Anatomy and Physiology – Sensory Physiology

Anatomy and Physiology – Sensory Physiology

Sensory Physiology

• All sensory receptors can be classified by their structure and by the type of
• stimulus that they detect. Structurally, there are 3 classes of sensory
• receptors: free nerve endings, encapsulated nerve endings, and specialized
• cells. Free nerve endings are simply free dendrites at the end of a neuron that
• extend into a tissue. Pain, heat, and cold are all sensed through free nerve
• endings. An encapsulated nerve ending is a free nerve ending wrapped in a
• round capsule of connective tissue. When the capsule is deformed by touch
• or pressure, the neuron is stimulated to send signals to the CNS. Specialized
• cells detect stimuli from the 5 special senses: vision, hearing, balance, smell,
• and taste. Each of the special senses has its own unique sensory cells—such
• as rods and cones in the retina to detect light for the sense of vision.
• Functionally, there are 6 major classes of receptors: mechanoreceptors,
• nociceptors, photoreceptors, chemoreceptors, osmoreceptors, and
• thermoreceptors.
• Mechanoreceptors. Mechanoreceptors are sensitive to mechanical stimuli
• like touch, pressure, vibration, and blood pressure.
• Nociceptors. Nociceptors respond to stimuli such as extreme heat, cold, or
• tissue damage by sending pain signals to the CNS.
• Photoreceptors. Photoreceptors in the retina detect light to provide the sense
• of vision.
• Chemoreceptors. Chemoreceptors detect chemicals in the bloodstream and
• provide the senses of taste and smell.
• Osmoreceptors. Osmoreceptors monitor the osmolarity of the blood to
• determine the body's hydration levels.
• Thermoreceptors. Thermoreceptors detect temperatures inside the body and
• in its surroundings.
• The Nervous System and Reflexes
• In general, nerve function is dependent on both sensory and motor fibers,
• sensory stimulation evoking motor response. Even the autonomic system is
• activated by sensory impulses from receptors in the organ or muscle. Where
• especially sensitive areas or powerful stimuli are concerned, it is not always
• necessary for a sensory impulse to reach the brain in order to trigger motor
• response. A sensory neuron may link directly to a motor neuron at a synapse
• in the spinal cord, forming a reflex arc that performs automatically. Thus,
• tapping the tendon below the kneecap causes the leg to jerk involuntarily
• because the impulse provoked by the tap, after traveling to the spinal cord,
• travels directly back to the leg muscle. Such a response is called an
• involuntary reflex action.
• Commonly, the reflex arc includes one or more connector neurons that exert
• a modulating effect, allowing varying degrees of response, e.g., according to
• whether the stimulation is strong, weak, or prolonged. Reflex arcs are often
• linked with other arcs by nerve fibers in the spinal cord. Consequently, a
• number of reflex muscle responses may be triggered simultaneously, as
• when a person shudders and jerks away from the touch of an insect. Links
• between the reflex arcs and higher centers enable the brain to identify a
• sensory stimulus, such as pain; to note the reflex response, such as
• withdrawal; and to inhibit that response, as when the arm is held steady
• against the prick of a hypodermic needle.
• Reflex patterns are inherited rather than learned, having evolved as
• involuntary survival mechanisms. But voluntary actions initiated in the brain
• may become reflex actions through continued association of a particular
• stimulus with a certain result. In such cases, an alteration of impulse routes
• occurs that permits responses without mediation by higher nerve centers.
• Such responses are called conditioned reflexes, the most famous example
• being one of the experiments Ivan Pavlov performed with dogs. After the
• dogs had learned to associate the provision of food with the sound of a bell,
• they salivated at the sound of the bell even when food was not offered. Habit
• formation and much of learning are dependent on conditioned reflexes. To
• illustrate, the brain of a student typist must coordinate sensory impulses
• from both the eyes and the muscles in order to direct the fingers to particular
• keys. After enough repetition the fingers automatically find and strike the
• proper keys even if the eyes are closed. The student has "learned" to type;
• that is, typing has become a conditioned reflex.
• Disorders of the Nervous System
• A number of diseases can significantly affect the proper functioning of the
• nervous system. Parkinson's disease, Huntington's disease, myasthenia
• gravis, andamyotrophic lateral sclerosis (commonly known as Lou Gehrig's
• disease) are some of the more severe diseases affecting the nervous system.
• Strokes, which are related to circulatory disorders, also may have permanent
• effects on the nervous system. Certain plant derivatives, such
• as belladonna, cocaine, and caffeine, have a variety of stimulatory,
• inhibitory, and hallucinatory effects on the nervous system.
• Sense organs
• Aristotle (384 BC – 322 BC) is credited with the traditional classification of
• the five sense organs: sight, smell, taste, touch, and hearing. As far back as
• the 1760's, the famous philosopher Immanuel Kant proposed that our
• knowledge of the outside world depends on our modes of perception. In
• order to define what is "extrasensory" we need to define what is "sensory".
