Body Coordination, Senses, and Blood Circulation

Coordination Centers: Nervous & Endocrine Systems

Processing Information: The coordination centers receive information sent by the receptors, process it, generate orders, and send them to the effector organs. The coordination centers are the nervous system, which is responsible for nervous coordination, and the endocrine system, which is responsible for endocrine coordination.

Nervous System

The nervous system is responsible for analyzing the internal and external stimuli perceived by the receptors, generating orders, and sending them to the effectors. It carries out these functions through nerve impulses, which are a kind of electrical current that is transmitted between the cells that make up the nervous system. These cells are called neurons. The nervous system coordinates fast, short-lived responses, such as muscle contraction.

The Endocrine System

The endocrine system is made up of a series of endocrine glands that release the substances they generate into the bloodstream. These substances are called hormones. Hormones coordinate the internal organs by triggering chemical reactions. This system coordinates responses that are slower but longer-lasting than those coordinated by the nervous system.

Effectors and Responses

Responses: Effectors are the organs responsible for executing the body’s response. They include muscles, which respond by contracting, and endocrine glands, which respond by secreting substances.

Human Senses: How We Perceive the World

Sense of Smell (Olfaction)

Smell receptors are chemoreceptors that are sensitive to volatile or gaseous substances in the air.

How Odors Reach the Brain:

• The volatile or gaseous substances in the air enter the nasal passages.
• The olfactory cells, which are located in the upper lining of the nasal passages (called the olfactory mucosa), perceive the substances.
• This lining also contains glands that secrete mucus. We can only smell substances if they are dissolved in mucus and present in sufficient concentration.
• When the olfactory cells are stimulated, they send nerve impulses through the olfactory nerve to the brain, which interprets the information and identifies the smell.

Sense of Sight (Vision)

Sight receptors are located in the eyes and are photoreceptors that are sensitive to variations in light intensity. They enable us to see.

How Our Eyes Work:

• Light reaches the cornea, which directs it towards the pupil.
• The pupil opens or closes depending on the intensity of the light at that particular moment.
• The light then travels through the lens, which focuses it onto the retina.
• In the retina, photoreceptor cells generate nerve impulses which they send through the optic nerve to the brain, where they are converted into visual images.

Hearing and Balance: The Ear’s Functions

Receptors in the ear are mechanoreceptors responsible for either hearing or balance. Hearing receptors are called auditory cells and are sensitive to vibrations in the air; balance receptors are called balance cells and are sensitive to movements.

How the Ear Works: Hearing

• Sound waves enter the outer ear and reach the eardrum, which begins to vibrate.
• This vibration is transmitted along the ossicles to the fluid inside the cochlea.
• The movements of the fluid stimulate the hearing receptor cells, which send nerve impulses through the auditory or cochlear nerve to the brain, where they are transformed into sounds.

How the Ear Works: Balance

• The sensory balance cells are located in the semicircular canals and the cavities found at their base.
• When we move, the fluid inside these structures also moves and stimulates the balance cells.
• These cells send nerve impulses through the vestibular nerve to the brain, which provides us with information about our body’s position.

Blood Vessels: Arteries, Veins, and Capillaries

• Arteries: These are blood vessels with thick, elastic walls. They carry blood from the heart to the organs. They branch off into other, smaller arteries called arterioles.
• Veins: These are blood vessels with thinner and less elastic walls than arteries. They have valves, which prevent blood from flowing backwards. They channel the blood from the organs to the heart. They are formed by the joining of small veins called venules.
• Capillaries: These are microscopic blood vessels that reach all the cells. They join the arterioles and the venules to form a closed circuit. Their walls are very thin and allow nutrients, gases, and waste to be exchanged between the blood and the cells.