Session 4 - Basal Ganglia And Internal Capsule Flashcards
WHAT ARE THE BASAL GANGLIA?
The basal ganglia are a group of deep nuclei of the brain that contribute to the coordination, control and inhibition of motor function. There are five main named parts to the basal ganglia, and they are spread throughout the cerebrum, diencephalon, and midbrain. They are located close to the thalamus. Very complex excitatory and inhibitory pathways exist between each nucleus of the basal ganglia, but these pathways will not be covered in detail here. There is a left and right nucleus for each part of the basal ganglia.
What is included in the basal ganglia?
- Caudate nucleus – a c-shaped structure that rests immediately lateral to, and follows the curvature of, the lateral ventricle.
- Globus pallidus – a triangular-shaped nucleus that can be divided into an internal and external part.
- Putamen – an oval-shaped nucleus found immediately lateral to the globus pallidus.
- Substantia nigra – a black nucleus found in the midbrain. Notable for producing dopamine.
- Subthalamic nucleus – a small nucleus, located inferior to the thalamus, but superior to the substantia nigra.
What are teh grps of molecules in the bg?
ome of the parts of the basal ganglia are grouped together due to the similarity in their functions:
• Lentiform nucleus – putamen and globus pallidus.
• Striatum – caudate nucleus and putamen.
• Corpus Striatum – caudate nucleus and lentiform nucleus.
What structures lie close to the BG?
Certain additional structures are located very close to the basal ganglia and are anatomically considered to be part of it. However, these structures are not involved in the motor control function of the basal ganglia and contribute to functions of the limbic system instead:
• Nucleus accumbens – located at the anterior junction between the caudate nucleus and putamen, this nucleus plays a role in reward systems and is a subject of research into addiction.
• Amygdala - a small, spherical nucleus at the tip of the inferior horn of the caudate nucleus. It is involved in memory and emotional responses such as fear and anxiety.
What is the internal capsule?
Amongst the basal ganglia, between the globus pallidus and putamen and the thalamus, is a bundle of white matter tracts known as the internal capsule. This very important structure forms part of the route of the majority of sensory and motor axons travelling to and from the cortex. The fibres within the internal capsule are examples of projection fibres, as they connect the cortex to deeper structures. Damage to the internal capsule (for example, from a stroke) can cause significant contralateral motor and sensory dysfunction.
The axons that pass from the internal capsule to the cortex form the corona radiata. These fibres are shaped such that they ‘radiate’ out of the internal capsule towards the cortex.
What is PD?
Parkinson’s Disease
Parkinson’s disease is caused by degeneration of the dopamine-producing neurones of the substantia nigra. This leads to a reduction in the passage of impulses within the basal ganglia which impairs the initiation and inhibition of movement. The most characteristic symptom is a ‘pill-rolling’ resting tremor. Other symptoms include a shuffling gait with small steps which is difficult to initiate and difficult to stop, ‘cogwheel’ rigidity best seen in the upper limb muscles, micrographia (very small handwriting) and a ‘mask-like’ loss of facial expression. Dopamine can be replaced with an oral precursor drug called levodopa which can temporarily reduce the severity the symptoms
What is HD?
Huntington’s disease (or Huntington’s chorea) is an autosomal-dominant genetic disorder that leads to gradual damage to cells in various places within the brain. Symptoms include mood and personality changes, cognitive impairment, and motor dysfunction. Within the basal ganglia, Huntington’s disease mainly affects the striatum, and this leads to the characteristic movement disorder known as ‘chorea’. Chorea involves sudden, jerky and uncontrollable movements of the face, arms and legs.
