MBBS NOTES

 Physiological anatomy of Spinal cord  Spinal cord lies in the vertebral canal. Its length is 45-50 cms and has diameter of about 2 cm.  The whole length of spinal cord is divided into 31 segments. Each segment gives rise to a pair of spinal nerve. Depending on the region, the spinal nerves are named and numbered.  Cervical 8 segments: C1-C8 Thoracic 12 segments: T1-T12 Lumbar 5 segments: L1-L5 Sacral 5 segments: S1-$5 Coccygeal 1 segment: Cx Total 31 pairs of spinal nerves, Arrangement of gray and white matter in spinal cord:  In cross section, the spinal cord contains gray matter inside and white matter outside. Gray matter: The gray matter looks like English letter 'H'. The dorsal and ventral projections of grey matter look like horns and hence they are called dorsal horn and ventral horn  In addition in the thoracic and upper lumbar segments of spinal cord there is 'lateral horn'.The grey matter contains cell bodies of neurons. They can be classified into: Dorsal ho

 Definition Reflex is automatic motor response to a sensory impulse through the involvement of center (CNS).   Reflex Arc Pathway for any reflex action is known as reflex arc. It consists of:  1) Receptor- Is end organ which receive stimulus and when stimulated generates impulses in afferent nerve  2) Afferent nerve- afferent or sensory nerve transmits impulses from receptor to the center.  3) Centre- This is the part of CNS where afferent limb ends and either synapses directly with efferent motor neuron or establish connection with the efferent neuron via internuntial or intercalated neurons.   4) Efferent nerve- efferent or motor nerve transmits impulses from center to effector organ.   5) Effector organ- It may be muscle or gland which show response to the stimulus    Significance Protection, various GIT, CVS, RS, CNS functions are due to reflex activities Classification of reflexes 1. Clinical classification i) Superficial reflexes- These are the reflexes which are initiated b

1) One way conduction (or law of forward conduction by Sherington)  Synapse permits transmission of impulse only in one direction from pre synaptic to post synaptic neuron. It is extremely important for orderly organization of neural functions Although in electrical synapse transmission can be in both ways.  2) Synaptic delay When an impulse reaches the pre synaptic terminal there is minimal time interval before responses (initial depolarization) is obtained at post synaptic membrane. This time is due to release of synaptic transmitter and its action on postsynaptic receptor. Usual delay at one synapse is about 0.5 msec. Thus this time interval can be used to calculate number of synapses in the neural pathway. Although electrical synapses hardly show any synaptic delay 3) Fatigue When an excitatory synapse is repetitively stimulated, in first few stimuli response is increased (due to beneficial effect) but eventually response becomes progressively less and less. It is mainly due to dep

  Definition of synapse Synapse is junction between two neurons through which impulse passes from one neuron (called presynaptic neuron) to the other (called postsynaptic neuron)  Apart from transmission impulses are also manipulated in many ways at synapse like summation, block, inhibition, direction change etc. Anatomical classification 1. Axosomatic: Synapse between axon of one neuron and cell body of the next neuron. e.g Motor neurons in spinal cord, cerebrum and cerebellum.  2. Axodendritic: Synapse between axon of one neuron and dendrite of the next neuron. Most of the synapses are of this type. e.g. Motor neurons in spinal cord, autonomic ganglia, cerebellum.   3. Axoaxonic: Synapse between axon of one neuron and axon of other neuron. e.g. spinal cord.   4. Dendrodendritic: Synapse between dendrite of one neuron and dendrites of second neuron. Very rare. e.g. in olfactory bulb Physiological classification 1. Chemical synapse (diagram-A): Most of the synapses are of this type

 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