Anatomy of the Basal Ganglia Flashcards
What are the basal ganglia?
large interconnected nuclear masses (grey matter) located deep within:
1. Cerebral hemispheres
2. Diencephalon
3. Mid brain
What is the function of basal ganglia?
They play an important role in the control of posture and voluntary movement
Abnormalities of the basal ganglia result in what conditions?
- Parkinson’s disease
- Huntington disease
Name the group of nuclei of the basal ganglia?
- Corpus striatum (in the cerebral hemispheres)
- Subthalamic nucleus (in the Diencephalon)
- Substantia nigra (in the Mid brain)
Describe the structure of the corpus striatum?
Subdivided by internal capsule into two nuclei:
1. Caudate nucleus – in the wall of lateral ventricles
2. Lentiform nucleus
Describe the caudate nucleus?
- Large C-shaped or comma-shaped mass of grey matter.
- Lies in close relation to lateral ventricle.
- It has a Head, Body, and Tail
Describe the parts of the caudate nucleus?
- Head :(Anterior) Large, & rounded and forms the lateral wall of anterior horn of lateral ventricle.
- It is continuous inferiorly with putamen of lentiform Nucleus. - Body : Long & narrow continuous with head at the interventricular foramen
- It forms part of the floor of body of lateral ventricle. - Tail : Long & narrow, and lies in the roof of inferior horn of lateral ventricle.
- It is connected anteriorly with Amygdaloid nucleus
Describe the lentiform nucleus?
- wedge shaped/ lens shaped
- It is a mass of grey matter wedge-shaped or (biconvex lens).
- It has 2 capsules, external capsule laterally & internal capsule medially.
> Internal capsule separates between lentiform nucleus laterally & caudate nucleus and thalamus medially.
> External capsule separates between lentiform nucleus and Claustrum. - Inferiorly putamen is continuous with the head of caudate nucleus
Name and describe the segments of the lentiform nucleus?
- The Putamen - Larger darker lateral portion. located laterally between external capsule and globus pallidus
- The Globus pallidus – Smaller, lighter medial portion: located btween putamen and internal capsule.
- Further subdivided into :
> Lateral segment (outer)
> Medial segment (inner)
What is the amygdaloid nucleus?
- Almond-shaped small mass of grey matter lies in temporal lobe close to the Uncus.
- Lies Anterosuperior to inferior horn of lateral ventricle.
- It is connected to the tail of caudate nucleus.
- It is the smell center & part of limbic system
What is the claustrum?
Thin sheet of gray matter which lies lateral to external capsule & medial to the Insula
What is the subthalamic nucleus?
- Large nucleus in the subthalamus
- Located ventral to the thalamus
- Wedge shaped division of the diencephalon
Name the 3 nuclei contained in the subthalamic nucleus?
- Zona incerta- dorsolaterally
- Prerubral field –dorso medially
- Subthalamic nucleus - ventrally
What is the sustantia nigra?
Largest nucleus in the midbrain
What are the 2 parts of the sustantia nigra?
- Compact part – dorsal
- Contains neurones filled with melanin (dopaminergic neurons) - Reticular part - ventrally
Describe the function of the substantia nigra?
produces dopamine
> control of movement via the signals it sends to the striatum
> enables precision movement
The basal ganglia links with?
- thalamus
- cerebral cortex
Connections of the basal ganglia are divided into?
- Input from sources outside basal ganglia
- Interconnections between nuclear masses within the basal ganglia.
- Output connections from basal ganglia to other parts of the brain.
Describe the afferent fibers (input) of the corpus striatum?
I- Corticostriate Fibers: From all parts of cerebral cortex (mostly from sensory- motor cortex) axons pass to caudate nucleus and putamen.
Glutamate is the neurotransmitter of this fibers.
II-Thalamostriate Fibers : From intralaminar nuclei of thalamus axons pass to caudate nucleus and putamen.
III- Nigrostriate Fibers : Axons from Substantia nigra of midbrain pass to caudate nucleus and putamen.
Neurotransmitter is Dopamine.
IV_Brain stem Strial Fibers : Ascending fibers from brain stem end in caudate nucleus & putamen.
Serotonin is the neurotransmitter.
It is believed that the last 2 groups are inhibitory in function
Name the efferent (output) fibers of the corpus striatum?
1-Striatopallidal fibers:
These fibers pass from corpus striatum (caudate nucleus & putamen) to globus pallidus.
Gamma-aminobutyric acid (GABA) is the neurotransmitter.
2-Striatonigral fibers:
These fibers pass from caudate nucleus & putamen to Substantia nigra.
Some fibers use GABA as a neurotransmitter, and others use Substance P.
Describe the functions of the basal ganglia?
- Design of plans, which convert thoughts and ideas into motor actions
> to produce a coordinated organized purposeful movement e.g. dressing. - Determining the timing and scale of movement
> to what extent the movement will be fast, and how long it will last. - Storage of motor programs of familiar motor actions
e.g. signature
Describe the consequences of a lesion of the basal ganglia?
- Involuntary movement during rest
Chorea, athetosis, hemiballismus, and tremor. - Changes in muscle tone.
A- Chorea: (Dance). Lesion: in caudate N
> Features:
- Involuntary, quick, Jerky, irregular, nonrepetitive and purposeless movement
e.g. Swift grimaces, and sudden movement of head or limb.
What is huntingtons disease?
deterioration of brain tissue usually begins age 30to 40
- no cure but have medications to cope with symptoms
- people usually die 15-20 years after onset of degeneration
- autosomal, dominant
Describe the pathology of huntingtons chorea?
- degenration of cerebral cortex and the basal ganglia
- loss of GABAergic neurons in the striatum
- severe striata; atrophy with resulting enlargement of ventricles
Describe the clinical presentation of huntingtons chorea?
- twitching movements of head
- grimacing movements in face, lips and tongue
- gesticulating movements in distal parts of upper limbs
- jerking movements in distal parts of lower limbs
Describe athetosis?
(Greek= Not fixed).
Lesion: Putamen & Globus pallidus.
Features: Involuntary, slow, sinuous, writhing movements involving distal part of limb (hand).
Describe Hemiballismus?
(Greek= Jumping)
Lesion: Subthalamus
Features: Sudden, involuntary, spasmodic movements that involves one limb or one side of the body (Limb suddenly flies about in all directions out of control)
Describe parkinsonism?
Lesion: Neuronal degeneration in substantia nigra leading to reduction of dopamine within corpus striatum
Describe the pathophysiology of Parkinsons disease?
- loss of dopaminergic input to striatum
- degeneration of neurons in substantia nigra pars compacta
- disrupted signalling betweem basal ganglia, cortex and thalamus
What are the features of Parkinsonism?
1- Tremors: Pill-rolling, involuntary, rhythmic, oscillating movements. It occurs during waking time during rest, it is called static tremors.
2- Rigidity: It occurs in both flexors, and extensors, but more in flexors giving flexion attitude.
> It is called lead pipe rigidity.
3- Akinesia: it means lack of movement; Absence of swinging arm during walking, mask face, low- volume slow monotonous speech, and shuffling gait
Types of chorea?
- Sydenham (rheumatic fiver) more in female
- Huntington’s, (hereditary), chorea Gravidarum, or chorea of contraceptive pills.
