1. Describe the appearance of the brain, and identify the terms used to indicate directions and planes of section.
2. Describe the divisions of the nervous system, the meninges, the ventricular system, and the flow of cerebrospinal fluid through the brain and its production.
3. Outline the development of the central nervous system.
4. Describe the telencephalon-one of the two major structures of the forebrain.
5. Describe the two major structures of the diencephalon.
6. Describe the major structures of the midbrain, the hindbrain, and the spinal cord.
7. Describe the peripheral nervous system, including the two divisions of the autonomic nervous system.

• Neuraxis, an imaginary line drawn through the spinal cord up to the front of the brain. The front end is anterior, and the tail is posterior. Rostral (toward the beak) and ceudal (toward the tail). The top of the head and the back are part of the dorsal surface, ventral (front) surface faces the ground. Lateral and medial, toward the side and toward the midline.
• Ipsilateral refers to structures on the same side of the body. Contralateral refers to structures on opposite sides of the body.
• To see what is in the nervous system, we have to cut it open.

1. Transversely, cross sections (frontal sections, referring to the brain)
2. Parallel to the ground, horizontal sections
3. Perpendicular to the ground and parallel to the neuraxis, giving us sagittal sections, the midsagittal plane.

• The nervous system consists of the brain and spinal cord, which make up the central nervous system (CNS), and the cranial nerves, spinal nerves, and peripheral ganglia, which make up the peripheral nervous system (PNS). The CNS is encased in bone: The brain is covered by the skull, and the spinal cord is encased by the vertebral column.
• The brain is a large mass of neurons, glia, and other supporting cells. It is the most protected organ of the body, encased in a tough, bony skull and floating in a pool of cerebrospinal fluid. The brain receives a copious supply of blood and is chemically guarded by the blood-brain barrier.

• Dura meter, means "hard mother." The middle layer of the meninges, the arachnoid membrane. The pia mater means "pious mother." Between the pia mater and arachnoid membrane is a gap called the subarachnoid space. This space is filled with a liquid called cerebrospinal fluid (CSF).
• The peripheral nervous system (PNS) is covered with only two layers of meninges: the dura mater and the pia mater. The middle layer (arachnoid membrane), with its associated pool of CSF, covers only the brain and spinal cord. Outside the central nervous system, the outer and inner layers (dura mater and pia mater) fuse and form a sheath that covers the spinal and cranial nerves and the peripheral ganglia.

• The brain is very soft and jellylike. The considerable weight of a human brain (approximately 1400 g), along with its delicate construction, necessitates that it be protected from shock.

• Because the brain is completely immersed in liquid, its net weight is reduced to approximately 80 g.
• The brain contains a series of hollow, interconnected chambers called ventricles. Lateral ventricles and third ventricle. The cerebral aqueduct, a long tube, connects the third ventricle to the fourth ventricle.
• Cerebrospinal fluid is extracted from the blood and resembles blood plasma in its composition. It is manufactured by a special structure that is rich in blood vessels called the choroid plexus, which protrudes into all four of the ventricles. Circulation of CSF begins in the lateral ventricles, flows into the third ventricle, then flows through the cerebral aqueduct into the fourth ventricle. From there, it flows through a set of openings into the subarachnoid space, which encases the entire central nervous system. Finally, the fluid is reabsorbed into the blood supply. The total volume of CSF is approximately 125 milliliters (ml), and the half-life (the time it takes for half of the CSF to be replaced by fresh fluid) is about 3 hours.
• obstructive hydrocephalus

• Anatomists have adopted a set of terms to describe the locations of parts of the body. Anterior is toward the head, posterior is toward the tail, lateral is toward the side, medial is toward the middle, dorsal is toward the back, and ventral is toward the front of surface of the body. In the special case of the nervous system, rostral means toward the beak (or nose) and caudal means toward the tail. Ipsilateral means same side, and contralateral means other side. A cross section (or in the case of the brain, a frontal section) slices the nervous system at right angles to the neuraxis. A horizontal section slices the brain parallel to the ground. A sagittal section slices it perpendicular to the ground and parallel to the neuraxis.
• The central nervous system consists of the brain and spinal cord, and the peripheral nervous system consists of the spinal and cranial nerves and peripheral ganglia. The CNS is covered with the meninges: dura mater, arachnoid membrane, and pia mater. The space under the arachnoid membrane is filled with cerebrospinal fluid, in which the brain floats. The PNS is covered with only the dura mater and pia mater. Cerebrospinal fluid is produced in the choroid plexus of the lateral, third, and fourth ventricles. It flows from the two lateral ventricles into the third ventricle, through the subarachnoid space, and finally back into the blood supply. If the flow of CSF is blocked by a tumor or other obstruction, the result is hydrocephalus: enlargement of the ventricles and subsequent brain damage.

