Cognitive neuroscience is the scientific field, concerned with the study of the biological processes and aspects that underlie cognition, with a specific focus on the neural connections in the brain which are involved in mental processes. It addresses the questions of how cognitive activities are affected or controlled by neural circuits in the brain. Cognitive neuroscience is a branch of both neuroscience and psychology, overlapping with disciplines such as behavioral neuroscience, cognitive psychology, physiological psychology and affective neuroscience. Cognitive neuroscience relies upon theories in cognitive science coupled with evidence from neurobiology, computational modeling. Parts of the brain play an important role in this field. Neurons play the most vital role, since the main point is to establish an understanding of cognition from a neural perspective, along with the different lobes of the cerebral cortex. Methods employed in cognitive neuroscience include experimental procedures from psychophysics and cognitive psychology, functional neuroimaging, electrophysiology, cognitive genomics, behavioral genetics.
Studies of patients with cognitive deficits due to brain lesions constitute an important aspect of cognitive neuroscience. The damages in lesioned brains provide a comparable basis with regards to healthy and functioning brains; these damages change the neural circuits in the brain and cause it to malfunction during basic cognitive processes, such as memory or learning. With the damage, we can compare how the healthy neural circuits are functioning, draw conclusions about the basis of the affected cognitive processes. Cognitive abilities based on brain development are studied and examined under the subfield of developmental cognitive neuroscience; this shows brain development over time, analyzing differences and concocting possible reasons for those differences. Theoretical approaches include computational cognitive psychology. Cognitive neuroscience is an interdisciplinary area of study that has emerged from neuroscience and psychology. There were several stages in these disciplines that changed the way researchers approached their investigations and that led to the field becoming established.
Although the task of cognitive neuroscience is to describe how the brain creates the mind it has progressed by investigating how a certain area of the brain supports a given mental faculty. However, early efforts to subdivide the brain proved to be problematic; the phrenologist movement failed to supply a scientific basis for its theories and has since been rejected. The aggregate field view, meaning that all areas of the brain participated in all behavior, was rejected as a result of brain mapping, which began with Hitzig and Fritsch’s experiments and developed through methods such as positron emission tomography and functional magnetic resonance imaging. Gestalt theory and the cognitive revolution were major turning points in the creation of cognitive neuroscience as a field, bringing together ideas and techniques that enabled researchers to make more links between behavior and its neural substrates. Philosophers have always been interested in the mind: "the idea that explaining a phenomenon involves understanding the mechanism responsible for it has deep roots in the History of Philosophy from atomic theories in 5th century B.
C. to its rebirth in the 17th and 18th century in the works of Galileo and Boyle. Among others, it’s Descartes’ idea that machines humans build could work as models of scientific explanation." For example, Aristotle thought the brain was the body’s cooling system and the capacity for intelligence was located in the heart. It has been suggested that the first person to believe otherwise was the Roman physician Galen in the second century AD, who declared that the brain was the source of mental activity, although this has been accredited to Alcmaeon. However, Galen believed that personality and emotion were not generated by the brain, but rather by other organs. Andreas Vesalius, an anatomist and physician, was the first to believe that the brain and the nervous system are the center of the mind and emotion. Psychology, a major contributing field to cognitive neuroscience, emerged from philosophical reasoning about the mind. One of the predecessors to cognitive neuroscience was phrenology, a pseudoscientific approach that claimed that behavior could be determined by the shape of the scalp.
In the early 19th century, Franz Joseph Gall and J. G. Spurzheim believed that the human brain was localized into 35 different sections. In his book, The Anatomy and Physiology of the Nervous System in General, of the Brain in Particular, Gall claimed that a larger bump in one of these areas meant that that area of the brain was used more by that person; this theory gained significant public attention, leading to the publication of phrenology journals and the creation of phrenometers, which measured the bumps on a human subject's head. While phrenology remained a fixture at fairs and carnivals, it did not enjoy wide acceptance within the scientific community; the major criticism of phrenology is. The localizationist view was concerned with mental abilities being localized to specific areas of the brain rather than on what the characteristics of the abilities were and how to measure them. Studies performed in Europe, such as those of John Hughlings Jackson, supported this view. Jackson studied patients with brain damage those with epilepsy.
