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
Myaesthenia Gravis
Is a serious and sometimes fatal, autoimmune disease in which skeletal muscles are weak and tire easily. The myoneural junction is unable to transmit signals from the nerve fibers to muscle fibers, thereby causing paralysis of the involved muscles. Women are affected more than men in 3:2 ratio,.
Etiology- It is caused by the formation of circulating antibodies to the nicotinic acetylcholine receptors. The anti-AchR antibodies have following three major functions: they compete with Ach to bind to AchR, producing receptor blockade; they induce endocytosis of AchR; and they damage the postsynaptic membrane. Thus, the Ach released at the nerve terminal is not able to produce adequate EPP (end plate potential) to excite the muscle fiber. The reason for the development of autoimmunity to Ach receptors in this disease is still unknown,
Clinical Features- The weakness increases during prolonged use of the muscle and improves after rest or sleep. Thus, the patient feels better in the morning, but symptoms aggravate towards evening or after exertion The extraocular muscles and the lids are often involved early in the course of the disease, Therefore, diplopia and ptosis are early symptoms. Proximal limb muscles are commonly affected. In severe cases respiratory muscle paralysis leads to death.
Diagnosis- There is decremental response to repetitive nerve stimulation on EMG recording from the affected muscle.
Treatment-
1) Administration of AchE inhibitors like neostigmine and pyridostigmine increase the concentration of Ach at the neuromuscular junction
2) Thymectomy- It blunts down the immune response and improves the condition
3) Plasmapheresis- removes the AchR antibodies from the plasma
4) Immunosuppression- Immunosuppressive drugs glucocorticoids and azathioprine inhibit the immunological mechanisms
Lambert-Eaton Syndrome
It is a presynaptic disorder of NMJ due to production of autoantibodies against the voltage-gated calcium channels. The decreased calcium influx in the presynaptic axon terminals results in impaired Ach release from the nerve endings. The muscular weakness is primarily seen in the limb muscles. Patients show incremental response to repetitive nerve stimulation on EMG as calcium level rises with each action potential. Thus, with prolonged contractions, muscle strength increases,
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