Cerebellum and Basal Ganglia Anatomy Quiz

Neuroanatomy Introduction

• Neuroscience is the scientific study of the nervous system, from its structure to function, development to degeneration, in both health and disease.
• The nervous system coordinates voluntary and involuntary actions and transmits signals between different parts of the body.
• Neuroanatomy is the study of the brain's structural components and the associated peripheral nervous system. A fundamental knowledge of neuroanatomy is crucial for understanding neuroanatomy.
• The nervous system functions by sending and receiving information.

Branches of Neuroscience

• Neuroanatomy
• Neurophysiology
• Neuropharmacology
• Behavioral neuroscience
• Developmental neuroscience
• Cognitive neuroscience
• Systems neuroscience
• Molecular neuroscience

Divisions of Neuroscience

• Cognitive science includes science writing, epistemology, ethics, legal analysis, political justice, AI and computer science, neuroprosthetics, and neurodevelopment.
• Neuropsychology includes gerontology and neuropsychological disorders.
• Neurobiology includes medicine and sensory biology
• Neuroscience includes neuroanatomy, neurophysiology, neuropharmacology, behavioural neuroscience, developmental neuroscience, cognitive neuroscience, systems neuroscience, and molecular neuroscience

Functions of the Nervous System

• The nervous system is responsible for sending and receiving information.
• It regulates and controls the body, especially the maintenance of body temperature, stable levels of water, salt, and urea, and regulates waste and undigested food levels.
• The nervous system works alongside the endocrine system to regulate and maintain homeostasis.
• The nervous system is the control center for all mental activity, including thought, learning, and memory.

The Central Nervous System (CNS)

• The CNS consists of the brain and spinal cord.
• Its roles include integrating and coordinating incoming and outgoing neural signals.
• It performs higher mental functions.

What is a Neuron?

• Signaling activity of the nervous system is composed of electrical activity within neurons and chemical flow between them.
• Neurons are the structural and functional units of the nervous system, specialized for rapid communication.
• The function of each neuronal component is unique. DNA transcription happens only in the soma (cell body), while protein synthesis (using polysomes and endoplasmic reticulum) takes place in both soma and dendrites.

Structure of a Neuron

• Soma (cell body) is the neuron's life-support center.
• Dendrites receive messages from other cells.
• Axon passes messages away from the cell body to other neurons, muscles, or glands.
• Myelin sheath covers some axons, increasing the speed of neural impulses.
• Axon ending transmits chemical messages.

Synapse

• Neurons communicate at synapses, points of contact between neurons.
• Neurotransmitters are chemical agents released from one neuron to excite or inhibit another neuron.

Neuron Classifications

• Structural: Unipolar, bipolar, multipolar
• Functional: Sensory, motor, associated/interconnected

Neurotransmitters production

• Dopamine is an important neurotransmitter in the motor system.
• Acetylcholine is linked to memory and neuromuscular functions.
• Serotonin is an important distributor for sensory channels in the CNS and in expressing emotions.
• Noradrenaline increases reaction excitability in the CNS and sympathetic neurons.
• Glutamate and GABA are involved in signaling.

Neuroglia

• Neuroglia (glial cells/glia) are non-neuronal cells that support, insulate, and nourish neurons.
• They outnumber neurons by approximately five times.
• In the CNS, neuroglia includes oligodendrocytes, astrocytes, ependymal cells, and microglia.
• In the PNS, neuroglia includes satellite cells and neurolemma (Schwann) cells.
• Glial cells also physically support neurons and regulate the internal environment, especially the fluid surrounding neurons and their synapses. They also supply nutrients and oxygen to neurons; insulates one neuron from the other; destroys pathogens; and remove dead neurons.

What is Brain?

• The brain is the crown jewel of the human body.
• The seat of the central nervous system, encased in the cranium.

External Brain Structure

• The cerebrum has a highly convoluted appearance, consisting of sulci (grooves/depressions) and gyri (ridges/elevations).
• The brain is divided into two anatomically symmetrical hemispheres by the longitudinal fissure, a major sulcus that runs in the median sagittal plane.
• The falx cerebri (a fold of dura mater) descends vertically to fill this fissure.
• The two cerebral hemispheres are connected by a white matter structure called the corpus callosum.

Parts of the Brain

• Cerebrum: involved in touch, vision, hearing, speech, reasoning, emotions, learning, and fine control movements
• Cerebellum: responsible for coordinating muscle movements, posture, and balance.
• Brainstem: acts as a relay center connecting the cerebrum and cerebellum to spinal cord. It regulates breathing, heart rate, body temperature, wake-sleep cycles, and processes such as coughing, sneezing, swallowing, vomiting, and more.

