We learn that the equator is a line around the wide waist of the world. Pleasure cruisers often make a great toâdo about crossing this line on the ocean. Any passenger who owns up to the fact that this is his first crossing may be put through ceremonies such as walking the plank and other merry goingsâon.
Ectoderm â Outer or External Layer â differentiates into the nervous system, epidermis, and the outer part of the integument system â forms the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands.
While neurons are the building blocks of the bodyâs communication system, it is the networks of neurons that allow signals to move between the brain and body. These organized networks, composed of up to one trillion neurons, make up what is known as the nervous system. The human nervous system is composed of two parts: the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which is composed of nerves and nerve networks throughout the body. The endocrine system is also essential to communication. This system utilizes glands located throughout the body, which secrete hormones that regulate a variety of things such as metabolism, digestion, blood pressure and growth. While the endocrine system is not directly linked to the nervous system, the two interact in a number of ways. The Central Nervous System The central nervous system (CNS) is made up of the brain and spinal cord.