CH 16 - PowerPoint Presentation

CH 16 sense organs general senses chemical senses, hearing & equilibrium vision

general properties - a stimulus  stimulates a receptor  which sends impulses  via transduction to an effector - transduction = the changing of one form of energy into another (touch to electrical) - sense organs transmit 4 types of information - modality = type of stimulus (labelled line code) - location = receptive field, sensory projections, projection pathways – - intensity = how many fibers are firing and firing frequency - duration = phasic (quickly adapts) or tonic (adapts slowly)

types of receptors (modality) thermoreceptors = respond to heat and cold photoreceptors = respond to light nociceptors = respond to pain, tissue injury, or situations that may cause damage chemoreceptors = respond to chemicals, smell and taste mechanoreceptors = vibrations, touch, pressure, tension they make you aware of your internal and external environment

receptors by origin of stimulus (location) exteroceptors = sense things outside the body interoceptors = senses arise from internal organs and tissues proprioceptors = position, body movements, muscles, joints, tendons general (somatosensory & somatoesthetic ) = simple receptors, widely distributed receptors for senses we are aware of & others we do not perceive consciously (BP, BV, O2, touch) special senses = limited to the head, use cranial nerves, and sense arises from complex organs (eyes, ears, smell)

general senses (simple structures) unencapsulated - free nerve endings = skin, mucus membranes, warm, cold, pain - tactile corpuscles (discs) = Merkels discs for light touch, sense textures, edges, and shapes, star shaped cells with projections - peritrichial (hair receptors) = fiber curls about hair follicle and responds to movement of the hair and quickly adapt encapsulated - Meisners tactile corpuscles = phasic, light touch, texture, in skin - Krauses end bulbs = mucous membranes of lips and tongue, conjunctiva, and epineurium of large nerves - thermoreceptors - Pacinian lamellar corpuscles = phasic, deep touch, stretch, tickle, and vibration, periosteum of bone, joint capsules, viscera and genitalia - bulbous Raffini corpuscles = tonic, heavy touch, pressure, joints, skin, in dermis, subcutaneous tissue and joint capsules

somatosensory projections & pathways - initial injury causes sharp pain by fast myelinated fibers - rate is from 12 to 30 m/sec - followed by unmyelinated slow fibers at 0.5 to 2.0 m/sec - longer lasting dull diffuse pain cause bradykinin release pathways - head and neck to brainstem to cortex and cerebellum - below neck spinothalamic, spinoreticular , to reticular formation to hypothalamus to limbic to emotional response to be checked by cerebellum and cerebrum - gracile fasciculus to spinocerebellar tract to thalamus to cortex and cerebellum

modulation for pain - mental and physical state affects perception - endogenous opioids in CNS are analgesics ( enkephalins , endorphins, & dynorphins ) - endogenous opioids are secreted by CNS (midbrain gray matter), pituitary, GI tract, other organs - they are neuromodulators by spinal gating to stop nerve fibers for pain at the posterior horn from firing - this affect is the result of descending analgesic fibers and mechanical stimulation of the injured area

pain modulation parthway - nociceptor stimulates 2 nd order nerve fiber causing it to release subP - 2 nd order nerve fiber signals up spinothalamic tract to thalamus - thalamus relays info through 3 rd order neurons to cerebral cortex where it is perceived as pain - hypothalamus and cerebrum feed info to midbrain for integration - midbrain sends signals down to reticular formation of medulla - medulla sends descending serotonin analgesic fibers through the reticulospinal tract to the posterior horns of the cord - these synapse & feed inhibitory enkephalins to 2 nd order cord pain fibers - at higher levels presynaptic inhibition can take place in the medulla by blocking release of subP

the chemical senses taste, smell, sound, equilibrium, vision - taste = gustation, tastants interact with about 4000 taste buds - buds are found on the tongue, inside cheeks, soft palate, pharynx, and epiglottis - there are 4 types of taste buds ( papillae ) 1. fungiform = mushroom shape, 3 buds at apex, tip & sides of tongue 2. foliate = in kids, gone by 3, near molars and premolars on tongue 3. circumvallate = large, V at rear of tongue, 7-12 but 50% of all buds, 250 buds on each papillae surrounded by a deep trench 4. filiform = tiny spikes & no taste buds, most abundant papillae on human tongue with no role in taste

