Lecture 3 : Somatosensory pathway Flashcards
Where do the somatic sensory pathways relay information to and from
From the sensory receptors to the primary somaticsensory area in the cerebral cortex and cerebellum.
What pathway is for the discriminative sensory system
Dorsal column medial lemniscus pathway
What pathway is for the non-discriminative sensory system
anterolateral pathway / lateral spinothalamic tract.
What is discriminative vs non discriminative sensation mean
Discriminative sensation is a sensory modality that allows subject to localise touch/pressure and tell two points of touch apart whereas non discriminative touch is pain, temperature and crude touch.
At the spinal cord segmental level what is the dorsal columns
Bundles of white matter in the dorsal part of the spinal cord made of the axons of sensory neurons going to th brain stem. It has fasciculi and these are made of funiculi.
Where are the first order neurons in the dorsal column leminscus medial pathway going to and from
From the receptor it goes through the dorsal root into the spinal cord to the Gracile fasciculus or Cuneate fasciculus depending on whether it came from legs or above legs. It goes to synapse with 2’ neurons in the gracile/cuneate nucleus in the medulla.
What info is gracile vs Cuneate parts receiving?
Gracile is receiving from lower limbs and lower trunk while cuneate is receiving from upper limbs, upper trunk, neck and posterior
Where are the second order neurons in the dorsal column leminscus medial pathway going to and from
The axons of the second neurons cross to the opposite side of the medulla via arcuate internal fibres and enter the medial lemniscus which goes to the ventral posterior nucleus of the thalamus
Where are the third order neurons in the dorsal column leminscus medial pathway AND the anterolateral pathway going to and from
They go from ventral posterior nucleus of the thalamus through the internal capsule ot the primary somatosensory area of the cerebral cortex- cortical area of the homuncular map
Where are the first order neurons in the Anterolateral pathway going to and from
The free nerve ending receptor goes through the dorsal root where it goes to through the tract of Lessauer to the posterior grey horn where it synapses with 2 order neurons
Where are the second order neurons in the Anterolateral pathway going to and from
Axons of 2 order neurons cross to the opposite side of the spinal cord through the ventral anterior white commisure and continue through the lateral spinothalamic tract (joining the medial lemniscus) which goes up to the ventral posterior nucleus of the thalamus.
What are the main differences between the Discriminative and Non discriminative pathways
- Myelination: the discriminative is heavily myelinated for efficiency and speed as it is used often.Non is not as it doesn’t have to be as efficient.
- Conduction speed: discrim: 50m/s, non: 1m/s
- Place of 1st neuron termination: dis is in the medulla of gracile/cuneate nucleus. non is in the dorsal grey matter of spinal cord.
- Point of dessucation: dis is in the internal arcuate fibres in the medulla. non is at the segmental level of the spinal cord.
What is the order that body parts are represented in the primary somatosensory cortex from medial to lateral
Genitals,, Toes to trunk, Neck, Head, Shoulder to thumb, Eye, nose, face, Lips, Mouth, pharynx and intra abdominal
What does ‘sensory homunculus’ mean and where is it located in the brain
This is map of the body where each area receives impulses from a specific part of the body which allows you to pinpoint where somatic sensations come from. Located in the post central gyri of the parietal lobes of the cerebral cortex. Sensations from the left side of body are received by right hemisphere and vice versa
Why do some body parts receive greater representation in the sensory homunculus
The size of the cortical area receiving impulses depends on the number of receptors present rather than the size of the body part. Eg. more lip and fingers than legs and arm to the wrist.
