Interaction in Humans - ESO 3 Biology and Geology

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In this section: - Summary of contents covered by this page.

The meaning of interaction and coordination in multicellular beings.
Interaction and coordination in humans: stages involved (from stimuli to receptors); organ systems involved (receptors, nervous system, endocrine system and motor apparatus).
Receptors: internal and external; types according to the stimuli detected, how the eye works; how the ear works; the skin as a receptor.
The nervous tissue: neurones (and their structure) and glial cells, nerves, nerve impulse, synapse, neurotransmitters.
The nervous system: structure, main organs (and their functions), types of nerves, types of nervous circuits.
The endocrine system: endocrine glands, hormones (main kinds and their effects), target organs and target cells, stages and types of endocrine coordination, homeostasis, endocrine glands as effectors.
The motor apparatus: main muscles and bones; the muscles as effectors.

Basic Information

Vocabulary

Coordination	One of the main three vital functions. It refers the ability of one living being to be aware of the events happening inside or outside itself and react to them accordingly. It requires (a) the detection of the stimuli by some receptor, such as the sensory organs, (b) the transmission of that sensory information to some control centre, (c) interpreting that sensory information and generating the response by the mentioned control centre, (d) transmitting the motor information that refers the response, and (e) performing the response by some effector, which, in the human body, is a muscle or a gland. In the human body, the aforementioned stages are performed by the following structures: (a) by sensory organs or disperse sensory cells; (b) by the afferent nerves; (c) by the Central Nervous System; (d) by the efferent nerves, the endocrine glands and the hormones; (e) by the muscles and the glands.
Neurone	Or neuron (Am), or nerve cell. It is the main type of cells in the nervous system. They work in groups and communicate between each other by transmitting nerve impulses. There are three types: (a) sensory neurones, which transmit sensory information from the receptors to the CNS, (b) motor neurones, which transmit the motor information from the CNS to the effectors, and (c) relay neurones, that occur in the CNS, and are the ones that decide the responses once they have interpreted the sensory information generated by a stimulus.
Nervous circuit	It is a circuit formed by a sequence of neurones that connect a receptor with an effector, in order to trigger an appropriate response to the stimulus that has been detected. It consists of, at least, one sensory neurone, one relay neurone, and one motor neurone.
Ganglion	It is a cluster of somas and dendrites of a group of neurones. They belong to the PNS, and often interconnect with other ganglia to form a more complex cluster known as a plexus.
Nerve	Bundles of bundles of axons of many neurones packed together. They belong to the PNS and (a) convey sensory information from the receptors to the CNS (afferent nerves), or (b) motor information from the CNS to the neurones (efferent nerves), or (c) both (mixed nerves).
Hormone	Chemicals secreted by the endocrine glands into the bloodstream, that act as chemical messengers, this is, they trigger certain responses in the target cells that are meant to react to some variation of the external medium (as when a secretion of adrenaline helps you to face succesfully some sort of threat) or some variation of the internal medium (as when a secretion of insulin helps you to keep an adequate level of sugar in your blood).
Target cell	The target cells (which belong to the so called target organs) are called like that because they are the specific target of an specific hormone. This means that, although the hormones are released into the bloodstrem, and therefore reach every cell in the organism, only a group of cells are going to react to the arrival of any particular hormone: these are the target cells, and what makes them be such, is the possession in the surface of their membranes of molecules that act as specific receptors to one specific hormone. It is the coupling of a hormone to those receptors what triggers the final response accomplished by the target cells (opening up your pupils, lowering the levels of glucose, etc.).

Structural Organisation of the Nervous System

Central Nervous System

· Brain (= encephalon). Enclosed by the skull and the meninges. Main organs: cerebrum, cerebellum and brain stem.
· Spinal cord. Enclosed by the backbone (= spinal column, = spine) and the meninges.

Peripheral Nervous System

· Nerves: bundles of neurones' axons. Types: afferent, efferent or mixed.
· Ganglia: clusters of neurones' somas.

Facts About Neurones

· They occur only in the Nervous System, but they are not the unique type of cells in it: there are, also, the glial cells, which assist the neurones in several tasks (nutrition, disposal of wastes, defense, regeneration...).

· They have two parts: the cell body or soma, and the nerve fibers: these are prolongations of the soma that can be two kinds: the axon (single, long, branched only at the end) and the dendrites (usually many, short and highly branched). The dendrites may be lacking.

· Their function is transmitting an electric current called nerve impulse along circuits that connect the sensory information collected by the receptors with the responses performed by the effectors.

· The nerve impulse is transmitted always in the same direction: from the dendrites (if any) to the soma, and from the soma to the axon. The axon terminals will make connections with other neurones or, at the end of the circuit, with an effector.

· Many axons (the ones of the PNS and the ones that make up the white matter of the CNS) are wrapped by Schwann cells, that make up the myelin sheath, which helps speeding up the transmission of the nerve impulse.

· The demyelination of myelinated axons is characteristic of some serious diseases such as multiple sclerosis.

· The regeneration of damaged neurones in the CNS is not possible, but the myeline layer helps regenerate the damaged axons of the PNS (only).

· Two consecutive neurones in a nervous circuit do not touch each other, and so, the nerve impulse has two "jump" over that gap (the synapse); this is acomplished by means of certain molecules called neurotransmitters (e.g. dopamine, endorphin).

