An instinct, therefore, is regarded as a mechanism made up of three parts: First, an afferent or cognitive part, through which it is stimulated.
These afferent impulses when perverted by functional derangement or disease may become serious disturbing influences.
Normally, afferent impulses are constantly flowing from the viscera to the central nervous system and by this reflex process their blood supply is regulated, and their functional activity is governed.
We have here to fall back upon facts rather than upon a definite knowledge of what happens in the shadowy border-land across which the mind takes over and organizes and acts upon what is presented to it by the afferent nervous system.
In the fish the ventral aorta gives rise to five afferent branchial arteries carrying the blood to the gills, though these may not all come off as independent trunks from the aorta.
From the gills the afferent branchials carry the blood to the median dorsal aorta.
Also, the afferent or sensory nerves of the skin over the whole of this head-region are supplied by the trigeminal nerve, while the afferent nerves to the visceral surfaces are supplied by the vagus, glossopharyngeal and facial nerves.
These nerves cannot be classed among the afferent nerves of the skin any more than the nerves of the optic and olfactory apparatus; they require separate consideration.
It is this kind of proliferation which, in my opinion, would bind together the separate relays of efferent and afferent neurones, and {469}so give origin to reflex actions at different levels.
The characteristic of the vertebrate is the origin of every segmental nerve from two roots, of which one contains the efferent fibres, while the other possesses a sensory ganglion, and contains only afferent fibres.
Each possesses its own afferent branchial blood-vessel from the ventral aorta, and its own efferent vessel to the dorsal aorta (Fig.
On the afferent side especially free nerve-terminations are largely recognized, or, as in Barker's book, nerves are spoken of as arising in connective tissue.
Conveying sensory or afferent impulses; Ð said of nerves.
When a bad smell causes a grimace, there is a reflex action through the same motor nerve, while the olfactory nerves constitute the afferent channels.
When the whole body starts at a loud noise, the afferent auditory nerve gives rise to an impulse which passes to the medulla oblongata, and thence affects the great majority of the motor nerves of the body.
When the eyelids wink at a flash of light, or a threatened blow, a reflex action takes place, in which the afferent nerves are the optic, the efferent, the facial.
So far, then, we have highly satisfactory evidence of tissue-tracts performing the function of afferent nerves.
The modification effected by the cortex on afferent impressions is obvious in altered motor reactions, which appear with the stamp of cortical intervention, herein differing from bulbo-spinal phenomena.
A distinction most nevertheless be drawn between the two cases, inasmuch as in the one the afferent path is peripheral, in the other it is cortico-spinal, and there is a corresponding difference in the clinical picture.
Should the cortex be functioning harmoniously, afferent impulse and efferent reaction stand in due proportion one to the other; but any disturbance of psychical equilibrium--e.
Developmentally the grey matter of the cerebral convolutions is ectodermic, as is the skin, and capable of functioning as a sensory surface; it may be considered the end organ of an afferent path that conducts to medullary reflex centres.
The appropriate movements constitute the spontaneous reaction to afferent impulses; they are simple bulbar reflexes.
The caudal vein bifurcates at the posterior extremity of the kidneys to form the afferent trunks of the renal-portal system along the lateral border of the kidneys, from which the advehent veins of the renal-portal system are derived.
Here the vessel is connected by the transverse branch above described with the afferent renal portal system derived from the caudal vein.
The latter are seen entering the afferent renal-portal vein, derived from the bifurcation of the caudal vein, along the lateral border of the kidneys.
About the middle of the kidney each afferent vein is joined by a large transverse branch from the abdominal vein (Fig.
It is a large trunk, continuous below with the pelvic vein, terminating above in two branches, which enter the liver as afferent veins, being joined just prior to the division by the hepatic portal vein.
The caudal vein is, however, no longer the only afferent vein of this system.
This vessel traverses the liver, receiving the hepatic afferentveins of the portal system.
The opposite or oesophageal extremity of the stomach is less well differentiated from the afferent tube of the oesophagus.
In its simplest primitive condition the loop presents a proximal, descending or efferent limb, an apex, and an ascending, returning or afferent limb (Fig.
Ascending in the substance of this gland and receiving the afferent hepatic veins (Fig.
This lack of blood and sensation of cold are at once telegraphed over the afferent nerves to headquarters in the brain, and from there the command goes forth to the nerve centers regulating the circulation: "Send blood into the surface!
At once this sensation is telegraphed over theafferent nerves to the nerve centers in the brain or spinal cord.
