FUNCTIONAL ANATOMY - Spinal Reflexes

Question 1

What is a response?

Answer 1

A voluntary, learned response integrated within the prosencephalon (forebrain)

Question 2

What is a spinal reflex?

Answer 2

An involuntary, unlearned response

Question 3

When carrying out neurolocalisation, which regions of the spinal cord can you localise lesions to?

Answer 3

C1 to C5
C6 to T2
T3 to L3
L4 to S3

You can further localise L4 to S3 (L4 - S1, S1 - S3)

Question 4

Which three spinal reflexes can be used to assess lumbosacral plexus function?

Answer 4

Patellar reflex
Hindlimb withdrawal reflex
Perineal reflex

Question 5

Explain the concept of the patellar reflex

Answer 5

Percussion of the the patellar tendon stretches the quadriceps muscle which is detected by intrafusal fibres. Sensory (afferent) neurones transport this sensory information and enter the spinal cord via the dorsal nerve root(s). These sensory (afferent) neurones synapse with motor neurones within the spinal cord. These motor (efferent) neurones exit the spinal cord via the ventral nerve root(s) and transmit motor information to the quadriceps muscle, causing it to contract and extend the leg

Also inhibits the antagonistic muscles

Question 6

Which specific spinal cord segments are assessed through testing the patellar reflex?

Answer 6

L4 to L6 spinal cord segments

Question 7

Which peripheral nerve is assessed through testing the patellar reflex?

Answer 7

Femoral nerve

Question 8

Explain the concept of the hindlimb withdrawal reflex

Answer 8

Pinching the skin between the digits stimulates the sensory receptors in the skin. Sensory (afferent) neurones transport this sensory information to the dorsal nerve root(s) of the spinal cord and synapse with interneurones within the spinal cord. These interneurones synpse with motor (efferent) neurones within the spinal cord, which exit the spinal cord via the ventral nerve root(s) and transmit motor information to the appropriate muscles so stimulate hip, stifle and tarsus flexion

Also inhibits the antagonistic muscles

Question 9

Which specific spinal cord segments are assessed through testing the hindlimb withdrawal reflex?

Answer 9

L4 to S1 spinal cord segments

Question 10

Which two peripheral nerves are assessed through testing the hindlimb withdrawal reflex?

Answer 10

Femoral nerve
Sciatic nerve

Question 11

Explain the basic concept of the perineal reflex

Answer 11

Pinching the perineum should result in the contraction of the anal sphincter and flexion of the tail

Question 12

Which specific spinal cord segments are assessed by testing the perineal reflex?

Answer 12

S1 to Cd5 spinal cord segments

Question 13

How can you further localise the lesion using the perineal reflex?

Answer 13

If there is no contraction of the anal sphincter however there is still flexion of the tail, this further localises the lesion to S1 - S3

Question 14

Which two peripheral nerves are assessed through testing the perineal reflex?

Answer 14

Pudendal nerve
Caudal nerve

Question 15

Which two spinal reflexes can be used to assess brachial plexus function?

Answer 15

Forelimb withdrawal reflex
Cutaneous trunci reflex

Question 16

Explain the basic concept of the forelimb withdrawal reflex

Answer 16

Pinching the skin between the digits should result in flexion of the shoulder, elbow and carpus

Question 17

Which specific spinal cord segments are assessed by testing the forelimb withdrawal reflex?

Answer 17

C6 to T2 spinal cord segments

Question 18

Which nerves are assessed through testing the forelimb withdrawal reflex?

Answer 18

Brachial plexus

Question 19

Explain the concept of the cutaneous trunci reflex

Answer 19

Bilaterally pinching the skin of the dorsum lateral to L6-T1 stimulates sensory receptors in the skin. Sensory (afferent) neurones transport this sensory information via the fasciculus proprius tract cranially through the spinal cord to T1 spinal cord segments where the lateral thoracic nerve arises from. Motor information will travel down the lateral thoracic nerve to the cutaneous trunci muscle which will contract, resulting in a skin twitch

Question 20

What are the two functional classifications of motor (efferent) neurones?

