Animal Form
&
Function
Group 3 Off G
Ardhena Sastya Mahalanny 200342616895
Muhammad Alfin Hidayat 200342616859
Nawal Kamilah Ismail 200342616807
Rodiah Amin Hamidah 200342616837
Syalwa Dida Wuryanti 200342616813
Muhammad Alfin Hidayat Animal Form and Function
Basic Principles of Animal Form and Function
Animal form and function are correlated at all levels of organization
• Physical laws constrain the evolution of an animal’s size and shape. These constraints contribute to convergent evolution, the similar but independent adaptations of different species to a common environmental challenge.
• Each animal cell must have access to an aqueous environment. Simple two-layered sacs and flat shapes maximize exposure to the surrounding medium. More complex body plans have highly folded internal surfaces specialized for exchanging materials.
• In the hierarchical organization of animal bodies, groups of cells with a common structure and function make up tissues. Different tissues make up organs, which together make up organ systems. Animal tissues fall into four main groups, each with distinct functions. Epithelial tissue forms active interfaces with the environment on external and internal surfaces of the body.
Connective tissue binds and supports other tissues. Muscle tissue contracts, moving the parts of the body. Nervous tissue transmits nerve impulses throughout the body.
• The endocrine and nervous systems are the two means of communication between different locations in the body. The endocrine system broadcasts signaling molecules called hormones everywhere via the bloodstream, but only certain cells are responsive to each hormone. The nervous system uses dedicated cellular circuits involving electrical and chemical signals to send information to specific locations.
Feedback control maintains the internal environment in many animals
• Faced with environmental fluctuations, animals regulate (control) certain internal variables while allowing other internal variables to conform to (correspond to) external changes. Homeostasis is the maintenance of a steady state despite internal and external changes.
• Homeostatic mechanisms are usually based on negative feedback, in which the response reduces the stimulus. In contrast, positive feedback involves amplification of a stimulus by the response and often brings about a change in state, such as the transition from pregnancy to childbirth.
• Regulated change in the internal environment is essential to normal function. Circadian rhythms are daily fluctuations in metabolism and behavior tuned to the cycles of light and dark in the environment. Other environmental changes may trigger acclimatization, a temporary shift in the steady state.
Homeostatic processes for thermoregulation involve form, function, and behavior
• An animal maintains its internal temperature within a tolerable range by thermoregulation.
Endotherms are warmed mostly by heat generated by metabolism. Ectotherms get most of their heat from external sources. Endothermy requires a greater expenditure of energy. Body temperature may vary with environmental temperature, as in poikilotherms, or be relatively constant, as in homeotherms.
• In thermoregulation, physiological and behavioral adjustments balance heat gain and loss, which occur through radiation, evaporation, convection, and conduction. Insulation and countercurrent exchange reduce heat loss, whereas panting, sweating, and bathing increase evaporation, cooling the body. Both ectotherms and endotherms adjust their rate of heat exchange with their surroundings by vasodilation or vasoconstriction and by behavioral responses.
• Many mammals and birds adjust their amount of body insulation in response to changes in environmental temperature. Ectotherms undergo a variety of changes at the cellular level to acclimatize to shifts in temperature.
• The hypothalamus acts as the thermostat in mammalian regulation of body temperature. Fever reflects a resetting of this thermostat to a higher set point in response to infection.
Energy requirements are related to animal size, activity, and environment
• Animals obtain chemical energy from food, storing it for shortterm use in ATP. The total amount of energy used in a unit of time defines an animal’s metabolic rate. Metabolic rates are generally higher for endotherms than for ectotherms.
• Under similar conditions and for animals of the same size, the basal metabolic rate of endotherms is substantially higher than the standard metabolic rate of ectotherms. Minimum metabolic rate per gram is inversely related to body size among similar animals. Animals allocate energy for basal (or standard) metabolism, activity, homeostasis, growth, and reproduction.
• Torpor, a state of decreased activity and metabolism, conserves energy during environmental extremes. Animals may enter torpor during sleep periods (daily torpor), in winter (hibernation), or in summer (estivation).
Animal Nutrition
An animal’s diet must supply chemical energy, organic molecules, and essential nutrients
• Food provides animals with energy for ATP production, carbon skeletons for biosynthesis, and essential nutrients—nutrients that must be supplied in preassembled form. Essential nutrients include certain amino acids and fatty acids that animals cannot synthesize; vitamins, which are organic molecules; and minerals, which are inorganic substances.