He discovered that the epileptic patients made the same clonic and tonic movements of muscle during their seizures, leading Jackson to believe that they must be occurring in the same place e
In musical terminology, tempo is the speed or pace of a given piece. In classical music, tempo is indicated with an instruction at the start of a piece and is measured in beats per minute. In modern classical compositions, a "metronome mark" in beats per minute may supplement or replace the normal tempo marking, while in modern genres like electronic dance music, tempo will simply be stated in bpm. Tempo may be separated from articulation and meter, or these aspects may be indicated along with tempo, all contributing to the overall texture. While the ability to hold a steady tempo is a vital skill for a musical performer, tempo is changeable. Depending on the genre of a piece of music and the performers' interpretation, a piece may be played with slight tempo rubato or drastic accelerando. In ensembles, the tempo is indicated by a conductor or by one of the instrumentalists, for instance the drummer. While tempo is described or indicated in many different ways, including with a range of words, it is measured in beats per minute.
For example, a tempo of 60 beats per minute signifies one beat per second, while a tempo of 120 beats per minute is twice as rapid, signifying one beat every 0.5 seconds. The note value of a beat will be that indicated by the denominator of the time signature. For instance, in 44 the beat will be a crotchet; this measurement and indication of tempo became popular during the first half of the 19th century, after Johann Nepomuk Maelzel invented the metronome. Beethoven was one of the first composers to use the metronome. Instead of beats per minute, some 20th-century classical composers specify the total playing time for a piece, from which the performer can derive tempo. With the advent of modern electronics, bpm became an precise measure. Music sequencers use the bpm system to denote tempo. In popular music genres such as electronic dance music, accurate knowledge of a tune's bpm is important to DJs for the purposes of beatmatching; the speed of a piece of music can be gauged according to measures per minute or bars per minute, the number of measures of the piece performed in one minute.
This measure is used in ballroom dance music. In different musical contexts, different instrumental musicians, conductors, music directors or other individuals will select the tempo of a song or piece. In a popular music or traditional music group or band, the bandleader or lead singer may select the tempo. In popular and traditional music, whoever is setting the tempo counts out one or two bars in tempo. In some songs or pieces in which a singer or solo instrumentalist begins the work with a solo introduction, the tempo they set will provide the tempo for the group. In an orchestra or concert band, the conductor sets the tempo. In a marching band, the drum major may set the tempo. In a sound recording, in some cases a record producer may set the tempo for a song. In classical music it is customary to describe the tempo of a piece by one or more words, most in Italian, in addition to or instead of a metronome mark in beats per minute. Italian is used because it was the language of most composers during the time these descriptions became commonplace.
Some well-known Italian tempo indications include "Allegro", "Andante" and "Presto". This practice developed during the baroque and classical periods. In the earlier Renaissance music, performers understood most music to flow at a tempo defined by the tactus; the mensural time signature indicated. In the Baroque period, pieces would be given an indication, which might be a tempo marking, or the name of a dance, the latter being an indication both of tempo and of metre. Any musician of the time was expected to know how to interpret these markings based on custom and experience. In some cases, these markings were omitted. For example, the first movement of Bach's Brandenburg Concerto No. 3 has no tempo or mood indication whatsoever. Despite the increasing number of explicit tempo markings, musicians still observe conventions, expecting a minuet to be at a stately tempo, slower than a Viennese waltz. Genres imply tempos. Thus, Ludwig van Beethoven wrote "In tempo d'un Menuetto" over the first movement of his Piano Sonata Op. 54, though that movement is not a minuet.
