Ch. 49: Nervous Systems

The central nervous system (CNS): the brain and the spinal cord Many animals have a complex nervous system that consists of The central nervous system (CNS): the brain and the spinal cord The peripheral nervous system (PNS) consists of neurons/ nerves and ganglia (clusters of neurons) carrying information into and out of the CNS. The neurons of the PNS, when bundled together, form nerves Brain Region specialization is a hallmark of both systems Spinal cord (dorsal nerve cord) Sensory ganglia (h) Salamander (vertebrate)

Central nervous system (CNS) Brain Cranial nerves Spinal cord Figure 49.6 Central nervous system (CNS) Brain Cranial nerves Spinal cord Peripheral nervous system (PNS) Ganglia outside CNS Spinal nerves Figure 49.6 The vertebrate nervous system

Glia Glial cells, or 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 Radial glial cells and astrocytes can both act as stem cells Researchers are trying to find a way to use neural stem cells to replace brain tissue that has ceased to function normally

Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell) Most neurons are nourished or insulated by cells called glia or glial cells 80 µm Glia Cell bodies of neurons

Capillary Neuron CNS PNS VENTRICLE Cilia Ependymal cells Astrocytes Figure 49.3 Capillary Neuron CNS PNS VENTRICLE Cilia Figure 49.3 Glia in the vertebrate nervous system Ependymal cells Astrocytes Oligodendrocytes Microglia Schwann cells

Organization of the Vertebrate Nervous System The CNS develops from the hollow nerve cord The cavity of the nerve cord gives rise to the narrow central canal of the spinal cord and the ventricles of the brain The canal and ventricles fill with cerebrospinal fluid, which supplies the CNS with nutrients and hormones and carries away wastes

The brain and spinal cord contain Figure 49.5 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 Gray matter White matter Figure 49.5 Ventricles, gray matter, and white matter Ventricles

The spinal cord also produces reflexes independently of the brain The spinal cord conveys information to and from the brain and generates basic patterns of locomotion 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

Cell body of sensory neuron in dorsal root ganglion Figure 49.7 Cell body of sensory neuron in dorsal root ganglion Gray matter White matter Quadriceps muscle Spinal cord (cross section) Hamstring muscle Figure 49.7 The knee-jerk reflex Key Sensory neuron Motor neuron Interneuron

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 The PNS is further broken down into the motor division which we have voluntary control over, and the involuntary autonomic division, further broken down into the antagonistic sympathetic and parasympathetic divisions as well as the enteric division.

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 The autonomic nervous system has sympathetic and parasympathetic 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

CENTRAL NERVOUS SYSTEM (information processing) Figure 49.8 CENTRAL NERVOUS SYSTEM (information processing) PERIPHERAL NERVOUS SYSTEM Afferent neurons Efferent neurons Autonomic nervous system Motor system Sensory receptors Control of skeletal muscle Figure 49.8 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

Parasympathetic division Sympathetic division Figure 49.9 Parasympathetic division Sympathetic division Constricts pupil of eye Dilates pupil of eye Stimulates salivary gland secretion Inhibits 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 glucose release from liver; inhibits gallbladder Stimulates gallbladder Figure 49.9 The parasympathetic and sympathetic divisions of the autonomic nervous system Lumbar Stimulates adrenal medulla Promotes emptying of bladder Inhibits emptying of bladder Sacral Promotes erection of genitalia Promotes ejaculation and vaginal contractions Synapse

Concept 49.2: The vertebrate brain is regionally specialized Specific brain structures are particularly specialized for diverse functions The vertebrate brain has three major regions: the forebrain, midbrain, and hindbrain The forebrain has activities including processing of olfactory input, regulation of sleep, learning, and any complex processing The midbrain coordinates routing of sensory input The hindbrain controls involuntary activities and coordinates motor activities

Figure 49.10 Comparison of vertebrates shows that relative sizes of particular brain regions vary These size differences reflect the relative importance of the particular brain function Lamprey Shark ANCESTRAL VERTEBRATE Ray-finned fish Amphibian Figure 49.10 Vertebrate brain structure and evolution Crocodilian Key Bird Forebrain Midbrain Hindbrain Mammal

During embryonic development the anterior neural tube gives rise to the forebrain, midbrain, and hindbrain The midbrain and part of the hindbrain form the brainstem, which joins with the spinal cord at the base of the brain The rest of the hindbrain gives rise to the cerebellum The forebrain divides into the diencephelon, which forms endocrine tissues in the brain, and the telencephalon, which becomes the cerebrum

Figure 49.11b Embryonic brain regions Brain structures in child and adult Telencephalon Cerebrum (includes cerebral cortex, basal nuclei) Forebrain Diencephalon Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain Mesencephalon Midbrain (part of brainstem) Metencephalon Pons (part of brainstem), cerebellum Hindbrain Myelencephalon Medulla oblongata (part of brainstem) Mesencephalon Cerebrum Diencephalon Metencephalon Midbrain Myelencephalon Hindbrain Diencephalon Figure 49.11b Exploring the organization of the human brain (part 2: brain development) Midbrain Pons Brainstem Medulla oblongata Telencephalon Forebrain Cerebellum Spinal cord Spinal cord Embryo at 1 month Embryo at 5 weeks Child