• Animals can suffer from two types of malnutrition: an inadequate intake of essential nutrients and a deficiency in sources of chemical energy. Studies of genetic defects and of disease at the population level help researchers determine human dietary requirements.
The main stages of food processing are ingestion, digestion, absorption, and elimination
• Food processing in animals involves ingestion (eating), digestion (enzymatic breakdown of large molecules), absorption (uptake of nutrients by cells), and elimination (passage of undigested materials out of the body in feces).
• Animals differ in the ways they obtain and ingest food. Most animals are bulk feeders, eating large pieces of food.
• Compartmentalization is necessary to avoid self-digestion. In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles that have fused with lysosomes. In extracellular digestion, which is used by most animals, enzymatic hydrolysis occurs outside cells in a gastrovascular cavity or alimentary canal.
Organs specialized for sequential stages of food processing form the mammalian digestive system
Evolutionary adaptations of vertebrate digestive systems correlate with diet
• Vertebrate digestive systems display many evolutionary adaptations associated with diet. For example, dentition, which is the assortment of teeth, generally correlates with diet. In addition, herbivores usually have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation. Many herbivores, including cows, also have fermentation chambers where microorganisms digest cellulose, a form of mutualism.
Feedback circuits regulate digestion, energy storage, and appetite
• Nutrition is regulated at multiple levels. Food in the alimentary canal triggers nervous and hormonal responses that control the secretion of digestive juices and that promote the movement of ingested material through the canal. The availability of glucose for energy production is regulated by the hormones insulin and glucagon, which control the synthesis and breakdown of glycogen.
• Vertebrates store excess calories in glycogen (in liver and muscle cells) and in fat (in adipose cells). These energy stores can be tapped when an animal expends more calories than it consumes.
If, however, an animal consumes more calories than it needs for normal metabolism, the resulting overnourishment can lead to the serious health problem of obesity.
• Several hormones, including leptin and insulin, regulate appetite by affecting the brain’s satiety center. The problem of maintaining a healthy weight may stem partly from our evolutionary past, when fat hoarding may have been important for survival.
Rodiah Amin Hamidah 200342616837 CIRCULATION AND GAS EXCHANGE Open and Closed Circulatory Systems
Arthropods and most molluscs have an open circulatorysystem,.
In a closed circulatory system, a circulatory fluid called blood is confined to vessels and is distinct from the interstitial fluid
Single & Double Circulation
• The blood passes through the heart once in each complete circuit, an arrangement called single circulation
• The circulatory systems of amphibians, reptiles, and mammals have two circuits, an arrangement called double circulation
The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle.
The contraction, or pumping, phase of the cycle is called systole.
The relaxation, or filling, phase of the cycle is called diastole.
The cardiac cycle
• The heart rate, also called the pulse Is the number of beats per minute.
• The cardiac output Is the volume of blood pumped into the systemic circulation per minute Blood Pressure and Gravity
Blood pressure is determined partly by cardiac output and partly by peripheral resistance due to variable constriction of the arterioles
Blood flow in veins
In the thinner-walled veins. Blood flows back to the heart mainly as a result of muscle action Blood components function in exchange, transport, and defense As
• Blood in the circulatory systems of vertebrates Is a specialized connective tissue
• Blood consists of several kinds of cells suspended in a liquid matrix called plasma
• The cellular elements occupy about 45% of the volume of blood
• Blood plasma is about 90% water
• Among its many solutes are inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes
Cellular Elements
• Suspended in blood plasma are two classes of cells -Red blood cells, which transport oxygen
-White blood cells, which function in defense
• A third cellular element, platelets are fragments of cells that are involved in clotting Gas exchange occurs across specialized respiratory surfaces
• In the remainder of this chapter, we will focus on the process of gas exchange.
• Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide How a Mammal Breathes?
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs How a Bird Breathes?
Besides lungs, bird have eight or nine air sac that function as bellows that keep air flowing through the lungs
THE IMMUNE SYSTEM
Internal Cellular and Chemical Defenses
• Internal cellular defenses depend mainly on phagocytosis
• Phagocytes, types of white blood cells ingest invading microorganisms, initiate the inflammatory response
Natural killer (NK) cells
patrol the body and attack virus-infected body cells and cancer cellsand and trigger apoptosis in the cells they attack
Acquired immunity includes two branches
• The humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies
• The cell-mediated immune response involves the activation and clonal selection of cytotoxic T cell
OSMOREGULATION AND EXCRETION Osmoregulation
Regulates solute concentrations and balances the gain and loss of water Excretion
Gets rid of metabolic wastes
Animals That Live in Temporary Waters This adaptation is called anhydrobiosis Land Animals
Land animals manage their water budgets by drinking and eating moist foods and by using metabolic water.
