sensorimotor system

Question 1

types of motor control (4)

Answer 1

voluntary (run, talk)
goal-directed (conscious, explicit, controlled)
habit (unconscious, implicit, automatic)
involuntary (eye movements, cardiac, posture)

Question 2

3 response pathways (evolutionary - for defence)

Answer 2

all lead to the motor, autonomic, and endocrine systems for defence-related output

pain –> spinal cord –> escape reaction
e.g. move hand away from hot object

loom → sensorimotor midbrain → “avoid”
e.g. basic visual processing of large threat, therefore not in oculomotor area - more complex than pain reaction needing more processing

learned threat → cortex and limbic system → “avoid”
e.g. learned that a gun is a weapon before knowing it is a threatening thing, so know to be scared and avoid it

Question 3

hierarchical control architecture –> where different stimuli is processed in the brain to produce output (7)

bad (3)
neutral (3)
cognitive analysis (1)
complexity

Answer 3

noxious/contact –> spinal cord –> reflexive withdrawal
sudden distal –> hindbrain –> startle response
species-specific threat –> midbrain and hypothalamus –> species specific response - fight flight or freeze

neutral –> thalamus
complex neutral –> sensory cortex
context –> hippocampus and septum
–> these 3 lead to the amygdala for conditioned emotional responses

cognitive analysis –> frontal cortex –> response suppression

more complex and sophisticated threat detection and avoidance behaviour needs more complex processing/neural systems

Question 4

sensorimotor system
- top down
- bottom up

Answer 4

descending and ascending motor circuits for control and sensory feedback

top down - descending motor circuits
association cortex –> secondary motor cortex –> primary motor cortex –> brainstem motor nuclei –> spinal motor circuits –> motor units –> effect
also with input high up from basal ganglia (what to do) and cerebellum (how to do it)

bottom up - sensory feedback
muscles sensory systems passes messages to each of the higher up regions - and basal ganglia and cerebellum to change based on this feedback

Question 5

3 types of muscle

Answer 5

skeletal
smooth
cardiac

Question 6

antagonistic arrangement of muscle fibres

Answer 6

combined co-ordinated action - e.g. 6 muscles in eye allow it to move in different directions very precisely
fibres can only contract or relax

Question 7

recruitment of muscle fibres

Answer 7

small or large motor units are used depending on what needs to happen - fine and precise movements or strong ones

Question 8

what about fibres determines strength

Answer 8

number of fibres varies between people - doesn’t change much with time or training - due to genetics
muscle size and strength can be changed with training and is from the cross sectional area of individual fibre types

Question 9

muscle contraction process

Answer 9

myosin cross-bridge forms as myosin head attaches to actin filament (due to influx of Ca2+ from action potential) and bends to move the actin filament
it then releases using ATP, extends again, and reattaches
during this, ACh is released, triggering biochemical cascade in muscles - Ca2+, Mg2+, ATP

sarcomere = basic contractile unit of muscle fibre made of actin and myosin

Question 10

rigor mortis

Answer 10

release of ACh leads to Ca2+ being released
triggers myosin to bind to actin, as in muscle contraction
ATP is required to break bond between actin and myosin but isn’t present due to no oxidative metabolism in death
therefore muscles remain contracted until enzymes breakdown the actin and myosin

Question 11

motor unit

Answer 11

one motor neuron and all the muscle fibres it innervates
number of fibres innervated depends on functional requirements of the muscle - either control or strength
often many MNs for each muscle, some only have a few

Question 12

size principle of muscle units

Answer 12

units are recruited in order of size from smallest to largest
fine control required at low forces, but then precision is substituted for strength
therefore moving heavy objects is jerky as small motor units aren’t used

Question 13

fast and slow muscle fibres (3)

Answer 13

slow = keep going all day - don’t fatigue e.g. for standing
fast fatigue resistant = for walking and running, use for a while before they fatigue
fast fatigable = kept in reserve for short bursts of movement e.g. jumping and so fatigues very quickly

explains why sprinters aren’t as good at long distance as they train their fat fatigable muscles not the fatigue resistant ones for endurance

Question 14

LMNs

Answer 14

lower motor neurons
alpha = innervate extrafusal fibres for muscle movement and function
gamma = innervate intrafusal fibres for stretch detection
cell bodies found in grey matter of spinal cord or brainstem
fewer fibres in unit = greater resolution

all or nothing - LMN activates all fibres
all fibres in a unit are the same type of fibre, distributed throughout muscle for evenly distributed force, reducing effect of damage

Question 15

motor pool

Answer 15

all LMNs that innervate a single muscle
pool contains both alpha and gamma LMNs arranged in a rod like shape in ventral horn of spinal column
cell bodies activated by:
sensory info from muscles (dorsal root) e.g. reflexes
descending info from the brain e.g. voluntary control to withstand reflexes or make co-ordinated movements

