Ascending Pathways Flashcards
Which of the following areas in the primary somatosensory cortex?
Where is it located and what information is received in this area?
Red - this is the post-central gyrus
the information received in this area is :
- Pain and temperature sensation
- Touch sensation
(green = auditory, blue = visual)
How are senses transmitted in general?
Through the 31 pairs of spinal nerves and 12 pairs of cranial nerves
senses are transmitted by specific spinal or cranial nerves
What is the name of the pathways involved in the perception of senses?
What is their role?
General sensory (somaesthetic) pathways
they carry information of different types or modalities from the skin, mucous membranes, joints and muscles to the brain
What types of sensory modalities are carried via somaesthetic pathways?
- Vibration
- touch and pressure
- pain
- temperature
- proprioception - this is the knowledge of the position of a limb in space
How are sensory modalities detected?
Each modality is detected by specific sensory receptors / specialised nerve endings
the receptors are specialised to detect different sensory modalities
What is the definition of a dermatome?
A specific region of skin of the body innervated by the sensory fibres of a single segmental spinal nerve
(spinal cord segment)
What is the equivalent of a dermatome in the face?
Areas of the skin of the face are supplied by a single cranial nerve and can be identified and mapped
these are not called dermatomes
What are the dermatomes at the level of the nipple and umbilicus?
Level of the nipple - T4
Level of the umbilicus - T10
How is herpes zoster infection related to dermatomes?
This is an infection of the sensory roots of specific spinal nerves
the virus remains dormant in the root of the spinal nerve and can be reactivated
this leads to eruption of vesicles localised to an area of skin supplied by a particular spinal nerve
What are the 2 groups of somaesthetic modalities?
What are examples of each group?
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
What is the difference in conduction between the modalities that are essential to survival and the modalities that increase detail?
Modalities that are essential to survival:
- carried via thin, poorly myelinated or unmyelinated fibres
- conduction relatively slow
Modalities that increase detail:
- carried via large diameter, heavily myelinated fibres
- fast conduction
Label the transverse section of the spinal cord
What is the difference between the dorsal, lateral and ventral grey horns?
Dorsal grey horn:
- contains synapses for sensory information
Lateral grey horn:
- contains preganglionic visceral motor fibres (autonomic)
Ventral grey horn:
- contains cell bodies of motor neurones (somatic control)
Label the following major ascending and descending fibre tracts
What sensations are associated with the dorsal column and spinothalamic tracts?
Dorsal column pathway:
- fine touch
- vibration
- pressure
- joint position
- this is ipsilateral (from same side of body)
Spinothalamic tract:
- crude touch
- pain
- temperature
- this is contralateral (from opposite side of the body)
What are the roles of the lateral and ventral corticospinal tracts?
Lateral corticospinal tract:
- voluntary motor movement
- ipsilateral
Ventral corticospinal tract:
- voluntary motor movement
- contralateral
Label the features of the 3 neurone chain involved in a general sensory pathway
What type of neurone is the 1o neurone in the sensory pathway?
Where does it travel to and from?
Pseudounipolar
it runs from a sensory receptor in the periphery and has its cell body in a sensory ganglion
this is either the cranial nerve ganglion** or **dorsal root ganglion
It then synapses within the CNS
Where is the cell body of the 2o located?
What is its pathway like?
The cell body is within the CNS
its axon crosses the midline
it then ascends to the ventroposterolateral nucleus of the thalamus
What is the passage of the 3o neurone in a general sensory pathway like?
It runs from the synapse in the VPL of the thalamus
the axon projects to the post-central gyrus in the parietal lobe
this is the primary sensory cortex
Where do the cell bodies of second order neurones in the general sensory pathway lie?
within the CNS
they are within the ipsilateral grey matter
the axon then crosses the midline to ascend to the VPL nucleus of the thalamus
Where are the cell bodies of third order neurones located?
Within the thalamus
the axons project into the somatosensory cortex
What is the organisation of sensory pathways like?
They are somatotopic
What is the passage of neurones involved in the spinothalamic pathway like?
Label the diagram
What are the stages involved in the spinothalamic pathway?
- 1o neurone cell body is located in the dorsal root ganglion
- the central process uses the dorsal root to enter the dorsal horn via the Lissauer’s tract
- the 1o synapses with the 2o neurone in the dorsal grey horn, or ascends 1-2 segments then synapses
- the 2o neurone axon crosses the midline in the ventral white commisure
- 2o fibres ascend in the spinothalamic tract towards the thalamus
What is meant by the spinothalamic pathway being somatotopically organised?
Fibres bringing information from specific areas of the body are located in specific regions
arm is more medial, trunk and then leg is more laterally
What sensory modalities are concerned with the spinothalamic pathway?
- Pain
- temperature
- crude touch
- some pressure