Chapter Summary

Structural Organization of the Brain

1. During embryonic development, five regions of the brain are formed: the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon.
1. The telencephalon and diencephalon constitute the forebrain; the mesencephalon is the midbrain, and the hindbrain is composed of the metencephalon and the myelencephalon
2. The CNS begins as a hollow tube, and thus the brain and spinal cord are hollow. the cavities of the brain are known as ventricles.

Cerebrum

1. The cerebrum consists of two hemispheres connected by a large fiber tract called the corpus callosum.
1. The outer part of the cerebrum, the cerebral cortex, consists of gray matter.
2. Under the gray matter is white matter, but nuclei of gray matter, known as the basal nuclei, lie deep within the white matter of the cerebrum.
3. Synaptic potentials within the cerebral cortex produce the electrical activity seen in an electroencephalogram (EEG).
2. The two cerebral hemispheres exhibit some degree of specialization of function, a phenomenon called cerebral lateralization.
1. In most people, the left hemisphere is dominant in language and analytical ability, whereas the right hemisphere is more important in pattern recognition, musical creation, singing, and the recognition of faces.
2. The two hemispheres cooperate in their functions; this is aided by communication between the two via the corpus callosum.
3. Particular regions of the left cerebral cortex appear to be important in language ability; when these areas are damaged, characteristic types of aphasias result.
1. Wernicke's area is involved in speech comprehension, whereas Broca's area is required for the mechanical performance of speech.
2. Wernicke's area is believed to control Broca's area by means of the arcuate fasciculus.
3. The angular gyrus is believed to integrate different sources of sensory information and project to Wernicke's area.
4. The limbic system and hypothalamus are regions of the brain that have been implicated as centers for various emotions.
5. Memory can be divided into short-term and long-term categories.
1. The medial temporal lobes, in particular the hippocampus and perhaps the amygdaloid nucleus, appear to be required for the consolidation of short-term memory into long-term memory.
2. Particular aspects of a memory may be stored in numerous brain regions.
3. Long-term potentiation is a phenomenon that may be involved in some aspects of memory.

Diencephalon

1. The diencephalon is the region of the forebrain which includes the thalamus, epithalamus, hypothalamus, and pituitary gland.
1. The thalamus serves an important relay center for sensory information, among its other functions.
2. The epithalamus contains a choroid plexus, where cerebrospinal fluid is formed. The pineal gland, which secretes the hormone melatonin, is also part of the epithalamus.
3. The hypothalamus forms the floor of the third ventricle, and the pituitary gland is located immediately inferior to the hypothalamus.
2. The hypothalamus is the main control center of visceral activities.
1. The hypothalamus contains centers for the control of thirst, hunger, body temperature, and (together with the limbic system) various emotions.
2. The hypothalamus regulates the secretions of the pituitary gland. It controls the posterior pituitary by means of a fiber tract, and it controls the anterior pituitary by means of hormones.

Midbrain and Hindbrain

1. The midbrain contains the superior and inferior colliculi, which are involved in visual and auditory reflexes, respectively and nuclei that contain dopaminergic neurons that project to the corpus striatum and limbic system of the forebrain.
2. The hindbrain consists of two regions: the metencephalon and the myelencephalon.
1. The metencephalon contains the pons and cerebellum. The pons contains nuclei for four pairs of cranial nerves, and the cerebellum plays an important role in the control of skeletal movements.
2. The myelencephalon consists of only one region, the medulla oblongata. The medulla contains centers for the regulation of such vital functions as breathing and the control of the cardiovascular system.

Spinal Cord Tracts

1. Ascending tracts carry sensory information from sensory organs up to the spinal cord to the brain.
2. Descending tracts are motor tracts and are divided into two groups: the pyramidal and the extrapyramidal systems.
1. Pyramidal tracts are the corticospinal tracts. They begin in the precentral gyrus and descend, without synapsing, into the spinal cord.
2. Most of the corticospinal fibers decussate in the pyramids of the medulla oblongata.
3. Regions of the cerebral cortex, the basal nuclei, and the cerebellum, control movements indirectly by synapsing with other regions that give rise to descending extrapyramidal fiber tracts.
4. The major extrapyramidal motor tract is the reticulospinal tract, which has its origin in the reticular formation of the midbrain.

Cranial and Spinal Nerves

1. There are twelve pairs of cranial nerves. Most of these are mixed, but some are exclusively sensory in function.
2. There are thirty-one pairs of spinal nerves. Each of these contains both sensory and motor fibers.
1. The dorsal root of a spinal nerve contains sensory fibers, and the cell bodies of these neurons are contained in the dorsal root ganglion.
2. The ventral root of a spinal nerve contains motor fibers.
3. A reflex arc is the pathway that involves a sensory neuron and a motor neuron; one or more association neurons also may be involved in some reflexes.

After studying this chapter, students should be able to . . .

1. locate the major brain regions and describe the structures within each of these regions.
2. describe the organization of the cerebrum and the primary roles of its lobes.
3. describe the location and function of the sensory cortex and motor cortex.
4. explain the lateralization of functions in the right and left cerebral hemispheres.
5. describe the structures involved in the control of speech and explain their interrelationships.
6. describe the different types of aphasias that result from damage to specific regions of the brain.
7. describe the structures included in the limbic system and discuss the possible role of this system in emotion.
8. distinguish between different types of memory and describe the roles of different brain regions in memory.
9. describe the location of the thalamus and explain the significance of this organ.
10. describe the location of the hypothalamus and explain the significance of this organ.
11. describe the locations and structures contained in the midbrain and hindbrain, and explain the role of the medulla oblongata in the control of visceral functions.
12. explain how the spinal cord is organized and how ascending and descending tracts are named.
13. describe the origin and pathways of the pyramidal motor tracts and explain the significance of these descending tracts.
14. explain the role of the basal nuclei and cerebellum in motor control via the extrapyramidal system, and describe the pathways of this system.
15. explain the structures and pathways involved in a reflex arc.