• The central nervous system begins its existence early in the embryonic life as a hollow tube, and it maintains this basic shape even after it is fully developed. The cells that give rise to neurons are found on the inner surface of the tube. These cells divide and produce neurons, which then migrate in a radial direction, away from the center.
• Early in development, the central nervous system contains three interconnected chambers. These chambers become ventricles, and the tissue that surrounds them becomes the three major parts of the brain: the forebrain, the midbrain, and the hindbrain. As development progresses, the rostral chamber divides into three separate chambers, which become the two lateral ventricles and the third ventricle. The region around the lateral ventricles becomes the telencephalon ("end brain"), and the region around the third ventricle becomes the diencephalon ("interbrain"). In its final form the chamber inside the midbrain (mesencephalon) becomes narrow, forming the cerebral aqueduct, and two structures develop in the hindbrain: the metencephalon and the myelencephalon ("marrowbrain").
• Once neurons have migrated to their final locations, where they collect in groups, they begin forming connections with other groups of neurons. They grow dendrites, which receive the terminal buttons from the axons of other neurons, and they grow axons of their own.
• The axons of approximately 50 percent of these neurons do not find vacant postsynaptic cells of the right type with which to form synaptic connections, so they die.

• The forebrain surrounds the rostral end of the neural tube. Its two major components are telecephalon and the diencephalon.

