Sensory Physiology Flashcards
What is the primary process by which sensory receptors convert external stimuli into electrical signals?
Sensory transduction involves stimulus-gated ion channels that open in response to mechanical, thermal, or chemical stimuli, leading to graded receptor potentials that may trigger action potentials.
What are the main types of sensory receptors and their functions?
• Mechanoreceptors – Touch, vibration, proprioception
• Thermoreceptors – Temperature changes
• Nociceptors – Pain perception
• Chemoreceptors – Taste, smell, chemical detection
• Photoreceptors – Vision (rods/cones)
What are the two major pathways for somatosensory information, and what do they carry?
• Dorsal column-medial lemniscus (DCML) – Fine touch, vibration, proprioception
• Spinothalamic tract (STT) – Pain, temperature, crude touch
What is the function of the thalamus in sensory perception?
The thalamus acts as a relay center for sensory input (except smell) before sending signals to the primary somatosensory cortex.
What is the difference between rapidly adapting and slowly adapting receptors?
• Rapidly adapting receptors (phasic) – Respond to stimulus onset and offset (e.g., Meissner corpuscles)
• Slowly adapting receptors (tonic) – Respond continuously to stimuli (e.g., Merkel cells)
What are the two types of thermoreceptors, and how do they function?
• Cold receptors (Aδ and C fibers) – Activate at lower temperatures
• Warm receptors (C fibers) – Activate at higher temperatures
• Paradoxical cold response – Extreme heat (>45°C) can activate cold receptors
What are the two primary types of pain fibers, and what do they transmit?
• Aδ fibers – Fast, sharp, localized pain (first pain)
• C fibers – Slow, dull, burning pain (second pain)
How do peripheral and central sensitization contribute to chronic pain?
• Peripheral sensitization – Increased nociceptor sensitivity due to inflammatory mediators (prostaglandins, bradykinin).
• Central sensitization – “Wind-up” phenomenon causes spinal neurons to become hyperexcitable.
How does the gate control theory explain pain modulation?
• Non-painful stimuli (Aβ fibers) activate inhibitory interneurons, which suppress pain transmission in the spinal cord, “closing the gate.”
What brain regions are involved in endogenous pain modulation?
• Periaqueductal gray (PAG) – Releases endorphins, modulates pain
• Rostral ventromedial medulla (RVM) – Regulates pain inhibition/excitation
• Dorsolateral pontine tegmentum – Inhibits spinal pain transmission
What is the difference between hyperalgesia and allodynia?
• Hyperalgesia – Increased pain perception from normally painful stimuli
• Allodynia – Pain in response to non-painful stimuli (e.g., light touch)
What are key inflammatory mediators that increase pain perception?
• Prostaglandins – Increase nociceptor sensitivity
• Bradykinin – Directly stimulates pain receptors
• Substance P – Enhances pain transmission in spinal cord
• Histamine – Released by mast cells, contributes to pain and itch
What causes neuropathic pain, and how is it different from nociceptive pain?
• Neuropathic pain results from nerve damage (e.g., diabetes, nerve injury).
• Characterized by burning, tingling, or electric shock-like pain.
• Unlike nociceptive pain, it persists without a noxious stimulus.
How do opioids reduce pain perception?
Opioids (e.g., morphine) bind to μ-opioid receptors in the brainstem, spinal cord, and peripheral nerves, inhibiting neurotransmitter release (e.g., glutamate, substance P) and reducing pain transmission.
What mechanisms explain phantom limb pain?
• Cortical reorganization – The brain remaps the missing limb’s sensory representation.
• Peripheral nerve hyperactivity – Spontaneous firing from severed nerves contributes to pain perception.
