Lecture 9: Spinal pathways Flashcards
What sort of fibers feed into the dorsal column medial lemniscus pathway?
Myelinated A fibers carrying discriminative (fine) touch, vibration and proprioception
What sort of fibers feed into the spinothalamic tract?
A+C fibers feed convey pain and temperature to the spinothalamic tract.
From free nerve endings.
What travels alongside the spinothalamic tract?
Spinoreticular pathway
Describe the trigeminal projections of the brainstem:
Trigeminal nerve is both sensory and motor
Trigeminal sensory nuclei:
- Primary sensory trigeminal nucleus is located in the PONS (For discriminative touch, vibration, proprioception) ipsilateral to the trigeminal nerve. It then sends fibers which decussate and project up to the thalamus. This is then relayed to the primary sensory cortex.
- Spinal trigeminal nucleus is divided into three areas;
- > Pars oralis (crude touch)
- > Pars interpolaris (Temperature)
- > Pars caudalis (Pain)
Motor nuclei:
- In pons
- Receives fibers from primary motor cortex. (corticobulbar tract) which feed to nuclei on the ipsilateral and contralateral side. These projects fibers into the trigeminal nerve.
Scenario 1: Bilateral loss of motor function, pain, temperature sensation below the site of injury; vibration and fine touch is not lost. Whats the damage?
- > Dorsal column pathway preserved?
- > CST
- > Spinothalamic lost
= Ant. spinal artery occluded / lost bilaterally.
Known as ant. cord syndrome. It is bilateral because both halves receive art. one midline ant. spinal artery
Scenario 2: Ipsilateral loss of proprioception, vibration and touch and contralateral loss of pain and temperature below the lesion; Whats the damage?
- Incomplete loss.
- Transaction / hemisection of spinal cord.
Scenario 3: Bilateral loss of motor function with upper extremities more affected than lower. Whats the damaged:
Damaged to the medial CST. i.e central cord syndrome i.e central area / middle is damaged.
What is dissociative vs associative sensory loss?
Associative loss: (Brainstem damage): Contralateral loss of sensation
Dissociative loss: AKA Brown Sequard Syndrome
- Loss of contralateral pain + Temp
- Loss of ipsilateral discriminative touch etc
Describe the dorsal column - medial lemniscus pathway:
Primary neuron enters the dorsal horn and travels up the ipsilateral dorsal column (legs medial, arms lateral) and synapses with the CUNEATE (ARMS) and GRACILE (LEGS) nuclei in the MEDULLA.
Secondary neurons decussate immediately at the level of the cuneate and gracile nuclei before projecting up through the medial lemniscus pathway and synapse in the VPm of the thalamus.
Third order neurons project from here through the internal capsule to the primary sensory cortex.
Describe the spinothalamic tract:
A delta and c fibers (primary neurons) carry info into the dorsal horn and synapse at the same level. The second order decussate immediately through the ant. white commissure and project up through the spinothalamic tract.
This travels through the brainstem where collateral branches synapse with the reticular formation (Spinoreticular pathway). THe second order then synapses with the thalamus (intralaminar thalamic nuclei also) and third order projects to the post central gyrus.
What is significant about the corticobulbar tract?
Each hemisphere projects to the motor nuclei on both sides! Therefore motor symptoms dont always occur.
Describe the importance of the trigeminal nerve and its nuclei:
Trigeminal nerve has four nuclei
Mesencephalic nuclei
Primary sensory nuclei (boring) (PONS)
Spinal trigeminal nuclei (very important)
1) Pars oralis (CRUDE TOUCH) [PONS]
2) Pars interpolaris (TEMPERATURE) [Medulla]
3) Pars Caudalis (PAIN) [Medulla / spine junction]
The sensory fibres project contralaterally to the brain from these nuclei.!!!!!! Travel via the medial laminiscus pathway.
AFFERENT FOR BLINK REFLEX
What cranial nerves input to the spinal trigeminal nuclei?
5,7,9,10