· The low production of certain neurotransmitters (or the inhability to use them) is the hallmark of several diseases such as the Parkinson's disease.

Endocrine Control

In many cases, when an endocrine gland releases a hormone, it is upon request of some controlling organ, which, at the end of the hierarchical chain, is always the brain. But who tells the brain to tell the hypothalamus (the so called master gland), to tell the hypophisis to tell the breasts (via the secretion of oxytocin) to secrete milk? The sensory cells (receptors) that detect the baby's suckling do. They send nerve impulses to the brain informing of this event, and then the brain starts the chain of orders.

There are also cases in which it is the same gland that produces the hormone the one that detects the stimulus that will finally lead to the secretion of the hormone. It is the pancreas itself the organ that learns about the rise of the level of sugar in blood, and responds to it by secreting insulin. And if the pancreas notices a low level of glucose in blood, it, without asking anyone, will release glucagon, which will help to take more glucose into the blood. Insulin and glucagon are antagonist hormones, because they do opposite things. The have in common who secretes them (the pancreas) and their target organs (chiefly the liver and the muscles).

As more glucose in blood leads to less glucose in blood (through the action of the insulin) and less glucose in blood leads to more glucose in blood (via glucagon), these two are examples of negative feedback in endocrine control. But secreting milk when the baby suckles leads to keep on secreting more milk: the stimulus empowers itself, and this is called positive feedback.

External Links

Nervous System

The nervous system.To understand the human nervous system, with a special emphasis on the central nervous system. Interactive lesson at Skoool.co.uk.

The nervous system at Web-books.com.Very good overall view, with images and text, on the nervous system: cells, organs and organization. The left menu contains a link to a wide series of neurological diseases.

The nervous system at Faqs.org.Another wide overall view, with text and images, on the neurons, the organs of the nervous system and their functions, the nervous disorders, a glossary and additional readings.

Neuroscience for kids.Absolutely comprehensive site to learn everything about the neurones, the nervous system, the brain habilities, drugs, diseases... With an extensive table of contents at the top.

The nervous system.Lots of info and images on the nervous system.

The brain museum.Lots of images of both the whole brain and of cross-sections of it. Through the left menu you can access images of brains of many other mammals.

Right Brain vs. Left Brain.The test will not tell you what you're most likely to vote when you're 18, but you may want to know if you are the logical or the intuitive type.

Caffeine Facts.Learn how caffeine picks you up and which are its most remarkable effects on the nervous system.

Sensory Organs

KEWL - Our five senses.Basic introduction to vision, hearing, smell, touch and taste.

The skin at Web-books.com.Very good overall view, with images and text, on the skin and all its layers. The left menu contains a link to a wide series of skin diseases.

The ear at Web-books.com.Very good overall view, with images and text, on the ear, its sections and its functions. The left menu contains a link to a wide series of ear diseases.

The eye at Web-books.com.A first overview on the eye and its parts. The left menu contains a link to a wide series of eye diseases.

The special senses at Faqs.org.Another wide overall view, with text and images, on the eye, the ear, the sense of smell, the sense of taste, and the way they all work. Also with a description af the main sensorial pathologies, a glossary and additional readings.

Endocrine System

The endocrine system at Web-books.com.Very good overall view, with images and text, on the endocrine glands and their hormones. The left menu contains a link to a wide series of endocrine diseases.

The endocrine system at Faqs.org.Another wide overall view, with text and images, on all the endocrine glands and the way they work, the hormones and their effects, the endocrine disorders, a glossary and additional readings.

The endocrine system.To dig deeper, visit this website with lots of info and images on the endocrine system.

Motor Apparatus

The muscular system at Web-books.com.A first overview on the types of muscular tissues. The left menu contains a link to a wide series of muscle diseases.

The muscular system at Faqs.org.A wide and good overall view, with text and images, on the muscular system, the muscular cells, the main muscles, and the way they all work. Also with a description of the main muscular disorders, a glossary and additional readings.

The skeletal system at Web-books.com.A first overview on the types of bone tissues and types of bones. The left menu contains a link to a wide series of bone diseases.

The skeletal system at Faqs.org.A wide and good overall view, with text and images, on the skeletal system, the main bones, the joints, and the way they all work. Also with a description of the main skeletal disorders, a glossary and additional readings.

The muscular and skeletal systems.To dig deeper, visit this website with lots of info and images on the muscular and skeletal systems.

Movies, Animations and Audios

In this section: - Series of movies and animations related to this page's topic.

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Nervous System

Nervous system.Short introductory video on the function of the nervous system.

Backbone anatomy.Cervical spine and intervertebral disc anatomy.

Sensory Organs

Skin, nails and hair.Short introductory video on the function of the skin, the nails and the hair.

Seeing.Short introductory video on the process of seeing.

Hearing and balance (I).Short introductory video on the senses of hearing and equilibrium.

Hearing and balance (II).Hearing and equilibrium explained through drawings.

Smelling and tasting.Short introductory video on the senses of smelling and tasting.

Endocrine System

Endocrine system.Short introductory video on the function of the endocrine system and the hormones.

Motor Apparatus

Motor apparatus.Short introductory video on the function and components of the motor apparatus.

Images

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