Diencephalon, Basal Ganglia and Cerebral Cortex

Locate and identify the key structures of the diencephalon

Recall the components of the basal ganglia and explain their general functional roles in motor control

Locate and name the major gyri and sulci (landmarks) of the cerebral hemispheres

Describe the key functional cortical areas and integrate this knowledge with previously learned concepts (i.e., descending motor pathways and ascending sensory pathways).

Describe the Brodmann system for cortical mapping and the sensory and motor homunculi

Label this image and identify the uncus

Define the diencephalon

key division of the forebrain situated between the telencephalon and midbrain, surrounding the third ventricle. Comprising the thalamus, hypothalamus, epithalamus, and subthalamus, it acts as a central relay/processing hub for sensory information, endocrine control, and emotional regulation

Locate the diencephalon in this right brain midsagittal section

What are subdivisions of the diencephalon?

hypothalamus, thalamus, subthalamus, epithalamus (made up of habenula and pineal body)

Define the telencephalon

comprising 85% of total human brain weight. It includes the cerebral cortex, subcortical structures (hippocampus, basal ganglia), and olfactory bulbs

What are the 3 nuclear groups of the thalamus?

anterior, medial, lateral

Role of the anterior nuclear group of the right thalamus

Involved in memory and emotion (part of the limbic system)

Role of the medial nuclear group of the right thalamus

Associated with individual awareness and emotional processing

Role of the lateral nuclear group of the right thalamus

The largest group, which handles most sensory and motor relays

What are the subdivisions of the lateral nuclear group of the right thalamus? What does each section connect with?

Lateral Dorsal (LD) and Lateral Posterior (LP) nuclei are part of the lateral nuclear group of the thalamus, primarily functioning in cognitive and sensory association

• LD nucleus connects with the limbic system (cingulate gyrus) and plays roles in emotional processing

• LP nucleus (related to the pulvinar) acts as a higher-order relay for visual, parietal, and sensory inputs

Functions of the thalamus

It’s a bit like directory enquiries!

1. Sensory relay

2. Support for Motor systems

3. Mental operation regulation

Which sensory pathways pass through the thalamus?

reactive and discriminative ie spinothalamic and dorsal column-medial lemniscus pathways

What is this arrow pointing to?

mammillary body, pair of small, round nuclei located on the inferior surface of the posterior hypothalamus, part of the diencephalon and the limbic system. They are crucial for memory, spatial navigation, and emotion, receiving inputs from the hippocampus

What makes up the basal ganglia?

• Caudate

• Putamen

• External globus pallidus

• Internal globus pallidus

• Subthalamic nucleus

• Nucleus accumbens

• Substantia nigra

Locate the structures that make up the basal ganglia

What is the external capsule sandwiched between?

between putamen and claustrum

What type of matter are the internal and external capsules?

white matter

label this right brain parasagittal view of the brain with the structures making up the basal ganglia

thalamus, nucleus accumbens, subthalamic nucleus and substantia nigra evident

Label this coronal anterior section of the brain

What are the 3 types of cerebral white matter/fibres?

association, commissural and projection fibres

Which pathways pass through the basal ganglia?

motor pathways - corticospinal and corticonuclear

What is the function of basal ganglia?

• Direct: facilitates movements by Disinhibition.

• Indirect: Inhibition of unwanted movements.

What do these structures make up?

cerebral cortex

What does the limbic system include?

parts of the cerebral cortex, basal nuclei, the thalamus, the hypothalamus, and the olfactory cortex

What does the limbic system control?

visceral functions through the autonomic nervous system and the endocrine system and is involved in emotions and memory, reproduction and nutrition.

What are the different areas of cortical function ?

motor control (frontal), sensory processing (parietal), auditory processing (temporal), and vision (occipital): eg

Primary Motor Cortex (Frontal Lobe): Initiates and controls voluntary movements.

Prefrontal Cortex (Frontal Lobe): Involved in high-level cognitive processes such as planning, decision-making, and personality.

Broca’s Area (Frontal Lobe): Responsible for speech production and language processing.

Primary Somatosensory Cortex (Parietal Lobe): Processes sensory information regarding touch, temperature, pressure, pain, and body position.

Explain the Brodmann method of numbering

a system of numbering regions of the cerebral cortex based on their cytoarchitecture

What are the homunculi? Which 2 homunculi are visible on this image?

Sensory and Motor Homunculi (Representations of the body mapped onto the primary somatosensory and motor cortices, illustrating the proportion of cortex dedicated to different body parts)

What are sulci and gyri and their function?

The human brain's surface is characterised by ridges known as “gyri” (singular: gyrus) and grooves called “sulci” (singular: sulcus). These structures increase the brain's surface area, allowing for a greater number of neurons and enhanced cognitive abilities. 

Describe key neural connection pathways in the brain?