Answer 20

Upper motor neurones (UMNs)
Lower motor neurones (LMNs)

Question 21

What are upper motor neurones (UMNs)?

Answer 21

Upper motor neurones (UMNs) are motor neurones with neuronal cell bodies originating in the motor cortex and the brainstem nuclei which transmit voluntary motor information to the lower motor neurones (LMNs) and modulate the activity of lower motor neurones (LMNs) through inhibitory control

Question 22

What are lower motor neurones (LMNs)?

Answer 22

Lower motor neurones (LMNs) are motor neurones with neuronal cell bodies originating in the cranial nerve nuclei of the brainstem and the ventral grey matter horn of the spinal cord which send voluntary and involuntary motor signals the muscles and glands. Lower motor neurones also maintain basal muscle tone

Question 23

What are four clinical signs of an upper motor neurone (UMN) lesion?

Answer 23

Weakness/paralysis
Normal or exaggerated spinal reflexes
Spiffness/spasticity
Disuse atrophy

Question 24

What causes the the exaggerated spinal reflexes, stiffness and spasticity associated with upper motor neurone (UMN) lesions?

Answer 24

The exaggerated spinal reflexes, stiffness and spasticity are caused by the loss of inhibitory control of the lower motor neurones (LMNs)

Question 25

What are four clinical signs of a lower motor neurone (UMN) lesion?

Answer 25

Weakness/paralysis
Decreased or absent spinal reflexes
Flaccidity
Neurogenic atrophy

Question 26

What causes the flaccidity associated with lower motor neurone (LMN) lesions?

Answer 26

The loss of basal muscle tone

Question 27

What is pseudohyperreflexia?

Answer 27

Pseudohyperreflexia is where a reflex may appear exaggerated however this is due to the atrophy or weakness of the antagonistic muscles (i.e. muscles that would normally oppose the reflex), creating an imbalance in muscle tone

Question 28

Scenario: Patient has absent patellar and hindlimb withdrawal reflexes with normal forelimb reflexes. Localise the lesion

Answer 28

Lumbosacral plexus or L4 to S3 spinal cord segments. The absence of spinal reflexes also suggests a lower motor neurone lesion

Question 29

Scenario: Patient has an absent forelimb withdrawal reflex with normal hindlimb reflexes. However there is a loss of voluntary control in all four limbs. Localise the lesion

Answer 29

Brachial plexus or C6 to T2 spinal cord segments. The absence of spinal reflexes also suggests a lower motor neurone lesion

Question 30

Describe how a lesion from C1 to C5 would present

Answer 30

Voluntary control would be affected in all four limbs. There would be upper motor neurone signs in all four limbs such as normal/exaggerated reflexes, rigidity/spasticity and possibly disuse atrophy

Question 31

Describe how a lesion from C6 to T2 would present

Answer 31

Voluntary movement would be affected in all four limbs. There would be lower motor neurone signs in the forelimbs such as dereased or absent reflexes, flaccidity and neurogenic atrophy

Question 32

Describe how a lesion from T3 to L3 would present

Answer 32

Voluntary movements would be affected in the hindlimbs. There would be upper motor neurone signs in the hindlimbs such as normal/exaggerated reflexes, rigidity/spasticity and possibly disuse atrophy

Question 33

Describe how a lesion from L4 - S3 would present

Answer 33

Voluntary movements would be affected in the hindlimbs. There would be lower motor neurone signs in the hindlimbs such as decreased/absent reflexes, flaccidity and neurogenic atrophy

Question 34

What neurolocalisation is indicated by lower motor neurone dysfunction in all four limbs?

Answer 34

Peripheral nervous system (PNS) lesion

Question 35

Describe the grading scale for spinal reflexes

Answer 35

0: Absent
1: Decreased
2: Normal
3: Increased
4: Clonus

Question 36

What is a clonus reflex?

Answer 36

A repetitive reflex following a single stimulus

Question 37

Why is the withdrawal reflex not used to evidence pain?

Answer 37

The withdrawal of the limb is only a reflex and thus should not be used to evidence pain. Only a behavioural response to noxious stimuli is indicative of conscious pain perception