Bio117 Chapter 9: Sensory System

Transducers

translators via chemicals

Sensory Stimulus

any environmental condition which the body can detect

Sensation

any sensory information that reaches the level of consciousness

Perception

how we consciously interpret a sensation

Sensory Stimuli must be ___

coded into a language that the CNS can understand (i.e. nerve impulses)

• graded potentials

• action potentials

Sensory Unit

a single sensory neutron and all the sensory receptors attached to it

Receptive field

area that the sensory unit covers

Overlapping of Receptive Fields

affects ability to locate stimuli

Sensory Modality

• Different types of receptors respond to different types of stimuli

• the type of receptor activated communicates the type of sensation involved

Photoreceptor

Sensory Stimulus: Light

Modality: Vision (sight)

Thermoreceptor

Sensory Stimulus: Heat

Modality: Temperature

Mechanoreceptor

Sensory Stimulus: Physical pressure, stretch, strain, or sheering

Modality: Touch, pressure, audition (hearing), position, balance and equilibrium

Chemoreceptor

Sensory Stimulus: Chemicals

Modality: Olfaction (smell) and Gustation (taste)

Nociceptor

Sensory Stimulus: Injuries (various)

Modality: Pain

Sensory Coding Mechanisms

• All sensory info ends up getting transferred to neurons, either:

  • Directly

    • Free nerve ending

      • detected stimuli cause neurons to generate graded receptor potentials that vary in magnitude and direction of change with stimulus strength

  • Indirectly

    • Separate sensory cell

      • detected stimuli cause receptor cells to secrete neurotransmitters in proportion to the magnitude of the receptor potentials

      • neurotransmitters then generate EPSPs and IPSPS in proportion to stimulus strength

Receptor Potential

graded potentials caused by sensory signal

Neural Grade Potentials

• EPSP and IPSP

• Pacemaker potentials

  • “leaks” membrane potentials (unstable membrane potential)

    • rhythmically reaches threshold

• Receptor potentials

Sensory stimuli magnitude and direction affect action potential ___

frequency

Lateral Inhibition

improves localization of stimulus by inhibiting interneurons between overlapping receptive fields

Sensory Adaptation

reduces magnitude of the receptor’s response to non-life-threatening repetitive stimuli

• reduces sensory overload on CNS

• ex. touch, smell, sounds

Receptor Classification

• Fast-Adapting

  • touch, sight, hearing, smell receptors

• Slow-Adapting

  • pain, balance, equilibrium receptors

Specific Ascending Pathways

• axonal bundles in spinal cord

• carry single sensory modalities to specific primary areas of the cerebral cortex

Sensory Function: Somatosensory Cortex

Cortical Primary Area: Pariental Lobes

Sensory Function: Visual Cortex

Cortical Primary Area: Occipital Lobes

Sensory Function: Auditory Cortex

Cortical Primary Area: Temporal Lobes

Sensory Function: Olfactory Cortex

Cortical Primary Area: Frontal Lobes (and Temporal?)

Sensory Function: Taste Cortex

Cortical Primary Area: Pariental Lobes