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Neuroscience > week 7: Movement > Flashcards

week 7: Movement Flashcards

1
Q

Types of muscle (3)

A
  • skeletal
  • cardiac
  • smooth
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2
Q

Structures involved in muscle contraction (3)

A

Actin

Myosin

Sarcomere

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3
Q

Motor unit

A

Alpha motor neuron

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4
Q

What is a neuromuscular junction

A

Synapse between a motor neuron and a muscle fibre

1. AP in motor neuron 
2. = Release of ACh 
3. EPSP in muscle fibre (endplate potential) 
4. = AP in muscle fibre 
5. = Contraction (twitch)
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5
Q

Sensory feedback to motor neurons: 2 parts involved

A
  • muscle spindles (in fibres)
  • Golgi tendons (in tendon of muscle)
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6
Q

Sensory feedback: Muscle spindles

A

▪ Fibrous capsules containing specialised muscle fibres
▪ Detects change in muscle length
▪ Contracts of spindle poles to keep 1a axons within working range
▪ → muscle contraction

(e.g. rolling your ankle = a rapid change in muscle length detected = contraction of muscle to keep in within working range.)

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7
Q

Sensory feedback: Golgi tendon organs

A

▪ Located at the junction of muscle and tendon
▪ Innervated 1b sensory axons
▪ Monitors muscle tension (tendon stretch)
▪ →muscle inhibition

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8
Q

Control of movement by the spinal cord: Monosynaptic reflexes

A

e.g. the platella tendon reflex

- All reflexes go along the Reflex arc
- A neural pathway
	a. Receptors
	b. Afferent neurone
	c. Integrating centre
	d. Efferent neurone
            e. Effector

1. Activation of a receptor (by stimulus)
2. Activation of a sensory/ afferent neurone (starts in muscle, ends in spinal cord)
3. Integrating centre and information processing (occurs only in the cell body of the motor neurone)
4. Activation of a motor / efferent neurone (from spinal cord to muscle/ effector) Effector receives AP = reflex action
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9
Q

Polysynaptic reflexes

A

(Withdrawal reflex)
- Also solely uses the spinal cord to react, however pain signals can also be sent to the brain (e.g. if pick up a hot object)
1. Receptors detect pain
2. Afferent neurone to spinal cord
3. Integrating centres here found in spinal cord, does not synapse onto a motor neurone directly, goes to an interneuron, before going to a motor neurone and also an inhibitory neurone which goes to the muscle affected, inhibiting it from touching the hot object again
4. Efferent neurones
5. Effector

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10
Q

Different between monosynaptic and polysynaptic reflexes

A

Mono = one synapse

Poly = uses more than 1 synapses, involving interneuron

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11
Q

Cerebral cortex control of movement: Structures involved

A
  • Primary motor cortex
    • Supplementary motor area
    • Premotor cortex
  • Mirror neurons
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12
Q

Primary motor cortex: structure

A

(dorsal of frontal lobe)

Organised somatotopically: motor homunculus
(disproportionate area of cortical space needed for hands and mouth compared to other areas, as they need to do more finer movements)

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13
Q

Primary motor cortex

A

primary motor cortex is the primary commander in executing movement

Input:
▪ Frontal association cortex
▪ Primary somatosensory cortex (S1)
* S1 neurons in particular location send info to primary motor cortex area responsible for muscles in that body part
* Rapid feedback to the motor system

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14
Q

Supplementary motor area (& Pre-SMA)

A

Learning and planning of behaviours consisting of sequences of movements (e.g. playing the piano)

Pre-SMA (in orange on diagram) is associated with the (perception of) control of spontaneous movement

▪ Stimulation of SMA (in yellow) and PreSMA provokes the urge to make a movement or the anticipation that a movement will occur
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15
Q

Damage to supplementary motor area?

