autonomic control

Question 1

What role does the autonomic nervous system (ANS) play during exercise?

Answer 1

The ANS mediates cardiovascular adjustments to meet the metabolic demands of exercising muscles.

It is essential for maintaining performance and sustaining physical activity.

Question 2

How does the autonomic nervous system control cardiovascular responses during exercise?

Answer 2

Parasympathetic withdrawal (vagus nerve):

Increases heart rate (HR)

Increases ventricular contractility

Increases stroke volume → cardiac output

Sympathetic activation:

Further increases HR and contractility

Stimulates epinephrine release from adrenal medulla → enhances cardiac output

Question 3

How does the sympathetic nervous system redistribute blood flow during exercise?

Answer 3

Non-exercising muscles & visceral organs: Sympathetic vasoconstriction → reduces blood flow.

Active skeletal muscles: Sympathetic vasoconstriction is attenuated (functional sympatholysis) due to muscle metabolites.

Result: Cardiac output is redirected to active muscles → supports exercise performance.

Question 4

How is blood flow redistributed during exercise?

Answer 4

Non-exercising muscles & visceral organs: Sympathetic vasoconstriction → reduces blood flow.

Active muscles: Vasoconstriction is attenuated by local metabolites (functional sympatholysis) → vessels stay open.

Result: Cardiac output is redirected to active muscles → supports performance.

Question 5

Is functional sympatholysis a complete override of sympathetic vasoconstriction in active muscles?

Answer 5

No. Functional sympatholysis attenuates but does not fully block sympathetic vasoconstriction.

Sympathetic activity still partially restricts blood flow in active muscles.

This partial restriction is important for maintaining arterial blood pressure during exercise.

Question 6

Why are autonomic adjustments important during exercise?

Answer 6

Patients with autonomic failure cannot maintain even light exercise, even when lying down (supine) to increase central blood volume and venous return.

This highlights the critical role of the autonomic nervous system in:

Adjusting heart rate and cardiac output

Redistributing blood flow

Maintaining blood pressure

Question 7

Q: How is heart rate regulated during exercise

Answer 7

mmediate HR increase at exercise onset:

Mainly due to parasympathetic withdrawal (vagus nerve).

Evidenced by reduced heart rate variability.

Low-to-moderate intensity:

Parasympathetic withdrawal is the dominant factor in HR increase.

Contribution decreases as HR approaches 90–100 bpm (SA node intrinsic rate).

Higher intensity:

Sympathetic stimulation increasingly drives HR.

Comes from both neural signals and endocrine hormones (norepinephrine, epinephrine).

Question 8

What is the role of the sympathetic nervous system in peripheral regulation during exercise?

Answer 8

Sympathetic activity = key for redistributing blood flow and ensuring stable blood pressure during physical activity

Question 9

: How does the timing of peripheral sympathetic responses compare to heart rate changes at exercise onset

Answer 9

Heart rate: Increases almost immediately at exercise onset.

Peripheral muscle sympathetic response: Delayed ~30–60 seconds.

Reason: Likely due to a combination of:

Build-up of metabolites in active muscles

Stimulation of muscle afferents (group III/IV sensory neurons)

Question 10

How does sympathetic activity to the skin and kidney change at the start of exercise?

Answer 10

Sympathetic adjustments to non-exercising organs help support active muscles and match cardiovascular output to metabolic demand.

Question 11

What is central command and how does it regulate exercise responses?

Answer 11

Neural signals originate in the medulla and pons.

Simultaneously drives heart rate, ventilation, and sympathetic activity at exercise onset.

Prepares the body before muscle activity fully begins.

Question 12

What is the exercise pressor reflex?

Answer 12

Feedback from muscle afferents (group III & IV neurons).

Sensitive to mechanical and chemical changes in working muscles.

Modulates sympathetic activity to maintain blood pressure and blood flow during exercise.

Question 13

hat is the arterial baroreflex and its role during exercise?

Answer 13

Baroreceptors in carotid sinus and aortic arch detect changes in arterial pressure.

Adjusts heart rate and vascular tone to maintain stable blood pressure.

Ensures adequate perfusion of muscles during dynamic activity.