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Science Olympiad Study Material, Study notes of Anatomy

Anatomy

Anatomy & Physiology For Senses

Typology: Study notes

2025/2026

Uploaded on 03/21/2026

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atul-nitin 🇺🇸

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SENSE ORGANS HANDOUT
Sensory Receptors - receive input, generate receptor potentials and with enough summation, generate action
potentials in the neurons they are part of or synapse with
5 Types of Sensory Receptors - based on the type of stimuli they detect:
1. Mechanoreceptors - pressure receptors, stretch receptors, and specialized mechanoreceptors involved
in movement and balance.
2. Thermoreceptors - skin and viscera, respond to both external and internal temperature
3. Pain receptors - stimulated by lack of O2, chemicals released from damaged cells and inflammatory
cells
4. Chemoreceptors - detect changes in levels of O2, CO2, and H+ ions (pH) as well as chemicals that
stimulate taste and smell receptors
5. Photoreceptors - stimulated by light
Distribution of Receptors in the body:
Special Senses
• mediated by relatively complex sense organs of the head, innervated by cranial nerves
• vision, hearing, equilibrium, taste and smell
General (somesthetic, somatosensory)
• receptors widely distributed in skin, muscles, tendons, joints, and viscera
• they detect touch, pressure, stretch, heat, cold and pain, blood pressure
Special Senses
Sensation and perception
• Vision – Eye
• Hearing – Ear
• Equilibrium – Ear
• Taste – Taste receptors
• Smell – Olfactory system
General Senses
• Skin – Hot, cold, pressure, pain
• Muscles, joints, and tendons – proprioceptors- stretch receptors respond to stretch or compression
• Pain Receptors – somatic or visceral
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SENSE ORGANS HANDOUT

Sensory Receptors - receive input, generate receptor potentials and with enough summation, generate action potentials in the neurons they are part of or synapse with

5 Types of Sensory Receptors - based on the type of stimuli they detect:

  1. Mechanoreceptors - pressure receptors, stretch receptors, and specialized mechanoreceptors involved in movement and balance.
  2. Thermoreceptors - skin and viscera, respond to both external and internal temperature
  3. Pain receptors - stimulated by lack of O 2 , chemicals released from damaged cells and inflammatory cells
  4. Chemoreceptors - detect changes in levels of O 2 , CO 2 , and H
    • ions (pH) as well as chemicals that stimulate taste and smell receptors
  5. Photoreceptors - stimulated by light

Distribution of Receptors in the body:

Special Senses

  • mediated by relatively complex sense organs of the head, innervated by cranial nerves
  • vision, hearing, equilibrium, taste and smell General (somesthetic, somatosensory)
  • receptors widely distributed in skin, muscles, tendons, joints, and viscera
  • they detect touch, pressure, stretch, heat, cold and pain, blood pressure

Special Senses

Sensation and perception

  • Vision – Eye
  • Hearing – Ear
  • Equilibrium – Ear
  • Taste – Taste receptors
  • Smell – Olfactory system

General Senses

  • Skin – Hot, cold, pressure, pain
  • Muscles, joints, and tendons – proprioceptors- stretch receptors respond to stretch or compression
  • Pain Receptors – somatic or visceral

SPECIAL SENSES

Eye - Vision

Processes

  • Light energy is transduced into neural activity
  • Neural activity is processed by the brain
  • Note: For an analogy, you can imagine taking a picture with a camera. The eye is the camera, the retina, which is a specialized part of the brain at the back of the eye, is the film, and the parts of the brain that process visual information is the photoshop. Human visual systems permit light reflected off distant objects to be:
  • Localized relative to the individual within his or her environment
  • Identified based on size, shape, color, and past experience
  • Perceived to be moving (or not)
  • Detected in a wide variety of lighting conditions Sequence of events
  • Light entering the eye is focused on the retina
  • Retina converts light energy into neuronal activity
  • Axons of the retinal neurons are bundled to form the optic nerves
  • Visual information is distributed to several brain structures that perform different functions

