NERVOUS SYSTEMS , SENSE ORGANS , AND ANIMAL BEHAVIOR
SISTEM NERVES, ORGAN/ BAGIAN BADAN [PERASAAN/PENGERTIAN], DAN PERILAKU BINATANG
All living protoplasm is irritable. Because of this, every organism is sensitive to changes of stimuli from both it's external environments ; to these it responds or reacts in various ways. Every type of organic response , from the simplest action of an amoeba to the most complex bodily function or metal process in humans, result from this fundamental characteristic of excitability. To perceive stimuli, to transmit these to various body parts, and to effect responses, most animals have sense organs and a nervous system (fig. 9.1) this system (together with endocrine glands in some) serves also to coordinate and integrate the functions cells, tissues and organ system so that they act harmoni ously as aunit, resulting in what we see as the behavior animals.
Semua protoplasma hidup dapat menimbulkan amar. Oleh karena ini, tiap-tiap organisma adalah sensitip ke perubahan stimul dari kedua-duanya adalah lingkungan eksternal; ke ini [itu] menjawab atau bereaksi dalam berbagai jalan. Tiap-Tiap jenis tanggapan organik, dari tindakan yang paling sederhana dari suatu amoeba kepada fungsi [yang] jasmani yang paling rumit atau proses metal di (dalam) manusia, diakibatkan oleh karakteristik pokok sifat dapat dirangsang ini. Untuk merasa stimuli, untuk memancarkan ini [bagi/kepada] berbagai komponen badan, dan untuk mempengaruhi tanggapan, kebanyakan binatang mempunyai organ/ bagian badan [perasaan/pengertian] dan suatu sistem nerves ( gambar 9.1) sistem ini ( bersama-sama dengan endocrine kelenjar/penekan dalam beberapa) melayani juga untuk mengkoordinir dan mengintegrasikan sel fungsi, organ/ bagian badan sistem dan jaringan/tisu sedemikian sehingga mereka bertindak harmoni [yang] ously sebagai unit, menghasilkan apa yang [kita kami] melihat sebagai binatang perilaku.
Any physical or chemical change capable of exciting an organism or its parts ia a stimulus. Common external stimuli derive from temperature, moisture, light gravity, contact, pressure, oxygen supply, salt concentrations, and odors (chemical emanation). Internal stimuli result from the quantity of food, water, oxygen, ar wastes in the body and from fatigue, pain , disease, or other conditions,. Some stimuli act directly upon cells or tissue and elicit a direct response ( e.g., sunburn), but most animals have various kinds of specialized receptors (sense organs) to receive stimuli.
Manapun bahan kimia atau phisik ber;ubah untuk mampu kegairahan [adalah] suatu organisma atau komponen nya ia [adalah] suatu stimulus. stimuli Eksternal umum berasal dari temperatur, embun, [cahaya/ ringan] gaya berat, kontak, tekanan, oksigen menyediakan, menggarami konsentrasi, dan bau ( pancaran kimia). Stimuli internal diakibatkan oleh kwantitas makanan, air, oksigen, ar menyia-nyiakan badan dan dari kelelahan, sakit, penyakit, atau kondisi-kondisi lain,. Beberapa stimuli bertindak secara langsung [atas/ketika] jaringan/tisu atau sel dan menimbulkan suatu tanggapan langsung( e.g., kulit menggelap terbakar matahari), tetapi kebanyakan binatang mempunyai berbagai macam [dari;ttg] sel yang peka rangsangan khusus ( merasakan organ/ bagian badan) untuk menerima stimuli.
a receptor is a cell or organ having an especial sensitivity (lowered threshold) to some particular kind or kinds of stimulus, as the eye to light and the ear sound. Exteroceptors receive stimuli from the external environment, and interoceptors from within the body, as with hunger or thirst. (see also proprioceptors, par. 9-14.) A stimulus causes the receptor to generate nerve impulses whivh travel along nerves to the central nervous system; the latter integrates the sensory information and the initiates impulses whih excite terminal structures, or effectors (muscles, glands), to bring about responses.
