The sensorimotor system Flashcards
what is motor control?
conscious and unconscious regulation of muscle force informed by continuous and complex sensory feedback
what are the different types of motor control?
voluntary
goal directed
habit
involuntary
what are some features of goal directed motor control?
conscious
explicit
controlled
what are some features of habit motor control?
unconscious
implicit
automatic
give some examples of involuntary motor control movements
eye movement facial expressions jaw, tongue postural muscles hand and fingers diaphragm cardiac intercostals digestive tract
what system kicks in to protect you when you trip?
vestibular system
list from low to high areas of hierarchical control
spinal cord > sensorimotor midbrain > cortex and limbic system
what is at the top of the motor control hierarchy?
association cortex and motor cortex
the lower motor neuron begins with its cell body in the _____ _____ or _____ ____ and projects to the _______
brain stem / spinal cord, muscle
the sensorimotor system is a _______ control system but with lots of ________ feedback
descending, ascending
how do individual muscle fibres act in a ‘all or none’ manner?
they are either fully relaxed or fully contracted
what does control of muscle force depend on?
the way in which lower motor neurone activate different types of muscle fibre
muscle makes up about __% of muscle weight
40
what are the 3 different types of muscle?
cardiac
smooth
skeletal
what are the smallest, largest and strongest muscles?
smallest = stapedius (inner ear), largest = gluteus maximus, strongest = masseter (jaw)
what are the hardest working muscles?
heart as it doesn’t rest
eye muscles have 10,000 precisely controlled movements
neck keeps 5kg head in position
what type of muscle has the most voluntary motor control?
skeletal
which muscle types have the most unconscious, involuntary motor control?
cardiac and smooth muscle
if muscles are all or none, how do we achieve such a range of movements and forces?
antagonistic arrangement
recruitment of muscle fibres (fast/slow twitch, small and large motor units)
thick filaments =
myosin
thin filaments =
actin
distance between 2 z lines =
sarcomere
what neurotransmitter is released that triggers the biochemical cascade in muscle cells?
acetylcholine
describe the biochemical cascade of muscle cells when acetylcholine is released
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
what is required to break the bond between the myosin head and the actin to allow the muscle to relax?
ATP
rigor mortis =
stiffness when you die
what causes rigor mortis?
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
the average number of muscle fibres innervated by a single motor unit varies according to what 2 things?
level of control (precision)
strength
what will be the precision and strength of 1 alpha neuron contacting 1 single muscle fibre?
high precision/level of control
small amount of force e.g. eye muscle fibres
what will be the precision and force of 1 alpha neuron contacting 3000 muscle fibres?
low precision/more general control but have a lot of force e.g. postural muscles
what is the size principle?
units are recruited in order or size with the smallest first
precise control is typically required at lower forces
muscle fibres that use 100% of force continually =
slow muscle fibres
muscle fibres used for walking, jogging, will tire after some time of use =
fast fatigue resistant
muscle fibres that have high force that quickly declines, used for jumping, sprinting =
fast fatigable
originate in the grey matter of the spinal cord or in the brain stem =
lower alpha motor neurone
what represents the ‘unit of control’ of muscle force?
an alpha neuron and the muscle fibres it connects to
single alpha neuron and all the muscle fibres it innervates =
motor unit
do different motor neurons innervate different numbers of muscle fibres?
yes, one motor neuron may innervate 1 muscle fibre or up to 3000
fewer fibres being innervated =
greater movement resolution (e.g. finger tips and tongue)
activation of an alpha motor neuron _______ and causes contraction of all muscle fibres in that unit
depolarises
why are muscle fibres innervated by each unit the same type of fibre and distributed evenly through the muscle?
to provide evenly distributed force, which reduces the effect of damage
more motor units firing = more fibres contracting = more or less power?
more
collection of motor units that innervate a particular muscle =
motor pool
a motor pool contains both _____ and _____ neutrons
alpha, gamma
how are motor pools often arranged?
rod like shape within the ventral horn of the spinal column
sensory input comes from the _____ root
dorsal (back)
motor output comes from the _____ root
ventral (front)
these can be simple or complex and operate without engaging the brain =
reflexes
what are critical for avoidance of injury and effective motor control?
reflexes
what is a key part of proprioception?
sensing in muscles
a good control system needs to know what 2 things?
how much tension is on the muscle
what is the length (stretch) of the muscle
what senses tension on muscles?
golgi tendon
what senses stretch of muscles?
muscle spindles
what sends ascending sensory info to the brain via the spinal cord about how much force there is in the muscle?
golgi tendon organs
where are golgi tendon organs located?
within the tendon where the muscle joins to the bone
under extreme tension conditions how does the golgi tendon organ prevent damage from overloading?
acts to inhibit muscle fibres via a circuit in the spinal cord
what do muscle spindles sense?
the length of muscles (info forms a key part of reflex circuits)
what is the most simple reflex?
monosynaptic e.g. patellar tendon reflex
what are within extrafusal muscle fibres?
intrafusal muscle fibres that have muscle spindles wrapped around them (sense stretch of muscle)
if intrafusal muscle fibres are sensory which route do they take into the spine?
dorsal (back)
why are intrafusal muscle fibres controlled and innervated separately by gamma motor neurons? (compared to extrafusals that are controlled by alpha motor neurone)
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
what is the simplest reflex?
the stretch reflex (maintains body position and posture despite changes in the environment)
innervation of antagonistic muscles explains why contraction of one muscle induces the relaxation of the other = ?
Sherrington’s law of reciprocal innervation
what does the idea of reciprocal innervation permit?
execution of smooth movements
give an example of a automatic withdrawal reflex
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
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?
vestibular righting reflex (reason cats always land on their feet)
cell bodies in the ventral form are activated by _____ info from the muscle and _______ info from the brain
sensory, descending
where does motor command originate?
motor cortex pyramidal cells (upper motor neurons)
where is the cell body located in descending projections from cortical motor areas?
grey matter of cortex
where does the pyramidal cell axon project to?
directly or indirectly to spinal cord and onto lower brainstem motor neurons
what do axons from cortical motor areas form?
pyramidal tract
most cortical projections innervate ________ motor units
contralateral (activation on left side of the brain controls motor output on opposite right side of body)
what 2 control systems are likely to operate in co-operation together?
pyramidal cortical control and brainstem control
what has direct access to lower motor neurone and interneurons?
the motor cortex
what 2 brain areas are key for regulating movement?
cerebellum and basal ganglia
how does the cerebellum and basal ganglia regulate movement?
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
basal ganglia =
inhibitory
cerebellum =
excitatory
describe the descending projections of the dorsolateral tract from the motor cortex
direct connection from upper motor neurone down to spine where it crosses over to contralateral lower motor neurons to distal muscles
describe the descending projections of the ventromedial tract from the motor cortex
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
what are the similarities between the dorsolateral and ventromedial tracts
both contain a direct corticospinal route, both obtain an indirect route via brain stem nuclei
the dorsolateral tracts contain an indirect route via which brain stem nuclei?
red nucleus
the ventromedial tracts contain an indirect route via which 4 brain stem nuclei?
tectum
vestibular nuclei
reticular formation
cranial nerve nuclei
dorsolateral tracts innervate ________ side of one segment of spinal cord
contralateral
ventromedial tracts diffuse innervation projecting to ____ sides and ______ segments of spinal cord
both, multiple
where do dorsolateral tracts project to?
distal muscles e.g. fingers
where do ventromedial tracts project to?
proximal muscles of trunk and limbs
what is the difference between dorsolateral and ventromedial tracts in their level of control?
dorsolateral = fine motor control, ventromedial = diffuse widespread control
