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| Stimulus (physiology) |
Stimulus (physiology)In physiology, a stimulus is a detectable change in the internal or external environment.
When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction.
A stimulus is often the first component of a homeostatic control system.
When a sensory nerve and a motor nerve communicate with each other, it is called a nerve stimulus.
category:physiology
PhysiologyPhysiology (in Greek physis = nature and logos = word) is the study of the mechanical, physical, and biochemical functions of living organisms.
Physiology has traditionally been divided into plant physiology and animal physiology but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells.
The field of animal physiology extends the tools and methods of human physiology to non-human animal species. Plant physiology also borrows techniques from both fields.
Its scope of subjects is at least as diverse as the tree of life itself. Due to this diversity of subjects, research in animal physiology tends to concentrate on understanding how physiological traits changed throughout the evolutionary history of animals.
Other major branches of scientific study that have grown out of physiology research include biochemistry, biophysics, biomechanics, and pharmacology.
History
It was Abu Bakr Al Razi (popularly known as Rhazes) who described certain physiological parameters when he went to establish a hospital at Baghdad in the eighth century AD. Razi was followed by Al Kindi, who wrote a treatise on human physiology. Anatomist William Harvey described blood circulation in the 17th century, providing the beginning of experimental physiology. Herman Boerhaave is sometimes referred to as the father of physiology due to his exemplary teaching in Leiden and textbook 'Institutiones medicae'(1708).
Areas of physiology
Human and animal
Human physiology (main article) is the most complex area in physiology. This area has several subdivisions which overlap with each other. Many animals have similar anatomy to humans and so share many of these areas.
- myophysiology deals with the operation of muscles
- neurophysiology concerns the physiology of brains and nerves
- cell physiology addresses the functioning of individual cells
- membrane physiology focuses on the exchange of molecules across the cell membrane
- respiratory physiology goes into the mechanics of gaseous exchange at the lung
- circulation also known as cardiovascular physiology, deals with the heart, blood and blood vessels and issues arising
- renal physiology focuses on the excretion of ions and other metabolites at the kidney
- endocrinology covers endocrine hormones which affect every cell in the body
- neuroendocrinology concerns the complex interactions of the neurological and endocrinological systems which together regulate physiology
- reproductive physiology concerns the reproductive cycle
Plant
Plant physiology has differing subdivisions. For example, since plants do not have muscles and nerves, neither myophysiology nor neurophysiology applies.
- Transpiration is the study of water loss from the plant leaves
- Photosynthesis is the conversion of sunlight energy, water and CO2 to form sugars (glucose).
Category : Subjects Taught in Medical School
ja:生理学
simple:Physiology
th:สรีรวิทยา
Sensory receptorIn a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. In response to stimuli the sensory receptor initiates sensory transduction by creating graded potentials or action potentials in the same cell or in an adjacent one.
Location
The sensory receptor may be a specialized portion of the plasma membrane, or a separate cell associated with a neuron ending.
Functions
The sensory receptors involved in taste and smell contain receptors that bind to specific chemicals. Odor receptors in olfactory receptor neurons, for example, are activated by interacting with molecular structures on the odor molecule. Similarly, taste receptors (gustatory receptors) in taste buds interact with chemicals in food to produce an action potential.
Other receptors such as mechanoreceptors and photoreceptors respond to physical stimuli. For example, photoreceptor cells contain specialized proteins such as rhodopsin to transduce the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically streched.
The sensory receptor functions as the first component in a sensory system.
Sensory receptors respond to specific stimulus modalities. The stimulus modality to which a sensory receptor responds is determined by the sensory receptor's adequate stimulus.
The sensory receptor responds to its stimulus modality by initiating sensory transduction.
Classification by adequate stimulus
The sensory receptor's adequate stimulus is the stimulus modality to which a sensory receptor responds by initiating sensory transduction. Adequate stimulus can be used to classify sensory receptors:
- Chemoreceptors respond to chemical signals
- Mechanoreceptors respond to touch or pressure
- Thermoreceptors respond to heat
- Photoreceptor cells respond to light
- Baroreceptor cells respond to pressure
- Osmoreceptor cells respond to the level of fluids (such as in the hypothalamus)
- Proprioreceptor cells respond to motion, position or balance
Classification by location
Sensory receptors can be classified by location:
- Cutaneous receptors are sensory receptors found in the dermis or epidermis.
- Muscle spindles contain mechanoreceptors that detect stretch in muscles.
See also
- Sense
- Sensory neuron
- Proprioception
Category:Sensory receptors
Stimulus transductionIn physiology, transduction is the conversion of a stimulus from one form to another.
Transduction in the nervous system typically refers to synaptic events wherein an electrical signal, known as an action potential, is converted into a chemical one via the release of neurotransmitters. Conversely, in sensory transduction a chemical or physical stimulus is transduced by sensory receptors into an electrical signal.
For example, in the visual system, sensory cells called rod cells in the retina convert the physical energy of light signals into electrical impulses that travel to the brain. The light causes a conformational change in a protein called rhodopsin. This conformational change sets in motion a series of molecular events that result in a reduction of the electrochemical gradient of the photoreceptor. The decrease in the electrochemical gradient causes a reduction in the electrical signals going to the brain. Thus, in this example, more light hitting the photoreceptor results in the transduction of a signal into fewer electrical impulses.
category:physiology
Category:Physiology
Physiology is the branch of science that describes mechanisms and functions in organisms.
physiology
Category:Medicine
ja:Category:生理学
Willi HennigWilli Hennig (20 april 1913 – 5 november 1976) was een Duitse bioloog en wordt algemeen gezien als de 'vader' van het taxonomische systeem van de cladistiek.
Externe link
- [http://www.cladistics.org/about/hennig.html info over Willi Hennig]
Hennig, Willi
Hennig, Willi
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