• Each of the 5 senses consists of organs with specialized cellular structures
• that have receptors for specific stimuli. These cells have links to the nervous
• system and thus to the brain. Sensing is done at primitive levels in the cells
• and integrated into sensations in the nervous system. Sight is probably the
• most developed sense in humans, followed closely by hearing.
• An organ of the body which responds to external stimuli by conveying
• impulses to the sensory nervous system. The sense organs — eyes, ears,
• tongue, skin, and nose — help to protect the body. The human sense organs
• contain receptors that relay information through sensory neurons to the
• appropriate places within the nervous system.
• Each sense organ contains different receptors.
• General receptors are found throughout the body because they are
• present in skin, visceral organs (visceral meaning in the abdominal
• cavity), muscles, and joints.
• Special receptors include chemoreceptors (chemical receptors) found in
• the mouth and nose, photoreceptors (light receptors) found in the eyes,
• and mechanoreceptors found in the ears.
• There are five senses: sight, hearing, taste, smell and touch. There are organs
• connected with these sense that take in information that is sent to the brain
• so that the body can act on it.
• We use senses to gauge or understand the environment around us. In order
• for us to use our senses, we needstimuli. Stimuli are signals. These signals
• are gathered by receptors, and then neurons transmit the signal to the brain
• for interpretation. Your brain interprets the stimuli and responds
• accordingly. Sometimes, in response to stimuli, the brain will send back a
• signal for you to move your hand if something is too hot; or maybe the brain
• will tell you to continue to feel an object to get more information. Each of
• the senses has different receptors that gather stimuli before sending it to the
• neurons for transmission to the brain.
• You can think of the process of stimuli getting to the brain as a relay race.
• The receptors are the first person in a relay race, and the stimuli is the baton
• that gets passed along. Neurons are the second person in the replay race, and
• receptors pass the baton or the stimuli to the neurons. Lastly, the neurons
• pass the stimuli to the brain for interpretation.
• The five senses are the five main tools that humans use to perceive the
• world. Those senses are sight, smell, hearing, taste, and touch. We see with
• our eyes, we smell with our noses, we listen with our ears, we taste with our
• tongue, and we touch with our skin. Our brain receives signals from each of
• these organs, and interprets them to give us a sense of what's happening

around us.

The Five Senses

• Neurologists might argue that in reality there are far more than five senses –
• anywhere from 9 to 21. These include things like perception of heat,
• pressure, pain, and balance, among others.
• But the five basic senses are still useful to know and far easier to remember.
• They're vitally important to how our bodies operate. Without our senses, we
• wouldn't have any idea what was going on around us and the human body
• would be functionally useless. Each of the senses therefore provides
• important functions and serves a particular intended purpose. Let's talk about
• some of those functions.
• What Are the Functions of the Five Senses?
• Eyes obviously allow us to see. But if you break it down, they do a more
• than just that. Using our eyes, we can judge depth, interpret new
• information, and identify color (the wavelengths of light that reflect off
• surfaces).
• Seeing is believing: Sight
• The eye is the organ of vision. It has a complex structure consisting of a
• transparent lens that focuses light on the retina. The retina is covered with
• two basic types of light-sensitive cells-rods and cones. The cone cells are
• sensitive to color and are located in the part of the retina called the fovea,
• where the light is focused by the lens. The rod cells are not sensitive to
• color, but have greater sensitivity to light than the cone cells. These cells are
• located around the fovea and are responsible for peripheral vision and night
• vision. The eye is connected to the brain through the optic nerve. The point
• of this connection is called the "blind spot" because it is insensitive to light.
• Experiments have shown that the back of the brain maps the visual input
• from the eyes.
• The brain combines the input of our two eyes into a single three-dimensional
• image. In addition, even though the image on the retina is upside-down
• because of the focusing action of the lens, the brain compensates and
• provides the right-side-up perception. Experiments have been done with
• subjects fitted with prisms that invert the images. The subjects go through an
• initial period of great confusion, but subsequently they perceive the images
• as right side up.
• The range of perception of the eye is phenomenal. In the dark, a substance
• produced by the rod cells increases the sensitivity of the eye so that it is
• possible to detect very dim light. In strong light, the iris contracts reducing
• the size of the aperture that admits light into the eye and a protective obscure
• substance reduces the exposure of the light-sensitive cells. The spectrum of
• light to which the eye is sensitive varies from the red to the violet. Lower
• electromagnetic frequencies in the infrared are sensed as heat, but cannot be
• seen. Higher frequencies in the ultraviolet and beyond cannot be seen either,
• but can be sensed as tingling of the skin or eyes depending on the frequency.
