BIO 160 - Ch. 16 - FA 2024 Part 2 - Senses PDF

Ch. 16 – Senses BIO 160 10th Ed. Summary Properties and Types of Sensory Receptors The General Senses The Chemical Senses Hearing Equilibrium Vision Omit: Sensory Transduction in the Retina: Generating the Optic Nerve Signal Equilibrium Combination of balance and orientatio...

Ch. 16 – Senses BIO 160 10th Ed. Summary Properties and Types of Sensory Receptors The General Senses The Chemical Senses Hearing Equilibrium Vision Omit: Sensory Transduction in the Retina: Generating the Optic Nerve Signal Equilibrium Combination of balance and orientation in 3-dimensional space Divided into static and dynamic equilibrium: Static: perception of orientation of head when body is stationary. Utricle (horizonal position) and saccule (vertical position) Dynamic: perception of head while moving (motion or acceleration) a) Linear: change in velocity in a straight line (in a car or elevator) = utricle and saccule b) Angular: change in the rate of rotation (swivel in a rotating chair, turn a corner when walking) = semicircular ducts Equilibrium Receptors: hair cells when stereocilia bend, hair cells release neurotransmitters that synapse on vestibular nerve (1st order neuron) hair cells contained within vestibular apparatus which is filled with endolymph Equilibrium Vestibular Apparatus Includes: Utricle and Saccule, and the Semicircular ducts Utricle (posterior chamber): patch of hair cells (macula) lies horizontally on floor of utricle, hair cells embedded in gelatinous membrane (otolithic membrane) static: tilt head – membrane sags and bends cilia on hair cells and informs brain that head is tilted in a certain plain dynamic (linear): car moves forward – membrane lags behind (like a tail) and bends cilia backwards (hair cells stimulated), come to a stop and membrane keeps going forward and stimulates hair cells = informs brain of changes in linear velocity Equilibrium Vestibular Apparatus Includes: Utricle and Saccule, and the Semicircular ducts Saccule (anterior chamber): patch of hair cells (macula) lies vertically on side of saccule, hair cells embedded in gelatinous membrane (otolithic membrane) dynamic (linear): elevator moves up – membrane sags and pulls down on cilia (hair cells stimulated), come to a stop and membrane keeps move up and stimulates hair cells = informs brain of changes in vertical movement Equilibrium 3 semicircular ducts: receptors stimulated by rotation of head e.g., spin in a chair, turn a corner while walking provide info about change in rate of rotation of head: anterior (up/down), posterior (tilting), lateral (side to side) Each duct ends in an ampulla  inside is a mound of hair cells (crista ampullaris) with stereocilia and kinocilium embedded in a gelatinous cap (cupula) Turn head and duct rotates but fluid lags and pushes on cupula with the stereocilia = hair cells bend Orientation of duct causes a different duct to be stimulated by rotation of head in different planes Equilibrium Motion sickness = Discordance of signals Static equilibrium system vs. the dynamic equilibrium system are providing opposing information on what the body is doing Projection–Pathways From anterior and posterior chambers and semicircular ducts 1st order neuron: travels in vestibular nerve then merges into vestibulocochlear nerve (VIII) to vestibular nuclei alongside pons and medulla 2nd order neuron from the vestibular nuclei  Thalamus (& many additional side branches) 3rd order neuron from the thalamus to the vestibular cortex Side Branches include: cerebellum (motor control); nuclei that control eye movements (cranial nerves and head movement); reticular formation (changes to BP and breathing); spinal cord (vestibulospinal tract) Figure 16.21 REVIEW Which component of the vestibular apparatus functions in signaling horizontal movement? A. Semicircular canals B. utricle C. saccule REVIEW! Where is the vestibular apparatus located? A. Outer ear B. Middle ear C. Inner ear REVIEW What brain structures require vestibular input to ensure the eyes can track an object when the body is moving? A. cerebellum B. nuclei of cranial nerves III, IV, and VI C. thalamus D. nuclei of cranial nerves V and VII REVIEW What is the destination of the 2nd order neuron carrying vestibular information so we can have a conscious perception of our head position? A. cerebellum B. nuclei of cranial nerves III, IV, and VI C. thalamus D. nuclei of cranial nerves