Desert animals
Get major water savings from simple anatomical features The type and quantity of an animal’s waste products
Animals that excrete nitrogenous wastes as ammonia -Need access to lots of water
-Release it across the whole body surface or through the gills
• The liver of mammals and most adult amphibians -Converts ammonia to less toxic urea
• Urea is carried to the kidneys, concentrated -And excreted with a minimal loss of water
• Insects, land snails, and many reptiles, including birds -Excrete uric acid as their major nitrogenous waste
• Uric acid is largely insoluble in water
-And can be secreted as a paste with little water loss
Excretory systems
Regulate solute movement between internal fluids and the external environment The process of excretory
1. Filtration 2. Reabsorption 3. Secretion 4. Excretion
SYALWA DIDA WURYNATI 200342616813 HORMONE AND ENDOCRINE SYSTEM
Have we ever ask, “What brings about such a complete change of body form or metamorphosis?”
The answer to this and many other biological processes are a type of molecule called a hormone (from the Greek hormone, to excite). In animals, hormones are secreted into the extracellular fluid, circulate in the hemolymph or blood, and communicate regulatory messages throughout the body.
In the case of the caterpillar, a hormone called ecdysteroid stimulates the growth of adult cells, the programmed death of larval cells, and even the behaviors that bring about the motionless pupal stage. Communication within the body by ecdysteroid and other hormones also regulates the timing of metamorphosis and ensures that different parts of the swallowtail’s adult body develop in unison.
Endocrine signaling is just one of several ways information is transmitted between animal cells.
Let’s consider the similarities and differences in these various signaling processes, there are:
1. Endocrine Signal
Hormones secreted into extracellular fluids by endocrine cells reach targer cells via bloodstream (or hemolymph)
2. Paracrine Signal
The target cells lie near the secreting cell.
3. Autocrine Signal
The target cell is the secreting cell itself.
Our body have a nine endocrine glands and many of hormones that always works every day.
All organs are sure very important but there are two types of function that I will describe.
How Insulin and Glucagone works
How Hypothalamus work to be a central endocrine signal?
the hypothalamus receives information from nerves throughout the body, including the brain. In response, the hypothalamus initiates endocrine signaling appropriate to environmental conditions.
In many vertebrates, for example, nerve signals from the brain pass sensory information to the hypothalamus about seasonal changes. The hypothalamus, in turn, regulates the release of reproductive hormones required during the breeding season. Signals from the hypothalamus travel to the pituitary gland, a gland located at its. Roughly the size and shape of a lima bean, the pituitary has discrete posterior and anterior parts, or lobes, that secrete different sets of hormones.
ANIMAL REPRODUCTION
Animal mating system is influenced by may thing, such us: day length, seasonal temperature, rainfall, and lunar cycles.
Comparing internal and external fertilization across many species reveals that internal fertilization is typically associated with the production of fewer gametes but the survival of a higher fraction of zygotes. Better zygote survival is due in part to the fact that eggs fertilized internally are sheltered from potential predators. However, internal fertilization is also more often associated with mechanisms that provide greater protection of the embryos and parental care of the young.
For example, the internally fertilized eggs of many species of terrestrial animals exhibit adaptations that protect against water loss and physical damage during their external development.
In the case of birds and other reptiles, as well as monotremes (egg-laying mammals), the zygotes consist of eggs with calcium- and protein-containing shells and several internal. In contrast, the fertilized eggs of fishes and amphibians have only a gelatinous coat and lack internal membranes.
Rather than secreting a protective eggshell, some animals retain the embryo for a portion of its development within the female’s reproductive tract. Embryos of marsupial mammals, such as kangaroos and opossums, spend only a short period in the uterus; the embryos then crawl out and complete fetal development attached to a mammary gland in the mother’s pouch. However, embryos of eutherian (placental) mammals, such as humans, remain in the uterus throughout fetal development. There they are nourished by the mother’s blood supply through a temporary organ, the placenta. The embryos of some fishes and sharks also complete development internally, although typically the embryo and mother in such species lack a connection dedicated to nutrient exchange.
