Download Neuroanatomy 2

NEUROANATOMY 2 – The neuroanatomy of sensation
Blood supply to the Spinal Cord
Identify:
• Single anterior spinal artery
• A pair of posterior spinal arteries
All receive segmental branches from the vertebral, deep cervical, intercostals and lumbar arteries. They
anastomose with the spinal arteries via ventral and dorsal radicular arteries.
The venous drainage of the cord passes via 6 longitudinal channels in the pia mater:
• 2 median longitudinal veins: anterior and posterior
• 2 anterolateral longitudinal veins behind the ventral nerve roots
• 2 posterolateral longitudinal veins behind the dorsal nerve roots
All the veins drain into the internal vertebral venous plexus in the epidural space (and hence into the intervertebral
veins). Near the base of the skull the spinal veins communicate with the vertebral veins and end in the inferior
cerebellar veins of the inferior petrosal sinus. The internal vertebral plexus is continuous via the foramen magnum
with the venous sinuses of the skull,
Medulla (External Appearance)
Identify posteriorly:
• Posterior median sulcus
• Gracile tubercles
Underlying nuclei of the same name receive fibres from the dorsal column, and are therefore
referred to as dorsal column nuclei
• Cunate tubercles
th
• Vestibular nuclei (in the floor of the 4 ventricle)
Thalamus (External Appearance)
The thalamus is approximately oval in cross section. The posterior aspect, called the pulvinar, is elongated and
overhangs the superior colliculi.
Identify:
• The medial flattened grey disc, the interthalamic adhesion, joining the two thalami
• Posteriorly, the medial and lateral geniculate bodies (metathalamus)
Nuclei of the Medulla
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The dorsal column nuclei are found on the dorsal surface of the medulla
Fibres of the general sensory system traverse the medulla, pons and midbrain before they reach the
thalamus. Here they all make synaptic contacts before being relayed forward to relevant parts of the
sensory cortex (post-central gyrus of the cerebral hemispheres)
Nuclei of the Thalamus
The thalamus is divided into three regions by the presence of the internal medullary lamina:
• Anterior nuclear group
• Medial nuclear group
• Lateral nuclear group
There are also two further groups of nuclei:
• A group within the internal nedullary lamina called the midline nuclei
• A small group of cell aggregations near the inter-thalamic adhesion called the midline nuclei
Lateral group
• The ventral posterior nucleus is concerned with somatosensory information
o The lateral division receives information about most of the body
o The medial division receives information about the face (via the trigeminal)
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The ventral lateral nucleus projects to the primary motor cortex
The ventral anterior nucleus projects to the premotor cortex
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The lateral geniculate nucleus relays visual information
The medial geniculate nucleaus relays auditory information
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The dorsolateral group comprises of the lateralis dorsalis nucleus, lateralis posterior nucleus and the
pulvinar, which are reciprocally interconnected with the association cortex of the parietal, occipital and
temporal lobes
Receive fibres form the cerebellum (dentate
nucleus) and the globus pallidus
Anterior group
• Contains anterodorsal, anteroventral and anteromedial nuclei and is part of the limbic system
• Receives fibres from the fornix and mammillo-thalamic tract, projecting to the cingulated cortex
Medial group
• Formed by the mediodorsal nucleus projecting to the prefrontal association cortex
Intralaminar group
• These are the centromedian nucleus and the parafascicular nuclei
• Both project to the basal ganglia as well as to the cortex
• Both receive fibres from the reticular formation and from tracts projecting to the main thalamic nuclei
• The centromedian nucleus receives fibres from the globus pallidus and cerebellum
Pathways in the Somatosensory System
Sensory information can be divided into four categories:
1.
2.
3.
4.
GSA – Pain, temperature (anterolateral) fine touch, vibration, proprioception (dorsal column)
GVA – Baro receptors, chemoception
SSA – Vision, hearing, balance
SVA – Taste (not always distinguished from the GVA category)
Anterolateral
• Axons enter the spinal cord and make synaptic contact in the dorsal horn
• They then decussate immediately and ascend in the contralateral spine
• Reach the VPL nucleus of the thalamus
• Synapse again with thalamocortical neurones which project to the somatosensory cortex
Dorsal column
• Axon enters the spinal cord and ascends (without synapsing or decussating) until it reaches:
o The gracile nucleus from the lower limb
At the junction of the cord and the medulla
o The cunate nucleus from the upper body
• The decussate at the medulla and pass to the VPL of the thalamus
• Synapse again with thalamocortical neurones which project to the somatosensory cortex
In addition:
• Proprioceptive information from the dorsal column is relayed to the cerebellar cortex via the:
o Anterior spinocerebellar tract (contralateral)
o Posterior cerebellar tract (ipsilateral)
• Further proprioceptive fibres are sent to the olive (anterior medulla), which in turn sends fibres to the
cerebellar cortex
• Sensation from the face is relayed (almost exclusively) via the trigeminal nerve and is associated nuclei