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NSCI 201 > Pre-Midterm Content Conference (5-9) > Flashcards

Pre-Midterm Content Conference (5-9) Flashcards

1
Q

Spinal Cord and brainstem circuits

A
  • skeletal muscles and local circuit neurons
  • final common path for initiating movement
  • both voluntary and involuntary movements
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2
Q

Upper motor systems

A
  • cerebral cortex and brainstem centres
  • synapse of complex voluntary movements
  • primary motor cortex and premotor cortex essential for proper sequential movement
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3
Q

Basal Ganglia

A
  • initiation and termination of movement
  • prevents initiation of unwanted movements
  • prepares motor circuits for initiation of movements
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4
Q

cerebellum

A
  • attenuates and adjusts between intended movement vs actual movement executed
  • mediates real-time and long-term motor errors
  • feedforward control
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5
Q

Spinal Cord Motor Neurons

A
  • The distribution of lower motor neurons are spatially distinct according to the muscle innervation in the human.
  • Each lower motor neuron innervates the muscle fibres of a single muscle.
  • cervical enlargment: neurons that innervate the upper limbs.
  • lumbar enlargment: neurons that innervate the lower limbs.
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6
Q

Local Circuit Neurons

A

1) Long distance neurons
- locomotion and posture control in axial muscles

2) Short distance neurons
- skilled movement and fine motor control in distal muscles

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7
Q

Types of Lower Motor Neurons

A

1) alpha motor neurons (large diameter motor neurons) + striated muscle fibres (generate force for posture and movement) = one motor unit

2) gamma motor neurons (small diameter neurons), in muscle spindles, embedded intrafusual muscle fibres, sensory information about muscle length.

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8
Q

What are the different types of motor units: muscle fibres?

A

1) Slow (S)
- resistant to fatigue
- low level of force

2) Intermediate (FR)
- fast and fatigue-resistant
- greater force than S

3) Fast (FF)
- Fast and fatigable
- important for short bursts of high force

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9
Q

Muscle Force Generation

A
  • the size of an alpha motor neuron determines the size of a motor unit and the amount of force that can be generated.
  • the size principle: more stimulation, larger motor units, more force!
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10
Q

What are the two muscle receptors?

A

Spindes and Golgi tendon organ

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11
Q

What is the difference between tonic activity and phasic activity?

A

1) Tonic activity:
- fibres show resistance to fatigue and have longer durability

2) Phasic activity:
- fibres generate force during quick action only when needed and have shorter durability.

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12
Q

Muscle Spindles: Muscle Length - difference between intrafusal muscle fibres and extrafusal muscle fibres

A

Intrafusal muscle fibres:
- small diameter fibres innervated by gamma motor neurons.

Extrafusal muscle fibres:
- large diameter fibres producing movement via large diameter alpha motor units.

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13
Q

The Stretch Reflex

A
  • a negative monosynaptic feedback loop balancing muscle length in response to load.
  • reciprocal innervation: contraction of agonist + relaxation of antagonist.
  • Steady tension (muscle tone) comes from Group II afferents
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14
Q

Golgi Tendon Organ

A
  • innervated by single group 1b sensory afferents.
  • they are most sensitive to muscle tension increase due to active muscle contraction, and are insensitive to passive stretch.
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15
Q

Locomotion

A
  • central pattern (CPGs) in the spinal cord control rhythmic movements.
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16
Q

Upper Motor Control Pathways

A

1) Cerebral Cortex (Skilled Movements):
Upper motor neurons in the cerebral cortex.
Descend ipsilaterally, then cross to contralateral side through the lateral white matter of the spinal cord.
Synapse onto lower motor neurons in the lateral ventral horn.
Control distal limb muscles.

2) Brainstem (Posture, Balance, Locomotion):
Upper motor neurons in the brainstem.
Descend through the anterior-medial white matter of the spinal cord.
Axial and Proximal Limb Muscles (Ipsilateral):
Synapse onto lower motor neurons in the medial ventral horn.
Control posture, balance, and locomotion.
Or Across Midline (Contralateral):
Synapse onto lower motor neurons in the contralateral medial ventral horn.
Control posture, balance, and locomotion.