• The cerebral hemispheres are covered by the cerebral cortex and contain the limbic system and the basal ganglia. The limbic system and the basal ganglia are primarily in the subcortical regions of the brain-those located deep within it, beneath the cerebral cortex.
• Cerebral Cortex. Cortex means "bark". Cerebral cortex surrounds the cerebral hemispheres like the bark of a tree. Sulci (small grooves), fissures (large grooves), and gyri (bulges between adjacent sulci or fissures). The total surface area is approximately 2360 cm2 (2.5 ft2), and the thickness is approximately 3mm.
• The cerebral cortex consists mostly of glia and the cell bodies, dendrites, and interconnecting axons of neurons. The cerebral cortex has a grayish brown appearance, and it is called gray matter. Millions of axons run beneath the cerebral cortex and connect its neurons with those located elsewhere in the brain. The large concentration of myelin around these axons gives this tissue an opaque white appearance-hence the term white matter.
• Different regions of the cerebral cortex perform different functions. Primary visual cortex, receives visual information, is located at the back of the brain, on the inner surfaces of the cerebral hemispheres. The primary auditory cortex, which receives auditory information, is located on the upper surface of a deep fissure in the side of the brain-the lateral fissure. The primary somatosensory cortex, a vertical strip of cortex just caudal to the central sulcus, receives information from the body senses.
• With the exception of olfaction, sensory information from the body or the environment is sent to the primary sensory cortex of the contralateral hemisphere.
• The region of the cerebral cortex most directly involved in the control of movement is the primary motor cortex.
• Motor association cortex. The region of the frontal lobe rostral to the primary motor cortex.
• Prefrontal cortex. The region of the frontal lobe rostral to the motor association cortex.
• Lateralized. Said of a function that is primarily controlled by neural circuits located in only one side of the brain.
• Corpus callosum (ka loh sum). The largest commissure of the brain, interconnecting the areas of neocortex on each side of the brain.
• Neocortex. The phylogenetically newest cortex, including the primary sensory cortex, primary motor cortex, and association cortex.
• Limbic cortex. Phylogenetically old cortex, located at the edge ("limbus") of the cerebral hemispheres; part of the limbic system.
• Cingulate gyrus (sing yew lett). A strip of limbic cortex lying along the lateral walls of the groove separating the cerebral hemispheres, just above the corpus callosum.
• Commissure (kahm I sher) A fiber bundle that interconnects corresponding regions on each side of the brain.
• Limbic system. A group of brain regions including the amygdala, hippocampus, limbic cortex, and parts of the hypothalamus, as well ass their interconnecting fiber bundles.
• Hippocampus. A forebrain structure of the temporal lobe, constituting an important part of the limbic system; includes the hippocampus proper (Ammon’s horn), dentate gyrus, and subiculum.
• Amygdala. A structure in the interior of the rostral temporal lobe, containing a set of nuclei; part of the limbic system.
• Fornix. A fiber bundle that connects the hippocampus with other parts of the brain, including the mammillary bodies of the hypothalamus.
• Mammillary bodies. A protrusion of the bottom of the brain at the posterior end of the hypothalamus, containing some hypothalamic nuclei.
• Basal ganglia. A group of subcortical nuclei in the telencephalon, the caudate nucleus, the globus pallidus, and the putamen; important parts of the motor system.
• Diencephalon. A region of the forebrain surrounding the third ventricle; includes the thalamus and the hypothalamus.
• Thalamus. The largest portion of the diencephalon, located above the hypothalamus; contains nuclei that project information to specific regions of the cerebral cortex and receive information from it.
• Projection fiber. An axon of a neuron in one region of the brain whose terminals form synapses with neurons in another region.
• Lateral geniculate nucleus. A group of cell bodies within the lateral geniculate body of the thalamus that receives axons from the retina and projects axons to the primary visual cortex.
• Medial geniculate nucleus. A group of cell bodies within the medial geniculate body of the thalmus; receives axons from the auditory system and projects axons to the primary auditory cortex.
• Ventrolateral nucleus. A nucleus of the thalamus that receives inputs from the cerebelum and sends axons to the primary motor cortex.
• Hypothalamus. The group of nuclei of the diencephalon situated beneath the thalamus; involved in regulation of the autonomic nervous system, control of the anterior and posterior pituitary glands, and integration of species-typical behaviors.
• Optic chiasm. A cross-shaped connection between the optic nerves, located below the base of the brain, just anterior to the pituitary gland.
• Anterior pituitary gland. The anterior part of the pituitary gland; an endocrine gland whose secretions are controlled by the hypothalamic hormones.
• Neurosecretory cell. A neuron that secretes a hormone or hormonelike substance.
• Posterior pituitary gland. The posterior part of the pituitary gland; an endocrine gland that contains hormone-secreting terminal buttons of axons whose cell bodies lie within the hypothalamus.
• Midbrain. The mesencephalon; the central of the three major divisions of the brain.
• Mesencephalon. The midbrain; a region of the brain that surrounds the cerebral aqueduct; includes the tectum and the tegmentum.
• Tectum. The dorsal part of the midbrain; includes the superior and inferior colliculi.
• Superior colloculi. Protrusions on top of the midbrain; part of the visual system.
• Inferior colliculi. Protrusions on top of the midbrain; part of the auditory system.
• Brain stem. The "stem" of the bain, from the medulla to the diencephalon, excluding the cerebellum.
• Tegmentum. The ventral part of the midbrain; includes the periaqueductal gray matter, reticular formation, red nucleus, and substantia nigra.
• Reticular formation. A large network of neural tissue located in the central region of the brain stem, from the medulla to the diencephalon.
• Periaqueductal gray matter. The region of the midbrain surrounding the cerebral aqueduct; contains neural circuits involved in species-typical behaviors.
• Red nucleus. A large nucleus of the midbrain that receives inputs from the cerebellum and motor cortex and sends axons to motor neurons in the spinal cord.
• Substantia nigra. A darkly stained region of the tegmentum that contains neuron that communicate with the caudate nucleus and putamen in the basal ganglia.
• Hindbrain. The most caudal of the three major divisions of the brain; inludes the metencephalon and myelencephalon.
• Cerebellum. A major part of the brain located dorsal to the pons, containing the two cerebellar hemispheres, covered with the cerebellar cortex; an important component of the motor system.
• Cerebellar cortex. The cortex that covers the surface of the cerebellum.
• Deep cerebellar nuclei. Nuclei located within the cerebellar hemispheres; receive projections from the cereballar cortex and send projections out of the cerebellum to others parts of the brain.
• Cerebellar peduncle. One of three bundles of axons that attach each cerebellar hemisphere to the dorsal pons.
• Pons. The region of the metencephalon rostral to the medulla, caudal to the midbrain, and ventral cerbellum.
• Medulla oblongata. The most caudal portion of the brain; located in the myelencephalon, immediately rostral to the spinal cord.

