Basal Ganglia Anatomy and Functions
Delve into the intricate anatomy of the basal ganglia, its nuclei, functions, and associated structures. Learn about the caudate nucleus, lentiform nucleus (globus pallidus and putamen), substantia nigra, and subthalamic nucleus. Explore how these components interconnect and contribute to motor control and cognitive processes.
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Presentation Transcript
Basal ganglia SPP4
objectives 01 Part of Basel ganglia. 02 Functions of Basel ganglia. 03 Blood supply of Basel ganglia. Connection of afferent and efferent of Basel ganglia. 04 Lesion of Basel ganglia
Nuclei of the Basal Ganglia The anatomy of the basal ganglia is complex since it is spread throughout the forebrain. Its components can be divided into input nuclei, output nuclei and intrinsic nuclei. Input nuclei receive in formation, which is then relayed to intrinsic nuclei for processing, and further passed to output nuclei Input Nuclei Output Nuclei Intrinsic Nuclei External globus pallidus Subthalamic nucleus Pars compacta of the s ubstantia nigra Caudate nucleus an d putamen (neostriat um) Internal globus pallidus Pars reticulata of the su bstantia nigra 01 02 03
Caudate Nucleus The caudate nucleus forms the lateral wall of the lateral ventricle and follo ws the telencephalic expansion during development. It has a characteristic ventricular C-shape when fully developed. It can be identified as the collection of gray matter on the wall of the lateral ventricles. During development, the caudate nucleus is separated from the putamen by descending white matter fibres, which at this level are known as internal capsule
Lentiform Nucleus (Globus Pallidu s and Putamen) The lentiform nucleus is comprised of globus pallidus and the putamen. Althou gh anatomically related, they share no functional relationship. It can be identifie d as a collection of gray matter laying de ep within the hemispheres. The putamen forms the lateral aspect of the lentiform nucleus. On its concave inn er surface lies the most exterior of the globus pallidus, the GPe, and the most internal structure is the GPi. The putame n is separated from the GPe by the lateral medullary lamina, and the medial medullary lamina separates the GPe from the GPi
Substantia Nigra The substantia nigra is conspicuous in gross specimens an d can be seen in cuts through the midbrain, having a dark a ppearance due to the neuromelanin present in the cells of th e SNc.
Subthalamic Nucleus The subthalamic nucleus, as the name implies, lies inferior to the thalamus, and right above the substantia nigra
Functions 01 Control of muscle tone. Control of motor activity. 02 03 Control of automatic associated movement Role in Arousalmechanism. 04 Role of neurotransmitter in the functions of basal ganglia
Control of Muscle Tone Caudate nucleus increases the muscle tone Mechanism: by stimulating the facilitatory reticular formation (gamma), the vestibular & inferior olivary nuclei (alpha). The lentiform nucleus decreases the muscle tone Mechanism: by decreasing the activity of the alpha neurons through: Inhibition of the primary motor cortex (i. e. area 4), vestibular nucleus. Inhibiting the facilitatory reticular for mation inhibition of Gamma. Stimulating the inhibitory reticular forma tion (gamma) & red nucleus (alpha). Generally it is inhibitory to the muscle tone
Control of MotorActivity Regulation of voluntary movement Control complex patterns of motor activity e.g. writinga. Skilled movements performed subconscious ly e.g. cutting paper with scissors, hammerin g nails. Control timing and intensity Cognitive control of motor activity Cognition = thinking process using sensory + memory stored. (i.e. converting thoughts into motor actions).
3. Control of automatic associated movement. As a part of the extrapyramidal system, the BG initiate subconscious automatic movements (e.g. swinging of the arms during walking) and produce postural adjustments that maintain equilibrium.
Blood supply Blood supply of the basal ganglia is provided via three arteries, anterior choroidal, middle cerebral and anterior cerebral. The caudate nucleus with its extended gray mass is C-shaped with a head, that is continual with the putamen, a body and a tail.
Striatum receives afferent inputs from motor and prem otor areas of cerebral cortex. From striatum impulses, efferent impulses reach pars reticulata of substantia ni gra. Efferent impulses from striatum also reach globus pallidus. Basel ganglia: i. Striatum to substantia nigra striatonigral pathway. ii. Striatum to globus pallidus striatopallidal pathway. its closed circuit of connection. There is a lot of mutual influence between various nuclei of basal ganglia. From pars compacta region, efferent connection going to striatum is known as nigrostriatal pathway. The neur otransmitter released by this pathway is dopamine. Fr om globus pallidus, impulses go to subthalamic nucleu s. Impulses will also come back to globus pallidus (effe rent) from subthalamic nucleus. Also, efferent impulse s from subthalamic nucleus will reach pars reticulata of substantia nigra.
From globus pallidus, impulses (efferent) come to centromedian, ventroanterior and ventrolateral nuclei of thalamus. From centro median nucleus, efferent impulses reach striatum. From ventrola teral, ventroanterior and centromedian nuclei impulses are relay ed back to motor and pre-motor areas of cerebral cortex. So wh ole of basal ganglia connection is like a closed loop.
Chorea Definition : sudden spontaneous purposeless involuntary dancing m ovements (jerky with short duration) affect all muscles EXCEPT exte rnal ocular muscle. Lesion : in caudate nucleus ( degeneration of neurons in caudate nu cleus and putamen that secret GABA i.e inhibitory transmitter). Causes of chorea : 1- Rheumatic fever( in children) 2- Toxemia of pregnancy 3- Gene defect (Huntington s disease)
Parkinsons disease Site of lesion : in substantia nigra mostly due to depletion of dopa mine secretion from nigro-striate fibers. Manifestations of Parkinsonism : (1)Rigidity: stuffiness in muscles during movement Flexor (ghorilla like) attitude. Cog-wheel rigidity or lead pipe rigidity. (2) Tremors : rhythmic alternating contraction of opposing muscle groups Static. Mainly in distal joints.
Akinesia Its loss of subconscious associated movement. Mask ( expressioniess ) face Slow, low and monotonus speech. Shuffling (festinating) gait. False paralysis ( paralysis agitans) Intolerance to cold
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