Week 3 Flashcards
What is the function of a muscle spindle?
muscle receptors that provide feedback to the CNS about muscle length (stretch) and rate of change
What is alpha-gamma co-activation?
during a voluntary contraction, we activate both alpha MNs and gamma MNs together so the spindle maintains it sensitivity during shortening
Why does a tendon tap cause a reflexive kick?
spindles lengthen and Ia (primaries) sensitive to stretch activate MN via monosynaptic reflex
Why are the gamma motor neurons so important?
prevents muscle spindles from becoming unloaded and sensitive to stretch
Where are golgi tendon organs located?
in the tendon junction
How are spindles spread in the muscle? What about GTO?
Spindles = lie in parallel
GTO= lie in series with the muscle fiber
What afferent fiber innervates the GTO?
Ib afferent
GTOs are bundles within a _______ including…..
capsule; nerve endings and collagen fibers
Nerve endings are ____________ among collagen fibers
interdigitate
What is the function of GTO receptors?
- Muscle receptors that provide feedback to the CNS about muscle force/tension
- primarily active muscle force/tension
What technique allows experimenter to record action potentials from sensory afferents in awake humans?
microneurography
Describe the sensitivity of a GTO
- level of force necessary to excite a GTO depends on mode of activation
- passive stretch requires ~ 2 newtons
- active contraction (i.e., whereas activation of single muscle fiber) can activate GTO ~30-90 milinewtons
- GTOs much more sensitive to actively generated forces than passive stretch
Golgi tendon organs inhibit…
agonist muscles
How GTOs provide motor feedback?
- feedback to spinal cord via Ib afferent
- Ib inhibitory interneuron
- disynaptic connection to motor neuron
What is the autogenic inhibition-reflex
- inhibits agonist motor neurons
- decreased force output
GTOs are sensitive to muscle tension and are activated when….
muscle tension increases
Reflexive inhibition of motor neuron activity is used as a protective mechanism when…
muscle tension gets too great
What is there to remember about GTOs and low forces?
Remember GTOs are sensitive to muscle tension, therefore are activated at low forces too
- help with modulating force control for low force tasks
Describe joint receptors
- within joint capsules, there is joint ligaments and loose articular tissue
- no receptors in cartilaginous surfaces of the joint or in synovial membranes
What are the roles of joint receptors?
- respond primarily to the limits of joint movement (extremes)
- respond to joint pressure (e.g. joint swelling)
- respond to flexion and extension
Joint receptors code _________ for joint movements
ambiguously
The Joint receptors reflex suggest a __________ role
protective
What is the joint receptors reflex?
- reflex activity on alpha-motor neurons
- joint receptors cause weak and infrequent effects on alpha motor neuron
- knee ligaments must be heavily stretched before any measurable EMG activity can be detected
Name the Vestibular End organs and their different parts
Semicircular canals
- anterior, posterior, horizontal
Otolith organs
- utricle and saccule
What do the hair cells (mechanoreceptors) in the ear do?
transform mechanical energy into neural activity
What are the two types of hair cells?
- Kinocilium - apex of the hair cell
- Stereocilium - linked stair like structure
How do the hair cells work?
When stereocilia are pushed towards the kinocilium, the hair cell depolarizes; when they are pushed away the hair cell repolarizes
What do the stereocilia and kinocilium respond to?
acceleration or gravity that is in line with hair cells
What are the parts of the semi-circular canals?
canal: filled with fluid (endolymph)
cupula: house hair cells in the crista
Describe how the semi-circular canals detect angular acceleration
- at rest, background firing rates (i.e. leaky ion channels)
- acceleration leads to increased firing rates, while deceleration leads to hyperpolarization (decreased firing) in the 8th nerve afferents
- during periods of constant velocity, the hair cells return to normal leakiness and the 8th nerve afferents return to baseline firing rates
Describe the semi-circular canals and head rotation
- balance between left and right excitation and inhibition that leads to sensation of head rotation
- head rotation causes opposite endolymph fluid movement
- this causes stereocilia to be pushed towards kinocilium in the left SSC = excitation
- the opposite response in the right SSC = inhibition
What do the otolith organs detect?
linear acceleration
What are otoliths or otoconia?
small calcium carbonate crystals embedded into gelatinous material
What projects into the gelatinous material?
hair cells
The utricle detects…
horizontal linear acceleration
The saccule detects…
vertical linear acceleration
What causes the cilia from the hair cells to move?
shearing of the membrane
How does the otolith organs work?
When the head tilts or accelerates, gravity causes the otoliths to slide, pulling the stereocilia and causing the hair cells to depolarize