V and VII REVIEW What cortical location gives us a conscious perception of our head position? A. cerebellum B. Inferior temporal lobe C. Superior temporal lobe D. Inferior post-central gyrus 16.5 Vision Light and Vision Light – electromagnetic radiation (photons) that travel in waves (& particles) Visible light is in the range of 400 nm – 700 nm (red  purple) Vision - perception of objects in the environment by means of the light they emit or reflect Accessory structures of the orbit Accessory Structures of the Orbit Eyebrows provide facial expression, intercept perspiration Eyelids block foreign objects, help with sleep, blink to moisten eyelashes help keep debris from eye Conjunctiva Covers inner surface of the eyelid and superficial eyeball Mucous membrane Highly vascular conjunctivitis ‘pink eye’ = bacterial or viral infection Conjunctiva Transparent mucous membrane lines eyelids and covers anterior surface of eyeball except cornea Richly innervated and vascular (heals quickly) Accessory Structures of the Orbit Lacrimal apparatus (tear gland and ducts) Lacrimal gland located superior- lateral to eyeball Tears cleanse, lubricate, deliver nutrients Empty into lacrimal canal into nasal cavity Tears flow across eyeball help to wash away foreign particles, help with diffusion of O2 and CO2 and contain bactericidal enzyme Accessory Structures of the Orbit Extrinsic Eyes Muscles 6 muscles inserting on eyeball 4 rectus (up/down/side to side), superior and inferior oblique muscles Accessory Structures of the Orbit Innervation of Extrinsic Eye Muscles Supplied by Cranial Nerves oculomotor (III), trochlear (IV), abducens (VI) Anatomy of the Eye Main components of the eye: A) Tunics  Fibrous layer, vascular layer, inner layer B) Optical components  cornea, aqueous humor, lens & vitreous Body C) Neural components  Retina & cone/rod cells Tunics of the Eyeball Fibrous layer (outer) - sclera and cornea Vascular layer (middle) - choroid, ciliary body and iris Inner layer- retina and optic nerve A) TUNICS: 3 layers form wall of eyeball Fibrous Tunic: outer Sclera: Most superficial covering of eyeball; covers most of the eyeball (not over cornea portion) “Whites” of the eye Cornea Most superficial covering of eyeball, covers anterior most portion Transparent – covers iris and pupil, admits light into eye Protects the eye and transmits and refracts light A) TUNICS: 3 layers form wall of eyeball 2. Vascular Tunic: middle Choroid Highly vascular and provides blood to the retina  sits behind retina, pigmented (black) Highly pigmented to absorb stray light Ciliary body Secretes aqueous humor into posterior chamber Muscular ring around lens, extension of choroid Contracts like a sphincter muscle to aid in lens adjustment Loosens the suspensory ligaments that hold the lens Lens flattens or thickens to focus for near vision A) TUNICS: 3 layers form wall of eyeball 2. Vascular Tunic: middle Iris Set of 2 muscular rings that are controlled by autonomic nervous system. Adjustable diaphragm controls size of pupil Parasympathetic nervous system = pupil constriction (CN = III Oculomotor) Sympathetic nervous system = dilation contain pigmented cells called chromatophores ( melanin = black – brown,  melanin = blue, green, gray) A) TUNICS: 3 layers form wall of eyeball 2. Vascular Tunic: middle Lens Transparent lens that refracts light; highly elastic Shape is controlled by the ciliary bodies relaxation of the ciliary bodies  tension of the suspensory ligament and flattening of the lens for far vision. The suspensory ligaments flatten to focus on near objects A) TUNICS: 3 layers form wall of eyeball 3. Neural Tunic: inner Retina Pigmented layer absorbs light Neural layer contains photoreceptors beginning of Optic nerve (CN II) Blindness in Canada  Diabetes  breakdown of blood vessels in the choroid and leak into the retina B) Optical Components Structures that admit and refract light rays to focus on retina Cornea transparent cover on anterior surface of eyeball admits and refracts light Aqueous humor serous fluid secreted by ciliary body into posterior chamber between iris and lens fluid circulates through pupil into anterior chamber (btwn cornea and iris) and out via scleral venus sinus and reabsorbed by ciliary body B) Optical Components lens suspended behind pupil by suspensory ligament changes shape to help focus light, size controlled by suspensory ligaments taut ligaments = flat lens (far