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
What are some lower motoneuron nerve signs
- Flaccid muscle weakness
- Muscle hypotonia or atonia
- Muscle hyporeflexia or areflexia
- Denervation muscle atrophy
What are the 2 skeletal structures that make the largest contribution to ones height and what are the respective percentages that they contibute
- Vertebral column (42%)
- Femur (25%)
What percentage of the height of the vertebral column is attributed to the IVDs
- Around 25% of vertebral column
- Which is around 20 cm
What part of the IVD is responsible for the size of the IVD
- Central region - nucleus pulposus
How many times in the day should height be measured for an accurate clinical reading and why is this
- 3 times a day (ideally 8 hours apart)
- The IVD’s ability to hold water changes throughout the day so height must be measured several times
What are the palpable bony landmarks used to measure limb length
- ASIS (of the hip)
- Medial Malleolus (of the tibia)
What are the 2 measurements of length of the lower limb
- True length - lower tip of ASIS to lower tip of medial malleolus
- Apparent length - Umbilicus to lower tip of medial malleolus
What is a true length discrepancy
When the true length between the left and right lower limbs are not equal
What is an apparent length discrepancy
When the apparent length between the left and right lower limbs are not equal
What causes apparent shortening of the limb
- Posterior dislocation of the hip joint
- Congenital causes of hip dislocation
- Tilting of the hip (due to things like scoliosis)
What causes true shortening of the limb
- A congenitally short lower limb compared to the opposite side.
- A fracture of one or more of the long bones of the lower limb (overlapping)
- Disorders of growth
- Scoliosis
