Voluntary Movement Flashcards
What are the 3 types of movement?
- Involuntary actions - reflexes
- Semi-automatic actions e.g. CPGs in breathing
- Voluntary actions
Describe features of voluntary actions
- Self-initiated
- Purposeful: goal directed
- Learned
- Improved with practice
- Adaptable
Describe features of semi-automatic actions
- ‘Voluntary’; but you don’t have to think about them
- Often, they are repeated movement sequences
- Appear stereotyped but are very adaptable
What are some examples of semi-automatic actions?
Walking, breathing, chewing
What are central pattern generators (CPGs)?
Neuronal circuits that produce rhythmic motor actions in the absense of sensory input
What drives semi-automatic actions?
- May be driven by CPGs
- CPGs are specific to the the action they initiate/maintain
Which components are involved in voluntary movement that are not involved in reflexes?
- Recruitment and influences from subcortical areas (thalamus, basal ganglia)
- Also higher processing in cortical areas
What is the motor homunculus?
Map of brain areas dedicated to motor processing for different parts of the body
Where is the primary motor cortex located?
Precentral gyrus (motor neurons here)
What effect(s) can injury/lesion to the spinal cord have on sensory and motor functions?
- Can affect ability to perceive sensory information or to initiate voluntary movement
What is the corticobulbar pathway?
Descending pathway that innervates several cranial nerves
Which 4 cranial nerves does the corticobulbar pathway directly innervate?
Corticobulbar pathway directly innervates the nuclei of the following cranial nerves:
- Trigeminal (V)
- Facial (VII)
- Vagus (X)
- Hypoglossal (XII)
What does CN V3 innervate?
Muscles of mastication
What does CN VII innervate?
Muscles of facial expression
What does CN X innervate?
Soft palate, pharynx, larynx
What does CN XII innervate?
Extrinsic muscles of the tongue
Describe the corticobulbar pathway
- Neurons project from motor cortex through the internal capsule of the brain and down through the brainstem
- Activates lower motor neurons in the brainstem
- Lower motor neurons target motor nuclei for CN V, CN VII, CN X and CN XII.
- These cranial nerves innervate specific muscle groups resulting in contraction
- Innervate muscle groups on both sides of the body
What is the corticospinal pathway?
Descending pathway that innervates spinal nerves
Describe the corticospinal pathway
- Upper motor neurons descend axons down through the internal capsule of the brain and down through the brainstem
- As they progress down, at the level of the medulla, 85% of these axons cross over to the opposite side of the body
- This is called pyramidal decussation
- Motor pathways typically innervate opposite side of body
What can damage to descending pathways cause?
Paralysis or palsy
Nature of palsy depends on location of lesion
Describe the effects of damage to lower motor neurons
- Nerve injury e.g. polio
Inability to initiate any type of muscle contraction - Won’t be able to initiate reflex responses or voluntary responses
Describe the effects of damage to upper motor neurons
- Corticospinal tract, corticobulbar tract
- Doesn’t impact upon ability to generate reflex response as this occurs at spinal level
What does damage to the insular cortex affect?
Emotion, perception and motor control
Describe Bell’s Palsy
- Unilateral event
- Dysfunction of CN VII
- Unsure of underlying causes; may be an inflammatory response
- Dissipates within 2 weeks on its own
- No treatment required
Where do pathways to motor neurons that control distal muscles (hands, feet, lower half of the face and tongue) originate from?
Opposite side of the brain
Which motor neurons receive bilateral cortical commands?
Motor neurons controlling muscles of the upper half of the face
Where are upper motor neurons located?
Motor cortex
Where are lower motor neurons located?
Brainstem/spinal cord
What can cause damage to upper motor neurons?
Stroke
What can cause damage to lower motor neurons?
Nerve injury, viral infection (polio)
Where do additional descending motor projections arise from and what do they do?
- Arise from various areas of the cerebrum and brainstem e.g. basal ganglia, cerebellum, brainstem
- Serve to co-ordinate movement
- Help maintain posture/balance
- Help integrate the actions of several muscles
What do descending motor projections arising from various areas of the cerebrum and brainstem do?
- Co-ordinate movement
- Maintain posture/balance
- Integrate actions of several muscles
What is the basal ganglia comprised of?
Several interconnected sub-cortical nuclei
What does the basal ganglia do?
- Influences/regulates output from the motor cortex
- Acts to initiate actions and to switch from one action to another
What are the 5 interconnected sub-cortical nuclei that make up the basal ganglia?
- Body of caudate nucleus
- Putamen
- Globus pallidus
- Thalamus
- Substantia Nigra
What is the corpus striatum composed of?
Caudate nucleus, putamen, globus pallidus
Which disorder does damage to the substantia nigra result in?
Parkinson’s disease
Which disorder does damage to the striatum result in?
Huntington’s disease
Name 2 basal ganglia disorders
Parkinson’s disease and Huntington’s disease
Describe Parkinson’s disease
- Hypokinetic disorder (decreased movements)
- Resting tremor
- Poverty of movement
- Mask-like face
- Difficulty initiating movemnts
- Dopamine deficiency in the substantia nigra
What is ‘paralysis agitans’?
Resting tremor - another term for Parkinson’s disease
Describe Huntington’s disease (chorea)
- Hyperkinetic disorder (increased movements)
- Excessive, uncontrolled movements
- Imbalance of neurotransmitters - decreased levels of GABA
What is the cerebellum important for?
- Co-ordinating movement
- Regulates the actions of antagonistic muscle groups
- Important in maintaining balance - receives inputs from proprioceptor
- Acts to compare actual performance with what is intended
Describe cerebellar disorders
- Characterised by loss of co-ordination
- Unsteady gait (ataxia)
- Imprecise actions
- Inability to co-ordinate alternating contractions of antagonistic muscles
- Intention tremor (resting tremor in Parkinson’s)
Which reflexes are important in maintaining posture?
Stretch reflexes mediated by muscle spindles
What effect do correcting actions have on posture?
Correcting actions help keep the position of the head in line with the body’s centre of gravity
What do motor projections from the basal ganglia, cerebellum and brainstem do?
- Co-ordinate movements
- Maintain posture/balance
- Help integrate actions of several muscles
