Sensory Processing and Senses
16-1 Transduction
Transduction: Conversion of one form of energy (e.g., light, heat) into electrical energy (nerve signals or Action Potentials).
Receptors: Function to transduce stimulus energy into electrical energy.
A. General Definitions
Receptor Potential: A small, local electrical change in receptor cell due to stimulus.
Leads to neurotransmitter release or a volley of action potentials generating nerve signals to the CNS.
Sensory Receptors: Structures that detect stimuli (e.g., light).
Ranges from simple nerve endings to complex organs enhancing specific stimuli.
Page 2 Sensation
Sensation: Subjective awareness of a stimulus, primarily a function of the cerebral cortex.
Alerts us to environmental changes critical for survival (e.g., danger).
Not all monitored stimuli lead to conscious awareness; some stimuli are filtered by the brainstem/thalamus before reaching the cerebral cortex.
16-3 Four Kinds of Information Transmitted by Receptors
Modality: Type of stimulus or sensation it produces (e.g., vision, touch) determined by where the signal ends in the cerebral cortex.
Location: Site of stimulus identified through a projection pathway.
Intensity: Includes loudness, brightness, etc.
Duration: How long the sensation lasts, related to sensory adaptation.
16-4 Modality
Modality is interpreted based on the final destination of nerve signals in the cerebral cortex.
Nerve signals in the occipital lobe are interpreted as images.
Page 5 Location
Location: Identified through projection pathways followed by sensory signals to the cerebral cortex.
Example: somatic senses have widespread receptors.
Receptive Field: Area where a sensory neuron detects stimuli; varies in size and sensitivity.
Page 7 Intensity
Intensity: Encoded in three ways:
Increased stimulus intensity leads to more frequent AP firing.
Increased stimulus results in recruitment of more neurons.
Neurons have different thresholds of activation.
Page 8 Duration
Duration: Refers to the persistence of a sensation (sensory adaptation):
Tonic Receptors: Adapt slowly, continue firing (e.g., proprioceptors).
Phasic Receptors: Adapt quickly, stop firing if a stimulus persists (e.g., smell).
Page 10 Receptors Classified by Modality
Types of Receptors:
Thermoreceptor: Detect hot/cold (skin).
Photoreceptor: Detect vision (eyes).
Nociceptor: Detect pain (skin, viscera).
Proprioceptor: Detect body position (muscles, tendons).
Taste Receptor: Detect taste (tongue, cheeks).
Page 12 Receptors Classified by Distribution
General/Somatic Senses:
Widespread receptors in the body (e.g., touch, temperature).
Special Senses:
Complex organs limited to the head (e.g., vision, hearing).
Page 13 Somatosensory Receptors
Located primarily in:
Skin (dermis/epidermis).
Muscles.
Mucous membranes.
Page 14 Unencapsulated Nerve Endings
Associated with:
Merkel Cells: Light touch.
Free Nerve Endings: Pain and temperature.
Page 15 Encapsulated Nerve Endings
Types of Encapsulated Endings:
Tactile Corpuscle (Meissner’s): Light touch.
Bulbous Corpuscle: Heavy touch.
Lamellar Corpuscle: Deep pressure, vibration.
Page 17 Somatosensory Projection Pathways
Mainly consist of 3 ascending neurons (first, second, third order) from receptor to the primary somatosensory cortex.
Page 18 Pain
Pain: Discomfort from tissue injury or harmful stimulation.
Nociceptors: Free nerve endings that detect pain through neurotransmitter release.
Page 19 Pain Classification
Visceral: Pain from internal organs.
Somatic: Pain from skin, muscles, joints.
Page 20 Pain Projection Pathways
Travel via:
Spinothalamic Tract: Carries most somatic pain signals.
Spinoreticular Tract: Involved in emotional response to pain.
Page 22 CNS Modulation of Pain
Analgesics: Neuropeptides that block pain signals; includes endorphins, enkephalins, etc.
Page 24 Referred Pain
Pain felt distant from the actual injury due to converging projection pathways in the brain.
Page 25 The Special Senses
A. Taste (Gustation): Chemicals in food bind to receptors mostly on the tongue, causing a taste sensation.
Five primary taste sensations: sweet, salty, sour, bitter, umami.
Page 26 Taste Sensation
Taste cells contain receptors that trigger neurotransmitter release if enough receptor potential is created.
Page 30 Taste Projection Pathway
Nerve fibers from taste buds are bundled into cranial nerves that send signals to the brain
Primary Gustatory Cortex in the insula processes conscious taste.
Page 32 B. Olfaction (Smell)
Evaluates chemical signals in the air, plays a role in detecting dangers (e.g., fire).
Page 39 C. Hearing and Equilibrium
Hearing: Response to sound vibrations.
Equilibrium: Sense of motion and body orientation.
The ear consists of three sections: outer, middle, and inner.
Page 44 The Inner Ear
Cochlea: Organ of hearing.
Contains hair cells that transduce sound vibrations into nerve signals.
Page 47 The Auditory Projection Pathway
Hair cells in cochlea send signals to the primary auditory cortex for sound perception.
Page 48 Hearing Loss
Sensorineural Hearing Loss: Damage to hair cells.
Conductive Hearing Loss: Blockage or damage affecting sound transmission.
Page 51 D. Equilibrium
Receptors in the vestibular apparatus detect head position and movement.
Page 58 Vision
Vision is the perception of objects through light, requiring transduction of light by photoreceptors within the eye.
Page 60 Regulating Amount of Light
Controlled by iris adjustments resulting from contraction of smooth muscle.
Page 64 Retina
Contains photoreceptors (rods and cones) that transduce light into electrical signals for the optic nerve.
Page 78 The Visual Projection Pathway
Visual signals processed in the thalamus and visual cortex for perception.
Conclusion
Understanding sensory processing and the roles of the various types of receptors, as well as their pathways from stimulus detection to perception, is critical for grasping how we interact with our environment. The differentiation between modalities, location, intensity, and duration of stimuli enhances our ability to react and adapt to surroundings efficiently.