Many tempo markings indicate mood and expression. For example and allegro both indicate a speedy execution, but allegro connotes joy. Presto, on the other hand indicates speed. Additional Italian words indicate tempo and mood. For example, the "agitato" in the Allegro agitato of the last movement of George Gershwin's piano concerto in F has both a tempo indication and a mood indication. Composers name movements of compositions after their tempo marking. For instance, the second movement of Samuel Barber's first String Quartet is an Adagio. A particular musical form or genre implies its own tempo, so composers need place no further explanation in the score. Popular music charts use terms such as bossa nova, ballad
Autonomic nervous system
The autonomic nervous system the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, thus influences the function of internal organs. The autonomic nervous system is a control system that acts unconsciously and regulates bodily functions such as the heart rate, respiratory rate, pupillary response and sexual arousal; this system is the primary mechanism in control of the fight-or-flight response. Within the brain, the autonomic nervous system is regulated by the hypothalamus. Autonomic functions include control of respiration, cardiac regulation, vasomotor activity, certain reflex actions such as coughing, sneezing and vomiting; those are subdivided into other areas and are linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving ANS regulatory input from the limbic system to do so; the autonomic nervous system has three branches: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system.
Some textbooks do not include the enteric nervous system as part of this system. The sympathetic nervous system is considered the "fight or flight" system, while the parasympathetic nervous system is considered the "rest and digest" or "feed and breed" system. In many cases, both of these systems have "opposite" actions where one system activates a physiological response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as "excitatory" and "inhibitory" was overturned due to the many exceptions found. A more modern characterization is that the sympathetic nervous system is a "quick response mobilizing system" and the parasympathetic is a "more activated dampening system", but this has exceptions, such as in sexual arousal and orgasm, wherein both play a role. There are excitatory synapses between neurons. A third subsystem of neurons that have been named non-noradrenergic, non-cholinergic transmitters have been described and found to be integral in autonomic function, in particular in the gut and the lungs.
Although the ANS is known as the visceral nervous system, the ANS is only connected with the motor side. Most autonomous functions are involuntary but they can work in conjunction with the somatic nervous system which provides voluntary control; the autonomic nervous system is divided into the sympathetic nervous system and parasympathetic nervous system. The sympathetic division emerges from the spinal cord in the thoracic and lumbar areas, terminating around L2-3; the parasympathetic division has craniosacral “outflow”, meaning that the neurons begin at the cranial nerves and sacral spinal cord. The autonomic nervous system is unique in; the preganglionic, or first, neuron will begin at the “outflow” and will synapse at the postganglionic, or second, neuron's cell body. The postganglionic neuron will synapse at the target organ; the sympathetic nervous system consists of cells with bodies in the lateral grey column from T1 to L2/3. These cell bodies are "GVE" are the preganglionic neurons. There are several locations upon which preganglionic neurons can synapse for their postganglionic neurons: Paravertebral ganglia of the sympathetic chain cervical ganglia thoracic ganglia and rostral lumbar ganglia caudal lumbar ganglia and sacral gangliaPrevertebral ganglia Chromaffin cells of the adrenal medulla These ganglia provide the postganglionic neurons from which innervation of target organs follows.
Examples of splanchnic nerves are: Cervical cardiac nerves & thoracic visceral nerves, which synapse in the sympathetic chain Thoracic splanchnic nerves, which synapse in the prevertebral ganglia Lumbar splanchnic nerves, which synapse in the prevertebral ganglia Sacral splanchnic nerves, which synapse in the inferior hypogastric plexusThese all contain afferent nerves as well, known as GVA neurons. The parasympathetic nervous system consists of cells with bodies in one of two locations: the brainstem or the sacral spinal cord; these are the preganglionic neurons, which synapse with postganglionic neurons in these locations: Parasympathetic ganglia of the head: Ciliary, Submandibular and Otic In or near the wall of an organ innervated by the Vagus or Sacral nerves These ganglia provide the postganglionic neurons from which innervations of target organs follows. Examples are: The postganglionic parasympathetic splanchnic nerves The vagus nerve, which passes through the thorax and abdominal regions innervating, among other organs, the heart, lungs and stomach The sensory arm is composed of primary visceral sensory neurons found in the peripheral nervous system, in cranial sensory ganglia: the geniculate and nodose ganglia, appen
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is roughly divided into the Archaic period, Classical period, Hellenistic period, it is succeeded by medieval Greek. Koine is regarded as a separate historical stage of its own, although in its earliest form it resembled Attic Greek and in its latest form it approaches Medieval Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects. Ancient Greek was the language of Homer and of fifth-century Athenian historians and philosophers, it has contributed many words to English vocabulary and has been a standard subject of study in educational institutions of the Western world since the Renaissance. This article contains information about the Epic and Classical periods of the language. Ancient Greek was a pluricentric language, divided into many dialects; the main dialect groups are Attic and Ionic, Aeolic and Doric, many of them with several subdivisions.
