Functionality of Cardiac and Skeletal Muscles

Authors Avatar

Tavakoli

        

Functionality of Cardiac and Skeletal Muscles

Sean Tavakoli

April 14, 2010

Section: A020

Abstract:

        Lab exercises 8 and 9 were performed to learn about the physiological properties of skeletal and cardiac muscles. In lab exercise 8, the gastrocnemius muscle was isolated from a bullfrog and several experiments were performed with a kymograph to test the effect of stimulus intensity on a muscle, the timing of muscular contraction, and testing titanic contraction. In lab exercise 9, a bullfrog heart was used to understand the properties of cardiac muscle. Cardiac muscle is very unique, because it can only be found in the heart organ. Experiments in lab exercise 9 included controlling the heart rate with four different agents: adrenalin, cold ringer’s solution, warm ringer’s solution, and acetylcholine. Additionally, the initiation and transmission of cardiac contraction was tested by stopping the SA node and finally looking at the reaction properties of cardiac muscle with the assistance of a kymograph (Stefaniak pg 84).

Introduction:

Skeletal and Cardiac muscles can be very similar. They possess the ability to contract due to the actin and myosin sliding filaments, which is a trait in every type of muscle tissue. They are also both striated and when stimulated, can cause action potentials. This means that they both follow the sliding-filament model, which is based on the interactions between the proteins myosin and actin. Actin makes up the thin filaments of a myofibril, while myosin makes up the thick filaments and together with the help of ATP, causes a muscles to physically contract (Campbell pg 1106). Despite having the same basis for contraction, cardiac and skeletal muscles are very different.

Cardiac and skeletal muscles can only be found in certain places of the body. Skeletal is only found on bones, while cardiac can only be found in the heart. Skeletal muscles voluntary contract, which means you can control the contraction and is mediated by the nervous system. There are two mechanisms that the nervous system produces graded contractions. The first is that the number of individual muscle fibers that contract can be increased in response to different levels of stimuli, known as recruitment. The heavier the force is on the muscles, the greater the stimulus and thus the more fibers stimulated to contract. The other mechanism is increasing the rate at which stimuli are sent to the muscle fibers. The more stimuli sent will mean that the muscle will have less time to relax from its contraction. This gives increased force to the tendons and muscles. When a muscle is in a sustained contraction due to a high rate of stimuli impulses, it is called tetanus (Campbell pg 1105)

Cardiac muscles are involuntarily, which means that a person cannot control them. Hearts are myogenic, so it is not controlled by the nervous system like skeletal muscles, but rather by the heart tissue itself. The pacemaker, or sino-atrial node is responsible for the contractions in the heart. Gap junctions, in intercalated disc regions of the heart allow signals that commence contractions to progress throughout the whole heart. Additionally, unlike skeletal muscles, heart muscles do not have summation or tetanus, because of a long refractory period.

Join now!

Hypothesis 1: Up to a certain point, increasing stimulus intensity (after it passes the subthreshold) will give increasingly stronger contractions for skeletal muscles.

Hypothesis 2: Rapid succession of stimuli to skeletal muscles can create tetanus.

Hypothesis 3: The effects of adrenalin and acetylcholine on cardiac muscle are integral to controlling the heart rate.

Hypothesis 4: Increasingly stronger stimulus intensity, after it passes the subthreshold, will not give a stronger cardiac muscle contraction, but it would rather all be equal.

Materials and Methods:

Hypothesis 1:

        The materials used in order to test this hypothesis are a kymograph, stimulators ...

This is a preview of the whole essay