This circuit of communication from the cell over the afferent nerves to the nerve centers in the brain or spinal cord, and from these centers over the efferent nerves back to the cell or to other cells is called the reflex arc.
The afferent vessels dilate, and not only more blood, but various materials taken up from the foods and products of digestion, many of them having directly stimulating effects, also pass to the organ.
As the walls of the clefts assume their respiratory function the aortic arch becomes broken into a network of capillaries in its respiratory portion, and there is now distinguished a ventralafferent and a dorsal efferent portion of each arch.
In the Cyclostomes the dorsal afferent and ventral efferent nerves are still, as in Amphioxus, independent, but in the gnathostomatous fishes they are, as in the higher vertebrates, combined together into typical spinal nerves.
Ligation of the main afferent vessels, or of the external or common carotid, has been followed by recurrence, owing to the free anastomatic circulation in the scalp.
It consists of a lamellar process of the mesoblast cells round the eye, passing through the choroid slit near the optic nerve, and enveloping part of the afferent branch of the vascular loop above mentioned.
From this capsule a duct passes to the atrial cavity, which, though called the oviduct, functions as an afferent duct for the spermatozoa.
Inflammation of lymph glands results from the advent of an irritant, usually bacterial or toxic, brought to the glands by the afferent lymph vessels.
A nævus is a collection of dilated capillaries, the afferent arterioles and the efferent venules of which often share in the dilatation.
In some cases ligation of the afferent vessels has been successful.
The tubercle bacilli usually gain access to the gland through the afferent lymph vessels, which convey them from some lesion of the surface within the area drained by them.
When electrolysis is employed, it should be directed towards the afferent vessels; and if it fails to arrest the flow through these, it is useless to persist with it.
Branchial hearts are formed on the afferent vessels of the branchiae.
In Nautilus this vena cava gives off at the level of the gills four branchial afferent veins (fig.
By reflex action of which the afferentstimulus acts upon the eyes as in fishes, the chromatophores assume a condition which approximates the colour of the animal to that of surrounding objects.
Branchial hearts are developed on the two branchial afferent blood-vessels (fig.
Each afferent vessel is expanded into a contractile branchial heart, which is provided with a glandular appendage.
The principal vein is a vena cava passing backwards ventrally from the cephalic region and dividing into two afferent branchial veins, each of which receives a pallial and an abdominal vein.
From the dilated branchial heart the branchial afferent vessel proceeds, running up the adpallial face of the gill-plume.
Renal glandular masses on the walls of the afferentbranchial veins (see fig.
Each of these afferent branchial vessels is enclosed in the cavity of a renal organ and is covered externally by the glandular tissue which forms the excretory part of the "kidney" (fig.
The renal organs are always paired sacs, the walls of which invest the branchial afferent vessels (figs.
The glandular renal tissue is, in fact, confined to a tract extending along that part of the sac's wall which immediately invests the great branchial afferent vein.
The latter corresponds to the glandular masses which are attached to the afferent branchial veins in Nautilus, and to the pericardial glands of other Molluscs.
Afferent branchial vessels (branches of the vena cava, see fig.
This nerve-change is caused by a stimulus having its origin in the end-organ of the afferent nerve, and we naturally refer the impression outwards to the place of its source of origin under ordinary and normal conditions.
The next thing that we have to note is that it is not so much the sensation itself, as that which gives origin to it, that we habitually refer outwards to the recipient end of the afferent fibre.
And in it the transmitted stimuli, brought in by the afferent nerves, are modified, through intervention of the co-ordinants, into stimuli carried out by the efferent nerves.
To this central nervous system, as it is called, nerves (afferent nerves) run inwards from the recipient organs.
In the healthy organism the afferent nerves convey impressions of the external world in their full freshness to the brain, and the stimulation of the brain-cell is in direct ratio to the intensity of the stimulus conducted to it.
Naturally those cells would be the most strongly excited which are directly connected with the afferent nerves.
Klein found increase of nuclei (probably epithelial) upon the glomeruli and hyaline degeneration of the intima of minute arteries, especially marked in the afferent arterioles of the Malpighian bodies.
The lesions of the arteriosclerotic kidney are due to narrowing and eventual obstruction of the afferent vessels.
Changes in other organs as the result of arteriosclerosis of their afferent vessels occur, but are not so characteristic as in the kidney.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "afferent" in a variety of sentences. We hope that you will now be able to make sentences using this word.
