neuromuscular and spinal cord control of movments

Question 1

contact ratio in synapses

Answer 1

1:1 in muscle, 10K to 1 in CNS (ie 10000 synapses go to CNS)

Question 2

what is neuromuscular junction

Answer 2

synapse between motor neurone and MOTOR END PLATE

Question 3

miniature end plate potentials

Answer 3

at rest ACH released at low rate, causing mini potentials

Question 4

alpha motor neurons

Answer 4

lower motor neurons of brainstem and ventral horn of spinal cord, going to skeletal muscles to cause contraction

Question 5

location of alpha motor neurons in spinal cord DIAGRAM

Answer 5

sort of somatotopic mapping- alpha motor neurons for extensor muscles are more ventral, for flexor more dorsal, more proximal muscles more medial, more distal muscles more lateral

Question 6

define motor unit DIAGRAM

Answer 6

SINGLE motor neurone and ALL muscle fibres innervated by it- smallest functional unit that produces force

Question 7

types of motor units DIAGRAM

Answer 7

slow (type 1)- small diameter of cell bod and dendritic tree, thinnest axons and slowest velocity fast fatigue resistant (type 11A)- larger diameter of cell bodies and dendritic trees, thicker axons and faster velocity fast fatiguable (type 11B)- same as before type 1 goes first, then 11A, then 11B, so in order- thus these are different dependent on tension formed, speed of contraction and fatiguability

Question 8

distribution of motor unit types DIAGRAM

Answer 8

an ATP stain can be used to show which fibre is which

Question 9

how brain regulates muscle force- recruitment DIAGRAM

Answer 9

two mechanisms, first recruitment- motor units recruited by SIZE- smaller are recruited first ie slow, and as more force is needed, other units recruited, allowing control eg writing requires little force, so all subtypes of motor units not needed

Question 10

how brain regulates muscle force- rate coding DIAGRAM

Answer 10

also by rate coding- motor units fire at different frequencies, with slow units firing at a low frequency- when firing rate increases, force produced increases, ALTHOUGH summation occurs when frequency too fast for muscle to relax

Question 11

effect of neutrotrophic factors DIAGRAM

Answer 11

growth factor for neurons after injury, and prevent death in leg, normally soleus innervated by slow and FDL innervated by fast- but cross innervation can cause soleus to be innervated by fast, and FDL innervated by slow

Question 12

plasticity of motor unit subtypes

Answer 12

Type 11B can become A after training to help recovery type 1 to 11 occurs in spinal cord injury or when going into space at zero gravitiy ageing causes loss of both subtypes, more type 11 ie slower contraction with age

Question 13

motor tracts in spinal cord

Answer 13

pyramidal tracts are lateral and anterior corticospinal tracts extrapyramidal modifiy corticospinal tracts- are rubrospinal tract (from midbrain to spinal cord- movement of arm in response to balance change ie when falling, your arms move to help), reticulospinal tract (coordinate mvoements when reacting to painful stimuli) and vestibulospinal tract (regulates posture to maintain balance)

Question 14

how reflexes differ from voluntary movements

Answer 14

once reflexes start, they cannot be stopped

Question 15

importance of afferents for reflexes DIAGRAM

Answer 15

reflexes need it- if dorsal root not present, force generated much lower

Question 16

monosynaptic (stretch) reflex DIAGRAM

Answer 16

when knee is hit, this stretch stimulates sensory receptors, which passes impulses to dorsal root, then integrating centre in spinal cord, which sends impulses to muscle- BRAIN NOT INVOLVED impulses also sent to antagonist muscle to relax due to inhibitory interneuron

Question 17

hoffman reflex importance

Answer 17

done in labs to patients to have had spinal cord injuries- tests their reflexes

Question 18

polysynaptic reflexes- flexion withdrawal + crossed extensor DIAGRAM

Answer 18

stepping on pin will cause flexor muscle to be innervated to move leg- this does not just occur at one spinal levels- multiple levels act to innervate the same muscle at same time inhibitory input goes to other leg to maintain balance, known as crossed extensor

Question 19

supraspinal control of reflexes

Answer 19

reflexes are automatic but they can be modified and accentuated by supraspinal control (top to bottom)- eg when clenching teec and knee tapped, your leg moves even more

Question 20

proof there is supraspinal control

Answer 20

normally cerebellum and cortex have inhibitory input on stretch reflexes, but if brain is DECEREBRATED in an experiment, overactive stretch reflex occurs ie rigidity, showing supraspinal control

Question 21

explain how higher centre influences reflexes

Answer 21

activates alpha motor neurones, gamma motor neurones (involved in muscle), and inhibitory interneurons cortex involved in corticospinal tract (limb movements), rubrospinal tract (movements of arm in response to balance change), vestibulospinal (changing posture to keep balance) and tectum (tectospinal tract for head movements)

Question 22

extrafusal vs intrafusal fibres- gamma reflex loop

Answer 22

extrafusal fibres for voluntary control of muscle, intrafusal fibres react to change in spindle length via gamma motor neurons if knee extended but muscle becomes slack, gamma motor neurons react and spindle ie muscle is shortened to maintain sensitivity- known as gamma reflex loop- thus alpha motor neurons allow voluntary muscle movement, gamma motor neurones modify muscle contraction dependent on spindle length

Question 23

hyper-reflexia

Answer 23

loss of descending inhibition eg due to stroke clonus- muscular spasm of eg foot babinskis sign- extension of big toe (due to alpha motor neurone problem) with other toes going other way

Question 24

hyporeflexia

Answer 24

below normal reflexes due to lower motor neurones