammalian circadian rhythms rely on a biological clock, molecular mechanism that directs periodic gene expression Biological clocks are typically synchronized to light and dark cycles © 2011 Pearson Education, Inc.

The SCN acts as a pacemaker, synchronizing the biological clock In mammals, circadian rhythms are coordinated by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (SCN) The SCN acts as a pacemaker, synchronizing the biological clock © 2011 Pearson Education, Inc.

After surgery and transplant Figure 49.12 RESULTS Wild-type hamster  hamster Wild-type hamster with SCN from  hamster  hamster with SCN from wild-type hamster 24 23 22 Circadian cycle period (hours) 21 Figure 49.12 Inquiry: Which cells control the circadian rhythm in mammals? 20 19 Before procedures After surgery and transplant

Emotions Generation and experience of emotions involve many brain structures including the amygdala, hippocampus, and parts of the thalamus These structures are grouped as the limbic system The limbic system also functions in motivation, olfaction, behavior, and memory © 2011 Pearson Education, Inc.

Thalamus Hypothalamus Olfactory bulb Amygdala Hippocampus Figure 49.13 Figure 49.13 The limbic system. Olfactory bulb Amygdala Hippocampus

Generation and experience of emotion also require interaction between the limbic system and sensory areas of the cerebrum The structure most important to the storage of emotion in the memory is the amygdala, a mass of nuclei near the base of the cerebrum © 2011 Pearson Education, Inc.

Nucleus accumbens Amygdala Happy music Sad music Figure 49.14 Figure 49.14 Impact: Using Functional Brain Imaging to Map Activity in the Working Brain Happy music Sad music

Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions The cerebrum, the largest structure in the human brain, is essential for awareness, language, cognition, memory, and consciousness Four regions, or lobes (frontal, temporal, occipital, and parietal), are landmarks for particular functions © 2011 Pearson Education, Inc.

Motor cortex (control of skeletal muscles) Figure 49.15 Motor cortex (control of skeletal muscles) Somatosensory cortex (sense of touch) Frontal lobe Parietal lobe Prefrontal cortex (decision making, planning) Sensory association cortex (integration of sensory information) Visual association cortex (combining images and object recognition) Broca’s area (forming speech) Figure 49.15 The human cerebral cortex. Temporal lobe Occipital lobe Auditory cortex (hearing) Visual cortex (processing visual stimuli and pattern recognition) Cerebellum Wernicke’s area (comprehending language)

Language and Speech Studies of brain activity have mapped areas responsible for language and speech Broca’s area in the frontal lobe is active when speech is generated Wernicke’s area in the temporal lobe is active when speech is heard These areas belong to a larger network of regions involved in language © 2011 Pearson Education, Inc.

Hearing words Seeing words Speaking words Generating words Figure 49.16 Max Hearing words Seeing words Figure 49.16 Mapping language areas in the cerebral cortex. Min Speaking words Generating words

Lateralization of Cortical Function The two hemispheres make distinct contributions to brain function The left hemisphere is more adept at language, math, logic, and processing of serial sequences The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing © 2011 Pearson Education, Inc.

The differences in hemisphere function are called lateralization Lateralization is partly linked to handedness The two hemispheres work together by communicating through the fibers of the corpus callosum © 2011 Pearson Education, Inc.

Information Processing The cerebral cortex receives input from sensory organs and somatosensory receptors Somatosensory receptors provide information about touch, pain, pressure, temperature, and the position of muscles and limbs The thalamus directs different types of input to distinct locations © 2011 Pearson Education, Inc.

Adjacent areas process features in the sensory input and integrate information from different sensory areas Integrated sensory information passes to the prefrontal cortex, which helps plan actions and movements In the somatosensory cortex and motor cortex, neurons are arranged according to the part of the body that generates input or receives commands © 2011 Pearson Education, Inc.

Shoulder Elbow Trunk Knee Forearm Hip Wrist Hand Fingers Thumb Neck Figure 49.17a Shoulder Elbow Trunk Knee Forearm Hip Wrist Hand Fingers Thumb Neck Brow Eye Face Toes Figure 49.17 Body part representation in the primary motor and primary somatosensory cortices. Lips Jaw Tongue Primary motor cortex

Primary somatosensory cortex Figure 49.17b Upper arm Trunk Head Neck Hip Leg Elbow Forearm Hand Fingers Thumb Eye Nose Face Lips Genitalia Teeth Gums Figure 49.17 Body part representation in the primary motor and primary somatosensory cortices. Jaw Tongue Pharynx Primary somatosensory cortex Abdominal organs

Frontal Lobe Function Frontal lobe damage may impair decision making and emotional responses but leave intellect and memory intact The frontal lobes have a substantial effect on “executive functions” © 2011 Pearson Education, Inc.

