Voluntary movement Flashcards
What are the 3 types of movement?
involuntary actions (reflexes), semi-automatic actions, voluntary actions
What are semi-automatic actions?
voluntary actions that do not require though (often repeated movement sequences, appear stereotypes but very adaptable)
Examples of semi-automatic actions
walking, breathing, chewing (can be voluntarily adjusted)
What is the name of the collection of neurons that drive semi-automatic actions?
central pattern generators (CPGs)
What are the basic components of a neuron?
Dendrites (cell projections that receive inputs), cell body, axon, axon terminal (contain synaptic vesicles for synaptic release)
What are central pattern generators (CPGs)?
collection of neurons with rhythmic output that will influence motor patterns of muscle groups
What are the 2 feedback loops involving the CPG?
reflex feedback and central feedback
Describe the reflex feedback of the CPG?
CPG output innervate effector organs which feedback to the CPG (repeats)
Describe the central feedback involving CPGs?
CPG outputs innervate higher control neurons which reinnervate CPG (ensure output is constantly relevant)
How can the environment influence semi-automatic actions?
Environment provides sensory feedback either directly to the CPG or indirectly to higher control neurons that innervate CPG
Characteristics of voluntary actions
self-initiated, purposeful, learned, improved with practice, adaptable
What section of the brain is involved in voluntary movements?
motor cortex
Describe the location of the sensory cortex
posterior to the central sulcus
Describe the location of the motor cortex
anterior to the central sulcus
Name of the mapping of the brain dedicated to motor processing different regions of the body
motor homunculus
Why do the trunk and lower limbs have less representation in the motor homunculus?
muscles are large, just require power not precision. Low density of motor units
Why do the hands and face have a great motor homunculus representation?
high density of motor neurons as the muscles are very small (to allow greater movement precision)
How many neurons are involved in sensory pathways?
3 neurones
What are the 2 motor/descending pathways (voluntary)?
corticospinal and corticobulbar pathways
How many neurons are involved in corticospinal/corticobulbar pathways?
2 motor neurons
Outline the general corticospinal/corticobulbar pathway
motor cortex innervates the upper motor neuron which projects down to the brainstem/spinal cord where it synapses with a lower motor neuron which innervates the effector muscle
Where are the cell bodies of upper neurons located?
motor cortex
Where are the cell bodies of lower motor neurons located?
either in brainstem or spinal cord (depending on location of target muscle)
What are the 3 sections the white matter of the spinal cord is divided into?
dorsal funiculus, lateral funiculus, ventral funiculus
What are the 2 possible areas of white matter in the spinal cord that descending axons can pass through?
dorso-lateral funiculus (lateral corticospinal tract) or ventro-medial funiculus (anterior corticospinal tract)
Which motor neurons are innervated by the corticobulbar pathway?
cranial nerve nuclei (bilateral)
Where is the term corticobulbar derived from?
cortico - as upper motor neuron nuclei located in cortex
bulbar - lower motor neuron nuclei located in brainstem
Which motor neurons are innervated by the corticospinal pathway?
motor neurons with their nuclei located in the spinal cord
Where is the term corticospinal derived from?
cortico - upper motor neurons have their nuclei in the motor cortex
spinal - lower motor neurons have their nuclei in the spinal cord (ventral horn)
Function of the corticobulbar pathway
carries motor information from the primary motor cortex to the muscles of the head and neck by synapsing with motor cranial nerves in the brainstem
Function of the corticospinal pathway
Carries motor innervation from the primary motor cortex to the muscles of the trunk and limbs
Examples of nerves innervated by the corticobulbar pathway
trigeminal (V), facial (VII), vagus (X), hypoglossal (XII)
Motor function of trigeminal nerve (V)
muscles of mastication
Motor function of the facial nerve (VII)
muscles of facial expression
Motor control of the vagus nerve
soft palate, pharynx, larynx
Motor control of the hypoglossal nerve (XII)
extrinsic muscles of tongue
Describe the route of the upper motor neurons in the corticobulbar pathway
cell bodies located in motor cortex. Axon descends through basis pedunculi (part of midbrain) towards either the pons (trigeminal or facial motor nuclei) or to the medulla (nucleus ambiguus) where the upper neuron bifurcates for bilateral innervation
Which part of the midbrain do the upper motor neurons for both the corticobulbar and corticospinal pathways descend through?
basis pedunculi
Where is the trigeminal motor nucleus located?
pons
Where is the facial motor nucleus located?
pons
Where are the vagus and hypoglossal motor nuclei located?
nucleus ambiguus in the medulla
What is the main difference between the corticobulbar and corticospinal pathways?
axons in the corticospinal pathway project further as they descend into the spinal cord whereas corticobulbar upper motor neurons only descend into the brainstem (pons or medulla)
What percentage of corticospinal projections cross to the contralateral side at the medulla?