Lobes of the Cerebrum

• Frontal lobe: Involved in motor control, problem-solving, and speech production.
• Temporal lobe: Involved in auditory processing, language comprehension, memory, and retrieval.
• Parietal lobe: Involved in sensation, body posture, speech, language processing, cognition (episodic memory), information processing, touch sensation, and spatial orientation.
• Occipital lobe: Involved in vision processing, integration, and interpretation of visual stimuli.

Lobes of Cerebrum (detailed)

• The cerebrum is the largest part of the brain, located superiorly and anteriorly with respect to the brain stem. it lies within the bony cranium and extends from the frontal bone anteriorly to the occipital bone posteriorly. This structure is divided into lobes. The lateral sulcus differentiates the frontal lobe from the temporal lobe and the temporal from the parietal lobe. The lunate sulcus separates the frontal and parietal from the occipital lobe.
• The main gyri are: precentral gyrus (location of primary motor cortex), postcentral gyrus (location of primary somatosensory cortex), and superior temporal gyrus (involved in reception and processing sounds).

The Cerebellum

• The cerebellum is the "little brain," located posterior to the brainstem, below the occipital lobe and within the posterior cranial fossa. It has a midline area (vermis) that connects the two hemispheres.
• The cerebellum is composed of grey matter that forms the cerebellar cortex and white matter containing four cerebellar nuclei (dentate, emboliform, globose, and fastigial nuclei).
• The cerebellum is subdivided into anatomical lobes (anterior, posterior, and flocculonodular lobes), zones (vermis, intermediate, and lateral), and functional divisions. It regulates muscle tone, coordinates voluntary movement, plans voluntary activity, and maintains balance and control of eye movements.

Cerebellar Peduncles

• Three pairs of peduncles are located above and around the fourth ventricle, connecting the cerebellum to the brain stem.
• The inferior cerebellar peduncle primarily contains fiber systems from the spinal cord (including dorsal and cuneocerebellar tracts)
• The middle cerebellar peduncle contains inputs from the contralateral pontine nuclei.
• The superior cerebellar peduncle predominantly includes efferent fibers, transmitting signals to the thalamus and red nuclei.

Cerebellar Cortex Layers

• The cerebellar cortex has three layers: the molecular layer, Purkinje cell layer, and granular layer.
• Granule cells are excitatory neurons located within the granular layer, responsible for sending axons to the molecular layer where they bifurcate into parallel fibers, forming excitatory synapses with Purkinje cells. Glutamate is the neurotransmitter at these synapses.
• Brush cells, located within the granular layer, possess a single dendrite. They synapse with mossy fibers.

Purkinje Cells

• They are the primary output neurons from the cerebellar cortex–located in the Purkinje cell layer.
• Their axons project to the deep cerebellar nuclei (especially the dentate nucleus) forming inhibitory synapses.

Cerebellar Vasculature

• The cerebellum receives its blood supply from three paired arteries: superior cerebellar artery (SCA), anterior inferior cerebellar artery (AICA), and posterior inferior cerebellar artery (PICA).

Cerebellar Dysfunction

• Dysfunction can present in a wide range of symptoms and signs. The causes vary—stroke, physical trauma, tumors, and aging are most common.
• The clinical picture differs depending on which functional area of the cerebellum is affected. Cerebrocerebellar and spinocerebellar damage manifest with problems of skilled and planned movement, as well as motor learning. Symptoms include ataxia, dysarthria, and scanning speech dysmetria.

Brain Stem

• The brainstem is the most inferior portion of the brain, adjoining the spinal cord.
• It's a tube-shaped mass of nervous tissue, located under the cerebrum and is about 3 inches long and thick as a thumb.
• Situated in the posterior cranial fossa.
• It's crucial for communicating with the periphery.
• It contains nerve connections from motor and sensory systems of the cortex allowing them to communicate with the peripheral nervous system
• Includes the midbrain, pons, and medulla oblongata.

Functions of Brain Stem

• Pathways between cerebral cortex and spinal cord
• Site for origin of cranial nerves III–XII.
• Nuclei and related fibers (reticular formation) responsible for consciousness, pain perception, and regulation of cardiovascular and respiratory systems.

Basal Ganglia

• A group of subcortical nuclei in the forebrain, acting as a unified functional unit.
• Consists of the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra.
• Key role in action selection and execution of behaviors at a given moment.
• They are also responsible for regulating voluntary movements.

