Neuroanatomy Flashcards
Striatum
Caudate+Putamen
Lentiform
Globus pallidus+Putamen
Direct pathway
Projects from cortex -(+)-> striatum -(-)-> GPi/SNr -(-)-> thalamus (+). Named because signal heads directly to GPi/SNR.
(+) Glu, (-) GABA
Increases excitatory thalamic output to the cortex
INCREASES MOTOR ACTIVITY
Dopamine from SNc acts on striatum via D1 receptors, enhancing response to glutamate, resulting in increased motor activity
Indirect pathway
From cortex -(+)-> striatum -(-)->GPe -(-)-> STN -(+)->GPi/SNr -(-)-> thalamus (+).
Detours at GPe and STN.
(+) Glu, (-) GABA
Decreases excitatory thalamic output to the cortex
DECREASES MOTOR ACTIVITY
Dopamine from SNc acts on striatum via D2 receptors, decreasing response to glutamate, resulting in increased motor activity
Striatal projects in the basal ganglia
Primarily inhibitory
Dopamine in the direct pathway
From substantia nigra, pars compacta → striatum (via nigrostriatal projections)
Enhances striatal response to glutamate via D1 receptors (more activation)
Increases GPi and SNr inhibition by striatum
INCREASES MOTOR ACTIVITY
Dopamine in the indirect pathway
Substantia nigra, pars compact → striatum (via nigrostriatal projections
Decreases striatal response to glutamate via D2 receptors
Decreases striatal inhibition on GPe→Increases STN inhibition by GPe→Decreases activation of GPi and SNr
INCREASES MOTOR ACTIVITY
Acetylcholine in BG
Aspiny neurons - striatal interneurons, release ACh
Excite both pathways – BU prefer the indirect pathway
Anticholinergic medications (trihexyphenidyl, benztropine, procyclidine) can be beneficial in Parkinson’s disease
Primary output nuclei from the basal ganglia
The internal segment of the globus pallidus sends outputs to the thalamus through the ansa lenticularis and the lenticular fasciculus.
Each enters into the thalamic fasciculus to synapse on VL (ventrolateral) and VA (ventral anterior) of the thalamus.
VA nucleus of the thalamus later projects to the premotor cortex and is responsible for initiating movement
VL nucleus of the thalamus projects to the primary motor, supplementary motor, and premotor cortices and assists with initiation and learning of skilled movements.<p></p>
Parkinson’s disease BG lesio
SNc degeneration: Loss of dopamine→net inhibition of the thalamus
DECREASES MOTOR ACTIVITY
Hemiballismus BG lesion
Subthalamic nucleus lesion → reduced thalamic inhibition
INCREASES MOTOR ACTIVITY CONTRALATERAL TO THE LESION
Huntington’s disease BG lesion
Degeneration of striatal neurons in caudate and putamen
More severe damage to the indirect pathway→reduced thalamic inhibition
INCREASES MOTOR ACTIVITY
**Eventually all striatum degenerates à hypokinetic, parkinsonian
Basal ganglia circuity other. name
Cortico-striato-thalamo-cortical
<p>D2 receptors and prolactin</p>
<p>D2 receptors are found in the pituitary gland; activity at D2 receptors in the pituitary inhibits prolactin release, hence the hyperprolactinemia seen in patients taking antipsychotics (which antagonize D2 receptors).</p>
VPM thalamus
Somatosensory information from the contralateral face
-Pain (spinal nucleus of CN V)
-Temperature (spinal nucleus of CN V)
-Fine touch (chief sensory nucleus of CN V)
-Proprioception (mesencephalic nucleus of CN V)
Taste
Visceral pain
VPL thalamus
Somatosensory information from the contralateral body
The ventral posterolateral (VPL) nucleus is involved in sensory relay from the body, while the ventral posteromedial (VPM) nucleus is involved in sensory relay from the face, both of which project to the somatosensory cortex.
Cheiro-Oral Syndrome
Lacunar syndrome
Contralateral sensory deficits of the hemi-mouth and hand/fingers
Localizes to the VPM and VPL nuclei of the thalamus
Thalamic astasia
Lesion to the VPL, supplied by posterior choroidal artery branches of the posterior cerebral artery
Cannot stand or sit unassisted
Fall backwards or to the side opposite of the lesion
Varying degrees of sensory loss
Normal strength
Thalamic Vascular Supply
Posterior communicating artery
PCA
Anterior choroidal artery (Lateral thalamus - LGN)
Lateral Geniculate Nucleus thalamus
Visual relay nucleus
Optic tract -> LGN -> primary visual cortex
Medial Geniculate Nucleus thalamus
Auditory relay nucleus
Inferior colliculus -> MGN -> primary auditory cortex
Dorsal medial thalamus
Innervates the entire pre-frontal cortex
Receives input from the amygdala
Involved in control of affect, behavior, executive function
Lesion -> disinhibition, poor executive function
Anterior nucleus thalamus
Involved in memory
Hippocampus, hypothalamus, mammillary bodies (mammillothalamic tract) -> AN -> cingulate gyrus
Part of Papez circuit, limbic system
Lesion -> amnesia
The anterior nucleus is mostly involved in limbic relay and memory formation (part of Papez circuit).
Fatal familial insomnia
Preferentially affects:
Dorsomedial nucleus (receives input from the amygdala)
Anterior nucleus