• Spinal cord. The cord of the nervous tissue that extends caudally from the medulla.
• Spinal root. A bundle of axons surrounded by connective tissue that occurs in pairs, which fuse and form a spinal nerve.
• Cauda equina. A bundle of spinal roots located caudal to the end of the spinal cord.
• Caudal block. The anesthesia and paralysis of the lower part of the body produced by injection of a local anesthetic into the cerebrospinal fluid surrounding the cauda equina.
• Dorsal root. The spinal root that contains (afferent) sensory axons.
• Ventral root. The spinal root that contains outgoing (efferent) motor axons.

• The brain consists of three major divisions, organized around the three chambers of the tube develops early in embryonic life: the forebrain, the midbrain, and the hindbrain. The development of the CNS is illustrated in Figure 3.7 and Table 3.1 outlines the major divisions and subdivisions of the brain.
• The forebrain, which surrounds the lateral and third ventricles, consists of the telencephalon and diencephalon. The telencephalon contains the cerebral cortex, the limbic system, and the basal ganglia. The cerebral cortex is organized into the frontal, parietal, temporal, and occipital lobes. The central sulcus divides the frontal lobe, which deals specifically with movement and the planning of movement, from the other three lobes, which deals primarily with perceiving and learning. The limbic system, which includes the limbic cortex, the hippocampus, and the amygdala, is involved in emotion, motivation, and learning. The basal ganglia participate in the control of movement. The diencephalon consists of the thalamus, which directs information to and from the cerebral cortex, and the hypothalamus, which controls the endocrine system and modulates species-typical behaviors.
• The midbrain, which surrounds the cerebral aqueduct, consists of the tectum and tegmentum. The tectum is involved in hearing and the control of visual reflexes and reactions to moving stimuli. The tegmentum contains the reticular formation, which is important in sleep, arousal, and movement; the periaqueductal gray matter, which controls various species-typical behaviors; and the red nucleus and the substantia nigra, both parts of the motor system . the hindbrain, which surrounds the fourth ventricle, contains the cerebellum, the pons, and the medulla. The cerebellum plays an important role in integrating and coordinating movements. The pons contains some nuclei that are important in sleep and arousal. The medulla oblongata, too, is involved in sleep and arousal, but it also plays a role in control of movement and in control of vital functions such as heart rate, breathing, and blood pressure.
• The outer part of the spinal cord consists of white matter: axons conveying information up or down, to or from the brain. The central gray matter contains cell bodies.

• Spinal nerve: A peripheral nerve attached to the spinal cord.
• Afferent axon: An axon directed toward the central nervous system, conveying sensory information.
• Dorsal root ganglion: A nodule on a dorsal root that contains cell bodies of afferent

spinal nerve neurons.

• Efferent axon (eff ur ent): An axon directed away from the central nervous system,

conveying motor commands to muscles and glands.

• Somatic nervous system: The part of the peripheral nervous system that controls the movement of the skeletal muscles or transmits somatosensory information to the central nervous system
• Autonomic nervous system(ANS): The portion of the peripheral nervous system that controls the body’s vegetative functions.
• Sympathetic division: The portion of the autonomic nervous system that controls the functions that accompany arousal and expenditure of energy.
• Spinal sympathetic ganglia: Sympathetic ganglia either adjacent to the spinal cord in the sympathetic chain or located in the abdominal cavity.
• Sympathetic ganglion chain: One of a pair of groups of sympathetic ganglia that lie ventrolateral to the vertebral column.
• Preganglionic neuron: The efferent neuron of the autonomic nervous system whose cell body is located in a cranial nerve nucleus or in the intermediate horn of the spinal gray matter and whose terminal buttons synapse upon postganglionic neurons in the autonomic ganglia.
• Parasympathetic division: The portion of the autonomic nervous system that controls functions that occur during a relaxed state.

The spinal nerves and the cranial nerves convey sensory axons into the central nervous system and motor axons out from it. Spinal nerves are formed by the functions of the dorsal roots, which contain incoming (afferent) axons. The autonomic nervous system consists of two divisions: the sympathetic division, which controls activities that occur during excitement or exertion, such as increased heart rate; and the parasympathetic division, which controls the activities that occur during relaxation, such as decreased heart rate and increased activity of the digestive system. The pathways of the autonomic nervous system contain preganglionic axons, from the brain or spinal cord to the sympathetic or parasympathetic ganglia, and postganglionic axons, from the ganglia to the target organ.