Eye – the organ used to sense light

Three layers –

1. Outer layer consists of sclera and cornea 2. Middle layer consists of choroid, ciliary body and iris 3. Inner layer consists of retina Extraocular muscles --attached to the eye and skull and allow movement

Common eye defects include

  • myopia or nearsightedness where the eyeball is too long or the cornea is too steep;
  • hyperopia or far sightedness where the eyeball is short or lens cannot become round enough:
  • presbyopia where the muscles controlling the bulging of the lens become weak as we age;
  • cataracts where the lens becomes fogged;
  • nyctalopia or night blindness where vision is impaired in dim light and in the dark due to pigment rhodospin in the rods not functioning properly External features of the eye Cross sectional anatomy
  • Lens-- transparent surface that contributes to the formation of images (w/i 9 meters)
  • Ciliary muscles --change the shape of the lens and allow focusing
  • Vitreous humor --more viscous than the aqueous humor - Lies between the lens and the retina and provides spherical shape
  • Retina - inner most layer of cells at the back of the eye - Transduces light energy into neural activity

Images

  • the cornea and the lens help to produce the image on the retina
  • images formed by the lens are upside down and backwards when they reach the retina
  • two types of receptors on the retina
  • Rods – 125 million on a single retina – extremely sensitive to all wavelengths of visible light but do not distinguish different color – in dim light only rods are activated where one can see objects but not as sharp images and are not able to distinguish their color – most dense in peripheral view – nighttime vision Rods have a pigment called rhodospin
  • As amount of light increases, the cones – 7 million on a single retina – mainly in central view are stimulated and the color becomes clear – daytime vision
  • There are three types of cones which distinguish the three colors – blue, red, green
  • Fovea – point of central focus – great density of cones - center of the eye's sharpest vision and the location of most color perception - the layers of the retina spread aside to let light fall directly on the cones
  • Light stimulates rods and cones and sends impulse via optic nerve to brain areas for vision
  • The Optic Nerve exits the eye just off center near the Fovea - the Optic Nerve exits is referred to as the Blind Spot due to the lack of the receptors in this area
  • The two Optic Nerves come together at the Optic Chiasm located just under the hypothalamus - a crucial part of vision and perception must happen - cross-over of information from the right eye crosses over to the left side and visa versa happens here at the Optic Chiasm
  • Information from each eye must be processed in both halves of the brain
  • Information leaves the chiasm via the optic tract.
  • Reorganized optic tract leaves the Optic Chiasm and passes onto the lateral geniculate nucleus
  • At the lateral geniculate nuclei the information is separated, organized, and relayed to different areas of the visual cortex
  • The different zones of the visual cortex process the different aspects of vision and information, taken from both visual fields, is processed and an image is perceived

Ear – Equilibrium

Equilibrium

  • Equilibrium is a response to movements of the head - Example: a cat landing on its feet if dropped from upside down
  • Vestibular Apparatus: the equilibrium receptors of the inner ear
  • Divided into static and dynamic equilibrium Static Equilibrium
  • When the body is not moving
  • Maculae : receptors within the membrane sacs of the vestibule that report on the position of the head with respect to the pull of gravity when the body is not moving.
  • Each macula is a patch of receptor cells with their “hairs” embedded in the otolithic membrane
  • Otolithic Membrane : a jelly-like substance containing otoliths
  • Otoliths : tiny stones made of calcium salts that roll in response to changes in the pull of gravity. When otoliths move, they pull on the gel and this bends the hairs. Activated hair cells send impulses along the vestibular nerve
  • Vestibular Nerve: (Cranial Nerve VIII) transmits signals to the cerebellum Dynamic Equilibrium
  • Receptors in the semicircular canals respond to angular or rotary movements of the head.
  • Semicircular canals are oriented in the three planes of space
  • Crista Ampullaris : receptor region that consists of a tuft of hair cells covered with a gelatinous cap called the cupula
  • When the head moves in an angular direction: o The endomlymph lags behind o As the cupula drags against the stationary endolymph, the cupula bends o This stimulates hair cells to transmit signals to the vestibular nerve
  • When you are moving at a constant rate, receptors stop sending impulses
  • You no longer have the sensation of motion until you change speed or direction Vision plays a significant role in balance. Approximately twenty percent of the nerve fibers from the eyes interact with the vestibular system.

