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Sensation
Chapter 14 - A & P Lecture
| Question | Answer |
|---|---|
| sensation | the detection of stimuli |
| perception | the interpretation of that data |
| Two Major Categories of Senses: | General Senses (Widely Distributed) & Special Senses (Localized Organs) |
| General Senses occur throughout the body. There are two subtypes: | Somatic senses & Visceral senses |
| Somatic senses | (body + environment) Touch Pressure Temperature Pain Proprioception (position and movement of body parts) |
| Visceral senses | (internal organs) Pain Pressure |
| Special Senses are more complex and occur in specialized organs: | Vision (eyes) Hearing (ears) Balance (inner ear) Taste (tongue) Smell (nose) |
| Key difference in General & Special Senses | General senses: receptor directly generates an action potential Special senses: receptor releases neurotransmitter → activates neuron |
| Classification of Sensory Receptors: | Based on stimulus type & Based on location |
| Based on stimulus type: | Mechanoreceptors Chemoreceptors Thermoreceptors Photoreceptors Nociceptors |
| Mechanoreceptors | Respond to physical forces: Touch Pressure Stretch Sound Balance |
| Chemoreceptors | Respond to chemicals: Taste Smell |
| Thermoreceptors | Respond to temperature changes |
| Photoreceptors | Respond to light (vision) |
| Nociceptors | Respond to harmful stimuli → pain |
| Based on location: | Cutaneous receptors Visceroreceptors Proprioceptors |
| Cutaneous receptors | skin |
| Visceroreceptors | organs |
| Proprioceptors | muscles, joints, tendons |
| Key receptor types: | Free nerve endings Merkel disks Hair follicle receptors Pacinian corpuscles Meissner corpuscles Ruffini endings Muscle spindles Golgi tendon organs |
| Free nerve endings | Simplest and most widespread Detect: pain, temperature, itch |
| Merkel disks | Light touch and pressure Located in epidermis |
| Hair follicle receptors | Deep pressure and vibration Onion-like structure |
| Pacinian corpuscles | Deep pressure and vibration Onion-like structure |
| Meissner corpuscles | Fine touch Responsible for two-point discrimination This is why fingertips are so sensitive. |
| Ruffini endings | Detect continuous pressure and skin stretch |
| Muscle spindles | Detect muscle length (stretch) Critical for posture and reflexes |
| Golgi tendon organs | Detect tendon tension Prevent excessive force → protect muscles |
| How Sensory Receptors Respond | Stimulus interacts with receptor Produces a graded potential Called a receptor potential If strong enough → triggers action potential |
| Two receptor categories: | Primary receptors → directly generate action potentials Secondary receptors → release neurotransmitters |
| Adaptation | Receptors become less sensitive over time. |
| Types of Adaption: | Tonic receptors (slow adaptation) & Phasic receptors (fast adaptation) |
| All sensory info travels via as___________ pathways. Each pathway carries a specific type of _______ | ascending; sensation |
| Spinothalamic Tract (Anterolateral System) Function: | Pain Temperature Crude touch |
| Spinothalamic Tract Pathway (3 neurons): | 1. Primary neuron → spinal cord 2. Secondary neuron → crosses (decussates) → ascends 3. Tertiary neuron → thalamus → cortex |
| Dorsal Column–Medial Lemniscus System Function: | Fine touch Vibration Proprioception |
| Dorsal Column–Medial Lemniscus System Key feature: | *Does NOT cross immediately* 1. Primary neuron → ascends to medulla 2. Secondary neuron → crosses 3. Tertiary neuron → cortex |
| Pain is not just physical—it is a sensory and emotional experience that triggers _______ and ______ responses. | autonomic; behavioral |
| Two types of pain signals: | Fast pain & Slow pain |
| Fast pain | Sharp, localized Travels on large, myelinated fibers |
| Slow pain | Dull, aching, diffuse Travels on small fibers |
| Gate Control Theory | Pain signals can be inhibited by other sensory input. Example: rubbing a sore area reduces pain. |
| Referred Pain | Pain felt in a different location than its source. Example: Heart pain → felt in left arm Reason: Signals converge in the same spinal segment |
| Chronic Pain | Not always linked to immediate injury May involve: neurological changes & psychological components |
| All sensory pathways ultimately reach the .... | cerebral cortex |
| Primary sensory areas: | Primary somatosensory cortex & Sensory homunculus |
| Primary somatosensory cortex | Located in postcentral gyrus Processes touch, pain, temperature |
| Sensory homunculus | Body map distorted by receptor density |
| Other sensory regions: | Taste → insula Smell → temporal lobe Hearing → temporal lobe Vision → occipital lobe |
| Primary areas _____ ______ Association areas ______ ______ Example: Primary area → detects shape Association area → recognizes it as a “phone” | detect signals; interpret them |
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