Corpus striatum

• Caudate
• Putamen
• Globus pallidus

Caudate nucleus

• Head
• Body
• Tail

Globus pallidus

• External (lateral)
• Internal (medial) segments.

Striatum

Collective term for the:

• Caudate
• Putamen

Derived from the striations that connect them.

Lentiform nucleus

Collective term for the:

• Globus pallidus
• Putamen

Given their lens-shaped appearance. This is an important term to know because it makes sense of the syndrome of hepato-lenticular degeneration.

Pallidum

• Descriptor for the globus pallidus because bundles of myelinated fibers traverse the globus pallidus, giving it a pale appearance.
• The pallidum is sometimes referred to as the paleostriatum because the globus pallidus is derived from the phylogenetically older portion of the brain — the diencephalon.
• The neostriatum refers to the caudate and putamen, which are derived from the phylogenetically newer part of the brain — the telencephalon.

Fiber pathways

• The corpus striatum also encompasses several fiber pathways that pass between the globus pallidus and the subthalamic nucleus and thalamus: the ansa lenticularis, lenticular fasciculus, subthalamic fasciculus, and thalamic fasciculus.These fibers comprise a considerable portion of the white matter region inferolateral to the thalamus, which is called the fields of Forel (aka prerubral fields or Forel’s Field H).

Basal nuclei vs Basal ganglia

• Basal ganglia is more correctly referred to as the basal nuclei because a ganglion is a neuronal aggregation within the peripheral nervous system and the basal nuclei lie within the central nervous system, but the term basal ganglia is the common parlance, so we use it here.

ANATOMY

AXIAL VIEW

Key landmarks: the frontal horn and body of the lateral ventricles, thalamus, and the claustrum, and insula

Anatomical Structures

• Caudate head in the wall of the frontal horn
• Caudate tail at the posterolateral tip of the thalamus (the body is not visible in this section)
• Lens-shaped lentiform nucleus, which subdivides into the putamen, laterally, and the globus pallidus, medially

Early in development, the globus pallidus migrates into the medial wall of the putamen…

• Thus, we can envision the lentiform nucleus as a globus pallidus core surrounded by a putaminal shell.
• The internal capsule lies in between the lentiform nucleus and the head of the caudate and thalamus.
• The external capsule lies in between the putamen and the claustrum.
• The extreme capsule lies in between the claustrum and the insula.

CORONAL VIEW: ANTERIOR

Key landmarks: optic chiasm, frontal horn of lateral ventricle, corpus callosum, and the basal forebrain

Anatomical Structures

• The combined putamen and head of the caudate.
• The nucleus accumbens, which is the bridge that persists between the head of the caudate and putamen after the anterior limb of the internal capsule separates the head of the caudate from the putamen.
  • It is important in rewarding behavior.

CORONAL VIEW: POSTERIOR

Key landmarks:

• Optic tract
• Frontal horn of lateral ventricle
• 3rd ventricle
• Corpus callosum

Anatomical Structures

• Caudate Head in the wall of the frontal horn
• Putamen
• Globus pallidus
• The lateral medullary lamina separates the putamen and globus pallidus.
• The medial medullary lamina subdivides the globus pallidus into an internal (or medial) segment and an external (or lateral) segment.
• The internal capsule lies in between the lentiform nucleus and the caudate.
• Beneath the globus pallidus, lies the basal forebrain and the horizontally-oriented anterior commissure in between them.
  • Note that the globus pallidus actually extends beneath the anterior commissure as the ventral pallidum

SAGITTAL VIEW

Key landmarks:

• corpus callosum
• & the subjacent lateral ventricular system:
  • frontal horn
  • atrium
  • temporal horn

Anatomical Structures

• Caudate: head and body (the tail is not visible in this section)
• Putamen (anteriorly)
• Thalamus (posteriorly)

The internal capsule funnels inferiorly into the cerebral peduncle.

BASAL GANGLIA ISCHEMIC & HEMORRHAGIC STROKES

• Basal Ganglia Ischemic Stroke
• Basal Ganglia Hemorrhage

BASAL GANGLIA ANATOMY & CIRCUITRY: ADVANCED INFORMATION

Basal ganglia topography

• The prefrontal cortex acts through innervation of the head and body of the caudate nucleus.
• The parietal lobes act through innervation of both the putamen and caudate.
• The primary auditory cortex projects to the caudoventral putamen and tail of the caudate.
• The visual cortices project primarily to the nearest portion of the caudate nucleus.

Fields of Forel

Additional fiber pathways pass through Field H and H1 in their ascent into the thalamus they include:

• The cerebellothalamic fibers from the corticopontocerebellar pathway, the medial lemniscus, the nigrothalamic fibers, and the spinothalamic fibers of the anterolateral system pathway.

