Functional Neuroanatomy and the Evolution of the Nervous System
Chapter Two Functional Neuroanatomy and the Evolution of the Nervous System Anatomical Directions
Rostral or anterior Head end of four legged animal Caudal or posterior Tail end of four legged animal Inferior or ventral Towards the belly Superior or dorsal Towards the back Figure 2.1 Anatomical Directions. Anatomists use directional terms to name and locate brain structures. Because standing upright puts an 80-degree angle in the human neuraxis, the dorsal surface of the human brain also forms an 80-degree angle with the dorsal spinal cord. ( 2016 Cengage Learning) Anatomical Directions (contd.)
Figure 2.1 Anatomical Directions. Anatomists use directional terms to name and locate brain structures. Because standing upright puts an 80-degree angle in the human neuraxis, the dorsal surface of the human brain also forms an 80-degree angle with the dorsal spinal cord. ( 2016 Cengage Learning) Planes of Section Sagittal Coronal Horizontal Parallel to midline
Divides nervous system front to back Horizontal (axial, transverse) Divides brain from top to bottom Figure 2.2 Planes of Section. Anatomists use the horizontal, coronal, and sagittal sections to view three-dimensional structures as two-dimensional images. ( 2016 Cengage Learning) Planes of Section (contd.)
Figure 2.2 Planes of Section. Anatomists use the horizontal, coronal, and sagittal sections to view three-dimensional structures as two-dimensional images. ( 2016 Cengage Learning) Protecting and Supplying the Nervous System
Meninges Three layers of meninges provide protection Cerebrospinal fluid Secreted in hollow spaces in the brain knownas ventricles Circulates through ventricles, subarachnoidspace, and central canal of the spinal cord Blood supply Brain receives nutrients through the carotidarteries and vertebral arteries The Skull and Three Layers of Membrane Protect the Brain
Figure 2.3 (top/left) The Skull and Three Layers of Membrane Protect the Brain. In addition to the protection provided by the skull bones, the brain and spinal cord are covered with three layers of membranes known as meninges. Going from the skull to the brain, we find the dura mater, the arachnoid layer, and the pia mater. Between the arachnoid and pia mater layers is the subarachnoid space, which contains cerebrospinal fluid (CSF). In the peripheral nervous system (PNS), only the dura mater and pia mater layers cover the nerves. There is no CSF in the PNS. ( 2016 Cengage Learning) Figure 2.4 (bottom/right) Meningitis Results from Infection of the Meninges. Viruses and bacteria can invade the layers of the meninges, causing meningitis. Meningitis causes headache and stiffness of the neck, which can be followed by incoherence, drowsiness, coma, and death. This photo shows a fatal case of meningitis with large areas of pus within the meninges. (Sebastian Kaulitzki/Shutterstock.com) Cerebrospinal Fluid Circulation
Figure 2.5 Cerebrospinal Fluid Circulates Through the Ventricles, Spinal Cord, and Subarachnoid Space. Cerebrospinal fluid (CSF) is produced by the choroid plexus that lines the walls of the ventricles. From the lateral ventricles, the CSF flows through the third and fourth ventricle and into the central canal of the spinal cord. At the base of the cerebellum, CSF exits into the subarachnoid space and is reabsorbed by veins near the top of the head. ( 2016 Cengage Learning) Hydrocephalus Figure 2.6 (left) Hydrocephalus Results from Blockage in the Circulation of Cerebrospinal Fluid. This photograph shows a baby born with the condition of hydrocephalus, which results when the normal circulation of cerebrospinal fluid (CSF) is blocked. Note the large size of the babys head, which has expanded to accommodate all of the CSF. Untreated, hydrocephalus causes intellectual disability, but, today, shunts installed to drain off the excess fluid can prevent any further damage to the childs brain. (Barts Medical Library/Phototake) Figure 2.7 (right) Shunt for Hydrocephalus. Hydrocephalus in newborns used to be a major cause of intellectual disability. Contemporary treatment consisting of shunts inserted into the ventricle that drain excess cerebrospinal fluid (CSF) to the abdomen or heart has reduced the damage done to the brains of individuals with this condition. The Brain Has a Generous Supply of Blood
Figure 2.8 The Brain Has a Generous Supply of Blood. Blood reaches the brain either through the carotid arteries on either side of the neck or through the vertebral arteries entering through the base of the skull.Once in the brain, these arteries branch into the anterior cerebral artery, and middle cerebral artery, and the posterior cerebral artery. ( 2016 Cengage Learning) The Organization of the Nervous System
The central nervous system Brain and spinal cord The peripheral nervous system All nerves that leave from the brain and spinalcord and extend to and from all parts of thebody Figure 2.9 The Organization of the Nervous System. The nervous system has two major components, the central nervous sytem (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which contains all the nerves that exit the brain and spinal cord. ( 2016 Cengage Learning) The Organization of the Nervous System
Figure 2.9 The Organization of the Nervous System. The nervous system has two major components, the central nervous sytem (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which contains all the nerves that exit the brain and spinal cord. ( 2016 Cengage Learning) The Central Nervous System The Spinal Cord
Anatomy Extends from the medulla to the first lumbarvertebra 31 spinal nerves (cervical, thoracic, lumbar,sacral, coccygeal) White matter (nerve fibers); gray matter (cellbodies) Reflexes Patellar reflex Withdrawal reflex Instructors may want to discuss the reticular formation at this time. The Anatomy of the Spinal Cord
Figure 2.10 The Anatomy of the Spinal Cord. The spinal cord is divided into cervical, thoracic, lumbar, sacral, and coccygeal segments. The spinal nerves exit either side of the cord between the surrounding bony vertebrae. ( 2016 Cengage Learning) Embryological Divisions of the Brain
Table 2.1 | Embryological Divisions of the Brain Structures of the Brainstem
Figure 2.11 Structures of the Brainstem. (a) This sagittal section displays many of the important structures found in the brainstem. ( 2016 Cengage Learning) Structures of the Brainstem (contd.)