vision): cilliary body relaxed loose ligaments = fat lens (near vision): cilliary body contract Cataracts = clouding of the lens Lens loses elasticity with age  loss of near vision i.e., reading glasses vitreous body (humor) Jelly fills space between lens and retina Glaucoma = increased pressure in the vitreous body  retinal damage  blindness Optical Components C) Neural Components Includes retina and optic nerve Retina Sight of conversion of light energy into action potentials (nerve impulses) forms as an outgrowth of the diencephalon thin transparent membrane, attached to the choroid for blood supply attached only at the optic disc (blind spot) and at ora serrata pressed against rear of eyeball by vitreous body (incorrect pressure  loss of blood flow to retinal cells = blindness) contains photoreceptor nerve cells (rods and cones) to transduce light signals C) Neural Components Includes retina and optic nerve Retina Cone cells = highly detailed day/photopic and colour/trichromatic vision Rod cells = low resolution night/scotopic and gray/monochromatic vision macula lutea located in the back of the eye in the center of the retina, an area of concentrated photoreceptor nerve cells (cone cells and rods) fovea centralis center of macula; responsible for generating finely detailed images due to many cone cells (colour: red, green, blue) Blind Spot Optic Disk – the area in back of eye where all nerve fibers from the retina converge and then exit the eye to form the OPTIC NERVE no receptor cells here  no image is produced on this part of retina = blind spot there is a dark blotch in our vision in this area; the brain uses the image surrounding the blind spot to “fill in” the blotch = visual filling The optic disc is medial to the fovea centralis for both eyes. Draw. the LEFT eye and show why it HAS a blind spot in this situation. Label the fovea centralis and optic disc nose Optic disc Fovea centralis Draw the RIGHT eye and show why it DOES NOT have a blind spot in this situation Optic disc nose Fovea centralis Ophthalmoscopic Exam of Eye light and magnification used to look at back of eye and retina optic disk, macula lutea, fovea centralis, blood vessels can be examined direct evaluation of blood vessels for signs of hypertension, atherosclerosis, atrophy of optic nerve etc. Which eye is this? The LEFT The optic nerve is always MEDIAL to the fovea centralis REVIEW What do the lens and the cornea do to light entering the eye? Bend the light (refract) REVIEW! How can the lens change its shape to refract the light even more? Contract ciliary muscle Suspensory ligaments loosen Lens fattens Formation of an Image Overview 1. Light rays enter the eye via cornea 2. cornea (1º focussing structure) bends (refracts) light rays through pupil 3.Pupil controls amount of light that reaches the lens (dilation or constrictions) 4. Lens finely focuses light to back of eye on retina 5. Photoreceptor cells on the retina (rods/cones) change light rays into electrical impulses 6. Optic nerve receives electrical impulses  brain 7. Occipital lobe (1º visual cortex) interprets electrical impulses into an image Formation of an Image Distance Near Vision  Emmetropia (Far Vision) The Near Response Eyeballs are Diverged (straight ahead) Converged Pupils are Dilated Constricted Lens is Flat due to: Fat due to: Relaxation of ciliary muscle Contraction of ciliary muscle Tightening of suspensory Loosening of suspensory ligaments ligaments *Accommodation of the lens Near Response involves 3 processes: 1.Convergence of eyes eyes rotate medially to focus the object on each fovea centralis 2.Constriction of pupil blocks peripheral light rays and reduces spherical aberration (blurry edges), directs light on center of lens 3.Accommodation of lens (change in the curvature of the lens) ciliary muscle contracts, lens takes convex shape – light refracted more strongly and focused onto retina with age: lose near vision first = arms length reader! – lens stiffens and ciliary muscles tire – near point of vision increases (age 10=9cm, 60=83cm) Sensory Transduction in the Retina Retina is the sight of conversion of light energy into action potentials (nerve impulses) Retina has two components: 1.pigment epithelium (most posterior layer of retina, similar in function to choroid) Absorbs stray light to prevent it from reflecting back into the eye and degrading the visual image Histology - Layers of Retina Sensory Transduction in