Muscle Stretch Reflexes and Lower Limb Length Flashcards
When assessing the motor system what reflex is tested for
- The muscle stretch reflex
What does the muscle stretch reflex allow us to test the health of for
- Neurones of the stretch reflex.
- Synapses of the stretch reflex
- Wider circuits bult from the stretch reflex
What features must you look out for during a visual examination of the MSK system
- Appearance of MSK muscles
- Symmetry of muscle bulk
- Location of libs and other muscle
- Posture
- Gait
What are some ways you can test for a patients ability to move
- Evoking reflex movements
- Displacement of a limb or muscle
- Muscle tone
- Any other specialist movements
What makes up a motor unit
- Alpha-motoneuron
- All the muscle fibres supplied by the alpha-motoneuron
What is a reflex
- Involuntary, unlearned, repeatable, automatic reaction to a specific stimulus that does not require the brain to be intact
What is the neural pathway describing a reflex known as
- Reflex arc
What are the 5 components that make up a reflex arc
- A receptor
- An afferent fibre
- An integration centre
- An efferent fibre
- An effector organ
What is the role of the muscle stretch reflex in neurology
-Basic template for all other motor circuits in the body.
- Underlies all movement of muscles of the body.
- Sets all the muscle tone of the body.
What are muscle spindles
- Muscle length receptors embedded within the fibres of the muscle
what makes up the pathway that is known as the stretch reflex arc
- Muscle spindles
- Cell bodies of lower motoneurons
- The synapse between the 2
How does the muscle stretch reflex occur
- A muscle that is not contracting is relaxing (lengthening or stretching)
- When the stretch is detected, action potentials are fired via muscle spindle afferent fibres which synapse with alpha-motoneurons in the spinal cord.
- Action potential travels along alpha motoneurone towards NMJ where Ach is released.
-m Ach causes muscle to contract and return to its original length.
What does the stretch reflex aim to maintain
- Aims to maintain the muscle at a constant length
Where are the action potentials from the afferent muscle spindle fibres also sent to
- The cerebral cortex (via dorsal columns)
- The cerebellum (via spino-cerebral tracts)
Where is the cell body of the spindle afferent fibres found
- Dorsal root ganglion
Where do the axons synapse with the motoneuron
- Level of ventral horn in lamina XI
How does the axon of the alpha motoneuron leave the spinal cord and where does it go
- Leaves via ventral roots
- Leaves to supply muscle
What is muscle tone also known as
- Motor tone
What is muscle tone
- The small force a muscle has due to back ground minimal contractions.
What causes background minimal contractions in a muscle
- The background electrical impulses supplied by lower motoneurons in a normal awake neurological status.
What is motor tone like in utero and early life
- Present but low in utero
- Supressed during birth (otherwise baby would resist birth)
- Returns within months and informs of presence or absence of injury to the brain during birth
When beside birth is muscle tone also inhibited and is this in all muscles?
- During deep (REM) sleep in all muscles except:
> Muscles of breathing
> Extra-ocular muscles
> Urinary sphincter muscles
> Anal sphincter muscles
What happens when to the body when it generates too little muscle tone
- Becomes limp
- Cannot support its weight
- Normal posture is lost
- Too little muscle tone can range from hypotonia (reduced muscle tone) to atonia (no muscle tone)
What happens when to the body when it generates too much muscle tone
- Normal body posture
- The muscles become stiff
- Spastic paralysis
- Stiffness of joints and loss of ability to move