The thalamic fasciculus

• The term is sometimes broadened to include the cerebellothalamic fibers and it is also sometimes used synonymously with the term Field H1, just as the term lenticular fasciculus is sometimes used synonymously with term Field H2.
• The thalamic fasciculus projects to multiple thalamic nuclei, including the ventroanterior nucleus, which most notably communicates with the globus pallidus; the ventrolateral nucleus, which most notably communicates with the cerebellum; the dorsomedial nucleus, which most notably communicates with the prefrontal cortex and basal ganglia; and the centromedian and parafascicular nuclei (the main intralaminar nuclei), which most notably
  communicate with the striatum and frontal lobes.

BASAL GANGLIA: ADVANCED NOMENCLATURE

Advanced Nomenclature

• The striatum further subdivides into dorsal and ventral divisions.
• The dorsal striatum comprises the bulk of the caudate and putamen, whereas the ventral striatum is limited to only the ventromedial caudate and putamen, but the ventral striatum also encompasses the nucleus accumbens and select basal forebrain structures.
• The dorsal striatum is involved in a wide array of processes, including the sensorimotor circuits, whereas the ventral striatum associates principally with the limbic system and is primarily involved in emotional and behavioral processes.
• Just as the striatum divides dorsally and ventrally, so the pallidum further subdivides into a dorsal pallidum and ventral pallidum. Similar to the striatum, the dorsal pallidum refers to the bulk of the globus pallidus, whereas the ventral pallidum refers to the anteromedial portion of the globus pallidus that lies below the anterior commissure. However, although we consider the ventral striatum and ventral pallidum to be divisions of the striatum and pallidum, here, certain texts distinguish these ventral structures as entirely separate nuclei (ie, they distinguish the ventral pallidum from the pallidum, itself).
• The corpus striatum also encompasses several fiber pathways that pass between the globus pallidus and the subthalamic nucleus and thalamus: the ansa lenticularis, lenticular fasciculus, subthalamic fasciculus, and thalamic fasciculus. These fibers comprise a considerable portion of the white matter region inferolateral to the thalamus, which is called the fields of Forel (aka prerubral fields or Forel’s Field H).
• As a final note, the subthalamic nucleus and substantia nigra are functionally but not developmentally associated with the basal ganglia; therefore, although they are variably included as part of the basal ganglia, we do not include them in our definition of the basal ganglia, here, in accordance with the Terminologia Anatomica.

Lobes

• The anterior cerebellar lobe
• The posterior cerebellar lobe

The primary fissure separates the the anterior lobe from the posterior lobe.

• The flocculonodular lobe: nodule in midline and flocculus out laterally.

The posterolateral fissure separates the corpus cerebelli from the flocculonodular lobe.

Zones

• The midline cerebellum is the vermis (which means wormlike)
• Lateral to it, lies the paravermis (aka the intermediate zone)
• Lateral to it, lies the hemisphere (aka the lateral zone)

FUNCTIONAL MODULES

Clinical Correlation: Ataxia & Incoordination

Vestibulocerebellum

• Phylogenetically the oldest portion of the cerebellum and is referred to as the archicerebellum.
• It is derived from the flocculonodular lobe and the anterior tip of the vermis (the lingula).
• The vestibulocerebellum receives its name because of its midline vestibulo- and olivocerebellar fibers, which project to the deep, medial-lying cerebellar fastigial nuclei.
• It is important for equilibrium and eye movements.

Clinical Correlation – Nystagmus

Spinocerebellum

• Phylogenetically the next oldest and is referred to as the paleocerebellum.
• It is derived from the anterior lobe and the majority of the vermian and paravermian posterior lobe.
• The spinocerebellum receives its name from its major input fibers: the spinocerebellar tracts.
• It plays a major role in postural stability.

Clinical Correlations – Truncal ataxia, Gait Ataxia

Pontocerebellum

• Phylogenetically the newest portion of the cerebellum and is referred to as the neocerebellum.
• It is derived from the remainder of the posterior lobe.
• The pontocerebellum receives its name because it acts through the corticopontocerebellar pathway.
• It is geared towards fine motor movements, which are typically goal-oriented.

Clinical Correlation – Incoordination

ALCOHOL TOXICITY & CEREBELLAR DEGENERATION

Acute alcohol intoxication, the entire cerebellum is affected (vestibulo-, spino-, pontocerebellum).

• Nystagmus occurs from toxicity to the vestibulocerebellum, truncal ataxia occurs from toxicity to the spinocerebellum, and incoordination occurs from toxicity to the pontocerebellum.

