Sensory Reception Chapter 35

Sensory Systems The means by which organisms receive signals from the external world and internal environment Many animals can sense stimuli that humans cannot

Sensory Receptors Convert the energy of a stimulus into action potentials Mechanoreceptors Thermoreceptors Pain receptors Chemoreceptors Osmoreceptors Photoreceptors

Assessing a Stimulus Action potentials don’t vary in amplitude Brain tells nature of stimulus by: –Particular pathway that carries the signal –Frequency of action potentials along an axon –Number of axons recruited

Recordings of Action Potentials Figure 35.3 Page 609

Sensory Adaptation A decrease in response to a stimulus being maintained at constant strength

Somatic Sensations Touch Pressure Temperature Pain Motion Position

Somatosensory Cortex Figure 35.4 Page 610

Receptors in Skin Free nerve ending Ruffini ending Pacinian corpuscle Bulb of Krause Meissner’s corpuscle Figure 35.5 Page 611

Referred Pain Sensations of pain from internal organs may be wrongly projected to part of the skin surface Heart attack can be felt as pain in skin above the heart and along the left shoulder and arm

Taste A special sense Chemoreceptors Five primary sensations: –sweet, sour, salty, bitter, and umami Figure 35.8 Page 612

Smell A special sense Olfactory receptors Receptor axons lead to olfactory lobe olfactory bulb receptor cell Figure 35.7 Page 612

Balance and Equilibrium In humans, organs of equilibrium are located in the inner ear Vestibular apparatus vestibular apparatus saccule utricle semicircular canals Figure 35.9b Page 613

Moving in response to gravity, otoliths bend projections of hair cells and stimulate the endings of sensory neurons Acceleration-Deceleration hair cellotolithsmembrane vestibular nerve Figure 35.9b Page 613

Dynamic Equilibrium Rotating head movements cause pressure waves that bend a gelatinous cupula and stimulate hair cells inside it cupula Figure 35.9c Page 613

Properties of Sound Ear detects pressure waves Amplitude of waves corresponds to perceived loudness Frequency of waves (number per second) corresponds to perceived pitch

Anatomy of Human Ear cochlea auditory nerve eardrum auditory canal hammer anvil stirrup Fig a Page 614

Sound Reception Sound waves make the eardrum vibrate Vibrations are transmitted to the bones of the middle ear The stirrup transmits force to the oval window of the fluid-filled cochlea

Sound Reception Movement of oval window causes waves in the fluid inside cochlear ducts Figure 35.11b Page 615 eardrumround window oval window (behind stirrup) scala vestibuli scala tympani

Sound Reception hair cells in organ of Corti tectorial membrane lumen of cochlear duct basilar membrane lumen of scala tympani to auditory nerve Figure 35.11c Page 615

Vision Sensitivity to light does not equal vision Vision requires two components –Eyes –Capacity for image formation in the brain

Invertebrate Eyes Limpet ocellus sensory neuron epidermis cuticle lens Land snail eye Compound eye of a deerfly ommatidium Figures & Pages 616 & 617

Human Eye sclera choroid iris lens pupil cornea aqueous humor ciliary muscle vitreous body retina fovea optic disk part of optic nerve Figure Page 618

Pattern of Stimulation Light rays pass through lens and converge on retina at back of eye The image that forms on the retina is upside down and reversed right to left compared with the stimulus Brain accounts for this during processing

Pattern of Stimulation Figure Page 619

Visual Accommodation Adjustments of the lens Ciliary muscle encircles lens When this muscle relaxes, lens flattens, moves focal point farther back When it contracts, lens bulges, moves focal point toward front of eye

Organization of Retina Photoreceptors lie at the back of the retina, in front of a pigmented epithelium For light to reach the photoreceptors, it must pass layers of neurons involved in visual processing

Organization of Retina Signals from photoreceptors are passed to bipolar sensory neurons, then to ganglion cells Figure 35.21a Page 620

The Photoreceptors Rods –Contain the pigment rhodopsin –Detect very dim light, changes in light intensity Cones –Three kinds; detect red, blue, or green –Provide color sense and daytime vision

Receptive Fields Restricted areas that influence the activity of individual sensory neurons Response of neuron to orientation of bar signals to oscilloscope time (sec) Figure Page 621

Retina to Brain retina optic nerve lateral geniculate nucleus visual cortex Figure Page 621

Disorders of the Eye (1) Color blindness Focusing problems –Nearsightedness and farsightedness Eye diseases –Trachoma –Histoplasmosis –Herpes simplex infection

Disorders of the Eye (2) Age-related problems –Cataracts –Macular degeneration –Glaucoma Injuries –Retinal detachment