• The human eye is not sensitive to the polarization of light, i.e., light that
• oscillates on a specific plane. Bees, on the other hand, are sensitive to
• polarized light, and have a visual range that extends into the ultraviolet.
• Some kinds of snakes have special infrared sensors that enable them to hunt
• in absolute darkness using only the heat emitted by their prey. Birds have a
• higher density of light-sensing cells than humans do in their retinas, and
• therefore, higher visual acuity. Color blindness or "Daltonism" is a common
• abnormality in human vision that makes it impossible to differentiate colors
• accurately. One type of color blindness results in the inability to distinguish
• red from green. This can be a real handicap for certain types of occupations.
• To a colorblind person, a person with normal color vision would appear to
• have extrasensory perception. However, we want to reserve the term
• "extrasensory perception" for perception that is beyond the range of the
• normal.
• When you look at an eye, the iris is the colored part. The iris actually is a
• pigmented muscle that controls the size of the pupil, which dilates to allow
• more light into the eye or contracts to allow less light into the eye. The iris
• and pupil are covered by the cornea.
• Behind the pupil is an anterior chamber. Behind the anterior chamber is
• thelens. The ciliary body contains a small muscle that connects to the lens
• and the iris. The ciliary muscle changes the shape of the lens to adjust for far
• or near vision. The lens flattens to see farther away, and it becomes rounded
• for near vision. The process of changing the shape of the lens is called
• accommodation. People lose the ability of accommodation as they grow
• older, prompting the need for glasses.
• Behind the lens of the eye is the vitreous body, which is filled with a
• gelatinous material called vitreous humor. This substance gives shape to the
• eyeball and also transmits light to the very back of the eyeball, where
• the retina lies. The retina contains photoreceptors, which detect light.
• Two types of sensors detect light:
• Rods detect motion. The rods work harder in low light.
• Cones detect fine detail and color. The cones work best in bright light.
• There are three types of cones: one that detects blue, one that detects
• red, and one that detects green. Color blindness occurs when one type of
• cone is lacking.
• When light strikes the rods and cones, nerve impulses are generated. The
• impulse travels to two types of neurons: first to bipolar cells and then to
• ganglionic cells. The axons of ganglionic cells form the optic nerve.
• The optic nerve carries the impulse directly to the brain. Approximately 150
• million rods are in a retina, but only 1 million ganglionic cells and nerve
• fibers are there, which means that many more rods can be stimulated than
• there are cells and nerve fibers to carry the impulses. Your eye must
• combine ―messages‖ before the impulses are sent to the brain.
• The eye is the organ of the sense of sight. Eyes detect light, and convert it to
• electro-chemical impulses in neurons.
• Parts of the eye:
• The transparent window at the front of the eye which is covered in a thin
• layer of tears.
• Aqueous humor On the other side of the cornea is more moisture. This
• clear, watery fluid is the aqueous humor. It circulates throughout the front
• part of the eye and keeps a constant pressure within the eye.
• Pupil and iris:The pupil is the circular opening in the colored part of the eye
• which is the iris. The iris dilates or opens and contracts to let in more or less
• light.
• Lens:Resembles the lens of a camera and focuses the light, changing shape
• as it takes in light reflected from objects near and far.
• Vitreous:A clear jelly that the focused light passes through to the retina.
• Retina:The inner lining at the back of the eye. It contains blood vessels
• which bring nutrients to the nerve cells. The macula is at the very center of
• the retina and contains the fovea. The photoreceptors of the retina are the
• rods and cones. The cones perceive color and finer elements. The retinal
• pigment epithelium, choroid and sclera are three more layers. The
• photoreceptors send light and images to a large nerve called the optic nerve.
• This carries the information to the occipital lobe of the brain where they are
• interpreted.
• Eyelids and eyelashes:These protect the eye and along with tears keep the
• eye clear and moist.
• Now hear this: Sound
• The ear is the organ of hearing. The outer ear protrudes away from the head
• and is shaped like a cup to direct sounds toward the tympanic membrane,
• which transmits vibrations to the inner ear through a series of small bones in
• the middle ear called the malleus, incus and stapes. The inner ear, or
• cochlea, is a spiral-shaped chamber covered internally by nerve fibers that
• react to the vibrations and transmit impulses to the brain via the auditory
• nerve. The brain combines the input of our two ears to determine the
• direction and distance of sounds.
• The inner ear has a vestibular system formed by three semicircular canals
• that are approximately at right angles to each other and which are
• responsible for the sense of balance and spatial orientation. The inner ear has
• chambers filled with a viscous fluid and small particles (otoliths) containing
• calcium carbonate. The movement of these particles over small hair cells in
• the inner ear sends signals to the brain that are interpreted as motion and
• acceleration.
• The human ear can perceive frequencies from 16 cycles per second, which is
• a very deep bass, to 28,000 cycles per second, which is a very high pitch.
