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4. Anatomy of the Nervous System.pdf

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York University
PSYC 2240

4. Anatomy of the Nervous System Friday, June 21, 2012:33 AM Main Ideas 1) Each part of the nervous system has specialized functions, and the parts work together to produce behavior. Damage to different areas results in different types of behavioral deficits. 2) The cerebral cortex, the largest structure in the mammalian brain, elaborately processes sensory information and provides forfine control of movement. 3) As research has identified the different functions of different brain areas, a new question has arisen: How do the areas worktogether to produce unified experience and behavior? 4) It is difficult to conduct research on the functions of the nervous system. Conclusions come from multiple methods and careful behavioral measurements. 4.1 Structureof the VertebrateNervousSystem • Neuroanatomy-- the anatomy of the nervous system • Individual neurons have specialized functions but the activity of a single cell by itself has no more meaning than the letterh out of context Terminologyto Describe theNervousSystem • The central nervous system (CNS) is the brain and the spinal cord • The peripheral nervous system (PNS) consists of the nerves outside the brain and spinal cord ○ Part of the PNS is the somatic nervous system, which consists of the axons conveying messages from the sense organs to the CNS and from the CNS to the muscles  Controls voluntary muscles ○ Autonomic nervous system-- controls the heart, intestines, and other organs  Controls involuntary muscles • The distinction between the CNS and the PNS is artificial because part of each cell is in the CNS (the cell body) and part inthe PNS (the axons) • Textbook Notes Page 1 • Textbook Notes Page 2 • TheSpinal Cord • The spinal cord is part of the CNS within the spinal column • The spinal cord communicates with all the sense organs and muscles except those of the head • According to the Bell-Magendie law, the entering dorsal roots (axon bundles) carry sensory information, and the exiting ventral roots carry motor information • The cell bodies of the sensory neurons are in clusters of neurons outside the spinal cord, called thedorsal root ganglia ○ Ganglia is the plural of ganglion-- a cluster of neurons ○ A neuron cluster outside the CNS is called a ganglion, and a cluster inside the CNS is called a nucleus • The cell bodies of the motor neurons are inside the spinal cord • The H-shaped gray matter in the center of the cord is densely packed with cell bodies and dendrites • Many neurons of the spinal cord send axons from the gray matter to the brain or other parts of the spinal cord through thewhite matter, which consists mostly of myelinated axons • Each segment of the spinal cord sends sensory information to the brain and receives motor commands from the brain TheAutonomicNervousSystem • Two parts: 1) The sympathetic nervous system-- a network of nerves that prepare the organs for vigorous activity, consists of chains of ganglia just to the left and right of the spinal cord's central regions (the thoracic and lumbar areas)  Increases breathing and heart rate and decreases digestive activity  Mostly uses the neurotransmitter norepinephrine 2) The parasympathetic nervous system-- facilitates vegetative, nonemergency responses  Decreases heart rate, increases digestive activity, and conserves energy  Uses the neurotransmitter acetylcholine TheHindbrain • The brain has 3 major divisions: 1) The hindbrain 2) The midbrain 3) The forebrain • The hindbrain, the posterior part of the brain, consists of the medulla, the pons, and the cerebellum • The brainstem is made up of the medulla, pons, the midbrain, and certain central structures of the forebrain ○ The medulla is just above the spinal cord and controls some vital reflexes-- breathing, heart rate, vomiting, salivation, coughing, and sneezing-- though the cranial nerves, which control sensations from the head, muscle movements in the head, and much of the parasympathetic output to the organs  Damage to the medulla is frequently fatal • The receptors and muscles of the head and organs connect to the brain by 12 pairs of cranial nerves Textbook Notes Page 3 • The receptors and muscles of the head and organs connect to the brain by 12 pairs of cranial nerves • • Each cranial nerve originates in a nucleus (cluster of neurons) that integrates the sensory information, regulates the motor output, or both ○ The cranial nuclei for nerves 