Some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are several historical forms. Homeric Greek is a literary form of Archaic Greek used in the epic poems, the "Iliad" and "Odyssey", in poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic and other Classical-era dialects; the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period, they differ in some of the detail. The only attested dialect from this period is Mycenaean Greek, but its relationship to the historical dialects and the historical circumstances of the times imply that the overall groups existed in some form. Scholars assume that major Ancient Greek period dialect groups developed not than 1120 BCE, at the time of the Dorian invasion—and that their first appearances as precise alphabetic writing began in the 8th century BCE.
The invasion would not be "Dorian" unless the invaders had some cultural relationship to the historical Dorians. The invasion is known to have displaced population to the Attic-Ionic regions, who regarded themselves as descendants of the population displaced by or contending with the Dorians; the Greeks of this period believed there were three major divisions of all Greek people—Dorians and Ionians, each with their own defining and distinctive dialects. Allowing for their oversight of Arcadian, an obscure mountain dialect, Cypriot, far from the center of Greek scholarship, this division of people and language is quite similar to the results of modern archaeological-linguistic investigation. One standard formulation for the dialects is: West vs. non-west Greek is the strongest marked and earliest division, with non-west in subsets of Ionic-Attic and Aeolic vs. Arcadocypriot, or Aeolic and Arcado-Cypriot vs. Ionic-Attic. Non-west is called East Greek. Arcadocypriot descended more from the Mycenaean Greek of the Bronze Age.
Boeotian had come under a strong Northwest Greek influence, can in some respects be considered a transitional dialect. Thessalian had come under Northwest Greek influence, though to a lesser degree. Pamphylian Greek, spoken in a small area on the southwestern coast of Anatolia and little preserved in inscriptions, may be either a fifth major dialect group, or it is Mycenaean Greek overlaid by Doric, with a non-Greek native influence. Most of the dialect sub-groups listed above had further subdivisions equivalent to a city-state and its surrounding territory, or to an island. Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, Northern Peloponnesus Doric; the Lesbian dialect was Aeolic Greek. All the groups were represented by colonies beyond Greece proper as well, these colonies developed local characteristics under the influence of settlers or neighbors speaking different Greek dialects; the dialects outside the Ionic group are known from inscriptions, notable exceptions being: fragments of the works of the poet Sappho from the island of Lesbos, in Aeolian, the poems of the Boeotian poet Pindar and other lyric poets in Doric.
After the conquests of Alexander the Great in the late 4th century BCE, a new international dialect known as Koine or Common Greek developed based on Attic Greek, but with influence from other dialects. This dialect replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, spoken in the region of modern Sparta. Doric has passed down its aorist terminations into most verbs of Demotic Greek. By about the 6th century CE, the Koine had metamorphosized into Medieval Greek. Ancient Macedonian was an Indo-European language at least related to Greek, but its exact relationship is unclear because of insufficient data: a dialect of Greek; the Macedonian dialect (or l
Heart rate variability
Heart rate variability is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat interval. Other terms used include: "cycle length variability", "RR variability", "heart period variability". Methods used to detect beats include: ECG, blood pressure, ballistocardiograms, the pulse wave signal derived from a photoplethysmograph. ECG is considered superior because it provides a clear waveform, which makes it easier to exclude heartbeats not originating in the sinoatrial node; the term "NN" is used in place of RR to emphasize the fact that the processed beats are "normal" beats. Reduced HRV has been shown to be a predictor of mortality after myocardial infarction although others have shown that the information in HRV relevant to acute myocardial infarction survival is contained in the mean heart rate. A range of other outcomes and conditions may be associated with modified HRV, including congestive heart failure, diabetic neuropathy, post–cardiac-transplant depression, susceptibility to SIDS and poor survival in premature babies.
