Spinal cord & reflexes Flashcards
What fibres are present in the dorsal root?
Sensory afferent fibres
What fibres are present in the ventral root?
Motor efferent fibres
Where is the grey matter in the spinal cord?
Central
Where is the white matter in the spinal cord?
Peripheral
In which horn are motor fibres found?
Ventral horn
White mater is arranged in how many columns in the SC?
3 - posterior, lateral & anterior
What are the 3 important tracts in the SC?
Dorsal column
Corticospinal
Spinothalamic
What type of sensation does the spinothalamic fibres carry?
Pain & temperature
Where do fibres in the corticospinal tract originate?
Primary motor cortex
Where do lateral corticospinal fibres cross over?
Medulla (pyramids)
How many neurons are present in descending motor pathways?
2 - upper & lower motor neurons
Where is the site of the lower motor neurone?
Ventral horn
How many neurons are present in sensory ascending pathways?
3 - afferent sensory, medulla, thalamus
What type of sensation does the dorsal column carry?
Touch, vibration, pressure & proprioception
Where does the 2nd order neuron decussate in the ascending pathway?
Medulla
What is another name for the ascending sensory tracts in the brain?
Medial lemniscus
Where do neurons radiate from the thalamus in ascending pathways?
Post central gyrus
In the spinothalamic tract, where neurons cross over?
At the spinal level it enters
In the spinothalamic tract where does the 1st order neuronal synapse onto the 2nd order neuron?
Dorsal horn
What is a reflex?
An involuntary response to sensory stimuli
Where are reflexes mediated?
Spinal cord
Name a monosynaptic reflex
Stretch reflex
Name a polysynaptic refelx
Flexor reflex
In the stretch reflex, stretching of the tendon causes what?
Contraction of the agonist (quad)
Inhibition of the flexor
What initiates reflexes?
Painful stimuli
What does the flexor reflex initiate?
Flexor activity (withdrawal) Extensor inhibition
Crossed extensor reflex - contraction of extensor on contralateral limb
Which neurons (UMN/LMN) mediate reflexes?
LMN
In an UMN lesion, what happens to reflexes?
Exaggerated
What happens to tone in UMN lesions?
Spasticity (hypertonicity)
What happens in LMN lesions?
Flaccidity (hypotoncity)
What happens in UMN lesion, left-sided at the IC?
Right sided paralysis, hyper-reflexia & increased tone
What happens in UMN lesion on left side below decussation?
Left sided paralysis, increased reflexes & tone
What happens to left sides LMN lesion?
Left sided paralysis, no reflexes & flaccidity
Is motor neurone disease, UMN or LMN?
LMN disease at the ventral horn
In sensory pathways, a lesion below decussation will result in feeling lost on which side?
Ipsilateral sensory loss
In sensory pathways, a lesion above decussation will result in feeling lost on which side?
Contralateral sensory loss
A lesion affecting the spinothalamic tract will result in temperature/ pain being lost where?
Contralateral side (as crosses over at the level it enters)
What is the simplest spinal reflex?
Stretch reflex
What is the best example of the stretch reflex?
Patellar tendon (knee-jerk reflex)
In the stretch reflex, what afferent fibres are activated?
1a neurons
In the stretch reflex, what muscle fibres initiate the reflex?
Alpha motor receptors
In the stretch reflex, where are sensory nerves found in the muscle?
Muscle swindle
Ho many connections do the spindle sensory afferents make?
3
What do alpha motor neurones activate?
Agonist muscle (stretch muscle)
What type of reflex is the reflex arc?
Monosynaptic
What other connections can the sensory afferents make at the spinal cord during stretch reflex?
Activate inhibitory interneurons (relax antagonist muscle)
In the stretch reflex, the relaxation of an antagonist muscle is called?
Reciprocal inhibition
Name another type of connection which occurs in stretch reflex
Spindle afferent ascend in dorsal column to higher brain centres
The inverse stretch reflex is also called..
Clasp-knife reflex or Golgi-tendo organ reflex
What does the GTO monitor?
Muscle tension
In the inverse stretch reflex, what sensory fibres type carries info from GTO?
1b afferent fibres
In inverse stretch reflex, what happens to the agonist muscle?
Relaxes
In inverse stretch reflex, what happens to the antagonist muscle?
Contracts
What types of reflex is the inverse stretch reflex?
Polysynaptic
What is the role of the GTO reflex?
Prevents muscle from contracting so hard the tendon is torn
Protective
The flexor or withdrawal reflex uses inputs from which sensory pathway?
Pain receptors
What is the role of the withdrawal reflex?
Protective in order to remove body from painful stimuli
What afferent fibres are responsible for the withdrawal reflex?
Small diameter Ao nociceptors
What do afferents in the flexor reflex activate?
Excitatory interneurons to flexor muscles
Inhibitory interneurons to extensor muscles
What is the efferent fibre type observed in the flexor reflex?
Alpha motorneurons
In order to prevent falling over, what else happens in the withdrawal reflex?
Crossed extensor reflex
What happens at the spinal cord in order to achieve crossed extensor reflex?
Excitatory interneurons will cross & activate contralateral extensors
Inhibitory interneurons will cross & inhibit contralateral flexors
What tract do sensory fibres ascend in during the withdrawal reflex?
Spinothalamic (contralateral)
Which is slower, stretch reflex or withdrawal? Why?
Withdrawal reflex
Because nociceptive fibres are narrower therefore conduct slower
How can the GTO reflex be overridden?
From voluntary inputs from CNS
Can the stretch reflex be overrridden?
Yes, by descending inhibitory pathways
How can inhibitory descending pathways be overridden when testing stretch reflex?
Reinforcement
Clench teeth or Pull arms apart
