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Skeletal muscles.


  • Skeletal muscles or voluntary muscles can be controlled by our will.
  • These are also known as striated muscles as well as voluntary muscles.
  • Skeletal muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle.

  • It is a formed of striated muscle tissue which is under the 'voluntary' control of the somatic nervous system.

  • Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons.



For both your questions answer is YES.


  • Depending on the type of chemicals released from axonic terminal (=presynaptic knob) there are either excitatory or inhibitory synapses.

  • Acetylcholine, epinephrine and glutamate are common excitatory neurotransmitters. Release of such chemicals in synaptic cleft and subsequent stimulus to postsynaptic membrane leads to opening of Na channels. An action potential is generated in postsynaptic neuron and nerve impulse transmission can continue.

  • Most common inhibitory neurotransmitter in human brain is gamma aminobutyric acid (GABA). Release of inhibitory neurotransmitter leads to flooding of postsynaptic end with negatively charged Cl ions. Hence an action potential is not generated to fire the postsynaptic neuron.

  • Neurotransmitters like acetylcholine, etc should be broken down at synapse after being released, to prevent continuous stimulation or overstimulation. Break down of neurotransmitter at synapse is also necessary to keep receptors free for next stimulus.

  • An enzyme, acetylcholinesterase, breaks down acetylcholine in choline and acetate. Choline returns inside presynaptic knob where it is reused for synthesis of acetylcholine. Importance of acetylcholinesterase could be noted from the fact that many insedticides, like carbamates and organophosphates, are actually acetylcholinesterase inhibitors. Application of these chemicals exhaust ATP molecules in insects due to continuous neuromuscular transmission.


Here's my understanding of the mechanism.


Hydrochloric acid is produced by the parietal cells in the stomach.

These cells secrete about 60 mL #"HCl"# per hour at a concentration of
roughly 0.16 mol/L.

This is about #3 × 10^6# times the concentration of #"H"^"+"# ions in blood.

Thus, the secretion of hydrochloric acid depends on active transport.

The key player is a proton pump #bb((1)"# located in the cell membrane.

The dissociation of water within the cell generates #"H"^"+"# and #"OH"^"-"# ions.

The #"OH"^"-"# ions combine with #"CO"_2# to form #"HCO"_3^"-"# and are transported out of the cell by anion exchange for #"Cl"^"-"color(white)(l)bb((2))# .

The #"Cl"^"-"# ions are transported out of the cell by conductance channels #bb((3))#.

The proton pump removes #"H"^"+"# ions from the cell in exchange for #"K"^"+"# ions. This effectively recycles the #"K"^"+"# ions.

The net effect is that one #"H"^"+"# ion and one #"Cl"^"-"# ion leave the cell for each water molecule that dissociates.




These are the main diaphragms present in our body,which acts as partitioning agent as well as weight bearer.

1 .THE DIAPHRAGM : Present at the junction of thoracic and abdominal cavity.

2 .PELVIC DIAPHRAGM : Present at the junction of abdomen proper above and pelvic cavity below.

3 .UROGENITAL DIAPHRAGM : Present at the junction of greater pelvis above and perineum below.

4. DIAPHRAGMA ORIS : This is a muscle bulk formed by the myelohyoid muscle which bears the weight of the tongue.

5. DIAPHRAGMA SELLA : It covers the pituitary gland,present inside the middle cranial fossa.


The thickness is about 1.6 mm.


The skin has two principal layers: the epidermis and the dermis.

The dermis contains two layers: the papillary layer and the reticular layer.

The thickness of the skin differs at various body sites.

The thinnest skin is on the eyelids. It is about 0.5 mm thick.

The thickest skin is on the heels of the feet, where it can be up to 5 mm thick.

Here is a chart showing the thickness (in millimetres) of skin on the neck (an average of 121 persons).

#ulbb(color(white)(mmmmmmmmmmmmmll) "layer"color(white)(mmml)"layer"color(white)(mmmmm))#
#"Upper neck"color(white)(mmmll)0.11color(white)(mmmm)0.12color(white)(mmmml)1.44color(white)(mmm)1.67#
#"Lower neck/"#


Here's what I find.


What is fainting?

Fainting is a brief, sudden loss of consciousness.

You become unresponsive and may fall.

The medical term for fainting is syncope (from Greek syn "together" + kope
"a cutting short") [of blood flow to the brain].

How does standing for a long time cause fainting?

It is harder for the heart to pump blood up to the brain than down to the toes.

When you stand for a long time, especially in the heat, blood from your upper body can pool in your legs.

The blood supply to the brain decreases, and you faint.

What is happening in the body?

Your body has a feedback system of sensors in the arteries leading to the brain.

These sensors control many nerve and hormone signals that change your heart rate, constrict your blood vessels, and maintain your blood pressure.

When the blood pools in your legs, the feedback system triggers your heart rate and blood pressure to drop suddenly.

The blood flow to your brain decreases.

How is the brain involved?

The brain needs a constant supply of sugar and oxygen.

If blood flow drops, the brain goes into an energy-conserving shutdown.

It sends signals to your nerves and muscles to stop.

You lose consciousness and slump to the ground.

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