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Adrenaline, also called epinephrine, is an endogenous catecholamine messenger: the body makes it and can release it into blood as a hormone. The adrenal medulla, the inner region of an adrenal gland, secretes adrenaline in response to sympathetic nervous system stimulation. A circulating hormone broadcasts a signal, but each receiving biological cell interprets it through its own receptors and intracellular machinery. Adrenaline activates both alpha-adrenergic receptors and beta-adrenergic receptors; it does not command one identical response everywhere.^[ref][ref]

Fuel mobilization is a useful example. A beta-adrenergic receptor can increase adenylyl cyclase activity through a stimulatory G protein, increasing the intracellular second messenger cAMP. Protein kinase A responds to cAMP; a phosphorylation relay through phosphorylase kinase activates glycogen phosphorylase, favoring glycogenolysis. Here adrenaline is the extracellular message, cAMP is the intracellular message, and glycogen is the reserve being mobilized. These are three different roles.^{[ref][ref][ref]}

The two reserves provide different material. Glycogenolysis draws on glycogen; lipolysis breaks down stored triglycerides, releasing fatty acids and glycerol. A skeletal muscle biological cell's own reserve and fuel released by adipose tissue are different supplies. Increasing a signal cannot mobilize an empty reserve: receptor activation changes the use of available material rather than creating fuel. The adrenergic adipocyte assay below gives direct human evidence for the lipolysis branch.^[ref]

Receptor context can even oppose this branch. In the human adipocyte preparation below, beta-adrenergic receptors promoted cAMP accumulation, whereas alpha-2 adrenergic receptors opposed it. Alpha-1 adrenergic receptors were associated with a different phospholipid readout. The balance of these responses matters more than the name of the messenger alone.^[ref]

This separation is useful when explaining signal transduction: ask which receptor is present, which relay it controls, which reserve or target is available, and which response was actually measured. Receptor binding occupancy, second messenger production and final fuel release are distinct observations. A stronger cAMP signal need not imply an equally large change in every downstream process; substrate availability and the rest of the receiving biological cell still matter.

The extract-transfer experiment under second messenger supplies the earlier experimental separation between hormone reception and an intracellular intermediary. Its existing account includes the preparations and controls. The complementary adrenergic adipocyte assay asks a different question: can the same adrenaline stimulus engage opposing receptors within a human preparation?

The part of the nervous system regulating organs, glands and related internal functions. It includes the sympathetic nervous system and parasympathetic nervous system. Its activity supports bodily regulation during emotion, exercise and many nonemotional states; no single recording is a direct readout of a private feeling.

A small ganglion between the optic nerve and lateral rectus muscle. Preganglionic fibres of the parasympathetic nervous system relay here; sensory and already postganglionic fibres of the sympathetic nervous system traverse it without another relay.^[ref]

Identity and early work: Wellcome catalogue: Neue Untersuchungen über das Nervensystem, 1851, identifying Budge as a contributor.

Autonomic recordings can support probabilistic discrimination of emotional states under specified conditions; they do not establish a person's experienced emotion with certainty. The distinction matters because a physiological response, an experimenter's induction label and a subjective feeling are different things. A useful psychophysiology study must justify how its labels relate to experience before assessing how well a bodily measure predicts them.

The autonomic nervous system regulates organs and glands through interacting pathways, including the sympathetic nervous system and parasympathetic nervous system. An electrocardiogram supplies cardiac timing and hence heart rate; heart rate variability describes variation in successive intervals. Electrodermal activity can be recorded with skin electrodes, while a temperature sensor supplies peripheral temperature. Breathing and blood-pressure measurements add other information. These measurements differ in what generates them and in their temporal response. In particular, sweat-related skin conductance provides information about sympathetic sudomotor activity, whereas a faster heart rate can reflect several autonomic influences and physical demands. Facial electromyography is useful complementary evidence, but records skeletal muscle activity through the somatic nervous system; it should not be counted as another autonomic channel.

