POINTS ONLY - PHYSIOLOGY

These section of 'POINTS ONLY ' consists of random points of very importance in each subjects, asked previously in many exams and  made specifically for the purpose of quick revision.

1. Ventromedial Hypothalamus - responsible Rage Reaction on food restriction.

2. Stimulation of left stellate ganglion does not increase heart rate. (coz. SA node is supplied by right vagus)

3. Equillibrium potential - NERNST Equation.

4. Magnitude of Membrane potential - GOLDMAN Constant Field Equation.

.........

will be updated soon....

Physiology : LIMBIC CORTEX : Mnemonic

Parts of the CNS forming the Limbic Cortex can be remembered by the Mnemonic "CASH".


C - Cingulate Gyrus.

A - Amygdala.

S - Septal Nuclei

H - Hippocampal Formation (Hippocampus + Dentate Nucleus)

Golgi Bottle Neuron Vs Golgi Tendon Organ

Golgi Bottle Neuron is the inhibitory interneuron which is involved in the phenomenon of Reciprocal Innervation by which the antagonist muscles relax during protagonist muscle contraction.

Now Golgi Tendon organ os involved in Autogenic inhibition or Lengthening Reaction or commonly called Inverse Stretch Reflex, by which muscles relax after a critically high muscle tension is reached, it helps to prevent muscle rupture or tendon avulsion. 

Stretch Reflex involves Muscle Spindle.

NOTE :

Golgi Tendon organ - senses muscle tension.

Muscle Spindle - senses muscle length.

CNS and Neurons

CNS and Neurons..........go through these useful points.

(CNS) contains about 10(raised to)11 (100 billion) neurons. It also contains 10–50 times this number of glial cells.

Protein Zero (P0) responsible for compaction of myelin, mutations of protein zero causes peripheral neuropathy. Nodes of Ranvier are 1micro meter in size placed 1 mm apart.

Slowly rising currents fail to fire the nerve because the nerve adapts to the applied stimulus, a process called accommodation.

Anelectrotonic-hyperpolarizing potential change, catelectrotonic- depolarizing potential change.

Absolute refractory period, corresponding to the period from the time the firing level is reached until repolarization is about one-third complete.

A decrease in extracellular Ca2+ concentration increases the excitability of nerve and muscle cells by decreasing the amount of depolarization necessary to initiate the changes in the Na+ and K+ conductance that produce the action potential.

Erlanger and Gasser Classification of Nerve Fibers into A, B, and C groups, further subdividing the A group into alpha, beta, gamma and delta fibers.

Maximum speed of construction A-delta fibers, maximum size for A-delta fibers.

Which are preganglionic autonomic fibers? Ans: Type B fibers.

A and B fibers are myelinated; C fibers are unmyelinated.

Neurons Classification and susceptility to pressure, anesthesia and hypoxia

Always expect one MCQ in physiology especially from the second portion of the chart.

Renin–Angiotensin System

Few important points regarding the Renin–Angiotensin System

- Renin is an aspartyl protease, contains 340 AA, t ½ <>

- After Nephrectomy the prorenin levels may actually rise (from ovaries), but rennin falls to 0.

- Angiotensinogen is found in the 2-globulin fraction.

- Angiotensinogen -> AT-I (decapeptide) -> (ACE) AT-II (octapeptide) in Lungs. ACE is a dipeptidyl carboxypeptidase that splits off histidyl - leucine from the physiologically inactive angiotensin I. AT II t ½ 1-2 minutes. The normal PRA in supine subjects eating a normal amount of sodium is approximately 1 ng of angiotensin I generated /mL/hr. The plasma angiotensin II concentration in such subjects is about 25 pg/mL (approximately 25 pmol/L).
- Dry Cough in ACEI is d/t increased Bradykinin.

- AT1 receptors are serpentine receptors coupled by a G protein (Gq).
- 1. JG cells (granular cells) - in the media of the afferent arterioles – intra renal pressure sensor, 2. Agranular lacis cells those are located in the junction between the afferent and efferent arterioles in the mesangium, 3. Macula densa (part of tubule – start of DCT, senses Na+) All 3 constitutes JGA.

- GOLDBLATT Hypertension – Syn. Renal Hypertension – decreased blood supply to one kidney -> increased renin.

Cerebral Blood Flow & Its Regulation

Cerebral Blood Flow & Its Regulation


- Inhaled nitrous oxide (N2O) (Kety method). The average cerebral blood flow in young adults is 54 mL/100 g/min. The average adult brain weighs about 1400 g, so the flow for the whole brain is about 756 mL/min. In resting humans, the average blood flow in gray matter is 69 mL/100 g/min compared with 28 mL/ 100 g/min in white matter.

- Because brain tissue and spinal fluid are essentially incompressible, the volume of blood, spinal fluid, and brain in the cranium at any time must be relatively constant (Monro–Kellie doctrine).

- In the brain, auto regulation maintains a normal cerebral blood flow at arterial pressures of 65–140 mm Hg.

- O2 consumption by the human brain (cerebral metabolic rate for O2, CMRO2) averages about 3.5 mL/ 100 g of brain/min (49 mL/min for the whole brain) in an adult. This figure represents approximately 20% of the total body resting O2 consumption.

- Glucose enters the brain via GLUT 1 in cerebral capillaries.

- Blood Flow in Various Parts of the Brain – Best is P.E.T (2 Deoxy Glucose).

- CPP = MAP – CVP/ICP (whichever is higher), (Normal CPP 80-100 mmHg, ICP <10mm Hg.)

- Most important extrinsic influence on CPP is Arterial pCO2.

- Cerebral Blood Flow changes by 5-7 % with 10C change of temperature.