Spinal Cord and Periphery (neuroanatomy) Flashcards
Which type of neurone is in the sensory dorsal root?
Pseudounipolar
Which type of neurone is in the sensory motor root?
Multipolar
There are ascending and descending tracts in the spinal cord and brain.
They carry information.
How can you tell if a tract is an ascending tract?
Based on how it is named i.e. if it starts with spino- e.g. spinocerebellar tract
There are ascending and descending tracts in the spinal cord and brain.
They carry information.
How can you tell if a tract is an descending tract?
Based on how it is named i.e. if it ends in -spinal e.g. corticospinal tract
Do ascending tracts carry sensory or motor information?
Sensory
Do descending tracts carry sensory or motor information?
Motor
What does the corticospinal tract do?
Carries motor impulses from motor cortex to skeletal muscles.
Which type of sensory impulses does the dorsal column carry?
Carries touch, tactile localisation, vibration sense and proprioception
Which type of sensory impulses does the lateral spinothalamic tract carry?
Pain and temperature
Where does the corticospinal tract pathway start from?
Motor cortex (area 4)
Where do the corticobulbular fibres go?
Contralateral cranial nerve nuclei
RECAP- which cranial nerves arise from the brainstem?
CN 3-12
If you want to move your hands, which plexus of the upper limb will the nerves have to pass through?
Brachial plexus
What is the root value of the brachial plexus?
C5-T1
Which nerve plexus do nerves supplying the lower limb need to go through?
Sciatic plexus
What is the root value for the sciatic plexus?
L4-S3
When the motor fibres travel down the brainstem, where will they sit in the midbrain?
In the crus cerebri, part of the midbrain which sits anterior to the substancia nigra
What happens to the bundle of motor fibres when it reaches the pons?
Motor fibres still remain anterior but broken into a number of different bundles.
When the motor fibres reach the medulla, they come together again and form projections.
What are these projections called?
Pyramids
What happens at the lower part of the pyramids?
Fibres cross over (decussation).
How many motor neurons are in the motor pathway?
Two- we can call these the upper and lower motor neuron.
Where would you find the cell body of the upper motor neuron?
Grey matter of the precentral gyrus
The upper motor neuron travels down the corona radiata, internal capsules, brainstem before crossing over at the pyramidal decussation.
Where does the upper motor neuron eventually synapse?
Ventral horn of the grey matter in the spinal cord
Where does the lower motor neuron start?
Ventral horn of the spinal cord
What does the lower motor neuron travel out along to get to the skeletal muscle?
Spinal nerves
Where is the dorsal column situated?
Posterior white matter of the spinal cord
(can be known as the posterior column).
Is the posterior/dorsal column a descending or ascending tract?
Ascending tract
Where are the receptors for sensation found?
Skin
If the touch receptor in your right index finger was stimulated, where would the sensory fibre go?
Would go through brachial plexus, through the dorsal roots, continues up the dorsal column until it reaches the medulla.
What happens to the neuron when it reaches the medulla after travelling up the dorsal column?
Synapses. Another axon picks up tis impulse- this is known as the second order as it is the second nucleus.
->could be worth drawing this pathway out for the motor and sensory neurons and the ascending/descending trunks? Just a revision idea :)
Which type of neuron was the:
1. First order neuron
2. Second order neuron
- Pseudounipolar
- Multipolar
->this is because…honestly I’m not sure. I looked it up and couldn’t find much…sorry x
What does the second order nucleus?
Crosses over (decussates) in the medulla
After the crossing over of the second order neuron, the dorsal tract is no longer called this as it is not in the posterior column of the spinal nerve.
What is it called after the decussation?
Medial lemniscus
Where does the medial lemniscus pass through?
Medulla, pons and midbrain and then reaches the thalamus
What happens in the thalamus after the second order nucleus has sent to information up?
Third order nucleus takes over
Where does the third order nucleus go to and from?
From thalamus to the post-central gyrus
RECAP- which areas cover the post-central gyrus?
Areas 3, 1, 2
Why does the third order neuron take the impulse to the postcentral gyrus?
Site of the primary sensory area in the parietal lobe
Is the lateral spinothalamic tract an ascending or descending tract?
Ascending tract as carries sensory info
Why is there two sensory pathways?
Lateral spinothalamic tract carries pain and temperature info.
Therefor, the body needs to respond more quickly to these as they could potentially be harmful, hence why there is another, quicker pathway
Which type of neuron would carry sensation if the right index finger felt pain?
Pseudounipolar
Describe the pathway taken by the pseudounipolar nucleus if carrying information due to pain?
Comes through brachial plexus, through dorsal root and dorsal ganglion and enters the spinal cord.
(so far, same as the dorsal column route).
What happens to the first order neuron when it reaches the spinal cord when carrying information responding to pain?
Axon enters grey matter of spinal cord and ends at the level at which it entered.
In response to pain or temperature, what happens once the first order neuron ends?
Second order neuron picks up impulse and and crosses over the reach lateral spinothalamic tract
What happens when the second order nucleus reaches the lateral spinothalamic tract?
Ascends up entire spinal cord and goes to brainstem.