ANIMAL DEVELOPMENT
,
1 the sperm meets the ovum
2 Sperm opening the acrosome and sper containing egg cell with
HYALURONIDASE to dissolve the zona pleusida in the ovum. hormone
3 Sperm opening the acrosome and sper containing egg cell with
HYALURONIDASE to dissolve the zona pleusida in the ovum. hormone
Furthermore, the sperm will enter and join the vtelin membrane which will make the potential tension in the ovum cell turn high so that other sperm cells will die when they enter the egg
4
5 After that, the sperm will release the cell nucleus and move with the ovum cell nucleus then fuse and form a zygote.
NAWAL KAMILAH ISMAIL
48. Neuron, Synapses, and Signaling
48.1. Neuron Organization and Structure Reflect Function in Information Transfer
The ability of a neuron to receive and transmit information is based on a highly specialized cellular organization. Most of a neuron’s organelles, including its nucleus, are located in the cell body. A typical neuron has numerous highly branched extensions called dendrites. Together with the cell body, the dendrites receive signals from other neurons.
A neuron also has a single axon, an extension that transmits signals to other cells. Axons are often much longer than dendrites, and some, such as those that reach from the spinal cord of a giraffe to the muscle cells in its feet, are over a meter long. The cone-shaped base of an axon, the axon hillock, is typically where signals that travel down the axon are generated. Near its other end, an axon usually divides into many branches. Each branched end of an axon transmits information to another cell at a junction called a synapse. The part of each axon branch that forms this specialized junction is a synaptic terminal. At most synapses, chemical messengers called neurotransmitters pass information from the transmitting neuron to the receiving cell.
48.2. Ion Pumps and Ion Channels Establish The Resting Potential of A Neuron
The sodium-potassium pump generates and maintains the ionic gradients of Na and K. The pump uses ATP to actively transport Na out of the cell and K into the cell. Although there is a substantial concentration gradient of sodium across the membrane, very little net diffusion of Na occurs because there are very few open sodium channels. In contrast, the large number of open potassium channels allow a significant net outflow of K. Because the membrane is only weakly permeable to chloride and other anions, this outflow of K results in a net negative charge inside the cell.
Ionic gradients generate a voltage difference, or membrane potential, across the plasma membrane of cells. The concentration of Na is higher outside than inside; the reverse is true for K.
In resting neurons, the plasma membrane has many open potassium channels but few open sodium channels. Diffusion of ions, principally K, through channels generates a resting potential, with the inside more negative than the outside.
48.3. Action Potentials Are The Signals Conducted by Axons
Neurons have gated ion channels that open or close in response to stimuli, leading to changes in the membrane potential. An increase in the magnitude of the membrane potential is a hyperpolarization; a decrease is a depolarization. Changes in membrane potential that vary continuously with the strength of a stimulus are known as graded potentials.
An action potential is a brief, all-or-none depolarization of a neuron’s plasma membrane.
When a graded depolarization brings the membrane potential to the threshold, many voltage-gated ion channels open, triggering an inflow of Na that rapidly brings the membrane potential to a positive value. A negative membrane potential is restored by the inactivation of sodium channels and by the opening of many voltage-gated potassium channels, which increases K outflow. A refractory period follows, corresponding to the interval when the sodium channels are inactivated.
A nerve impulse travels from the axon hillock to the synaptic terminals by propagation of a series of action potentials along the axon. The speed of conduction increases with the diameter of the axon and, in many vertebrate axons, with myelination. Action potentials in myelinated axons jump between the nodes of Ranvier, a process called saltatory conduction.
48.4. Neurons Communicate With Other Cells at Synapses
This figure illustrates the sequence of events that transmits a nerve impulse across a chemical synapse. In response to binding of neurotransmitter, ligand-gated ion channels in the postsynaptic membrane open (as shown here) or, less commonly, close. Synaptic transmission ends when the neurotransmitter diffuses out of the synaptic cleft, is taken up by the synaptic terminal or by another cell, or is degraded by an enzyme
In an electrical synapse, electrical current flows directly from one cell to another. In a chemical synapse, depolarization causes synaptic vesicles to fuse with the terminal membrane and release neurotransmitter into the synaptic cleft.
