ms Lecture 6
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What are proprioceptors?
A class of sensory receptors which signal to CNS information about the relative position of the body parts with respect to one another.
What is muscle sense?
Conscious sensation arising from receptors in the skeletal muscles
What are the 3 receptors in use in a proprioceptor and expand?
- 1. Muscle receptors: a) muscle spindles(in the belly of muscles - give rise to tendon jerk reflex… mainly concerned with detecting muscle length)
- b) Golgi tendon organs ( signal contractile force produced by muscles)
- 2. Joint receptors (help detect position of joints)
- 3. Cutaneous receptors
What is shape of a muscle spindle? What is found at the ends? And what is found in the middle section? What is so special about the these two?
- The shape is a fusiform/capsule.
- Only the ends (poles) are contractile. The middle section contains sensory fibres coiled around meaning that when the spindle lengthens or shortens due to contraction, this is sensed as some kind of stretch at the sensory endings.
Where are the motor endings found? And what are they?
Motor endings are found towards the bottom and these are the gamma motor neurones which innervate the intrafusal muscle fibres.
What are the sensory functions of a muscle spindle? Give reference to length and the kind of endings.
- Muscle length/ stretch detectors - related to joint angle.
- Primary endings:
- Velocity (rate of change of muscle length): Dynamic sensitivity
- Position (absolute length, steady state length of muscle(different level of AP firing depending on muscle length): Static sensitivity
- Secondary endings – position: Static sensitivity (and minor velocity component)
How do gamma motor neurones affect the function of muscle spindles?
- Gamma motor neurones adjust the responsiveness of muscle spindles to the contraction of extrafusal skeletal muscles.
- This may be important to avoid any moment of lack of data from muscle spindles (about muscle length) being supplied to the CNS.
What the increase in gamma motor neurones activity lead to?
- ⇒contraction of polar regions (contractile regions) of intrafusal muscle fibres
- ⇒ elongation of equatorial region bearing sensory nerve endings
- ⇒ increases sensitivity of muscle spindle and increases afferent firing of APs.
What is the advantage of having the system of adjusting the sensitivity of muscle spindles?
With the action of gamma neurones, muscle contraction (shortening) does not cause spindle AP firing to cease. WOAH!
Where are golgi tendon organ (GTO) receptors located? They are innervated by...? What do they respond to? Firing increases with what? A step wise increase in motor contraction results from a step wise increase in what? And why?
- Located at junction of skeletal muscle and its tendon.
- Innervated by single Group Ib myelinated (large) afferent(sensory fibre).
- Respond to muscle active contractile force (and passively applied tension).
- Firing increases with recruitment of motor units.
- Their discharge often shows a step-wise increase in firing as you get a step wise increase in motor contraction as more and more motor units are activated.
Name the structurally different types of joint receptors.
- I – Ruffini endings
- II – Paciniform endings
- III – Golgi endings
- IV – free nerve endings
Cutaneous Mechanoreceptors respond to what? And what are these produced by?
Respond to mechanical deformation of skin – OFTEN PRODUCED BY MOVEMENTS/ CONTRACTIONS
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