Lecture 28: Reflexes and Muscle tone- C3

Question 1

What is the myotatic reflex and its two components

Answer 1

This is reflex muscle contraction when the muscle is lengthened (stretched)

1. Phasic component: brisk and brief tendon reflex: (tested by tapping)
2. Tonic component: weaker and long-lasting tone. (testing the resistance as you stretch the muscle)

Question 2

What factors determine the strength of response for a tendon reflex. Is it voluntary? fatiguing?

Answer 2

Tendon reflexes are involuntary, stereotyped and non fatiguing.

Response strength differs between individuals, and is determined by the stimulus strength (until a threshold)

It is increased by muscle activation in same segment and other muscles (clenching muscles elsewhere) known as Reinforcement

It is increased by anxiety and reduced in sleep

Question 3

What are the 5 steps to the normal tendon reflex

Answer 3

1. Tapping the muscle tendon stretches the muscle sensed by the muscle spindle
2. Sends 1a afferent to the dorsal root where it enters the SC.
3. It synapses with alpha motorneurons
   a) homonymous muscle
   b) synergist muscle
   and
4. Ia inhibitory interneuron
5. alpha motoneuron to antagonist muscle

Question 4

What is the cranial nerve/nerve root for tendon reflexes of jaw jerk, biceps, brachioradialias, triceps, fingers, knee, ankles

Answer 4

Jaw jerk: trigeminal nerve
Biceps: C5/6
Brachioradialis: C6
Triceps: C7
Fingers: C8
Knee: L3/4
Ankles: S1

Question 5

What are the grades of myotatic reflexes and why are they graded

Answer 5

0: absent
\+: normal 
\++: normal brisk
\+++: exaggerated (abnormal)
\++++ clonus (repeated contraction)

Important because reflexes can change over time so allows comparison between different examiners

Question 6

What is tone, the components of muscle tone and how is it assessed

Answer 6

Tone: resistance of muscle to passive lengthening

1. Muscle elasticity
2. Neural (tonic or stretch reflex)

Assessed by passive flexion and extension of limb and varying speeds

Question 7

What is the main points for while doing the examination of reflexes

Answer 7

1. Patient in anatomic position; examine from the right. Clear instructions but don’t explain what you are testing.
2. Check muscle wasting between two sides.
3. Check for fasciculations (small twitches)
4. Flex, pronate, sup muscles starting distally to more proximal muscles.
5. For power make the patient lift their arms with their arms closed and see how they can hold it.
6. Can see clonus at the ankle
7. Cerebellar testing for dysdiadokinesia: toe taps/ hand nose.

Question 8

How would an upper motor neuron lesion present:

Change in tone, tendon reflexes, plantar response, power, muscle wasting and fasciculation, rapid alternating movements

Answer 8

Descending fibre not suppressing the reflexes

• Increased tone: spasticity:
• Increased tendon reflexes : 3+4+ especially in faster muscle stretch compared to slow stretch- clasp knife
• Plantar response extensor (+)
• Power is reduced
• No muscle wasting and fasciculation
• Reduced rapid alternating movements

Question 9

How would an lower motor (peripheral) lesion present:

Change in tone, tendon reflexes, plantar response, power, muscle wasting and fasciculation, rapid alternating movements

Answer 9

• Reduced/ normal tone:
• Reduced/absent reflexes (0).
• Flexor plantar response (big toe down)
• Power is reduced
• Muscle wasting (efferent input absent) and muscle fasciculations : yes
• Normal rapid alternating movements

Question 10

How would an basal ganglia/ extra pyramidal lesion present:

Change in tone, tendon reflexes, plantar response, power, muscle wasting and fasciculation, rapid alternating movements

Answer 10

• Increased tone: lead pipe rigidity and ticking cog wheel.
• Normal tendon reflexes
• Flexor plantar response
• Power is normal
• No muscle wasting or fasciculation
• Reduced rapid alternating movements