• Bats and dolphins can detect frequencies higher than 100,000 cycles per
• second. The human ear can detect pitch changes as small as 3 hundredths of
• one percent of the original frequency in some frequency ranges. Some
• people have "perfect pitch", which is the ability to map a tone precisely on
• the musical scale without reference to an external standard. It is estimated
• that less than one in ten thousand people have perfect pitch, but speakers of
• tonal languages like Vietnamese and Mandarin show remarkably precise
• absolute pitch in reading out lists of words because pitch is an essential
• feature in conveying the meaning of words in tone languages. The Eguchi
• Method teaches perfect pitch to children starting before they are 4 years old.
• After age 7, the ability to recognize notes does not improve much.
• The ear not only is the organ of hearing, but it also is responsible for
• maintaining equilibrium — or balance. To maintain equilibrium, the ear
• must detect movement. To hear, the ear must respond to mechanical
• stimulation by sound waves.
• The outer ear is the external opening to the ear canal. Sound waves are
• shuttled through the ear canal to the middle ear. The eardrum sets the
• mechanics in motion:
• When a sound wave hits the eardrum, the eardrum moves tiny bones —
• the malleus, incus, and stapes — which subsequently move.
• This movement is picked up by the mechanoreceptors in the inner ear,
• which exist on hair cells containing cilia between the end of the
• semicircular canals and the vestibule.
• When the cilia move, the cells create an impulse that is sent through the
• cochlea to the eighth cranial nerve, which carries the impulse to the
• brain.
• The brain then interprets the information as a specific sound.
• The fluid within the semicircular canals of the inner ear moves, and that
• movement is ultimately detected by the cilia. When the fluid doesn‘t stop
• moving, you can develop motion sickness. The cilia transmit impulses to the
• brain about angular and rotational movement, as well as movement through
• vertical and horizontal planes, which helps your body to keep its
• balance.The ear is the organ concerned with hearing. The ear has three parts:
• the outer ear, the middle ear and the inner ear.
• Outer ear: Pinna: The outermost part of the ear made of cartilage that is
• connected to the outer tube called the auditory canal. This leads to the
• eardrum.
• Middle Ear Eardrum, stirrup, anvil and hammer: This membrane
• vibrates and along with the three tiny bones in the middle ear, the hammer,
• anvil and stirrup, and sends the stiumuli to the cochlea.
• Inner Ear: Cochlea: Is spiral shaped and it transforms sound into nerve
• impulses that travel to the brain.
• Semicircular canals: These fluid filled tubes attach to the cochlea and
• nerves in the inner ear. They send information on balance and head position
• to the brain.
• Eustachian tube: Drains fluid from the middle ear into the throat behind the
• nose.
• Mmm, mmm, good: Taste
• Tongue:
• The receptors for taste, called taste buds, are situated chiefly in the tongue,
• but they are also located in the roof of the mouth and near the pharynx. They
• are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue
• also can detect a sensation called "umami" from taste receptors sensitive to
• amino acids. Generally, the taste buds close to the tip of the tongue are
• sensitive to sweet tastes, whereas those in the back of the tongue are
• sensitive to bitter tastes. The taste buds on top and on the side of the tongue
• are sensitive to salty and sour tastes. At the base of each taste bud there is a
• nerve that sends the sensations to the brain. The sense of taste functions in
• coordination with the sense of smell. The number of taste buds varies
• substantially from individual to individual, but greater numbers increase
• sensitivity. Women, in general, have a greater number of taste buds than
• men. As in the case of color blindness, some people are insensitive to some
• tastes.
• The senses of smell and taste work closely together. If you cannot smell
• something, you cannot taste it, either. Taste buds on your tongue contain
• chemoreceptors that work in a similar fashion to the chemoreceptors in the
• nasal cavity. However, the chemoreceptors in the nose will detect any kind
• of smell, whereas there are four different types of taste buds, and each
• detects different types of tastes: sweet, sour, bitter, and salty.
• A common misconception is that the little bumps on your tongue are the
• taste buds. As with all misconceptions, this idea is wrong, too. The little
• bumps on your tongue are called papillae, and the taste buds actually lie
• down in the grooves between each papilla.
• Foods contain chemicals, and when you put something into your mouth, the
• taste buds in your tongue can detect what chemicals you are ingesting. Each
• taste bud has a pore at one end with microvilli sticking out of the pore, and
• sensory nerve fibers attached to the other end. Chemicals from food bind to
• the microvilli, generating a nerve impulse that is carried through the sensory
• nerve fibers and eventually to the brain.
• Is a muscular organ in the mouth. The tongue is covered with moist, pink
• tissue called mucosa and tiny bumps called papillae. Thousands of taste buds
• cover the surfaces of the papillae. Taste buds are collections of nerve-like
• cells that connect to nerves going into the brain. There are four types of taste
• buds: sour, sweet, bitter and salty. The tongue is vital in tasting and chewing
• food and in speech.
