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
What is Lac Operon: Lac operon is a unit of gene expression in the bacterial cell. Lac operon includes structural gene gene (Z,Y,A) , inhibitor gene (i), control elements and promoter and operator area. In bacterial cell, Z gene is encodes beta-galactosidase. beta-galactosidase is hydrolytic enzyme which hydrolyze lactose into galactose and glucose. Y gene encodes enzyme permease which transports lactose into cell. A gene is responsible for production of enzyme thiogalactoside transacetylase. since, Z,Y and A gene codes for a structure of protein they are called structural gene. these gene are present as contiguous segment of DNA. The RNA polymerase bind to the promoter and transcribes three structural gene as a single mRNA. this type of mRNA call polysistonic RNA. Transcription in Normally Repressed Transcription of the structural gene is done under the control of regulator or the "i" (i=inhibitor) gen