Exam 1 Study Guide Lesson 1 Learning Objectives 1 Describe the differences between the afferent and efferent divisions of the nervous system a Afferent division signals APPROACH the nervous system Comprised of sensory neurons which relay sensory information to the CNS Depolarization of sensory receptors by stimuli cause graded potentials at the dendrites of sensory neurons which relay information down their axons to CNS if action potential threshold is met b Efferent division signals LEAVE the nervous system Comprised of motor neurons which carry signals from the brain or spinal cord to effectors via motor tracts or nerves c Some nervous system terminology These terms are dependent on location while the afferent efferent distinction is based on direction All have afferent and efferent parts 2 Describe the types of stimuli that are detected by our general senses and Nerve bundle of axons in the PNS Tract bundle of axons in the CNS Ganglion cluster of cell bodies in the PNS Nucleus cluster of cell bodies in the CNS i ii iii iv special senses What is the difference between these two senses a General senses temperature thermoception pain nociception touch pressure vibration and relative position proprioception i The receptors of our general senses are not as complexly specialized as those of our special senses and are distributed throughout the body b Special senses smell olfaction sight vision taste gustation balance equilibrium and hearing i Special senses are provided by specialized sensory receptors located in various sense organs within the head 3 Explain the difference between sensation and perception a Sensation the physical neuronal signals produced by our sense organs b Perception conscious awareness of sensations c E g the action potentials transduced by photoreceptors in the eye sensations do not themselves account for what it is we see These signals are sent to the occipital lobe where they are processed in a way that allows for conscious perception of what we see Sensations gives rise to perception by the way our brain processes and integrates them 4 Explain why receptor specificity and the size of the receptive field are important in stimulus detection and localization a All receptors are specific to a certain set or type of stimuli e g eyes sensitive to light ears to sound hands to touch Thus receptor cells will not depolarize in the presence of stimuli to which they are not specific stimulus detection will not occur b A receptive field is the area monitored by a single receptor cell Receptive fields can vary greatly in size and can even overlap These two factors are involved in how our nervous system localizes stimuli i E g compare the free nerve endings in the palms of our hands with those on the backs of our arms Each receptive field is monitored by the branched dendrites of a single neuron So because the dendrites all connect to the same axon depolarization of that axon will let our nervous system know only that a stimulus is within that receptive field Thus it is harder to pinpoint a stimulus in a large receptive field like on the back of our arm than a small one like on our palms When receptive fields overlap our brains can interpret signals sent from multiple receptive fields as coming from the space shared by those fields 5 Explain how specific stimuli are relayed to the central nervous system what is labeled line a Interpretation of sensory information in the cortex is thought to be based on the pattern of neuronal firing between the sensory receptor and the area in the cortex the signal is sent These patterns are called labeled lines each a series of axons carrying info about one type of stimulus modality to their respective brain areas b The CNS interprets frequency and pattern of action potential firing as variations in strength and duration of stimuli Our perception of sensory information is determined in large part by the frequency pattern of firing as well as the path it takes in the CNS the labeled line 6 Describe adaptation and how it can affect our perception of a stimulus What is the difference between central and peripheral adaptation a Adaptation is a reduction in sensitivity to the presence of a constant stimulus which causes a reduction in perception of that stimulus Two kinds i Peripheral adaptation occurs at the level of the receptor stimulus activity changes and the receptor responds strongly at first but then stops This is characteristic of phasic receptors Central adaptation occurs in the CNS via inhibition of nuclei along a sensory pathway ii 7 Explain the difference between tonic and phasic receptors a Tonic receptors aka slow adapting receptors are always active and show very little peripheral adaptation Action potentials generated by these receptors is proportional to the level of background stimulation so stimulus increase greater action potential frequency stimulus decrease lesser action potential frequency b Phasic receptors aka fast adapting receptors are normally inactive and provide information about the intensity and rate of change of a stimulus Activated when a change in stimulation occurs e g thermoceptors are phasic receptors that detect rapid changes in temperature 8 Describe the three broad categories of sensory receptors a Exteroceptors provide info about the external environment b c Proprioceptors provide info about the relative positions of skeletal muscles Interoceptors monitor visceral organs and body functions and joints no info about our viscera 9 Describe the four types of general sensory receptors What are some specific example of these receptors and their function a Nociceptors pain are tonic receptor free nerve endings with large receptive fields found in superficial portions of skin within joint capsules and the periosteal of bones and around the walls of blood vessels The branching dendrites of these nerve endings can be activated by many stimuli including extreme temperatures mechanical damage and dissolved chemicals i Two types of axons 1 Type A large myelinated axons quickly carry sensations of fast pain prickling searing to the primary sensory cortex often triggering somatic reflexes 2 Type C small unmyelinated axons carry sensations of slow pain dull burning aching to the reticular formation in the brainstem and thalamus where it causes general activation ii iii Analgesia inability to feel pain Hypergesia increased sensitivity to pain b Thermoreceptors temperature are phasic receptor free nerve endings
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