Figure 2.11 Structures of the Brainstem. (b) With the cerebral hemispheres removed, we can see spatial relationships between the major structures of the brainstem. The key-to-slice allows us to view a horizontal section of the medulla and several of the important structures found at this level of the brain. ( 2016 Cengage Learning) The Central Nervous System: The Hindbrain
Medulla (myelencephalon) Breathing, heart rate, blood pressure Reticular formation Consciousness, arousal, movement, and pain Metencephalon Pons: balance, motion sickness Cerebellum Voluntary movements, muscle tone, balance,speech, motion sickness, executive functions, andemotional processing The Internal Structure of the Midbrain
Periaqueductal gray Natural pain management Red nucleus Motor output pathway Substantia nigra Parkinsons disease Superior and inferior colliculi Visual and auditory stimuli Figure 2.12 The Internal Structure of the Midbrain. Important structures in themidbrain include the superior and inferior colliculi, the cerebral aqueduct, the periaqueductal gray, the substantia nigra, and the red nucleus. ( 2016 Cengage Learning) The Internal Structure of the Midbrain
Figure 2.12 The Internal Structure of the Midbrain. Important structures in themidbrain include the superior and inferior colliculi, the cerebral aqueduct, the periaqueductal gray, the substantia nigra, and the red nucleus. ( 2016 Cengage Learning) Important Structures in the Brainstem
Table 2.2 Important Structures in the Brainstem The Central Nervous System The Forebrain
The forebrain is composed of thediencephalon and the telencephalon Diencephalon Thalamus Receives sensory input Hypothalamus Regulation of the endocrine system The Thalamus and Hypothalamus of the Diencephalon
Figure 2.13 The Thalamus and Hypothalamus of the Diencephalon. The thalamus lies close to the center of the brain, and the hypothalamus is located rostrally and ventrallyrelative to the thalamus. Directly below the hypothalamus is the pituitary gland, which is an important part of the endocrine system. ( 2016 Cengage Learning) The Central Nervous System The Forebrain (contd.)
Telencephalon Basal ganglia Motor control Parkinsons and Huntingtons disease; ADHD Limbic sstem Learning, motivated behavior, and emotion Cerebral cortex Four lobes Sensory cortex, motor cortex, and associationcortex The Basal Ganglia and the Limbic System
Figure 2.14 (left) The Basal Ganglia. The basal ganglia include the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and nucleus accumbens. (The subthalamic nucleus and nucleus accumbens cannot be seen from this point of view). The substantia nigra of the midbrain is usually considered to be a part of this system. ( 2016 Cengage Learning) Figure 2.15 (right) The Limbic System Participates in Learning and Function. A number of closely connected forebrain structures are included in the limbic system, which participates in many emotional, learning, and motivated behaviors. ( 2016 Cengage Learning) Structures of the Limbic System
Table 2.3 Structures of the Limbic System The Hippocampus Figure 2.16 (left) The Hippocampus. The hippocampus curves away from the midline out towards the rostral temporal lobe. This structure plays important roles in learning, memory, and stress. Figure 2.17 (right) Amygdala Abnormalities Can Lead to Irrational Violence. In very rare cases, abnormalities of the amygdala are associated with uncharacteristic, totally irrational violence. Charles Whitman, who led a previously unremarkable life, killed several family members and then climbed a clock tower at the University of Texas at Austin, in He methodically opened fire on people below, killing 15 and injuring 31. Whitman, who was killed by police, was later found to have a tumor pressing on his amygdala. (Bettmann/Corbis) Comparative Convolutions of the Cortex
Figure 2.18 Comparative Convolutions of the Cortex. The relative degree of cortical convolution is positively correlated with the cognitive abilities of a species. The Layers of the Cerebral Cortex
Figure 2.19 The Layers of the Cerebral Cortex. The cerebral cortex covers the outer surface of the brain. Six distinct layers are apparent in most areas of the cortex. Three different views of these layers are shown here. The Golgi stain highlights entire neurons, and the Nissl stain highlights cell bodies. Note the large pyramid cells shown by the Nissl stain in layer V. The Weigert stain highlights pathways formed by myelinated axons through the cortex. Brodmanns Map of the Brain
Figure 2.20 Brodmanns Map of the Brain. Early 20th-century German neurologist Korbinian Brodmann divided the cerebral cortex into 52 different areas, based on the distribution of cell bodies in each area. One hundred years after Brodmanns system was first published, it remains the most widely used system for describing cortical architecture. ( 2016 Cengage Learning) The Lobes of the Cerebral Cortex
