Biology Question Essay Example | Topics and Well Written Essays - 1250 words

Biology Question - Essay Example The neurons transmit information to each other through the dendrites. Action potentials are however comparably large in size. They signal strength of stimulus by frequency and not by amplitude. Graded potentials on the other hand are generated in dendrites and sensory receptors. Graded potentials sometimes generate action potentials and thus referred to as generator potentials. In case of an incoming signal, a pre synaptic excitatory neuron fires releasing neurotransmitters to the synaptic cleft. Consequently, if the transmitter binds to the post synaptic dendritic membrane, it elicits a transient depolarization called Excitatory Post Synaptic Potential (EPSPs) (Akers and Denbow 214). Inhibitory neurons on the other hand, elicit partial hyper-polarizations known as Inhibitory Post Synaptic Potentials (IPSPs) (Akers and Denbow 214). Summarily, EPSPs and IPSPs are both graded potentials. Finally, a number of pre synaptic neurons maybe firing simultaneously, hence impacting on the level of activity of post synaptic neurons. Hence, the total potential in the post synaptic neuron; that is, Grand Post Synaptic Potential (GPSP) is a summation of all EPSPs and IPSPs occurring approximately simultaneously (Dowling 242). 2) What is the functional significance of spatial and temporal summation being performed by axon hillocks of neurons? Axon hillock is the most excitable portion of a neuron. It is the region at the beginning of an axon. Action potentials are generated in this region. The occurrence of an action potential at the axon hillock is by either temporal summation or spatial summation. Action potentials usually occur in three stages, namely Resting, Depolarization and Repolarization phases. (Brown, Miller and Eason 223).Temporal summation simply refers to addition of a number of EPSPs that manifest close together in time, as a result of a subsequent firing of a single presynaptic neuron. Conversely, spatial summation refers to addition of EPSPs originating at the same time from several pre-synaptic neurons (Sherwood 107). This implies that the position of a synapse on the neuron is significant in determining the generation of an action potential. Summarily, synapses closer to the axon hillock have higher level of activity than those further away. Furthermore, the central integrative state of a neuron is also determined by temporal and spatial summation (Beck 135). 3) How are action potentials generated at axon hillocks and propagated along unmyelinated axons? Action potential is propagated along unmyelinated axon by a mechanism known as continuous propagation. The membrane is considered as a sequence of adjacent segments. The action potential starts at the initial segment. In the first step, the transmembrane potential becomes briefly positive, rather than negative. In the second step, a local current develops due to the influx of sodium ions into the cytosol and extracellular fluid, and in step three and four, the local current spreads in all directions hence depolarizing adjacent segments of the membrane. Usually, the axon hillock like the rest of the cell body, cannot respond with action potential because it lacks gated ion channels. However, when the initial portion of the axon is depolarized to threshold, an action potential develops there. The process thus proceeds in a chain reaction until distant portions of cell are afflicted. Every time a local current occurs, action potential moves forward, and not backward, since

Medieval ages and Modern time Essay Example | Topics and Well Written Essays - 1250 words

Medieval ages and Modern time - Essay Example However, the period laid most of the foundation in modern time professions and beliefs that still persists in most rural and indigenous societies around the globe. Among the trained people who defended the medieval societies were archers, foot soldiers, and the most explicit group referred as the knights. The knights were ranked the richest of all soldiers in the time, and were equipped with more expertise than others. Any knight had to pass through a session of training, and could only become one through his valor prior or after battles, or if he was a son of a noble family (â€Å"Becoming a knight,† thinkquest.org). This selection criterion is quite different in the modern society for individuals desiring to pursue military. Of course, it did prevent individuals in the society who would have liked to be come one, but since they were not from noble families or could not express their courage, they missed out the chance. The knights dressing code was rather heavy and uncomfortable especially under the hot sun. Apart from their linen shirt and a pair of pants, they wore woolen pads underneath the metal ringed tunic, which was later repla ced with metal plates, covering most of their body parts (â€Å"The Medieval knight,† thinkquest.org). They highly used swords, knives and spears as defense weapons and held tournaments to exercise their loyalty in service while acting as mock battles in front of audience. Basically the knight was purposefully skilled to protect his lord and the castle against external attacks more than the entire society. In the modern society, military selection is open for individuals who qualify to a certain level, without being biased to social status not unless the system is corrupt, it doe not matter whether one comes from poor or rich background, but the procedure follows strictly and individuals who qualify can specialize in the profession. The purpose for the military is to serve the area of jurisdiction by ensuring its