Basal Ganglia "Circuitry"

• A system including cortex, striatum (caudate & putamen), globus pallidus (internal segment and external segment), subthalamic nucleus, and substantia nigra.
• The input from the cortex to the striatum; output of GABA from GPi and SNc to the thalamus; and the thalamic output to the cortex (are part of the circuitry).

Basal Ganglia Input

• Inputs from the parietal cortex (primary and secondary somatosensory/secondary visual information), temporal cortex (secondary visual and auditory information), cingulate cortex (limbic and emotional status information), frontal cortex (primary and secondary motor information), and prefrontal cortex.

Neurotransmitters of Basal Ganglia

• Dopamine pathway (substantia nigra to caudate nucleus and putamen)
• GABA pathway (caudate nucleus + putamen to globus pallidus, and globus pallidus to substantia nigra)
• Acetylcholine pathway (cortex to caudate nucleus to putamen)
• Glutamate pathway (involved in excitatory signals balancing out the inhibitory signals)
• Dopamine modulates excitatory/inhibitory effects of the caudate/putamen pathway via D₁) and D₂) receptors (respectively).

Functional Neural Circuits

• Corpus striatum does not directly connect to spinal cord but acts as a lateral and medial part of the single functional unit (GPi & SNpr).

Functions of Basal Ganglia

• Control of voluntary motor activity-
• Control of reflex muscular activity
• Control of muscle tone.
• Role in arousal mechanism.

Disorders of Basal Ganglia

• Parkinson's disease
• Huntington's disease
• Chorea
• Athetosis
• Hemiballism
• Wilson's disease

Parkinson's Disease

• A disorder affecting movement, with symptoms including paralysis agitans (shaking palsy).
• Symptoms include tremors, rigidity, and bradykinesia.
• Aetiology: The pathogenesis of the disorder involves imbalances in excitation and inhibition. Loss of dopamine in the putamen leads to increased inhibition of the Globus Pallidus, which causes a decreased inhibitory output from the subthalamic nucleus (STN), Increasing excitatory output from Globus Pallidus to the thalamus and reducing the excitatory drive to the cerebral cortex.

Extrapyramidal Side Effects

• Bradykinesia, as part of the extrapyramidal side effects of Parkinson's Disease, is a slowing or absence of voluntary movement
• Other side effects include rigidity and tremors.

Movement and Tracts

• Movement (motion) is a fundamental and essential property of animal life.
• The human motor system is a complex neuromuscular network.
• Reflexes are controlled at the spinal or higher level.
• Stereotypic repetitive movements (walking or swimming) are governed by neural networks (Central Pattern Generators).
• Specific goal-directed movements are initiated at the level of the cerebral cortex.

Tracts

• A tract is a collection of nerve fibers within the central nervous system that connect two masses of gray matter having the same origin, course, and termination.
• Fiber bundles having a common function are called tracts.
• Tracts may be ascending (e.g., dorsal-column-medial lemniscal pathway,) or descending (e.g., corticospinal tracts).
• Tracts are usually named after the masses of gray matter connected by them.

Types of Tracts

• "Spino-" (e.g., spinocerebellar, spinothalamic) indicates a sensory tract that delivers information from the spinal cord.
• "Spinal" (e.g., vestibulospinal) indicates a motor tract that delivers information to the spinal cord from the vestibular apparatus.

Ascending Tracts

• Fasciculus gracilis
• Fasciculus cuneatus
• Dorsal spinocerebellar Tract
• Lateral spinothalamic Tract
• Ventral spinocerebellar Tract
• Spinospinal Tract
• Spino-tectal and Spino-olivary
• Anterior spinothalamic tract

Descending Tracts

• Lateral corticospinal tract,
• Rubrospinal tract,
• Olivospinal tract,
• Lateral reticulospinal tract,
• Vestibulospinal tract,
• Medial reticulospinal tract
• Tectospinal tract
• Ventral corticospinal tract

Tract Neuronal Order

• 1st-order neuron: Sensory impulses from receptors in the skin, muscles, or tendons are transmitted to the spinal cord or brain stem, where they synapse with 2nd-order neurons. The cell bodies of these neurons reside in ganglia (dorsal root or cranial).
• 2nd-order neuron: Impulses are carried to higher levels (brain stem); in most tracts, the 2nd-order neurons synapse to the third-order neurons, which are located in the thalamus.
• 3rd-order neuron: The sensory signals are sent from the thalamus to the cerebral cortex.