Figure 2.21 The Lobes of the Cerebral Cortex. The cortex is traditionally divided into the frontal, parietal, temporal, and occipital lobes. ( 2016 Cengage Learning) The Corpus Callosum and the Anterior Commissure
Figure 2.22 The Corpus Callosum and the Anterior Commissure. Two fiber bundles, the very large corpus collosum and the much smaller anterior commissure, connect the right and left cerebral hemispheres. ( 2016 Cengage Learning) Localization of Function in the Cortex
Frontal lobe Primary motor cortex, cognitive processes Dorsolateral prefrontal cortex, orbitofrontalcortex Phineas Gage Lobotomies Brocas area Lateralization of function The Case of Phineas Gage
Figure 2.23 The Case of Phineas Gage. Mid-19th-century railroad worker Phineas Gage suffered an accident in which an iron rod was shot through the frontal lobe of his brain. Although Gage survived, he was described by his friends as a changed man. Gages case illustrates the localization of higher-order cognitive functions in the frontal lobe. (Patrick Landmann/Science Source) Brain Circuits and the Connectome
The Human Connectome Project Mapping the neural connections within thebrain Cellular and macro levels of investigation The Peripheral Nervous System
The cranial nerves Enter and exit the brain directly to serve theregion of the head and neck The spinal nerves 31 pairs provide sensory and motor pathwaysto the torso, arms, and legs Mixed nerves (afferent and efferent) The autonomic nervous system Manages the vital functions of the bodywithout conscious effort or awareness The Twelve Pairs of Cranial Nerves
Figure 2.24 The Twelve Pairs of Cranial Nerves. Twelve pairs of cranial nerves leave the brain directly to carry sensory and motor information to and from the head and neck areas. The red lines represent sensory functions, and the blue lines show motor control. Some cranial nerves are sensory only, some are motor only, and some are mixed. ( 2016 Cengage Learning) The Structure of the Spinal Cord
Figure 2.25 The Structure of the Spinal Cord. This cross-section of the spinal cord shows a number of important anatomical features. Three layers of meninges surround the cord. The gray matter of the cord is located in a butterfly shape near the central canal, which contains cerebrospinal fluid (CSF). The dorsal afferent (sensory) nerves join the ventral efferent (motor) nerves beyond the spinal ganglion to form a mixed nerve. ( 2016 Cengage Learning) The Autonomic Nervous System
The sympathetic nervous system Fight-or-flight system The parasympathetic nervous system Provides rest, repair, and energy storage The enteric nervous system Serves the gastrointestinal tract The endocrine system Hypothalamic control of hormone release Pituitary gland The Sympathetic and Parasympathetic Nervous Systems
Figure 2.26 (left) The Autonomic Nervous System. The sympathetic and parasympathetic divisions of the autonomic nervous system often have opposite effects on target organs. To carry out their respective tasks, sympathetic neurons form their first synapse in the sympathetic chain, whereas parasympathetic neurons synapse on ganglia close to the target organs. In addition, the systems use different neurotransmitters at the target organ. ( 2016 Cengage Learning) The Evolution of the Human Brain and Nervous System
Natural selection and evolution Natural selection favors the organism with thehighest degree of fitness Evolution of the nervous system Fairly recent; vertebrates or chordates areanimals with spinal columns and real brains Evolution of the human brain Outstanding modern feature is our brain size Brain development occurred very recently Timeline for the Evolution of the Brain
Figure 2.28 Timeline for the Evolution of the Brain. When compared with the entire time scale of evolution, nervous systems represent a very new development, appearing for the first time in the form of simple neural nets about 700 million years ago. Advanced brains, such as the human brain, are more recent still. ( 2016 Cengage Learning) The Evolution of Chordate Brains
Figure 2.29 (top) True Brains are Found in Chordates. Compared with invertebrates, such as the Aplysia californica (a type of sea slug) on the right, chordates have true brains as opposed to ganglia. The chordate nervous system runs near the dorsal rather than the ventral surface of the animals body. ( 2016 Cengage Learning) Figure 2.30 (bottom) Chordate Brains Continued to Evolve. More complex chordate brains feature increased convolutions and larger cerebrums and cerebellums. ( 2016 Cengage Learning) Human Brain Development Proceeded Swiftly
Figure 2.31 Human Brain Development Proceeded Swiftly. Hominin brains advanced rapidly from those of the early australopithecines, shown on the left, who had brains about the size of modern chimpanzees, to Homo erectus (700 cubic centimeters; shown in the center), to Homo sapiens (1,400 cubic centimeters; shown on the far right). Brain development then appears to have leveled off. You are reading this text with essentially the same size brain that has worked for Homo sapiens for the past 200,000 years. (Australian Museum)