Control of movement
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What is the output of the somatic motor system?
LMN in the SC or brainstem
All reflexes are mediated by the __ __.
What comprises the somatic motor system?
Skeletal muscles and parts of the nervous system that control them (aka muscles and their neurons)
The ___ ___ is linked to the __ via the ___-___. (regarding muscle fiber structures)
- sarcoplasmic reticulum
- t-tubule (transverse tubule)
A sensory neuron can synapse directly onto the __ (aka __ __) or it can synapse onto an __ which synapses onto the LMN (aka __ __).
- -(aka Monosynaptic reflex)
What is a small motor unit used for?
- Fine motor movements (fingers)
- <10 fibers
What is a reflex?
A local motor response to a local sensation
The synapse between the axon of a LMN and a muscle is the ___ ___.
The ACh release causes ___ ___ on the ____.
The __ __ __ with its target __ __ constitutes a __ __.
- Lower motor neuron
- muscle fibers
- motor unit
the membrane has specific receptors that recognize Ach. These receptors are known as __ __.
Explain the events that occur at the neuromuscular junction.
- 1. AP goes down axon of LMN to the terminal
- 2. Ca2 channels open
- 3. Synaptic vesicles dock @ presynaptic membrane
- 4. ACh is released into neuromuscular junction
- 5.ACh diffuses and binds with receptors at the motor end plate (post synaptic membrane) and fuses with ACh receptors
A lower motor neuron resides in the __ or the __ __. Its axons project to __ or __ muscles.
AP triggers the release of __ ions from the __ __ causing __.
- Sarcoplasmic reticulum
What is an example of a mono synaptic reflex?
Mono: Knee jerk
Di: Step on a tack (info has to go to spinal cord AND brain)
What areas of the cortex are responsible for initiating motor movement?
Cortical motor areas
LMNs exit the spinal cord via __ __ and join fibers with the __ __ and form a __ __.
- Ventral root
- Dorsal root
- Spinal nerve
The motor and plate is also known as the __ __ of a __.
Post synaptic membrane
Only the __ __ __ directly command muscle contraction, so they are referred to as the __ __ __.
The cylindrical structures within muscle fibers are called ___.
Muscle fibers are surrounded by the ___. It is an ___ membrane.
When calcium ions are taken back into the sarcoplasmic reticulum, ___ occurs.
LMNs are this type of neuron (classified by structure).
What is a large motor unit for?
More powerful movements; not precise (quad muscle)
When the ACh receptor opens, it causes __ which causes an ___.
Depolarization (Na+ enters)
What are the two principal neurons in motor pathways?
__ __ surrounds the myofibril and contains __ ions.
How does a LMN communicate with a muscle fiber?
By releasing ACh at the neuromuscular junction.
An UMN cell body resides at __ __ in the __ nervous system and whose axon projects to the __ __ __.
lower motor neurons
** Reside in the cortex
What are the functions of the 3 sources of input to LMN?
- UMN in brain-initiate and control voluntary movement
- Muscle spindles- feedback about muscle length
- Spinal interneurons-generate reflexes
What are the 3 main sources of input to the LMN?
- UMN in brain
- Sensory input from muscle spindles
- Spinal interneurons
What is the posterior parietal cortex (primary somatosensory cortex) responsible for in movement control?
Receives somatosensory; Awareness (proprioceptive, visual, and auditory inputs from the environment)
What is the prefrontal cortex responsible for in regards to movement control?
Retrieves information from parietal and frontal lobe; idea; decides WHAT action is desired
What are the premotor and supplementary motor areas responsible for in regards to movement control?
Programming; decide how actions will be performed; Planning motor movements
What is the primary motor cortex responsible for in regards to movement control?
Execution; Implements the plan and executes it
What are the basal ganglia and cerebellum responsible for in regards to movement control?
Feedback to the primary motor cortex
Where do UMNs synapse with LMNs?
In the brainstem (cranial nerves) and spinal cord (spinal nerves)
What will damage to the supplementary motor cortex result in?
Alien-Limb syndrome (person feels unable to control movement of body part and may believe their limb is an alien and has its own personality)
What is the purpose of a pyramidal tract?
Carry motor information to LMNs in the brain stem and spinal cord
Fibers the synapse with cranial nerves are called ___ ___.
Fibers that synapse with spinal nerves are called __ __.
What are the 2 major motor tracts and what are they important for?
What is the extrapyramidal system important for? (5)
- Speech production
- Automatic motor movements
- Muscle tone
- Facial expression
- *AKA indirect activating system
The 4 tracts of the extrapyramidal system do what?
Originate in brainstem, receive input from cortex, thalamus, and cerebellum; carry motor impulses to muscles in the body for speech & swallowing
What is the function of the cerebellum in regards to movement control?
- Uses various sensry inputs to assess/monitor status of executed behavior
- Modifies behavior via primary motor cortex (fine tunes)
- Plays a role in motor adaptation and motor learning
- Detects mismatch between intention and actual movement
**Cerebellum receives input from the cortex and sends the info back to the cortex via the thalamus
What is the function of basal ganglia in regards to movement control?
- Part of the extrapyramidal system
- Organize automatic action sequences
- Keeps inappropriate movements from being expressed (inhibiton/disinhibition)
How can movement disorders occur?
Dysfunction of UMN, motor unit (LMN-cell body, axon, neuromuscular junction-neuropathy, muscle fibers-myopathy)
Can also result from damage to basal ganglia and cerebellum, but have indirect effect
What happens in primary neuropathy?
# of motor units decreases, but size increases (increase in motor unit potential)
What are denervated nerves and what is their role in neuropathy?
Nerves that are no longer receiving information or innervation
They secrete substances that induce branching of nearby axons; the new axon branches re-innervate formerly denervated muscle fibers
What are symptoms of primary neuropathy?
muscle weakness & atrophy, fasciculations, reduced reflexes, emotional lability, and/or somatosensory abnormality
What happens in primary myopathy?
# of motor units remains constant, but size decreases
Muscle fibers & LMNs maintained by trophic substances; LMN will die without trophic substances
# of motor units wil decrease in later stages of myopathy
What are some symptoms of myopathy?
Weakness, fatigue, atrophy, muscle cramps, stiffness, and/or muscle spasms
What are congenital (inherited) myopathies called?
What are causes of non-congenital (non-inherited) myopathy?
Toxins, drugs, inflammation, endocrine abnormalities
What is a motor neuron disease that affects UMNs and LMNs?
What is a motor unit disease that is primary neuropathy (involving the neuromuscular junction)?
What are diseases of the basal ganglia?
- Parkinson's disease
- Huntington's disease
How common is ALS, between what ages are typical onset, and what is the expected lifespan?
1 in 20,000
3-5 years (90% will die within this period)
What are symptoms of ALS?
- Muscle weakness/atrophy
- Fasciculations (twitching of muscles under skin)
- muscle cramps
- tight and stiff muscles (spasticity)
- exaggerated reflexes (hyperreflexia)
- **May also affect higher level executive functions (attention, memory, confrontation naming, verbal fluency)
- **Does not typically affect sensation or basic cognition, but patient is aware of what is happening
What is bulbar ALS?
If the brainstem nuclei are affected first, swallowing and speech may be affected and there may be a slight change in vocal quality
Bulbar is less common and usually has a shorter life expectancy; succumb within 1-3 years
What are the main causes of death in ALS?
Respiratory complications or pneumonia (aspiration)
How do reflexes play an important role in the motor control of speech?
Maintain muscle tone for speech musculature
Work in conjunction with voluntary movements that help with precise movements of articulators
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