Anatomy – Bodily Systems, Coursework Example

Interdependent Actions In Ascending Stairs to Answer a Ringing Telephone

A Gestalt Analysis

The telephone rings. Cognitively, your ears are able to take in the sound; the mind interprets the meaning of the sound as a telephone ringing, recognizes the need to answer the phone, and sends the body in motion toward the direction of the sound at a quickened pace, with the additional understanding that the phone must be answered promptly or it may stop ringing. The body’s musculoskeletal synergy function enables the body to move once the brain has sent the appropriate signals to the appropriate muscles.

Sound is drawn into the outer ear canal after entry through the pinna. The eardrum vibrates relative to the frequency of the noise, which is the phone ringing in this scenario. Immediately following that, the hammer, stirrup and anvil vibrate. They comprise the middle ear. The vibration continues its movement to the cochlea. At this point, the minute hairs that line the membrane of the cochlea create an electric impulse, sending a message to the brain about the exact sound that arose and the direction from which it came. The average human ear is able to interpret sounds between the range of 20 to 20,000 Hertz (Marieb, p335).

On a macroscopic level, the brain first makes the decision to step up the stairs in the frontal lobe of the brain. It is after this that the signal travels to the motor cortex and shoots down through the cerebellum to the spinal cord out of the peripheral nerves and across the neuromuscular junction to each muscle involved in the process of stepping up one step onto a ladder.

The electric impulse travels from the dendrites of the neuron to the axon where it is expelled across the synapse to the next dendritic end which will receive the signal and continue on to its axon. This action is repeated from the brain down to the actual muscles used in the action of stepping up on the stair. Initially, the brain is at a resting potential, with Na⁺ at 15 mM (Millimoles per liter) within the membrane and Na⁺ at 150 mM on the outside of the membrane (Dupuy, 2006). The K⁺ is approximately 150 mM within the membrane and outside of the membrane the level of K⁺ is 5mM (Ibid). This polarized state represents the action potential of the resting membrane. Although the Na⁺ wants to diffuse into the membrane but can only do this at a slower rate than the K⁺ that steadily leaves the membrane. This disparity in the rate of positive ions leaving and entering the cell creates a relative negativity within the membrane. This membrane potential of about -70mV negative within the membrane causes the return at a rate of 3Na⁺ out of the cell for every 2K⁺ transport back into the cell (Ibid).

The first event when a chemical signal is fired off is the depolarization of the membrane, which causes the sodium channels to open up and the voltage-regulated Ca⁺² channel in the presynaptic axonal terminal. The opening of the calcium channel is brief and in this time, the Ca⁺² ions flood into the terminal from the extracellular fluid. Then the chemical signal acetylcholine is released via exocytosis due to the flood of calcium into the terminal axon of the presynaptic cell. The synaptic vesicles then merge with the axonal membrane and empty the contents into the synaptic cleft. The calcium ions are then removed by mitochondria or an active calcium pump. At this point the neurotransmitter acetylcholine binds to the postsynaptic vesicle, taken in by the dendrites of the neighboring neuron. Receptor proteins accept acetylcholine and send it through to the axonal terminal where this process will repeat until the chain of neurons finally reach the neuromuscular junctions of the muscles involved in stepping up.

Macroscopically, in reaching out for the phone, the long head of the biceps brachii muscle contracts, pulling on the humerus to cause flexion across the shoulder’s ball and socket joint to raise the arm and reach for the glass of water. The forearm extends with the contraction of the triceps at the elbow’s hinge joint and the receiver is gripped by the interossei which are used to rotate the phalanges and the flex the metacarpophalangeal muscles. The receiver is then brought toward the ear with the flexion of the biceps brachii at the elbow, bending the forearm and decreasing the angle between the ulna and the humerus bone.

On a microscopic level, the sliding filament theory involves actin filaments sliding along the myosin filaments which pull the z lines of the muscle cells. The cross bridges on the myosin filament attach to the actin filament pulling them inward as the myofibril contracts (Marieb, 2007). The sarcoplasmic reticulum stores the calcium which is released upon being stimulated by the acetylcholine crossing the neuromuscular junction and entering it. The calcium then binds with troponin which is located in the actin filaments causing tropomysosin to make the actin and myosin bridges flex quickly (Marieb, 2007). Once the cross bridges pull the actin in, the cross bridge detaches from the actin and repeats the process all over again. ATP binds to the cross bridge, causing the detachment. Then with the hydrolysis of the ATP, ADP is formed and the cross bridges are replaced in their original positions. This is followed by the flow of Ca⁺² back into the sarcoplasmic reticulum.

References

Dupuy, A. Molecular Motion. New York: Simon & Schuster, 2006

Marieb, E. Anatomy & Physiology. San Francisco: Pearson Education, Inc., 2007

Rubin, Emanuel et. al.. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. Philadelphia, PA: Lippincott Williams & Wilkins, 2005