Some stimuli are gradual, and response is slow, as in the chilling that precedes a sneeze, like the jab of a pin. Beyond a certain minimum there may be no quantitative relation between the intensity of a stimulus and the kind or magnitude of a responses that it produces (that aa-or-none-effect); this depends upon the kinds of cell or organs excited and their physiological condition. Several weak stimuli in rapid succession may bring a responses although each individually is too slight to do so; this is called this summation effect. Uon being excited, muscles contract produce movement, and gland cell pour forth the secretions previously synthesized witin them.
NERVOUS SYSTEM
9-1 Neourons and nerves nervous system are composed af nerve cells, or neurons, with cell processes known as dendrites and axons. Dendrites transmit impulses toward the cell body and axon away. The Neurons are varied form (fig. 2-14)in the system of different animal and in the several parts of any one nervous system. Each neuron is a distinct anatomical cell, having no protoplasmic continuity with other neuron, and also physiologically distinct. Injury to the nucleus or cell body destroys a neuron but does not always effect adjacent neurons. The neuron Is the functional unit of the nervous system, which consists chiefly of neurons in orderly arrangement. They comprise about 10 percent of the cell in the huan nervous system. The remainder are gliacell , which are not excitable but which support the neurons physically, probably also sustain them metabolically, and are believed to participate actively in barin function. Between any two neurons related in function there is delicate contact , or synapse ; this is a "physiological valve" that passes nerve impulses in only one direction, from the axon of one neuron to the dendrite of the other. A nerve consists of one to many nerve fibers (axons or dendrites) bound together by connective tissue and including blood vessels to supply nutrients and oxygens.
9-2 The nerve impulse the Impulse, or acion potential, that passes along a nerve fiber involves both chemical and electrical change. It requires energyand the presence oxygen, and produces a minute but measurable amount of carbon dioxide, and also a rise in temperature. The impulse moves at a uniform speed with the same intensity throughout. A wave of electrical change accompanie the impulse.
The resting nerve fiber (neuron) is electrically polarized. The outside of its semipermeable membrane is relatively positive, and the inside a negative. What causes the polarization, and how is it maintained? The numbers of positive and negative ions are about the same outside and inside cell, but the concentrations of some ion siffer greatly. There are about 10-15 times more sodium (Na+) ions in the extracellular fluid than inside the neuron. Potassium (K+) ions, however, are about 30 timesgreather within than without. Movement of both by diffusion and active transport and permeability characteristics of the cell membrane can account for the potential difference. Na+ ions tend to diffuse inward K+ ions toward in the direction of their concentration gradients. The membrane of a resting cell, however, is less permeable to Na+ than K+ ; this and the concentration difference causes Na+ to enter more slowly than K+ leaves. The result is an excess of negative ions within and of positive without. The differences in the concentration gradients would gradually sisappear were is not for a preseumed"ion pump" of carrier molecules within the cell. By active transport, the pump is thought to move Na+ ions the cell surface, where they are expelled as fast as they "leak" i. K+ ions are taken from the surface into the cell.
How is the nerve impulse transmitted? If a sufficient stimulus is applied to the cell membrane, it becomes depolarized at the palce stimulated, and a self-propagating wave of depolarization spreads outward in the membrane. The cell produces a current pulse of its own that amplifies the original stimulus. The immediate effect is to increase Na + permeability, and the flow of Na+ ions into the cell promptly increases. Flow of other Na+ ions is prompted, and inward movement of all these positive ions locally reduces part of the exceee negative charge inside—further reducing voltage differences across the cell membrane. When voltage declines to impulse threshold level, Na+ ions enter in such quantity that the internal potential becomes positive. The nerve impulse so initiated changes membrane permeability immediately ahead, so that Na+ ions enter in a progression to the end of the cell. The membrane returns to the resting state soon after the impulse has moved on. Polarization is restored by an outward surge of K+ ions shortly after influx of Na+ ions, restoring the original internal negative change.