Question 16

proprioception

Answer 16

ability to sense movement and action
CNS needs to know how stretched or tense muscles are
sensed by golgi tendon organs (GTO) and muscle spindles

Question 17

golgi tendon organs (GTO)

Answer 17

sense tension in muscle - force
within tendons (where muscle joins bone)
under extreme tension, GTOs can inhibit muscle fibres via circuit in spinal cord to prevent damage

Question 18

muscle spindles

Answer 18

sense stretch in muscle - muscle length
integral to reflex circuits - e.g. patellar reflex is caused by muscle elongating and jerking

Question 19

two types of muscle fibre

Answer 19

extrafusal = do the work of the muscle
intrafusal = within muscle, sensory fibre containing the muscle spindle - sensory neuron connected,

Question 20

intrafusal fibres

Answer 20

can change amount of force needed in response to changing environment (e.g. when object changes weight whilst being held)
detects strength regardless of current muscle length - it is kept to a set length
controlled by gamma LMNs so it can always detect slight changes

Question 21

complex reflex - withdrawal reflex

Answer 21

reciprocal innervation - antagonistic muscles contract when others relax
e.g. steady self when one leg is lifted by taking more weight through the other leg, otherwise you would fall

Question 22

vestibular reflex - righting reflex

Answer 22

detection that body isn’t upright and acceleration due to gravity from falling
combines this with visual, somatosensory, and proprioceptive sensory input to specify pattern of motor activity to restore uprightness
cerebellum = intended motor plans combined with current situation to compute desired motor activity

Question 23

function of pathways in brainstem and midbrain

Answer 23

smooth out movement, mainly unconscious e.g. balance, postural control

Question 24

speech - evolutionary brain areas

Answer 24

speech = primitive sound sculpted by cortex - evolutionary (grunts etc)
ancient and modern (cortical) control systems work co-operatively

Question 25

primary motor cortex (M1) control

Answer 25

top-down control over muscles, directs action
sometimes only has one synapse in spine between cortical neuron and innervation of muscle

Question 26

where does motor command in motor cortex come from

Answer 26

pyramidal cells layer 5-6
cell bodies in grey matter of cortex
axons can project directly or indirectly to spinal cord and LMNs
axons form the pyramidal tract
pyramidal cortical control can be in co-operation with brainstem for complex sequences of movement
e.g. excitatory effect of cerebellum and inhibitory of basal ganglia

most projections are contralateral (right controls left)

Question 27

projections from motor cortex down 2 different tracts

Answer 27

both have direct (corticospinal route) and indirect routes via brainstem nuclei (different nuclei tho)

dorsolateral:
- indirect via red nucleus
- innervates contralateral side of one segment of spinal cord
- sometimes direct to alpha motor neurons (LMNs)
- project distally e.g. to fingers

ventromedial:
- indirect via tectum, vestibular nuclei, reticular formation, cranial nerve nuclei
- diffuse innervation projecting to both sides and multiple segments of spinal cord
- projects proximally e.g. trunk and limbs

Question 28

what is the basal ganglia

Answer 28

group of nuclei beneath cortex:
substantia nigra (pars compacta and pars reticulata)
caudate and putamen (together = striatum)
subthalamic nucleus
globus pallidus (internal and external segments)

role in motor control isn’t fully understood
has excitatory input from many areas of cortex (glutamate)
inhibitory output (GABA)

not just motor loops - also oculomotor, prefrontal, and limbic

Question 29

basal ganglia selection problem

Answer 29

multiple command systems spatially distributed for parallel processing but motor resources cannot complete them all
needs to resolve to decide what to do

Question 30

basal ganglia disinhibitory gating of motor cortex output LOOK AT NOTION PAGE!!!!!!!

Answer 30

look at diagram to understand!!!!!!!

Question 31

cerebellum

Answer 31

parallel processor for smooth coordinated movement and cognitive tasks
no direct projections to LMNs
modulates activity of UMNs - contains hald of CNS neurons and projects to almost all UMNs

Question 32

cerebellum inputs

Answer 32

cortical (via pons) = mostly from motor cortex - copies of motor commands, also somatosensory and visual areas of parietal cortex

spinal = proprioceptive info about limb position and movement - muscle spindles and other mechanoreceptors

vestibular = rotational and acceleratory head movement - semi-circular canals/otoliths in inner ear

Question 33

cerebellum function

Answer 33

knows current motor command from cortex
knows body position and movement from spine and vestibular
projects info back to motor cortex to compute motor error and adjust cortical motor commands accordingly
learning - along with basal ganglia and cortical circuits
adjusts cognition and movements

Question 34

exoskeletons and neurorehabilitation

Answer 34

converting brain activity (either from electrode in brain or on scalp surface) to signals for the exoskeleton (wearable robotics) allows for movements when motor function is impaired

using these devices over a period of weeks can help motor recovery