L5

Question 1

muscle receptors are proprioceptors. signal?

Answer 1

signal position of body parts, movement and force

Question 2

2 main proprioceptive organs

Answer 2

muscle spindles

golgi tendon organs

Question 3

afferents in muscle spindles

Answer 3

Ia = fastest. 120 m/sec quadrapeds. 60 m/sec in human.

group II afferents = low conduction velocity.

Question 4

afferents in GTO

Answer 4

Ib afferents = fast conduction ~60m/sec in human.

Question 5

muscle spindles

• structure.
• what innervates them? purpose?

Answer 5

intrafusal muscle fibres, no contraction, produce no force. passive, measure muscle length changes.
- Gamma MN innervate : sensitize spindle to stretch. CNS downregulates

Question 6

biasing firing rate

Answer 6

= change in firing rate from rest level.

Question 7

4 hypotheses of g-MN action in normal movement

Answer 7

Y-loop hypothesis
servo-assistance
fusimotor set hypothesis
fusimotor prediction of intended movement

Question 8

y-loop hypothesis

Answer 8

• descending command from GMN to spindles, - info up to alpha MN= down to muscles = displacement info back to spindles.

Question 9

servo-assistance hypothesis

Answer 9

a and g-mn are co-activated.
a cause muscle shorten
g keep spindle sensory region taught to maintain singalling of unplanned muscle length changes.
a = control, G = mediates, makes it easier

Question 10

fusimotor set hypothesis

Answer 10

a and G activated independently.
- task-related setting of spindle sensitivity by g-mn action.
a can do muscle displacement on its own. g-mn chime in when behaviour is novel or difficult

Question 11

fusimotor prediction of intended movement

Answer 11

static G increased and decreased according to expected muscle shortening and lengthening = activately changes activity throughout movement.
a - works on its own
g - chimes in whenever expected muscle length cahnge

Question 12

2 pathways underlie stretch reflex

Answer 12

1. sensory receptor monosynaptic connection to spinal cord

2. long loop - info goes up to brain stem, cerebellum, BG, thalamus, cortex

Question 13

muscle stretch elicits firing in :

involving polysynaptic through interneurons = task-dependent.

Answer 13

1. spindle - group Ia & II

2. GTO - Ib

Question 14

monosynaptic (spinal) reflex

- tendon jerk response

Answer 14

rapid stretch by striking neurons. evoke Ia firing (MS) = activate a-MN of muscle = muscle contraction that resists length change.
- antagonist of this muscle inhibited by Ia afferent
GTO - respond to increase in force - disynaptically inhibit a- MN to resist change in force

Question 15

length and force feedback “compete” during muscle stretch
- spindle-mediated reflex is strong =?
- GTO reflex is strong =?
GTO excitation in weight-bearing muscle = ?

Answer 15

Spindle = stiff spring
GTO = compliant spring

positive force feedback = increased stiffness of muscle

Question 16

study at UBA of effect on stretch reflex on fear of heights

Answer 16

• postural threat high = response doubled
  electrically stimulating spindle afferents did not change. = no muscle stretch, neither intrafusal nor spinle sensory was involved.
• significant postural threat = increase G-MN activity enhances spindle sensitivity = enhances stretch - evoked reflex.
  a-MN excitability not elevated.

Question 17

interneuron function
- Ia inhibitory 
Renshaw
Ib inhibitory
interneurons of withdrawal reflex

Answer 17

1a = transmit spinle Ia input from agonist muscle to inhibit antagonist
renshaw: activated by a -mn. mediate recurrent inhibition back onto these and neighbouring agonist of a-MN. - inhibit self, to ensure it can keep firing with excess force = muscular wisdom
IB - GTO Ib input from agonist to inhibit agonist a-MN (feedback control of force)
interneuron ; nociceptive afferent. flex leg on pain, extend contralateral leg

Question 18

stretch EMG - short latency M1

long-latency M2 - long loop.

Answer 18

more stretch, bigger ratio btw M1 and M2. M1 gets bigger, M2 doesnt.

Question 19

anti-spastic drugs

Answer 19

GABA-A agonist = benzodiazapenes
DABA-B agonist = baclofen
A2 agonist: tizanidine & clonidine
cyproheptidine: ihibit 5HT mediated excitability.
botox & dentrolene = block NMJ
*also cause weakening, fatigeu and voluntary movement

Question 20

stretch reflexes increase after stroke and spinal cord injury

Answer 20

corticospinal tract lesion = opposite side body is weak/paralyzed
arm felxors = hyperreflexia due to increased sensitivity of stretch reflex pathway.

Question 21

evidence for transcortical pathway for longer-latency M2 component

Answer 21

klippel-feil syndrome