Ch 10

Sensory Systems Overview

Sensory Input and Kiara's Example

  • Kiara's running exemplifies the significance of sensation in both conscious and subconscious forms.

  • Sensation involves awareness of body position and movement, integrating:

    • Somatosensory senses: perceptions related to the body, including touch, temperature, pain, and proprioception.

    • Proprioception: the sense of joint position, crucial for coordination during physical activities.

  • Sensory processing involves a sequence of receptor cells and neurons, each contributing to overall sensory experience.

Chapter 10 Learning Objectives

  • 10.1a: Create a framework to describe and compare the types of senses.

  • 10.1b: Establish a framework of the types of sensory receptors.

  • 10.1c: Construct and describe a model of receptive fields, including lateral inhibition.

  • 10.1d: Develop a model of the input/output relationship of neurons considering signal intensity and duration.

  • 10.1e: Explain sensory receptor adaptation mechanisms and compare tonic and phasic neurons.

  • 10.2: Describe neuron organization leading to somatotopic and retinotopic maps.

Types of Senses (Vocabulary - LO 10.1a)

  • Special senses:

    • Vision (light energy)

    • Hearing (mechanical sound waves)

    • Taste (chemical)

    • Smell (chemical)

    • Equilibrium (mechanical)

  • Somatic senses:

    • Touch

    • Temperature

    • Pain

    • Itch

    • Proprioception

Sensory Divisions

  • Special Senses:

    • Vision: Utilizes light energy to facilitate sight.

    • Hearing: Involves mechanical sound waves for auditory processing.

    • Taste: Chemical detection through taste buds.

    • Smell: Chemical detection via olfactory receptors.

    • Equilibrium: Relies on mechanical inputs to maintain balance.

  • Somatic Senses:

    • Touch, Temperature, and Pain all processed consciously.

    • Proprioception processed subconsciously, aiding in body awareness.

Processing of Somatic and Special Senses

  • Conscious Processing:

    • Vision, Touch, Hearing, Temperature, Taste, Pain, Itch

  • Subconscious Processing:

    • Somatic stimuli (muscle length, tension), Visceral stimuli (internal bodily states).

Types of Sensory Receptors (Vocabulary - LO 10.1b)

  • Receptor types include:

    • Chemoreceptors: Respond to chemical stimuli.

    • Mechanoreceptors: Detect pressure and movement.

    • Thermoreceptors: Sense heat.

    • Photoreceptors: Respond to visible electromagnetic energy (light).

Receptor Cell Characteristics

  • Receptor cells feature nerve endings that determine the type of stimuli they respond to:

    • Free nerve endings: Unmyelinated; simple receptors with minimal structures.

    • Complex neural receptors: Enclosed in connective tissue, often more delicate and specific to stimuli.

    • Special senses receptors: Generally involve specialized receptor cells that release neurotransmitters onto sensory neurons, triggering action potentials.

Receptive Fields (Vocabulary - LO 10.1c)

  • Receptive field: The area capable of influencing a sensory neuron's response, either increasing or decreasing it.

  • Categories of receptive fields:

    • Primary receptive fields: Directly associated with sensory input.

    • Secondary receptive fields: Result from the convergence of primary fields.

Acuity and Convergence in Receptive Fields

  • Acuity: The clarity or sharpness of perception, which is influenced by the size of receptive fields.

    • Higher acuity: Features can be distinguished clearly.

    • Smaller receptive fields lead to better resolution.

  • Convergence: Refers to the combining of inputs from multiple primary fields into fewer secondary fields, affecting resolution and acuity.

Lateral Inhibition

  • Lateral inhibition: Enhances the contrast and sharpness of sensory signals by inhibiting neighboring neurons, leading to improved acuity.

  • Characteristics of lateral inhibition include:

    • Neurons inhibit their neighboring fibers proportional to their stimulation intensity, increasing acuity.

    • Inhibition typically occurs through inhibitory interneurons, contrasting with the direct sensory input.

Input/Output Relationships (Vocabulary - LO 10.1d)

  • The relationship dictates how sensory stimuli are transformed into neuronal responses:

    • Input: Stimulus detected by sensory receptors.

    • Output: Time and amount of neurotransmitter released, leading to action potentials.

Key Components of Input/Output Relationships

  • Stimulus parameters: Amplitude and duration affect the resulting neuronal firing rates.

    • Frequency of action potentials correlates with the intensity of the stimulus.

    • Neurotransmitter dynamics: Release patterns depend on the action potential frequency.

Adaptation (Vocabulary - LO 10.1e)

  • Adaptation refers to how receptors change their response to continuous stimuli.

    • Tonic neurons: Continuously fire action potentials throughout the stimulus duration.

    • Phasic neurons: Fire in response to changes in stimulus intensity, returning to a baseline level during constant stimuli.

Neural Organization and Mapping (Vocabulary - LO 10.2)

  • Sensory inputs organized to align neighboring receptive fields with corresponding CNS regions.

    • Somatotopic maps: Organizational system for body sensory representation.

    • Retinotopic maps: Sensory organization for visual input, maintaining spatial relevance.

    • Similar principles apply to motor regions of the brain for coordinated function.