The tiger

                                        The Tiger

                                           

The tiger is a most beautiful animal and the powerful animal which is the symbol of power and bravery. The tiger is of red and white color  and it had a black strips on the body. All those the tiger is much attractive and so beautiful animal and which is much intelligent in hunting.

The tigers cubs mostly live with there mother for about two months and then leave there home and their mother. After leaving there home they had to established there kingdom and their own family.They had to struggle a lot for making their great empire and they had to fight with other tigers and defeat them. After victory they to mate with there female tiger and had to produce the cubs.

The tiger is the national animal of India and India had about 2000 tigers preserved. India is famous for the one of the worlds beautiful tiger the royal bengal tiger which can defeat the lion also and which much powerfull animal in the world.

Now a days the tigers are being hunting for there skin and there bones and there teeth. The chines kill the tiger for there penis because they believe that the medicine made with the tiger penis may increase the power of sex. so due to the illegal hunting of the tiger the tiger are decreasing day by day in number so seeing this government had taken a strict action to save the tigers.

we all had to try not to increase the pollution and try to save the animals.There are some different types of tigers also which are mainly of white color and they are known as the great white tiger.

Here are some beautiful images of tigers :

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Endangered animals on earth

  Top 20 endangered animals species

1.Tiger

2.Artic wolf

3.Jaguar

4. Whale shark

5. Red panda

6. Sea red turtle

 7.sea green turtle

8. Amur leopord

9. Bengal tiger

10. Orangutan

11. Black spider monkey

12. Rinosorous

13. Mountain plover

14. Elephant

15. snow bear

16. Panda

17. Little rocked deer

18. Platypus

19.ghadiyal

20. Kangaroo

The beautiful birds

                  The most beautiful birds

1. lilac Breasted roller

2. Banded cotinga

3. Gentoo penguin

4.cock of the rock

5.Waved albatros

6.saffron taucanet

7.back headed berry eater

8.hook billed hermit

9.pin tailed manakin

10.peacock

Signal transmission by synapse

      Signal transmission by synapse

Synapse

➢ It is the junctional region between two cells which may or may not be neurons.

➢ The presynaptic cell is generally a neuron.

➢ Postsynaptic cell may be neuron, muscle cell or gland.

Electrical synapse

➢ At an electrical synapse, action potentials conduct 

directly between adjacent cells through gap junctions. 

➢ Each gap junction contains a hundred or so tubular 

connexons, which act like tunnels to connect the 

cytosol of the two cells directly.

➢ Gap junctions are common in 

○ Visceral smooth muscle. 

○ Cardiac muscle.

○ Developing embryo.

○ CNS.

Advantages of electrical synapse:

1.Faster communication

➢ At an electrical synapse, the action potential passes directly from the 

presynaptic cell to the postsynaptic cell. 

➢ The events that occur at a chemical synapse take some time and delay 

communication slightly.

2.synchronization

➢ Electrical synapses can synchronize (coordinate) the activity of a group of 

neurons or muscle fibers. 

➢ In other words, a large number of neurons or muscle fibers can produce action 

potentials in unison if they are connected by gap junctions. 

➢ The value of synchronized action potentials in the heart or in visceral smooth 

muscle is coordinated contraction of these fibers to produce a heartbeat or move 

food through the gastrointestinal tract.

Neurotransmitter

➢ Biochemical substances which are involved in the transmission of impulse 

across synapse. 

➢ Some neurotransmitters bind to their receptors and act quickly to open or 

close ion channels in the membrane.

➢ Others act more slowly via second-messenger systems to influence chemical 

reactions inside cells. 

Impulse transmission across unmylinated axon

Impulse transmission across unmylinated axon

Ion channels

➢ Ion channels open and close due to the presence of “gates.” 

➢ The gate is a part of the channel protein that can seal the channel pore shut 

or move aside to open the pore.

Types of ion channels:

1.leakage channel

➢ The potassium ion leakage channels are leakier than the sodium ion leakage 

channels. 

➢ Thus, the membrane’s permeability to K+

is much higher than its permeability to 

Na+.

2.ligand gated channel

➢ Ligand-gated channel opens and closes in response to a specific chemical 

stimulus. 

➢ A wide variety of chemical ligands— including neurotransmitters, hormones, 

and particular ions—can open or close ligand-gated channels.

3.Mechanical gated channel

➢ These channels open or close in response to mechanical stimulation in the 

form of 

○ Vibration and touch.

○ Pressure and tissue stretching.

4. Voltage gated channel

➢ A voltage-gated channel opens in response to a change in membrane 

potential (voltage). 

➢ These participate in the generation and conduction of action potential

Resting membrane potential (rpm)

➢ In neurons, the resting membrane potential ranges from -40 to -90 mV.

➢ A typical value is -70 mV. 

➢ The minus sign indicates that the inside of the cell is negative relative to the 

outside. 

➢ A cell that exhibits a membrane potential is said to be polarized.

Factors contributing to resting membrane potential (rpm)

➢ The resting membrane potential arises from three major factors:

○ Unequal distribution of ions in the ECF and cytosol.

○ Inability of most anions to leave the cell.

○ Electrogenic nature of the Na+

/K+ ATPases.

Impulse transmission by mylenated axon

Impulse transmission by mylenated axon

Saltatory condition

➢ Action potentials propagate more rapidly along myelinated axons than along 

unmyelinated axons.

➢ It occurs because of the uneven distribution of voltage-gated channels. 

➢ Few voltage-gated channels are present in regions where a myelin sheath 

covers the axolemma. 

➢ At the nodes of Ranvier (where there is no myelin sheath), the axolemma has 

many voltage-gated channels. 

➢ Hence, current carried by Na+ and K+ flows across the membrane mainly at the 

nodes.

➢ When an action potential propagates along a myelinated axon, an electric 

current flows through the extracellular fluid surrounding the myelin sheath 

and through the cytosol from one node to the next. 

➢ Action potential at the first node generates ionic currents in the cytosol and 

extracellular fluid that depolarize the membrane to threshold.

➢ It opens voltage-gated Na+ channels at the second node.

➢ The resulting ionic flow through the opened channels constitutes an action 

potential at the second node. 

➢ Then, the action potential at the second node generates an ionic current that 

opens voltage-gated Na+ channels at the third node, and so on.

➢ Flow of current across the membrane only at nodes of Ranvier has two 

consequences.

○ The action potential appears to “leap” from node to node as each nodal 

area depolarizes to threshold, thus the name “saltatory.”

○ Opening a smaller number of channels only at the nodes represents a 

more energy-efficient mode of conduction. 

Factors that affect the speed of propagation:

Amount of myelination

➢ Action potentials propagate more rapidly along myelinated axons than along 

unmyelinated axons.

Axon diameter

➢ Larger-diameter axons propagate action potentials faster than smaller ones 

due to their larger surface areas. 

Temperature

➢ Axons propagate action potentials at lower speeds when cooled.

Encoding of stimulas intensity

➢ How can your sensory systems detect stimuli of differing intensities if all nerve 

impulses are the same size? 

➢ Why does a light touch feel different from firmer pressure?

➢ The main answer to this question is the frequency of action potentials.

➢ A light touch generates a low frequency of action potentials. 

➢ A firmer pressure elicits action potentials that pass down the axon at a higher 

frequency. 

➢ In addition to this “frequency code,” a second factor is the number of sensory 

neurons recruited (activated) by the stimulus. 

➢ A firm pressure stimulates a larger number of pressure-sensitive neurons than 

does a light touch.