Check Your Understanding Critical Thinking and Application Question 2 REVIEW 1 Y
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Question
Check Your Understanding Critical Thinking and Application Question 2 REVIEW 1 You dendrite? How can you tell? s this an axon or a process and you find that it generates action potentials, h it gener amining another neuron, and find that it has two processes, sthe structural class of this neuron? How did you come to this conclusion? both of which generate action potentials. You A damaged axon in the PNS may be able to regenerate only if the cell body is intact. Why do you think cell body must be intact for regeneration to occur? (Hint: Think about the function of the organelles a structures located in the cell body.) 3 Introduction to the Nervous SystExplanation / Answer
Dendrites.
Neuron is a microscopic structure which consists of 3 major parts, namely the Cell Body/ Soma/ Cyton , Dendrites and the axon. Let me explain you the functions of all these three parts in detail on by one.
Cell body basically consists of cytoplasm with cell organelles and granular bodies called as "Nissl's granules" which are the remains of Rough Endoplasmic Reticulum. Over the Cyton or the Cell body which is the main part, containing the nucelus there are a few short fibres which branch out of it and furthermore contain Nissl's granules also - this part ie, the short fibres branching out are called as "Dendrites". These are really important as they help in the transmission of impulses TOWARDS the Cyton or the Cell Body. The rod like structure which comes out of the Cell body is termed as the Axon. It's a long fibre, whose distal end is brached. The ends of these branches terminates into a bulb-like structure called "synaptic Knob" which possess the synaptic vesicles which further contain chemicals called "neurotransmitters". Function of Axon is to transmit the nerve impulses in the form of chemical impulses away from the cell body to the synapse. Synapse is basically the junction of a neuron with the muscle OR in simple words the "neuro-muscular junction". Axon is surrounded by cells known as "Schawnn cells" throughout it's lngth. The gaps between these cells on the axon Is termed as "Nodes of Ranvier". Axon is Hillock, meaning the srtucture which lacks Nissl's granules. There is a sheath termed as Mylelin sheath which encompasses the axon over the cells present. Which even further helps in the fast conduction of nerve impulses , conduction is known as the Saltatory Conduction. The neurons which lack this sheath are slower in conduction comparatively. And their conduction is known as "Continuous Conduction". Neurons are basically the excitable cells as their membranes are always in a polarized state. There are different kinds of ion channels present over the membranes of axons in order to help transfer ions from outside to inside and vice versa. These channels are Selectively permeable to different ions. We do know, that The amount of Pottasium ions inside our cells is more compared to the number of K+ ions outside the cells. So when a neuron isn't conducting any impulse, it possesses the tendency to take in Potassium ions and NOT Sodium ions. ie, permeable to Pottasium ions and immpermeable to Sodium ions. Whereas outside the neuron, there is a huge amount of Na+ ions distributed and lesser of Pottasium ions. Thereby creating a concentration gradient. These ionic gradients across the resting axonal membrane are maintained by the active transport of ions by Sodium-Potassium pump which transports 3 sodium ions outside and 2 Potassium ions into the cell. Hence, due to this the outer surface of the axonal membrane gets a positive charge while it's inner surface get's the negative charge. and therefore gets polarized. This electrical potential difference across the resting plasma membrane of the axon is called as the resting potential.
Now, to this state, if a stimulus has been applied at a site say SITE 1, this membrane at point SITE 1 bcomes permeable to Sodium ions. This leads to a rapid influx of Na ions which is further followed by the reversal of the polarity at that SITE 1. To be more clear, the outer surface of the axonal plasma membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at that SITE 1 is thus reversed and hence, depolarised. This electrical potential difference across the axonal plasma membrane at SITE 1 is called as ACTION POTENTIAL. ( the electrical nerve impulse via which info is transfered from one neuron to the next via the synapse in form of neurotransmitters ). and now as the nerve impulse glides further the previous site's polarity changes to that of the resting membrane's polarity attaining the resting potential. This continues until the Concentration of Ions doesn't get back to normal. The rise in the stimulus induced permeability to Na ions is very short lived, it is quickly accompained by the rise in permeability of K+ ions and within nano seconds K+ diffuses outside the axonal membrane and restores the resting mebrane potential at the site of excitation and the fibre becomes ready to take in an other stimulus and repeat it's activity.
Hope that helps, Cheers !