S03/S04-Topography of the major sensory systems Flashcards
What are the clinical signs of loss of proprioception?
Use Rombergs test.
Use three sensory systems to maintain truncal stability which are vision, proprioception (conscious and unconscious) and Vestibular sense.
Require two of these to maintain posture so if you ask patient to stand with feet together and close eyes if they sway then it means proprioception isn’t working as will not have sight to help.
What simple tests would you carry out to discriminate between fine touch, vibration and proprioception?
Fine touch would be tested with a single point in various dermatomes.
Vibration is tested with placing a vibrating tuning fork on a patients toes or fingers and asking them to tell you when vibration stops, make sure not on bone.
Proprioception is tested by asking patient to close eyes and testing joint position sense.
What is the somatotopic organisation of the internal capsule?
The internal capsule is the fibrous expressway that connects the cerebral cortex to the basal ganglia, thalamus, brain stem (motor nuclei, pontine nuclei and reticular formation) and spinal cord. In addition, it carries the fibers connecting the thalamus to the cerebral cortex. The internal capsule is divided into three regions: the anterior limb, genu, and posterior limb. These three regions are best seen in a axial (horizontal) section.
The nerves are grouped into axons which formed descending pathways that supply the face, arm, trunk & leg from superior to inferior.
What is the result of a complete hemisection of the left hemisphere of the spinal cord at the height of L1? Describe sensory and motor signs
Result to left leg: Loss of proprioception, fine touch and vibration (loss of dorsal column as decussates in medulla). Loss of unconscious proprioception (as lower limb neurones don’t decussate in spinocerebellar tract). There will also be loss of motor function due to UMN being cut.
Result to right leg: Loss of pain, crude touch and temperature as spinothalamic tract decussates at the level the neurone enters the cord. Motor function is retained.
What is the sensory function of the spinothalamic tract?
Temperature and pain (lateral) Crude touch (anterior)
What is the path of the spinothalamic tract?
The primary neurone enters the dorsal rootlets of the spinal cord and some synapse here. Some of these neurones ascend or descend one or two spinal levels via lissaeuer’s (dorsolateral) tract before synapsing.
The secondary neurone immediately deccusates at that spinal level before ascending the spinal cord through the spinal lemniscus in the brainstem. Upper limb fibres run medial to lower limb fibres. Synapse in the venteral posterior lateranl nucleus of thalamus.
Tertiary neurones travel through the internal capsule and corona radiata to terminate in the appropriate area of the primary sensory cortex.
What affect does a spinal lesion have on the spinothalamic tract?
Would cause contralateral loss of pain, temperature and crude touch because would have already decussated. However, tract of lissaeuer means that not complete loss.
What is the result of extreme stimuli to the spinothalamic tract? (pain, temp etc.)
The spinothalamic tract also alerts centres in the brainstem:
- reticular alerting system-alerts nervous system to burning main or cold
- limbic system-reports about nature of stimulus (pleasurable or aversive)
What is the sensory function of the dorsal column?
Conscious proprioception, discriminate touch and vibration sense.
What is the pathway of the dorsal column?
Primary neurone enters through the dorsal horn and does not decussate. Immediately ascends to the brainstem in either gracile (medial) or cuneate (lateral) nucleus. For levels T6 and below (lower limb) this is in the gracile nucleus and T6 and above (upper limb) are in the cuneate nucleus. Synapses with secondary neurone in the medulla of the brainstem.
Secondary neurones decussate in the medulla and ascend to the VPL via dorsal column pathways.
Tertiary neurones synapse in the VPL then travel through internal capsule and corona radiata to synapse in the appropriate area of the primary sensory cortex
What would happen to the dorsal column as a result of a spinal cord lesion?
It would cause ipsilateral loss of conscious proprioception, discrimitive touch and vibration sense. This is because the lesion would be below the decussation so would be ipsilateral.
What is the main sensory function of the trigeminothalamic tract?
Inputs from several cranial nerves that synapse in the trigeminal nuclei.
Trigeminal (V)- Face including teeth
Facial (VII)-Outer ear
Glossopharangeal (IX) - Back of tongue, pharynx, middle and inner ear
Vagus (X)-Pharynx, trachea, larynx and external ear
What are the three branches of the trigeminal nerve and through which foramina do they pass?
Opthalamic branch- Superior orbital fissure
Maxiallary branch-Foramen rotundum
Buccal branch-Foramen ovale
Which nucleus of the trigeminal ganglion receives which sensory input?
Mesencephalic nucleus - Proprioception
Chief nucleus - Light touch and pressure
Spinal nucleus - Pain and temperature
What is the pathway of the trigeminothalamic pathway?
The primary neurones pass though the trigeminal ganglia and synapse in the brainstem. The proprioceptive fibres synapse in the mesencaphalic nucleus, their cell bodies are also there. The light touch and pressure fibres synapse in the chief nucleus and the pain and temperature fibres in the spinal nucleus. Both of these fibres have cell bodies in the trigeminal ganglion.
Secondary neurones decussate to form the contralateral trigeminothalamic tract. This ascends to the thalamus.
The tertiary neurones pass through the internal capsule to synapse in the sensory cortex.