Cerebrum Forebrain Thalamus Hypothalamus Pituitary gland Midbrain Pons Figure 49.UN07 Cerebrum Forebrain Thalamus Hypothalamus Pituitary gland Midbrain Figure 49.UN07 Summary of key concepts: vertebrate brain regions Pons Spinal cord Hindbrain Medulla oblongata Cerebellum

Diencephalon Thalamus Figure 49.11d Diencephalon Thalamus Pineal gland Hypothalamus Midbrain Pituitary gland Pons Figure 49.11d Exploring the organization of the human brain (part 4: diencephalon and brainstem) 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 These neurons control the timing of sleep periods characterized by rapid eye movements (REMs) and by vivid dreams Sleep is also regulated by the biological clock and regions of the forebrain that regulate intensity and duration Sleep is essential and may play a role in the consolidation of learning and memory

Input from nerves of ears Figure 49.12 Eye Input from nerves of ears Figure 49.12 The reticular formation Reticular formation Input from touch, pain, and temperature receptors

Some animals have evolutionary adaptations allowing for substantial activity during sleep Dolphins, for example, sleep with one brain hemisphere at a time and are therefore able to swim while “asleep” Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Location Time: 0 hours Time: 1 hour Left hemisphere Figure 49.13 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 Such rhythms rely on a biological clock, a molecular mechanism that directs periodic gene expression and cellular activity Biological clocks are typically synchronized to light and dark cycles 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

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 Generating and experiencing emotion often require interactions between different parts of the brain 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

Thalamus Hypothalamus Olfactory bulb Amygdala Hippocampus Figure 49.14 Figure 49.14 The limbic system in the human brain Olfactory bulb Amygdala Hippocampus

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

Motor cortex (control of skeletal muscles) Figure 49.16 Motor cortex (control of skeletal muscles) Sensory association cortex (integration of sensory information) Somatosensory cortex (sense of touch) Frontal lobe Parietal lobe Prefrontal cortex (decision making, planning) Visual association cortex (combining images and object recognition) Broca’s area (forming speech) Figure 49.16 The human cerebral cortex Temporal lobe Occipital lobe Auditory cortex (hearing) Cerebellum Visual cortex (processing visual stimuli and pattern recognition) Wernicke’s area (comprehending language)

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 Information received at the primary sensory areas is passed to nearby association areas that process particular features of the input

Primary somatosensory cortex Figure 49.17 Frontal lobe Parietal lobe Shoulder Upper arm Forearm Elbow Trunk Knee Trunk Hip Head Neck Forearm Elbow Hip Leg Wrist Fingers Hand Hand Fingers Thumb Thumb Neck Eye Brow Nose Face Eye Lips Genitalia Face Toes Teeth Figure 49.17 Body part representation in the primary motor and primary somatosensory cortices Gums Lips Jaw Jaw Tongue Pharynx Tongue Primary motor cortex Primary somatosensory cortex Abdominal organs

Language and Speech Studies of brain activity have mapped areas responsible for language and speech Patients with damage in Broca’s area in the frontal lobe can understand language but cannot speak Damage to Wernicke’s area causes patients to be unable to understand language, though they can still speak

Max Hearing words Seeing words Min Speaking words Generating words Figure 49.18 Max Hearing words Seeing words Figure 49.18 Mapping language areas in the cerebral cortex Min Speaking words Generating words

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”

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 facial and pattern recognition, spatial relations, and nonverbal thinking The differences in hemisphere function are called lateralization The two hemispheres work together by communicating through the fibers of the corpus callosum

Memory and Learning Neuronal plasticity describes the ability of the nervous system to be modified after birth The formation of memories is an example of neuronal plasticity Short-term memory is accessed via the hippocampus The hippocampus also plays a role in forming long-term memory, which is later stored in the cerebral cortex Some consolidation of memory is thought to occur during sleep

Study hard….. study often…. N1 N1 N2 N2 Figure 49.20 N1 N1 Study hard….. study often…. N2 N2 (a) Connections between neurons are strengthened or weakened in response to activity. Figure 49.20 Neural plasticity (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses.

Concept 49.5: Many 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 These are a major public health problem Genetic and environmental factors contribute to diseases of the nervous system

Schizophrenia Depression About 1% of the world’s population suffers from schizophrenia. Schizophrenia is characterized by hallucinations, delusions, and other symptoms. Evidence suggests that schizophrenia affects neuronal pathways that use dopamine as a neurotransmitter Depression Two broad forms of depressive illness are known 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, which increase the activity of biogenic amines in the brain

The Brain’s Reward System and Drug Addiction 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 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

Nicotine stimulates dopamine- releasing VTA neuron. Figure 49.23 Inhibitory neuron Nicotine stimulates dopamine- releasing VTA 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 Parkinson’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 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

Neurofibrillary tangle 20 µm Figure 49.24 Amyloid plaque Neurofibrillary tangle 20 µm Figure 49.24 Microscopic signs of Alzheimer’s disease

Figure 49.11a Figure 49.11a Exploring the organization of the human brain (part 1: MRI)