At many synapses, the neurotransmitter binds to ligand-gated ion channels in the postsynaptic membrane, producing an excitatory or inhibitory postsynaptic potential (EPSP or IPSP). The neurotransmitter then diffuses out of the cleft, is taken up by surrounding cells, or is degraded by enzymes. Temporal and spatial summation at the axon hillock determines whether a neuron generates an action potential.
Different receptors for the same neurotransmitter produce different effects. Some neurotransmitter receptors activate signal transduction pathways, which can produce long-lasting changes in postsynaptic cells. Major neurotransmitters include acetylcholine; the amino acids GABA, glutamate, and glycine; biogenic amines; neuropeptides; and gases such as NO.
49. Nervous Systems
49.1. Nervous Systems Consist of Circuits of Neurons and Supporting Cells
Invertebrate nervous systems range in complexity from simple nerve nets to highly centralized nervous systems having complicated brains and ventral nerve cords.
In vertebrates, the central nervous system (CNS), consisting of the brain and the spinal cord, integrates information, while the nerves of the peripheral nervous system (PNS) transmit sensory
and motor signals between the CNS and the rest of the body. The simplest circuits in the vertebrate nervous system control reflex responses, in which sensory input is linked to motor output without involvement of the brain. Vertebrate neurons are supported by several types of
glia, including astrocytes, oligodendrocytes, Schwann cells, and ependymal cells.
Afferent neurons carry sensory signals to the CNS. Efferent neurons function in either the motor system, which carries signals to skeletal muscles, or the autonomic nervous system, which regulates smooth and cardiac muscles. The sympathetic and parasympathetic divisions of the autonomic nervous system have antagonistic effects on a diverse set of target organs, while the enteric division controls the activity of many digestive organs.
49.2. The Vertebrate Brain is Regionally Specialized
The cerebrum has two hemispheres, each of which consists of cortical gray matter overlying white matter and basal nuclei, which are important in planning and learning movements.
A thick band of axons, the corpus callosum, provides communication between the right and left cerebral cortices.
Within each region of the brain, particular structures have specialized functions. The pons and medulla oblongata are relay stations for information traveling between the PNS and the cerebrum. The reticular formation, a network of neurons within the brainstem, regulates sleep and arousal. The cerebellum helps coordinate motor, perceptual, and cognitive functions. It is also involved in learning and remembering motor skills. The thalamus is the main center through which sensory and motor information passes to the cerebrum. The hypothalamus regulates homeostasis and basic survival behaviors. Within the hypothalamus, the suprachiasmatic nucleus (SCN) acts as the pacemaker for circadian rhythms.
The generation and experience of emotions involve many regions of the brain. However, the amygdala plays a key role in recognizing and recalling a number of emotions
49.3. The Cerebral Cortex Controls Voluntary Movement and Cognitive Functions
Each side of the cerebral cortex is divided into four lobes, and each lobe has specialized functions, some of which are listed here. Some areas on the left side of the brain (shown here) have different functions from those on the right side (not shown).
Each side of the cerebral cortex has four lobes—frontal, temporal, occipital, and parietal—
that contain primary sensory areas and association areas. Specific types of sensory input enter the primary sensory areas. Association areas integrate information from different sensory areas.
Portions of the frontal and temporal lobes, including Broca’s area and Wernicke’s area, are essential for generating and understanding language. These functions are concentrated in the left cerebral hemisphere, as are math and logic operations. The right hemisphere appears to be stronger at pattern recognition and nonverbal thinking. At least some of this lateralization of functions relates to handedness.
In the somatosensory cortex and the motor cortex, neurons are distributed according to the part of the body that generates sensory input or receives motor commands.
Primates and cetaceans, which are capable of higher cognition, have an extensively convoluted neocortex, the outermost part of the cerebral cortex. In birds, a brain region called the pallium contains clustered nuclei that carry out functions similar to those performed by the cerebral cortex of mammals. Some birds can solve problems and understand abstractions in a manner indicative of higher cognition.
49.4. Changes in Synaptic Connections Underlie Memory and Learning
During development, more neurons and synapses form than will exist in the adult. The programmed death of neurons and elimination of synapses in embryos establish the basic structure of the nervous system. In the adult, reshaping of the nervous system can involve the loss or addition of synapses or the strengthening or weakening of signaling at synapses. This capacity for remodeling is termed neural plasticity. Defective remodeling of synapses is partly responsible for the developmental abnormalities of autism.
