Chapter 49 Campbell - Sensory System

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Information is transmitted in the nervous system as

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action potentials

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sensations

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impulses arriving from sensory neurons, are routed to different parts of the brain that interpret them, producing perceptions of various stimuli

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sensory reception

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the detection of energy from a particular stimulus by sensory cells

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sensory receptors

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usually modified neurons or epithelial cells that occur singly or in groups within sensory organs

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exteroreceptors vs. interoreceptors

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sesnsory receptors that detect stimuli from the external environment vs. those that detect from an internal environment

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sensory transduction

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the conversion of stimulus energy into a receptor potential, a graded changee in the membrane potential of a receptor cell that is proportional to the strength of the stimulus

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amplification

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amplification of stimulus energy either by accessory structures of sense organs or as part of the transduction process.

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Transmission

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of receptor potential to the central nergvous system may occur either as a result of the generation of an action potential when the sensory receptor is a sensory neuron, or by the release of neurotransmitter from a receptor cell into a synspse with a sensory neuron, which then may transmit an action potential.

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Integration

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processing of sensory infromation begins with the summation of graded potentials from receptors.

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sensory adaptation

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caused by continuous stimulation result in a decline in sensitivity of the receptro cell

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mechanoreceptors

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sensory receptros that respond to the mechanical energy of pressure, touch, stretch, motion, and sound. Bendin or stretching of the mechanoreceptor cell membrane increases its permeability to sodium and potassium ions, creating a receptor potential.

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touch receptors

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modified dendrites of sensory neurons

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muscle spindles

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stertch receptors that monitor the length of skeletal muscles

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Hair cells -

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mechanoreceptors (motion detection) in the ear, when motion produces bending in the cilia or microvilli projecting from a hair cell, ion permeabilities either increase or decrease, and the rate of action potential firing changes.

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Pain receptors = nociceptors

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naked dendrites in the epidermis called nociceptors, different groups of receptors respond to exceess heat, pressure, or chemicals released by injured cells.

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Thermoreceptors

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in skin or hypothalamus - respond to heat or cold and help to regulate body temperature.

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chemoreceptors

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include both general receptors that monitor total solute concentration or specific receptors. Gustatory (taste) and olfactory (smell) receptors respond to groups of chemicals

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Electromagnetic receptors

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respond to various forms of electromagnetic energy.

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Photoreceptors

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detect visible light and are foten orgainized into eyes.

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eye cup

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in planarians, detect light intensity and direction, consists of receptor cells within a cup formed from darkly pigmented cells. Brain compared impulses to help the animal navigate a direct path away from a light source.

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compound eye

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contains up to thousnads of light detectors called ommatidia, each with its own lens.

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single-lens eye

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light is focused through the signle lens onto the retina containing light

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sclera

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tough, outer connective tissue layer of the eye

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choroid

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thin, pigmented inner layer of eye

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conjunctiva

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a mucous memvrane covering the sclera.

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cornea

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sclera becomes this at front of the eye, functions as a fixed lens

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iris

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chroid at front of eye, reguluates the amount of light entering through the pupil.

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retina

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innermost layer, containts the photoreceptors cells, the optic nerve attaches to the eye at the optic disk, forming a blind spot on the retina

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lens

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focuses an image onto the retina

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ciliary body

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produces the aqueous humor that fills the anterior eye cavity, vitreous humor fills the posterior cavity.

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accommodation

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the way in which mammals focus on objects in which ciliary muscles contract, causing suspensory ligaments to slacken and hte elstic lens to become rounder.

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rod cells and cone cells

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the photoreceptors in the retina. The relative proportion of each of these receptors correlates with the activity pattern of the animal: Rods are more light sensitive and enable night vision, whereas cones distinguish colors. In the human eye, rods are most concentrated towart the edge of the retina, whereas the center of the visual field, the fovea, is filled with cones.

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ommatidia

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The facets of the compound eye of arthropods and some polychaete worms.