• Oooh, that smell: Olfaction
• Nose:
• The nose is the organ responsible for the sense of smell. The cavity of the
• nose is lined with mucous membranes that have smell receptors connected to
• the olfactory nerve. The smells themselves consist of vapors of various
• substances. The smell receptors interact with the molecules of these vapors
• and transmit the sensations to the brain. The nose also has a structure called
• the vomeronasal organ whose function has not been determined, but which
• is suspected of being sensitive to pheromones that influence the reproductive
• cycle. The smell receptors are sensitive to seven types of sensations that can
• be characterized as camphor, musk, flower, mint, ether, acrid, or putrid. The
• sense of smell is sometimes temporarily lost when a person has a cold. Dogs
• have a sense of smell that is many times more sensitive than man's.
• The nose, along with the mouth, lets air in and out of the body. It also helops
• us distinguish different smells in that air. The nasal root is the top of the
• nose, forming an indentation at the suture where the nasal bones meet the
• frontal bone. The anterior nasal spine is the thin projection of bone at the
• midline on the lower nasal margin, holding the cartilaginous center of the
• nose.[1] Adult humans have nasal hairs in the anterior nasal passage.
• Olfactory cells line the top of your nasal cavity. On one end, olfactory cells
• have cilia — hair-like attachments — that project into the nasal cavity. On
• the other end of the cell, are olfactory nerve fibers, which pass through the
• ethmoid bone and into the olfactory bulb. The olfactory bulb is directly
• attached to the cerebral cortex of your brain.
• As you breathe, anything that is in the air that you take in enters your nasal
• cavity: hydrogen, oxygen, nitrogen, dust, pollen, chemicals. You don‘t
• ―smell‖ air or dust or pollen, but you can smell chemicals. The olfactory
• cells are chemoreceptors, which means the olfactory cells have protein
• receptors that can detect subtle differences in chemicals.
• The chemicals bind to the cilia, which generate a nerve impulse that is
• carried through the olfactory cell, into the olfactory nerve fiber, up to the
• olfactory bulb and to your brain. Your brain determines what you are
• smelling. If you are sniffing something that you haven‘t experienced before,
• you need to use another sense, such as taste or sight, to make an imprint in
• your brain‘s memory.
• A touchy-feely subject: Touch
• The sense of touch is distributed throughout the body. Nerve endings in the
• skin and other parts of the body transmit sensations to the brain. Some parts
• of the body have a larger number of nerve endings and, therefore, are more
• sensitive. Four kinds of touch sensations can be identified: cold, heat,
• contact, and pain. Hairs on the skin magnify the sensitivity and act as an
• early warning system for the body. The fingertips and the sexual organs have
• the greatest concentration of nerve endings. The sexual organs have
• "erogenous zones" that when stimulated start a series of endocrine reactions
• and motor responses resulting in orgasm.
• The skin contains general receptors. These receptors can detect touch, pain,
• pressure, and temperature. Throughout your skin, you have all four of these
• receptors interspersed. Skin receptors generate an impulse when activated,
• which is carried to the spinal cord and then to the brain.
• The skin is not the only tissue in the body to have receptors, however. Your
• organs, which are made of tissues, also have receptors. Joints, ligaments, and
• tendons contain proprioceptors, which detect the position and movement of
• the limbs.
• Skin: The skin is the largest organ of the body, with a total area of about 20
• square feet. The skin protects us from microbes and the elements, helps
• regulate body temperature, and permits the sensations of touch, heat, and
• cold. The epidermis, the outermost layer of skin, provides a waterproof
• barrier and creates our skin tone.
• Layers: The dermis, beneath the epidermis, contains tough connective
• tissue, hair follicles, and sweat glands.
• The deeper subcutaneous tissue (hypodermis) is made of fat and connective
• tissue.
• The skin's color is created by special cells called melanocytes, which
• produce the pigment melanin. Melanocytes are located in the epidermis.
• Beyond the five sense organs.
• In addition to sight, smell, taste, touch, and hearing, humans also have
• awareness of balance (equilibrioception), pressure, temperature
• (thermoception), pain (nociception), and motion all of which may involve
• the coordinated use of multiple sensory organs. The sense of balance is
• maintained by a complex interaction of visual inputs, the proprioceptive
• sensors (which are affected by gravity and stretch sensors found in muscles,
• skin, and joints), the inner ear vestibular system, and the central nervous
• system. Disturbances occurring in any part of the balance system, or even
• within the brain's integration of inputs, can cause the feeling of dizziness or
• unsteadiness.
• Kinesthesia is the precise awareness of muscle and joint movement that
• allows us to coordinate our muscles when we walk, talk, and use our hands.
• It is the sense of kinesthesia that enables us to touch the tip of our nose with
• our eyes closed or to know which part of the body we should scratch when
• we itch.
