Subcortical anatomy week 5 Flashcards
How many nuclei comprise the basal ganglia?
What function are basal ganglia primarily involved with?
Name the 5 basal ganglia and state their locations within the brain.
Basal Ganglia comprised of 5 nuclei that are primarily involved with motor control:
In the Cerebrum:
- Caudate nucleus
- Putamen
- Globus pallidus
In the Diencephalon:
- Subthalamic nucleus
In the Rostral Midbrain:
5.Substantia Nigra
Note that ppl with basal ganglia disorders also have cognition issues because of connection ot cortex
What are the caudate and putamen called collectively? Why?
The Caudate and Putamen are collectively called the Neostriatum (or Striatum) because of the bridges of gray matter crossing the internal capsule between these 2 nuclei giving it a striated appearance.
What are the putamen and globus pallidus called collectively?
What is the anatomical relationship btwn these two nuclei? (which is more anterior, lateral, etc.)
What lies medial to the putamen and globus pallidus? Lateral?
Why is the globus pallidus paler than the putamen in unstained sections?
What are the 2 parts of the globus pallidus?
Putamen and Globus pallidus are collectively referred to as the Lenticular or Lentiform nucleus and are physically opposed to each other with the putamen located more laterally. Together they appear like a wedge lateral to the internal capsule and medial to the insular cortex. The globus pallidus is much paler than the putamen in unstained sections because it has a large number of myelinated fibers located within it; it has an internal (GPi) and external (GPe) segment.
Where is the caudate nucleus located specifically?
What are the parts of the caudate?
Other than movement, what function does the caudate have? What portion of the cortex does it connect to?
What is the anatomical relationship btwn the caudate and putamen?
The Caudate nucleus is located in the lateral wall of the lateral ventricle and grows with it into a C-shaped structure with a large head bulging into the anterior horn, a body in the body of the lateral ventricle, and a tail in the inferior (temporal) horn.
The caudate is also involved in cognition via its connections with the prefrontal cortex; plays a role in higher ordered executive functions.
The Putamen is lateral to the caudate nucleus.
Identify the indicated parts.
Note: Head of Caudate in lateral wall of lateral ventricle with the Putamen laterally located and the Anterior limb of the internal capsule between the two
What is the corona radiata?
What is the internal capsule?
What are the parts of the internal capsule?
Some fibers from the internal capsule converge and enter what part of the brainstem? What fibers does this include? What structure do they bypass?
What fibers within the internal capsule link the thalamus with the cortex?
Corona radiata: array of myelinated axons entering (ascending fibers) or exiting (descending fibers) the cerebral cortex.
Internal Capsule: Funnel of fibers from corona radiata converging in subcortical areas; has an anterior (A) limb, genu, posterior (P), retrolenticular (R) and Sublenticular (S) limb.
Some fibers from the internal capsule converge in the brainstem and enter the crus cerebri (i.e. cerebral peduncles) of the brainstem. These efferent fibers from the cerebral cortex (primarily motor areas) bypass the thalamus and include corticospinal, corticobulbar and corticopontine fibers.
The internal capsule also consists of afferent fibers linking the thalamus to the cortex and includes the dorsal column, trigeminal and spinothalamic inputs to the sensory cortex.
Identify the numbered parts of the brain.
Note fibers from posterior limb of Internal capsule streaming into the Crus Cerebri (in midbrain) and some Corticospinal fibers eventually forming the pyramids of the medulla.
What is the anterior limb of the internal capsule located btwn?
What is the posterior limb of the internal capsule located btwn?
What are optic radiations?
The internal capsule is V-shaped in horizontal brain sections. It has anterior and posterior limbs and a genu (G) between the two.
Anterior limb (AL): located between the caudate nucleus medially and putamen laterally.
Posterior limb (PL) located between the Putamen and Globus pallidus (Lentiform Nucleus) laterally and the thalamus medially.
Optic radiations: Visual afferent fibers from the Lateral geniculate nucleus in the thalamus streaming into the occipital lobe (visual cortex); located in the most posterior aspect of the internal capsule (retrolenticular limb).
What fibers and from what structures are contained within the anterior limb (AL) of the internal capsule?
What fibers and from what structures are contained within the posterior limb (PL) of the internal capsule?
The Anterior limb (AL) contains thalamocortical fibers from:
1) nuclear groups in the thalamus to limbic cortical areas (cingulate and prefrontal cortex)
2) from Va/VL (Ventral anterior and Ventral lateral nuclei) that provide basal ganglia & cerebellar input (primarily motor) to the frontal lobe
Also contains Corticopontine fibers (from frontal cortex) which then connect with pontine nuclei; from there pontocerebellar fibers enter the cerebellum to provide motor information (more in cerebellar lecture).
