Lecture 6: Introduction to Movement Flashcards Preview

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Flashcards in Lecture 6: Introduction to Movement Deck (97)
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1
Q

Three Steps underlying voluntary movement

A
  1. brain sends motor commands to motor neurons in the spinal cord
  2. Motor neurons in spinal cord release ACh at neuromuscular junction
  3. ACh binds to nicotinic ACh receptors on muscle fibre and trigger muscle contraction
2
Q

Nicotinic ACh receptors

A

Respond to NT, Acetylcholine. At the neuromuscular junction they are the primary receptor in muscle responsible for muscle-nerve communication that controls muscle contraction.

3
Q

Where are motor neurons found?

A

In the ventral horns of spinal cord

4
Q

How does AP travel to muscle from spinal cord?

A

Through the ventral roots

5
Q

Where is acetylcholine released? What does it do once released?

A
  • At the neuromuscular junction
  • Released ACh binds to receptors on muscle fibre causing postsynaptic potentials (PSPs) to arise (same rules of temporal and spatial summation apply) and trigger action potentials in muscle fibre
6
Q

What type of receptor are Nicotinic ACh receptors?

A

nAChR receptors are ionotropic

7
Q

What attaches muscle to bone?

A

Tendon

8
Q

Muscles are…

A

a bundle of fibres called myofiber; each fibre is ONE cell with multiple DNA containing nuclei

9
Q

Why do singular muscle fibres have multiple nuclei?

A

They are a product of cellular fusion

10
Q

What is myofiber made of?

A

cylinder shaped bundles of protein polymers called myofibrils

11
Q

What is myofibril composed of?

A

Each myofibril is composed of repeats of a functional unit called sarcomere

12
Q

What is a key factor in muscle contraction?

A

The dynamic change in the structure of the protein polymers (myofibrils)

13
Q

Sarcomere

A

Basic contractile unit that makes up myofibril. Each unit has a myosin (thick) and actin (thin) protein filament.

14
Q

Where would you find myosin and actin?

A

These protein filaments are found in each sarcomere, which is found in myofibril which composes myofiber.

15
Q

Breakdown of muscles

A

muscles –> myofiber –> myofibril –> sarcomere –> actin and myosin

16
Q

Muscles contract when…

A

thick and thin filaments pass each other

17
Q

What is the function of the tropomyosin complex?

A

In a resting state, the tropomyosin complex masks the myosin binding sites in the actin filaments so the myosin head cannot grab the actin fibre

18
Q

What exposes the myosin binding sites on actin?

A

Binding of ACh to nACh receptors trigger APs in muscle fibre which causes release of Ca2+ from sarcoplasmic reticulum (storage for Ca2+). Calcium ion binds to troponin pulling tropomyosin to the side exposing binding sites.

19
Q

What role does calcium play in muscle contraction?

A

calcium ions are released from sarcoplasmic reticulum and bind to troponin revealing the binding sites

20
Q

What does the myosin head do when myosin binding sites are exposed? What does it do?

A

It binds to actin (grabs it) and the bending motion pulls on the actin filaments causing them to slide

21
Q

one motor neuron can be responsible for…

A

multiple muscle contractions

22
Q

Somatic Nervous System

A

Receives sensory info from sensory organs (skin, eyes, ears) and controls movement of skeletal muscles. Carries motor and sensory information both to and from the CNS.

23
Q

Muscles contain what types of sensory nerves (also number)?

A

2 types: muscle spindle and golgi tendon

24
Q

Afferent nerves

A

SENSORY NERVES - carry info from various body parts close to external environment to the CNS

25
Q

Efferent nerves

A

MOTOR NERVES - carry info from CNS to the skeletal muscle

26
Q

Muscle spindle

A

muscle fibre that report muscle length, composed of intrafusal muscle fibres

27
Q

Intrafusal

A

skeletal muscle fibres that serve as specialized sensory organs that detect the amount and rate of change in length of a muscle

28
Q

What innervates muscle spindle?

A

Mechanosensory axon terminals

29
Q

Innervate

A

to supply with nerves

30
Q

Knee-jerk reflex is an example of

A

a stretch reflex

31
Q

How does knee-jerk reaction work?

A
  1. sudden stretch of a muscle causes stretching of muscle spindle fibres
  2. triggers depolarization of sensory nerves in the muscle spindle
  3. directly activates firing of spinal motor neurons leading to contraction of muscle –> thus leg moves
32
Q

Are the neural circuits involved in pain and muscle stretches different?

