Anatomical Concept of Muscle Stretch Reflexes

Question 1

What are you looking for in a visual assessment of the MSK system at rest?

Answer 1

• Appearance of skeletal muscles
• Symmetry of muscle bulk between L+R
• Presentation of limbs + other muscle systems
• Visually noteworthy features of muscles (posture, gait, etc.)

Question 2

What are you looking for when testing a patient’s ability to move?

Answer 2

• Can reflex movements be evoked from the patient?
• Can a limb or muscle be displaced on command?
• Can motor power be generated?
• Is there muscle tone?
• Can other specialist movements be evoked if required in specific tests?

Question 3

Reflex definition

Answer 3

Involuntary, unlearned, repeatable, automatic reaction to a specific stimulus that does not require brain to be intact

Question 4

5 components of a reflex arc

Answer 4

• Receptor (/transducer)
• Afferent fibre
• Integration centre
• Efferent fibre
• Effector organ

Question 5

Where are muscle length receptors found?

Answer 5

Embedded within fibres of a muscle

Question 6

What are muscle length receptors called?

Answer 6

Muscle spindles

Question 7

What are afferent nerves of muscle spindles permanently connected to?

Answer 7

Cell bodies of motoneurones

Question 8

How does a stretch reflex work?

Answer 8

• Muscle lengthens when it relaxes
• Receptors detect lengthening and fire action potentials
• Results in reflex recruitment of motoneurones + muscle contracts

Question 9

Where are action potentials from muscle length receptors sent to?

Answer 9

• Brain
• Cerebellum
• Spinal motorneurones

Question 10

What is muscle tone?

Answer 10

• Lower motoneurones supply muscles with background electrical impulses
• This leads to minimal contraction of the muscle giving a small amount of force
• This is muscle tone

Question 11

When is muscle tone absent, and what are the exceptions to this?

Answer 11

• Deep (REM) sleep
• All muscles except:
  > Muscles of breathing
  > Extra-ocular muscles
  > Urinary + anal sphincters

Question 12

What happens when muscles generate too little tone?

Answer 12

• Body becomes limp
• Unable to support weight
• Normal body posture is lost

Question 13

What happens when muscles generate too much tone?

Answer 13

• Muscles become stiff
• Reciprocal inhibitory relationships between (ant)agonists is disrupted
• Both become equally stiff simultaneously
• Normal body posture altered
• Ability to move affected limbs lost
• Fluidity of joints lost
• Spastic paralysis

Question 14

Different lower motoneurone signs

Answer 14

• Flaccid muscle weakness
• Hypotonia/atonia
• Hyporeflexia/areflexia
• Denervation muscle atrophy
• Fasciculations (acute phase)
• Muscle wasting