● The `color{violet}("nerve fibres")` of the `color{violet}("PNS")` are of two types :

(a) `color{brown}("Afferent fibres")`
(b) `color{brown}("Efferent fibres")`

● The afferent `color{violet}("nerve fibres transmit impulses")` from `color{brown}("tissues/organs to the CNS")` and the efferent `color{violet}("fibres transmit")` regulatory impulses from the `color{brown}("CNS")` to the `color{brown}("concerned peripheral tissues/organs.")`

● The `color{violet}("PNS")` is divided into two divisions called `color{brown}("somatic neural system")` and `color{brown}("autonomic neural system.")`

● The `color{violet}("somatic neural system")` relays impulses from the `color{brown}("CNS to skeletal muscles")` while the `color{violet}("autonomic neural system transmits impulses")` from the `color{brown}("CNS")` to the `color{brown}("involuntary organs")` and `color{brown}("smooth muscles")` of the body.


● The `color{violet}("autonomic neural system")` is further classified into `color{brown}("sympathetic neural system")` and `color{brown}("parasympathetic neural system")`

● A `color{violet}("Neuron")` is the `color{brown}("structural and functional unit")` of `color{violet}("neural system.")`

● A `color{violet}("neuron")` is a `color{violet}("microscopic structure")` composed of three major parts, namely, `color{violet}("cell body")`, `color{violet}("dendrites and axon.")`

● The `color{violet}("cell body")` contains cytoplasm with typical `color{violet}("cell organelles")` and certain granular bodies called `color{brown}("Nissl’s granules.")`

● Short `color{violet}("fibres")` which branch repeatedly and project out of the `color{violet}("cell body ")` also contain `color{violet}("Nissl’s granules")` and are called `color{brown}("dendrites.")`

● These `color{violet}("fibres transmit impulses")` towards the `color{violet}("cell body.")`

● The `color{brown}("axon")` is a `color{violet}("long fibre")`, the `color{violet}("distal end")` of which is branched.

● Each branch terminates as a `color{violet}("bulb-like structure")` called `color{brown}("synaptic knob")` which possess `color{violet}("synaptic vesicles")` containing chemicals called `color{brown}("neurotransmitters.")`

● The `color{violet}("axons transmit")` nerve impulses away from the `color{violet}("cell body")` to a `color{brown}("synapse")` or to a `color{brown}("neuro-muscular junction.")`

● Based on the number of `color{violet}("axon and dendrites,")` the `color{violet}("neurons")` are divided into three types, i.e.,

`star` `color{brown}("Multipolar")` (with one axon and two or more dendrites; found in the `color{brown}("cerebral cortex")`)
`star` `color{brown}("Bipolar")` (with one axon and one dendrite, found in the `color{brown}("retina of eye")`)
`star` `color{brown}("Unipolar")` (cell body with one axon only; found usually in the `color{brown}("embryonic stage")` ).

● There are two types of `color{violet}("axons,")` namely, `color{brown}("myelinated")` and `color{brown}("nonmyelinated.")`

● The `color{violet}("myelinated")` nerve `color{violet}("fibres")` are enveloped with `color{brown}("Schwann cells,")` which form a `color{violet}("myelin sheath")` around the axon.

● The `color{violet}("gaps between")` two adjacent `color{violet}("myelin sheaths")` are called `color{brown}("nodes of Ranvier.")`

● `color{violet}("Myelinated nerve fibres")` are found in `color{brown}("spinal and cranial nerves.")`

● Unmyelinated nerve fibre is enclosed by a `color{violet}("Schwann cell")` that does not form a `color{violet}("myelin sheath")` around the axon, and is commonly found in `color{brown}("autonomous")` and the `color{brown}("somatic neural systems.")`