ch 12, part two

Sensation of Pain

• Types of Pain Fibers

  • Fast Pain Fibers (A Delta Fibers)

  • Characteristics: Myelinated, conduct impulses at high speed (up to 30 m/s)

  • Associated with: Sharp, acute pain localized to a specific area (e.g., pricking a finger with a needle)

  • Slow Pain Fibers (C Fibers)

  • Characteristics: Unmyelinated, conduct impulses at a slower pace (up to 2 m/s)

  • Associated with: Dull, aching, chronic pain that is poorly localized (e.g., pain from internal organs)

• Pain Pathways in the Brain

  1. Synapse in the Reticular Formation (part of the brainstem)

  2. Relay to the Thalamus (acts as a relay center)

  3. Direct to the Hypothalamus (major control center affecting emotions and homeostasis)

  4. Finally to the Cerebral Cortex (where pain is interpreted and responses are planned)

Pain Regulation

• Neurotransmitters Involved

  • Substance P

  • Role: Acts to increase pain perception

  • Endorphins

  • Role: Work to inhibit pain signals, leading to pain relief

  • Serotonin

  • Role: Can modulate pain perception; also known as a 'happy hormone'

• Gray Matter and White Matter distinctions:

  • Gray Matter: On the outside of the brain; contains the processing centers for sensations

  • White Matter: On the inside; contains the axons that transmit signals

Proprioception

• Definition: The sense of the relative position of one's own body parts

• Types of Proprioceptors:

  • Muscle Spindles: Detect muscle stretch; initiate stretch reflexes

  • Golgi Tendon Organs: Found in tendons; inhibit excessive contraction and prevent injury

• Examples of Proprioceptive Responses

  • Muscle contractions in response to excessive stretch (protecting muscles)

  • Responses to maintain posture and prevent muscle/tendon damage

Sensory Neurons and Receptors

• General Sensory Receptors: Dispersed throughout the body

• Special Senses: Localized in specific organs (e.g., eyes for sight, ears for hearing)

Special Senses Overview

• Sight: Eyes

• Hearing and Equilibrium: Inner ear structures (e.g., cochlea, semicircular canals)

• Taste: Taste buds in the mouth

• Smell: Olfactory receptors in the nasal cavity

Olfaction (Sense of Smell)

• Olfactory Receptors: Located in the nasal cavity; detect odorants dissolved in mucus

• Processing Path:

  1. Odorants bind to receptors in olfactory epithelium

  2. Signals sent via olfactory nerves to the olfactory bulbs

  3. Transmitted to the limbic system (emotions) for processing

Taste (Gustation)

• Taste Buds: Located throughout the mouth and throat

• Five Primary Taste Sensations:

  1. Sweet: Stimulated by carbohydrates

  2. Sour: Triggered by acids (e.g., H+ ions)

  3. Salty: From sodium ions (Na+)

  4. Bitter: Diverse organic compounds (e.g., Mg2+, Ca2+)

  5. Umami: Meaty taste, stimulated by amino acids (e.g., MSG)

• Taste Receptors: Rapidly replaced (every 3 days); located within taste pores

• Taste Sensation Locations on the Tongue:

  • Sweet: Front tip

  • Sour: Sides

  • Salty: Under tongue

  • Bitter: Back of the tongue

  • Umami: Front two-thirds

Synesthesia

• Definition: A condition where stimulation of one sense leads to involuntary experiences in another sensory modality

• Examples:

  • Seeing colors when hearing sounds (graphing color synesthesia)

  • Specific tastes or smells associated with certain names or words

• Genetics and Prevalence:

  • Probably caused by genetic mutations; affects approximately 1 in 2000 people, often found in creative individuals

Summary

• Pain: Understanding types of pain fibers, pathways, and neurotransmitters is crucial in managing pain.

• Proprioception: An essential sense for body awareness and posture regulation.

• Special Senses: Each sense has distinct pathways and receptors, providing a rich experience of the world.