#16 Neuromotor System Flashcards
1
Q
Motor Cortex Inputs, Outputs
A
- Gives rise to corticobulbar and corticospinal tracts
- Input:
- Premotor cortex
- Ventrolateral thalamus
- Output: (via Corticobulbospinal tracts)
- Local circuit neurons (CPGs)
- Motor neuron pools
2
Q
Premotor Cortex Input, Output
A
- Planning, executing, directing voluntary movements
- Consistes of premotor area (PMA) and supplementary motor area (SMA)
- Input:
- Non-motor cortical areas
- Ventral anterior thalamus
- Output:
- Motor cortex
- Basal ganglia
3
Q
Non-Motor Cortical Areas, Input, and Output
A
- Visual Cortex: Visual guidance of movements
- Parietal Cortex: Integrates visual, proprioceptive, and mechanosensory signals
- Input:
- Premotor cortex
- Output:
- Premotor cortex
- Basal ganglia
- Cerebellum
4
Q
Side Loop Structures
A
- Basal Ganglia
- Cerebellum
- Thalamus
5
Q
Basal Ganglia Function, Input, Output
A
- Side Loop structure
- Initiates movements, suppresses non-synergistic movements, “chunks” element into action sequences (muscle memory for patterns of movement)
- Consolidation of procedural memory
- Activation of internally generated movements
- Automation of movements
- Input:
- Non-motor cortical areas
- Premotor cortex
- Output:
- Ventral anterior thalamus
- Pedunculopontine nucleus (PPN)
6
Q
Cerebellum Function, Input, Output
A
- Side Loop structure
- Coordinates movements and corrects error in performance (move smoothly, accurately)
- Input:
- Non-motor cortical areas
- Brainstem UMNs
- Proprioceptive feedback
- Output:
- Ventrolateral thalamus
7
Q
Thalamus Input, Output
A
- Input:
- Basal ganglia
- Cerebellum
- Output:
- Premotor cortex
- Motor cortex
8
Q
Brainstem Components
A
- Brainstem UMNs: Extrapyramidal pathways adjust tone
- Pedunculopontine Nucleus: midbrain locomotor center activates spinal pattern generators for stepping/locomotion
9
Q
Brainstem UMN Function, Input, Output
A
- Extrapyramidal pathways adjust tone (partial contraction of a muscle) and posture
- Input:
- PPN
- Cerebellum
- Output: via reticulospinal & vestibulospinal path?
- Local circuit neurons (CPGs)
10
Q
Pedunculopontine Nucleus Function, Input, Output
A
- Midbrain locomotor center activates spinal pattern generators for stepping/locomotion
- Input:
- Basal ganglia
- Output:
- Brainstem UMNs
11
Q
Local Circuit Neurons
A
?
12
Q
Motor Neuron Pools
A
?
13
Q
Skeletal Muscles Function, Input, Output
A
- Move the body
- Input:
- Motor neuron pools
- Output:
- Proprioceptive feedback
14
Q
Proprioceptive Feedback Function, Input, Output
A
- Sensory consequences of movement
- Input:
- Skeletal muscles
- Output:
- Cerebellum
- Local circuit neurons (CPGs)
15
Q
Types of Muscle Spindle Stretchable Fibers
A
- Nuclear chain fibers: deformation signals info about static length of muscle
- Nuclear bag fibers: deformation encodes rate of change of muscle length
16
Q
2 Muscle Spindle Afferent Types
A
- Type Ia
- Wrap around both types of fibers (nuclear chain AND bag) to provide info to CNS about muscle length and velocity
- Dynamic, fast-adapting, fast-conducting
- Involved in monosynaptic (deep tendon) reflex
- Type II
- Only innervate nuclear chain fibers, so only signal muscle length
- Static, slower-adapting, active during steady state
17
Q
Types of Motor Neurons and Where their Axons End
A
- Alpha: axons end in motor end plates of contractile muscle units
- Gamma: axons end in contractile end portions of muscle spindles
18
Q
Premotor Area Function, Input, Output
A
- Input:
- Parietal cortex (PC) - sensory
- Dorsolateral prefrontal cortex (DLPFC) - cognitive
- Supplementary motor cortex (SMA) - cognitive
- Basically, integrates “where is the world” (parietal) and “what do I want to do about it?” (DLPFC)
- Projects mainly to the primary motor cortex (M1) which is responsible for control of individual muscles via the corticospinal system
- Forms part of a neural network that integrates sensory and cognitive info into goal-directed actions
- Is involved in planning and preparing movements in response to external cues, particularly visual cues
- Also represents “ownership” of the limbs and perception of their movements (sense of agency)
19
Q
Side Loop Structures & Function
A
- Basal Ganglia: initiates movement
- Cerebellum: coordinates movement & corrects errors
- Thalamus: relay center
20
Q
Brainstem Components & Functino
A
- Brainstem UMNs
- Partial contraction of muscles for tone, posture
- Pedunculopontine Nucleus
- Activation of locomotion pattern generators
21
Q
Functional Effector Groups & Function
A
- Local Circuit Neurons
- CPGs in reticular core
- Motor Neuron Pools
- LMNs innervating whole muscles for contraction
- Skeletatl muscles
- Proprioceptive feedback
22
Q
Pyramidal vs Extrapyramidal
A
- Pyramidal: corticospinal tract because it decussates in the pyramids
