Overview
This lecture explains the types and classifications of sensory receptors, focuses on somatic and visceral sensations, and describes related sensory pathways in the nervous system.
Sensory and Motor Pathways
- Sensory pathways transmit information from receptors to the CNS for processing.
- Motor pathways carry signals from the CNS to muscles and glands.
- Sensation begins at sensory receptors and follows a specific pathway to the brain.
Sensory Receptors and Adaptation
- Sensory receptors are specialized cells that detect environmental changes (stimuli).
- Adaptation is decreased receptor sensitivity after constant stimulation.
- Tonic receptors are always active and indicate background levels of stimulation.
- Phasic receptors are usually inactive but respond quickly to changes in stimuli.
Classification of Sensory Receptors
- Sensory receptors are classified by the type of stimulus detected: nociceptors, thermoreceptors, mechanoreceptors, and chemoreceptors.
General Sensory Receptors
- Nociceptors detect pain and are found in skin, joints, and some organs.
- Thermoreceptors sense temperature changes.
- Mechanoreceptors respond to physical distortion such as touch, pressure, and vibration.
- Chemoreceptors monitor chemical concentrations (e.g., blood pH, COâ‚‚, Oâ‚‚).
Types of Mechanoreceptors and Tactile Receptors
- Mechanoreceptors include tactile receptors, baroreceptors (pressure), and proprioceptors (body position).
- Six types of tactile receptors in skin: free nerve endings, root hair plexus, tactile discs, bulbous (Ruffini) corpuscles, lamellar (Pacinian) corpuscles, and tactile (Meissner) corpuscles.
- Each tactile receptor type responds to specific touch or pressure conditions.
Sensory Pathways and Neuron Order
- Sensory pathways use first-order, second-order, and third-order neurons.
- First-order neurons carry sensory information to the CNS.
- Abnormalities in these pathways can cause sensory deficits.
Key Terms & Definitions
- Somatic sensation — sensory input from skin, joints, and skeletal muscles.
- Visceral sensation — sensory input from internal organs.
- Adaptation — reduction in response to constant stimulation.
- Tonic receptor — always active receptor type.
- Phasic receptor — receptor that quickly adapts and only responds to changes.
- Nociceptor — pain receptor.
- Thermoreceptor — temperature receptor.
- Mechanoreceptor — responds to physical deformation.
- Chemoreceptor — detects chemical changes.
- Proprioceptor — senses body and limb position.
Action Items / Next Steps
- Review the types of sensory receptors and their functions.
- Study the pathways for somatic and visceral sensations.
- Prepare for questions about sensory adaptation and receptor types for the quiz.