The key neural connections (ascending and descending pathways) between the cortex, basal ganglia, brainstem, spinal cord, and cerebellum, including Spinothalamic tract, Dorsal column-medial lemniscus pathway, Corticospinal tract and Corticobulbar tract.

Summarise the basal ganglia

group of subcortical nuclei involved in motor control and other functions. The main components include Caudate Nucleus, Putamen and Globus Pallidus, Nucleus accumbens, Subthalamic Nucleus and Substantia Nigra. Their modulatory roles in motor control are primarily achieved through two opposing internal circuits, the Direct Pathway (which promotes movement) and the Indirect Pathway (which inhibits movement)

Other names for diencephalon

interbrain and tweenbrain

Where is the diencephalon located?

nestled deep between the cerebral hemispheres, positioned superior to the brain stem.

Function of the diencephalon

serves as a vital connection point, relaying virtually all information traveling between the cerebrum (the largest part of the brain) and the rest of the nervous system, with the sole exception of the sense of smell (olfaction).

What forms the wall of the third ventricle? What is this latter structure?

diencephalon

fluid-filled cavity in the brain, underscoring its central and protected location within the skull

What are the 4 subdivisions of the diencephalon?

Thalamus, the Hypothalamus (inferior and anterior to the thalamus), the Epithalamus (posterior to the thalamus, containing the pineal gland), and the Subthalamus (ventral to the thalamus).

What is the largest part of the diencephalon? What does it consist of?

thalamus is the largest part, making up about 80% of the diencephalon's volume, and consists of paired ovoid structures on either side of the third ventricle

Role of the diencephalon

plays an indispensable role in maintaining essential bodily functions and consciousness

Role of thalamus

acts as the major relay station and processing center for almost all sensory and motor signals destined for the cerebral cortex

Role of hypothalamus

primary centre for regulating homeostasis, controlling the autonomic nervous system, body temperature, hunger, thirst, sleep, and emotional responses, and it directly controls the endocrine system through the pituitary gland.

Role of epithalamus

via the pineal gland, secretes melatonin to regulate the sleep-wake cycle (circadian rhythm)

Role of subthalamus

involved in modulating motor functions and is highly interconnected with the basal ganglia

Label this image

What are the primary components of the basal ganglia?

striatum (composed of the caudate nucleus and the putamen), the globus pallidus (divided into the external segment, GPe, and the internal segment, GPi), the subthalamic nucleus (STN), and the substantia nigra (SN)

Where are components of the basal ganglia found?

cluster of subcortical nuclei located deep within the white matter of the forebrain, diencephalon, and midbrain

What is the main input structure of the basal ganglia and what does it receive?

striatum, receiving excitatory signals from the entire cerebral cortex

What forms the output nuclei?

GPi and a part of the substantia nigra, the pars reticulata (SNr)

What do the output nuclei send projections to?

send inhibitory projections to the thalamus

Which intrinsic nuclei are essential for modulating flow of information?

STN, GPe, and the substantia nigra pars compacta (SNc)

What is the primary functional role of basal ganglia?

primarily as a gate-keeping mechanism for the initiation and execution of voluntary motor movements. It acts as a tonic "brake," constantly inhibiting the motor circuits in the thalamus and cortex, thereby preventing unwanted movements.

Define disinhibition/action selection

process of initiating a desired movement involves lifting this inhibitory brake on the specific motor program required

Which basal ganglia nucleus is central to its role of disinhibition?

striatum is central to this, integrating cortical signals and determining which motor program to "select" and allow through the basal ganglia-thalamo-cortical loop

Which opposing neural circuits achieve disinhibition?

• direct pathway: directly inhibiting the output nuclei (GPi/SNr), which in turn disinhibits the thalamus, allowing it to excite the motor cortex

• indirect pathway suppresses movement by ultimately increasing the inhibitory output of the GPi/SNr via a circuit involving the GPe and STN, which results in more inhibition of the thalamus

What is the consequence of dysfunction of basal ganglia disinhibition dysfunction?

Dysfunction in this system, such as dopamine loss in Parkinson's disease, leads to characteristic movement disorders.

Label this image

Label this image

What increases the surface area of the cerebral hemispheres?

defined by an intricate network of ridges, the gyri, and grooves, the sulci, which significantly increase the cortical surface area

What are major ridge landmarks?

• Central Sulcus (fissure of Rolando), which separates the frontal and parietal lobes

• Lateral Sulcus (fissure of Sylvius), which separates the temporal lobe from the frontal and parietal lobes.

How are key functional areas of the cerebral hemispheres mapped?

using the Brodmann system based on cytoarchitecture

What are other names for the primary motor cortex?

precentral gyrus and brodmann area 4

Which pathway originates at the primary motor cortex ? What does it control?

the origin of the descending Corticospinal Tract (Pyramidal Pathway) for voluntary movement, controlling the contralateral body

Which pathways terminate at the primary somatosensory cortex ? What does it control?

termination site for the ascending Dorsal Column-Medial Lemniscal Pathway (fine touch, vibration, proprioception) and the The Spinothalamic Tract  (also known as Anterolateral System; pain, temperature, crude touch), conveying sensory information from the contralateral side of the body.

