Chapters 6-7 (Part 1): Sensory System
Chapters 6-7 (Part 1): Sensory System PSB2000
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This 5 page Class Notes was uploaded by Sierra Gnecco on Friday September 30, 2016. The Class Notes belongs to PSB2000 at Florida State University taught by Maria Greenwood in Fall 2016. Since its upload, it has received 19 views. For similar materials see Introduction to Brain and Behavior in Natural Sciences at Florida State University.
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Date Created: 09/30/16
PSB2000 Chapter 6-7 Part I Sensory System By Sierra Gnecco 7.1 Principles of Sensory System Organization ● The three types of sensory areas of the cortex are the primary, secondary, and association. ● The interactions between these three types of sensory cortex and among other sensory structures are characterized by three major principles: hierarchical organization, functional segregation, and parallel processing. Hierarchical Organization ● Sensory structures are organized in a hierarchy by the specificity and complexity of their function. ○ Specificity and complexity increases with each level. ○ The higher the damage level, the more specific and complex the deficit. ● Sensation the process of detecting the presence of stimuli. ● Perception- the higher-order process of integrating, recognizing, and interpreting complete patterns of sensations. Functional Segregation ● It was once assumed that all areas of cortex at any given level of a sensory hierarchy acted together to perform the same function and were each functionally homogeneous. ● However, research has shown that functional segregation (each of the three levels of cerebral cortex contains different areas that specialize in diff. kinds of analysis) characterizes the organization of sensory systems. Parallel Processing ● Sensory systems are parallel systems in which info flows through the components over multiple pathways. 2 ● Parallel systems feature parallel processing. ○ Parallel processing- simultaneous analysis of signals along different pathways 7.2: Auditory System ● Function: perception of sound. ● Humans hear sounds (molecular vibrations) between 20 and 20,000 hertz (cycles per second). ● Amplitude: loudness (height, measured in decibels) ● Frequency: Pitch (measured in hertz) ● Complexity: Timbre The Ear ● Sound waves → auditory canal →ear drum (tympanic membrane) vibrates → ossicles (the small bones of the middle ear: malleus, incus, stapes) → oval window → cochlea (hair cells) ● Cochlea has an internal membrane running almost to its tip, which is the auditory receptor organ (organ of Corti). ● Organ of Corti is composed of two membranes: basilar membrane and tectorial membrane. ○ The auditory receptors (hair cells) are in the basilar membrane and the tectorial membrane rests on the hair cells (mechanoreceptors . Ear → Primary Auditory Cortex ● Axons of each auditory nerve are lead to the superior olives. ● Two different superior olives. One is medial and the other is lateral. ○ Medial- Differences in sound arrival (time); the location of sound. ○ Lateral- Differences in sound amplitude (sound is louder in the closest ear). ● Via the lateral lemniscus, the axons of the olivary neurons are projected to the inferior colliculi (responsible for auditory processing); NOTE: the superior colliculi is for visual processing NOT auditory processing. ● At the inferior colliculi, they synapse on neurons that project to the medial geniculate nuclei (nuclei of the thalamus). ● The geniculate nuclei projects them to the primary auditory cortex. ● Summary: Axons of each auditory nerve lead to the superior olives -> axons projected to the inferior colliculi -> medial geniculate nuclei -> primary auditory cortex. 3 Auditory Cortex Math ● Anterior auditory pathway- what is that sound? ● Posterior auditory pathway- where is that sound? ● Core region- comprises of the primary auditory cortex and its three areas. ● Belt- surrounds the core region and contains the areas of the secondary auditory cortex. ● Parabelt areas areas of second auditory cortex outside the belt. ○ About 20 separate areas of auditory cortex in primates. ● Auditory signals are conducted to two areas of association cortex. ○ Prefrontal cortex ○ Posterior parietal cortex Damage ● Complete hearing loss is usually temporary and recovers within weeks. (lesion studies support this) ○ This provides evidence for partially contralateral system. ● Two different types of deafness: ○ Conductive: damage to the ossicles. ○ Sensorineural (Nerve): damage to the cochlea or auditory nerve. ■ Typically due to the loss of hair cells. 7.3: Somatosensory System: Touch and Pain ● Somatosensations- sensations from the body. ● The system that mediates these sensations is the Somatosensory System, which consists of three interacting systems. ○ Exteroceptive- senses external stimuli that are applied to the skin. (cutaneous receptors) ○ Proprioceptive- body position 4 ○ Interoceptive- general information about body conditions (temperature, blood pressure, etc.) Cutaneous receptors ● Cutaneous receptors are receptors in the skin. ● Free nerve endings- the simplest cutaneous receptors which have no specialized structures on them. ○ Thermoceptors- respond to temperature. ■ Respond best to changes in temperature rather than absolute temperature. Ex: You can tell when it is cold, but you cannot tell the exact numerical temperature. ○ Nociceptors- respond to chemical changes in skin (noxious stimuli). ● Mechanoreceptors- respond to mechanical stimuli and are specialized to detect specific types of touch (vibration, pressure, etc.) Two Major Somatosensory Pathways ● Dorsal-column-medial-lemniscus system- carries info about touch and proprioception. ● Anterolateral system- tends to carry info about pain and temperature. ● Both of these pathways transmit contralaterally. Perception of Pain ● Pain perception is important for survival. ○ Study of Miss C who had congenital analgesia and felt no pain. She showed no changes in blood pressure, heart rate, or respiration she was presented electric shocks, burning hot water, and ice-cold water. Later on in life, she had pathological changes in her knees, hip, and spine. She died at a young age from massive infections and skin and bone trauma. ● Pain is not a stimulus but our brain’s interpretation of noxious stimuli. ● There is no particular cortex which responds to pain. ○ The cortical area that is most linked to pain is the anterior cingulate cortex, which is involved in the expectation of, emotional reaction to, and adaptive responses to pain. 7.4: Chemical Senses: Smell and Taste ● Olfaction (smell) and gustation (taste) both monitor the chemical content of the environment. ● The olfactory system responds to airborne chemicals drawn by inhalation. 5 ● The gustatory system responds to chemicals in solution in the oral cavity. ● Food molecules excite both smell and taste receptors and produce flavor. ● Pheromones- chemicals that influence the physiology and behavior of conspecifics (members of the same species). ○ Humans release sexual pheromones? ■ Findings: menstrual cycles of women living together tend to be synchronized, humans can detect the sex of another by the breath or underarm smell, kin recognition, and the olfactory sensitivity of women is greatest when they are ovulating or pregnant. Olfactory System ● Olfactory receptor cells are located in the upper part of the nose, embedded in a layer of mucus-covered tissue called the olfactory mucosa. ● Olfactory glomeruli- clusters of neurons near the surface of the olfactory bulbs where the same kind of receptor cells project to. ○ Each glomerulus receives input from several thousand olfactory receptor cells, all w/the same receptor protein. ● Olfactory pathway ○ The olfactory tract projects to several structures of the temporal lobes. ■ Structures: amygdala, piriform cortex, hippocampus, and entorhinal cortex. (NOTE: Thalamus is not included. The olfactory system is the only system which does not include the thalamus.)
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