Lecture 14 Sensory Physiology handout (2024) pptx

Sensory Physiology

General Properties of Sensory Systems and the Somatic Senses

Goals

• Describe the roles of senses and types of senses.

• Explain general properties of sensory systems with examples.

• Outline somatosensory physiology and pathways, including receptors and neural pathways.

Suggested Reading

• Chapter 10 - Pages 308-320 (Introduction, Section 10.1, Section 10.2)

Outline

1. Roles of senses and types of senses

2. Five General Properties of Sensory Systems

   1. Modality

   2. Transduction

   3. Receptive field

   4. Integration

   5. Coding and processing

3. Somatosensory pathways from receptor to brain

Roles of Senses

• Function of Senses:

  • Provide information about the environment (e.g., food, temperature, osmolarity, potential mates).

  • Offer insight into self (e.g., energy stores, temperature, and water/ion balance).

Types of Senses

• Conscious Senses:

  • Special Senses: Vision, Hearing, Taste, Smell, Balance

  • Somatic Senses: Touch (texture, vibration), Temperature, Pain, Itch, Proprioception

• Unconscious Senses:

  • Somatic Senses: Muscle tension, Proprioception

  • Visceral Senses: Blood pressure, GI distension, Glucose, Osmolarity, Oxygen/CO2 content of blood.

Five General Properties of Sensory Systems

1. Receptors: Sensitive to certain forms of energy or stimuli (modality).

2. Transduction: Converts stimuli into graded potentials.

3. Receptive Field: Area where a stimulus alters the firing of a sensory neuron.

4. Integration: CNS processes sensory information.

5. Coding and Processing: Distinguishes stimulus properties.

Detailed Properties

Modality of Receptors

• Receptors defined in two ways:

  • Protein that binds a ligand.

  • Structure that detects sensory information.

• Detected modalities: Chemoreceptor, Mechanoreceptor, Thermoreceptor, Photoreceptor.

Sensory Transduction

• Converts sensory signals into graded potentials.

• Types of channels involved:

  • Ligand-gated (chemical)

  • Mechano- and thermo-gated (touch, temperature, pressure, hearing, balance).

• Receptor Potential: The preferred type of stimulus leads to a graded potential.

Receptive Fields and Sensory Neurons

• Each sensory neuron has a receptive field; the area impacting the neuron’s firing.

• Convergence of primary sensory neurons leads to larger receptive fields with lower acuity.

• Example: The larger the converged area, the lower the acuity; perceived as a single point.

Integration by CNS

• Information may be processed in spinal cord/brainstem, sometimes without reaching conscious perception.

• In cortex, if awareness is needed, the information goes through synapses.

Sensory Pathways in the Brain

• Most sensory pathways pass through the thalamus to cerebral cortex.

  • Different sensory modalities such as gustatory, olfactory, visual, and auditory processed in specific cortical areas.

• Different pathways provide distinct integration and perception based on modality.

Coding and Processing

• Properties of stimuli: determined by modality, location, intensity, and duration through graded potentials and action potentials.

• Location Coding: Dependent on activated receptive fields; adjacent areas processed in adjacent brain regions (somatotopic maps).

• Lateral Inhibition: Enhances perception by increasing contrast between activated and non-activated receptors.

Recap of General Properties

1. Sensitivity to modalities.

2. Sensory transduction processes.

3. Receptive fields determine acuity.

4. CNS integration processes.

5. Coding and processing of stimulus characteristics.