Historically, the question was not simply whether the body changes during emotion, but whether bodily patterns distinguish categories. Paul Ekman and colleagues in 1983 used muscle-by-muscle facial instructions and reliving of past episodes. They reported autonomic differentiation among some negative states as well as between positive and negative states. This challenges the claim that autonomic activity is entirely undifferentiated. It does not show that the same pattern is a necessary and sufficient marker in every spontaneous episode: posing, recollection and the selection of categories constrain the result.^[ref]

Joint patterns can carry information that a single measure misses. Philip A. Kragel and colleagues combined electrodermal, cardiac, respiratory and gastric measures during film- and music-induced states. Their 2013 study reported 58.0% autonomic classification accuracy across six induced categories and a neutral condition, with training and testing on separate participant subsets, above its chance benchmark. This supports multivariate information about the tested states. It does not establish invariant bodily essences: a classifier can exploit overlapping distributions whose average patterns differ.^[ref]

Conversely, Erika H. Siegel and colleagues' 2018 synthesis found substantial within-category variation, and mean autonomic patterns that did not clearly separate the categories. Its laboratory adult samples do not exhaust every possible real-world measurement. Nevertheless, a universal fingerprint claim should generalize across episodes, and the observed variation is a substantial problem for that strong claim. Failure to establish a fingerprint does not imply that physiology contains zero predictive information; distributions can overlap without being identical.^[ref]

Several alternative explanations must therefore be tested. A film may make participants breathe differently because of its pacing; imagined confrontation may prepare action; an emotional task may differ from a neutral task in movement or attention. Exercise, room temperature, medication and individual baselines can change the recorded variables without a change in discrete emotional category. A classifier that recognizes the stimulus or task is not necessarily recognizing the feeling. Splitting trials while retaining the same people and clips in training and test sets can also overstate generalization. Appropriate cross-validation should hold out the people or inductions required by the intended claim, with preprocessing and feature selection fitted only to training data. Mixed feelings and changing episodes should be allowed rather than forced into one mutually exclusive label.

Even genuine conditional discrimination does not determine the reliability of a particular classification. Let $E$ denote one independently defined target state and $+$ a positive classifier result. Partitioning the positive results into target and nontarget cases and applying Bayes' theorem givesFor an explicitly hypothetical classifier with true-positive probability $0.8$ and false-positive probability $0.2$, a target base rate of $0.1$ produces $0.08/(0.08+0.18)\approx 0.308$. At a base rate of $0.5$, the same conditional performance produces $0.8$. The positive predictive value therefore depends on the setting as well as the instrument. This calculation illustrates a limit on inference; it is not an estimate from either study.

The strongest conclusion combines measures while respecting their different roles. Repeated self-report helps establish experienced feeling, independently coded behavior establishes action, and autonomic recording establishes bodily regulation. None is error-free, and agreement must be demonstrated. Psychophysiologists can estimate how much an autonomic pattern changes the probability of a reported or independently characterized state, with an explicit uncertainty and domain of validation. They can establish useful evidence about experienced emotion, but autonomic activity alone supplies a conditional inference rather than a uniquely identifying emotional signature.

The nervous system regulates visceral movement, glandular secretion, blood flow and coordinated bodily responses, while also influencing nutrition indirectly through those functions. Organic or vegetative life here means activities maintaining the body, such as blood circulation, digestion, pulmonary ventilation, secretion and excretion. It does not designate an independent form of living substance.

One influence is directly motor. Autonomic nerves alter the rate and force of the heart, contract or relax smooth muscle in the intestine, urinary bladder, airways and blood vessels, and coordinate movement with the opening and closure of sphincters. Their effect need not be excitatory: an active vagus nerve can slow the heart, while other pathways accelerate it. In the modern account, sympathetic and parasympathetic effects depend on the target and its receptors; they are not respectively universal accelerator and brake systems. Some organs receive both divisions, while others do not have a simple balanced double supply.^[ref]

A second influence is secretomotor. Activity in appropriate nerves can increase salivary secretion, alter gastric acid secretion and promote sweating. This is distinguishable from moving a duct or changing its calibre. A convincing experiment collects a secretion from a cannulated duct while a nerve is stimulated, rather than inferring secretion from a change of colour or organ size. For example, stimulation of the chorda tympani can evoke fluid from the submandibular gland. The response depends on functioning secretory biological cells; the nerve communicates a command rather than supplying the material constituents of saliva.