85% of corticospinal projections
Where in the medulla do 85% of corticospinal projections cross over?
pyramidal decussation
Where do the remaining 15% of corticospinal projections cross over?
at the level of the target lower motor neuron
What region of the white matter do the 85% of the corticospinal projections that cross over at the pyramidal decussation descend?
lateral corticospinal tract in the dorso-lateral funiculus
How far along the spinal cord does the lateral corticospinal tract (in dorso-lateral funiculus) descend?
entire length of the spinal cord
What region of the white matter do 15% of the corticospinal projections that remain on the same side descend in?
anterior corticospinal tract in the ventro-medial funiculus
How far along the spinal cord does the anterior corticospinal tract (in ventro-medial funiculus) descend?
to mid thoracic region only
Which side of the brain does the motor pathway controlling distal muscles (hands, feet, tongue, lower face) originate?
opposite side of the brain
Which muscles can receive bilateral descending cortical motor commands?
e.g. some muscles of the upper face. E.g. gag reflex involves bilateral innervation of nucleus ambiguus
Which 2 neurons can innervate the lower motor neuron causing muscle contraction?
upper motor neuron (voluntary from motor cortex) or muscle afferent (reflex from stretched muscle spindles)
What is the effect of an upper motor neuron lesion?
voluntary movement cannot occur, but reflex responses are still possible
Causes of upper motor neuron lesion
stroke, trauma
What is the effect of a lower motor neuron lesion?
loss of voluntary and reflex response - no movement can occur
Cause of lower motor neuron lesion
peripheral nerve injury
Name of the condition that involves temporary (unilateral) paralysis of the muscles of facial expression
Bell’s palsy
Which nerve is affected in Bell’s palsy?
facial nerve (CN VII)
What are the functions of additional descending motor projections?
coordinate movements, help maintain posture/balance, integrates actions of several muscles
Where do additional descending motor projections arise from?
basal ganglia, cerebellum, brainstem
What is the basal ganglia comprised of?
several interconnected sub-cortical nuclei
How is the basal ganglia linked to the cerebral cortex?
via feedback loops
Function of the basal ganglia
influence motor activity and motor control (influence/regulate output from motor cortex and initiate actions and switch from one action to another)
What structure connects the 2 cerebral hemispheres?
corpus callosum
What is the name of the bundles of white matter that relay information up to the sensory cortex / down from the motor cortex?
internal capsule
What are the names of the large holes in the central portion of the cerebral hemispheres?
2 lateral ventricles and third ventricle (become continuous in midline)
What are the components of the basal ganglia?
body of caudate nucleus, putamen, globus pallidus, thalamus, substantia nigra
Location of body of caudate nucleus
lateral protrusion into the lateral aspect of the lateral ventricles
What is the putamen?
collection of cells that form a cluster of grey matter within the basal ganglia
Location of putamen
lateral to internal capsule
What is the globus pallidus?
subnucleus of the basal ganglia
Location of globus pallidus
medial to putamen, lateral to internal capsule
Location of thalamus
medial to internal capsule, protruding into the lateral aspects of the third ventricle
How does the substantia nigra appear in a coronal section?
dark, speckled appearance
What are the 3 ‘action selection’ centres of the basal ganglia?
1) corpus striatum
2) sub-thalamic nuclei
3) substantia nigra
What is the corpus striatum composed of?
body of caudate nucleus, putamen, globus pallidus
What is the thalamus composed of?
7 principle subthalamic nuclei
2 examples of basal ganglia disorders
Parkinson’s disease and Huntington’s disease
Which part of the basal ganglia is affected in Parkinson’s disease?
Substantia nigra
What is the cause of Parkinson’s disease?
loss of dopamine expressing cells in substantia nigra (dopamine deficiency)
What are the effects of Parkinson’s disease?
hypokinetic disorder (reduce movements), resting tremor, poverty of movement, mask-like face, difficulty initiating movements
What is the resting tremor associated with Parkinson’s called?
Paralysis agitans
Which aspect of the basal ganglia is affected in Huntington’s disease?
Corpus striatum
What effects does Huntington’s disease cause?
hyperkinetic disorder (increase movements), excessive, uncontrolled movements
Cause of Huntington’s disease
imbalanced neurotransmitters in Corpus striatum - decreased GABA levels
Function of cerebellum
coordinates movements, regulates actions of antagonistic muscle groups, maintains balance, compares actual performance with what is intended
Which receptors transmit information to the cerebellum to maintain balance?
proprioceptors
Which reflex is important for maintaining posture?
stretch reflexes (mediated by muscle spindles)
What happens to maintain posture when you sway forwards?
muscles on the back of the leg are stretched which evokes the stretch reflex, pulling you back to the vertical position
What actions help maintain an upright posture?
correcting actions (slight rocking)
What structure connects the sensory and motor cortexes?
association cortex
