tract anatomy Flashcards
what are the two somatic ascending pathways?
dorsal column medial leminiscus and anterolateral/spinothalamic
what does the DCML concern?
proprioception, fine touch and vibration
where are first order neurons in the DCML?
dorsal column
where are second order neurons in the DCML?
gracile and cuneate nuclei
where are third order neurons in the DCML?
thalamus (ventral posteroateral nucleus)
description of DCML
- primary afferent neurons enter through dorsal roots of spinal nerves
- gracile fasciculus in sacral, lumbar and lower thoracic=below T6, cuneate fasciculus, upper thoracic and cervical=above T6
- form the dorsal columns of the ipsilateral side of the body
- ascend and synapse in the lower medulla to gracile and cuneate nuclei
- decussate in medulla as internal arcuate fibres and ascend as medial lemniscus
- synapse in the VPL of the thalamus
7.project to somatosensory cortex via internal capsule
what does the spinothalamic tract concern?
lateral- pain and temperature
anterior- crude touch and pressure
where are first order neurons in the spinothalamic tract?
dorsal root ganglion
where are second order neurons in the spinothalamic tract?
substantia gelatinosa
where ate third order neurons in the spinothalamic tract?
VPL in thalamus
description of spinothalamic tract
- first order neurons in DRG enter spinal cord through dorsal root
- entering sensory fibres are myelinated (alpha delta) or unmyelinated (C-fibres)
- synapse in substantia gelatinosa in dorsal horn
- decussates at the anterior wite commissure (contralateral)
- forms the spinal leminscus in the brainstem
- ascends and synapses with third order neurons in the VPL and project to somatosensory cortex
trigeminal pathway for proprioception, fine touch and vibration
1.first order neurons in trigeminal ganglion outside brainstem
2. axons in TG travel along different branches of trigeminal nerve
3. second order neurons in trigeminal brainstem nuclei (e.g mescenphalic) decussate across the midline and form the trigeminal leminsicus
4. third order neurons are in the ventral posteromedial nucleus (VPM) in the thalamus
5. projected to the cerebellum and somatosensory cortex
trigeminal pathway for pain (nociception)
- first order pseduounipolar neurons in the trigeminal ganglion recieve information from nociceptors
- synapse in the spinal trigeminal nucleus in the medulla
- decussate in medulla at ventral trigeminal leminscus
- third order neurons in the VPM and project to somatosensory cortex
what is the main descending pathway?
corticospinal tract
what does the corticospinal tract concern?
voluntary movement,fine motor control and movement precision in distal limbs and trunk
description of the corticospinal tract
- orginiates in the primary motor cortex (betz cells have largest axons)
- motor neurons pass through corona radiata and then the internal capsule, continuing to the brainstem via the cerebral peduncles (crus cerebri)
- decussation in the medulla oblongata at the pyramids for 80% of fibres which enter lateral corticospinal tract
- 20% decussate in the spinal cord and form anterior corticospinal tract
lateral cotricospinal tract
fine motor control and voluntary movement of distal muscles (hands, fingers)
= skilled and precise movements
anterior corticospinal tract
controls postural muscles for trunk stability and gross movements
proximal limb movements (shoulder, hip)
coordination between trunks and limbs
what is the corticobulbar/corticnuclear tract?
voluntary controls of the face through motor nuclei of cranial nerves
description of corticobulbar pathway
- originates in the primary motor cortex
- descend from internal capsule to corona radiata
- synapses with cranial nerves in the brainstem
- does not follow a strict pattern of decussation however many cross in the medulla
bilateral innervation of cortex in corticobulbar pathway
most nuclei except the facial motor nuceus and the hypoglossal nucleus which are contralateral
what are the extrapyramidal pathways?
rubrospinal
vestibulospinal
tectospinal
reticulospinal
rubrospinal tract
originates in the red nucleus of the midbrain and plays a role in coordinating voluntary movements of the upper limbs and shoulders
muscle tone and posture by influencing flexor muscles
ventral tegmemtal decussation- contralteral motor function
vestibulospinal tract
arises from the vestibular nuclei in the pons and medulla in and near the floor of the fourth ventricle
important for maintaining balance, posture and head positioning
two tracts= lateral vestibulospinal (no decussation) and medial vestibulospinal
tectospinal tract
originates from the tectum in superior colliculus and plays a key role in coordinating head and neck movements in response to visual and auditory stimuli (orientation response)
contralateral information
reticulospinal tract
originates in the reticular formations (pons and medulla) and is important for postural control, muscle tone regulation and voluntary movement
medial (pontine) reticulospinal tract is ipsilateral
lateral (medullary) reticulospinal tract is bilateral
lateral pathways definition and examples
control proximal and distal muscles
lateral corticospinal and rubrospinal
medial pathways definition and examples
control axial muscles
anterior corticospinal, vestibulospinal and reticulospinal
hierarchical model of movement
- posterior parietal cortex sends sensory information to the frontal cortex
- prefrontal cortex plans movemet
- premotor cortex organises movement sequences
- motor cortex produces specific movements
upper motor neuron damage
affects multiple muscles
paralysis and weakness
increased muscle tone
no fasciculations
no muscle atrophy
muscle mass maintained
altered reflexes (babinksi sign)
lower motor neuron damage
affects individual muscles
paralysis and weakness
loss of muscle tone
fibrilltaions and fasciculations
rapid muscle wasting
loss of tendon reflexes
superficial reflexes unaltered