Short-term memory relies on temporary links in the hippocampus. In long-term memory, these temporary links are replaced by connections within the cerebral cortex. This transfer of information from short-term to long-term memory is enhanced by the association of new data with that already in long-term memory. Long-term potentiation (LTP) is a lasting increase in the strength of synaptic transmission and appears to be an important process in memory storage and learning.
The adult human brain contains stem cells that can differentiate into mature neurons.
Therapy based on stem cells offers a potential method for replacing neurons lost to injury or disease.
49.5. Many Nervous System Disorders Can Be Explained in Molecular Terms
Research has identified the biochemical basis of a number of nervous system disorders.
Schizophrenia, which is characterized by hallucinations, delusions, and other symptoms, affects neuronal pathways that use dopamine as a neurotransmitter. Drugs that increase the activity of biogenic amines in the brain can be used to treat bipolar disorder and major depressive disorder.
The compulsive drug use that characterizes addiction reflects altered activity of the brain’s reward system, which normally provides motivation for actions that enhance survival or reproduction.
Alzheimer’s disease and Parkinson’s disease are neurodegenerative and typically age related. Alzheimer’s disease is a dementia in which neurofibrillary tangles and amyloid plaques form in the brain. Parkinson’s disease is a motor disorder caused by the death of dopamine- secreting neurons and associated with the presence of protein aggregates.
Alzheimer’s disease leads to the death of neurons in many areas of the brain, including the hippocampus and cerebral cortex. As a result, there is often massive shrinkage of brain tissue.
Postmortem examination of the remaining brain tissue reveals two characteristic features—
amyloid plaques and neurofibrillary tangles.
Ardhena Sastya Mahalanny 200342616895
ANIMAL FORM AND FUNCTION Sensory and Motor Mechanisms
Sensory receptors transduce stimulus energy and transmit signals to the central nervous system.
• Sensory receptors are usually specialized neurons or epithelial cells that detect external or internal stimuli. The detection of a stimulus by sensory cells precedes sensory transduction, the change in the membrane potential of a sensory receptor in response to a stimulus. The resulting receptor potential controls transmission of action potentials to the CNS, where sensory information is integrated to generate perceptions. The frequency of action potentials in an axon and the number of axons activated determine stimulus strength. The identity of the axon carrying the signal encodes the nature or quality of the stimulus. Signal transduction pathways in receptor cells often amplify the signal, which causes the receptor cell either to produce action potentials or to release neurotransmitter at a synapse with a sensory neuron.
• There are five basic types of sensory receptors.
Mechanoreceptors respond to stimuli such as pressure, touch, stretch, motion, and sound.
Chemoreceptors detecteither total solute concentrations or specific molecules. Electromagnetic receptors detect different forms of electromagnetic radiation. Various types of thermoreceptors signal surface and core temperatures of the body. Pain is detected by agroup of nociceptors that respond to excess heat, pressure, orspecific classes of chemicals.
The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particles
• Most invertebrates sense their orientation with respect to gravity by means of statocysts.
Specialized hair cells form the basis for hearing and balance in mammals and for detection of water movement in fishes and aquatic amphibians. In mammals, the tympanic membrane (eardrum) transmits sound waves to three small bones of the middle ear, which transmit the waves through
the oval window to the fluid in the coiled cochlea of the inner ear. Pressure waves in the fluid vibrate the basilar membrane, depolarizing hair cells and triggering action potentials that travel via the auditory nerve to the brain. Each region of the basilar membrane vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex.
Receptors in the inner ear function in balance and equilibrium.
Visual receptors in diverse animals depend on lightabsorbing pigments.
• Invertebrates have varied light detectors, including simple lightsensitive eyespots, image-forming compound eyes, and singlelens eyes. In the vertebrate eye, a single lens is used to focus light on photoreceptors in the retina. Both rods and cones contain a pigment, retinal, bonded to a protein (opsin).
The senses of taste and smell rely on similar sets of sensory receptors.
• Both taste (gustation) and smell (olfaction) depend on the stimulation of chemoreceptors by small dissolved molecules that bind to proteins on the plasma membrane. In humans, sensory cells within taste buds express a single receptor type specific for one of the five taste perceptions—sweet, sour, salty, bitter, and umami (elicited by glutamate). Olfactory receptor cells line the upper part of the nasal cavity and extend axons to the olfactory bulb of the brain. More than 1,000 genes code for membrane proteins that bind to specific classes of odorants, and each receptor cell appears to express only one of those genes.
