Motor Flashcards
Exam 2
reflex vs. voluntary movement
Spinal Reflex
- simple, unvarying, innate/unlearned responses
- do not require brain inputs to the spinal cord (nothing is actually coming down from the brain)
reflex vs. voluntary movement
Voluntary movements
- require brain inputs (cognition/brain involvement) to the spinal cord
- motor plan/program: “How will this movement be orchestrated?” is established before an action occurs
reflex vs. voluntar movement
proprioception
- knowing position and movement of body
- muscle length
- muscle tension/movement
- aka kinesthesia and is present in every muscle movement you have… it is the body’s awareness sense…innate
Circuits that drive movement process
- receptor
- sensory neuron
- integration center
- motor neuron
- effector
-(sense input to integration to motor output)
What do motor systems do?
- Sensing the outside world guides action selection (we have to know where things are around us). An action performed accurately approach reward and is reinforced, while an action performed poorly is not reinforced “withdraw from negative”
- CNS produces specific patterns of muscle contractions that lead to specific actions (motor outcome/behavior)
Motor systems
Primary motor cortex
initiates main commands
Motor systems
Non primary motor cortex
additional motor commands
Motor systems
Brainstem
- integrates motor commands from higher brain regions and transmits them to the spinal cord
- responsible for muslces of face, head, and neck
Motor systems
Cerebellum/basal ganglia
- modulates (modifies) motor control systems/fine tuning
Motor systems
Spinal cord
- reflexes
- also immplements commands from the brain
- muscles of body
Motor systems
Skeletal muscle system
determines possible movements
Synergists
muscles can be synergists, which means they contract together
antagonists
muscles can be antagonists and contract opposing each other
“flex” of bicep
motor neurons to biceps are excited while motor neurons to triceps are inhibited
How do muscles contract? - first three steps
- alpha motoneuron: sends an axon to a motor end plate that opposes a striated muscle (massive)
- Multiple axon terminals “contact” multiple muscle fibers
- synapses are called neuromuscular junctions
What occurs at a neuromuscular junction?
- presynaptic motor neuron terminal
- synapse
- postsynaptic muscle fiber
neuromuscular junction neurotransmission
- Alpha motoneuron releases ACh from the motor end plates
- ACh binds to nitoninc acetylcholine receptors (nAChR) to allow Na+ influx
- Creates EPP (end plate potential) which triggers muscle fiber contraction
What are Betz cells?
- Pyramidal neurons that produce glutamate and form the homunculus
- found in the primary motor cortex (M1)
Describe the structure of M1 pyramidal neurons
- M1 pyramidal neurons form axon bundles
- bundles cross (decussate) in the medulla
- then descend caudally in the spinal cord via corticospinal tract
- synapse onto ventral spinal cord alpha-motoneurons
- muscle fiber contracts
Where do M1 pyramidal neurons cross?
in the medulla
cross fancy word
decussate
Where do M1 pyramidal neurons synapse?
onto ventral spinal cord alpha-motoneurons
Where do M1 pyramidal neurons descend?
caudally in spinal cord via corticospinal tract
What does the contraction of simple msucle units in M1 do?
lead to simple movements
What do the Supplementary motor area (SMA) and premotor cortex do?
- control subsets of M1 neurons
- helpful in coordinating activity of muscle units particularly for complex movements
What does the SMA do?
- rehearses action before it occurs/plans
- doesn’t necessarily take the outside environment to account
What does the premotor cortex do?
directs movement based on external stimuli
Mirror neurons
- located in premotor cortex
- neurons active when performing a task are also active when watching someone else perform the same/similary task
- useful for learning or cooperation maybe
motor deficits
Apraxia
- impairment in beginning/executing voluntary movements even though no muscle parlysis
motor deficits
Ideomotor apraxia
- the inability to carry out a simple motor activity in response to verbal command, even though this ame activity is readily performed spontaneously
motor deficits
ideational apraxia
the inability to carry out a sequence of actions, even though each element or step can be done correctly
What is the EMS and what does it do?
- The Extrapyramidal Motor System
- Contains the basal ganglia and cerebellum
- Connects w motor cortices to form a closed loop (cortex to EMS to cortex)
What is the basal ganglia a part of? What is the basal ganglia’s function?
- the basal ganglia is part of the Extrapyramidal Motor System
- involved in the initiation of motor action (related to motivational systems and cognition)
What is the Cerebellum’s function and what is it a part of?
coordination, precision, and accurate timing
EMS activation timeline
- the cerebellum and non-primary motor cortices activate after the basal ganglia and primary motor cortex
D1 and D2 dopamine receptors
- D1 and D2 are dopamine receptors
- D1 receptors exictatory-activate neuron-GO/DIRECT pathway
- D2 receptors inhibit neurons- STOP/INDIRECT pathway
in basal ganglia
What does dopamine do to the GO and STOP pathways?
- dopamine turns on the GO pathway, which leads to reward-seeking
- dopamine turns off the STOP pathway, wich leads to reward-seeking
parkinson’s disease
- resting tremor, impaired gair, difficult initiating movements
- progressive: eventually affects all behavior, including swallowing
- unknown etiology (partially genetic, partially environmental)
- loss of substantia nigra dopamine neurons
- pharmacological therapy involves dopamine replacement
Huntington’s disease
- chorea
- genetic; caused by single allele
- longer repeat sequences, earlier onset
- eventual striatum cell death
What gene causes HD?
trinucleotide expansion in huntingtin gene (>40 repeats)
longer repeat sequences, earlier onset
