Development

• Ectoderm differentiates into neuroectoderm to create the neural plate.
• Edges of the neural plate fold and fuse → neural tube
• 3 primary vesicles develop:
  • Prosencephalon
  • Mesencephalon
  • Rhombencephalon
• Prosencephalon develops into 2 secondary vesicles:
  • Telencephalon
  • Diencephalon
• Telencephalon eventually forms several major brain structures, including the basal ganglia.

General Features

Definition

The basal ganglia are a cluster of subcortical nuclei deep to cerebral hemispheres and are involved in the initiation, maintenance, and inhibition of movement.

Major structures

The striatum is composed of:

• Caudate nucleus:
  • An elongated, C-shaped structure
  • Divided into head, body, and tail, which do not have distinct boundaries from each other
  • Runs adjacent to the lateral ventricle
  • The pear-shaped head is continuous with the putamen.
  • The caudate tail tapers and terminates near the amygdala in the temporal lobe.
• Putamen:
  • Large nucleus forming the lateral portion of the basal ganglia
  • Anteriorly and ventrally, the putamen fuses with the head of the caudate.

The lenticular nucleus is made up of:

• Globus pallidus (GP):
  • Smaller triangular structure consisting of numerous myelinated fibers
  • Has a GP internal segment (GPi) and GP external segment (GPe)
  • Both regions acquire inputs from the putamen and caudate and communicate with the subthalamic nucleus.
• Putamen:
  • Larger convex gray mass
  • Lies lateral and inferior to the insular cortex

Substantia nigra:

• Has a ventral portion called the substantia nigra pars reticulata
• The more dorsal substantia nigra pars compacta contains the darkly pigmented dopaminergic neurons.
• Degeneration of the dopaminergic neurons is an important pathogenic mechanism in Parkinson disease.

Subthalamic nucleus:

• Under the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus lies the spindle- or cigar-shaped subthalamic nucleus.
• Unlike the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus, the subthalamic nucleus is derived embryologically from the midbrain rather than the forebrain.

Functions

• Significant role in controlling posture and voluntary movement through connections to the:
  • Thalamus
  • Cerebral cortex
  • Basal nuclei
• Has connections to limbic system Limbic system The limbic system is a neuronal network that mediates emotion and motivation, while also playing a role in learning and memory. The extended neural network is vital to numerous basic psychological functions and plays an invaluable role in processing and responding to environmental stimuli. Limbic System pathways, which govern the expression of various behaviors and motivational states
• Plays a major role in making decisions
• Plays a role in controlling eye movements

Vasculature

• Main arterial supply: lenticulostriate arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • Perforating arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • Arise from:
    • Anterior cerebral artery
    • Middle cerebral artery
  • Contain:
    • Lateral lenticulostriate arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Medial lenticulostriate arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • Note: The medial striate artery (recurrent artery of Heubner) is often the only angiographically visible artery of this group.
• Venous drainage: striate branches → internal cerebral and basal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins → great cerebral vein

Neural Pathways and Intrinsic Relations

Pathways

• Direct (excitatory): striatum → GPi → thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus → cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex → feedback to the striatum
• Indirect (inhibitory): striatum → GPe → subthalamic nucleus → GPi → thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus → cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex → feedback to the striatum
• Nigrostriatal:
  • Substantia nigra → striatum
  • Directly modulates both the direct and indirect pathways

Intrinsic relations

• Inhibitory (GABAergic):
  • Striatopallidal
  • Striatonigral
  • GPe is inhibitory to the subthalamus.
• Excitatory:
  • Subthalamic output (glutamatergic)
  • Nigrostriatal (dopaminergic)

