Ascending Sensory Pathways Flashcards
What are the somatosensory pathways responsible for?
- Consist of the chain of neurons, from receptor organ to cerebral cortex
- Start with the peripheral first-order (1°) afferent
- End in the cerebral cortex
- Responsible for the perception of bodily senses
What are the somatosensory pathways for the body?
- Spinothalmic pathway: Pain, temperature, crude touch, pressure
- Dorsal column medial lemniscus pathway: Fine touch, vibration, pressure and position
Which of the following corresponds to the primary somatosensory cortex? Where is it located?

Red (where all the somatosensory pathways end) –> post central gyrus
What information is received in the primary somatosensory cortex?
Pain, temperature and touch sensation
Which area is responsible for perceiving visual information?

Blue (occipital lobe)
Which area is responsible for perceiving auditory information?

Green - The auditory cortex is the part of the temporal lobe
What is another word for somatosensory?
Somaesthetic
The general sensory (somaesthetic) pathways carry information to the brain from where? What are examples of these modalities?
- Skin
- Mucous membranes
- Joints and muscles
Modalities: vibration, touch, pressure, pain, temperature, proprioception

What is proprioception?
Our awareness of where our body parts are in space
What is each modality detected by (in the general somaesthetic pathways)?
Each modality is detected by specific sensory receptors / specialised nerve endings
e.g. specific receptor for vibration
These receptors then send their axons all the way via the spinal peripheral nerves to enter the spinal cord.

How does sensory info enter the spinal cord?
Dorsally
Sensory pathways travel from peripheral nerves into the CNS and ascend through spinal cord/brainstem to the brain.
Which nerves transmit sensory info from:
- the body?
- the head, face and neck?
In the body: info transmitted by spinal nerves
In head, face and neck: info transmitted by cranial nerves.

What is a dermatome?
A specific region of skin of the body innervated by the sensory fibres of a single segmental spinal nerve (spinal cord segment):
- E.g. Any sensation at level of nipple is transmitted by the T4 segmental spinal nerve
- E.g. Any sensation at level of umbilicus is transmitted by the T10 segmental spinal nerve

Similar to dermatomes, areas of skin of the face supplied by a single cranial nerve can be identified and mapped. BUT this is not called dermatome.
What is the cranial nerve that supplies sensation to areas of the face?
Branches of CN V trigeminal
The herpes varicella zoster virus causes chickenpox. After you recover from chicken pox, the virus can enter your nervous system and lie dormant for years.
- Where does the varicella zoster virus lie dormant?
- What can it reactivate as?
- Which dermatome is affected during reactivation?
- Lies dormant in the sensory (dorsal) roots of specific spinal or cranial nerves
- Shingles
- Cause of reactivation is not well known (but could be linked to dip in immunity)
- Only affects at level of sensory spinal nerves where virus remained dormant
- E.g. in photo, eruption of vesicles is localised to the area of skin supplied by the T4 spinal nerve

What are the 2 groups of somaesthetic modalities?
- Modalities that are essential to survival
- Pain, temperature
- Some touch and pressure
- Modalities that increase detail
- Discriminative touch: 2-point discrimination and pressure vibration
- Proprioception
How are modalities that are essential to survival carried? What is the conduction rate?
- Carried via thin, poorly myelinated or unmyelinated fibres -
- Conduction relatively slow
How are modalities that increase detail carried? What is the conduction rate?
- Carried via large diameter, heavily myelinated fibres
- Fast conduction
Review of Spinal Cord - Transverse Section
- Grey matter confined to inside and subdivided into regions:
- Dorsal grey horn
- Receives sensory fibres
- Many synapses occur here
- Lateral grey horn
- Contains preganglionic visceral neurons
- Ventral grey horn:
- Contains motor somatic neurons
- Dorsal grey horn
- White matter on outside –> this is where we will find the sensory and motor pathway
- Dorsal white column
- Lateral white column
- Ventral white column
- Ventral white commissure
- Allows fibres to cross from either side

Are the sensory and motor pathways found in grey or white matter?
White matter
Functionally, what can the ascending/somatosensory tracts be divided into?
- Conscious tracts: comprised of the dorsal column-medial lemniscal pathway and the anterolateral system.
- Unconscious tracts: comprised of the spinocerebellar tracts.
DCML Pathway:
- What is it?
- Location?
- What information does it carry?
- Where do fibres decussate?
- What: Ascending sensory pathway
- Location: Dorsal column (white matter) of spinal cord
- Information:
- Fine touch
- Vibration
- Joint position sense (proprioception)
- Decussation: Level of medulla

What side of the body does the DCML pathway convey sensory info from? (i.e. ipsilateral or opposite)
Ipsilateral: If the lesion occurs in the spinal cord (which is most common), the sensory loss will be ipsilateral –> decussates at level of brainstem
How would a lesion of the DCML pathway present?
A loss of proprioception and fine touch. However, a small number of tactile fibres travel within the anterolateral system, and so the patient is still able to perform tasks requiring tactile information processing.



















































