MBBS NOTES

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

  Special types of Active Transport (Macro- Molecules)  This includes vesicular transport...which includes Endocytosis and Exocytosis ENDOCYTOSIS  Endocytosis includes.. 1. Pinocytosis (cell drinking)  2. Phagocytosis (cell eating)  3. Receptor mediated endocytosis  Vesicular exocytosis includes basically release of neuro transmitter e.g. ACh Pinocytosis (Cell drinking) It is the process of engulfing liquid substances by enfolding of cell membrane e.g. Reabsorption by renal tubular epithelial cells  Phagocytosis (cell eating)  Engulfing the solid particles e.g. bacteria, dead cells and foreign particles by the cells. This process involves three steps i) Attachment stage i) Engulfment stage iii) Degradation stage   Receptor mediated endocytosis In this process substance binds with special receptor protein on the cell membrane. Then protein-substance complex is engulfed by the cell membrane by the process of endocytosis e.g. Transport of iron, cholesterol into the cell, LDL and Vita B12

  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 Caspase

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

  Membrane Transport Proteins 1) Pores: rare, eg. Aquaporins (Water Channels) by ADH at DCT & CT (osmosis),  2) Channels: eg. Ion Channels (Ligand gated, Voltage gated, Mechanically gated) simple diffusion   3) Carriers:   a. Uniporters (facilitated diffusion), b. Pumps (primary active transport),  c. Symporters (secondary co-active transport),  d. Antiporters (secondary counter-active transport)   Classification of Transport across cell membrane   1) Passive transport- Passive transport is the transport of a substance along electrochemical gradient. It does not require energy. Its types are-  1.1 Osmosis 1.2 Simple Diffusion 1.3 Facilitated Diffusion 2) Active transport- Active transport is the transport of a substance against electrochemical gradient (uphill). It requires energy  2.1) primary active transport 2.2) secondary- coactive transport & secondary- counter active transport  3) Special types of Active Transport (Macro- Molecules)-  3.1) Endocytosis  3.2) Exocytosis

The pineal gland is a small, pea-shaped gland in the brain. It produces and regulates hormone melatnoni.  It is known from comparative anatomy that the pineal gland is a vestigial remnant of what was a third eye located high in the back of the head in some lower animals Functions of Pineal gland  Pineal gland is believed to have role in the following functions.  (1) enhancing sex,  (2) staving off (preventing) infection,  (3) promoting sleep,  (4) enhancing mood, and  (5) increasing longevity (as much as 10 to 25 percent) MELATONIN & CIRCADIAN RHYTHMS Pineal pinealocytes contain melatonin and the enzymes responsible for its synthesis from serotonin, and they secrete the hormone into the blood and the cerebrospinal fluid Secretion of melatonin The cyclic activity of the suprachiasmatic nucleus (SCN) sets up a circadian rhythm for melatonin release. This rhythm is entrained to light/dark cycles by neurons in the retina. Light signals are relayed via the retinohypothalamic (RHT) fiber

Thymus is a specialized primary lymphoid organ of the immune system. It is situated behind the sternum in upper and anterior part of chest. It consists of a capsule, outer cortex and inner medulla. T cell maturation Functions of Thymus The thymus facilitates the maturation of T cells which are responsible for cell mediated immunity. T cells begin as hematopoietic precursors from the bone-marrow, and then migrate to the thymus for maturation, where they are referred to as thymocytes.  In the thymus they undergo a process of maturation, which involves ensuring the cells react against antigens (positive selection), but that they do not react against antigens found on body tissue (negative selection). Once mature, T cells emigrate from the thymus to lymphnodes to provide vital functions in the immune system  Positive selection This process occurs in the cortex of Thymus. The survival and nature of the T cell in thymus depends on its interaction with surrounding thymic epithelial cells. Her

 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