Clinical Relevance

• Parkinson disease: a degenerative disease of the basal ganglia characterized by a clinical syndrome manifesting with diminished facial expression, bradykinesia, festinating gait (progressively shortened and accelerated steps), cogwheel rigidity, and a “pill-rolling” tremor at rest. The finding of Lewy bodies in the brain postmortem is the only confirmation for the disease. Treatment includes supportive physical and emotional care plus medications such as levodopa/carbidopa, monoamine oxidase type B inhibitors, and dopamine agonists.
• Huntington disease Huntington disease Huntington disease (HD) is a progressive neurodegenerative disorder with an autosomal dominant mode of inheritance and poor prognosis. It is caused by cytosine-adenine-guanine (CAG) trinucleotide repeats in the huntingtin gene (HTT). The most common clinical presentation in adulthood is a movement disorder known as chorea: abrupt, involuntary movements of the face, trunk, and limbs. Huntington Disease: a progressive neurodegenerative disorder with an autosomal dominant Autosomal dominant Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Autosomal Recessive and Autosomal Dominant Inheritance mode of inheritance and poor prognosis. The most common clinical presentation in adulthood is chorea, characterized by abrupt, involuntary movements of the face, trunk, and limbs. Diagnosis is primarily clinical, often with a positive family history, and is followed by genetic confirmation. Management is supportive with the goal of maintaining the quality of life.
• Hemiballismus: unilateral, hyperkinetic, involuntary movements of the ipsilateral arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm and/or leg Leg The lower leg, or just "leg" in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg. Hemiballismus is usually caused by damage to the contralateral subthalamic nucleus. Causes can also include an ischemic infarct, traumatic brain injury, neoplasm, or vascular malformation. Antipsychotics or deep brain stimulation can be used to treat severe symptoms, although hemiballismus is usually a self-limiting condition.
• Tourette syndrome Tourette Syndrome Tics and related diseases represent a set of neurobehavioral disorders of childhood that are characterized by sudden, repeated, nonrhythmic, stereotyped muscle movements sometimes accompanied by sounds or vocalizations. Tourette syndrome is a severe form with symptoms lasting more than 1 year and involving both motor and vocal tics. Tics and Tourette Syndrome: a disorder characterized by at least 1 motor and vocal tic. Tourette syndrome Tourette Syndrome Tics and related diseases represent a set of neurobehavioral disorders of childhood that are characterized by sudden, repeated, nonrhythmic, stereotyped muscle movements sometimes accompanied by sounds or vocalizations. Tourette syndrome is a severe form with symptoms lasting more than 1 year and involving both motor and vocal tics. Tics and Tourette Syndrome is potentially related to disinhibition of the limbic and motor systems due to disruption of the cortico-striatal-thalamic-cortical (mesolimbic) circuit. Tourette syndrome Tourette Syndrome Tics and related diseases represent a set of neurobehavioral disorders of childhood that are characterized by sudden, repeated, nonrhythmic, stereotyped muscle movements sometimes accompanied by sounds or vocalizations. Tourette syndrome is a severe form with symptoms lasting more than 1 year and involving both motor and vocal tics. Tics and Tourette Syndrome is clinically diagnosed and the treatment involves behavioral therapy, antipsychotics, and treatment of comorbid conditions.
• Athetosis: a condition characterized by writhing and twisting movements of the limbs, face, and trunk. Important causes include perinatal hypoxia involving the basal ganglia, kernicterus caused by severe neonatal jaundice Jaundice Jaundice is the abnormal yellowing of the skin and/or sclera caused by the accumulation of bilirubin. Hyperbilirubinemia is caused by either an increase in bilirubin production or a decrease in the hepatic uptake, conjugation, or excretion of bilirubin. Jaundice, Wilson disease, ataxia-telangiectasia Ataxia-telangiectasia Ataxia-telangiectasia, also known as Louis-Bar syndrome, is a neurocutaneous syndrome, which involves multiple systems but mainly affects the neurological system. Ataxia-telangiectasia is an autosomal recessive genetic disorder caused by a mutation in the ATM gene (ATM serine/threonine kinase or the ataxia-telangiectasia mutated gene). Ataxia-telangiectasia, Huntington disease Huntington disease Huntington disease (HD) is a progressive neurodegenerative disorder with an autosomal dominant mode of inheritance and poor prognosis. It is caused by cytosine-adenine-guanine (CAG) trinucleotide repeats in the huntingtin gene (HTT). The most common clinical presentation in adulthood is a movement disorder known as chorea: abrupt, involuntary movements of the face, trunk, and limbs. Huntington Disease, and the use of antipsychotic Antipsychotic Antipsychotics, also called neuroleptics, are used to treat psychotic disorders and alleviate agitation, mania, and aggression. Antipsychotics are notable for their use in treating schizophrenia and bipolar disorder and are divided into 1st-generation antipsychotics (FGAs) and atypical or 2nd-generation antipsychotics. First-Generation Antipsychotics or antiemetic medications.
• Dystonia Dystonia Dystonia is a hyperkinetic movement disorder characterized by the involuntary contraction of muscles, resulting in abnormal postures or twisting and repetitive movements. Dystonia can present in various ways as may affect many different skeletal muscle groups. Dystonia: abnormal, involuntary muscle contractions that cause postural distortions. Dystonia Dystonia Dystonia is a hyperkinetic movement disorder characterized by the involuntary contraction of muscles, resulting in abnormal postures or twisting and repetitive movements. Dystonia can present in various ways as may affect many different skeletal muscle groups. Dystonia can be generalized, unilateral, or focal. Focal dystonias include torticollis, which involves the neck muscles; blepharospasm, which involves the facial muscles around the eyes; spasmodic dysphonia, which involves the laryngeal muscles; and writer’s cramp. Dystonia Dystonia Dystonia is a hyperkinetic movement disorder characterized by the involuntary contraction of muscles, resulting in abnormal postures or twisting and repetitive movements. Dystonia can present in various ways as may affect many different skeletal muscle groups. Dystonia is presumed to be caused by basal ganglia dysfunction, although usually no focal lesion is found.