EXTRAPYRAMIDAL DISORDERS Flashcards
Function of the basal ganglia?
It’s like a collection of brakes or accelerators
To fine-tune voluntary movements
It recieves impulses fron the cerebral cortex, processes them and adjusts them and then covey this infromation to the thalamus and then back to the cortex
Ultimately the fine-tuned movement instruction is sent to skeletal muscles via the spinal cord
Also involves in planning, modulation of movements, memory, eye movements, reward processing and motivation
Components of the basal ganglia?
Caudate nucleus
Putamen
Nucleus accumbens and olfactory tubercle
Globus pallidus
Subthalamic nucleus
Substantia nigra
Which part of the striatum is part of the basal ganglia?
The dorsal striatum
What are the 2 components of the striatum?
The caudate nucleus and the putamen
What forms the corpus striatum?
The striatum and the globus pallidus
Input nuclei of the basal ganglia?
The striatum and the caudate nucleus
What is the nucleus accumbens?
The most cranial aspect of the striatum where the caudate nucleus and the putamen join together
Function of striatum?
It recieve excitatory glutamatergic inputs from the cerebral cortex.
The synapsing pattern reflects topography of the cortex e.g. caudal parts of the cortex project to the caudal part of the brain the striatum
Structure of the caudate nucleus?
Consists of a head, tail and the body
Terminates by connecting with the amygdala at the tail of the caudate nucleus
Function of the caudate nucleus?
Integrates sensory information about the spatial position of the body and according to that sends infromation about necessary fine tunes of motor response to that stimuli to the thalamus
Also contributes to body & limb posture and speed &accurary of directed movements
Intrinsic nuclei of the basal ganglia?
External globus pallidus
Subthalamic nuclei
Pars compacta of the substantia nigra
Output nuclei of the basal ganglia?
Internal globus pallidus
Pars reticulata of the substantia nigra
Function of putamen?
To regulate motor functions and influence various types of learning
It uses dopamine
What are the 2 divisions of the globus pallidus?
The internal globus pallidus and the external globus pallidus
What are the 2 components of the substantia nigra?
The pars compacta and the pars reticulata
Function of the substantia nigra pars compacta?
Output to the basal ganglia circuit, supplying the striatum with dopamine through specific D1 and D2 neurones within the nigrostriatal pathways
Function of the substantia nigra pars reticulata?
Serves as input - conveys signals from the basal ganglia to the thalamus
Why does the substantia nigra have a dark appearance?
Due to the neuromelanin present in the cells in the pars compacta
Arterial supply to the basal ganglia?
Middle cerebral artery - main aretry is the lenticulostriate artery
Direct pathway of basal ganglia structure
Glutamate neurones project from the thalamus to motor regions of cerebral cortex = excitatory = stimulates movement
Neurones from the globus pallidus internal and substantia nigra pars reticulata project to the thalamus and release GABA = inhibition = suppression of movement to prevent unwanted movements from occurring
Infromation from movement is sent from cortex to striatum via the corticostriatal pathway. Glutamate nuyerones excite neurons on the striatum. Activated stiatam neurones release GABA in the globus pallidus internal and substantia nigra pars reticulata = inhibition of these regions = stops inhibition of neurones in the thalamus which are involved in movement = movement can occur!
Neurones from the substantia nigra pars compacta travel to the striatum via the nigrostriatal pathway and release dopamine in the striatum = facilitates activity in direct pathway
Indirect pathway of the basal ganglia structure
GABA neurones project from globus pallidus external to the Subthalamic nucleus = inhibition on glutamate neurones in Subthalamic nucleus
Signals from cerebral cortex causes activation of GABA neurones in the striatum which projects to the globus pallidus external and inhibits thr activity of neurones there. This prevents globus pallidus external neurones from inhibiting the neurones in the Subthalamic nucleus
Projections from the cortex activate the Subthalamic nucleus neurones and stimulate GABA neurones in the globus pallidus internal and substantia nigra pars reticulata = project to the thalamus = inhibits thalamic neurones that travel the motor regions of the cerebral cortex to stimulate movement = therefore inhibits movement
This antagonises the activity of the direct pathway and acts to keep unwanted movements from occurring
Neurones from the substantia nigra pars compacta travel to the striatum via the nigrostriatal pathway. These can modulate the activity of the indirect pathway through dopamine release in the striatum = inhibition of activity in indirect pathway = facilitation of movement
What broadly causes movement disrders?
Disturbance of the cerebellum and extrapyramidal system e.g. basal ganglia, thalamus, Subthalamic nuclei and red nucleus
Positive symptoms of movement disorders?
Chorea
Athetosis
Ballismus
Dystonia
Tremor
Rigidity
(Due to disinhibition of undamaged parts of the motor system)
Negative symptoms of movement disorders?
Hypokinesia and bradykinesia