Pain sensation Pain receptors are also called as nociceptors They are located at the ends of small 'C unmyelinated or myelinated A delta fibers a) Definition Pain sensation is unpleasant but protective sensation aroused by noxious stimuli that damage or can damage body tissues b) Physiology (properties & reaction) Purpose or importance: Protective Stimulus: noxious (chemicals like- Ach, bradykinin, serotonin, hydrogen ions, potassium ions, prostaglandins or mechanical or thermal) Receptors: free nerve endings (polymodal receptors) Adaptation : non or slow adapting receptors Nerve fibers: fast pain is carried by A-delta nerve fibers while slow pain by 'C' type. Neurotransmitters: glutamic acid (at spinal cord) for fast pain, substance P (at spinal cord) for slow pain and Lewis P factor for muscle pain, Pathway: lateral spinothalamic (specific neo spinothalamic for fast pain and diffuse and non specific paleo spinothalamic for slow pain) Reaction : pain is a
Definition of Apoptosis
Apoptosis word comes from Greek word Apo means- away and ptosis means fall. Apoptosis is defined as programmed cell death.
For example - RBC's life span is 120 days while WBC's life span is only few days. Majority of the cells show apoptosis. But rate of apoptosis varies from cell to cell,
Some cells have very high rate of apoptosis, for example cells in intestine & and in bone marrow.
Physiological significance & mechanism
i)During embryogenesis & developmental stage, there is high rate of apoptosis. During embryogenesis, degeneration of Mullerian duct in male foetus occur due to apoptosis Webs between fingers and toes are removed due to apoptosis
Developmental brain remodelling and immune system development require apoptosis
ii)During adult life too, apoptosis plays an important role by removing old and less functioning cells. These cells are replaced by to better functioning young cells
Mechanism- Procaspases activated to Caspases, which is a protease enzyme. Cells own gene (specially p53) and mitochondria play an important role in the activation of Caspases. Caspases will lead cells to shrink, condense, fragment & finally cells are broken down into apoptic bodies. Apoptic bodies are phagocytosed and cleared by nearby macrophages.
Clinical significance
1)Lack of apoptosis- can lead to Cancer due to accumulation of cells,
2)Excess apoptosis- can cause neurodegenerative diseases like Alzheimer's disease.
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