There is interest in HRV in the field of psychophysiology. For example, HRV is related to emotional arousal. High-frequency activity has been found to decrease under conditions of acute time pressure and emotional strain and elevated state anxiety related to focused attention and motor inhibition. HRV has been shown to be reduced in individuals reporting to worry more. In individuals with post-traumatic stress disorder, HRV and its HF component is reduced whilst the low-frequency component is elevated. Furthermore, PTSD patients demonstrated no HF reactivity to recalling a traumatic event; the polyvagal theory describes pathways in the autonomic nervous system that mediate HRV. This theory emphasizes the role of heart rate variability in understanding the magnitude and nature of vagal outflow to the heart; this theory decomposes heart rate variability based on frequency domain characteristics with an emphasis on respiratory sinus arrhythmia and its transmission by a neural pathway, distinct from other components of HRV.
There is physiological evidence for a polyvagal control of the heart. The neurovisceral integration model describes how the prefrontal cortex regulates activity in limbic structures which act to suppress parasympathetic activity and activate sympathetic circuits. Variation in the output of these two branches of the autonomic system produces HRV and activity in the prefrontal cortex can hence modulate HRV. Variation in the beat-to-beat interval is a physiological phenomenon; the SA node receives several different inputs and the instantaneous heart rate or RR interval and its variation are the results of these inputs. The main inputs are the parasympathetic nervous system and humoral factors. Respiration gives rise to waves in heart rate mediated via the PSNS, it is thought that the lag in the baroreceptor feedback loop may give rise to 10 second waves in heart rate, but this remains controversial. Factors that affect the input are the baroreflex, hormones, sleep-wake cycle, physical activity, stress.
Decreased PSNS activity or increased SNS activity will result in reduced HRV. High frequency activity has been linked to PSNS activity. Activity in this range is associated with the respiratory sinus arrhythmia, a vagally mediated modulation of heart rate such that it increases during inspiration and decreases during expiration. Less is known about the physiological inputs of the low frequency activity. Though thought to reflect SNS activity, it is now accepted that it reflects a mixture of both the SNS and PSNS. There are two primary fluctuations: Respiratory arrhythmia; this heart rate variation is associated with respiration and faithfully tracks the respiratory rate across a range of frequencies. Low-frequency oscillations; this heart rate variation is associated with Mayer waves of blood pressure and is at a frequency of 0.1 Hz or a 10-second period. Errors in the location of the instantaneous heart beat will result in errors in the calculation of the HRV. HRV is sensitive to artifact and errors in as low as 2% of the data will result in unwanted biases in HRV calculations.
To ensure accurate results therefore it is critical to manage artifact and RR errors appropriately prior to performing any HRV analyses. Robust management of artifacts, including RWave identification and exclusion requires a high degree of care and precision; this can be time consuming in large studies with data recorded over long durations. Software packages are able to assist users with a variety of robust and tested artifact management tools; these software programs include some automated capability but it is important that a human review any automated artifact management and edit accordingly. The most used methods can be grouped under time-domain and frequency-domain. A joint European and American task-force described standards in HRV measurements in 1996. Other methods have been proposed, such as non-linear methods; these are based on the beat-to-beat or NN intervals, which are analysed to give variables such as: SDNN, the standard deviation of NN intervals. Calculated over a 24-hour period.
