module 4 Flashcards
What is the sequence of top-down processing?
*the hierarchy of motor control
1. Cortex
2. Subcortex
3. Brainstem
4. Cranial and Spinal Nerves
5. Muscle
What are the two major types of descending pathways?
Direct/Pyramidal Tract
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Indirect/Extrapyramidal Tract
What is the corticobulbar tract?
the fibers that innervate cranial nerves break off from the pyramidal motor pathway at diff spots in midpons/midmedulla & form the corticobulbar tract
What is the corticospinal tract?
A descending somatic motor tract responsible skilled movements of the extremities and postural adjustments
What is the location and purpose of the anterior corticospinal tract?
-Travels down the spinal cord with the anterior column
-Involved in coordinating postural adjustments during voluntary movements
What is the location and purpose of the lateral corticospinal tract?
-Travels down the spinal cord within the lateral column
-Involve in precise, skilled and synergistic movement of the entire limb
What are Upper Motor Neurons?
- composed of cell bodies in the cerebral cortex and brain stem and their axons in the brain stem or spinal cord
- they connect the brain to lower motor neurons
- responsible for the initiation of voluntary movements and maintenance of tone in extensor muscles for posture
What role do projection fibers play in the corticospinal tract?
Relay sensory & motor information between the cortex, sub cortex, brainstem, spinal cord & PNS.
What is the corticobulbar tract responsible for?
-Convert a respiratory channel into a digestive tract and back within 500 ms
-Breathing, chewing, laughing, smiling, swallowing all the way to digestion
What does CN VII do?
movement of facial muscles
What does CN IX do?
sensory for taste, motor for swallowing
What do CN X and XII do?
Control soft palate, pharynx, larynx, and intrinsic and extrinsic muscles of the tongue
Where is the primary motor cortex located?
precentral gyrus of frontal lobe
What is the primary motor cortex responsible for?
initiation of voluntary movement
the concept of the motor homunculus and its functional importance to clinical practice.
represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body
Direct Pathways
corticospinal tract and corticobulbar tract
components of motor control
initiation of movement, coordination of muscle groups, proprioception, postural adjustments, sensory feedback, termination of a movement, unconscious processing/patterns
indirect pathways
rubrospinal, tectospinal, vestibulospinal, and reticulospinal tracts
characteristics of direct pathways
signals are sent directly from motor strip to a neuron that carries the signal to the muscle; UMNs synapse onto LMNs which synapse onto skeletal muscle
characteristics of indirect pathways
tracts provide indirect influences on skeletal muscle; signal from motor cortices are sent to basal ganglia/nuclei in brainstem before influencing LMN signals
corticospinal pathway functions (anterior and lateral)
provides voluntary control over skeletal muscles; 2 divisions
*A descending somatic motor tract responsible skilled movements of the extremities and postural adjustments
anterior corticospinal tract function and location
postural adjustment during voluntary movements and stability of the trunk; anterior column of SC
-Travels down the spinal cord with the anterior column
lateral corticospinal tract function and location
coordination of skilled movement of the extremities; lateral column of SC
makes up 90% of the corticospinal tract
corticospinal tract origin
motor cortex (form the corona radiata and pass through the posterior limb of the internal capsule)
corticospinal tract: internal capsule
fibers descend through the posterior limb (white matter) which holds many projection fibers
brainstem pyramids
located at the medulla; are a prominent site of decussation and responsible for voluntary motor activity (why direct is called pyramidal)
corticobulbar pathway function
controls all voluntary movement for speech production, descends from motor cortex through internal capsule
corticobulbar pathway composition
primary motor cortex, internal capsule, cerebral peduncles, brainstem, CN III, CN V, CN VII, CN IX, CN X, CN XII, and spinal nerves
What does CN VII do? 7
movement of facial muscles
What does CN IX do? 9
sensory for taste, motor for swallowing
What do CN X and XII do? 10/12
Control soft palate, pharynx, larynx, and intrinsic and extrinsic muscles of the tongue
primary motor area/cortex function
responsible for motor output on contralateral side of the body, outflow makes up the corticospinal tract, located in precentral gyrus
supplemetary motor area/premotor association area function
located anterior to the primary motor area in the frontal lobe, contains maps for posture and higher order processing
basal ganglia definition
four masses of gray matter in the cerebrum and upper brainstem that are involved in movement and coordination
basal ganglia function
regulation of motor cortical output and muscle tone; cognitive functions with multiple projections to prefrontal lobe
structures of the basal ganglia
striatum (caudate nucleus and putamen), globus pallidus, and associated structures (substantia nigra and subthalamic nucleus)
basal ganglia motor function
select and maintain purposeful motor activity while suppressing unwanted movement, monitors and coordinates slow, sustained contractions related to posture, inhibits muscle tone, and regulates amplitude/velocity/initiation of movement
neuromodulation of basal ganglia
maintains purposeful activity while suppressing unwanted or useless movement (inhibitory and excitatory loops)
basal ganglia and communication
communication generates components of motor programs for speech (discrete)
characteristics of basal ganglia disease
tremor and other involuntary movements, changes in posture and muscle tone, and slowness of movement
(also cognitive changes)
What are Upper Motor Neurons?