A third influence is vasomotor. Changing the calibre of arterioles changes local vascular resistance and perfusion. The classic comparison of an ear before and after interruption of its cervical sympathetic supply illustrates loss of vasoconstrictor tone: the vessels dilate and the ear becomes warmer because more warm blood reaches it. Stimulation of the peripheral cut pathway can produce the converse vascular effect. Warmth therefore need not mean that the local nerves themselves generate more heat. Vascular control also changes the delivery of oxygen and nutrients to a gland or tissue, so it can modify function indirectly.

These outputs are organized by sensory feedback and reflexes. Distension of the intestine can evoke coordinated movement; changes in blood pressure or blood-gas composition influence heart rate and breathing. Local circuits in the enteric nervous system permit some digestive activity without an intact connection to the brain, while longer reflexes involve the spinal cord or brainstem. Central states also matter: the sight or expectation of food can initiate preparatory digestive responses, and fear can alter heart rate, sweating and visceral movement.^[ref]

Somatic motor activity also supports vegetative functions. Breathing uses the respiratory diaphragm and other skeletal muscles; swallowing and continence use coordinated skeletal muscle as well as smooth muscle. Thus organic function cannot be identified solely with the anatomical distribution of the sympathetic nervous system.

The historical idea of a direct trophic influence requires discrimination. A denervation region may change through loss of movement, altered perfusion, loss of protective sensation or changed secretion. Those observations alone do not establish a special nutritive fluid flowing down the nerve. Modern biology recognizes molecular signalling between nerves and their targets, as well as neuroendocrine signalling pathways: the hypothalamus can influence hormone release, and sympathetic input can evoke adrenal medulla secretion. These are mechanisms added to, rather than evidence for an undefined historical nutritive force. A useful experimental design measures the motor, vascular and secretory consequences separately before assigning a residual effect to direct trophic action.

The two pneumogastric nerves are the right and left vagus nerves, the tenth cranial nerves: mixed sensory, branchial motor and parasympathetic pathways from the medulla oblongata to the neck, thorax and abdomen. A useful description separates their apparent origin at the surface of the brain from the origins and terminations of their component fibres.

Rootlets emerge in the groove behind the inferior olive, between the glossopharyngeal nerve above and the accessory rootlets below. Branchial motor fibres arise chiefly in the nucleus ambiguus; preganglionic parasympathetic fibres arise in the dorsal motor nucleus of the vagus and, particularly for cardiac control, the nucleus ambiguus. Visceral sensory fibres have their cell bodies chiefly in the inferior vagal ganglion and terminate centrally in the nucleus of the solitary tract; somatic sensory fibres associated with the superior vagal ganglion project to the spinal trigeminal nucleus. Consequently a sensory fibre is not accurately described as originating in a motor nucleus simply because its peripheral nerve emerges nearby.^[ref]

Each vagus nerve leaves the skull through the jugular foramen, with the glossopharyngeal nerve and accessory nerve. It bears the small superior vagal ganglion at the foramen and the larger inferior vagal ganglion below it. Connections include communications with adjacent cranial nerves and the cervical sympathetic nervous system. Traditional descriptions assign fibres joining the vagus nerve from the cranial part of the accessory nerve to the latter peripheral nerve; their modern classification is more nuanced and does not change the peripheral branches being described. In the neck the vagus nerve descends in the carotid sheath, behind and between the internal jugular vein and the internal, then common, carotid artery.

