The sensorimotor system

Question 1

what is motor control?

Answer 1

conscious and unconscious regulation of muscle force informed by continuous and complex sensory feedback

Question 2

what are the different types of motor control?

Answer 2

voluntary
goal directed
habit
involuntary

Question 3

what are some features of goal directed motor control?

Answer 3

conscious
explicit
controlled

Question 4

what are some features of habit motor control?

Answer 4

unconscious
implicit
automatic

Question 5

give some examples of involuntary motor control movements

Answer 5

eye movement
facial expressions
jaw, tongue
postural muscles
hand and fingers
diaphragm
cardiac
intercostals
digestive tract

Question 6

what system kicks in to protect you when you trip?

Answer 6

vestibular system

Question 7

list from low to high areas of hierarchical control

Answer 7

spinal cord > sensorimotor midbrain > cortex and limbic system

Question 8

what is at the top of the motor control hierarchy?

Answer 8

association cortex and motor cortex

Question 9

the lower motor neuron begins with its cell body in the _____ _____ or _____ ____ and projects to the _______

Answer 9

brain stem / spinal cord, muscle

Question 10

the sensorimotor system is a _______ control system but with lots of ________ feedback

Answer 10

descending, ascending

Question 11

how do individual muscle fibres act in a ‘all or none’ manner?

Answer 11

they are either fully relaxed or fully contracted

Question 12

what does control of muscle force depend on?

Answer 12

the way in which lower motor neurone activate different types of muscle fibre

Question 13

muscle makes up about __% of muscle weight

Answer 13

40

Question 14

what are the 3 different types of muscle?

Answer 14

cardiac
smooth
skeletal

Question 15

what are the smallest, largest and strongest muscles?

Answer 15

smallest = stapedius (inner ear), largest = gluteus maximus, strongest = masseter (jaw)

Question 16

what are the hardest working muscles?

Answer 16

heart as it doesn’t rest
eye muscles have 10,000 precisely controlled movements
neck keeps 5kg head in position

Question 17

what type of muscle has the most voluntary motor control?

Answer 17

skeletal

Question 18

which muscle types have the most unconscious, involuntary motor control?

Answer 18

cardiac and smooth muscle

Question 19

if muscles are all or none, how do we achieve such a range of movements and forces?

Answer 19

antagonistic arrangement

recruitment of muscle fibres (fast/slow twitch, small and large motor units)

Question 20

thick filaments =

Answer 20

myosin

Question 21

thin filaments =

Answer 21

actin

Question 22

distance between 2 z lines =

Answer 22

sarcomere

Question 23

what neurotransmitter is released that triggers the biochemical cascade in muscle cells?

Answer 23

acetylcholine

Question 24

describe the biochemical cascade of muscle cells when acetylcholine is released

Answer 24

calcium is released from vesicles in the muscle cell fibre > it causes the head of myosin to change shape and attach to actin filament and pull in the filament (contract the muscle) before detaching and the process is repeated

Question 25

what is required to break the bond between the myosin head and the actin to allow the muscle to relax?

Answer 25

ATP

Question 26

rigor mortis =

Answer 26

stiffness when you die

Question 27

what causes rigor mortis?

Answer 27

when skeletal muscles stiffen because the muscle cells take calcium ions in but because the muscle is dead can't channel it back out. This causes the muscles to contract more and more

Question 28

the average number of muscle fibres innervated by a single motor unit varies according to what 2 things?

Answer 28

level of control (precision) | strength

Question 29

what will be the precision and strength of 1 alpha neuron contacting 1 single muscle fibre?

Answer 29

high precision/level of control | small amount of force e.g. eye muscle fibres

Question 30

what will be the precision and force of 1 alpha neuron contacting 3000 muscle fibres?

Answer 30

low precision/more general control but have a lot of force e.g. postural muscles

Question 31

what is the size principle?

Answer 31

units are recruited in order or size with the smallest first precise control is typically required at lower forces

Question 32

muscle fibres that use 100% of force continually =

Answer 32

slow muscle fibres

Question 33

muscle fibres used for walking, jogging, will tire after some time of use =

Answer 33

fast fatigue resistant

Question 34

muscle fibres that have high force that quickly declines, used for jumping, sprinting =

Answer 34

fast fatigable

Question 35

originate in the grey matter of the spinal cord or in the brain stem =

Answer 35

lower alpha motor neurone

Question 36

what represents the 'unit of control' of muscle force?

Answer 36

an alpha neuron and the muscle fibres it connects to

Question 37

single alpha neuron and all the muscle fibres it innervates =

Answer 37

motor unit

Question 38

do different motor neurons innervate different numbers of muscle fibres?

Answer 38

yes, one motor neuron may innervate 1 muscle fibre or up to 3000

Question 39

fewer fibres being innervated =

Answer 39

greater movement resolution (e.g. finger tips and tongue)

Question 40

activation of an alpha motor neuron _______ and causes contraction of all muscle fibres in that unit

Answer 40

depolarises

Question 41

why are muscle fibres innervated by each unit the same type of fibre and distributed evenly through the muscle?

Answer 41

to provide evenly distributed force, which reduces the effect of damage

Question 42

more motor units firing = more fibres contracting = more or less power?

Answer 42

more

Question 43

collection of motor units that innervate a particular muscle =

Answer 43

motor pool

Question 44

a motor pool contains both _____ and _____ neutrons

Answer 44

alpha, gamma

Question 45

how are motor pools often arranged?