Motor Commands Delivery

• Somatic nervous system (SNS): directs skeletal muscle contraction.
• Autonomic nervous system (ANS): directs activity of glands and smooth/cardiac muscles.

Pyramidal Tracts

• The pyramidal tracts originate from the cerebral cortex and travel through the medulla oblongata.
• They are responsible for voluntary movements in the body and face.
• Functionally, the pyramidal tract can be subdivided into two:
• Corticospinal tracts
• Corticobulbar tracts

Extrapyramidal Tracts

• The extrapyramidal tracts originate from the brainstem and travel through the spinal cord.
• They are responsible for the involuntary and automatic control of all musculature (muscle tone, balance, posture, locomotion)

Vestibulospinal Tracts

• Two pathways (medial and lateral) arise from vestibular nuclei (receiving input from balance organs).
• Convey balance information to the spinal cord (ipsilateral).
• Control balance and posture (innervating anti-gravity muscles).

Reticulospinal Tracts

• Two pathways (medial and lateral) arise from the reticular formation of the pons and medulla.
• Medial: Facilitates voluntary movements and increases muscle tone.
• Lateral: Inhibits voluntary movements and reduces muscle tone.

Rubrospinal Tracts

• Originates from the red nucleus in the midbrain.
• Decussates (crosses to the opposite side of the CNS) before descending into the spinal cord.
• Primarily controls movement of the upper extremities (hand movements).

Tectospinal Tracts

• Originates from the superior colliculi of the midbrain.
• Receives input from the optic nerves.
• Coordinates head movements in response to visual stimuli.

Ascending Tracts

• Pathways carrying sensory information from peripheral nerves to the cerebral cortex.
• Concious tracts: Include the dorsal column-medial lemniscal pathway and the anterolateral system
• Unconcious tracts: Include the spinocerebellar tracts

The Anterolateral System

• Consists of the anterior spinothalamic tract (crude touch and pressure) and the lateral spinothalamic tract (pain and temperature). Impulses are transmitted from the spinal cord to the thalamus.

The Spinocerebellar Tracts

• Carries sensory information in four pathways about the position and movement of the body and limbs from the spinal cord to the dorsal and ventral parts of the cerebellum.
• The paths are the posterior spinocerebellar tract, cuneocerebellar tract, anterior spinocerebellar tract and the rostral spinocerebellar tract.

Meningeal Structures of the Brain and Spinal Cord

• Dura mater: The outermost meningeal layer. It forms thick, dense folds called septa, which subdivide the cranial cavity into different compartments. These extensions are called dural reflections. Folds include the falx cerebri, tentorium cerebelli, and sellar diaphragm.
• A blow to the head may detach the periosteal layer of the dura from the calvaria without fracturing the skull bones.
• Arachnoid mater: The middle layer of the meninges. Delicate and loosely attached, it forms a system of delicate trabeculae that attaches it to the dura mater, forming the subarachnoid space. Arachnoid granulations project into dural venous sinuses to drain CSF .
• Pia mater: The innermost layer. A delicate membrane, it adheres closely to the surface of the brain, and extends into the sulci. There are also blood vessels in the outer layer of pia that supply the brain.
• Cerebrospinal fluid (CSF): A clear, colorless fluid that fills ventricles and the subarachnoid space. Acts as a shock absorber. CSF is obtained via lumbar puncture. CSF is secreted by choroid plexus, and drained via arachnoid villi.
• Cisterns: CSF-filled spaces in the subarachnoid space, including the cerebellomedullary cistern.

Clinical Correlates to Brain / Spinal Cord Structures

The pathologies of various neurological structures can cause: cranial nerve dysfunction, altered sensation, muscle weakness, vertigo, coordination problems, difficulties with swallowing and speech, and/or changes in voice. 

Cerebrovascular Disease/Stroke

• Results from vascular compromise or haemorrhage.
• One of the most common causes of neurological disability and third most common cause of death in industrialized societies.

Blood Supply of the Brain

• About 18% of the total blood volume in the body circulates in the brain (about 2% of body weight).
• Loss of consciousness will occur in less than 15 seconds after blood flow to the brain is stopped, and irreparable damage to the brain tissue will occur in 5 minutes.

Test your understanding of the anatomy and functions of the cerebellum and basal ganglia. This quiz covers key concepts such as the anatomical lobes, functional areas, and the roles of various nuclei. Challenge your knowledge and learn more about these critical components of the brain.