Where will the second order nucleus synapse when responding to pain or temperature?
Ventral posterolateral (VPL) nucleus of hypothalamus
(same as dorsal column pathway).
What happens after the second order neuron synapses in the thalamus after responding to pain?
Third order neuron picks up impulse and takes it the grey matte of the post-central gyrus.
->same as other route
Where does the second order neuron come out of in the descending motor tract?
Comes out through ventral roots and goes through spinal nerves to the muscle
Not all sensory information needs to be sent up to the brain.
When is this the case?
When an immediate response is required e.g. after touching something hot.
When an immediate response is required and sensory information is not passed up to the brain, what makes the decisions?
The spinal cord or other lower centres can make decisions, making up our reflexes.
What is a reflex?
An involuntary stereotyped pattern of response brought about by a sensory stimulus.
If reflexes are mediated at the level of the spinal cord, what type of reflex does this make them?
Spinal reflex.
The stretch reflex can be demonstrated by which test?
Knee jerk reflex
Which tendon is hit for the knee jerk reflex to occur?
Patellar tendon
Which muscle contracts to cause the knee jerk movement?
Quadricepcs femoris
What happens to the patellar tendon when it is hit?
The tendon stretches, causing muscle fibres within the quadriceps to also be stretched
What do proprioceptors do?
Sensory receptor which responds to how stretched or relaxed a muscle is
What is the quadriceps muscle innervated by?
Femoral nerve
What is the root value of the femoral nerve?
L2-4
Which plexus does the femoral nerve come from?
Lumbar plexus
What happens when the patellar tendon gets hit?
Muscle stretches and this causes proprioceptor fibres from the femoral nerve to get activated.
What happens after the proprioceptor fibres in the femoral nerve get activated?
Activated fibres are carried by the femoral nerve to lateral horns of L2-4.
Motor neurons then come out via femoral nerve and act on the quadriceps muscle, making it contract.
In order to stretch the quadriceps muscles, which muscles need to relax?
Hamstring muscles
How is the hamstring relaxed at the same time as the quadriceps stretched?
In addition to fibres going to L2-4 to get motor neurons to leave and cause muscle contraction, some fibres go down to sacral segments of spinal cord and inhibit the neurons which innervate the hamstring muscles, causing them to relax.
What type of reflex is the stretch reflex?
Monosynaptic arc reflex
Describe what would happen if you stepped on a pin.
This might be wordy but read and try to understand x
Pain receptors activated.
Sensory nerves carry impulse through branches of the sciatic nerve and through dorsal grey matter of spinal cord.
This acts on an inhibitory neuron, which stimulates a nerve in the ventral horn to go and contract hamstring and pull your foot away from the painful stimulus.
Part 2 hehe… your foot is off the ground and off the pin…great!
But now, describe what happens to maintain balance.
Crossed extensor response- stimulates femoral nerve which contracts the quadricep muscle, allowing you to gain balance.
If you want to contract any muscle on the left side of your body, where do the impulses come from?
Precentral gyrus on left side
What are reflexes mediated by?
Lower motor nerves
If there is a lesion affecting the upper motor neuron but not the lower motor neuron, what will happen?
Paralysis- however, as LMN still working, you can still have reflexes.
If the is an upper motor neurone lesion but still reflexes, what are these reflexes like?
Exaggerated, as if to compensate
Does tonicity of muscle require upper or lower motor neurons?
Lower motor neurons
Therefore, if there is an upper motor neuron lesion, what happens to the tone?
Also become exaggerated
What is increased tone known as ?
Spasticity
What happens if there is damage to the lower motor neuron?
Paralysis with lost reflexes and flaccidity
What would happen in a patient with a left upper motor neuron lesion at the internal capsule?
Right sided paralysis
Hyper-reflexia
Increased tone
What would happen in a patient with a left upper motor neuron lesion at the upper cervical spinal cord?
Left sided paralysis
Hyper-reflexia
Increased tone
->left not right because it is below the level of decussation
What would happen in a patient with a left lower motor neuron lesion?
Left sided paralysis
Absent reflexes
Flaccid
->again, left paralysis not right as a lower lesion
A patient presents with left sided paralysis. They still have reflexes but they are exaggerated. The muscles are very toned.
What could this be?
Depending on location- could be either:
-Right UMN lesion
-Left UMN lesion
but ultimately it’s a upper motor nerve lesion. If above the level of decussation, it will be a R UMN lesion.
Therefore, what do lesions above the level of decussation cause?
Contralateral paralysis
Therefore, what do lesions below the level of decussation cause?
Ipsilateral paralysis
Which group of diseases are caused by affected ventral horns of the spinal cord?
Motor neuron disease
In terms of the lateral spinothalamic tract, is pain and temperature info going to be contralateral or ipsilateral?
Contralateral
->Level of decussation is so low, lesions are going to be above it and affect opposite side
What happens in Brown-Sequard syndrome?
One side of the cervical vertebrae is affected resulting in weakness and paralysis on one side of the damage and loss of pain and temperature sensations on the opposite side.
This lectures are confusing but Asha explains them well so just rewatch these lectures before any exams :)
okay boss