- Extrapyramidal: all other descending motor systems
23
Q
Alpha Motor Neurons: Distal vs Proximal
A
- Distal muscles: AMNs receive
- Pyramidal (lateral corticospinal tract) input
- Fine control
- Proximal/Axial muscles: AMNs receive
- Extrapyramidal (vestibulospinal, reticulospinal, tectospinal) input
24
Q
Motor Unit
A
Single alpha motor neuron + extrafusal muscle fibers (that the AMN innervates)
25
Extrafusal muscle fiber
* Standard skeletal muscle fiber innervated by AMN
* Generate tension by contracting, thereby moving skeletal muscles
* As opposed to intrafusal muscle spindles embedded wihthin the muscle fiber
26
Contractile force of a motor unit
force-generating capability of muscle fiber types (slow or fast twitch)
x
of fibers innervatd by the alpha motor neuron
27
Fast vs slow twich
* Slow twitch: contracts for longer periods of time, but lower force
* Fast twitch: contracts quickly/powerfully, but fatigues very quickly
* Important in determining the contractile force of a motor unit ( x # of fibers innervated by AMN)
28
Rate Code
* Rate of action potential generation
* Increased rate code = increased muscle force of up to 4x
29
Size Principle
* With increasing strength of input, motor neurons in a motor pool are recruited from smallest size to largest
* Because smaller neurons are easier to depolarize
* Small neurons innervate slow-twitch fibers = postural control
* Medium neurons innervate fast-twitch, fatigue resistant fibers = normal movement
* Large neurons innervate fast-twitch, fatigable fibers = burts of movement
30
Motor Pool
* Collection of all motor neurons (motor units) that innervate a single muscle
* Arranged in columns
* Somatotopically organized:
* Dorsal: flexor
* Ventral: extensor
* Medial: axial/proximal (ex: trunk)
* Lateral: distal (ex: hand)
31
Biceps Brachii nerve & SC levels
* Musculocutaneous nerve of brachial plexus
* Motor pool locates in C5-C6
32
Intrafusal Muscle Fibers
Proprioceptive muscle spindles embedded in parallel with muscle fibers
33
Muscle Spindle Function
* Respond to muscle stretch
* Afferent: report back to DRG
* Facilitate maintance of muscle tone
* Muscle tone = partial contraction of extrafusal muscle fibers
34
Muscle Spindle Fiber Types
1. Nuclear chain fibers
* Signal static muscle length
2. Nuclear bag fibers
* Signal rate of change (velocity) [of muscle length]
35
Muscle Spindle Ending Types
* Type Ia
* Provide info to CNS about muscle length AND velocity
* So, wrap around both nuclear chain and nuclear bag types.
* Dynamic, fast-adpating, fast-conducting
* Type II
* Provide info to CNS about muscle length only
* So,w rap around nuclear chain fibers only
* Static, slower-adapting (though also fast-conducting)
* Active during steady state after change in muscle length
36
Alpha, Gamma motor neurons end on...
* Alpha: motor end plants of contractile muscle units
* EXTRAFUSAL
* Gamma: contractile end portions of muscle spindles
* INTRAFUSAL
* Keep muscles taut
37
Propriospinal Neurons
* Are made of yoked sensory and motor neurons
* Constitute circuit pattern generators (CPGs)
* Live in reticular core/intermediate zone of SC
* Project axons across different levels of SC
* Every alpha, gamma motor neuron is engaged by many propriospinal interneurons
38
Central Pattern Generators
* Generate patterns of rhythmic activity (even in absence of external feedback or supraspinal control)
* Supraspinal input = corticospinal, rubrospinal, vestibulospinal
* Live in SC intermediate zone/reticulare core
* Are made of propriospinal interneuons (=yoked sensory, motor (both alpha and gamma) neurons
* Input: peripheral sensory fibers, supraspinal neurons
* Output: mostly inhibitory to alpha and gamma motor neurons
39
SC Intermediate Zone
* AKA reticular core
* Home of CPGs
* Home of propriospinal interneurons
40
Types of CPG Movement
1. Voluntary: volitional and fractionated movements
2. Stereotypic: hard-wired from birth like grasping, walking, crawling
3. Postural: automatic corrections, based on cerebellum and control of gamma motor neurons to increase tone
41
Premotor Area
* Part of premotor cortex
* Heavily influences M1
* Also has some direct influence over SC via corticospinal tract
* Involved in planning and preparing movements in response to external cues, particularly visual
* Integrates the following inputs:
* Parietal cortex = sensory
* Dorsolateral prefrontal cortex = cognitive
* Supplementary motor area = cognitive
42
Supplementary Motor Area
* Part of the premotor cortex
* Appears to be involved in internally generated movements
* Heavily influence M1
43
Medulla, Pons Reticular Formation Function
* Contain interneuons which interact with moro neurons in brainstem tegmentum
* Regulate stereotypic movements of the head:
* Swallowing
* Respiration
* Coughing
* Vomiting
* Chewing
