Lab 4A: Sensory Physiology

Sensory Physiology

• Sensory physiology encompasses both conscious and subconscious processing.
• The five "special" senses (sight, hearing, taste, smell, and equilibrium) fall under conscious control.
• The lesser known conscious senses include the "somatic" senses (touch-pressure, temperature, pain, and proprioception).
• The subconscious senses include somatic stimuli and visceral stimuli.

Somatic Stimuli and Visceral Stimuli

• Somatic stimuli include muscle length and tension or force.
• Visceral stimuli include:
  • Blood pressure
  • pH and O2 content of blood
  • pH of cerebrospinal fluid
  • Lung inflation
  • Osmolarity of body fluids
  • Temperature
  • Blood glucose
  • Distention of the gastrointestinal tract

Afferent Sensory Pathways

• Afferent sensory pathways begin by sensing a stimulus (external or internal) via a sensory neuron.
• The sensory receptor transduces or changes the signal to an electrical graded signal.
• If the signals are strong and frequent enough, the neuron will reach threshold and produce action potentials.
• The central nervous system (CNS) will tell the efferent motor neuron to have an appropriate action.

Classification of Sensory Receptors

• Receptors can be classified structurally, regionally, or functionally.
• Examples of receptors include:
  • Tactile (touch) corpuscles of the skin
  • Eyes and ears
  • Mechanoreceptors (respond to mechanical stimuli)
  • Chemoreceptors (respond to chemicals)
  • Baroreceptors (respond to blood pressure)

Sensory Terms and Concepts

Proprioreceptors

• A somatic sensory receptor activated by movement of the limbs

Nociceptor

• A receptor that detects painful stimuli

Chemoreceptor

• Responds to chemicals that bind to the receptor (e.g. O2, pH, glucose)

Mechanoreceptor

• Responds to mechanical stimuli (e.g. pressure, vibration, sound)

Receptive Field

• The area that each neuron can receive information on, which may vary in shape and overlap with neighboring receptive fields

Transduction

• The conversion of a stimulus energy into a change in membrane potential

Threshold

• The minimum amount of depolarization needed to trigger an action potential

Two-point Discrimination

• The ability to distinguish between two points of stimulation on the skin, dependent on the density of touch receptors in that area

Cutaneous Sensations

• Detected by sensory receptors in the skin
• Sent to the brain via sensory (afferent) neurons
• Interpreted within the somatosensory cortex of the parietal lobe

Touch Receptors

• A type of mechanoreceptor
• Respond to mechanical force created by pressure
• Density of touch receptors varies across different parts of the body
• Sensitive areas (e.g. fingertips) have a high density, while less sensitive areas (e.g. back of the leg) have a lower density

Refraction and Visual Acuity

• Refraction is the bending of light waves
• Light waves entering the eye must be focused on a specific point of the retina
• The lens and cornea are involved in refraction of light

Myopia and Hyperopia

• Myopia: near-sightedness, in which objects up close are clear, but those in the distance appear blurry
• Hyperopia: far-sightedness, in which objects in the distance are clear, but objects up close are blurry
• Can be treated with concave or convex lenses

Snellen Eye Chart

• Used to test for myopia
• Interpreting the values:
  • First number: how far the person is standing from the chart
  • Second number: how far someone with normal vision can stand to read the same row of letters

Sensory Physiology

• Sensory physiology encompasses both conscious and subconscious processing.
• The five "special" senses (sight, hearing, taste, smell, and equilibrium) fall under conscious control.
• The lesser known conscious senses include the "somatic" senses (touch-pressure, temperature, pain, and proprioception).
• The subconscious senses include somatic stimuli and visceral stimuli.

Somatic Stimuli and Visceral Stimuli

• Somatic stimuli include muscle length and tension or force.
• Visceral stimuli include:
  • Blood pressure
  • pH and O2 content of blood
  • pH of cerebrospinal fluid
  • Lung inflation
  • Osmolarity of body fluids
  • Temperature
  • Blood glucose
  • Distention of the gastrointestinal tract

Afferent Sensory Pathways

• Afferent sensory pathways begin by sensing a stimulus (external or internal) via a sensory neuron.
• The sensory receptor transduces or changes the signal to an electrical graded signal.
• If the signals are strong and frequent enough, the neuron will reach threshold and produce action potentials.
• The central nervous system (CNS) will tell the efferent motor neuron to have an appropriate action.

Classification of Sensory Receptors

• Receptors can be classified structurally, regionally, or functionally.
• Examples of receptors include:
  • Tactile (touch) corpuscles of the skin
  • Eyes and ears
  • Mechanoreceptors (respond to mechanical stimuli)
  • Chemoreceptors (respond to chemicals)
  • Baroreceptors (respond to blood pressure)

Sensory Terms and Concepts

Proprioreceptors

• A somatic sensory receptor activated by movement of the limbs

Nociceptor

• A receptor that detects painful stimuli

Chemoreceptor

• Responds to chemicals that bind to the receptor (e.g. O2, pH, glucose)

Mechanoreceptor

• Responds to mechanical stimuli (e.g. pressure, vibration, sound)

Receptive Field

• The area that each neuron can receive information on, which may vary in shape and overlap with neighboring receptive fields

Transduction

• The conversion of a stimulus energy into a change in membrane potential

Threshold

• The minimum amount of depolarization needed to trigger an action potential

Two-point Discrimination

• The ability to distinguish between two points of stimulation on the skin, dependent on the density of touch receptors in that area

Cutaneous Sensations

• Detected by sensory receptors in the skin
• Sent to the brain via sensory (afferent) neurons
• Interpreted within the somatosensory cortex of the parietal lobe

Touch Receptors

• A type of mechanoreceptor
• Respond to mechanical force created by pressure
• Density of touch receptors varies across different parts of the body
• Sensitive areas (e.g. fingertips) have a high density, while less sensitive areas (e.g. back of the leg) have a lower density

Refraction and Visual Acuity

• Refraction is the bending of light waves
• Light waves entering the eye must be focused on a specific point of the retina
• The lens and cornea are involved in refraction of light

Myopia and Hyperopia

• Myopia: near-sightedness, in which objects up close are clear, but those in the distance appear blurry
• Hyperopia: far-sightedness, in which objects in the distance are clear, but objects up close are blurry
• Can be treated with concave or convex lenses

Snellen Eye Chart

• Used to test for myopia
• Interpreting the values:
  • First number: how far the person is standing from the chart
  • Second number: how far someone with normal vision can stand to read the same row of letters