tongue anatomy support cells = look like taste cells but no sensory role taste cells = banana shape epithelial cells with sensory hair cells, 7-10 days until replaced taste hairs = sensory receptors for tastants taste pore = pit into which chemicals descend basal cells = stem cells but may also have an integrative function sensory nerve = carry info to brainstem, thalamus, cerebrum, olfactory area synaptic vesicles = taste cells are not neurons but release neurotransmitters to activate sensory nerve

what makes up a taste salty = Na and K sour = acids umami = meat, amino acids sweet = many organics, flowering plants bitter = alkaloids

- taste cells release neurotransmitters - Info via facial nerve (VII) from 1 st 2/3 of tongue - info via glossopharyngeal from posterior 1/3 of tongue - vagus form palate, epiglottis, & pharynx - all to solitary nucleus in medulla oblongata - 2 nd order to hypothalamus and amygdala - projections to thalamus-insula-postcentral gyrus = taste - taste signals to orbitofrontal cortex and integrated with input from eyes and nose and forms a conclusion about the taste and emotional acceptance of the food

Smell (olfaction)

odorant – travels to olfactory mucosa – binds to receptor on olfactory hairs – hairs synapse with to glomerulus cells (each type for a specific odor) – integration laterally and vertically – mitral and tufted cells form nerve fibers - travelling into olfactory bulb primary olfactory cortex, thalamus, and hypothalamus some cells have nociceptor functions and identify noxious or painful substances or are hyper stimulated by others providing the sensation of pain (ammonia, chlorine menthol are noxious but capsaicin overstimulates)

- as the eyes see more the sense of smell diminishes - olfactory hairs in humans 5 cm 2 but cats have 20 cm 2 - women are more sensitive than men - most humans can identify 2000 -4000 odors but some 10,000 - some animals have as many as 12,000 receptor types - humans have about 350 different receptor types for odors

hearing (auditory, vibrations, equilibrium) - pitch = treble or base - human ear can hear from about 20 to 20,000 Hz (cps) - <20 = infrasonic and >20,000 = ultrasonic - best hearing 1500 to 5000 Hz most loss at 250 to 2100 - loudness = intensity = amplitude = dB = decibels - outer, middle, inner ear

outer ear - helix, external acoustic meatus, antitragus, lobule - carries vibrations to tympanic membrane - ear canal contains guard hairs, cerumen, low pH, lysosomes, waterproof epithelium, ceruminous & sebaceous glands middle ear - tympanic cavity and membrane, innervated by branches of the vagus (X) and trigeminal nerves (IV), contains the auditory ossicles (3 bones which transmit vibrations in the air into liquid pressure against inner ear nerve cells) inner ear - temporal bone labyrinth lined by membranous canals filled with perilymph and surrounded by endolymph

- the 3 ossicles are the smallest bones of the body - in order to function they are kept in position by muscles and ligaments - these function to protect the inner ear from too loud sounds - protects the oval window - auditory canal = the opening from the exterior to the tympanic membrane, where you should not put a Q tip - auditory tube = canal which joins the middle ear to pharynx - malleus, incus, stapes are the 3 ossicles

- vibrations as high and low pressure variations enter the external acoustic meatus - as they strike the tympanic membrane the muscles reduce the affect upon the oval window - malleus in and out, affects incus, which moves the stapes in and out - which causes the perilymph of the inner ear to move which in turn moves cochlear hair cells which initiate nerve impulses eventually to the vestibulocochlear nerve (cranial nerve VIII)

vestibule = contains the labyrinth for equilibrium, cochlea = contains the labyrinth for hearing modiolus = circular bone in which the labyrinths exist spiral organ ( Corti ) = within the cochlear duct is the spiral made up of hair and supporting cells and membranes whose function is to allow the hair cells to act as receptors for different frequencies which will be interpreted as sound inner hair cells = single row of about 3,500 medial hair cells, outer hair cells = three rows of about 20,000 hair cells arranged as Vs each with about 100 hair cells

sensory coding -the ability to differentiate loudness (amplitude) - and pitch (frequency) - soft sounds = slight amplitude and limited stimulation of cochlear hair cells - louder sounds = larger amplitude, higher frequency of firing & stimulation of more cochlear hair cells - proximal end (base)of cochlea narrow and stiff hairs for high pitch - distal end (apex) 5X wider, more flexible, low pitch

