Chapter 12 pt1

Sensory Receptors

• specialized cells/nerve endings and cells that detect specific sensory info/stimuli

• initiate neural impulses

Photoreceptors

• rods and cones

• absorbs light and allows us to sense different levels of light and shades of colour

• stimulated by light energy

Chemoreceptors

• stimulated by certain chemicals

(taste, smell, internal envt)

Mechanoreceptors

• stimulated by mechanical forces from some form of pressure

• touch/pressure/pain, hearing, balance, body position

> proprioceptors (in and near the muscles, provides info about body position + movement)

Thermoreceptors

• in the skin, detects heat and cold (temperature)

sensation

• occurs when neural impulse reaches cerebral cortex

• resulting sensation depends on the area of the brain that has interpreted the info

perception

• each person has unique perception

• results from how the cerebral cortex interprets the meaning of the sensory info

Sensory adaptation

• when the brain filters out redundant, insignificant information

• to process info quickly: brain parallels/splits up to input various areas of the brain

• sensory info sometimes does not reintegrated fully = perception diff from what we sense

> ex: optical illusion

Three Layers of the eye

External: Sclera, Cornea

Intermediate: Choroid, Iris, Ciliary Body

Inner: Retina

Sclera

• white, tough, fibrous protective later

Cornea

• transparent part of the sclera at the front of the eye

• light enters through

Choroid

• absorbs stray lights that are not detected by photoreceptors

• contains blood vessels that nourish the eye

Iris

• front part of choroid containing pupil

• allows light to enter the inner eye through said pupil

• iris adjusts the size of pupil based on light conditions (adaptation)

Ciliary muscles

• behind the iris

• attaches to the lens, focuses images on the retina

Retina

• internal of the eye

• thin layer of tissue that contains photoreceptors — rodes and codes

Optic Nerve

• rods and cones send impulses to the optic nerve

What is the lens attached to?

• suspensory ligaments

• divides the eye into two chambers > anterior and posterior

anterior chamber

• in-front of the lens

posterior chamber

• behind the lens

aqueous humor

• clear watery fluid

• maintains shape of cornea

• provides oxygen + nutrients for surrounding cells

vitreous humor

• clear jelly-like substance

• maintain the shape of the eyeball + supports surrounding cells

Rods

• sensitivity to light intensity

• detects motion

• responsible for peripheral vision

• contains pigment: rhodopsin (retinal and the protein opsin)

Rods in the dark

• releases inhibitory NT, inhibiting nearby nerve cells

Rods Absorbing light

• rhodopsin splits into retinal and opsin > triggering reactions that stops the inhibitory NT.. allowing transmission of a nerve impulse to the optic nerve

Cones

• sensitive to different colours, densely packed at the back called fovea centralis

• requires intense light to stimulate them

• detects red, blue, green

Cones Absorb Light

• similar to Rods

• except it has photopsin (which reacts to certain wavelengths of light)

Middle Layer

• Bipolar Cells

Colour Blindness

• inherited condition

• lack/deficiency in particular cones (usually red and green)

Outer Layer

• Ganglion cells

optic disc

• blind spot

Blind Spot

• area where ganglion cells merge to form optic nerve

• does NOT contain photoreceptors

• retina must send info to the optic nerve before integrating visual info from both eyes > info travels to the thalamus > occipital lobe

• left optic tract carries info from right visual field

• right optic tract carries info from left visual field

• image perceived as right side up

Binocular Vision

• use both eyes to look at and collect visual info about an object, depth perception, 3D images

focusing

• lights ray = bent, when passing through cornea, lens, fluid humors

• image focused on fovea centralis = smaller, upside down, reversed left to right

• lens = flexible, can change shape > allows finer focus

Farther Objects

• requires ciliary muscles to relax, suspensory ligaments tense (flattens lens)

Closer Objects

• requires ciliary muscles to contract, suspensory ligaments to relax (rounder lens)

Accomodation

• ability of lens to change shape in order to focus images on the retina

Cataracts

• grey white spots on the lens preventing light from passing through it

Astigmatism

• uneven curvature part of the cornea

• cornea is unable to bend light rays to meet at the correct focal point

Myopia

• nearsighted

• elongated eyeball, focused light falls in-front of retina

• corrected with CONCAVE LENS

Hyerpoia

• farsighted

• short eyeball, focused light falls behind the retina

• corrected with CONVEX LENS