A

Yes

33
Q

Withdrawal reflex is an example of

A

pain reflex

34
Q

How does withdrawal reflex work?

A
  1. Pain sent to spinal cord is captured by nociceptor fibres
  2. axon terminals of nociceptor fibres enter the dorsal horn and synapse on excitatory interneurons (relay neurons)
  3. Interneurons stimulate motor neurons, producing pain reflex movements
35
Q

Golgi Tendon Organ

A
  • found inside the tendon

- composed of collagen fibres

36
Q

What is golgi tendon organ innervated by?

A

mechanosensory axon terminals

37
Q

What happens to golgi tendon organs when a muscle contracts?

A

Tension on golgi tendon organ increases . Once a threshold tension is reached, AP is generated at golgi tendon which inhibits muscle contraction.

38
Q

Function of golgi tendon organs

A

prevent muscle damage

39
Q

Neuronal pathway involved in golgi tendon organs

A

AP is generated at golgi tendon organ and sensory nerve endings synapse on inhibitory interneurons in the spinal cord. The interneurons then inhibit motor neurons innervating the same muscle.

40
Q

Spinal reflex movements do not…

A

involve neurons in the brain

41
Q

Three cortical areas that control movement

A

Primary motor cortex, secondary motor cortex, and association cortex

42
Q

What is the association cortex responsible for?

A

Integrating and evaluating external stimuli

43
Q

What is the secondary motor cortex responsible for?

A

Plans the sequences of movements to perform tasks

44
Q

What is the primary motor cortex responsible for?

A

Executing motor commands by innervating motor neurons in the spinal cord

45
Q

Execution is to the primary motor cortex as planning is to the…?

A

secondary motor cortex

46
Q

Parts of the association cortex that control movement

A

Posterior parietal and dorsolateral prefrontal association cortex

47
Q

What is the posterior parietal association cortex responsible for?

A

Integrating visual, auditory, and somatosensory information from external objects and body parts (joints, muscles, etc)

48
Q

Where does output from posterior parietal association cortex go?

A

to the dorsolateral prefrontal association cortex

49
Q

What is the Dorsolateral Prefrontal Association Cortex responsible for?

A

evaluating external stimuli and initiating appropriate voluntary reactions

50
Q

Where does output from the dorsolateral prefrontal cortex go?

A

to secondary motor cortex and primary motor cortex

51
Q

Secondary motor cortex

A

Becomes active right before the initiation of a voluntary movement. Sends outputs to the primary motor cortex. Involved in planning movements.

52
Q

Primary motor cortex

A

Located anterior to central fissure

53
Q

How is the primary motor cortex similar to the somatosensory cortex?

A

Disproportionately larger areas are devoted to body parts that require complex movements (hands, mouth, tongue) than those requiring less precise motor control (trunk).

54
Q

Two major pathways that motor commands to spinal motor neurons travel along?

A

dorsolateral pathway and ventromedial pathway

55
Q

Dorsolateral pathway

A
  • runs through the dorsolateral side of spinal cord

- controls distal muscles in arms, legs, hands, fingers, and toes

56
Q

Distal and proximal muscles

A
  • muscles farther from centre of body

- muscles closest to midline of body

57
Q

Ventromedial pathway

A
  • runs through the ventromedial side of spinal cord

- controls proximal muscles in trunk and proximal limbs

58
Q

Pathways in the dorsolateral pathway

A

corticospinal tract and corticorubrospinal tract

59
Q

Dorsolateral: Corticospinal tract

A

Controls wrist, hands, fingers, toes

60
Q

Dorsolateral: Corticorubrospinal tract

A

Controls distal muscles of arms and legs (motor neurons of spinal cord) and some facial muscles (motor neurons in brainstem)

61
Q

Describe pathway of neurons in dorsolateral corticospinal tract

A
  • neurons in primary motor cortex directly synapse on motor neurons in the spinal cord
  • cortical axons descend through medullary pyramids then move across midline
62
Q

Describe pathway of neurons in dorsolateral corticorubrospinal tract

A
  • Cortical neurons synapse at the red nucleus
  • axons of red nucleus cross the midline at the level of the medulla and THEN synapse on motor neurons in the spinal cord AND some on motor neurons in brainstem
63
Q

How does the ventromedial corticospinal tract descend?

A

Ipsilaterally, the axons branch and synapse bilaterally in multiple spinal segments

64
Q

What does the ventromedial corticospinal tract control?