The Posterior limb (PL) contains:
1) Descending corticospinal fibers that enter the crus cerebri
2) Ascending thalamocortical fibers from VPM and VPL conveying sensory information from the trigeminal system, dorsal column-lemniscal system and the spinothalamic systems.
What fibers are contained within the genu of the internal capsule?
Explain the somatotopy within the posterior limb of the internal capsule.
What is contained within the sublenticular limb of the internal capsule?
What is contained within the retrolenticular limb of the internal capsule?
- The somatotopy in both of these systems is such that the arm is represented medially and the leg laterally with the trunk between the two. The head/face region for sensation is closest to the genu but is still in the posterior limb. Note that the head contains sensory fibers from the trigeminal system while the arm and leg contain sensory fibers from the spinothalamic and dorsal column tracts. Some use the HAL (head, arm, leg) acronym in describing this somatotopy.
- The Auditory radiations from the medial geniculate body of the thalamus are located in the Sublenticular limb of internal capsule (below Lenticular nuclei) heading to the auditory cortex.
- The Optic radiations from the lateral geniculate nucleus of the thalamus are located in the retrolenticular limb of the internal capsule and stream into the visual cortex.
Identify the colored structures.
What is the anatomical relationship btwn the thalmus and subthalamic nucleus (STN)?
What is the subthalamic fasiculus?
Subthalamic Nucleus (part of Basal Ganglia): located in diencephalon
- lies caudal and lateral to the thalamus.
- Located medially across posterior limb of internal capsule from the globus pallidus
- Subthalamic fasciculus: tract interconnecting STN with GP
What are the 2 parts of the substantia nigra? (just list)
substantia nigra pars compacta
substantia nigra pars reticularis
What is the coloration of the substantia nigra pars reticlaris?
What is the function of this part?
What is the anatomical relationship of the pars reticularis to the pars compacta?
Substantia nigra pars reticularis- closer to cerebral peduncle (CP) with non pigmented, loosely packed neurons. Note that the pars reticularis is more ventrally lcoated than the pars compacta. Major output nuclei of basal ganglia.
What are principal inputs to the basal ganglia? Be specific.
What are principal outputs from the basal ganglia? Be specific.
The basal ganglia affect movement (directly/indirectly) by connection loops with the motor and sensory cortex.
Lesions of basal ganglia cause effects on which side of the body with respect to the lesion? Explain.
Principal inputs to the basal ganglia are excitatory ones from the cerebral cortex to the Striatum.
Principle outputs are from the globus pallidus Interna and substantia nigra pars reticularis (SNpr) to the thalamus (VA, VL) which then relays back to the cortex.
The basal ganglia affect movement INDIRECTLY by connection loops with the motor and sensory cortex.
Most connections are primarily uncrossed (ipsilateral). But when lesioned on one side cause contralateral signs since the motor cortex controls the contralateral side of the body.
Explain the direct and indirect pathways. State the overall effect of stimulation of these pathways.
Explain the involvement of dopamine and the dopaminergic receptors involved in these pathways.
T or F: Normally, the indirect pathway is stimulated more than the direct pathway.
Together with the cerebral cortex and the VA/VL nuclei of the thalamus, the basal ganglia nuclei are interconnected to form 2 parallel but antagonistic circuits known as the Direct and Indirect pathways. Both pathways use a process known as “disinhibition” to mediate their effects, whereby one population of GABA inhibitory neurons inhibits a second population of GABA inhibitory neurons. Activation of the direct pathway results in an increased cortical excitation and the promotion of movement. Activation of the indirect pathway results in a decreased level of cortical excitation and a suppression of movement. (Mnemonic: Indirect Inhibits).
Normally there is a balance between the two pathways which fine tune and grade movement so that it is fluid.
Dopaminergic neurons in the substantia nigra pars compacta (SNc) in the midbrain project to the striatum. Dopamine drives the direct pathway through D1 receptors, increasing movement . Dopamine inhibits the indirect pathway through D2 receptors, also resulting in a net increase in movement.
Direct pathway: Inhibition of the globus pallidus interna (GPi) and substantia nigra pars reticularis (SN pr) by the striatum relieves inhibition of the thalamus by the GPi and SN pr. The thalamus stimulates the cortex which promotes movement.
Indirect pathway: Inhibition of the GPe by the striatum relieves inhibition of the subthalamic nucleus by the GPe. The subthalamic nucleus can then stimulate the GPi and SN pr which both inhibit the thalamus which inhibits movement.
What is the cause of Parkinson’s disease (PD)?
PD is the best known disorder of the _____ pathway.
What are the symptoms of a person with PD?
