Sensory  Systems  

Learning Objectives Nerve cells identify particular stimuli, depending on their type. Neurons carry signal to brain where it is decoded. The brain uses information about which nerve cells are involved, the frequency of impulses (action potentials), and number of neurons in order to identify the stimulus. What is referred pain? For each sense, specialized receptors sense the stimulus and transmit information to the brain: Skin – many types of receptors, including for pain, temperature, pressure Taste and smell – chemical receptors Hearing – vibrations of hair cells Vision – rods and cones identify b/w light and colored light respectively, though rods are much more sensitive to low light than are cones.

Perception – understanding of what that stimulus Sensory Systems • Sensation – conscious awareness of a stimulus • Perception – understanding of what that stimulus means

Sensory Receptors Mechanoreceptors: pressure, position, or acceleration Thermoreceptors: temperature Receptors • • • Nocireceptors: damage tissue (pain) Chemoreceptors: chemicals Osmoreceptors: water volume Photoreceptors: visible to • • • light

Nerve impulses are all the same – so how what’s going on? does the brain know • Which nerves are carrying the impulses? What is the frequency of the impulses? How many neurons responded to the stimulus? • •

Somatic Sensations (“of the body”) Touch, pressure, • heat, cold, pain, movement Free nerve ending: “Naked” dendrites Encapsulated receptor: Enclosed in tissue

Nociceptors (pain receptors) are free • Nociceptors (pain receptors) are free nerve endings

Referred Pain Pain from internal organs may be wrongly projected to parts of skin surface •

Taste Gustation = sense of taste •

Smell • Olfactory receptors: detect water-soluble or easily vaporized substances Communicate directly with • olfactory bulbs brain in

Hearing Sounds are waves of compressed air •

Detecting Sound Waves Pinnae -> Ear Canal -> Eardrum (vibrations) -> Ear Bones -> Oval Window -> Cochlea •

• Cochlear duct -> Organ of Corti (hair cells) Hair cells bend, release neurotransmitter to trigger action potential in auditory nerve

Hair cells are damaged with exposure to Progressive Deafness Hair cells are damaged with exposure to loud noises •

Vision 3 layers of the eye: Outer • Sclera (“white”): protection Cornea: focus light •

Ciliary Muscle: 3 layers of the eye cont. Middle • Iris: regulate light Pupil: entrance for light Lens: focus light Ciliary Muscle: bend lens • • Inner • Retina: light- sensitive tissue

Focusing of Light • Cornea is curved – bends light rays • Pattern on retina is upside-down & backwards

Signals criss-cross as they travel from the • Signals criss-cross as they travel from the retina to the brain (corrects upside-down / backwards issue)

Ciliary muscle adjusts the shape of the Fine-tuning the Focus Ciliary muscle adjusts the shape of the lens = accommodation •

Common Vision Problems • Nearsightedness, Farsightedness, Astigmatism

Photoreceptors with visual pigments found From visual signals to sight Photoreceptors with visual pigments found behind retina •

Colorblindness • If two kinds of cones missing = total color blindness Red-green colorblindness = lack most or all cones that respond to red or green