5-12 are in the medulla and pons; those for cranial nerves 1-4 are in the midbrain and forebrain • The pons lies anterior and ventral to the medulla and contains nuclei for several cranial nerves ○ This is where axons from each half of the brain cross to the opposite side of the spinal cord so that the left hemisphere con trols muscles of the right side of the body and vice versa • The medulla and pons contain the reticular formation and the raphe system ○ The reticular formation has descending and ascending portions; the descending portion is one of several brain areas that controls the motor areas of the spinal cord. The ascending portion sends output to much of the cerebral cortex, selectively increasing arousal a nd attention in one area or another ○ The raphe system also sends axons to much of the forebrain, modifying the brain's readiness to respond to stimuli • The cerebellum is a large hindbrain structure with many deep folds ○ Responsible for balance, coordination, and judging timing TheMidbrain • The midbrain is in the middle of the brain, surrounded by the forebrain • Tectum-- the roof of the midbrain • The swellings on each side of the tectum are the superior colliculus and the inferior colliculus ○ Important for sensory processing • Under the tectum lies the tegmentum-- the intermediate level of the midbrain ○ Contains the nuclei for the 3rd and 4th cranial nerves, parts of the reticular formation, and extensions of the pathways betw een the forebrain and the spinal cord or hindbrain • Another midbrain structure is the substantia nigra, which gives rise to the dopamine-containing pathway that facilitates readiness for movement TheForebrain • The forebrain is the most anterior and the most prominent part of the mammalian brain • Consists of two cerebral hemispheres-- the left and the right • The outer portion is the cerebral cortex • Under the cerebral cortex is the thalamus (the main source of input to the cerebral cortex) • A number of interlinked structures, known as the limbic system, form a border around the brainstem ○ Includes the olfactory bulb, hypothalamus, hippocampus, amygdala, and cingulate gyrus of the cerebral cortex Textbook Notes Page 4 ○ ○ Particularly important for motivations and emotions • Thalamus ○ A pair of structures (left and right) in the center of the forebrain ○ Most sensory information (except olfactory information) goes first to the thalamus, where it is processed and sent out to the cerebral cortex • Hypothalamus ○ Contains a number of distinct nuclei ○ Conveys messages to the pituitary gland, altering its release or hormones • Pituitary Gland ○ An endocrine (hormone-producing) gland attached to the base of the hypothalamus ○ Synthesizes and releases hormones into the bloodstream in response to messages from the hypothalamus • Basal Ganglia ○ A group of subcortical structures lateral to the thalamus, including 3 major structures: the caudate nucleus, the putamen, an d the globus pallidus ○ Exchanges information with different parts of the cerebral cortex, which are responsible for planning sequences of behavior a nd for certain aspects of memory and emotional expression ○ Impaired in Parkinson's disease and Huntington's disease • Basal Forebrain ○ Nucleus basalis-- receives input from the hypothalamus and basal ganglia and sends axons that release acetylcholine to widespread areas in the cerebral cortex ○ Key part of the brain's system for arousal, wakefulness, and attention • Hippocampus ○ Critical for storing certain kinds of memories TheVentricles • The central canal-- a fluid-filled channel in the center of the spinal cord • The ventricles-- 4 fluid-filled cavities within the brain • Cells called the choroid plexus inside the four ventricles produce cerebrospinal fluid (CSF), a clear fluid similar to blood plasma ○ Most CSF goes into the narrow spaces between the brain and the thin meninges, membranes that surround the brain and spinal cord  Although the brain has no pain receptors, the meninges do, and meningitis is very painful ○ Cushions the brain against mechanical shock when the head moves Textbook Notes Page 5 4.2 TheCerebral Cortex • The most prominent part of the mammalian brain is the cerebral cortex, consisting of the cellular layers on the outer surface of the cerebral hemispheres • Neurons in each hemisphere communicate with neurons in the corresponding part of the other hemisphere through two bundles ofaxons, the corpus callosum and the smaller anterior commissure • The cerebral cortex
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