Question

compare the contraction mechanism of skeletal, cardiac, and smooth muscle fibers.

distinguish among the CNS, PNS, and the ANS.

describe the structure of a typical neuron and describe the functions of each component.

Answer 1

Answer 1 About contraction of muscles
Excitation contraction coupling in muscles.

1)Action potential is transmitted along the sarcolemma of the muscle fiber and then down the T tubules

2)Depolarization of T-tubules causes conformation change in DHP receptors, opening the Ca++ release channels in the terminal cisternae of the sarcoplasmic reticulum.

3) This triggers release of Ca++ from the terminal cisterns of the L-tubule. Ca++ peaks at approximately 20 msec after the Action potential.

4)The released Ca++ binds to troponin-C Troponin-C facilitates movement of the associated tropomyosin molecule toward the actin filament The tropomyosin ‘moves away’, exposes the myosin binding site on the actin filament This triggers the cross-bridge cycling, including the powerstroke .

5)The active pumping of Ca++ back into the sarcoplasmic reticulum brings about relaxation

Mechanism of contraction is almost similar in all muscles except
In cardiac muscles
One important phenomenon in myocardium is CICR or calcium-induced calcium release. This means that Ca2+ entry from ECF into the cardiac muscle cell triggers the release of more Ca2+ from the sarcoplasmic reticulum.ECF Ca++ enters into cardiac muscle cell via L-type Ca++ channels and act on Ryanodine receptor on sarcoplasmic reticum and cause increase release of calcium from SR thus forceful contraction occur in myocardium .

6) Thus excitation contraction coupling in
muscle is termed electrochemical coupling (involving Ca2+-induced release of Ca2+), whereas excitation contraction coupling in skeletal muscle is termed electromechanical coupling (involving direct interactions between the DHPR in the T tubule and the RYR in the SR).

7 ) Smooth muscles mechanism is similar there intracellukar calcium binds with Myosin light chain kinase and cause phosphorylations and Generate energy which helps in contraction.

Answer 2) about CNS PNS ans ANS
2) Central nervous system is Brain and spinal cord
a)Brain - Function is to receive information from Peripheral nervous sytem and initiate resopses .Store memory ,concerne with emotions ans thought ,motor movemnt of body .

b)Spinal cord - Conducts signals to brain from periphery and back to periphery from brain .Reflex activity

Peripheral nervous system -
A) Motor neurons - comducts signals from CNS to muscles and glands

Two types ---
a) Somatic neurons - Deals with motor movemnts

b) Autonomic nevous system
2 types
1) Sympathetic nervous sytem -act during Stress Fight or flight response .
2) Parasymoathetic nervous system - Rest and digest

B) Sensory neurons to CNS eg sense of smell ,vision ,hearing etc.

Answer 3 about Neuron
Typical neuron is made up of
1.Perikaryon or soma or cell body: Contains many Nissl bodies and Golgi bodies.Cell body has nuckeus and is lined by cell membrane
Function - Organises and keep the cell functions .
Nucleus function is to control the neuron
Cell membrane protects the cell.

2. Dendrites: are known as receptor zone where it receives the signals fron other dendrites and graded electrogenesis occurs.

3. Axon hillock: The thickened area of cell body from which axon arises. They lack RER, free ribosomes, and Golgi apparatus.
Function - nerve impulse action potential begins here because highest concentration of Sodium channels / unit area is seen here .

4 Axon arises from axon hillock which has nodes of ranvier present over ita surface.Also Schwann cells present here helps in myelination .
Function - Transmits signals from one neruron to another
Schwann cell - myelination
Nodes of ranvier - allow diffuion of ions fast so inpulse travel from one node of ranvier to another becuase of myelination and conduction is faster called saltatory conduction .

5 .Axons terminate as Synaptic knobs .
Function - Vesicles contain acetycholine help in contraction .

Between 2 axons there is synapse which transmit the information from one axon to another .