Transcript 7. Control circuits

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