A

trunk and proximal limb muscles for goal-directed movements

65
Q

Which pathway is in charge of goal-directed movements

A

the corticospinal tract of the ventromedial pathway

66
Q

Tracts in the ventromedial pathway

A

corticospinal tract and cortico-brainstem-spinal

67
Q

Describe pathway of the neurons in the cortico-brainstem-spinal tract

A

They synapse on various brainstem structures (vestibular nuclei, tectum, reticular formation) which then innervate multiple spinal segments

68
Q

What does the cortico-brainstem spinal tract control?

A

body postures - adjusts trunk and proximal limb muscles in response to changes in sensory signals (vestibular, auditory, and visual)

69
Q

Evaluation, planning, and execution

A

association cortex, secondary motor cortex, primary motor cortex

70
Q

What’s the major driving force of voluntary movements

A

cortical inputs

71
Q

Non-cortical structures that make voluntary movements more streamlined?

A

basal ganglia and cerebellum

72
Q

What connects the secondary and primary cortex?

A

Secondary cortex sends signals to primary motor cortex through the basal ganglia and then the thalamic circuit

73
Q

Structures that make up the basal ganglia

A
  • striatum (which is made of caudate nucleus and putamen)
  • globus pallidus (between striatum and thalamus, has interna and externa sections)
  • substantia nigra (in the midbrain)
74
Q

Substantia Nigra is a source of…

A

dopamine

75
Q

Ventrolateral nuclei in the thalamus receive input from… and send…

A
  • basal ganglia

- excitatory outputs to motor cortex

76
Q

Which structures of the Basal Ganglia are GABAergic? What does it mean?

A

The striatum, globus pallidus interna (gp-i), globus pallidus externa (gp-e) are all GABAergic structures. This means they are inhibitory structures.

77
Q

Inhibitory structures are…while excitatory structures are

A
  • GABAergic

- glutamatergic

78
Q

Which structure is not active when you are at rest?

A

secondary motor cortex (no motor commands)

79
Q

What does it mean when globus pallidus is said to be tonically active? What does this activity do?

A

It means that it is continuously producing GABA which inhibits thalamic motor nuclei and prevents unnecessary movements

80
Q

What holds back the motor thalamus when you are at rest?

A

GABA produced by the globus pallidus interna

81
Q

What needs to occur for initiation of movements? What structure completes this function?

A

Tonic activity of gp-i must be inhibited. Striatum is activated by excitatory signals from secondary motor cortex and striatum then inhibits gp-i.

82
Q

Which structures of the movement system are inhibitory and which are excitatory?

A

Inhib: Striatum and gp-i
Excit: Secondary motor cortex and thalamus

83
Q

What is the “direct pathway of the Basal Ganglia”? What’s another name for it?

A

Direct pathway is from striatum to gp-i (inhibitory structure inhibiting inhibitory structure). Also called the D1 pathway.

84
Q

How does the D1 pathway get its name?

A

Striatal GABA neurons express dopamine receptor type 1 (D1R)

85
Q

What happens when D1R cells fire action potential spikes?

A

Movement is promoted because striatal neurons will inhibit gp-i

86
Q

What would an inhibitory structure between the striatum and gp-i do if the striatum is activated? Which structure is this?

A

Inhibit movement. The globus pallidus externa.

87
Q

What’s included in the indirect pathway of the basal ganglia? What’s another name for this pathway?

A

Striatum -> gp-e -> gp-i

Also called D2 pathway

88
Q

How does D2 pathway get its name?

A

striatal GABA neurons express D2R receptors

89
Q

Which dopamine receptors are associated with the GO and NO GO pathways?

A

D1R is GO, D2R is NO GO.

90
Q

What type of receptors are DRs?

A

Metabotropic receptors

91
Q

Neurons in the striatum express either…

A

D1R or D2R but not both—they are mutually exclusive.

92
Q

D1R has an… while D2R has an…

A

excitatory effect

inhibitory effect

93
Q

What role does dopamine play in the basal movement circuit?

A

Dopamine is required to inhibit the D2R pathway so that the direct pathway is functional. Glutamate alone from the cortex will activate both pathways.

94
Q

Parkinson’s disease

A

The substantia nigra is degenerated—no dopamine or less.

95
Q

Major inputs to the cerebellum

A
  1. input from the motor cortex via pons (info about motor commands)
  2. Input from the sensory and vestibular system (info about body position and movements)
96
Q

What does the cerebellum do and how does it do it?

A

Compares motor commands and body position and then adjusts movements as they occur—fine tunes motor controls.

97
Q

Cerebellum learns by…

A

sensory feedback