Taste and Smell – Chemical Receptors

Taste buds

  • The mouth contains around 10,000 taste buds, most of which are located on and around the tiny bumps on your tongue.
  • Every taste bud detects five primary tastes : o Sour o Sweet o Bitter o Salty o Umami - salts of certain acids (for example monosodium glutamate or MSG)
  • Each of your taste buds contains 50-100 specialised receptor cells.
  • Sticking out of every single one of these receptor cells is a tiny taste hair that checks out the food chemicals in your saliva.
  • When these taste hairs are stimulated, they send nerve impulses to your brain.
  • Each taste hair responds best to one of the five basic tastes. Smell Receptors or Olfactory receptors
  • Humans able to detect thousands of different smells
  • Olfactory receptors occupy a stamp-sized area in the roof of the nasal cavity, the hollow space inside the nose
  • Tiny hairs, made of nerve fibers, dangle from all your olfactory receptors. They are covered with a layer of mucus.
  • If a smell, formed by chemicals in the air, dissolves in this mucus, the hairs absorb it and excite your olfactory receptors.
  • A few molecules are enough to activate these extremely sensitive receptors.
  • Olfactory Hairs easily fatigued so you do not notice smells
  • Linked to memories - when your olfactory receptors are stimulated, they transmit impulses to your brain and the pathway is directly connected to the limbic system - the part of your brain that deals with emotions so you usually either like or dislike a smell
  • Smells leave long-lasting impressions and are strongly linked to your memories
  • Much of what we associate as taste also involves smell – that is why hot foods “taste” different than “cold” foods

Temperature

  • skin receptors register warmth and cold
  • each square centimeter of your skin contains 6 receptors for cold and 1 receptor for warmth
  • Cold receptors start to perceive cold sensations when the surface of the skin drops below 95 º F. They are most stimulated when the surface of the skin is at 77 º F and are no longer stimulated when the surface of the skin drops below 41 º F. This is why your feet or hands start to go numb when they are submerged in icy water for a long period of time.
  • Hot receptors start to perceive hot sensations when the surface of the skin rises above 86 º F and are most stimulated at 113 º F. Beyond 113 º F, pain receptors take over to avoid damage being done to the skin and underlying tissues.
  • thermoreceptors are found all over the body, but cold receptors are found in greater density than heat receptors – most of the time of our environment is colder than our body temperature
  • The highest concentration of thermoreceptors can be found in the face and ears so your nose and ears always get colder faster than the rest of your body on a chilly winter day

Proprioceptors - Stretch receptors located in joints, ligaments, and

tendons (respond to either stretch or compression)

  • Maintain some degree of continuous contraction (partial sustained contraction) or muscle tone
  • Muscle spindles – modified muscle fibers with sensory nerve endings wrapped around the middle (and also found at the ends)
  • Detect stretch and stimulate a reflex contraction; think about banging on your patellar ligament (just an extension of a quadriceps tendon) and watching your knee jerk up – the quadriceps contracted in response to the stretch of the patellar ligament, which stretched muscle spindles and ) impulses are sent to the hamstring group (the antagonists) to cause them to relax, so they don’t oppose the contraction of the quadriceps

Pain Receptors – nociceptors

  • Somatic nociceptors - from skin and skeletal muscle
  • Visceral nociceptors - receptors that help maintain internal homeostasis § Respond to stretch, lack of O 2 , chemicals released from damaged cells and inflammatory cells. § Referred pain – visceral pain afferents travel along the same pathways as somatic pain afferents, so sometimes the brain interprets the visceral pain as the more common somatic pain. Example – Often pain from the heart felt during a heart attack is perceived as a pain that originates in the left arm.