• Synesthesia.
• Some people experience a phenomenon called synesthesia in which one type
• of stimulation evokes the sensation of another. For example, the hearing of a
• sound may result in the sensation of the visualization of a color, or a shape
• may be sensed as a smell. Synesthesia is hereditary and it is estimated that it
• occurs in 1 out of 1000 individuals with variations of type and intensity. The
• most common forms of synesthesia link numbers or letters with colors.
• Definition of physiology: A branch of biology that deals with the
• functions and activities of life or of living matter (as organs,
• tissues, or cells) and of the physical and chemical phenomena
• involved.
• The organic processes and phenomena of an organism or any of
• its parts or of a particular bodily process
• The scientific study of an organism's vital functions, including growth andde
• velopment, the absorption and processing of nutrients, the synthesis anddistri
• bution of proteins and other organic molecules, and the functioning ofdiffere
• nt tissues, organs, and other anatomic structures.
• A physiology Studies the normal mechanical, physical, and biochemical
• process of animal‘s and plants.
• Physiology is the science of life. The discipline considers how molecules in
• cells interact to provide specific functions (molecular and cellular
• physiology) and how organs, which are collections of cell types, have local
• and distal actions via neural and humoral (e.g. hormones) communication to
• sustain the life of the organism. The latter represents systems or integrative
• physiology. Thus physiology is all about what makes our bodies work – how
• the organs – including the brain – function, how we grow and develop, how
• we sustain our bodily functions and what happens to these processes during
• disease and ageing. You can think of physiology as the functional side of
• biology – with the challenges and rewards of investigating living processes.
• Physiology contributes to all major aspects of biology, including
• comparative biology, neuroscience, and the allied disciplines of
• pharmacology, anatomy and pathology.
• Physiological studies date back to ancient civilizations of India, Egypt
• alongside anatomical studies but did not utilize dissections and
• vivisection. The study of human physiology as a medical field dates back to
• at least 420 BC to the time of Hippocrates, also known as the "father of
• medicine." Hippocrates incorporated his belief system called the theory of
• humours, which consisted of four basic substances: earth, water, air and fire.
• Each substance is known for having a corresponding humour: black bile,
• phlegm, blood and yellow bile, respectively. Hippocrates also noted some
• emotional connections to the four humours, which Claudis Galenus would
• later expand on. The critical thinking of Aristotle and his emphasis on the
• relationship between structure and function marked the beginning of
• physiology in Ancient Greece. Like Hippocrates, Aristotle took to the
• humeral theory of disease, which also consisted of four primary qualities in
• life: hot, cold, wet and dry. Claudius Galenus (c. ~130–200 AD), known as
• Galen of Pergamum, was the first to use experiments to probe the functions
• of the body. Unlike Hippocrates though, Galen argued that humeral
• imbalances can be located in specific organs, including the entire body. His
• modification of this theory better equipped doctors to make more precise
• diagnoses. Galen also played off of Hippocrates idea that emotions were also
• tied to the humors, and added the notion of temperaments: sanguine
• corresponds with blood; phlegmatic is tied to phlegm; yellow bile is
• connected to choleric; and black bile corresponds with melancholy. Galen
• also saw the human body consisting of three connected systems: the brain
• and nerves, which are responsible for thoughts and sensations; the heart and
• arteries, which give life; and the liver and veins, which can be attributed to
• nutrition and growth.[10]To top it off, Galen was also the founder of
• experimental physiology. And for the next 1,400 years, Galenic physiology
• was a powerful and influential tool in medicine.
• Physiology is the study of how molecules, cells and organs interact to form a
• whole being. The work of Physiological Society Members, advancing our
• knowledge of biological systems, is essential to the development of new
• treatments for disease. Since The Society's foundation in 1876, our
• membership has included more than 20 Nobel Prize winners from Ivan
• Pavlov to Andrew Huxley. The scientists who make up The Society have
• made many key discoveries, ranging from how our nervous system
• works, how our cells divide and the way in which our reflexes alter our
• behaviour. These have advanced our knowledge of biological systems and
• helped in the treatment of diseases such as cancer, cystic fibrosis and heart
• disease.
• Human physiology, a branch of general physiology, is concerned with how
• the human body works. It is common to approach the study of human
• physiology through an organ-system approach. Organ-systems are
• collections of cells, tissues and organs, which have dedicated functions in
• the body. In the human body, the organ-systems are the nervous system,
• endocrine system, cardiovascular system, respiratory system, urinary system,
• musculoskeletal system, integumentary system, reproductive system,
• digestive system, and immune system. While the proper function of each
• organ-system is essential, it is the collective and integrative functions of all
• organ-systems that contribute to a healthy state. A thorough study of human
• physiology includes an understanding of the organ-systems as well as the
• underlying tissue, cellular, and molecular principles. Human physiology is a
• life science and a branch of animal physiology. It is specifically the study of
• how systems of the body function in a well state, and this analysis of
• function is often at the cellular level, not of single cells but of how cells
• work in concert to achieve a normal state of function. Basic human
• physiology studies the body‘s systems that function appropriately and as
• expected, while other disciplines like patho physiology may look at the way
• body systems develop disease in attempts to find insight into how to cure
• diseases.
