biopsych

• In this lesson, we will learn about the remaining four of the five exteroceptive sensory systems: the auditory (hearing), somatosensory (touch), olfactory (smell), and gustatory (taste) systems. In addition, we will also explore the mechanisms of attention: how brains attend to a small number of sensory stimuli despite being continuously bombarded by thousands of them.
• The visual system we learned from last lesson is by far the most thoroughly studied sensory system and as a result, the most well understood. As more has been discovered about the other sensory systems, it has become increasingly clear that they are organized in a way similar to the visual system.
• Types of sensory cortex


  • Primary Sensory Cortex
  • Secondary Sensory Cortex
  • Association Cortex
• Principles of Sensory System Organization


  • Hierarchical organization
  • Functional segregation
  • Parallel processing
• Hierarchical organization


  The sensory areas of the cortex work in a hierarchical system. The receptors serve as the base of the system and they perform the simplest and most general analyses. At the top is the association cortex, which performs the most complex and specific analyses.

  
• Functional segregation


  Each of the three levels of cerebral cortex -- primary, secondary and association -- contains functionally distinct areas that specialize in different kinds of analysis.
• Parallel processing


  Sensory systems work in parallel systems which feature parallel processing -- the simultaneous analysis of a signal in different ways by the multiple parallel pathways of a neural network.
• Sound waves travel from the outer ear down the auditory canal and cause the tympanic membrane (eardrum) to vibrate.

  
• Aspects of sound perception

  • Amplitude (perception of loudness)
  • Frequency (perception of pitch)
  • Complexity (perception of timbre)

  
• Auditory pathway


  1. Axons from auditory nerves synapse in ipsilateral cochlear nuclei

  2. Projections lead to superior olives on both sides of brain stem

  3. Axons from olivary neurons project via lateral lemniscus to inferior colliculi

  4. Neurons project to medial geniculate nuclei of thalamus

  5. Thalamus projects to primary auditory cortex

  
• Anterior auditory pathway


  Identifying sounds
• Posterior auditory pathway


  Locating sounds
• Bilateral lesions to the auditory cortex result in complete loss of hearing (loss of the ability to localize sounds and impairment of the ability to discriminate frequencies).
• Types of deafness


  • Conductive deafness (damage to ossicles)
  • Nerve deafness (damage to cochlea or auditory nerve)
• Nerve deafness


  Caused by loss of hair receptors
• Tinnitus


  Ringing of the ears, caused by changes to the central auditory system due to deafness
• Hearing aids


  Devices worn in or behind the ear to make sounds louder, for those with less severe hearing loss
• Cochlear implants


  Bypass damage to auditory hair cells by converting sounds to electrical signals carried into the cochlea, for those with severe hearing loss
• Somatosensory subsystems


  • Exteroceptive system (senses external stimuli applied to skin)
  • Proprioceptive system (monitors body position)
  • Interoceptive system (provides information about internal body conditions)
• Exteroceptive stimuli


  • Mechanical (touch)
  • Thermal (temperature)
  • Nociceptive (pain)
• Cochlear implants


  Electrical signals are carried into the cochlea by a bundle of electrodes. Unlike hearing aids, cochlear implants require surgery.
• Somatosensory system subsystems


  • Exteroceptive system
  • Proprioceptive system
  • Interoceptive system
• Exteroceptive system


  • Senses external stimuli that are applied to the skin, including mechanical, thermal, and nociceptive (pain) stimuli