A neuron has an all-or-none response. If a stimulus is of threshold level, the impulse travels the length of the neuron at constant speed and uniform amplitude. Connecting a galvanometer at two points on an exposed nerve will show the current flow, or action potential. As an impulse passes, there is an abrupt peak, or spike, then a slower declines. Following the pek there is a refrectary period (0.001 to 0.005 second) during which the depolarized fiber cannot respond to another stimulus.
A nerve impulse travels 6 to 12 m/second in a lobster, 28 to 30 m/second in a frog, and up to 120 m/second insome mammalian fibers. Transmission is slower in nonmyelinated fibers than in tjose with a myelin sheath, and slower in small fibers. There is a short delay in passage at each synapse. An impulse, upon reaching the finely branched end of an axon, causes the latter to increase the secretion of a chemical transmitter(or neurohumor) which sets up an impulse in the next neurons. Acetylcholine is produced n many synapses, including those at the neuromuscular junction. In at least some sympathetic synapses the transmitter substance is epinephrine neropinephrine. The increased emounts of acetylcholine would continue to stimulate the next neuron but for the fact that an enzyme, cholinesterase, quickly inactivates it.
Sensory or afferent neurons are those which conduct impulse from receptors to or toward the central nervous system; and motos or efferent neurons conduct from the central nervous system to various effectors. Still other adjustor neurons in the brain and nerve cord join variously between sensory and motor neurons. Some nerve contains only sensory fibers, others only motor fibers, and many are mixed nerves including both types. A ganglion is a unit containing the cell bodies of few or many neurons, and certain ganglia in the brain are known as centres.
9-3 invertebrates nervous system (fig. 9-1) most protozoans show no structures for coordination, but some ciliates such as Paramecium have a definite system of fibrils or a neuromotor apparatus (fig. 15-13 B) ; this evidently receives stimuli, conduct impulses , and coordinates movement of the cell body. In sponges the cell about the openings (oscula) in the body wall contract slowly if touched, but these seem to be local responses without true propagation to nearby cells. There are no definite nerve cells or structures. Hydra and other cnidarians have a diffuse nerve net around the body in or under the epithelium, but no central ganglion. The net is composed of nerve cell, which are unlike typical neurons in being joined to on another by protoplasmic processes. They connect to both receptors (modified epithelial cells) in the epidermis and to the bases of epitheliomuscular cells thet contract slowly to alter the body shape. Nerve net also occur in ctenophores, echinoderms, enteropneusts, and ascidians and even on the blood vassels of vertebrates.
In bilaterally symmetrical animals the nervous system is linear, usually comprising one or more pairs of ganglia or a brain in the anterior end joined to one or more nerve cord that extend posteriorly through the body. The nerve cord of invertebrates are all vertal and solid, and nerves pass from the ganglia and cords to various organs. Flatworms usually ( Fig. 17-1) have two anterior ganglia, with nerves to the head region, and two separated nerve cords which are joined by cross-connectives. In mollusks, annelids, and artrhopodos the paired anterior ganglia lie above and below the esophagus and are joined by connectives. The more specialized mollusks lack vetral nerve cord but have large ganglia joined by connectives in the head, foot, and viscera. In annelid worms and the more primitive artrhopods, including some insects and their larvae, the two ventral nerve cord have a pir of ganglia and a pair or more of nerves in each body segment. In the higher crustaceans, insects, and arachnoids the vetral ganglia are concentrated anteriorly. The starfish and other echinoderms have a radially arranged nervous system in keeping with their symmetry.