SDANN, the standard deviation of the average NN intervals calculated over short periods 5 minutes. SDNN is therefore a measure of changes in hear
Emotion is a mental state variously associated with thoughts, behavioural responses, a degree of pleasure or displeasure. There is no scientific consensus on a definition. Emotion is intertwined with mood, personality and motivation. Research on emotion has increased over the past two decades with many fields contributing including psychology, endocrinology, history, sociology of emotions, computer science; the numerous theories that attempt to explain the origin, neurobiology and function of emotions have only fostered more intense research on this topic. Current areas of research in the concept of emotion include the development of materials that stimulate and elicit emotion. In addition PET scans and fMRI scans help study the affective picture processes in the brain."Emotions can be defined as a positive or negative experience, associated with a particular pattern of physiological activity." Emotions produce different physiological and cognitive changes. The original role of emotions was to motivate adaptive behaviors that in the past would have contributed to the passing on of genes through survival and kin selection.
In some theories, cognition is an important aspect of emotion. Those acting on the emotions they are feeling may seem as if they are not thinking, but mental processes are still essential in the interpretation of events. For example, the realization of our believing that we are in a dangerous situation and the subsequent arousal of our body's nervous system is integral to the experience of our feeling afraid. Other theories, claim that emotion is separate from and can precede cognition. Consciously experiencing an emotion is exhibiting a mental representation of that emotion from a past or hypothetical experience, linked back to a content state of pleasure or displeasure; the content states are established by verbal explanations of experiences, describing an internal state. Emotions are complex. According to some theories, they are states of feeling that result in physical and psychological changes that influence our behavior; the physiology of emotion is linked to arousal of the nervous system with various states and strengths of arousal relating to particular emotions.
Emotion is linked to behavioral tendency. Extroverted people are more to be social and express their emotions, while introverted people are more to be more withdrawn and conceal their emotions. Emotion is the driving force behind motivation, positive or negative. According to other theories, emotions are not causal forces but syndromes of components, which might include motivation, feeling and physiological changes, but no one of these components is the emotion. Nor is the emotion an entity that causes these components. Emotions involve different components, such as subjective experience, cognitive processes, expressive behavior, psychophysiological changes, instrumental behavior. At one time, academics attempted to identify the emotion with one of the components: William James with a subjective experience, behaviorists with instrumental behavior, psychophysiologists with physiological changes, so on. More emotion is said to consist of all the components; the different components of emotion are categorized somewhat differently depending on the academic discipline.
In psychology and philosophy, emotion includes a subjective, conscious experience characterized by psychophysiological expressions, biological reactions, mental states. A similar multicomponential description of emotion is found in sociology. For example, Peggy Thoits described emotions as involving physiological components, cultural or emotional labels, expressive body actions, the appraisal of situations and contexts; the word "emotion" dates back to 1579, when it was adapted from the French word émouvoir, which means "to stir up". The term emotion was introduced into academic discussion as a catch-all term to passions and affections; the word emotion was coined in the early 1800s by Thomas Brown and it is around the 1830s that the modern concept of emotion first emerged for English Language. "No one felt emotions before about 1830. Instead they felt other things - "passions", "accidents of the soul", "moral sentiments" - and explained them differently from how we understand emotions today."Some cross cultural studies indicate that the categorization of "emotion" and classification of basic emotions such as "anger" and "sadness" are not universal and that the boundaries and domains of these concepts are categorized differently by all cultures.
