Module E-09

Question 1

Spasticity

Answer 1

A hypertonic state with increased deep tendon reflexes.

Question 2

Flaccidity

Answer 2

Weakness, laxness and softness of muscle that offer limited

resistance to passive movement.

Question 3

Clonus

Answer 3

Rhythmic palpable oscillations between flexion and extension

Question 4

Monosynaptic Reflex (i.e., Deep Tendon or Myotatic Reflex)

Answer 4

• Afferent and efferent limbs are directly connected (one synapse)

Question 5

Polysynaptic reflex

Answer 5

• Afferent and efferent limbs are connected via one or more interneurons
• multiple synapses involved

Question 6

ex of Polysynaptic reflexes

Answer 6

• Pupillary light reflexes

- abdominal reflex

Question 7

Components of Reflex Arcs

Answer 7

• Sensory receptor (e.g., muscle spindle, Golgi tendon organ, free nerve ending)
• Afferent axon
• Synapse on interneurons or efferent neuron (LMN)
• Neuromuscular junction
• Muscle

Question 8

Components of Afferent LImb of Reflex

Answer 8

• Muscle spindles and Ia fibers
• Golgi tendon organs and Ib fibers
• Free nerve endings and Aδ fibers

Question 9

Components of Efferent limb of Reflex

Answer 9

Alpha motor neurons, homonymous, synergist and antagonist muscles

Question 10

Nature and Purpose of Deep Tendon Reflexes

Answer 10

• Passive stretching of muscle causes contraction.

- The reflex regulates muscle tone under modulation by upper motor neurons.

Question 11

Muscle and segment being tested in Inspiration

Answer 11

Muscle: Diaphragm
Segment: C3,4,5 (keep the phrenic alive ;P)

Question 12

Muscle and segment being tested in Shoulder Abduction

Answer 12

Muscle: Deltoid
Segment: C5

Question 13

Muscle and segment being tested in Elbow Flexion

Answer 13

Muscle: Biceps Brachii, Brachialis
Segment: C5,6

Question 14

Muscle and segment being tested in Wrist extension

Answer 14

Muscle: Extensor Carpi , Radialis Longus and Brevis
Segment: C6,7

Question 15

Muscle and segment being tested in Elbow Extension

Answer 15

Muscle: Triceps Brachii
Segment: C6,7,8

Question 16

Muscle and segment being tested in Finger Flexion

Answer 16

Muscle: Flexor digitorum superficialis and profundus
Segment: C8

Question 17

Muscle and segment being tested in Finger abduction and adduction

Answer 17

Muscle: Interossei
Segment: C8,T1

Question 18

Muscle and segment being tested in Thigh adduction

Answer 18

Muscle: Adductor longus and brevis
Segment: L2,3,4

Question 19

Muscle and segment being tested in Knee extension

Answer 19

Muscle: Quadriceps
Segment: L3,4

Question 20

Muscle and segment being tested in Great Toe extension

Answer 20

Muscle: Extensor hallucis longus
Segment: L5,S1

Question 21

Muscle and segment being tested in Ankle Plantar flexion

Answer 21

Muscle: Gastrocnemius, soleus
Segment: S1,2

Question 22

Muscle and segment being tested in Anal Contraction

Answer 22

Muscle: Sphincter ani externus
Segment: S2,3,4

Question 23

Scale for Reflex testing

Answer 23

• 4+ - Very brisk or hyperactive with clonus
• 3+ - Brisker than average (high normal)
• 2+ - Average (normal)
• 1+ - Somewhat diminished (low normal)
• 0 - No response

Question 24

Describe the pathway for the Stretch Reflex

Answer 24

1) The sensory signal for the stretch reflex arises in the muscle spindles.
2) The tapping a tendon with a reflex hammer stretches the muscle spindles, activating the associated Ia afferents.
3) The signals are transmitted to the spinal α motor neurons and then directly to the muscle.

Question 25

What causes Muscle Tone?

Answer 25

- Muscles are usually under some degree of stretch, so these reflex arcs are a vital determinant of ‘muscle tone’. - Muscular tone reflects basal partial contraction of extrafusal fibers.

Question 26

Purpose of Stretch reflex

Answer 26

The stretch reflex constitutes a feedback loop that maintains muscle length and hence dictates posture.

