Muscles - class-VII

Extensor muscles. Attached to the back of the spine, these muscles allow us to stand and lift objects. They include the large muscles in the lower back (erector spinae), which help hold up the spine, and gluteal muscles.

The stapedius muscle, which is innervated by the facial nerve (cranial nerve VII), is the smallest of all skeletal muscles.

The gluteus maximus is the largest muscle in the human body. These muscles help move the hips and thighs and also keep the trunk of the body in upright position. These muscles work against the gravity when we are walking up stairs. So, the correct answer is 'Gluteus maximus'.

Smooth muscles (found in organs) and cardiac muscles (found in the heart) are involuntary. Striated (skeletal) muscles are voluntary.

Skeletal muscles are involved in contraction and relaxation. An action potential travels through the motor neuron. The motor neurons are linked to the muscle fibers at the neuromuscular junction. When this nervous signal reaches the neuromuscular junction the neurotransmitter called acetylcholine is released. This neurotransmitter binds to the receptors on the surface of the muscle fiber leading to muscular contraction. Thus the correct answer is option A.

• Joints are points of contact between bones, or between bones and cartilages.
• Synovial joints are characterized by the presence of a fluid-filled synovial cavity between the articulating surfaces of the two bones. These joints help in locomotion and many other movements. The hinge joint is a type of synovial joint.
• extension refers to movement in the posterior direction. For example, when standing up, the knees are extended.
• Hence standing on tiptoe(HINGE JOINT AT ANKLE) is an example of an extension.
• So, the correct answer is 'Elevation'.

• A muscle that draws a body part backward is called Retractor.
• For example, The horizontal fibers of the temporalis muscle serve to retract the mandible(lower jaw).
  
• Hence retractor muscles move the lower jaw, tongue and the head backward.
• So,the correct answer is 'Retractor'.

• Sarcoplasm is the cytoplasm of a myocyte (muscle fibre, muscle cell).
•  It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen-binding protein. Hence, the Cytoplasm of a muscle cell is sarcoplasm.

• Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. 
• It is distantly related to haemoglobin which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. Hence, Muscles contain a red coloured oxygen-storing pigment called myoglobin.

• Muscle contains a red coloured oxygen-containing pigment called myoglobin. It is similar to hemoglobin pigment that stores oxygen in the blood cells. Myoglobin binds oxygen with its heme group.

1. sarcoplasmic reticulum is a specialized type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells. 
   
3. sarcoplasmic reticulum  is a membrane-bound structure found within muscle is also known as endoplasmic reticulum of muscle. so option A is correct answer .

• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
  
• In the centre of each ‘I’ band, there is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. 
• The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called sarcomere.
• Hence Sarcomere is the unit of contraction.
  

• Muscle is a  bundle of fibrous tissue in a body that has the ability to contract, producing movement in or maintaining the position of parts of the body.
  
• The total number of muscles in the human body comes in the range of 640-850.
  
• So,the correct answer is '640-850'

Movement is performed by muscular tissues. Every bone moves with the help of 2 muscles required to move it. 

•  Syncytial or syncytium is a multinucleated cell that can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus), which can result from multiple nuclear divisions without accompanying cytokinesis. 
• Syncytial is also referring to cells interconnected by the specialized membrane with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential. Hence, Condition of having a number of nuclei in a muscle fibre is syncytial.

• Cardiac muscle is specialized tissue that is found only in the heart.
•  It has characteristics similar to both smooth and skeletal muscle tissue, as well as specialized properties, that allow it to function with fast but sustained contractions, rapid conduction and coordinated movement. Hence,  the property of cardiac muscle is involuntary muscles, resistant to fatigue and striated muscle.

• The two major types of muscles that make up the calf (back portion of the lower leg) are gastrocnemius and soleus muscle.
• Along with the soleus muscle, the gastrocnemius forms half of the calf muscle. Its function is plantar flexing the foot at the ankle joint and flexing the leg at the knee joint.
  
• Hence gastrocnemius muscles are found in shank(a person's leg, especially the part from the knee to the ankle).
• So, the correct answer is 'Shank'.