● `color{brown}("Neural tissue")` exerts the `color{violet}("greatest control over the body’s")` responsiveness to changing conditions.

● `color{violet}("Neurons,")` the unit of neural system are `color{violet}("excitable cells.")`

● The `color{brown}("neuroglial cell")` which constitute the rest of the `color{violet}("neural system")` protect and support neurons.

● `color{violet}("Neuroglia")` make up more than one half the volume of neural tissue in our body.

● When a `color{violet}("neuron")` is suitably stimulated, an electrical disturbance is generated which swiftly travels along its plasma membrane.

●Arrival of the disturbance at the `color{violet}("neuron’s endings,")` or output zone, triggers events that may cause stimulation or inhibition of `color{violet}("adjacent neurons")` and other `color{violet}("cells.")`

● The `color{violet}("basic tissues")` mentioned above `color{violet}("organise")` to form `color{brown}("organs")` which in turn associate to form `color{brown}("organ systems")` in the `color{violet}("multicellular organisms.")`

● Such an `color{violet}("organisation")` is essential for more efficient and better coordinated activities of `color{violet}("millions of cells")` constituting an `color{violet}("organism.")`

● Each `color{brown}("organ")` in our body is made of one or more `color{violet}("type of tissues.")`

● For `color{brown}("example,")` our heart consists of all the `color{violet}("four types of tissues")`, i.e., `color{violet}("epithelial, connective, muscular and neural.")`

● We also notice, after some careful study that the complexity in `color{violet}("organ and organ systems")` displays certain discernable trend.

● This discernable trend is called `color{brown}("evolutionary trend.")`

● The subjects of study at most basic level include the `color{violet}("morphology and anatomy")` of three organisms at different `color{violet}("evolutionary levels ")` to show their `color{violet}("organisation")` and functioning.

● `color{brown}("Morphology")` refers to study of form or externally visible features.

● In the case of `color{violet}("plants or microbes,")` the term `color{violet}("morphology")` precisely means only this.

● In case of `color{violet}("animals")` this refers to the external appearance of the `color{violet}("organs")` or parts of the body.

● The word `color{brown}("anatomy")` conventionally is used for the study of morphology of internal organs in the animals.