A

Damage disrupts ability to execute well-learned sequences of responses

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16
Q

Premotor cortex

A

▪ Learning and executing of complex movements
▪ Guided by sensory information
▪ Contains Mirror neurons

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17
Q

Premotor cortex: Mirror neurones

A
  • (speculated that mirror neurones are why if you see someone yawning, you might too)
    • A subset of motor control neurones, fires when we watch other people doing something
    • Important to adopt another’s’ pov, imitation and emulation
    • Imitation and emulation can be linked to evolution
    • Mirror neurones for action, mirror neurones for touch
    • Mirror neurones for touch can be fired when wating another person being touched. Can empathise with other people, but you won’t feel the touch yourself because the receptors on your arm are not sensing a touch
    • Distinction of your consciousness to others? Phantom limbs = your arm is not there to sense that there is not a touch there, so may feel a phantom touch?
      Linked to empathy (side note: do psychopaths have these?)
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18
Q

Control of movement by subcortical areas

A
  • Basal ganglia
    • Cerebellum
      • Reticular formation
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19
Q

Example: how to diagnose a zombie?

A

Cerebellum ataxia

Wernicke’s area damage - related to understanding language

20
Q

Basal ganglia

A

▪ Part of telencephalon
▪ Important for the control of voluntary movement

Striatal nuclei receive input:
* Primary motor cortex
* Primary somatosensory cortex
* Substantia nigra
* + other cortices

Output:
* Primary motor cortex
* Supplementary motor cortex
* Premotor cortex
* Motor nuclei of the brainstem

21
Q

Basal Ganglia: Neurodegenerative diseases

A

Characterised by motor defecits

▪ Huntington’s disease

▪ Parkinson’s disease

22
Q

What is Huntington’s disease? (& causes)

A

▪ Hereditary disease caused by degeneration of the striatal neurons
(a cluster of neurones in the basal ganglia)

  • Loss of inhibition exerted on globus pallidus (from caudate nucleus and putamen - see diagram)
23
Q

Huntington’s symptoms:

A

▪ Uncontrollable jerky limb movements

▪ Impaired ability to cease movements

▪ Cognitive and emotional change
Lack of flexible thinking, difficult to pick up emotion, slow processing, difficulty taking in new info

24
Q

Huntington’s: who gets it?

A
  • Typically strikes from 30-50 although symptoms can be viewed earlier (prodromes)
    • Pattern of inheritance - 50% chance of being affected if parents have it
    • CAG (Huntington gene) repeats over a certain threshold
25
Q

Cerebellum: Sructure

A

▪ Not part of brainstem

▪ Part of metencephalon (along with Pons)

▪ 2 hemispheres

▪ Functions ipsilaterally (situating/ affecting the same side of the body - not contralaterally)

▪ Connected to brainstem 
	– cerebellar peduncles

▪ Outer surface = tightly folded
		§ increases surface area and density of neurons

▪ Accounts for >50% (around 80%) of brain neurons

26
Q

Cerebellum: Function

A

Involved in motor control functions
- Facilitates movement, refines it
▪ Smooths and integrates ongoing movement
▪ Important for independent rapid skilled limb movements
▪ Important for postural reflexes
▪ Integrates movement sequences
▪ Partly responsible for motor learning

27
Q

Cerebellum: Implications of damage

A

▪ Possible causes: stroke, haemorrhage, alcoholism, tumour, physical trauma,
chronic degenerative conditions

▪ Cerebellar Ataxia = lack of coordination of movements

▪ Can manifest as difficulty walking, particularly with narrow base (one foot in front of the other)

28
Q

Intention tremor

A

involuntary, rhythmic muscle contractions (oscillations) that occur during a purposeful, voluntary movement.