Alcoholic cerebellar degeneration

Clinical Correlation: Chronic Alcoholic Cerebellar Degeneration

• The pathology is predominantly restricted to the anterior superior cerebellar vermis. Because of this restricted area of injury, truncal ataxia is sometimes the sole deficit.

We may miss this exam finding, if we fail to ask our patients to stand during the exam.

GENERAL SOMATOTOPIC ORGANIZATION OF THE CEREBELLUM

• Unilateral cerebellar lesions affect the ipsilateral side of the body.
• The midline cerebellum plays a role in posture whereas the lateral cerebellum assists in fine motor, goal-oriented skills.
• For instance, to stand upright, you need the midline cerebellum, and to play the piano, you need the lateral cerebellar hemispheres.

• The somatotopic map of the cerebellum is in concert with its functional layout: the role of the spinocerebellar, anterior lobe is to provide postural stability, which requires the limbs and trunk, and the role of the neocerebellar, posterior lobe is to provide goal-oriented, fine motor movements, such as those of the fingers and mouth.

Key Structures:

Brainstem
Cerebellum
Diencephalon
Corpus callosum
Cerebral lobes

Brainstem

From superior to inferior:

Midbrain
Pons, anterior-lying: basis
Medulla oblongata: pyramidal tracts

Additional points of interest

• The brainstem transitions into the spinal cord, inferiorly.
• The tectum lies along the upper posterior surface of the brainstem.
• CSF funnels through the cerebral aqueduct (of Sylvius) in the upper brainstem.
• The fourth ventricle is the collection of CSF in the mid-brainstem level.

The cerebellum

• The cerebellum packs its vast surface area into the tightly-packed posterior/inferior skull (the posterior fossa).

The diencephalon

• Comprises numerous thalamic regions, most notably the thalamus and hypothalamus.

We can remember its central location by the clinical syndrome of central herniation, which typically first involves the diencephalon. And we can remember its autonomic function (from the hypothalamus) by the clinical syndrome of diencephalic autonomic storm (or dysautonomia).

The corpus callosum

• C-shaped, prominent white matter pathway, connects the bilateral cerebral hemispheres.

We can remember its function by corpus callosotomy (aka “split brain” surgery), which involves transection of the corpus callosum (and commissures), usually to stop the spread of seizures.

Clinical correlation, see callosal dysgenesis

Cerebral Lobes

The oft-forgotten limbic lobe surrounds the corpus callosum and diencephalon.

The additional cerebral lobes are the:

Frontal lobe (anteriorly)
Parietal lobe (behind it)
Occipital lobe (posteriorly)
Temporal lobe (inferiorly)

Sulci

• The central sulcus distinguishes the frontal lobe from the parietal lobe.

Show in your diagram that the primary motor cortex extends along the medial surface of the brain, as does, the primary sensory cortex does, as well.

• The parieto-occipital sulcus distinguishes the parietal and occipital lobes.
• The calcarine sulcus lies along mid-section of the occipital lobe.
• The primary visual cortex lies along the banks of the calcarine sulcus.

Key Gyri

• The cingulate gyrus lies within the superior limbic lobe.
• The uncus is the antero-inferior gyral thumb.

Prominent structures from superior to inferior:

• The fornix, which wraps around the thalamus, which underlies it.
• The interthalamic adhesion, which is the medial thalamic bump.
• The hypothalamus, beneath the thalamus (it surrounds the 3rd ventricle) and comprises numerous nuclei, including:
• The mammillary bodies, just anterior to the brainstem.
• A portion of the pituitary gland (anteriorly).
• The pineal gland (of the epithalamus) lies along the posterior diencephalon.

To help remember the position of the pineal gland above the tectum consider that pineal tumors can compress the tectum, which causes vertical gaze palsy, called Parinaud’s syndrome.

• Primary cortices (areas), which initiate motor output or are primary cortical sensory reception centers.
• Association cortices (areas), which process and integrate cortical information.

We divide the lateral surface of the brain into 4 key anatomic lobes:

Frontal lobe (anteriorly)
Occipital lobe (posteriorly)
Temporal lobe (inferiorly)
Parietal lobe (which borders each lobe)

Key Sulci

• The Sylvian fissure (aka the lateral sulcus) distinguishes the cerebral lobes.
• The central sulcus distinguishes the frontal and parietal lobes.

Key Gyri/Areas

• The primary motor cortex lies within the precentral gyrus (given its location in front of the central sulcus)
  • It comprises primary motor neurons in pathways that control skeletal muscle (under volitional control) (NOT smooth muscle (under autonomic control), thus it’s often called the somatic motor area (somatic implies conscious control).
  • Each hemisphere innervates the opposite side of the body.
  • See: Stroke: Precentral Gyrus

• The primary sensory cortex lies within the postcentral gyrus(given its location behind the central sulcus).
  • It receives sensory input from body regions that we consciously perceive, thus it’s often called the somatic sensory area.
  • Each hemisphere receives sensory input from the opposite side of the body.

