7.2 Central Command

Question 1

What did (Mitchell, 2013) suggest about parallel activation ??

Answer 1

Central control - brain goes to the exercising muscle and cv centre
Cv centre goes to heart and blood vessels

Peripheral control - brain goes straight to exercising muscle. Exercising muscle goes to CV centre - heart and blood vessels

Question 2

What did Mitchell (2013) say about parallel activation ?

Answer 2

Parallel activation of skeletal muscle activation and autonomic nervous system changes , which suggests a direct CV control centre

Question 3

Discuss the early experiments looking at CC??

Answer 3

Johanssen (1893) showed passive movement of a rabbit hindlimb cause a small increase in HR

Lindhard (1910) was the first experiment to look at using electrically evoked contractions in man

Question 4

Describe the Bergonie technique (Mitchell, 2013)

Answer 4

Subject is weighted down by 100kg of sand bags to increase the muscular work and diminish the violent movements.

Also, stimulating electrodes are placed on the calves, thighs, stomach and arms and HR, Ve rate is measured

Showed using this technique, HR always increased without CC
Also, HR onset increase shows a ‘latent’ period of one or more beats i.e. HR rise is slightly slower when exercise is electrically invoked.

Question 5

Discuss the Williams (1975) experiment?

Answer 5

Repeated the bergonie technique during dynamic exercise on a tandem bicycle.

With voluntary exercise - HR increased on the 1st beat after exercise initiation
With induced exercise - HR increased the 1st beat after exercise initiation but only if the exercise started in the first 1/3 of the R-R interval. If ex started on the latter 2/3 of the R-R interval, the increase in HR occurred on the second beat

Demonstrates a fine control mechanism

Question 6

Discuss Jordan and Marshall (1995)?

Answer 6

A partial NMB reduced strength by 50%

• showed same cv response when same relative force
• a greater CV response of same absolute force as more effort (CC) required
• at 25% MVC, the NMB caused an increase in bp compared to control .

Question 7

Discuss epidural blockades work from Jordan and Marshall (1995)??

Answer 7

Epidural anaesthesia reduces afferents feedback and blocks motor fibres

• for the same relative force , bp response is greater for control
• for the same absolute force, bp response is the same.

Question 8

Discuss the first experiment from Goodwin (1972)??

Answer 8

Had participants perform an isometric contraction (20%MVC) of the biceps for 3 minutes - with either unassisted CC or assisted CC by vibrating the 1a afferents to cause reflex activation
They found an increase in HR and BP in both conditions during exercise but less of an increase in the unassisted condition
- data suggests a role of cc in the CV response to exercise

Question 9

Discuss the second experiment by Goodwin (1972)

Answer 9

Participants performed an isometric contraction (35%) of MVC of triceps for 3 mins - either unassisted central command or opposed CC by vibrating 1a afferents of triceps to cause reflex activation and inhibition in the antagonist triceps muscle

• showed more CC was needed for the same force
• increased HR and BP in both conditions during exercise , but larger increases in the opposed conditions
• also suggests a role of CC In the CV response

Question 10

Discuss the third study by GOodwin et al 1972

Answer 10

He excited the antagonist spindle to inhibit the agonist muscle contraction.

Results showed, more CC was required for the same force

• metabolically the muscle was the same
• sustained contraction causes EPR, showed a greater breathing and HR reSponse

Question 11

Discuss the WIlliamson (2002) hypnosis study ??

Answer 11

Grouped participants on susceptibility to hypnosis , and trained them to maintain handgrip at a set intensity

3 minutes of real or imagined handgrip exercise
Results showed in the imagined condition , susceptible participants induced a CV response (⬆️HR AND MBP) and a higher RPE

Question 12

Discuss Williams (2001)???

Answer 12

Had participants exercise at 50W, amd were hypnotised to think they were cycling uphill or downhill.
The results showed RPE was rated easier when hypnotised downhill than uphill .
Also the uphill CV response to exercise increased, as RPE rated higher for perceived uphill, increased CC resulting in a slightly larger CV response (at 15 min,HR And MBP sig higher for perceived uphill).

Question 13

Discuss the Schibye (1981) study?

Answer 13

Had participants either maintain constant force at 20% MVC or maintain constant EMG activity. Used EMG as indirect measure of CC

Had subjects perform submaximal knee ext contraction for 5 mins
An increase in EMG for the same force indicates peripheral fatigue.
The EMG was ‘clamped’ for the same Cc -‘consequently force drops .
Also for ‘B’ less metabolite accumulation due to the lower force
This data provides evidence that CC drives HR.

Question 14

Discuss the work of Victor et al (1989)??

Answer 14

Looked at the responses to isometric contractions (handgrip) at either 15% or 30% of MVC in 8 normal subjects before NMB with tubocurarine - where attempted contractions yielded no force.

Showed a proportional cv response at 15 and 30 % intensity.
NMB resulted in roughly a 80% force reduction
Cc had minimal impact on driving MSNA activity
These data suggest a differential control of HR (CC) and BP (afferent)

Question 15

Hajduczok (1991) wanted to investigate the role of the CC on renal and lumbar SNS activity, what did he find?

Answer 15

Looked at decorticate cats capable of spontaneous locomotion
The results showed an increased sympathetic drive in the absence of skeletal muscle and baroreceptor afferents
No influence of the higher brain centres
Results may not be relevant to intact animals or humans.

Question 16

Discuss the brain activity found in Williams (2001)??

Answer 16

Co-registered SPECT give changes in regional cerebral blood flow and are mapped onto MRI scans.
Activity in the thalamus and insular cortex
- high effort = more activation when perceived going uphill
- low effort = less activation when perceived going downhill

Question 17

Discuss Williams (2003) ?

Answer 17

Further investigated areas of insular cortex associated with CC
- found a greater activation in the right inferior posterior and left inferior anterior insular regions during a static handgrip than PECO

-the right posterior insular region activation also correlated with mental stress (Critchley, 2000)

Question 18

Green (2007) measured neuronal cortical activity in patient groups receiving deep brain stimulation.
- 5 Parkinson (STN affected)
- 4 global dystonia (GPI affected)
- 3 with chronic neuropathic pain (affect PAG)
How and what did they find???

Answer 18

Rested 240s -> 10s anticipatory rise -> exercise (30-60s) 15w cycling -> rest (60s).
HR, MAP and respiratory rate all increased in anticipation and exercise itself

Minimal changes in the GPI.
Anticipation of exercise caused a mild CV response relative to rest.
During actual exercise, STN and PAG activity increased - supporting evidence from animal studies of STN involvement (no role in anticipation) in parallel activation.
PAG activity demonstrated a fight or flight response and EPR.

Question 19

Thornton (2002) looked at midbrain stimulation, what did he find???

Answer 19

Showed high frequency stimulation (>90Hz) of the STN, thalamus + SN increased HR and MAP. Low frequency stimulation had no effect.

Results show that STN is an important aspect of the circuitry underpinning the CV responses to exercise.

Question 20

Describe the neural circuitry of CC (Williamson , 2010)??

Answer 20

Regions of the ACC and IC may work in conjunction as a “cc network”

Interacts with with thalamic and brainstem structures of CV integration.

Cc reclassified as effort induced modulation of autonomic function
Can now function as a feedback system based on perceived exertion.