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17
Q

Name the cortex posterior to the primary motor cortex, what is it topographic organization in relation to the primary motor cortex?

A

-> Supplementary Motor Area (SMA):
- located on the medial surface of the hemisphere
- role in planning and initiation of motor movements
- involved in the coordination of bilateral movements

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18
Q

Upper Motor Pathways of Primary Motor Cortex

A

1) Corticospinal Tract: Lateral

2) Corticospinal Tract: Ventral

3) Corticobulbar Tract

Information from Descending Systems (upper motor neurons)
- Motor Cortex:
Planning, initiation, and directing voluntary movement
- Brainstem:
Rhythmic, stereotypes movements and postural control

Cortical motor neurons (pyramidal cells) travel down through brain and midbrain to spinal cord.

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19
Q

Corticospinal Tract: Lateral

A
  • (90%) decussate and terminate in contralateral ventral horn / intermediate zone of spine
  • synapse onto local circuit neurons or alpha motor neurons
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20
Q

Corticospinal tract: ventral

A
  • (10%) terminate in ipsilateral ventral horn
  • serve axial and proximal muscles
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21
Q

Corticobulbar Tract

A
  • head, face, and neck muscles
  • bilateral collaterals, synapse in brainstem nuclei
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22
Q

Upper Motor Neurons: Direction Sensitivity

A
  • upper motor neurons have a preferred direction. They fire before movement commences.
  • Population summation: different populations of cells are selectively tuned to a particular direction.
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23
Q

Premotor Cortex

A

1) Lateral Premotor
Closed-loop movement
Firing is based on the presence of a visual cue and signal to move

2) Ventrolateral Premotor
Observed Movement
Mirror neurons fire in performing and observing movement of others

3) Medial Premotor
Open-loop movement
Internal cues allows for selection and initiation of movement

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24
Q

Brainstem Pathways: Vestibular Nuclei

A
  • integrate information from vestibular system.
  • bilateral medial vestibulocervical tract.
  • ipisilateral vestibulospinal tract.
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25
Q

Brainstem Pathways: Reticular Formation

A
  • bilateral temporal and spatial coordination of limb and trunk movements.
  • feedforward postural adjustments to prepare for primary movement.
26
Q

Brainstem pathways: Superior Colliculus

A
  • controls axial muscles in the neck to support circuits for head orientation
  • direct and indirect pathways to spinal cord
27
Q

Brainstem pathways: Red nucleus

A
  • projects only to cervical cord, controls arm and head movements
    -active before movement onset
28
Q

Basal Ganglia

A
  • Basal Ganglia- large and functionally diverse set of nuclei that lies deep
    within the cerebral hemispheres.
  • General function- modulate movement.
  • Motor nuclei of the basal ganglia are divided in: input zone and striatum (caudate + putamen)

-the destinations of the incoming axons from the cerebral cortex are the medium spiny neurons.

  • the large types of these neurons colect and integrate input from cortical, thalamic and brainstem structures.
29
Q

Inputs to the Basal Ganglia

A
  • Axons from medium spiny neurons converge on neurons in the Pallidum- Globus pallidus + substantia nigra pars reticulata.
  • these are the main sources of output from the basal ganglia complex to other parts of the brain.
30
Q

Corticostriatal Pathway (inputs to the basal ganglia nuclei)

A
  • Nearly all regions of the cerebral cortex project directly to the striatum, making the cortex the source of the largest input to the basal ganglia.
  • The majority of these projections are from association areas in the frontal and parietal lobes, with contributions from the temporal, insular, and cingulate cortices, as well as the amygdala and hippocampal formation.
  • All these projections travel through the subcortical white matter on their way to the caudate and putamen.

-Parallel corticostriatal pathways within the striatum mirror the functional organization of the cortex.