• The primary visual cortex (V1) lies at the occipital pole and is far more prominent on the medial aspect of the brain.
  It mostly lies along the calcarine sulcus, which is on the medial surface of the brain.
  • Visual stimuli first reach the cortex within the primary visual cortex.
  • Each cerebral hemisphere receives visual input from the opposite visual field.
  • Each eye captures both halves of the visual world.
  • See: PCA Stroke

• The primary auditory cortex lies within the transverse temporal gyri (Heschl’s gyri).
  • Auditory stimuli first reach the cortex within the primary auditory cortex.
  • Each hemisphere receives auditory input from BOTH sides of the world.

• The somatosensory association cortex interprets and integrates sensory information and is an important sensory planning region.

• The premotor area assembles complex motor programs.

• Clinically we assume the frontal eye fields control volitional eye movements (in reality eye movements come from disparate motor areas).

• The prefrontal cortex in the anterior frontal lobe governs three discrete cognitive domains:
  • Laterally: Logistical (ie, task-sequencing) (use the L as a mneomnic)
  • Inferiorly: Impulse control (use the I)
  • Medially: Motivation (use the M)

• Broca’s area is the language output area.
  • It lies in the inferior frontal gyrus.
  • Broca’s aphasia is a non-fluent language disorder, meaning language output is severely impaired but comprehension is mostly preserved (it is hesitant and effortful). Broca’s aphasia localizes to Broca’s area but also to many other (mostly motor) brain regions.

• Wernicke’s area is the language reception area.
  • It lies within the superior temporal gyrus (posteriorly)
  • Wernicke’s aphasia is a fluent aphasia, meaning that there’s preserved speech output but poor comprehension (it is melodious but meaningless). Wernicke’s aphasia localizes to Wernicke’s area and neighboring temporo-parietal regions plus the insula.

• The occipital lobe comprises cortical visual processing; it’s so dedicated to vision that clinicians can easily miss large posterior cerebral strokes, they fail to check the patient’s visual fields.

We subdivide visual processing into:

• The dorsal stream (“where”) visual pathway, which lies along the superior occipital lobe and parietal lobe, and provides visuo-spatial localization processing.
• The ventral stream (“what”) visual pathway, which lies along the inferior occipital lobe and temporal lobe, and provides object recognition processing.

• The insula lies beneath the cerebral folds (the opercula).
  • It participates in many, varied (mostly subconscious) functions: pain modulation, appetite, visceral sensation, anxiety and emotion, socialization, and auditory processing.
  • See: Insular Stroke
• The motor homunculus is a representation of the topographical distribution of neurons that (through relay neurons) command volitional (striated) muscle.

Sensory homunculus is similar but NOT the same as the motor homunculus; it contains sensory input from regions NOT under volitional command (like the genitals and abdomen).

• The insula begins just above the sylvian fissure and wraps around the convexity, as follows:
  -tongue
  -face
  -thumb
  -hand

The aforementioned are enlarged compared to what follows because they require significant more muscular innervation to produce fine movements than the rest of the body.

-upper limb
-trunk
-lower limb
-foot (which ends just above what we’ll see is the cingulate gyrus (on the medial aspect of the brain)).

• We present the 5 cerebral lobes a diamond formation, which should be a helpful mnemonic:
  Frontal up front.
  Parietal on top.
  Occipital in the back.
  Temporal at the bottom.
  Limbic in the center.

The Sylvian fissure (aka the lateral sulcus)

• Distinguishes the cerebral lobes.

The central sulcus

• Distinguishes the frontal and parietal lobes.

The parieto-occipital sulcus

• Distinguishes the parietal and occipital lobes.

Brainstem anatomy

From superior to inferior:

Midbrain
Pons.
Medulla oblongata.

Cerebellum & Diencephalon

• The cerebellum rests on the back of the brainstem.
• The diencephalon lies within the center of the brain and contains the thalamus.
• The corpus callosum is a prominent white matter pathway.

The precentral gyrus (the primary motor cortex)

• Lies anterior to the central sulcus.

The postcentral gyrus (the primary sensory cortex)

• Lies behind the central sulcus.

2 reliable indicators:

-The characteristic omega-shaped knob of the precentral gyrus
-The precentral gyrus is thicker than the postcentral gyrus

Optic pathway.

• Optic nerves (anteriorly)
• Optic chiasm (when they cross) and transition into the:
• Optic tracts.

The pituitary gland

• Lies beneath the optic chiasm.

The mammillary bodies

• Are small but easily identifiable.