-each time a sound wave passes down the cochlea the perilymph moves like a wave and moves the inner and outer hair cells - as the hair cells move they pull on the prior cell and open an ion gate which allows K to rapidly flow down the concentration gradient and depolarize the hair cell - as the wave moves away the basilar membrane hair cells bend back and move in the opposite direction and the cells repolarize - during depolarization the hair cells release a neurotransmitter which stimulates the sensory dendrites of nerve fibers

- sound – vibration – perilymph movement – hairs move - cells depolarize/repolarize – initiate sensory impulse – to medulla – to pons - sends motor impulses to hair cells – which shorten and make basilar membrane less or more flexible – this allows hair cells to be more sensitive – and allows brain to – better differentiate between frequencies also pons sends efferents – to IHC – to inhibit some cells – so areas of most and least sensitivity can be differentiated

hair cell’s nerve fibers – to spiral ganglion – to cochlear nerve – joins vestibular nerve fibers – becomes cranial nerve VIII – goes to cochlear nuclei – which goes to the pons – where binaural hearing or comparison from left and right ears takes place - also to inferior colliculi – then 3 rd order to thalamus – 4 th order to primary auditory cortex – to temporal lobe – to perceive sound – much decussation along the way at the same time

branches of the vestibulocochlear nerve (VIII) as well as V and VII send efferents back to the tensor tympani and stapedius muscles to allow for better discrimination

equilibrium – original function of the ear - vestibular apparatus – 3 semicircular canals with 2 chambers - static equilibrium such as the orientation of the head when the body is still - semicircular duct measures active events such as motion, linear, angular, rotation - ducts are filled with endolymph, and hair cells - anterior saccules are vertically oriented - posterior saccules are horizontally oriented - medial duct is at a 30 degree angle

As you turn or bend your head etc. the endolymph in the semicircular canals does not move as fast as the motion of the head and it causes the hairs in the ampulla to bend which initiates impulses to the aural areas and cerebellum

the impulses synapse with sensory fibers of the vestibular nerve fibers which merges with the cochlear nerve and then VIII which leads to 4 vestibular nuclei in the pons and medulla they communicate with each other to learn about position and motion of the body then send info to the cerebellum, thalamus, and vestibulospinal tract to control balance thalamus sends reverberating fibers back to the postcentral gyrus and transitional zone between the primary sensory and motor cortex thalamus also sends info to III, IV, and VI for compensating eye movements, and the reticular system for control of blood pressure and breathing as posture changes

vision the perception of a small part of the electromagnetic spectrum from 400 to 700 nm (nanometers)

your eye eyebrows = communication palpebral = eyelids, protection, wet, sweep, medial and lateral canthi, orbicularis oculi muscles, tarsal plate with 20-25 tarsal glands which secrete oil that coats the eye and reduces evaporation eyelashes = guard hairs, blink reflex conjunctiva = transparent mucous membrane, covers anterior eyeball, except cornea, prevent drying, rich BV supply

lacrimal apparatus = almond sized glands in frontal bones at the superior lateral corner with 10-14 short ducts to the surface of the conjunctiva tears contains nutrients, lubricants, and antimicrobial lysosomes tears collect in the medial commissure, and flow into the lacrimal punctum at the corner of the eyes which connect to the lacrimal canaliculi which drain into the lacrimal sac which drains into the nasolacrimal duct and washes the tears into the inferior meatus of the nasal cavity, so runny eyes equals runny noses

- the eye has 6 extrinsic muscles - these attach to the walls of the orbit - and to the eyeball - these muscles are used to move the eyeball - there are 4 rectus (straight) muscles( sup,inf , med, lat ) - and 2 oblique (slanted) muscles (sup, inf ) - superior oblique innervated by trochlear nerve IV - lateral rectus is innervated by abducens VI -the rest if the muscles are innervated by oculomotor III

superior, inferior, medial, and lateral rectus muscles originate from a shared circular tendinous ring on the posterior wall of the orbit and inserts on the anterior eyeball just behind the white of the eye and move the eyeball up, down, medially, and laterally