Its meningeal and auricular branches supply small sensory territories of the cranial covering and external ear. Pharyngeal branches contribute to the pharyngeal plexus, supplying much of the soft palate and pharynx; the stylopharyngeus muscle belongs to the glossopharyngeal nerve and the tensor veli palatini muscle to the mandibular division of the trigeminal nerve. The internal branch of the superior laryngeal nerve supplies sensation above the vocal folds; its external branch supplies the cricothyroid muscle. The recurrent laryngeal nerve supplies the other intrinsic laryngeal muscles and sensation below the vocal folds. The right recurrent laryngeal nerve loops beneath the right subclavian artery; the left loops under the aortic arch beside the ligamentum arteriosum. Both return towards the larynx near the groove between trachea and oesophagus.^[ref]

In the thorax, both vagus nerves pass behind the roots of the lungs, contrasting with the anterior course of the phrenic nerves. Cardiac branches join the cardiac plexus; pulmonary branches join the pulmonary plexus. The trunks break up into the oesophageal plexus, then collect principally as an anterior trunk derived from the left vagus nerve and a posterior trunk derived from the right. Through the oesophageal hiatus they reach the stomach; hepatic and coeliac branches distribute to abdominal viscera. Their parasympathetic territory includes foregut and midgut derivatives, extending into the proximal colon, rather than every abdominal and pelvic organ.^[ref] This extensive distribution explains why the level of experimental section is indispensable information.

The main consequences of section can be organized by the interrupted functions:

A discriminating historical experiment would record respiratory movements and heart rate before and after section, distinguish unilateral from bilateral section, and compare an intact airway with an airway bypass. A tracheal cannula can separate obstruction at the glottis from changes in the respiratory rhythm, while the central-versus-peripheral stimulation comparison separates incoming reflex traffic from outgoing motor effects. Later separate-lung recordings confirmed that a change following unilateral section could affect both lungs, supporting a central reflex interpretation rather than simple local paralysis.^[ref] The gastric distinction is also borne out by measurements of persistent acidity after surgical vagotomy, despite major reductions in stimulated gastric acid secretion.^[ref]

Expose the orbit (anatomy) in layers, preserving the eye, extraocular muscles, nerves and blood vessels so that their relations can be demonstrated. This is a general explanation of the practical exercise, using present-day anatomy terminology. It does not assert findings in the individual head supplied in 1867. The essential result is an intelligible dissection, with structures traced to their attachments or continuations, rather than a collection of detached parts.

Begin by orienting the head and choosing a superior approach through the anterior cranial fossa. Useful apparatus consists of a small saw or bone-cutting forceps, a fine chisel, fine scissors, dissecting forceps and a blunt probe. The coarse instruments remove bone; the fine instruments separate connective tissue. Remove the dura mater from the orbital part of the frontal bone, then carefully remove the roof of the orbit (anatomy) while leaving the periorbita intact. Extend the exposure towards the apex without driving the instrument into the optic canal or the superior orbital fissure. Preserve the delicate medial wall and its anterior ethmoidal nerve, posterior ethmoidal nerve and accompanying blood vessels. Open the periorbita under direct vision. This establishes a continuous view from the anterior margin towards the apex.^[ref]

In the superficial plane, identify the frontal nerve above the levator palpebrae superioris, and follow its division into the supraorbital nerve and supratrochlear nerve. On the lateral side identify the lacrimal gland, lacrimal nerve and accompanying lacrimal artery. On the medial side find the superior oblique muscle and the trochlear nerve entering it. Separate small amounts of adipose tissue with a blunt probe instead of stripping out the contents in a single mass. Preserve the superior ophthalmic vein where recognizable. Before reflecting any structure, show its course in place: removal of an overlying structure should answer a particular question about what lies underneath it.^[ref]

Next isolate the levator palpebrae superioris and trace it forward towards the upper eyelid. Its expanded tendon reaches the upper tarsal plate and adjacent eyelid tissues; distinguish this from an attachment to the sclera. Divide the levator palpebrae superioris across its belly and reflect the ends, keeping its oculomotor nerve supply attached where practicable. The superior rectus muscle is now exposed. Isolate and reflect it in turn, preserving the superior division of the oculomotor nerve entering the deep surface. This successive exposure demonstrates why the superficial frontal nerve should be located before either muscle is divided.^[ref][ref]

