Integration of Nervous System Functions

• Sensation


  The means by which the brain receives information about the environment and body
• Special senses


  • Smell
  • Taste
  • Sight
  • Hearing
  • Imbalance
• Sensation or perception


  The conscious awareness of stimuli received by sensory receptors
• Types of sensory receptors

  • Mechanoreceptors (respond to mechanical stimulation)
  • Chemoreceptors (detect smell and taste)
  • Thermoreceptors (detect temperature)
  • Photoreceptors (detect light)
  • Nociceptors (detect pain)
• Exteroceptors and interoceptors


  • Exteroceptors (associated with skin, monitor external environment)
  • Interoceptors (associated with organs)
• Proprioceptors


  Receptors associated with joints and tendons that let the brain know where the limbs are in space
• Sensory nerve endings


  • Free nerve endings (respond to pain, temperature, itch, joint movement, proprioception)
  • Merkel's discs (detect light touch and superficial pressure)
  • Hair follicle receptors (detect light touch)
  • Meissner's corpuscles (for two-point discrimination)
  • Ruffini's end organs (for continuous pressure or touch)
  • Pacinian corpuscles (detect deep pressure, vibration, proprioception)
• Muscle spindles


  Detect muscle stretch and control muscle tone
• Golgi tendon organs


  Detect muscle contraction and tendon stretch, involved in proprioception and reflexes
• Primary sensory receptors


  Have axons that conduct action potentials (nerve impulses) in response to receptor potential
• Secondary sensory receptors


  Have no axons, receptor potentials cause release of neurotransmitter but do not result in action potentials
• Adaptation


  Decreased sensitivity to a continued stimulus, e.g. smell, taste, touch
• Proprioceptors


  • Tonic (know where limbs are without looking)
  • Phasic (know where limbs are as they move)
• Sensory nerve tracts in spinal cord

  • Spino-thalamic tract (conveys cutaneous sensory information, unable to localize stimulus)
  • Dorsal column-medial lemniscus tract (carries sensation of two-point discrimination, conscious proprioception, pressure, vibration)
• Contralateral


  Nerve tracts that cross over to the opposite side of the brain
• Ipsilateral


  Nerve tracts that stay on the same side of the brain
• Spino-cerebellar tract


  Carries unconscious proprioceptive information to the cerebellum
• Sensory areas of cerebral cortex

  • Primary sensory cortex
  • Sensory association areas
  • Visual cortex and association areas
  • Auditory cortex and association areas
  • Prefrontal cortex (personality)
• Broca's area


  Left hemisphere area for motor speech
• Wernicke's area


  Left hemisphere area for speech understanding
• Referred pain


  Sensation in one region of the body that is not the source of the stimulus
• Phantom pain


  Pain experienced in a limb or structure that has been amputated or removed
• Broca's area


  Area responsible for speech production, when damaged leads to inability to form words
• Wernicke's area


  Area responsible for speech comprehension, when damaged leads to fluent but nonsensical speech
• Primary auditory cortex


  Area responsible for sense of hearing
• Auditory association area


  Area responsible for sense of hearing
• Prefrontal area


  Area responsible for personality
• Phantom pain


  Pain experienced in a limb or body part that has been amputated or removed
• Chronic pain


  Pain not in response to immediate or direct tissue injury
• Acute/sharp pain transmission


  1. Larger nerve fibers

  2. Less resistance

  3. Faster transmission to brain
• Chronic pain transmission


  1. Smaller nerve fibers

  2. More resistance

  3. Slower transmission to brain
• TENS (Transcutaneous Electrical Nerve Stimulation)


  Electrical stimulation that rides along faster nerve fibers to short-circuit chronic pain
• Sensory homunculus


  Map of sensory areas in the brain, similar to motor homunculus
• Direct descending spinal pathways

  1. Motor cortex

  2. Internal capsule

  3. Cerebral peduncles

  4. Pons

  5. Medulla (pyramidal decussation)

  6. Lateral corticospinal tract

  7. Interneuron

  8. Lower motor neuron
• Indirect descending spinal pathways

  1. Motor cortex

  2. Thalamus

  3. Lentiform nucleus

  4. Midbrain (red nucleus, substantia nigra)

  5. Pons

  6. Medulla

  7. Rubrospinal tract

  8. Reticulospinal tract

  9. Anterior spinal cord

  10. Target muscles
• Aphasia


  Absent or defective speech or language comprehension
• EEG (Electroencephalograph)


  Records the brain's electrical activity and brainwave patterns
• Brainwave patterns


  • Alpha (resting state)
  • Beta (intense mental activity)
  • Theta (frustration, brain disorders)
  • Delta (deep sleep, infancy, brain disorders)
• Types of memory


  • Sensory memory (very short-term)
  • Short-term memory (seconds to minutes)
  • Explicit/declarative long-term memory (facts)
  • Implicit/procedural long-term memory (skills)
• Encephalitis


  Inflammation of the brain, often caused by viral infections