Chapter 36 Summary
Core Concepts Summary
36.1 Animal sensory receptors detect physical and chemical stimuli by changes in membrane potential.
Sensory receptors include chemoreceptors, mechanoreceptors, thermoreceptors, pain receptors, and electromagnetic receptors. page 764
Action potential firing rate correlates with the strength of a stimulus. Generally, strong stimuli induce high firing rates and weak stimuli induce low firing rates. page 764
Animal sensory receptors increase their sensitivity to stimuli by temporal and spatial summation, enhance their acuity by lateral inhibition, and adapt to continuous stimuli. page 765
36.2 Specialized chemoreceptors relay information about smell and taste.
Odorant molecules bind to membrane receptors on the surface of olfactory chemoreceptors. page 766
Olfactory sensory cells are neurons that fire action potentials when sending odor information to the brain. page 766
In humans, five taste receptors—
Taste receptors are sensory cells that do not fire action potentials but communicate by synapses with afferent neurons. page 766
36.3 Hair cells convey information about gravity, movement, and sound.
Hair cells are specialized mechanoreceptors that detect motion and vibration. page 767
The statocysts of invertebrates are sensitive to gravity, orienting an organism to “up” and “down.” page 767
The vestibular system of the vertebrate ear provides a sense of balance and gravity. page 768
The tympanic membrane in the outer ear transmits airborne sound waves to the middle ear, where the signal is amplified. The amplified sound waves are transmitted to the cochlea in the inner ear, where sound waves are converted to fluid pressure waves. These waves are then sensed by hair cells that convert the signal to an electrical impulse. page 769
36.4 The ability to sense light and form images depends on photosensitive cells with light-
Opsin is a G protein-
The eyecups of flatworms detect light and dark. page 771
The compound eyes of arthropods sense light using individual light-
The single-
The protein opsin present in photoreceptor cells converts light energy into chemical signals, altering the firing rate of neurons. page 774
Photoreceptor cells of the retina include rod cells, which detect light intensity, and three types of cone cells, which detect different wavelengths of light and allow color vision. page 774
Photoreceptor cells, bipolar cells, ganglion cells, horizontal cells, and amacrine cells form a network that processes visual information in the retina. page 775
783
36.5 The brain processes and integrates information from multiple sensory systems, with tactile, visual, and auditory stimuli mapped topographically in the cerebral cortex.
The vertebrate brain is organized into a hindbrain, midbrain, and forebrain, with the forebrain elaborated into the cerebral cortex in birds and mammals. page 777
The cerebrum is divided into frontal, parietal, temporal, and occipital lobes, which are specialized for different functions. page 778
Somatosensory, motor, auditory, and visual information is topographically mapped to specific areas in the cerebral cortex. page 780
36.6 Cognition is the ability of the brain to process and integrate complex information, remember and interpret past events, solve problems, reason, and form ideas.
The cerebral cortex integrates and processes information from diverse sources, giving rise to problem solving, reasoning, and decision making. page 780
The brain stores memories of past experiences and enables learning through the creation of more long-
Consciousness is an awareness of one’s own identity in relation to others. page 781
Self-Assessment
Give an example of a chemosensory, mechanosensory, and electromagnetic sensory cell.
Self-Assessment 1 Answer
Chemoreceptors respond to molecules that bind to specific protein receptors on the cell membrane. The interaction of molecules and chemoreceptors underlies the sense of smell and taste. An example is the detection by coral polyps of simple amino acids, a food source, in water.
Mechanosensory cells respond to physical deformations of their membrane that can be caused by touch, stretch, pressure, motion, and sound. Examples are the receptors in our skin that sense touch and pressure.
Electromagnetic sensory cells respond to electrical, magnetic, and light stimuli. Examples are the photoreceptors that sense light in different organisms.
Diagram a generalized sensory receptor cell and show how it changes its firing rate in response to detected stimuli.
Self-Assessment 2 Answer
State a hypothesis that explains why all animals have chemoreceptors.
Self-Assessment 3 Answer
All animals have chemoreceptors, so they can sense food sources.
Describe the three main stages by which the mammalian ear detects and codes sound.
Self-Assessment 4 Answer
The three main stages by which sound is detected and coded by the mammalian ear are as follows:
(1) Amplification: Sound vibrations are amplified by the bones in the middle ear. The vibrations are then transmitted to the oval window of the cochlea in the inner ear.
(2) Transfer of sound vibration to fluid pressure waves: Vibrations of the oval window cause fluid pressure waves in both canals of the cochlea at the same time.
(3) Mechanoreception by hair cells within the cochlea: Fluid vibrations within the cochlear canals bend the stereocilia of the hair cells back and forth, stimulating them to release excitatory neurotransmitters. These cause postsynaptic neurons to fire action potentials that are sensed as sound by neuronal networks in the brain.
Compare and contrast the roles of rod cells and cone cells in the retina.
Self-Assessment 5 Answer
Cone cells contain color-
sensitive pigments that allow the eye to detect color. Rod cells, which are differently shaped, sense light (most sensitive to blue- green light), which is interpreted by the brain as white, to shades of grey, to black. Because of their greater number and sensitivity to light, rod cells enable animals to see in low light. Cone cells predominate in the center of the retina, while rod cells predominate the periphery. Describe the role of the cornea and lens in vertebrate eyes.
Self-Assessment 6 Answer
The cornea is the transparent part of the sclera in the front of the eye. Light passes through the cornea before reaching the lens. The cornea and lens bend incoming light rays, focusing them on the retina at the back of the eye to form images.
Describe three different types of eye in animals.
Self-Assessment 7 Answer
Three different types of eyes in animals are eyecups, compound eyes, and single-
lens eyes. (1) Eyecups sense the direction and intensity of light but do not form images. Eyecups contain photoreceptors that point up and to the left or right. A pigmented epithelium layer is behind the photoreceptors so that eyecups only sense light from above and in front of the animal.
(2) Compound eyes are made up of multiple light-
focusing elements, each with a lens, called ommatidia. Ommatidia individually focus light onto a central region formed from multiple overlapping photoreceptors. Compound eyes provide a mosaic image and are extremely good at detecting motion and flashes of light. (3) Single-
lens eyes produce a sharply defined image of the animal’s visual field. A single lens focuses light rays on a particular region of photoreceptors, improving image quality and light sensitivity. Draw the brain, label the lobes, and describe their primary functions.
Self-Assessment 8 Answer
The frontal lobe is important in decision making and planning. The parietal lobe controls body awareness and the ability to do complex tasks. The occipital lobe processes visual information, and the temporal lobe processes sound.
Describe the importance of topographic mapping of sensory input to the cortex, using the primary somatosensory cortex as an example.
Self-Assessment 9 Answer
Neurons in the primary somatosensory cortex integrate tactile information from specific body regions. The area of the body that is sensed by particular sensory neurons in the skin can be mapped onto the cortex. Thus, if an injury occurs in a specific area of the brain, you might be able to predict which areas of the body may be most affected. For example, an injury in one region of the somatosensory cortex might affect touch sensation in part of your arm.
Explain how brain function can be understood by studying patients with brain injuries.
Self-Assessment 10 Answer
By correlating the area of the brain affected with the effects of the injury, you may be able to tell which functions or body areas that part of the brain controls. For example, if a person has an injury in a particular part of his or her brain and his or her sense of taste changes, there is a good probability that such an area controls taste perception.