The physical interaction of protein filaments is required for muscle function.
• The muscle cells (fibers) of vertebrate skeletal muscle contain myofibrils composed of thin filaments of (mostly) actin and thick filaments of myosin. Together with accessory proteins, these filaments are organized into repeating units called sarcomeres. Myosin heads, energized by the hydrolysis of ATP, bind to the thin filaments, forming cross-bridges, then release upon binding ATP anew. As this cycle repeats, the thick and thin filaments slide past each other, shortening the sarcomere and contracting the muscle fiber. myosin-binding sites on actin and thus initiating cross- bridge formation. A motor unit consists of a motor neuron and the muscle fibers it controls.
Recruiting multiple motor units results in stronger contractions. A twitch results from a single
action potential in a motor neuron. Skeletal muscle fibers can be slowtwitch or fast-twitch and oxidative or glycolytic.
• Cardiac muscle, found only in the heart, consists of striated cells that are electrically connected by intercalated disks and that can generate action potentials without input from neurons. In smooth muscles, contractions are slow and may be initiated by the muscles themselves or by stimulation from neurons in the autonomic nervous system.
Skeletal systems transform muscle contraction into locomotion.
• Skeletal muscles, often in antagonistic pairs, bring about movement by contracting and pulling against the skeleton. Skeletons may be hydrostatic and maintained by fluid pressure, as in worms;
hardened into exoskeletons, as in insects; or in the form of endoskeletons, as in vertebrates.
• Each form of locomotion—swimming, movement on land, or flying—presents a particular challenge. For example, swimmers need to overcome friction, but face less of a challenge from gravity than do animals that move on land or fly. Animals specialized for swimming expend less energy per distance traveled than similarly sized animals specialized for flying or running. For any of the three major modes of locomotion, larger animals are more efficient than smaller ones.
ANIMAL BEHAVIOR
Discrete sensory inputs can stimulate both simple and complex behaviors.
• Behavior is the sum of responses to external and internal stimuli and includes muscular as well as nonmuscular activity. Tinbergen developed a set of questions that highlight the complementary nature of two perspectives.
• The transmission and reception of signals constitute animal communication. Animals use visual, auditory, chemical (usually olfactory), and tactile signals, sometimes as part of a stimulus - response chain that governs a complex behavior. Chemical substances called pheromones transmit species-specific information through the environment in behaviors ranging from foraging to courtship.
Learning establishes specific links between experience and behavior.
• Cross-fostering studies can be used to measure the influence of social environment and experience on behavior.
• Learning, the modification of behavior based on experience, can take many forms: Imprinting, Cognition, Spatial learning, Associative learning, Social learning.
Selection for individual survival and reproductive success can explain most behaviors.
• An optimal foraging model is based on the idea that natural selection should favor foraging behavior that minimizes the costs of foraging and maximizes the benefits.
• Sexual dimorphism correlates with the type of mating relationship between males and females.
These include monogamous and polygamous mating systems. Variation in mating system and variation in the mode of fertilization affect certainty of paternity, which in turn has a significant influence on mating behaviorand parental care.
• Game theory provides a way of thinking about evolution in situations where the fitness of a particular behavioral phenotype is influenced by other behavioral phenotypes in the population.
Inclusive fitness can account for the evolution of behavior, including altruism.
• Genetic studies in insects have revealed the existence of master regulatory genes that control complex behaviors. Within the underlying hierarchy, multiple genes influence specific behaviors, such as a courtship song. Research with two species of voles has revealed that variation in a single gene can determine differences in complex behaviors involved in both mating and parenting.
• When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution. Field and laboratory studies have documented the genetic basis for a change in migratory behavior of certain birds and revealed behavioral differences in snakes that correlate with geographic variation in prey availability.
• On occasion, animals exhibit altruism. This behavior can be explained by the concept of inclusive fitness, the total effect an individual has on proliferating its genes by producing its
own offspring and by providing aid that enables close relatives to produce offspring. The coefficient of relatedness and Hamilton’s rule provide a way of measuring the strength of the selective forces favoring altruism against the potential cost of the “selfless” behavior. Kin selection favors altruistic behavior by enhancing the reproductive success of relatives. Altruistic behavior toward unrelated individuals can be adaptive if the aided individual returns the favor in the future, an exchange of aid called reciprocal altruism.