• There may be several main concerns in human physiology from a scientific
• standpoint. These concerns include the way interdependence between body
• systems occurs (such as the central nervous system and the musculoskeletal
• system). This is called integration.
• Another point of interest is communication, which is how the body‘s
• systems send signals to function in specific ways. These signals could be
• electrical impulses or the release of chemicals. Lastly, the physiologist wants
• to define and observe homeostasis, in any of the systems studied. In other
• words how does the body maintain a normal state, and what are the
• processes by which it does so?
• It might be oversimplification to say that human physiology attempts to
• answer the question of ―how things work.‖ However, this is fairly accurate,
• and it‘s an important question to answer. Understanding the normal function
• of the body‘s systems is valuable because it establishes baselines for
• understanding what is abnormal. It is very difficult to diagnose disease
• unless a clear deviation from the norm can be determined, and therefore
• establishing this norm is of great value in medicine and in human health.
• For instance, over time, physiology and biochemistry have helped to
• determine what constitutes normal blood levels of certain substances. When
• something like sugar levels become too high, it may have impact on various
• systems in the body and be indication of diseases like diabetes. Only by
• knowing baseline levels for various sugar types in blood, can doctors
• determine whether diabetes is present. This knowledge has been
• extrapolated to allow patients to keep records of their own blood sugar at
• home. With testing they can be assured that they are regulating blood sugar
• appropriately or they can make medication adjustments when blood sugar
• levels are too high or too low.
• It‘s suggested that early studies in human physiology and anatomy began
• over 2000 years ago, and names like Hippocrates and Aristotle are usually
• given as early physiologists. The trouble with early thought was it didn‘t
• allow for many examinations of humans, and most humans examined were
• dead. The idea of cells wouldn‘t be posited until much later in history. Much
• more was done in the field of anatomy, which is an intricately related
• discipline to human physiology, that describes the forms present in the body,
• and yet again, unless these forms were obvious and on the surface, they
• typically didn‘t get much exploration unless a person was dead.
• More studies were possible on animals, and actually animal physiology is
• still used and extrapolated to human beings all of the time. Even today when
• medical science is much more delicate, most well humans would not consent
• to studies of some of the ways their body systems work. Few people would
• volunteer to have abnormal rhythms of their heart induced as part of
• electrophysiological cardiology studies to determine what causes
• arrhythmias, as this might be dangerous. However electro physiologists can
• induce arrhythmias in animals to determine what factors destroy balance in
• the electrical system in the heart.
• Over time, human physiology has helped to define the major systems of the
• body and how they work to achieve wellness. Basic introductory courses
• tend to look at each of these systems, which may be roughly defined as the
• following: circulatory, respiratory, endocrine, reproductive, immune,
• musculoskeletal, nervous, integumentory, renal, and gastrointestinal.
• While breaking the body into systems can help describe function, it isn‘t
• always so neat from a scientific standpoint. Systems are interdependent on
• each other. Lose renal or respiratory function, and everything else becomes
• affected. Moreover, many vital organs or parts of the body may participate
• in several systems.
• The major systems covered in the study of human physiology are as
• follows:
•  Circulatory system: including the heart, the blood vessels, properties of
• the blood and how circulation works in sickness and in health
•  Digestive/excretory system: this domain charts the movement of solids
• from the mouth to the anus, and includes study of the spleen, liver and
• pancreas, the conversion of food into fuel and its consequent expulsion
• from the body
•  Endocrine system: the study of endocrine hormones that carry signals
• throughout the organism, helping it to respond in concert. The principal
• endocrine glands – the pituitary, thyroid, adrenals, pancreas, parathyroid
• and gonads – are a major focus, but nearly all organs release endocrine
• hormones
•  Immune system: the body's natural defense system comprises of white
• blood cells, the thymus and lymph systems. A complex array of receptors
• and molecules combine to protect the host from attacks by pathogens.
• Molecules such as antibodies and cytokines feature heavily
•  Integumentary system: the skin, hair, nails, sweat glands and sebaceous
• glands (secreting an oily or waxy substance)
•  Musculoskeletal system: the skeleton and muscles, tendons, ligaments
• and cartilage. Bone marrow – the site of red blood cell creation – and how
• bones store calcium and phosphate are included
•  Nervous system: the central nervous system (brain and spinal cord) and
• the peripheral nervous system. Study of the nervous system includes
• research into the senses, memory, emotion and thought
•  Renal/urinary system: including the kidneys, ureters, bladder and
• urethra, this system removes water from the blood, produces urine and
• carries away waste
•  Reproductive system: consisting of the gonads and the sex organs. Study
• of this system also includes investigating the way a fetus is produced and
• nurtured for 9 months
•  Respiratory system: consisting of the nose, naso pharynx, trachea, and
• lungs. This system brings in oxygen and expels carbon dioxide and water.