Question 27

Role of cortical pathways in Posture maintenance ( tone)

Answer 27

Descending motor pathways (e.g., corticospinal) comprising upper motor neurons can regulate muscle tone and hence posture by influencing components of the reflex arc. Deviations in muscular length from optimal levels trigger adjustments in the activity of α-motor neurons, yielding contraction of the stretched muscle and relaxation of opposing muscles

Question 28

Two systems involved in modulating the stretch reflex

Answer 28

1) Descending fibers (such as corticospinal tract) | 2) Efferent fibers (gamma motor neuron)

Question 29

Role of Gamma motor neurons (gamma loop) in posture maintence

Answer 29

- Smaller γ motor neurons modulate the excitability of muscle spindles. - When the muscle contracts, the tension of the muscle spindle is reduced, and the spindle is no longer able to measure changes of the muscle length. - The γ motor neurons therefore activate the contractile ends of the muscle spindle fibers and maintain the tension of the middle region of the intrafusal fibers where the sensory axons are located. - This co-activation of α and γ motor neurons (i.e., co-activation within the gamma loop) enables the spindles to function at all muscle lengths, thereby regulating both precision of movement and maintenance of posture.

Question 30

Why is the inverse stretch reflex (inverse myotatic or Golgi tendon reflex) is slower than the myotatic reflex?

Answer 30

1) The Ib fibers that constitute the afferent limb of the inverse myotatic reflex may be of marginally smaller diameter and hence, on average, support slightly lower conduction velocities than the Ia fibers. 2) It is polysynaptic (not monosynaptic), delaying responses.

Question 31

Function of the inverse stretch reflex

Answer 31

Protection of the muscle and tendon. Dangerously contracted muscles relax via negative feedback.

Question 32

Pathway of the inverse stretch reflex

Answer 32

1) Starts at golgi tendon organ 2) 1b fiber carries the signal to the spinal cord 3) synapses with inhibitory interneuron 4) Alpha motor neuron is inhibited and muscle relaxes

Question 33

What is the flexion reflex?

Answer 33

Noxious stimulation of the skin induces a polysynaptic reflex which produces ipsilateral excitation of flexor muscles (and inhibition of extensors) and contralateral excitation of extensor muscles (and inhibition of flexors) - causes withdrawal or protective flexion following a noxious stimulus

Question 34

Components of the Flexion reflex

Answer 34

* Afferent limb: nociceptive fibers (A delta and C). * CNS units: a number of excitatory and inhibitory interneurons over many spinal segments (Lissauer's Tract). * Efferent limbs: alpha motor neurons, ipsilateral flexors and contralateral extensors

Question 35

What is the flexion crossed extension reflex?

Answer 35

In the flexion reflex, when pulling away from a noxious stimulus ( activation of flexors and inhibition of extensors), some fibers cross over cause extension ( activation of extensors and inhibition of flexors) of the contralateral limb

Question 36

What is the normal response seen to the Plantar Reflex ( in those over 2 years old )?

Answer 36

Flexion of the toes, a response that may be masked by vigorous withdrawal of the leg ( if patient is too sensitive)

Question 37

What is the abnormal response seen to the Plantar Reflex ( in those over 2 years old )?

Answer 37

Dorsiflexion of the big toe, often accompanied by fanning of the other toes.

Question 38

What is the abnormal plantar response called?

Answer 38

Babinski's sign

Question 39

What does a Babinski's sign indicate?

Answer 39

a dysfunctional lateral corticospinal system. Such dysfunctions could reflect cortical or axonal disruptions, demyelination, etc.

Question 40

Why do newborns show an extensor plantar response?

Answer 40

because their pyramidal (corticospinal) tract is immature (incompletely myelinated).

Question 41

Is there a non pathlogical reason for exhibiting the extensor plantar response?

Answer 41

yes, during Sleep

Question 42

What does Hyperreflexia indicate?

Answer 42

- suggest an upper motor neuron lesion. - The damage may affect the motor cortex (e.g., precentral gyrus) or other corticospinal sites - In spinal cord lesions, hyperreflexia may develop after a phase of areflexia, which characterizes ‘spinal shock’

Question 43

What causes Spinal shock?

Answer 43

Extensive bilateral spinal damage

Question 44

What occurs in spinal shock?

Answer 44

- Transient areflexia occurs caudal to the site of the lesion. - Disrupted reflexes will typically re-emerge after several weeks.

Question 45

Causes of Hyporeflexia and Areflexia

Answer 45

Lesions of: 1) Peripheral sensory neurons (afferent limb) 2) Lower motor neurons (efferent Limb) 3) Neuromuscular junctions (eg: Myasthenia gravis) 4) Muscle (eg: Muscular dystrophies) 5) spinal cord segment