Question

Please formulate a short essays on:

1) Movement, muscle contraction and the Sliding Filament Theory. Include all the components at the molecular level of muscle contraction.

2) Sex differences & the Brain - Development of Males/Females and if you choose this essay please address Intersex babies and how they teach us about the Masculine or Feminine brain and its development.

3) James Papaez circuit or the "Emotion system" that is based on earlier work by Cannon-Bard. Please include the anatomy of the various structures that are in the circuit as well as the connections by those structures to the Dorsal and Ventral connections of the Anterior Cingulate Cortex (ACC) and how they are related to the Emotional expression, emotional experience and emotional coloring of a phenomenon.

Answer 1

1. Muscles contract by the interdigitation of protein filaments within them. These filaments are made of myosin and actin molecules. The head part of each myosin molecule is thought to interact with the actin filament in a cyclic manner driven by ATP hydrolysis, with each stroke of the cycle causing about 10nm of movement.

A muscle contraction can be explained by the cycle of molecular events that take place between actin and myosin filaments. Infact a myosin filament has many myosin heads. Each myosin filament is also surrounded by six actin filaments to which the different myosin heads can bind. Therefore, when a myosin head breaks it's contact with actin, other myosin heads still connect to actin filaments and thus prevent the sarcomere from sliding back to its relaxed position. So molecular level of muscle contraction is defined by myosin molecules pulling actin filaments. Sliding filament theory describes the position of myosin and actin filaments at various stages of contraction in muscle fibres.

Muscle contraction provides animals with great flexibility, allowing them to move in exquisite ways. The molecular changes that result in muscle contraction have been conserved across evolution in the majority of animals. By studying sarcomeres, the basic unit controlling changes in muscle length, scientists proposed the sliding filament theory to explain the molecular mechanism behind muscle contraction. Within the sarcomere, myosin slides along actin to contract the muscle fibres in a process that requires ATP. Scientists have also identified many of the molecules involved in regulating muscle contraction and motor behaviours, including calcium, troponin, and tropomyosin. This helped to know how muscles can change their shapes to produce movements.

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