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
What are the roles of Lissauer’s tract and the substantia gelatinosa?
They are involved in the dispersal of information
the cell bodies of 2o neurones are located in specific laminae
Complete the table
What is shown in this picture?
Crude touch fibres travel up a few segments to I, II and IV cells and then cross the midline to ascend more medially
Pain & temperature fibres pass through cells in II, the fibres then cross the midline immediately and ascend to the VPL and cortex
these fibres are both part of the spinothalamic tract
Label the components of the spinothalamic pathway
What is the spinothalamic tract and spinal lemniscus?
The axon of the 2o neurone travels within the spinothalamic tract
when it reaches the medulla, it changes its name to the spinal lemniscus
this travels to the thalamus
What sensory modalities are concerned with the dorsal column pathway?
- Discriminative touch
- vibration
- proprioception
- pressure
located in the dorsal columns of the white matter
Label the components of the dorsal column pathway
What are the stages involved in the dorsal column pathway at the level of the spinal cord?
- 1o neurone cell body is located in the dorsal root ganglion
- it travels through the dorsal root, Lissauer’s tract but does NOT enter the grey matter
- 1o fibres ascend in one of the ipsilateral dorsal columns - gracile or cuneate fascicle
What is the main difference between the gracile fascicle and cuneate fascicle?
The gracile fascicle runs the entire length of the spinal cord
The cuneate fascicle is only present above T6
Where do the gracile fascicle and cuneate fascicle travel to?
The medulla receives ascending sensory tracts from the spinal cord
they terminate in the gracile and cuneate tubercles
the tubercles contain the nuclei - this is where the 10 neurone synapses with the 2o neurone
Label the dorsal column pathway at the level of the closed medulla
What happens in the dorsal column pathway at the level of the closed medulla?
- 1o fibres ascend and synapse with 2o neurones in the gracile / cuneate nucleus
- the axons of the 2o neurones cross the midline via internal arcuate fibres
- the fibres then enter the medial lemniscus which ascends to the thalamus
Label the transverse section of the closed medulla
Label the summary of the dorsal column medial lemniscus pathway
What is the difference in the dorsal column medial lemniscus pathway below and above T6?
Spinal cord below T6:
- 1o sensory neurone enters the gracile fascicle
Spinal cord above T6:
- 1o sensory neurone enters the cuneate fascicle
What happens in the dorsal column medial lemniscus pathway at the level of the closed medulla?
- 1o sensory neurones contact 2o fibres within the gracile / cuneate nucleus
- 2o fibres cross the midline and enter the medial lemniscus
- medial lemniscus ascends to the VPL nucleus of the thalamus
- 2o neurones synapse with 3o neurones within the thalamus, which the project to the somatosensory cortex
What is the difference in the ways in which the spinothalamic and dorsal column pathways travel to the opposite hemisphere?
Spinothalamic pathway:
- they travel contralaterally within the cord
- fibres cross at the level of spinal cord entry
Dorsal column pathway:
- they travel ipsilaterally within the cord
- fibres cross at the level of the closed medulla
- both pathways use 3 neurones
If there was a lesion on the right hand side of the spinal cord in the torso regions, what symptoms would be expected?
- Loss of proprioception and two-point discrimatory touch sense over lower part of right torso and right lower limb
- sensation intact over the remainder of body
this is due to the dorsal column pathway which crosses in the closed medulla so ascends on the ipsilateral side of the SC
- analgesia and thermoanaesthesia over the left lower limb and left lower torso
- pain and temperature sensation intact over the rest of the body
this is due to the spinothalamic pathway which crosses at SC entry and travels on the contralateral side of the SC
In which cranial nerves is general sensation from the head carried in?
- Trigeminal - V
- Facial - VII
- glossopharyngeal - IX
- vagus - X
What type of sensation from the head is carried in the following cranial nerves?
What central pathway does information from all these nerves travel in?
All information from these nerves travel in the same central pathway - the trigeminal sensory pathway
Where are the cranial nerve nuclei located?
What is the difference between the motor and sensory cranial nerve nuclei?