Superior oblique starts on the medial wall of the orbit, travels through a fibrocartilage ring (trochlea) and inserts on the superolateral part of the eyeball. The inferior oblique starts at the inferior medial wall of the orbit and inserts at the inferolateral part of the eyeball.

the eyeball has 3 tunics (coverings) fibrosa = sclera, the white of the eye, cornea, made of collagen and stratified squamous epithelium anteriorly and simple squamous posteriorly, Na and H2O pumped out to prevent swelling, anterior tissue rich in stem cells for rapid healing vasculosa = uvea, middle layer, choroid, ciliary body (muscular ring about the lens and secretes the aqueous humor), iris (controls the diameter of the pupil, gives color to your eye), pupil (opening to allow light in) interna = retina and optic nerve

optical components of the eye - transparent parts which allow light to pass through - include cornea , aqueous humor , lens , vitreous body, & retina - light can pass straight through or be bent or be blocked - ciliary body makes aqueous humor and secretes it into the anterior chamber between cornea and iris - lens is made up of transparent flattened lens cells and is supported by a ring called the suspensory ligament attached to the ciliary body - vitreous body (humor) is a transparent jelly that fills the vitreous chamber behind the lens

neural component of the eye - retina is an outgrowth of the diencephalon (optic vesicles) - macula lutea and fovea centralis (most finely detailed images) has about 4,000 small cones and no rods, high resolution, no convergence, 1:1:1 (cone – bipolar – ganglion) - optic disc is an path for blood vessels, a blind spot - visual filling means the brain fills in the missing information - saccades - the eye is always flickering, fastest moves of body - photopupillary reflex – ANS reflex – pupillary dilator ( sym ) & constrictor ( parasym ) – result 5X light

refraction = change in direction of light beam emmetropia = focus 20 ft away is a relaxed eye near response = convergence, constriction, accommodation convergence = both eyes move to focus on an object constriction = reduce spherical aberration accommodation = ciliary muscles change shape of lens  = far vision,  = close vision

the retina (sensory transduction) sclera – outer layer of eyeball, dense collagenous CT+BV+nf choroid – dark vascular layer at back of retina pigment layer – stops stray light from hitting retina rods – receptor cells for black & white vision, not a neuron 130 cones – receptor cells for color vision, not a neuron 6.5 rod and cone nuclei = synapse with bipolar and horizontal cells bipolar cells = 1 st order neurons horizontal cells = integration of visual info ganglion cells = 2 different types (visual & light) glial cells = support and hold in place all cells

ganglion cells = 2 nd order neurons, form the optic nerve, receive info from bipolar cells and amarcine cells, some ganglion cells are photosensitive and send light info to brainstem for control of circadian rhthyms amacrine cells = integrate info from bipolar cells which received info from rods, cones, and horizontal cells and feed this info to ganglion cells

- light to retina – energy to chemical change - chemical to electrical change – electrical signal – synapse - integration and convergence - passage to brain rod/cone – bipolar – ganglion – optic nerve – optic chiasma – hemi decussation – lateral geniculate of thalamus – optic radiation to primary visual cortex of occipital but some photosensitive ganglion cells send info to superior colliculus (extrinsic muscle reflexes) and pretectal midbrain (pupillary reflexes)

color vision – 3 cones – blue(420) – green(531) – red(558) color is an integration of all 3 cones color blindness – lack of 1 of the opsins (usually sex linked) nocturnal = rods only diurnal = rods and cones

stereoscopic vision provides depth perception less than 100 feet focuses lateral to the fovea greater than 100 feet focuses medial to the fovea about 100 feet focuses on the fovea

action of light on rhodopsin 1) light enters eye 2) rhodopsin energized 3) cis-retinal becomes trans retinal 4) opsin on energized trans form initiates cGMP breakdown and 5) sends signals through optic nerve 6) trans retinal breaks down into opsin and retinal 7) trans retinal reverts enzymatically back to cis form 8) opsin and cis retinal combine back to regenerate rhodopsin