Tag: multicellular structure: tissue

The gluteus maximus (also known as glutus maximus or, collectively with the gluteus medius and minimus, the glutes) is the largest and most superficial of the three gluteal muscles. It makes up a large portion of the shape and appearance of the hips. It permits a variety of motion and allows us to sit upright.

myosin filament is a polymerised protein. Many monomeric proteins, called meromyosin constitute one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM). The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and are known as the cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.

Muscles cannot expand. They can only contract. Hence, muscles responsible for body movements frequently occur in pairs called agonist-antagonist pairs, for example, biceps and triceps. The biceps cause movement towards the body or central axis and triceps cause movement away from the body or away from the central axis.

There are two types of muscles, voluntary and involuntary. Voluntary muscles are under our own control while involuntary muscles are not. The arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end. Each arrector pili is composed of a bundle of smooth muscle fibres, which attach to several follicles (a follicular unit) and is innervated by the sympathetic branch of the autonomic nervous system. The contraction of the muscle is, therefore, involuntary stresses such as cold, fear etc., may stimulate the sympathetic nervous system and thus, cause contraction, but the muscle is not under conscious control.

Like all other mammals, camel also have 7 cervical vertebre. The only exceptions in mammals are the manatee and the 2-toed sloth, which have 6 cervical vertebrae and the 3-toed sloth having 9 cervical vertebrae.

Shivering is an involuntary action of striated muscles ( skeletal muscles). Shivering is also called as rigors or shuddering. It is a bodily function in response to early hypothermia or just feeling cold in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Skeletal muscles around begin to shake in small movements, creating warmth by expending energy. 

Autorhythmicity is a property of electrically active cells, that show rhythmic activity without being driven by the rhythmic external stimulation, e.g., heart muscle cells or neurons.
Thus, the correct answer is option (C), 'Heart'.

The shape of the skeletal muscle is cylindrical, while that of visceral muscle is pear-shaped or spindle-shaped. Actin filaments which are thin filaments and myosin which are thick filaments are contractile proteins in the skeletal muscle as well as in the visceral muscle.
Thus, the correct answer is the option (D), 'Presence of actin and myosin filaments'.

• Cardiac muscles have the property of both the striated muscles (or skeletal muscle) and unstriated muscle or smooth muscle.
• Cardiac muscle is involuntary, which is the property of smooth muscle.
• Cardiac muscles also have features of skeletal muscles. Like skeletal muscle, cardiac muscle cross striations formed by rotating segments of thick and thin protein filaments and the primary structural proteins of cardiac muscle are myosin and actin. 
• However, skeletal muscles are voluntary as they are supplied with the somatic nerve.

The muscles in the upper arm and shoulder are striated muscles. So, option B is incorrect.
Heart possesses unique muscles, called cardiac muscles, which are involuntary striated muscles. So, option C is incorrect.
The intestinal muscles are involuntary and are smooth muscle. So, option D is incorrect.