Physiology of pain

تمام ✅ هنا ملخص محاضرة Pain Sensation في شكل Notes سهلة للمراجعة:

🖇 Pain Sensation (Nociception)

📌 Basic Concepts

• Nociception = Pain Sensation (من مستقبل خاص اسمه Nociceptor).
• Specificity:
• ال Pain له مستقبل خاص
• • (مش استجابة قوية لمستقبلات أخرى).
  • إثبات: Analgesics ↓ pain فقط بدون تأثير على heat/cold/touch.
• Dissociation: ممكن فصل الإحساس بالألم عن باقي الأحاسيس.

📌 Characteristics of Pain

• High Intensity: لازم Stimulus قوي يسبب الألم.
• Non-Adaptation: لا يحدث تعود على الألم.
• Withdrawal Reflex: الألم يسبب سحب الطرف.
• Prepotent Reflex: Reflex الألم يتغلب على أي Reflex آخر يحدث في نفس الوقت.

📌 Location of Pain Receptors

• High Density (أكثر مناطق حساسية): Skin – Periosteum – Arterial walls – Joint surfaces – Dura & cranial sinuses.
• Low Density: Muscles – Joints – Intestine.
• Absent: Liver parenchyma – Lung alveoli – Brain parenchyma – Tooth enamel & Cornea.

📌 Mechanism of Pain

• Trigger = Tissue Damage → release of Pain Factors (P-factors):
• • Bradykinin (B factor) – Lactic acid – Histamine – K+ – Prostaglandins – Protoenzymes.
• هذه المواد تفتح Channels → Depolarization → AP في Nociceptors.

📌 Types of Pain & Pathways

Feature

🟠 Fast Pain (Acute/Sharp)

Fibers

Type A (myelinated)

Pathway

Neo-spinothalamic

NT

Glutamate

Localization

Accurate, well localized

Destination

Thalamus → Cortex (interpretation)

Function

Withdrawal reflex (avoidance)

🟣 Slow Pain (Chronic/Dull)

Fibers

Type C (unmyelinated)

Pathway

Paleo-spinothalamic

NT

Substance P

Localization

Diffuse, poorly localized

Destination

​Thalamus ± diffuse cortical activation

Function

Activates RAS → arousal, insomnia

• Deep Pain: muscles/joints (due to spasm → ischemia).
• Visceral Pain: من الأعضاء الداخلية، غالبًا مع Referred Pain (ألم يظهر في منطقة سطحية لها نفس Segment في SC).

📌 Pain Modification

• ↓ Pain by:
• • Pressure / Hypoxia.
  • Local Anesthesia (especially deep pain).
• Autonomic Effects: Severe pain → sweating, HR changes, even cardiac arrest.

🚨 Key Questions (Focus Points)

1. Specificity of pain receptors (Nociceptors ≠ other receptors).
2. Absence of pain receptors: Liver, brain tissue, lung alveoli, enamel, cornea.
3. Fast vs Slow pain:
4. • Fibers (A vs C)
   • Pathway (Neo vs Paleo spinothalamic)
   • NT (Glutamate vs Substance P).
4. Mechanism of pain: Release of P factors (Bradykinin, K+, etc).
5. Referred Pain: تعريف + مثال (heart → arm, gallbladder → shoulder).

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