  • Visual and somatosensory cortical projections are topographically mapped in regions of the putamen.
31
Q

Inputs to the basal ganglia (dopaminergic)

A
  • one important set of brainstem inputs to the medium spiny neurons is
    dopaminergic, and it originates in a subdivision called the substantia
    nigra pars compacta.
  • The dopaminergic synapses are located on the base of the spine, in close proximity to the cortical synapses, where they selectively modulate cortical input.
  • As a result, inputs from both the cortex and the substantia nigra pars
    compacta are relatively far from the initial segments of the medium spiny
    neurons’ axons, where the nerve impulses are generated.
32
Q

MSN’s (Medium Spiny Neurons)

A

1) Characteristics:
Exhibit very little spontaneous activity and must simultaneously receive many excitatory inputs to overcome the stabilizing influence of potassium conductance.
When MSNs do become active, their firing is associated with the occurrence of a movement.
Extracellular recordings show that these neurons increase the rate of discharge before an impending movement.

2) Putamen Neurons:
Discharge in anticipation of limb and trunk movements.

3) Caudate Neurons:
Fire prior to eye movements.

4) Encoding Movement Decision:
The activity of these cells may encode the decision to move towards a goal rather than the direction and amplitude of the actual movement necessary to reach the goal.

5) Firing Rate:
Medium spiny neurons increase their firing rate at the termination of a movement sequence.

6) Inputs Received:
Receive input from:
Cortical neurons.
Local circuit neurons.
Dopaminergic neurons from the substantia nigra.
Other medium spiny neurons.
Raphe nuclei, brainstem.

7) Input Integration:
Each MSN receives very few inputs from each cortical axon.
Each cortical axon contacts many MSNs.
A single MSN integrates input from thousands of cortical neurons.
Different inputs contact MSNs at different locations.
Cortical neurons synapse on dendritic spines.
Local circuit and thalamic neurons synapse on dendritic shafts and close to the soma, which modulates the effects of cortical inputs.

33
Q

Projections to the basal ganglia nuclei

A
  • The medium spiny neurons of the caudate and putamen give rise to
    inhibitory GABAergic projections that terminate in the globus pallidus and
    the substantia nigra pars reticulata in the pallidal nuclei of the basal
    ganglia.
  • The efferent neurons of the globus pallidus and substantia nigra pars
    reticulata together give rise to the major output pathways that allow the
    basal ganglia to influence the activity of upper motor neurons located in
    the motor cortex and in the brainstem.
34
Q

Projections from the basal ganglia to other brain regions

A

1) Pathway to the Cortex:
Arises primarily in the medial division of the globus pallidus, called the internal segment.
Reaches the motor cortex via a relay in the ventral anterior nuclei and ventral lateral nuclei of the dorsal thalamus.
These projections project directly to motor areas of the cerebral cortex and terminate in the motor areas of the frontal lobe.

2) Pathway from Substantia Nigra Pars Reticulata (SNr):
Efferent axons have more direct access to upper motor neurons.
Synapse on neurons in the superior colliculus that command head and eye movements without an intervening relay in the thalamus.

3) Output of Basal Ganglia is Inhibitory:
Efferent cells of both the globus pallidus and substantia nigra pars reticulata are GABAergic.
The main output of the basal ganglia is inhibitory.

4) Tonically Active Neurons in Output Structures:
Neurons in both the globus pallidus and substantia nigra pars reticulata have high levels of spontaneous activity.
Prevent unwanted movement by tonically inhibiting cells in the thalamus, superior colliculus, and other brainstem nuclei.

5) Medium Spiny Neurons of the Striatum:
GABAergic and inhibitory.
Net effect of phasic excitatory inputs is to open a physiological gate by inhibiting the tonically active inhibitory cells of the globus pallidus and substantia nigra pars reticulata.

35
Q

Disinhibitory Circuit

A

1) Basal Ganglia Inputs:
Medium spiny neurons receive excitatory input from the cortex.
Excitatory inputs inhibit tonically active inhibitory cells of the globus pallidus and substantia nigra pars reticulata.

2) Thalamic Relay:
Axons from the internal segment of the globus pallidus and substantia nigra pars reticulata reach the motor cortex via relay in the ventral anterior and ventral lateral nuclei of the dorsal thalamus.
These projections project directly to motor areas of the cerebral cortex and terminate in the motor areas of the frontal lobe.

3) Direct Pathway:
Efferent axons from substantia nigra pars reticulata synapse on neurons in the superior colliculus that command head and eye movements without an intervening relay in the thalamus.

