Special Senses

Name the passage of structures light must get through from air before reaching the two layers of retina?

Air - cornea - aqueous humor - lens - vitreous humor - inner two layers of retina

Define stimuli

Changes in the sensory information our receptors detect in our external or internal environment

How do the refracted image appear at the retina?

Inverted/backward and upside down

Where are general senses receptors found?

These are distributed throughout the body and are located in the skin and internal organs. Typically simple in structure

Sensory receptors may respond continuously or only to changes in stimuli, what are these types of receptors called?

Tonic receptors: Respond continuously to stimuli at a constant rate (ex: balance receptors in your ears) Phasic receptors: detect new stimulus or change in a stimulus that has already been applied but over time their sensitivity decreases. Phasic receptors undergo adaption like receptors in your skin, advantageous for the body not to be continuously bombarded by this sensory info.

Sensory information, whether about inside or outside environment, comes in many forms - name some examples.

Touch, taste, hearing, vision, smell, equilibrium

Some properties of sensory receptors is that it it acts as a transducer. What is a transducer?

Transducers change one form of energy into a different form. There are different types of receptors for different energy forms! Like light energy in eye or sound energy in ear

What criteria are necessary for receptors to be transducers?

1) Maintenance of resting membrane potential across a plasma membrane 2) Modality gated channels within plasma membrane - open in response to stimulus

What two requirements exist for refraction of light rays?

1. Light must pass btwn media of diff densities 2. Media meet at curved surfaces

What is refractive index?

A number representing comparative density of mediums

What are the different color cones are present? How is this distinction made?

BLUE, GREEN, and RED. Distinguished categorically on basis of which wavelength they most optimally detect.

Explain the difference btwn bipolar cells, horizontal cells, ganglion cells, and amacrine cells

Bipolar cells: rods and cones synapses on bipolar cells that converge the visual signals from photoreceptors (less bipolar cells than photoreceptor cells) Horizontal cells: Found btwn photpceptor cells and bipolar cells. These regulate and integrate the stimuli sent from photoreceptor layer to other cell layers. Ganglion cells are neurons that form innermost layer in neural layers. Neuronal convergence continues btwn bipolar neurons and ganglionic neurons. Ganglion axons extend into and through the optic disk Amacrine cells positioned btwn bipolar and ganglion cells. These help process and integrate stimuli as it passes btwn bipolar and ganglion cells.

Receptors can be classified according to the stimulus they perceive, called modality of stimulus. Name some groups of receptors based on their modality of stimulus?

Chemoreceptors - detect chemicals or specific molecules dissolved in fluid. Found in taste buds on tongue, in blood vessels to detect CO2 and O2 levels. Thermoreceptors - Respond to changes in temp, present in skin and hypothalamus. Photoreceptors - detect changes in light intensity, color, movement. Located in the eye Mechanoreceptors - Respond to touch, pressure, vibration, and stretch. Found on most cutaneous receptors, also located in ear Baroreceptors - Detects changes in stretch or distension. Branch repeatedly in vessel or organ walls. Stimulated by changes in wall deformation, involved in regulation of blood pressure. Nociceptors - Respond to painful stimuli. Somatic nocireceptors (chemical, heat, mechanical damage to surface or skeletal muscles). Visceral nocireceptors (detects internal body damage within viscera, O2 deprivation, overstretched smooth muscles, tissue trauma

What are the characteristics of cones?

Cones Less sensitive to light • Work in bright light •Less numerous than rods •Primarily located within fovea centralism •Provide precise visual sharpness and color recognition subdivided into blue, green, and red cones • One to one relationship with the ganglionic cells • Cover relatively small area 1μm2

For focusing light at objects closer than 20 feet, what is the state we find the eyes, lens, and pupil in?

Convergence of eyes: extrinsic muscles pull eyes medially - directs image of interest onto both fovea - weak eye muscle may cause dapple (double vision) Accommodation of lens: Ciliary muscle contraction thicken lens -slackened suspensory ligaments allow lens to thicken, refraction will increase Constriction of pupil: sphincter papillae contraction shrinks hole - light passes only through center of lens, avoiding blurriness that would result if thin edges of the lens were used

Receptors can also be classified by origin. What are the classifications within this category?

Exteroceptors detect stimuli from the external environment (includes receptors on your skin, mucous membranes exposed to environment outside like nasal cavity, oral cavity, vagina, anal canal) Interoreceptors detect stimuli in internal organs. Primarily stretch receptors in the smooth muscle within the walls of these organs. We are unaware of these receptor, mostly except stretch receptor in walls of stomach. Reports chemical change, pressure, temp, and perceived pain in visceral tissue) Proprioceptors are located in our useless, tendons, and joints. These detect body and limb movement, skeletal muscle contraction and stretch, and changes in joint capsule structure. These receptors continuously send this info to the CNS.

Receptors can be classified based on their distribution in the body. What are the two distribution types?

General senses and special senses

Where are special senses found?

Located within the head and are specialized, complex sense organs for the 5 special senses (taste/gustation, olfaction, vision, audition, and equilibrium)

Where is refraction of light maximized passing to the eye?

Maximal refraction occurs btwn the air and cornea

Is the shape of the cornea modifiable to focus light on the retina?

Nope, the shape of lens within the eye is changed to focus light on the retina via help of ciliary muscle contraction

Btwn bipolar cells, horizontal cells, ganglion cells, and amacrine cells, which cells are actually capable of AP?

Only amercing and ganglion cells in retina can produce AP, all other generate graded potential.

Each photoreceptor has both and outer segment that extends into the pigment layer of the retina and an inner segment. Describe the outer and inner segments.

Outer segment is composed of flattened membranous sacs containing photopigments capable of absorbing light energy. Discs get constantly replaced at the base, old discs get pushed into tip (closer to pigmented layer of eye) worn discs removed by phagocytic cells inner segment contains the organelles of the photoreceptor cells like mitochondria, connects directly to cell body

What are the different characteristics that can be used to classify receptors?

Receptor distribution, stimulus origin, and modality

Which photoreceptor cells are responsible for functioning under dim light, what about high-intensity light and color vision?

Rods for film light Cones for color

What are the characteristics of Rods?

Rods more sensitive to light • Work in dim light: night vision • More numerous than cones •Primarily located at peripheral regions • Ganglionic cells receive information from many rod cells producing a blurry image, cannot distinguish color; poor at sharpness of vision • Spatial summation • Cover relatively large area such as 1mm2

Where in the eye is the ratio of rods to cones highest? What about lowest (more cones than rods)?

Rods to cones highest at periphery of retina Rods to cones ratio lowest at fovea centralis (most cones)

What are the subdivisions of general senses receptors?

Somatic sensory receptors found within the skin or monitoring tactile sensations and within the joints, muscles, and tendons for detection of stretch, vibration, pain and pressure Visceral sensory receptors found int he walls of the viscera (internal organs) that respond to temp, chemicals, stretch, and pain

For focusing light at objects farther than 20 feet, what is the state we find the eyes, lens, and pupil in?

• Eyes face forward (not converged) • Lens is flattened (ciliary muscles relaxed, suspensory ligaments taut) • Pupil is relatively dilated ˗ Allows greater amount of light into the eye