3/20/13. :: Slide 1 :: :: Slide 39 :: How Is the Nervous System Organized? Central Nervous System Peripheral Nervous System and Endocrine System

Transcription

1 :: Slide 1 :: :: Slide 39 :: How Is the Nervous System Organized? Central Nervous System Peripheral Nervous System and Endocrine System The nervous system is organized into several major branches, each of which serves a somewhat different function. This chart shows the overall structure of the nervous system. Note about the image on this slide: Perceived social isolation or connectedness can produce changes in the cells of our immune system. 1

2 :: Slide 40 :: :: Slide 42 :: At the highest level of organization, the nervous system is divided into the central nervous system and the peripheral nervous system. The function of the central nervous system is to process incoming information, and send commands to the rest of the body. Unlike the peripheral nervous system, the central nervous system is encased in bone the skull and vertebrae. The peripheral nervous system consists of nerves, or fibers made of multiple neurons, that extend from the central nervous system to the rest of the body. The peripheral nervous system can be divided into two smaller branches, which sometimes run along the same nerve fibers. The somatic nervous system brings in information from the senses about the state of the body and the environment. The somatic nervous system also sends commands to voluntary muscles, like the skeletal muscles of the head, neck, arms, and legs. The other branch, the autonomic nervous system, sends commands to visceral organs such as the heart, lungs, and stomach. The central nervous system consists of many structures, each of which serves a somewhat different function. Structures that are more posterior, or toward the bottom of the central nervous system, tend to support simple, reflexive behaviors and the basic functions of life. Structures that are more anterior, or toward the front of the central nervous system, tend to support more complex cognitive and sensory processes. However, all of these structures communicate extensively with each other in normal brain function. 2

3 :: Slide 44 :: :: Slide 45 :: The medulla is needed to control basic functions such as heartbeat, breathing, and blood pressure. Damage to the medulla usually results in a quick death. The pons is involved in managing energy and alertness. The pons regulates sleep-wake cycles, as well as managing some aspects of attention. The midbrain includes regions that control sensory reflexes and the experience and management of pain. For example, the periacqueductal gray area of the midbrain is rich in receptors for endorphins, which reduce the intensity of pain messages traveling from the body to the brain. The cerebellum connects to the rest of the brain through fibers from the pons. The cerebellum plays important roles in precise motor movement, including balance and coordination. Researchers only recently realized how complex the cerebellum is, with more nerve cells than the rest of the brain combined, and receiving input from about 40 million cells throughout the brain. Recent studies suggest that the cerebellum may be important for all kind of automatic behavior, including perception and language as well as physical movement. 3

4 :: Slide 46 :: :: Slide 47 :: Several important structures of the brain are above the brainstem and midbrain, but buried beneath the wrinkly cortex on the surface of the brain. The thalamus collects input from the eyes, ears, taste buds, and other sensory organs. It integrates this information, and also sends some of it along to higher cortical structures that will process the information in more complex ways. The basal ganglia include a series of structures that wrap around the thalamus. The basal ganglia play an important role in voluntary movement, helping people to choose among multiple movement options rather than moving impulsively or compulsively (as in ADHD and obsessive-compulsive disorder). Several structures form a network that links emotion and memory. The hypothalamus is often called the body s thermostat. It maintains homeostasis by constantly assessing temperature, blood pressure, levels of oxygen and glucose in the bloodstream, and other factors. It then directs the autonomic nervous system to make changes needed to keep these factors in the narrow range that supports human life. The hypothalamus also responds strongly to stressful or emotional situations. The amygdalae are structures that respond strongly to emotional situations, especially threats such as spiders, snakes, and angry or intimidating people. The hippocampi, which are connected to the amygdalae, play important roles in explicit, long-term or episodic memory. Studies suggest that hippocampal memory formation is strengthened in emotional situations, and amygdala activation may help tag new emotional memories as especially important. The cingulate cortex, which wraps around these structures, is also important for many aspects of emotion and memory. 4

5 :: Slide 48 :: :: Slide 49 :: The cerebral cortex is responsible for complex sensory processing, planning motor activity, and for the complex, associative cognitive processes that take place between sensation and action. The frontal lobes are involved in planning, logical reasoning, problem solving, and judgment. Some areas of the frontal lobe appear to integrate emotional and rational factors in making good decisions. The primary motor cortex at the back of the frontal lobes acts as a map of the skeletal muscles, directing voluntary movement. The parietal lobe is important for processing sensations of touch, including body position, pressure, skin temperature, and pain. The primary somatosensory cortex at the front of the parietal lobes acts as a sensory map, just as the motor cortex acts as a motor map. The occipital lobes process minute details of visual information, such as object borders, shading, color, and movement. The temporal lobes are responsible for complex processing of sound. The temporal lobes also include regions that are important for understanding and producing language, as well as recognizing and labeling visual objects. The two halves of the cortex are structurally separate, but connected by a bridge called the corpus callosum. The right and left cortex can only communicate with each other by this pathway. Motor planning and sensation on the right half of the body are processed mainly by the left hemisphere, whereas these functions on the left half of the body are processed mainly by the right hemisphere. Many myths about right brain versus left brain abilities and personalities have not stood up to the tests of science. However, in most people language is processed primarily by the left hemisphere, and positive emotions may be lateralized to the left as well. Evidence suggests that spatial orientation and most negative emotions may be lateralized to the right hemisphere of the cortex. 5

6 :: Slide 51 :: :: Slide 52 :: One branch of the peripheral nervous system, the somatic nervous system, serves two functions. First, it carries sensory information from the sense organ and body to the central nervous system. Second, it carries commands for voluntary movement to the muscles. Sensory and motor neurons fibers within this system often travel along the same nerve fibers. This image shows the twelve pairs of nerves emerging directly from the brain (one to each side of the body). As an example, the fifth cranial nerve communicates sensations of touch and pain from the face, but also sends motor commands to the jaw muscles. In addition to these twelve cranial nerves, 31 pairs of nerves emerge from the spinal cord. The other branch, the autonomic nervous system, carries commands from the brain (especially the hypothalamus) to visceral organs such as the heart, lungs, blood vessels, digestive system, and genitalia. The ANS is divided into two further branches, which have largely opposing effects although they are independent systems. The sympathetic division is often called the fight-flight system, as it supports the body in physical exertion. When sympathetic activation is dominant the body is focused on delivering energy to the skeletal muscles. The parasympathetic division is sometimes called the rest and repair system. When parasympathetic activation is dominant the body is focused on digesting food, storing energy for the future, and directing energy toward growth and reproduction. 6

7 :: Slide 53 :: Triune Brain as an Organizing Concept: Reptile - instinct, physiology Neo-mammal/ neocortex(primate, human, dolphin) - thinking, cognition, emotional regulation Mammal emo(ons The endocrine system also carries instructions from the brain to the body, but by way of chemicals released into the bloodstream rather than nervous system pathways. These chemicals are called hormones. In some cases, the same chemical can act as a neurotransmitter or a hormone. Particularly involved in sleep-wake cycles, metabolism, growth, and sex. The triune brain model has become a widely-used way of thinking about the overall functional organization of the brain..developed by Paul Maclean (1990) it is a powerful organizing concept for understanding the evolution of the human brain and vertebrate brain general. 7