However, others argue that there are some basic universal but spurious bases of emotions in some cultures. In anthropology, an inability to express or perceive emotion is sometimes referred to as alexithymia; the Oxford Dictionary definition of emotion is "A strong feeling deriving from one's circumstances, mood, or relationships with others." Emotions are responses to significant external events. Emotions can be occurrences or dispositions, short-lived or long-lived. Psychotherapist Michael C. Graham describes all emotions as existing on a continuum of intensity, thus fear might range from mild concern to terror or shame might range from simple embarrassment to toxic shame. Emotions have been described as consisting of a coordinated set of responses, which may include verbal, physiological and neural mechanisms. Emotions have been categorized, with some relationships existing between emotions and some direct oppos
Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute. The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide, it is equal or close to the pulse measured at any peripheral point. Activities that can provoke change include physical exercise, anxiety, stress and ingestion of drugs; the American Heart Association states. Tachycardia is a fast heart rate, defined as above 100 bpm at rest. Bradycardia is a slow heart rate, defined as below 60 bpm at rest. During sleep a slow heartbeat with rates around 40 -- 50 bpm is considered normal; when the heart is not beating in a regular pattern, this is referred to as an arrhythmia. Abnormalities of heart rate sometimes indicate disease. While heart rhythm is regulated by the sinoatrial node under normal conditions, heart rate is regulated by sympathetic and parasympathetic input to the sinoatrial node; the accelerans nerve provides sympathetic input to the heart by releasing norepinephrine onto the cells of the sinoatrial node, the vagus nerve provides parasympathetic input to the heart by releasing acetylcholine onto sinoatrial node cells.
Therefore, stimulation of the accelerans nerve increases heart rate, while stimulation of the vagus nerve decreases it. Due to individuals having a constant blood volume, one of the physiological ways to deliver more oxygen to an organ is to increase heart rate to permit blood to pass by the organ more often. Normal resting heart rates range from 60-100 bpm. Bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people and do not require special attention. Tachycardia is defined as a resting heart rate above 100 bpm, though persistent rest rates between 80–100 bpm if they are present during sleep, may be signs of hyperthyroidism or anemia. Central nervous system stimulants such as substituted amphetamines increase heart rate. Central nervous system depressants or sedatives decrease the heart rate. There are many ways in which the heart rate slows down. Most involve stimulant-like endorphins and hormones being released in the brain, many of which are those that are'forced'/'enticed' out by the ingestion and processing of drugs.
This section discusses target heart rates for healthy persons and are inappropriately high for most persons with coronary artery disease. The heart rate is rhythmically generated by the sinoatrial node, it is influenced by central factors through sympathetic and parasympathetic nerves. Nervous influence over the heartrate is centralized within the two paired cardiovascular centres of the medulla oblongata; the cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve. During rest, both centers provide slight stimulation to the heart; this is a similar concept to tone in skeletal muscles. Vagal stimulation predominates as, left unregulated, the SA node would initiate a sinus rhythm of 100 bpm. Both sympathetic and parasympathetic stimuli flow through the paired cardiac plexus near the base of the heart; the cardioaccelerator center sends additional fibers, forming the cardiac nerves via sympathetic ganglia to both the SA and AV nodes, plus additional fibers to the atria and ventricles.
The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter norepinephrine at the neuromuscular junction of the cardiac nerves; this shortens the repolarization period, thus speeding the rate of depolarization and contraction, which results in an increased heartrate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions. Norepinephrine binds to the beta–1 receptor. High blood pressure medications are used to so reduce the heart rate. Parasympathetic stimulation originates from the cardioinhibitory region with impulses traveling via the vagus nerve; the vagus nerve sends branches to both the SA and AV nodes, to portions of both the atria and ventricles. Parasympathetic stimulation releases the neurotransmitter acetylcholine at the neuromuscular junction. ACh slows HR by opening chemical- or ligand-gated potassium ion channels to slow the rate of spontaneous depolarization, which extends repolarization and increases the time before the next spontaneous depolarization occurs.
Without any nervous stimulation, the SA node would establish a sinus rhythm of 100 bpm. Since resting rates are less than this, it becomes evident that parasympathetic stimulation slows HR; this is similar to an individual driving a car with one foot on the brake pedal. To speed up, one need remove one’s foot from the brake and let the engine increase speed. In the case of the heart, decreasing parasympathetic stimulation decreases the release of ACh, which allows HR to increase up to 100 bpm. Any increases beyond this rate would require sympathetic stimulation; the cardiovascular centres receive input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympath