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5.1 Chapter 5 - Central Nervous System I. systems that protect the CNS A. cerebrospinal fluid (CSF) 1. formed by selective transport across ependymal cells 2. volume is 125-150 ml and is replaced > 3 times/day 3. flow maintained by 10 mmHg pressure gradient between ventricles and dural sinuses 4. path: ventricles subarachnoid space (review from anatomy) 5. reabsorbed into blood in dural sinuses through arachnoid villi 6. functions are to: a. “float” the brain b. control brain tissue fluid composition c. cushion brain during normal head movements B. blood-brain barrier 1. role of capillary endothelial cells: a. tight junctions b. restriction of membrane transport 2. role of astrocytes a. induce formation of tight junctions b. help control transcellular transport 3. membrane transport restrictions a. materials that diffuse cannot be restricted (O2, CO2, alcohol, steroids, H2O) b. materials that require carrier transport are restricted (glucose, amino acids, and ions) c. materials that cannot pass (many drugs, amino acids, and ions) BIOL 2305/Strong/Spring 2007 5.2 4. functions of the blood-brain barrier a. protects NS from chemical fluctuations b. prevents entry of harmful substances and microbes c. prevents entry of molecules that would act as neurotransmitters 5. some areas of the brain do not have a blood-brain barrier (part of hypothalamus) II. brain functions A. cerebrum (cortex, tracts, basal nuclei) 1. functional areas of the cortex sensory areas motor areas association areas a. spatial representation / somatotopy somatosensory cortex primary motor cortex size of area and number of neurons for each body area is proportional to precision and complexity of movement of that part b. linking of cortical regions primary sensory areas higher sensory areas association areas higher motor area primary motor cortex c. language visual and auditory cortex parietal-occipital-temporal association cortex BIOL 2305/Strong/Spring 2007 5.3 Wernicke’s area Broca’s area primary motor cortex - B. cerebellum 1. vestibulocerebellum 2. spinocerebellum receives input concerning desired action from motor cortex receives input concerning actual action from proprioceptors, vestibular apparatus, eyes compares inputs and sends corrective signals to motor tracts 3. cerebrocerebellum - C. integrated brain functions 1. sleep-wake cycles a. how do we get to sleep? alertness is maintained by constant reciprocal stimulation between the cerebral cortex and the reticular activating system the RAS is constantly stimulated by sensory input and input from the cerebrum to get to sleep you have to interrupt that stimulation this involves signals from the slow wave (NREM) “sleep-on” neurons, which receive directions from the biological clock (suprachiasmatic nucleus) b. what happens while we are asleep? BIOL 2305/Strong/Spring 2007 5.4 we alternate between periods of slow wave (non rapid eye movement or NREM) sleep and paradoxical (rapid eye movement or REM) sleep each full cycle lasts about 90 minutes, and in each successive cycle the amount of paradoxical/REM sleep increases paradoxical sleep involves low muscle tone, increased cortical activity, and dreaming switching between slow wave/NREM and paradoxical/REM is controlled by paradoxical/REM “sleep-on” neurons c. how do we wake up? the RAS receives internal or external stimuli it then sends excitatory signals to the cortex, which returns to normal alertness and reciprocal stimulation with the RAS 2. memory = "storage of acquired knowledge for later recall" a. short term memory characteristics: seconds to hours limited capacity may be consolidated into long term memory mechanisms: temporary modifications of synaptic function changes in ion channels in the axon terminals presynaptic facilitation (cAMP) long-term potentiation glutamate AMPA receptors – generate EPSPs BIOL 2305/Strong/Spring 2007 5.5 NMDA receptors – open Ca channels second messenger formation increases # AMPA receptors release of nitric oxide (NO) acts on presynaptic neuron to increase neurotransmitter release b. long term memory characteristics: days to years unlimited capacity mechanisms: permanent physical changes in the brain formation of new synapses between existing neurons increased dendritic surface area increase in neurotransmitter receptors changes in neurotransmitter synthesis c. consolidation is affected by: amount of rehearsal pre-existing “hook” (association of new & old data) level of excitement/importance of information CREB/CREB2 d. memory is processed in the: hippocampus and medial temporal lobe short term memory and consolidation declarative memory (facts) requires conscious recall cerebellum motor skill memories (procedural) subconscious recall prefrontal cortex working memory –processes new and retrieved information temporary storage problem solving, planning, organizing BIOL 2305/Strong/Spring 2007 5.6 III. spinal reflexes reflex = automatic, predictable, unlearned and rapid motor response to a stimulus A. reflex arc pathway has 5 components: 1. receptor - monitors environment & produces action potentials 2. afferent pathway carries signals from receptor to CNS 3. integrating center = one or more synapses in CNS that process the information from the receptor 4. efferent pathway carries impulses from CNS to effector 5. effector (organ) - produces reflex response (contraction or secretion) a. somatic vs autonomic b. ipsilateral vs contralateral c. reciprocal innervation in somatic reflexes B. stretch reflexes monitor amount of stretch in skeletal muscles cause contraction in the muscle to counteract stretch 1. receptor 2. integrating center 3. effector example: BIOL 2305/Strong/Spring 2007 5.7 C. flexor/withdrawal reflex - protects body from damage 1. receptor 2. integrating center 3. effector response: D. crossed-extensor reflex may occur at same time as flexor reflex but never alone shares afferent pathway and part of integrating center with flexor reflex 1. receptor 2. integrating center 3. effector response: E. Golgi tendon - protects muscles from damage 1. receptor 2. integrating center 3. effector response: BIOL 2305/Strong/Spring 2007