Question

Explain:

(a) Myelinated axon: Some neurons, like most of the neurons in human body, have myelinated axons; the axons are wrapped around with segmented myelin sheaths. When compared with unmyelinated axons of the same axon diameter, the neural signal transmission speed along myelinated axons is much faster than that along unmyelinated axons. Qualitatively and briefly explain why.

(b) Hopfield model: Hopfield model can be considered as a form of neural net algorithm of retrieving information from a large database. When we compare the functioning of the Hopfield model with that of conventional database algorithms where information retrieval is carried out by examining all the entries in the entire database, one at a time, in view of retrieval criteria, what are the most significant differences? Qualitatively and briefly describe at least two significant differences. Assume that the database is very large.

Answer 1

(a). The transmission of neural signal is faster in myelinated axon than that of the unmyelinated axon due to saltatory conduction. The myelinated axons are covered by segments of myelin sheath with a gap of about 1micron (nodes of ranvier) in between them rather than being uniformaly covered. The node of ranvier aid the saltatory conduction(the action potential jumps from 1 node to another) by generating the action potential due to accumulation of clusters of voltage gated sodium channels. Also the myelin sheath provides insulation to the axon so that no impulse diffuses out of it thus increasing the speed of electrical impulse transmission.

(b). The hop field model consist of a network of neurons. Hopfield nets serve as associative memory systems with binary threshold nodes. These converge a local minimum and may converge to a false pattern rather than the stored pattern. Hopfield networks also provide a model for understanding human memory. The units of hopfield nets are binary threshold units,.i.e. Units only take on 2 different values for their states and value is determined by whether or not the unit input exceeds their threshold.