▪ Slow tremor of the extremities that occurs at the end of a purposeful movement (e.g., touching a finger to the tip of nose)

▪ Jerky, poorly coordinated, exaggerated movements
29
Q

Reticular formation

A

▪ Reticular formation includes a large number of nuclei in the brainstem (midbrain, pons and medulla oblongata)
▪ Important in a variety of motor functions:
▪ Regulates muscle tone (via gamma motor neurons)
▪ Controls (semi)automatic responses (e.g. respiration, coughing, vomiting)
▪ Controls posture
▪ Plays a role in locomotion

30
Q

Motor pathways: 2 major descending motor pathways

A

▪ Lateral pathways

▪ Ventromedial pathways

31
Q

Lateral pathways: Structure

A

▪ Originate in the cortex

▪ Composed of three tracts
	* Lateral corticospinal (light blue) 
		(hand & fingers)
	* Corticobulbar (green) 
		(face, neck, tongue, eye)
	* Rubrospinal (red) 
		(forearm)
32
Q

Lateral pathways: Functions

A

▪ Control voluntary independent movement of distal muscles (e.g. in forearm, hand, finger)

33
Q

Ventromedial pathways: structure

A

▪ Originate in the brain stem
▪ Composed of four tracts
* Ventral corticospinal tract
* Vestibulospinal tract
* Tectospinal tract
* Reticulospinal tract

34
Q

Ventromedial pathways: Function

A

▪ Control automatic movements of proximal and axial muscles (e.g. movements related to posture and locomotion)

35
Q

Recap: What connects the cerebellum to the brainstem?

A

Cerebellar penducles

36
Q

Reading: Extrafusal muscle fibres

A

(are served by axons of the alpha motor neurones). Contraction = provide muscles motive force

37
Q

Reading: Intrafusal muscle fibres

A

(are specialised sensory organs severed by 2 axons; one sensory, one motor).

A muscle fibre that functions as a stretch receptor, arranged parallel to the extrafusal muscle fibres, thus detecting changes in muscle length.

38
Q

Reading: Why is skeletal muscle striated?

A
  • A single muscle fibre consists of a bundle of myofibrils, each of which consists of overlapping strands of actin and myosin.

The regions in which the actin and myosin filaments overlap produce dark stripes, or striations.

39
Q

Reading: the mechanics behind contraction

A
  • AP fired = acetylcholine released from terminal buttons = depolarisation of postsynaptic membrane on the muscle cell = the endplate potential.
    • The endplate potential causes a contraction of the muscle fibre.

To produce a contraction in the muscle, myosin attaches to actin strands, bends in one direction, detaches itself, bends back, and reattaches to the actin at a point farther down the strand. This process repeats along the actin and myosin as they slide past each other to shorten the muscle, contracting it.

40
Q

Reading: What would happen if extra weight was added to your hand unexpectedly?

A

If the weight the person is holding is increased, the forearm begins to move downward. This movement lengthens the muscle and increases the firing rate of the muscle spindle afferent neurons, whose terminal buttons then stimulate the alpha motor neurons, increasing their rate of firing. Consequently, the strength of the muscular contraction increases, and the arm pulls the weight up.

41
Q

Reading: Polysynaptic inhibitory reflex

A

Golgi tendon organs can detect muscle stretch. If a muscle stretches too much, it could risk damage to the tendons or bones it is attached to. To help avoid this situation, the Golgi tendon organs have the important jobs of relaying information about how hard the muscle is pulling to the brain and helping decrease the strength of muscular contraction when there is danger of damage to the tendons or bones. A polysynaptic reflex is needed to make this happen

42
Q

Reading: The motor association cortex

A

The motor association cortex includes:

supplementary motor area

premotor cortex

43
Q

Reading: Premotor cortex

A

involved in learning and executing responses that are signalled by the presence of arbitrary stimuli. As a component of the mirror neuron system, the premotor cortex is also involved in imitating responses of other people and in understanding and predicting these actions. (also involved in planning how much force to use when picking up an object depending on its weight)

44
Q

Reading: The supplementary motor area

A

(SMA) plays a critical role in behavioral sequences. (Study where taught a routine, but researchers disrupt the SMA and people forgot what they had to do next in the routine after 1 second). = the SMA is involved in planning the elements yet to come in sequences of movements.

The actual execution of the movements is probably controlled elsewhere—likely by the primary motor cortex

45
Q

Reading: The cerebellum (subcortical): The Flocculonodular lobe

A

A region of the cerebellum; involved in control of postural reflexes.

Damage to the flocculonodular lobe or the vermis (along the midline) causes disturbances in posture and balance

Neuroscience (22 decks)

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