Developmental aspects of ANS During youth, ANS impairments are usually due to injury In old age, ANS efficiency declines, partially due to structural changes at preganglionic axon terminals Section 3: Special Senses Eye and Vision 70% of all sensory receptors are in the eye Nearly half of the cerebral cortex is involved in processing visual information Most of the eye is protected by a cushion of fat and the bony orbit Structure of the eye Eyebrows- shade the eye and protect it from perspiration Eyelids (palpebrae)- protect the eye anteriorly, eyelashes initiate reflex blinking Conjunctiva- transparent membrane that produces a lubricating mucous secretion Lacrimal apparatus- lacrimal glands and ducts that connect to the nasal cavity and produce tears Extrinsic eye muscles 6 strap-like extrinsic eye muscles that enable the eye to follow moving objects 4 rectus muscles provide movement to the eye 2 oblique muscles move the eye laterally and rotate the eye Structure of the eyeball Wall of eyeball contains three layers 1. Fibrous- outer most layer that contains the sclera and cornea 2. Vascular- middle pigment layer and contains three regions- choroid (supplies blood) ciliary body (controls lens shape) iris (colored part of the eye). (Pupil controls amount of light entering the eye.) 3. Sensory- the retina Pigmented layer absorbs light and stores vitamin A Neural layer has photoreceptors and transmits signals Optic disc is your blind spot due to lack of photoreceptors Photoreceptors (rods: operate in dim light and provide indistinct, fuzzy, non-color peripheral vision, cones: operate in bright light and provide a high-acuity color vision) Internal cavity is filled with humors fluid Lens separate internal cavity into anterior and posterior segments Taste Receptor organs are taste buds Taste sensations Sweet- sugars, saccharin, alcohol, and some amino acids Sour- hydrogen ions Salt- ions Bitter- alkaloids such as quinine and nicotine Umami- amino acids glutamate and aspartate Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence taste Temperature and texture enhance or detract from taste Smell Organ of smell is the olfactory epithelium in the roof of the nasal cavity Olfactory receptor cells-bipolar neurons with radiating olfactory cilia
Bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (cranial nerve 1) Supporting cells surround and cushion olfactory receptor cells Basal cells lie at the base of epithelium Hearing and Balance Parts to the Ear: External ear (hearing)- composed of the auricle (pinna), external acoustic meatus (auditory canal) and tympanic membrane (eardrum) Middle ear (hearing)- composed of a small air-filled, mucosa-lined cavity in the temporal bone, and the pharyngotympanic (auditory) tube equalizes pressure in the middle ear cavity with the external air pressure Internal ear (hearing and balance) Composed of three parts: vestibule, semicircular canals, and cochlea Three bones (ossicles) in the inner ear: malleus, incus, and stapes Receptors for hearing and balance Respond to separate stimuli Are activated independently Properties of sound Sound is the pressure disturbance produced by a vibrating object Pitch is the perception of different frequencies Loudness is subjective to interpretation of sound intensity Transmission of sound to the inner ear Sound waves vibrate the tympanic membrane Ossicles vibrate and amplify the pressure at the oval window. Pressure waves move through perilymph of the scala vestibule Waves of frequencies below the threshold of hearing travel through the helicotrema and scali tympani to the round window Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane at a specific location, according to the frequency of sound Auditory pathways to processing Impulses from the specific hair are interpreted as specific pitches Loudness is detected by increased numbers of action potentials that result when the hair cells experience larger deflections Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears Equilibrium and orientation Vestibular apparatus consists of the equilibrium receptors in the semicircular canals and vestibule Vestibular receptors monitor static equilibrium Semicircular can receptors monitor dynamic equilibrium Three modes of input for balance and orientation Vestibular receptors Visual receptors Somatic receptors Diagrams