4) Function:
Relieves inhibition, allowing the activation of specific pathways or motor responses.
Facilitates appropriate motor responses while inhibiting unwanted movements.

36
Q

Direct pathway to regulate initiation and suppression of movement

A

Direct pathway serves
to release upper
motoneurons from tonic
inhibition. Facilitates
movement

37
Q

Indirect pathway to regulate initiation and suppression of movement

A

Indirect pathway serves
to increase the tonic
level of inhibition.
Inhibits movement.

(direct and indirect function in opposition and determine if the BG will facilitate or suppress movement)

38
Q

Dopaminergic modulation of direct and indirect pathway

A

1) Dopamine facilitates the activity of the direct pathway by acting on dopamine receptors expressed by medium spiny neurons within the
striatum.

2) Activation of D1 receptors increase the excitability of MSNs in the direct pathway, promoting the release of upper motor neurons from tonic inhibition and facilitating movement
initiation.

3) Dopamine inhibits the activity of the indirect pathway by acting on dopamine D2 receptors expressed by MSN in the striatum.

4) Stimulation of D2 receptors leads to a reduction in the excitability of MSNs in the indirect pathway = decreased inhibitory output to the globus
pallidus.

5) Inhibiting the activity of the indirect pathway disinhibits thalmocortical circuits, allowing for the facilitation of movement initiation.

39
Q

What are associated diseases to the indirect pathway?

A

Huntington’s disease= neurons from the caudate degenerate and upper
motor neurons become activated by inappropriate signals.

Hemiballismus = violent, involuntary movements of the limbs, result to
damage to STN. Movements are initiated by abnormal discharges of upper motor neurons that are receiving less tonic inhibition from the basal ganglia.

40
Q

Parkinson’s Disease

A
  • major degeneration of the nervous system
  • tremors at rest
  • rigidity
  • bradykinesia
  • speech - hypophonia
  • micrographia
  • associated with dementia and dyskinesias
  • progressive loss of dopamine in neurons of substantia pars compacta. cause of generation not known.
41
Q

Parkinson’s is a hypokinetic movement disorder

A
  • in healthy brain, dopamine acts as D1 & D2 receptors to decrease inhibitory outflow of the BG, allowing excitation of upper motor neurons.
  • In parkinson’s brain, dopamine from the SNPC is reduced, making it more difficult to initiate and terminate movement.
  • most effective treatment is combined pharmacology and DBS (Deep brain stimulation) (levodopa)
42
Q

How is deep brain stimulation used for parkinsons?

A
  • DBS is used to treat
    the motor symptoms
    of parkinsons disease
  • Implantation of
    electrodes to specific
    areas of the brain
  • Most common targets:
    subthalamic nucleus
    and globus pallidus.
    There regions are
    involved in the
    dysregulated motor
    circuitry of parkisnons
    disease.
43
Q

Other Roles of basal ganglia

A
  • Associated with cognitive and emotional regulation
  • Parallel loops originate in different regions of the cerebral cortex
    1) Dorsolateral prefrontal loop
  • regulates initiation and termination of cognitive processes
    2) Limbic loop
  • Regulate emotional and motivated behavior and transitions
    between mood states
  • Ventral striatum is particularly implicated in reward, motivation
    and emotion
44
Q

Cerebellum

A
  • Does not project directly to the motoneurons of the spinal cord
  • Modifies movement by regulating upper motoneurons in the motor cortex
  • Made up of a cerebellar cortex and deep cerebellar nuclei
  • Primary function is to detect ‘motor error’ -> the difference between
    intended and actual movement and sensory motor integration
  • main parts defined by source of input:
    1) cerebrocerebellum
    2) Spinocerebellum
    3) Vestibulocerebellum
45
Q

cerebrocerebellum

A
  • Receives indirect input from many areas of cerebral cortex
  • Well developed in humans and other primates
  • Regulates highly skilled movement such as planning and execution of
    complex spatial and temporal sequences of movement such as speech
  • projects to dentate nucleus then to premotor cortex (motor planning) (pathways to upper motor neurons)
46
Q

