When arrector pili muscles contract (during cold or fright), the slanted hair follicle is pulled upright, dimpling the skin surface with goosebumps.
The arrector pili muscles attaches to the base of the hair and also to the dermal tissue from both the ends. When goosebumps appear, this action takes place due to the contract of these muscles. These muscles are triggered by the norepinephrine.
Hair follicle is a tube-like pore surrounding the root of the hair. These follicles are responsible for the hair growth. Various hormones, neuropeptides and immune cells are involved in this process of hair growth.
The muscles that contract (during cold or fright), the slanted hair follicle is pulled upright, dimpling the skin surface with goosebumps are called arrector pili muscle.
The arrector pili muscle are tiny muscle that attaches to the base of the hair follicle at one end and to the dermal tissue on the other end. When the body feels cold or fright the body generate heat and the arrector pili muscle contract all at once, that causes goosebumps on the skin.
The arrector pili muscle acts as the thermoregulator. Straight stand hair increases air trapping, so that the heat loss from the body decreases. The arrector pili muscle are mediated by the sympathetic nervous system.
To learn more about sympathetic nervous system here
I believe animals that possess homologous structures probably evolved from the same ancestor. Homologous structures are similar because of common ancestry. A homologous structure is an example of an organ or bone that appears in different animals, underlining anatomical commonalities demonstrating descent from a common ancestor.
Once you begin swallowing, the process becomes automatic. Your brain signals the muscles of the esophagus and peristalsis begins. Lower esophageal sphincter. When food reaches the end of your esophagus, a ringlike muscle—called the lower esophageal sphincter —relaxes and lets food pass into your stomach.