- composed of cell bodies in the cerebral cortex and brain stem and their axons in the brain stem or spinal cord
- they connect the brain to lower motor neurons
- responsible for the initiation of voluntary movements and maintenance of tone in extensor muscles for posture
What is the cortico-striatal-cortico loop?
*controls timing
* Structures of the Basal Ganglia function as part of a control circuit/loop that helps to regulate movements but does not send motor commands directly to muscles.
* Function of the loop: selection and initiation of willed movement.
* Dysfunctions can result in reduction of movement or uncontrolled movement, tremors and ticks.
How does the basal ganglia play an integral role in movement?
- The BG selects and maintains purposeful motor activity while
suppressing unwanted or useless movement
*Inhibitory and excitatory loops are critical for inhibition and excitation of movement
*Dopamine regulates movement and signals reward (Important for motor learning and motivation)
neurotransmitters involved in basal ganglia circuitry
- Glutamate = primary excitatory neurotransmitter
- GABA = primary inhibitory neurotransmitter
How does the cerebellum play an integral role in movement?
Compares intended movement (motor cortex) with actual movement in limbs (proprioceptive feedback) and adjusts the movement as needed.
key motor areas
primary motor cortex, premotor cortex, and supplementary motor areas
The cerebellar system
- Spinocerebellum: Motor coordination and execution
- Cerebrocerebellum: Motor learning & higher cognitive functions
- Vestibulocerebellum: Regulate posture and balance
dyskinesia
abnormal movements caused by the basal ganglia dysfunction
bradykinesia
Slowness of movement
akinesia
impairments in initiation of movement
rigidity
ncreased resistance to passive displacements
chorea
sudden, rapid, jerky, purposeless movement involving limbs, trunk, or face
ballism
large-amplitude movements of proximal limbs
dystonia
slower, twisting movements and sustained abnormal postures
tremor
involuntary, quivering movement
tics
brief, rapid, involuntary movements
hypokinetic disorders
impairments in initiation of movement, too little movement (bradykinesia, akinesia, rigidity, and tremor)
hyperkinetic disorders
characterized by involuntary movements, too much movement (chorea, ballism, dystonia, tics)
parkinson’s disease
failure of midbrain neurons (substantia nigra) to secrete dopamine, leads to tremors, muscle rigidity, flexion, akinesia
characteristics of PD
“pill rolling” tremor, bradykinesia, rigidity, and postural instability that causes unsteady gait, hurried/muttering quality of voice, micrographia, stooped posture, reduced arm swing, gait
huntington’s disease
hereditary disease of the CNS, manifests as dementia and chorea, death within 10-15 years
characteristics of HD
clumsiness, subtle chorea, tics, dystonic posture, psychiatric manifestations, cognitive impairments, dementia, COD usually respiratory
Hypotonia
reduced musle tone
*Cerebellum damage
Atasia
lack of coordination of limb and body postures across multiple joints
(difficulty walking)
*Cerebellum damage
Abasia
inability to maintain an upright posture against the force of gravity
(difficulty standing)
*Cerebellum damage
Ataxia
uncoordinated movements (greek: -taxis = order)
*Cerebellum damage
Dysmetria
abnormal targeting of movements
*Cerebellum damage
Nystagmus
Beating of the eyes
*Cerebellum damage
Action or intention tremor
Poor coordination of agonist and antagonist muscles
SCAN
- somato-cognitive action network
*1948 was depicting a continuous map of the body in primary motor cortex
*2022 are functional zones are represented by concentric rings with proximal body parts surrounding the relatively more isolatable distal ones