Trace the four rectus extraocular muscles from the common tendinous ring at the apex to the anterior sclera, behind the margin of the cornea. Demonstrate the medial rectus muscle and lateral rectus muscle along the corresponding sides of the eye, and the inferior rectus muscle below it. Trace the superior oblique muscle forwards to the trochlea of superior oblique; its tendon turns backwards and laterally beneath the superior rectus muscle to reach the sclera behind the equator of the eye. The inferior oblique muscle is the important exception to an apical origin: it begins on the anterior medial orbital floor of the maxilla, lateral to the lacrimal sac, and passes backwards and laterally beneath the inferior rectus muscle to the posterior lateral sclera.^[ref]

The following functional explanation makes the muscle display meaningful. The medial rectus muscle produces adduction of the eye, and the lateral rectus muscle produces abduction of the eye. The superior rectus muscle elevates and the inferior rectus muscle depresses, with additional adduction of the eye; the superior rectus muscle also produces intorsion of the eye, and the inferior rectus muscle produces extorsion of the eye. The superior oblique muscle produces intorsion of the eye, depression and abduction of the eye; the inferior oblique muscle produces extorsion of the eye, elevation and abduction of the eye. Depression by the superior oblique muscle is demonstrated most clearly with the eye adducted. Gentle traction on an isolated tendon, with the eye supported, can illustrate its line of pull in the preparation. This mechanical demonstration does not test living nerve function, and no observed movement in the historical specimen is supplied.^[ref]

In the deeper plane, identify the optic nerve entering the posterior eye and trace it back to the optic canal. Identify the nasociliary nerve crossing above it towards the medial wall; follow the long ciliary nerves towards the eye and the anterior ethmoidal nerve and posterior ethmoidal nerve towards the medial bone. On the lateral side of the optic nerve, between it and the lateral rectus muscle, seek the small ciliary ganglion. Preserve the short ciliary nerves that pass from its anterior aspect to the eye; an indiscriminate sweep through the surrounding adipose tissue would destroy precisely these small connections.^[ref]

Trace the inferior division of the oculomotor nerve towards the medial rectus muscle, inferior rectus muscle and inferior oblique muscle, including its connection to the ciliary ganglion. Trace the abducens nerve to the deep surface of the lateral rectus muscle, and the trochlear nerve to the superior oblique muscle. The lateral rectus muscle receives the abducens nerve, the superior oblique muscle receives the trochlear nerve, and the remaining listed extraocular muscles receive the oculomotor nerve. The ciliary ganglion is a relay for fibres of the parasympathetic nervous system carried with the oculomotor nerve towards the sphincter pupillae muscle and ciliary muscle. Sensory fibres connected with the nasociliary nerve, and already postganglionic fibres of the sympathetic nervous system, traverse the ciliary ganglion without another relay.^[ref]

Trace the ophthalmic artery from the optic canal and its continuity with the internal carotid artery, distinguishing it from the optic nerve. Follow recognizable branches: the central retinal artery towards and into the optic nerve, the posterior ciliary arteries towards the posterior sclera, the lacrimal artery towards the lacrimal gland, and the supraorbital artery, anterior ethmoidal artery and posterior ethmoidal artery towards their exits. The usual ophthalmic artery crosses above the optic nerve to reach the medial side, but an individual course must be established by tracing, not imposed on the preparation. ^[ref] Follow the superior ophthalmic vein towards the superior orbital fissure and cavernous sinus. The inferior ophthalmic vein also has communications towards the pterygoid plexus through the inferior orbital fissure.^[ref]

Finally, show the relations at the apex. The optic nerve and ophthalmic artery pass through the optic canal within the common tendinous ring. The divisions of the oculomotor nerve, nasociliary nerve and abducens nerve enter through the part of the superior orbital fissure enclosed by the common tendinous ring; the frontal nerve, lacrimal nerve and trochlear nerve enter outside it. Keep the eye attached until these relations have been displayed. A final labelled account should distinguish structures actually preserved from structures damaged or too small to demonstrate. That qualification matters in a practical dissection: an expected structure is a guide to search, not an observation.

Adjective referring to the sympathetic nervous system.