the Retina 2. photoreceptors: rods = low light/night vision, monochromatic images, mostly rods in areas other than macula lutea, contain visual pigment rhodopsin (opsin + retinal) cones = colour vision, require full light, densely packed in fovea centralis region, contain visual pigment photopsin (absorb 3 waves lengths: red, green, blue) Rod and Cone Cells Sensory Transduction in the Retina 3. Bipolar cells – 1st order neuron dendrites synapse with rods and cones (1st order neurons of visual pathway), axons synapse with ganglion cells 4. ganglion cells – 2nd order neuron (largest neurons in retina) closest to vitreous body, 2nd order neurons, axons form the optic nerve Axons of 2nd order neurons  thalamus  3rd order goes to the Visual Cortex Omit Generating the Optic Nerve Signal Visual Pigments Rods = Retinal (from vit A) + opsin = Rhodopsin Cones = Each type of cone has retinal + a different photopsin (blue = short, green = medium, red = long ) Photochemical Reaction – Rods Retinal has two forms cis and trans In the dark Retinal is in the cis (bent) form (ready to be activated) and is violet/purple In the light Retinal changes from cis to trans form and loses its colour (gets “bleached”) To get back to cis form, trans-retinal must be transport to pigment epithelium – takes time + in the dark Light adaptation (moving from dark to light) Pupils constrict, and cones adapt quickly Retinal in rods exposed to bright light converts from the cis the trans form. Rods are non-functional under normal light conditions Overstimulation of retina  pain Dark Adaptation (moving from bright to dark) In bright light, retinal is in the trans Must convert trans to cis  this happens in the pigment epithelium  Takes up to 30 min for full dark adaptation Cone cells do not work in the dark The Dual Vision System Why have both rods and cones? Duplicity theory – single receptor system cannot produce both high- sensitivity night and high-resolution daytime vision Different cells and neural circuits to be able to have both functions! Optimal human vision has both high resolution and high sensitivity The Dual Vision System Rods are sensitive due to high convergence Multiple rods converge on each bipolar cell, multiple bipolar cells on each ganglion cell Weak stimulation of many rods generates signal in one bipolar cell Weak stimulation of many bipolar cells generates a signal in one ganglion cell Very small amounts of light can be perceived = grainy image  The Dual Vision System Little neural convergence in phototopic (day) system as each cone has direct line to brain Cones provide detailed images 1:1:1 cone : bipolar : ganglion cell means much light is required to excite one ganglion cell Colour is only possible with lots of light Each nerve fiber = sharp image Can’t function in dim light because weakly stimulated cones cannot collaborate with rods Colour Vision 3 kinds of cones, based on absorption peaks of their photopsins: short-wavelength (S) cones – peak sensitivity at 420 nm “blue” medium-wavelength (M) cones – peak sensitivity at 531 nm “green” long-wavelength (L) cones – peak sensitivity at 558 nm “red” Other colours activate some combination of these cones, at different intensities. Colour blindness is most commonly due to lack of green or red cones Colour Vision Stereoscopic Vision Depth perception – judge how far away objects are Two eyes with overlapping visual fields Look at the same object from a slightly different angle with each eye  focuses on fovea centralis Retina interprets distance by focussing objects on different parts of the retina (fixation point) Objects further away than fixation point have image medial to the foveas Objects closer cast images more laterally Stereoscopic Vision  Visual Projection Pathway electrical impulse is transferred from photoreceptors  bipolar cells (1st order neurons) bipolar cells  ganglion cells (2nd order neurons) whose axons make the optic nerve ganglion cell axons leave each orbit and converge to form an X (optic chiasm) half the fibers of each optic nerve cross over to the opposite side of the brain (hemidecussation) and continue as the optic tracts  thalamus 3rd order neurons from thalamus 1º visual cortex of the occipital lobe Visual Projection Pathway Summary Properties and Types of Sensory Receptors The General Senses The Chemical Senses Hearing Equilibrium Vision Omit: Sensory Transduction in the Retina: Generating the Optic Nerve Signal