FUNCTIONAL ANATOMY - Spinal Reflexes Flashcards
What is a response?
A voluntary, learned response integrated within the prosencephalon (forebrain)
What is a spinal reflex?
An involuntary, unlearned response
When carrying out neurolocalisation, which regions of the spinal cord can you localise lesions to?
C1 to C5
C6 to T2
T3 to L3
L4 to S3
You can further localise L4 to S3 (L4 - S1, S1 - S3)
Which three spinal reflexes can be used to assess lumbosacral plexus function?
Patellar reflex
Hindlimb withdrawal reflex
Perineal reflex
Explain the concept of the patellar reflex
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
Which specific spinal cord segments are assessed through testing the patellar reflex?
L4 to L6 spinal cord segments
Which peripheral nerve is assessed through testing the patellar reflex?
Femoral nerve
Explain the concept of the hindlimb withdrawal reflex
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
Which specific spinal cord segments are assessed through testing the hindlimb withdrawal reflex?
L4 to S1 spinal cord segments
Which two peripheral nerves are assessed through testing the hindlimb withdrawal reflex?
Femoral nerve
Sciatic nerve
Explain the basic concept of the perineal reflex
Pinching the perineum should result in the contraction of the anal sphincter and flexion of the tail
Which specific spinal cord segments are assessed by testing the perineal reflex?
S1 to Cd5 spinal cord segments
How can you further localise the lesion using the perineal reflex?
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
Which two peripheral nerves are assessed through testing the perineal reflex?
Pudendal nerve
Caudal nerve
Which two spinal reflexes can be used to assess brachial plexus function?
Forelimb withdrawal reflex
Cutaneous trunci reflex
Explain the basic concept of the forelimb withdrawal reflex
Pinching the skin between the digits should result in flexion of the shoulder, elbow and carpus
Which specific spinal cord segments are assessed by testing the forelimb withdrawal reflex?
C6 to T2 spinal cord segments
Which nerves are assessed through testing the forelimb withdrawal reflex?
Brachial plexus
Explain the concept of the cutaneous trunci reflex
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
What are the two functional classifications of motor (efferent) neurones?
Upper motor neurones (UMNs)
Lower motor neurones (LMNs)
What are upper motor neurones (UMNs)?
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
What are lower motor neurones (LMNs)?
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
What are four clinical signs of an upper motor neurone (UMN) lesion?
Weakness/paralysis
Normal or exaggerated spinal reflexes
Spiffness/spasticity
Disuse atrophy
What causes the the exaggerated spinal reflexes, stiffness and spasticity associated with upper motor neurone (UMN) lesions?
The exaggerated spinal reflexes, stiffness and spasticity are caused by the loss of inhibitory control of the lower motor neurones (LMNs)
What are four clinical signs of a lower motor neurone (UMN) lesion?
Weakness/paralysis
Decreased or absent spinal reflexes
Flaccidity
Neurogenic atrophy
What causes the flaccidity associated with lower motor neurone (LMN) lesions?
The loss of basal muscle tone
What is pseudohyperreflexia?
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
Scenario: Patient has absent patellar and hindlimb withdrawal reflexes with normal forelimb reflexes. Localise the lesion
Lumbosacral plexus or L4 to S3 spinal cord segments. The absence of spinal reflexes also suggests a lower motor neurone lesion
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
Brachial plexus or C6 to T2 spinal cord segments. The absence of spinal reflexes also suggests a lower motor neurone lesion
Describe how a lesion from C1 to C5 would present
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
Describe how a lesion from C6 to T2 would present
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
Describe how a lesion from T3 to L3 would present
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
Describe how a lesion from L4 - S3 would present
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
What neurolocalisation is indicated by lower motor neurone dysfunction in all four limbs?
Peripheral nervous system (PNS) lesion
Describe the grading scale for spinal reflexes
0: Absent
1: Decreased
2: Normal
3: Increased
4: Clonus
What is a clonus reflex?
A repetitive reflex following a single stimulus
Why is the withdrawal reflex not used to evidence pain?
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
