Autonomic Nervous System (ANS) Function Tests

Vocabulary practice flashcards covering the anatomy, divisions, and clinical function tests of the Autonomic Nervous System based on practical physiology lecture notes.

Autonomic Nervous System (ANS)

The part of the nervous system suggested by Langley over 100 years ago that controls visceral activities, including cardiac muscle, smooth muscle, and glands.

Interoreceptors

Sensory nerves such as stretch receptors and chemoreceptors in blood vessels and viscera that monitor the internal environment and provide input to the ANS.

Efferent Pathway (ANS)

A two-neuron pathway consisting of preganglionic and postganglionic neurons, unlike the single motor neuron in the somatic system.

Sympathetic Division

The thoraco-lumbar component of the ANS that is catabolic, prepares the body for emergency situations, and typically has prolonged, widespread effects.

Parasympathetic Division

The cranio-sacral component of the ANS that is anabolic, conserves and stores energy, and typically has localized, short-lived effects.

QT-QS2 Ratio

An index used to measure sympathetic excitation of the heart.

QS2

The total electromechanical systolic interval, measured from the beginning of the QRS complex to the first major vibration of the aortic component of the second heart sound.

Sympathetic Skin Response (SSR)

Also called galvanic skin response, it is the change in skin potential resulting from sweat gland activation by sympathetic postganglionic cholinergic fibers.

Cold Pressure Response (CPR)

A test where plunging a hand into cold water at $4-5\,^{\circ}\text{C}$ acts as a pain stimulus, causing a rise in blood pressure due to sympathetic stimulation.

Hand-grip Test

A sympathetic function test involving sustained isometric exercise that causes a rise in heart rate and blood pressure.

30:15 RR Ratio

A cardiac vagal effect index calculated from the RR intervals at the $30^{th}$ and $15^{th}$ beats after sudden standing from a supine position; normal value is $> 1.04$.

Orthostatic Hypotension

A condition where systolic blood pressure and diastolic blood pressure fall more than $20\,\text{mm Hg}$ and $10\,\text{mm Hg}$ respectively upon standing.

Vasovagal Syncope

Hypotension accompanied by paradoxical bradycardia because the cardiac vagal supply is overactive.

Standing to Lying Ratio (S/L ratio)

The ratio of the average RR interval during 5 beats before lying down to the shortest RR interval during 10 beats after lying down, reflecting changes in vagal tone.

Valsalva Maneuver

A simple test for baroreceptor activity involving forced expiration against a closed glottis.

Valsalva Ratio

The ratio of the longest RR interval after strain to the shortest RR during strain; a normal ratio is greater than $1.45$.

Tachycardia Ratio

The ratio of the shortest RR interval during the Valsalva effort to the longest RR interval before the effort, used as an index of vagal activity.

Sinus Arrhythmia

A normal phenomenon where the heart rate increases during inspiration (decreased vagal activity) and decreases during expiration (increased vagal activity).

E:I Ratio

The expiration to inspiration ratio, calculated as the mean of maximum RR intervals during expiration divided by the mean of minimum RR intervals during deep inspiration.

Denervation Hypersensitivity

A phenomenon where an effector tissue becomes hypersensitive to a neurotransmitter $2-3\,\text{weeks}$ after it has been denervated.

Schirmer's Test

A test for lacrimation using a strip of filter paper ($25\,\text{mm}$ long and $5\,\text{mm}$ wide) placed in the lower eyelid; wetting of less than $10\,\text{mm}$ suggests parasympathetic insufficiency.