Answer 45

rod like shape within the ventral horn of the spinal column

Question 46

sensory input comes from the _____ root

Answer 46

dorsal (back)

Question 47

motor output comes from the _____ root

Answer 47

ventral (front)

Question 48

these can be simple or complex and operate without engaging the brain =

Answer 48

reflexes

Question 49

what are critical for avoidance of injury and effective motor control?

Answer 49

reflexes

Question 50

what is a key part of proprioception?

Answer 50

sensing in muscles

Question 51

a good control system needs to know what 2 things?

Answer 51

how much tension is on the muscle what is the length (stretch) of the muscle

Question 52

what senses tension on muscles?

Answer 52

golgi tendon

Question 53

what senses stretch of muscles?

Answer 53

muscle spindles

Question 54

what sends ascending sensory info to the brain via the spinal cord about how much force there is in the muscle?

Answer 54

golgi tendon organs

Question 55

where are golgi tendon organs located?

Answer 55

within the tendon where the muscle joins to the bone

Question 56

under extreme tension conditions how does the golgi tendon organ prevent damage from overloading?

Answer 56

acts to inhibit muscle fibres via a circuit in the spinal cord

Question 57

what do muscle spindles sense?

Answer 57

the length of muscles (info forms a key part of reflex circuits)

Question 58

what is the most simple reflex?

Answer 58

monosynaptic e.g. patellar tendon reflex

Question 59

what are within extrafusal muscle fibres?

Answer 59

intrafusal muscle fibres that have muscle spindles wrapped around them (sense stretch of muscle)

Question 60

if intrafusal muscle fibres are sensory which route do they take into the spine?

Answer 60

dorsal (back)

Question 61

why are intrafusal muscle fibres controlled and innervated separately by gamma motor neurons? (compared to extrafusals that are controlled by alpha motor neurone)

Answer 61

need a system to detect stretch regardless of current muscle length, if controlled my same motor neurones then won't be sensitive to slight changes. Gamma neutrons keep the intrafusal fibres set at a length to optimise stretch detection

Question 62

what is the simplest reflex?

Answer 62

the stretch reflex (maintains body position and posture despite changes in the environment)

Question 63

innervation of antagonistic muscles explains why contraction of one muscle induces the relaxation of the other = ?

Answer 63

Sherrington's law of reciprocal innervation

Question 64

what does the idea of reciprocal innervation permit?

Answer 64

execution of smooth movements

Question 65

give an example of a automatic withdrawal reflex

Answer 65

power of muscles automatically increase in other leg when you pick up one leg from stepping on something painful. This gives reflexive posture and balance

Question 66

vestibular system detects body isn't upright and detects falling. This info combined with visual, somatosensory and proprioceptive sensory input gives a pattern of motor activity that restores uprightness and safe landing = what reflex?

Answer 66

vestibular righting reflex (reason cats always land on their feet)

Question 67

cell bodies in the ventral form are activated by _____ info from the muscle and _______ info from the brain

Answer 67

sensory, descending

Question 68

where does motor command originate?

Answer 68

motor cortex pyramidal cells (upper motor neurons)

Question 69

where is the cell body located in descending projections from cortical motor areas?

Answer 69

grey matter of cortex

Question 70

where does the pyramidal cell axon project to?

Answer 70

directly or indirectly to spinal cord and onto lower brainstem motor neurons

Question 71

what do axons from cortical motor areas form?

Answer 71

pyramidal tract

Question 72

most cortical projections innervate ________ motor units

Answer 72

contralateral (activation on left side of the brain controls motor output on opposite right side of body)

Question 73

what 2 control systems are likely to operate in co-operation together?

Answer 73

pyramidal cortical control and brainstem control

Question 74

what has direct access to lower motor neurone and interneurons?

Answer 74

the motor cortex

Question 75

what 2 brain areas are key for regulating movement?

Answer 75

cerebellum and basal ganglia

Question 76

how does the cerebellum and basal ganglia regulate movement?

Answer 76

have a copy of the motor command, feedback in different ways to alter the pattern of activity in the motor cortex, FEEDBACK LOOP, makes sure the direct activitation of the lower motor neurone is the right one

Question 77

basal ganglia =

Answer 77

inhibitory

Question 78

cerebellum =

Answer 78

excitatory

Question 79

describe the descending projections of the dorsolateral tract from the motor cortex

Answer 79

direct connection from upper motor neurone down to spine where it crosses over to contralateral lower motor neurons to distal muscles

Question 80

describe the descending projections of the ventromedial tract from the motor cortex

Answer 80

sends innervation and crosses over at spinal cord. Is bilateral to proximal trunk and limb muscles so needs similar contraction on both sides of the body

Question 81

what are the similarities between the dorsolateral and ventromedial tracts

Answer 81

both contain a direct corticospinal route, both obtain an indirect route via brain stem nuclei

Question 82

the dorsolateral tracts contain an indirect route via which brain stem nuclei?

Answer 82

red nucleus

Question 83

the ventromedial tracts contain an indirect route via which 4 brain stem nuclei?

Answer 83

tectum vestibular nuclei reticular formation cranial nerve nuclei

Question 84

dorsolateral tracts innervate ________ side of one segment of spinal cord

Answer 84

contralateral

Question 85

ventromedial tracts diffuse innervation projecting to ____ sides and ______ segments of spinal cord

Answer 85

both, multiple

Question 86

where do dorsolateral tracts project to?

Answer 86

distal muscles e.g. fingers

Question 87

where do ventromedial tracts project to?

Answer 87

proximal muscles of trunk and limbs

Question 88

what is the difference between dorsolateral and ventromedial tracts in their level of control?

Answer 88

dorsolateral = fine motor control, ventromedial = diffuse widespread control