Parkinson’s Disease: caused by degeneration of nigrostrial neurons in the Substantia Nigra pars compacta resulting in loss of dopamine in the striatum and is the best-known disorder of the direct pathway. Because the cortex is underactive, Parkinson’s patients have problems initiating movements, combined with a reduction in the velocity and amplitude of the movements.
The cause of PD is typically multifactorial with contributions from genetic mutations, environmental toxins, and aging.
Symptoms include:
a. Bradykinesia (slow movements), hypokinesia (few movements) resulting in lack of facial expressions (“masked facies”), absent reciprocal arm swing during walking, difficulty with movement initiation, slow shuffling gait.
b. Rigidity: either lead-pipe (increased muscle tone throughout range of motion tested caused by co-contraction of flexors and extensors on both sides of joint ) or cogwheel (rigidity interrupted by series of relaxations so that when testing patient feels like cogs on a wheel).
c. Resting tremor which increases during stress. “Pill-rolling tremor”
d. Impaired postural reflexes (equilibrium reactions, protective responses)
e. Cognitive deficits: The dementia associated with PD has been estimated to affect at least 20% of patients, with prevalence higher among older patients.
What is the inheritance pattern of Huntington’s disease? What mutation causes this disease?
What part of the basal ganglia is affected with Huntington’s disease?
What pathway is affected with Huntington’s?
What movement disorder is observed? What other deficits occur?
Huntington’s Disease (HD) is an autosomal dominant neurodegenerative disorder, involving primarily the caudate nucleus. Symptoms of chorea typically start between 30-50 years with some cognitive and mood changes as well (via involvement of prefrontal cortical areas). With disease progression see more pronounced chorea, progressive loss of functional abilities and dementia.
Pathology - loss of striatal cholinergic and GABAergic cells with secondary over activity of dopaminergic system (lesion of indirect pathway).
Molecular biology - Trinucleotide genetic repeat disorder (GAG) now isolated to chromosome 4; gene codes for Huntingtin protein
Which basal ganglia is commonly lesioned with hemiballismus?
Abnormal movement is observed on which side of the body with respect to the lesion?
What most often causes hemiballismus?
Hemiballismus: (wild flailing of extremities on one side); most commonly caused by a lesion on the subthalamic nucleus which causes abnormal movement on the contralateral side. This is because subthalamic nucleus has relays via the GPi and SNr and VA/VL to the ipsilateral motor cortex which then controls the contralateral side. Most often caused by a stroke in the small perforating branches of the Posterior Cerebral Artery (PCA) (which supplies the thalamus and surrouding structures).
Where is the diencephalon? What are the 2 major parts of the diencephalon?
Diencephalon: strategically positioned between the cerebral cortex and the brainstem to serve as a relay and integrating center. Its two major divisions, the thalamus and hypothalamus are in the wall of the third ventricle.
Generally, what relays in the thalamus?
What is the function of the thalamus?
The Thalamus- gateway to the cerebral cortex- largest portion of the diencephalon.
Contains relay nuclei for sensory, motor and limbic systems.
- All sensory pathways (except olfaction) make relays in the thalamus; olfactory information is transmitted directly to the entorhinal cortex without a thalamic relay
- Many of the circuits used by the basal ganglia, cerebellum and limbic system also relay here
- Thalamic nuclei named for their location
What is the relationship of the thalamus to the third ventricle?
To the posterior limb of the internal capsule?
Thalamus (T) is lateral to the third ventricle (3) and medial to the posterior limb of the internal capsule (IC).
State what the functions of the following thalamic nuclei:
VPL
VPM
Ventral anterior, Ventral lateral (Va-VL)
Medial geniculate nucleus (MGN)
Lateral geniculate nucles (LGN)
Anterior nucleus (A),
Dorsomedial (DM)
Lateral dorsal (LD)
Pulvinar
- VPL: inputs from dorsal column-medial lemniscal and spinothalamic systems; outputs to somatosensory cortex
- VPM: inputs from trigeminal system (face); outputs to somatosensory cortex
- Ventral anterior, Ventral lateral (Va- VL): inputs from basal ganglia and cerebellum and outputs to motor cortical areas
- Medial geniculate (MGN): inputs from inferior colliculus carrying auditory information to Auditory cortex
- Lateral geniculate (LGN): visual inputs from optic tract; outputs to visual cortex
- Anterior nucleus (A): limbic system inputs from hippocampus and mamillary bodies and output to cingulate cortex.
- Dorsomedial (DM): inputs from prefrontal cortex, olfactory and limbic areas; output to prefrontal cortex
- Lateral Dorsal (LD): inputs from hippocampus; outputs to cingulate gyrus
- Pulvinar: interconnects sensory association areas. inputs from and outputs to parietal, occipital and temporal lobes