Spinocerebellum

A
  • Receives direct input from spinal cord
  • Lateral part regulates movement of distal muscles
  • Central part (vermis) regulates movement of proximal muscles and some eye movements
  • projects to interposed and fastigal nuclei and then to motor cortex and brainstem (motor execution) (pathways to upper motor neurons)
47
Q

vestibulocerebellum

A
  • Oldest part of the cerebellum
  • Receives input from vestibular nuclei in brainstem
  • Primarily involved in movements to maintain posture and balance and the
    vestibulo-ocular reflex
  • projects to vestibular nuclei and then lower motor neurons in spinal cord and brainstem (balance and vestibulocular regulation)
48
Q

Cerebellum Communication

A

1) Superior Cerebellar Peduncle:
Almost entirely efferent pathway.
Neurons in deep cerebellar nuclei project to:
Upper motor neurons in primary motor and premotor cortices.
Upper motor neurons in the superior colliculus to control orienting movements.

2) Middle Cerebellar Peduncle:
Afferent pathway to the cerebellum, the largest pathway in the brain containing more than 20 million axons.

3) Inferior Cerebellar Peduncle:
Contains multiple afferent and efferent pathways:
Afferents from:
Vestibular nuclei.
Spinal cord.
Brainstem tegmentum.
Efferents to:
Vestibular nuclei and reticular formation.

49
Q

Functional organization of inputs to cerebellum

A

1) Cerebellum Cerebral Cortex Input:
- Originates the largest input to the cerebellum, with the major destination being the cerebrocerebellum.

2) Pathway:
- Cortical axons synapse on neurons in the ipsilateral pontine nuclei.
- Pontine nuclei receive input from all areas of the cerebral cortex and the superior colliculus.

3) Transverse Pontine Fibers:
- Axons of the cells in the pontine nuclei.
- Cross the midline and enter the contralateral cerebellum via the middle cerebellar peduncle.

50
Q

Functional organization of inputs to
cerebellum/What regioms project to the pontine nuclei?

A

1) Motor and premotor cortex
-> motor control

2) Somatic sensory cortex
-> Sensory motor integration

3) Visual motion regions of the posterior parietal cortex (magnocellular processing stream)
-> Visuomotor coordination

51
Q

Projections from the cerebellum

A
  • Most of the cerebellar cortex projects to deep cerebellar nuclei prior to
    reaching the target.

-Thalamus is a major relay target from cerebellum to motor cortex

  • relay target from cerebellum to motor cortex
  • 4 major deep nuclei
52
Q

Cerebellar Nuclei Organization

A

1) Fastigial Nuclei:
More medial than interposed nuclei.
Mediate axial and proximal muscles.

2) Interposed Nuclei:
Mediate limbs.
Organized similar to the mediolateral organization seen in the spinal cord.

53
Q

What happens if there is damage to the cerebellum?

A
  • Causes persistent errors in movement on the same side of the body as the cerebellar deficit.
  • alcohol abuse
  • ataxia
54
Q

what happens if there is damage to cerebrocerebellum?

A

defecits in coordination and visuomotor integration

55
Q

what happens if there is damage to vestibulocerebellum?

A
  • impairs ability to stand upright and maintain direction of gaze.
56
Q

what happens if there is damage to spinocerebellum?

A
  • difficulty walking
  • other signs:
    dysmetria - over or under reaching target
    action or intention tremors
    speech deficits
57
Q

Difference between mossy fibres and climbing fibres (inputs to the cerebellum)?

A

1) Mossy fibers
○ Arise from many areas in the cortex and brainstem
○ Synapse into granule cells
○ Give rise to parallel fibers which have excitatory synapses onto the
dendritic spines of the Purkinje cells

2) Climbing fibers
○ Arise from inferior olive
○ Contact Purkinje cells directly
○ Excitatory synapses onto Purkinje cells

58
Q

Parietal Association Cortex

A
  • integrating of sensory information
  • attention
  • perception
  • memory
59
Q

temporal association cortex

A
  • memory
  • language
  • emotion
  • object recognition
60
Q

Frontal Association Cortex

A
  • decision making
  • working memory
  • planning
  • social behaviour
61
Q
A

NSCI 201 (5 decks)

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