• Other branches of physiology
• Defense physiology investigates nature's natural defensive reactions.
• There are a great number of disciplines that use the word physiology in their
• title. Below are some of the other physiological topics that have some
• relevance to medical science:
•  Cell physiology: studying the way cells work and interact, cell
• physiology predominantly concentrates on membrane transport and
• neuron transmission
•  Systems physiology: this discipline focuses on the computational and
• mathematical modeling of complex biological systems. It looks to
• describe the way individual cells or components of a system converge to
• respond as a whole. They often investigate metabolic networks and cell
• signaling
•  Evolutionary physiology: studying the way systems or parts thereof have
• adapted and changed over multiple generations. Research topics cover a
• lot of ground including the role of behavior in evolution, sexual selection
• and physiological changes in relation to geographic variation
•  Defense physiology: changes that occur as a reaction to a potential threat,
• such as preparation for the fight-or-flight response
•  Exercise physiology: as the name suggests, this is the study of the
• physiology of physical exercise. This might include research into
• bioenergetics, biochemistry, cardiopulmonary function, biomechanics,
• hematology, skeletal muscle physiology, neuro endocrine function and
• nervous system function.
• The topics mentioned above are but a small fraction of the available
• physiologies. The field of physiology is as essential as it is vast.
• Exercise Physiology is the identification of physiological mechanisms
• underlying physical activity, the comprehensive delivery of treatment
• services concerned with the analysis, improvement, and maintenance of
• health and fitness, rehabilitation of heart disease and other chronic diseases
• and/or disabilities.
• Sports science (also sport science) is a discipline that studies how the
• healthy human body works during exercise, and how sport and physical
• activity promote health from cellular to whole body perspectives. The study
• of sports science traditionally incorporates areas of physiology (exercise
• physiology), psychology (sportpsychology), anatomy,
• biomechanics, biochemistry and biokinetics. Sports scientists and
• performance consultants are growing in demand and employment numbers,
• with the ever-increasing focus within the sporting world on achieving the
• best results possible. Through the study of science and sport, researchers
• have developed a greater understanding on how the human body reacts to
• exercise, training, different environments and many other stimuli. Exercise
• physiology is the physiology of physical exercise. It is the study of the acute
• responses and chronic adaptations to a wide range of exercise conditions.
• Exercise physiologists study the effect of exercise on pathology, and the
• mechanisms by which exercise can reduce or reverse disease progression.
• Exercise Physiology is the study of how exercise alters the function and
• structure of the body. A sports physiologist examines the acute responses
• and chronic adaptations to athletic performance in a variety of environments.
• Sports physiology is the study of the long-and short-term effects of training
• and conditions on athletes. This specialized field of study goes hand in hand
• with human anatomy. Anatomy is about structure, where physiology is about
• function.
• Sports Training Principles are heavily rooted in this field. Effects of body
• composition, flexibility training, hydration, environmental conditions, and
• carbohydrate loading on athletic performance are only a few of the topics
• explored in this field.

Exercise physiologists, physicians, and athletic trainers can apply research findings from studies to advise athletes on topics concerning nutrition, sportrelated injuries, and other issues related to sports medicine.

• Exercise Physiology is the study of how exercise alters the function and
• structure of the body. A sports physiologist examines the acute responses
• and chronic adaptations to athletic performance in a variety of environments.
• The physiologist possesses a wide-ranging understanding of the body,
• enabling them to advise athletes and coaches of how training and preparation
• influence competition performance.
• Testing can take place in the lab, which ensures a controlled environment to
• compare exercise test results. However, it is not always possible to simulate
• sporting activity in a lab and with advances in technology physiologists use
• field-based testing as much as possible. This work is vital as it can evaluate
• training as it happens; allowing the athlete and coach to objectively monitor
• what impact a particular session has had on the body.
• Physiology can improve an athlete‘s performance
• objective information which can help coaches to adapt training programmes
• to maximize their desired outcome. This will depend on many factors
• including the environment, diet, gender, age and health.
• Exercise Physiology is the identification of physiological mechanisms
• underlying physical activity, the comprehensive delivery of treatment
• services concerned with the analysis, improvement, and maintenance of
• health and fitness, rehabilitation of heart disease and other chronic diseases
• and/or disabilities, and the professional guidance and counsel of athletes and
• others interested in athletics, sports training, and human adaptability to acute

and chronic exercise.