Sensory Systems Lecture, Johnson BSCII 1511

Mechanoreceptors

Responsible for touch, pressure, and sound detection. Can also sense blood pressure.

Sensing is based on the physical distortion of mechanoreceptor plasma membranes causing action potential releases.

Chemoreceptors

Responsible for smell and taste.

Nociceptors

Responsible for pain

Ionotropic receptors

Sensory receptor protein and ion channel are part of the same protein. Receptor conformational changes are what control ion channel opening.

Metabotropic Protein

Receptor proteins are linked to g-protein that causes a protein cascade to eventually open ion channels.

Receptor Potential

Change in membrane potential of a receptor cell ion response to a stimulus.

Stimulus Strength

The strength of the stimulus is encoded by the frequency of action potentials released by stimulated receptor cells.

Merkel’s Disc

Adapt slowly and provide continuous information. Surface skin mechanoreceptors

Meissner’s Corpuscles

Very sensitive and adapt fast. Surface skin mechanoreceptors

Ruffini Corpuscles

Adapt slow and sense low frequency vibrations. Deeper skin mechanoreceptors

Pacinian Corpuscles

Adapt fast and sense high frequency vibrations. Deeper skin mechanoreceptors

Cochlea Mechanoreceptors

Hair cells in the ear are responsible for hearing. They’re attached to different inner ear structures that move in response to cochlea fluid vibrating in response to sound.

Stereocillia

These are the tips of inner ear hair cells that move in response to sound. Its movements deform the membrane of the hair cell, resulting in an action potential.

Rhodopsins

Evolutionarily conserved photoreceptor proteins that contribute to vision. They consist of retinals and opsin.

Opsin

The transmembrane part of rhodopsin. it has 7 transmembrane domains

Retinal

The pigment protein part of rhodopsin. Light causes a conformation change from the resting cis- conformation to the excited trans- conformation

Phototaxis

The movement of single-cell plants like algae towards light. The cells detect light with a rhodopsin-based “eye” and move towards it with its flagella.

First “eye”

Patch of photoreceptors, senses light or dark.

Second “eye”

Cup-shaped patch of photoreceptors. Sense direction of light or dark.

Third “eye”

Closed up eye precursor that is a cup-shaped patch of photoreceptors filled with fluid and has a pinhole aperture. Has a endothelium cornea precursor. Allows the viewing of an image.

Fourth “eye”

Simple lens on a closed up eye precursor that has a pinhole aperture. Has a cornea. Allows the viewing of a clearer image.

Fifth “eye”

Complex lens on a closed up eye precursor that has a pinhole aperture. Has a cornea that can be contracted and relaxed. Allows the viewing of an even clearer image.

Ommatidium

Individual subunits of an insect eye. Each unit has a lens that focuses light onto the retinula cells. Each unit represents one colored pixel in the insect’s vision. Dense ommatidium results in clearer vision and vise versa. Larger ommatidium results in better light detection and vise versa.

Retinula

Insect photoreceptor cells that contain rhodopsin and use their axons to communicate to nervous cells.

Rod Cells

Modified neurons with outer and inner segments and a synaptic terminal. Inner segment contains mitochondria and nucleus. Outer segment has lots of rhodopsin dense membranes and captures photons. Light stimulation causes hyperpolarization.

Rod Cell Membrane Potential

Sodium channels remain open via cGMP in the dark. When light is absorbed by rhodopsin, it activates the G-protein Transducin, which activates cGMP phosphodiesterase. This causes cGMP degradation to GMP, closing sodium channels.

Light Reception through Eye

Light travels from Ganglion, Bipolar, then Photoreceptor cells. Photoreceptors then synapse their light detection in the opposite direction.

Bipolar Cells

2 types exist. Type 1 is ionotropic and gets depolarized by glutamate and hyperpolarized by light. Type 2 is the opposite in this respect. Glutamate released from dark photoreceptor cells open Chlorine channels and the bipolar cell hyperpolarizes. This fires an action potential to the ganglion cells.

Retina Blind Spot

Optic nerve area of retina contains no photoreceptors. This is usually filled in by brain or eliminated by eye FOV overlap.

Aqueous Humor

Fluid between cornea and lens.

Vitreous Humor

Fluid that fills whole eye.

Fovea

Point of retina that is most sensitive. Has most photoreceptors and cone cells, which is why the eye tries to focus light on it.

Lens

Responsible for the fine adjustments in vision. Lens is contracted by muscles to become more round to focus on close objects. Lens is flattened to view far objects.

Myopia

Nearsightedness caused by the eye elongating, resulting in light being focused before the fovea.

Hyperopia

Farsightedness caused by the eye shortening, resulting in light being focused after the fovea.

Presbyopia

Lens hardening that comes with age. This results in the eye being unable to focus the eye correctly.

Cone Cells

Photoreceptor cells that are responsible for color vision. variability in interactions between retinal and specific opsins are responsible for the different color perception. Red, Green, and Blue are the 3 main types in humans.

Vertebrate Eye vs Cephalopod Eye

In vertebrates, light reaches the photoreceptors last meaning that some of the light information is distorted. Cephalopods have the reverse order, so their photoreceptors deal with less light scattering.

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Vertebrate eyes have blind spots because the optic nerve is in front of the photoreceptors. Since the order is reversed in cephalopods, there is no blind spot.

Snake “Vision”

Snakes have specialized infrared light receptors that allow them to detect heat via infrared radiation. This allows vision in the dark, which helps snakes find prey.

Bee “Vision”

Bees have have specialized UV light receptors that allow them to see UV light at the cost of seeing red light. Since some flowers have UV light pigments, this aids the bees in finding flowers.