9-4 vertebrate nervous system in all vertebrates the nervous system ha a comparable embryonic origin (par. 10-17) and is always single, hollow, and dorsal to the digestive tract. In basic pattern is consists of (1) the central nervous system with a large anterior brain ( fig. 9-2) connected to a spinal or nerve cord and (2) the peripheral nervous system of 10 or 12 pairs of cranial nerves from the brain ( Table 9-1), a pair of spinal nerves from the accord for each primitive body segment, and the autonomic ( or sympathetic ) nervous system (fig. 9-5)
9-5 Brain the Brain is housed in the "brain box" or cranium. In dorsal view it includes, in lower vertebrates, (1) two olfactory lobes with nerves to the nasal chambers; (2) two cerebral hemispheres closely joined to the preceding and also attached to (3) the median dienchepalon . behind this are two rounded optic lobes , supported on (4) the midbrain below, and followed by (5) a small traserverse cerebellum ; this is over (6) the open-tooped medulla oblongata, which tapers to join the spinal cord (fig. 9-2). The diencephalon has a dorsal pineal body or epiphysis. Below the diencephalon is the optic chiasma ( crossing of the optic nerves) , followed by the infundibulum as a blunty triangular outgrowth with the hipophysis , or pituitary gland, at its posterior end.
The cavities within the brain are the first and second Ventricles in the cerebral hemispheres; these connect to a third vertical in the diecephalon. From the latter a small aqueduct of sylvius lead to the fourth ventricles located in the medulla. The fourth verticles is continous with a minute central canal throught the spinal cord. Cerebrospinal fluid fills the ventricles and other cavities and surrounds the brain. Metabolic exchanges for the brain are perfomed by arteries and veins over its surface and the by two dense network af blood vessels, the anterior choroid plexus over a dorsal opening in the diechepalon and the posterior choroid plexus above the medulla. The brain and spinal cord are surroundby two membranes, a thicker dura mater adhering to the enclosing bones and a delicate pia mater close over ther nervous tissue it self. Ten pairs of cranial nerves extend from various parts of the brain to sense organs, muscles, and other structures ( Table 9-1). In the adult shark and frog the parts of the brain are in linear arrangement ( Fig. 9-2 ). In higher vertebrates this primitive brain stem becomes folded ar flexed, and the cerebrum and the cerebellum become progressively enlarged ( Fig. 9-2) until in mammals and especially in humans ( Fih. 9-3) the cerebrum overlies all other parts. Furthermore, the outermost gray mater, or cortex, of the cerebrum is both thickened and increased in areas, so that it becomes folded or corvoluted. In humans it contains several billion neurons and their synapses comprising about three-fourths the weight of the entire nervous system. It is importantly involved in awareness of sensations and actions, in registering memories, and in motivation, but all these metal attributes are also influenced by other parts of the central nervous system. Destruction of cortical areas other than motor, sendory, or language centres does not always result in obvious behavioral changes. Three major association areas, frontal, temporal, and parieto-accipital, interconnect cortical regions. Memory pertaining to sensory experience may be stored in association areas. For example, the receptive area for sight provides awareness of the colors of a painting, but the adjacent visual association area is required for its recognition as a landscape. The increase in the bulk of the cortex among the higher vertebrates is in keeping with their greather metal abilities. There is, is however, no exact correlation between brain size and intelligence. The cerebellum is involved with coordination of movement and posture. It show special sevelopment in animals whose movements are quick and require precise coordination.
9-6 Spinal cord and nerves (Fig. 9-4) The outer White matter of the spinal cord consists of bundles of mylinated fibers connecting between various parts of the brain and the nuclei of spinal nerves and adjustor neurons. The inner gray matter contains adjustor neurons and the nuclei of motor neurons; nuclei of sensory neurosn are in the dorsal
root ganglia of spinal nerves. If dorsal root of spinal nerve is cut, any sensory impulses from the entering fibers fail to reach the cord and brain. Destruction of the ventral root block all motor control by fibers I that nerve. The ventral root are variously injured or destroyed in poliomyelitis, leding to impairment of muscular function.
