BIO1108 Exam 2 Study Guide Lectures 13 23 Lecture 13 Faced with environmental fluctuations animals regulate control certain variables while allowing other internal variables to conform to correspond to external changes Homeostasis is the maintenance of a steady state despite internal and external changes Homeostatic mechanisms are usually based on negative feedback in which the response reduces the stimulus In contrast positive feedback involves amplification of a stimulus by the response and often brings about a change in state such as the transition from pregnancy to childbirth Regulated change in the internal environment is essential to normal function Circadian rhythms are daily fluctuations in metabolism and behavior tuned to the cycles of light and dark in the environment Other environmental changes may trigger acclimatization temporary shift in the steady state Lecture 14 Invertebrate nervous systems range in complexity from simple nerve nets to highly centralized nervous systems having complicated brains and nerve cords Hydra cnidarian composed of a nerve net Salamander vertebrate In vertebrates the central nervous system CNS consisting of the brain and the spinal cord integrates information while the nerves of the peripheral nervous system PNS transmits sensory and motor signals between the CNS and the rest of the body The simplest circuits in the vertebrate nervous system controls reflex response in which sensory input is linked to motor output without involvement of the brain Vertebrate neurons are supported by several types of glia including astrocytes oligodendrocytes Schwann cells and ependymal cells Afferent neurons carry sensory signals to the CNS Efferent neurons functions in either the motor systems which carries signals to skeletal muscles or the autonomic nervous system which regulates smooth and cardiac muscles The sympathetic fight or flight and the parasympathetic rest and digest divisions of the autonomic nervous system have antagonistic effects on a diverse set of target organs while the enteric division controls the activity of many digestive organs The Cerebrum has two hemispheres each which consists of cortical gray matter overlying white matter and the basal nuclei which are important in planning and learning movements A thick band of axons the corpus callosum provides communication between the right and the left cerebral cortices Within each region of the brain particular structures have specialized functions The pons and medulla oblongata are relay stations for information traveling between the PNS and the cerebrum The reticular formation a network of neurons within the brainstem regulates sleep and arousal The cerebellum helps coordinate motor perceptual and cognitive functions It is also involved in learning and remembering motor skills The thalamus is the main center through which sensory and motor information passes to the cerebrum The hypothalamus regulates homeostasis and the basic survival skills Within the hypothalamus the suprachiasmatic nucleus SCN acts as the pacemaker of the circadian rhythms The generation and experience of emotions involve many regions of the brain However the amygdala plays a key role in recognizing and recalling a number of emotions Each side of the cerebral cortex has four lobes frontal temporal occipital and parietal that contain primary sensory areas and association areas Specific types of sensory input enter the primary sensory areas Association areas integrate information from different sensory areas Portions of the frontal and temporal lobes including the Broca s area and Wernicke s area are essential for generating and understanding language These functions are concentrated in the left cerebral hemisphere as are math and logic operations The right hemisphere appears to be stronger at pattern recognition and nonverbal thinking At least some of this lateralization of functions relates to handedness In the somatosensory cortex and the motor cortex neurons are distributed according to the part of the body that generates sensory input or receives motor commands Primates and cetaceans which are capable of higher cognition have an extensively convoluted neocortex the outermost part of the cerebral cortex In birds a brain region called the pallium contains clustered nuclei that carry out functions similar to those performed by the cerebral cortex of mammals Some birds can solve problems and understand abstractions in a manner indicative of higher cognition During development more neurons and synapses form than will exist in the adult The programmed death of neurons and the elimination of synapses in embryos establish the basic structure of the nervous system In adults reshaping of the nervous system can involve the loss or addition of synapses or the strengthening or weakening of signaling at synapses This capacity for remodeling is termed neural plasticity Defective remodeling of synapses is partly responsible for the developmental abnormalities of autism Short term memory relies on temporary links in the hippocampus In long term memory these temporary links are replaced by connections within the cerebral cortex This transfer of information from short term to long term memory is enhanced by the association of the new data with that already in long term memory Long term potentiation LTP is a lasting increase in the strength of synaptic transmission and appears to be an important process in memory storage and learning The adult human brain contains stem cells that can differentiate into mature neurons Therapy based on stem cells offers a potential method for replacing neurons lost to injury or disease Research has identified the biochemical basis of a number of nervous system disorders Schizophrenia which is characterized by hallucinations delusions and other symptoms affects neuronal pathways that use dopamine as a neurotransmitter Drugs that increase the activity of biogenic amines in the brain can be used to treat bipolar disorder and major depressive disorder The compulsive drug use that characterizes addiction reflects altered activity of the brain s reward systems which normally provides motivation for actions that enhance survival or reproduction Alzheimer s disease and Parkinson s disease are neurodegenerative and typically age related Alzheimer s disease is a dementia in which neurofibrillary tangles and amyloid plaques form in the brain Parkinson s disease is a motor disorder caused by the death of dopamine