What are other names for the primary somatosensory cortex?

Postcentral Gyrus and Brodmann Areas 1, 2, 3

Where are the motor and sensory homunculi located? Define these

cortical areas located in the primary motor and somatosensory cortexes

distorted topographic maps where the size of the body part is proportional to the density of motor or sensory innervation, resulting in disproportionately large representations for the hands, lips, and face

Locate the cingulate sulcus, gyrus, parahippocampal gyrus and uncus on this image

What does the Brodmann map refer to?

system of dividing the cerebral cortex into 52 numbered regions based on differences in cellular structure under a microscope rather than just gross anatomy or function, with each area having distinct cell layers and densities that correlate to specific functions, making it a foundational though sometimes refined map in neuroscience for localising brain activity

Label this image

What are the main components of the limbic lobe?

• Cingulate Gyrus (Brodmann Areas 23, 24, 33), located above the corpus callosum

• Parahippocampal Gyrus (Brodmann Area 28, the Entorhinal Cortex, is key for memory), which curls into the temporal lobe and contains the Hippocampus (crucial for memory formation) and the Amygdala (central for emotion and fear memory)

What is the limbic lobe and what role does it play?

C-shaped ring of cortex on the medial surface of the cerebrum, playing a central role in emotion, memory, and motivation

What is Brodmann area 6 and its function?

Premotor and Supplementary Motor Areas involved in motor planning

Brodmann area 44 and 45 and function

Broca’s area for speech production

Broca area 22 and function

Wernicke's Area for language comprehension

Broca area 17 and function

primary visual cortex - occipital lobe

Broca area 41 and 42 and function

primary auditory cortex, temporal lobe

difference between wernicke's area and broca's area

two key regions in the brain's left hemisphere responsible for language. Broca’s area controls speech production and articulation, while Wernicke’s area governs language comprehension.

A patient understands speech but can no longer coordinate and articulate it, what area is damaged?

broca’s area

A patient no longer comprehends speech, what area is damaged?

wernicke’s area

Which one statement is true concerning structure X?

This is the corpus callosum

This is the cingulate sulcus

This is the calcarine sulcus

This is the cingulate gyrus

This is the parieto-occipital sulcus

This is the cingulate sulcus

What is the gyrus immediately above the corpus callosum?

cingulate gyrus

It is the claustrum and little is known about its function

It is the temporal lobe, which plays a role in processing auditory information

It is the insula, which plays a role in interoception (internal sense) and social emotion

It is the parietal lobe, which plays a role in integrating sensory information

It is part of the basal ganglia, which plays a role in the coordination of movement

It is the insula, which plays a role in interoception (internal sense) and social emotion

The structure indicated by the arrow is involved in cerebrospinal fluid (CSF) circulation. What is the next immediate step in the process?

The CSF flows down the cerebral aqueduct

Additional CSF is produced in the third ventricle

CSF is resorbed into the dural venous sinuses

CSF flows through the interventricular foramina

The CSF flows down to the fourth ventricle

CSF flows through the interventricular foramina

The Brodmann area X is concerned with:

reading words - this is the primary visual cortex

The arrow indicates the decussation of tracts which originate in the:

motor cortex

Which statement(s) is/are true regarding the structure indicated by the arrow?

i. Is part of the thalamus.

ii. Is part of the hypothalamus.

iii. Is the interthalamic adhesion (massa intermedia).

iv. Is the infundibulum.

i and iii

The area of the brain indicated by the arrow (highlighted in green) is associated with:

making decisions and personality

Which of the following is the most complete and accurate answer concerning the structure indicated by X?

It is the substantia nigra

It is the substantia nigra and it is located in the tectum of the midbrain

It is the substantia nigra and is considered to be part of the basal ganglia

It is the substantia nigra and is considered to be part of the subthalamus

It is the substantia nigra and contains mostly serotonergic neurons

It is the substantia nigra and is considered to be part of the basal ganglia

What structure is indicated by the arrow?

A mammillary body

The optic tract

The head of the caudate nucleus

The body of the caudate nucleus

A part of the thalamus

A mammillary body

Which one statement best describes structure X?

This is the lateral geniculate nucleus and is a thalamic relay between the inferior colliculus and the auditory cortex

This is the lateral geniculate nucleus and is a thalamic relay between the optic tracts and the visual cortex

This is the medial geniculate nucleus and is a thalamic relay between the inferior colliculus and the auditory cortex

This is the medial geniculate nucleus and is a thalamic relay between the optic tracts and the visual cortex

This is the medial geniculate nucleus and is a thalamic relay between the superior colliculus and the auditory cortex

This is the medial geniculate nucleus and is a thalamic relay between the inferior colliculus and the auditory cortex