Evolution of Cognition in Vertebrates Previous ideas that a highly convoluted neocortex is required for advanced cognition may be incorrect The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be the clustering of nuclei in the top or outer portion of the brain (pallium) © 2011 Pearson Education, Inc.

Cerebrum (including cerebral cortex) Figure 49.18 Human brain Cerebrum (including cerebral cortex) Thalamus Midbrain Hindbrain Cerebellum Avian brain to scale Cerebrum (including pallium) Avian brain Figure 49.18 Comparison of regions for higher cognition in avian and human brains. Cerebellum Thalamus Hindbrain Midbrain

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 Only half the synapses that form during embryo development survive into adulthood © 2011 Pearson Education, Inc.

Neural Plasticity Neural plasticity describes the ability of the nervous system to be modified after birth Changes can strengthen or weaken signaling at a synapse © 2011 Pearson Education, Inc.

Synapses are strengthened or weakened in response to activity. Figure 49.19 N1 N1 N2 N2 (a) Synapses are strengthened or weakened in response to activity. Figure 49.19 Neural plasticity. (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses.

Memory and Learning The formation of memories is an example of neural plasticity Short-term memory is accessed via the hippocampus The hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortex Some consolidation of memory is thought to occur during sleep © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

NMDA receptor (closed) NMDA receptor (open) Stored AMPA receptor Figure 49.20a PRESYNAPTIC NEURON Ca2 Na Mg2 Glutamate NMDA receptor (closed) NMDA receptor (open) Figure 49.20 Long-term potentiation in the brain. Stored AMPA receptor POSTSYNAPTIC NEURON (a) Synapse prior to long-term potentiation (LTP)

Mg2 1 NMDA receptor AMPA receptor 2 3 Na Ca2 (b) Establishing LTP Figure 49.20b Mg2 1 NMDA receptor AMPA receptor 2 Figure 49.20 Long-term potentiation in the brain. 3 Na Ca2 (b) Establishing LTP

(c) Synapse exhibiting LTP Figure 49.20c 3 1 NMDA receptor AMPA receptor Figure 49.20 Long-term potentiation in the brain. 2 4 Action potential Depolarization (c) Synapse exhibiting LTP

Stem Cells in the Brain The adult human brain contains neural stem cells In mice, stem cells in the brain can give rise to neurons that mature and become incorporated into the adult nervous system Such neurons play an essential role in learning and memory © 2011 Pearson Education, Inc.

Concept 49.5: Nervous system disorders can be explained in molecular terms Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer’s disease, and Parkinson’s disease Genetic and environmental factors contribute to diseases of the nervous system © 2011 Pearson Education, Inc.

Genes shared with relatives of person with schizophrenia Figure 49.22 50 Genes shared with relatives of person with schizophrenia 12.5% (3rd-degree relative) 40 25% (2nd-degree relative) 50% (1st-degree relative) 100% 30 Risk of developing schizophrenia (%) 20 10 Figure 49.22 Genetic contribution to schizophrenia. Child Individual, general population Nephew/ niece Parent Fraternal twin Identical twin First cousin Uncle/aunt Grandchild Half sibling Full sibling Relationship to person with schizophrenia

Schizophrenia About 1% of the world’s population suffers from schizophrenia Schizophrenia is characterized by hallucinations, delusions, and other symptoms Available treatments focus on brain pathways that use dopamine as a neurotransmitter © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Drug Addiction and the Brain’s 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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Nicotine stimulates dopamine- releasing VTA neuron. Inhibitory neuron Figure 49.23 Nicotine stimulates dopamine- releasing VTA neuron. Inhibitory neuron Opium and heroin decrease activity of inhibitory neuron. Dopamine- releasing VTA neuron Cocaine and amphetamines block removal of dopamine from synaptic cleft. Figure 49.23 Effects of addictive drugs on the reward system of the mammalian brain. Cerebral neuron of reward pathway Reward system response

Alzheimer’s Disease Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain There is no cure for this disease though some drugs are effective at relieving symptoms © 2011 Pearson Education, Inc.

Neurofibrillary tangle 20 m Figure 49.24 Amyloid plaque Neurofibrillary tangle 20 m Figure 49.24 Microscopic signs of Alzheimer’s disease.

Parkinson’s Disease Parkinson’s disease is a motor disorder caused by death of dopamine-secreting neurons in the midbrain It is characterized by muscle tremors, flexed posture, and a shuffling gait There is no cure, although drugs and various other approaches are used to manage symptoms © 2011 Pearson Education, Inc.