They are located within the brainstem
Motor nuclei:
- give rise to motor fibres that leave the brainstem in cranial nerves
Sensory nuclei:
- Receive information from fibres entering the brainstem in cranial nerves
sensory fibres from trigeminal, facial, glossopharyngeal and vagus nerves run within the trigeminal sensory nucleus to the thalamus
Label the different components of the trigeminal sensory nucleus
The motor nuclei of the trigeminal lies medial to the sensory nuclei
V1, V2 and V3 are the branches of the trigeminal nerve carrying somatosensory information, which have cell bodies in the trigeminal ganglion
What are the 3 divisions of the trigeminal nerve?
Where are the 1o neurone cell bodies located?
V1 - opthalmic nerve
V2 - maxillary nerve
V3 - mandibular nerve
1o neurone cell bodies are located in the trigeminal ganglion (with one exception)
What is the distribution of the trigeminal nerve like?
Through which apertures do the different divisions leave the skull?
Opthalmic division supplies the skin at the level of the upper eyelid and above
It leaves via the superior orbital fissure
Maxillary division supplies skin between the upper eyelid and upper lip
It leaves via the foramen rotundum
Mandibular division supplies skin below the upper lip
It leaves via the foramen ovale
What are the three divisions of the sensory nucleus of the trigeminal nuclei?
The sensory nucleus is divided into three and different parts receive different sensory modalities
- mesencephalic nucleus
- pontine (chief sensory) nucleus
- spinal nucleus
What different sensory modalities are detected in different parts of the trigeminal nuclei?
Proprioception:
- mesencephalic nucleus in midbrain
Discriminative touch:
- pontine (chief sensory) nucleus
Simple touch and pressure:
- rostral parts of the spinal nucleus
Pain and temperature:
- caudal parts of the spinal nucleus
What is the exception to the generalisation that first order cell bodies are in the trigeminal ganglion?
Proprioception which is received in the mesencephalic nucleus
the cell bodies are located within the nucleus itself, opposed to the trigeminal ganglion
Label the components of the pain and temperature pathway
What are the stages involved in the pain and temperature pathway?
- 1o neurones have their cell bodies within the trigeminal ganglion
- 1o fibres run caudally in the spinal tract of the trigeminal nucleus
- they synapse with the 2o fibres in the caudal spinal nucleus
- 2o axon crosses the midline immediately and ascends in the trigeminothalamic tract to the VPM nucleus of the thalamus
Label the crude touch and pressure pathway
What are the stages involved in the crude touch and pressure pathway?
- 1o neurone cell bodies are within the trigeminal ganglion
- fibres descend in the spinal tract of the trigeminal nucleus
- 1o neurone synapses with the 2o neurone in the rostral spinal nucleus
- the 2o axon immediately crosses the midline to ascend in the trigeminothalamic tract to the VPM nucleus of the thalamus
Label the transverse section through the closed medulla
what would happen if there was a lesion affecting the lateral medulla?
Sensation from the face:
- ipsilateral loss of sensation
Sensation from the body:
- contralateral loss of sensation
What is the difference in the way the pain and temperature pathways from the head and body travel to project to the opposite hemisphere?
From the body:
- fibres carrying pain and temperature involved in spinothalamic pathway
- they travel contralaterally within the cord
- they cross at the level of spinal cord entry
from the head:
- fibres carrying pain and temperature involved in trigeminothalamic pathway
- they descend through the medulla to the spinal nucleus
- they cross below entry
Label the components of the discriminatory touch pathway
What are the stages involved in the discriminatory touch pathway?
- 1o neurone cell bodies located in trigeminal ganglion
- 1o neurone synapses with the 2o neurone within the pontine nucleus
- 2o axon crosses the midline and ascends in the trigeminothalamic tract
- it travels to the VPM nucleus of the thalamus
Label the components of the proprioception pathway
What are the stages involved in the proprioception pathway?
- the afferent 1o axons travel in the mandibular division of the trigeminal nerve
- 1o neurone cell bodies are within the mesencephalic nucleus
- the 2o axon crosses the midline and ascends in the trigeminothalamic tract and ascends to the thalamus
- other 1o fibres contact motor neurones in the trigeminal motor nucleus - these are involved in the jaw jerk reflex
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