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Brain, speech and language: Control circuits LCSC06 2015 Control circuits • Integrate and control the activities of the structures and pathways involved in motor performance • Key point: Neither the basal ganglia not the cerebellum project directly onto lower motor neurons. Control circuits: cerebellum and basal ganglia • The cerebellum: coordinates motor and sensory information • Gets info from the cortex about what muscles SHOULD be doing, and compares this with what is ACTUALLY happening • The basal ganglia: involved in control of background movement, and initiation of movement patterns Both the basal ganglia and the cerebellum project to the cortex: • The cerebellum forms a loop from cortex to pontine nuclei to cerebellum and back to the cortex via the thalamus. It also receives sensory information from the brain stem and spinal cord (e.g. proprioceptive stimuli via spinocerebellar tracts) • The basal ganglia form a complex collection of nuclei also involved in a loop from cortex to basal ganglia to thalamus and back to the cortex THE CEREBELLUM (‘little brain’ in Latin) Vestibulocerebellum = flocculonodular lobe Functions of the cerebellum • Stores learned sequences of movements • Participates in fine tuning and co-ordination of movements produced elsewhere in the brain • Integrates all of these things to produce fluid and harmonious movements. • So prime task is to ensure smooth coordination of muscles Flocculonodular lobe • The oldest part phylogenetically so aka the archicerebellum (or vestibulocerebellum). • Connects with the vestibule of the inner ear and is involved in balance. • Contains the fastigial nucleus which connects with the 4 vestibular nuclei in the brainstem • Modulates equilibrium (balance) and orientation of head and eyes Anterior cerebellum • Anterior lobe (spinocerebellum) =projection area for the spinocerebellar proprioceptive information. • Receives input from muscle and joint receptors via spinocerebellar tracts • Regulates posture, gait and truncal tone. It is connected to the spinal cord and controls postural muscle activity by influencing muscle tone. Posterior cerebellum • Connected to the contralateral cortex and thalamus • Lateral portions of the cerebellar hemispheres have a role in coordinating skilled, sequential voluntary muscle activity • Ensures that when one set of muscles initiates a movement, the opposing set acts as a brake, so that the body part in question arrives at its target precisely. Cerebellar peduncles (ref the You Tube clip posted on LS) • Fibre tracts enter/leave through the inferior, middle and superior cerebellar peduncles • Inferior =mostly afferent from spinal cord and brainstem; efferent to vestibular mechanisms and reticular formation • Middle = afferent from pontine nuclei • Superior = main efferent output via Purkinje cells Cerebellar control circuits 1: loop important in planning and programming learned movements Primary motor & premotor regions Ventral thalamus Deep cerebellar nuclei Pontine nuclei Lateral cerebellar hemispheres Cerebellar control circuits 2: Corticospinal/ Corticobulbar fibres Primary motor cortex Ventral thalamic nuclei Intermediate cerebellar hemispheres Deep cerebellar nuclei Summary of functions of cerebellar control circuits: • Coordinate the timing between the single components of a movement • Scale the size of muscular actions • Coordinate the sequence of agonists and antagonist Cerebellar speech motor control summary: 1. Cortex sends preliminary advance info re intended speech goals to cerebellum 2. These preliminary speech commands are provisional, imprecise and in excess of those needed to accomplish speech goal 3. Cerebellum is thus ‘primed’ to check the adequacy of the outcome, based on sensory information coming in from the periphery (ie muscle spindles, joint and tendon sensors) 4. Cerebellum updates the motor output from the cortex to help smooth the actions of agonist/antagonist muscle contractions Basal ganglia circuits • Important in generating components of motor programmes for speech • Cortex initiates impulses in excess of requirements to produce the motor act • One role of the BG is to damp (through inhibition) or modulate (through disinhibition) those impulses • Important in regulating muscle tone, goal directed activities, automatic activities Anatomy of the Basal Ganglia Basal ganglia control circuits Selectively activates and inhibits movements. Provides internal cues for planning and refining slow continuous movement http://www.youtube.com/watch?v=8hC6NGQReL4 The Basal Ganglia • Caudate nucleus and putamen (the striatum): act together as a functional unit - INPUT • Globus pallidus interna and substantia nigra pars reticulata - main OUTPUT • Globus pallidus externa, Sub thalamic nucleus, and substantia nigra pars compacta intermediate Two loops: • Direct = responsible for activating movement overall excitatory • Indirect = stopping unwanted movement overall inhibitory • The two pathways operate together to provide balanced control of descending pathways. • NB Do not confuse these loops with the direct/indirect activation pathway Normal direct/indirect loops of basal ganglia Green = excitatory pathways, Red = inhibitory pathways Premotor/motor cortex Striatum External globus pallidus Subthalamic nucleus Indirect loop Substantia nigra Internal globus pallidus Direct loop Thalamus Neurotransmitters: • Ach =acetylcholine (for neurons that synapse in the striatum) excitatory • Dopamine (manufactured in the substantia nigra) neuromodulatory • GABA = gamma aminobutyric acid inhibitory • Glutamate excitatory • Enkephalin and substance P = additional neurotranmitters • The balance of these is crucial to normal functioning of the loops and therefore motor output Neuromodulatory effect of dopamine: • Direct Pathway: Stimulates • Indirect Pathway: Inhibits • Overall Excitatory Other functions/loops of the Basal Ganglia An executive loop may regulate the initiation and termination of cognitive processes such as planning, working memory, and attention. The limbic loop may regulate emotional behaviour. The deterioration of cognitive and emotional function in both Huntington's disease and Parkinson's disease could be the result of disruption of these non-motor loops. Summary of motor pathways Same typical exams questions: 1. Which of the two following components of the basal ganglia form a functional unit? I. putamen and globus pallidus II. Substantia nigra and putamen III. Putamen and caudate nucleus 2. Complete the following: the lentiform nucleus is composed of………………………………………………. 3. Which of the following statements is NOT true of the functions of the cerebellum? I. Stores learned sequences of movements II. Ensures smooth coordination of muscles III. Regulates postural adjustments during skilled movements 4. In addition to its role in movement control, list 2 other posited functions of the basal ganglia 5. What to do now: • Read the scanned chapter by Ellison (2012), chapter 6, Moving On. This should consolidate your understanding of movement, and the complex pathways involved. • Chapter 10 in Atkinson and McHanwell provides a more comprehensive summary. • Chapter 2 in Duffy (2007), a text you will use next year also has a good summary