6.4 Proprioception Flashcards
What is proprioception
Signals contributing to conscious and subconcious mechanisms of motor control (6th sense). Proprioception can be broken into stataesthesis and kinaesthesis
What is stataesthesis
It is position sense, the conscious awareness of the relative positions of our body parts in space.
What is kinaesthesis
It is movement sense, giving speed of movement and direction of movement
Describe a motor sense that is not part of proprioception
The sense of effort and heaviness (e.g how much effort it takes to lift something. Instead of relying on proprioception this perception relies on corollary discharges.
Describe corollary discharges.
An internal signal from motor centres in the brain to sensory centres in the brain (a feed forward mechanism), for a another copy of the descending motor command. It is a mechanism that contributes to proprioception but not greatly.
Describe group I nerve fibres
They have Aa axons and are the widest (13-20µm), the most myelinated and the fastest (80-120 m/sec). They can be for proprioceptors of skeletal muscle.
Describe group II nerve fibres
They have Ab axons are are the second widest (6-12µm), the second most myelinated and the scond fastest (35-75 m/sec). They can be for mechanoreceptors of skin.
Describe group III nerve fibres
They have A§ axons and are the third widest (1-5µm), the third most myelinated and the third fastest (5-30 m/sec). They can be for nociceptors and thermoceptors.
Describe group IV nerve fibres
They have C axons and are the narrowest (0.2-1.5µm) and the slowest (0.5-2 m/sec). They are non myelinated and can be for nociceptors, thermoceptors and detecting itch.
Primarily, which nerve fibre groups are involved in proprioception
Group I and II
Proprioception comes from sensory feedback and is essential for coordinated movement. Give some evidence for this
There is a rare autoimmune condition where patients are deafferented. As they are without group 1 and 2 nerve fibres, they are without feedback from muscles, skin or joints below the neck. The patients loose the ability to move and coordinate movement.
Explain why golgi tendon organs are unlikely to contribute to the position sense.
They signal muscle tension, which can vary for the same joint position. So they dont contribute towards position sense, but they do contribute towards movement sense.
What are some receptors that provide signals appropriate for movement sense and position sense?
-cutaneous (skin) receptors
-joint receptors
-muscle spindle receptors
Describe how muscle spindle provides proprioception
Muscle spindles have 2 sensory endings, both primary and secondary, both endings are sensitive to the stretch of the muscles and signal the resulting changes in muscle length. The primary ending has high dynamic sensitivity and responds particularly to changing length and to tapping or vibrating the tendon. The muscle spindle receptors signal muscle length as it varies with joint position. Opposing muscles at a joint provide complementary information about joint angles in flexion and extension and between them cover the full range of joint angles.
Describe how somamatic sensory receptors in the skin (cutaneous) provide proprioception
Both slowly and rapidly adapting receptors exist in the skin. Rapidly adapting receptors in the skin can signal contact and slowly adapting receptors will signal maintained contact with external objects. Some cutaneous receptors are located in the skin over joints and they discharge during joint movement.
Describe how joint receptors provide proprioception
Both slowly and rapidly adapting receptors exist in joint capsules and ligaments, Rapidly adapting joint receptors can signal the occurrence and speed of movement. Slowly adapting joint receptors produce an impulse related to joint position
Describe how the CNS uses signals from the different receptors to provide proprioception
Kinaesthesia and position sense are conscious perceptions and there are multiple different proprioceptive signals. The input from specific groups of receptors can be reduced or enhanced. At the proximal joints (e.g elbow, hips knees) muscle spindles appear most important but at the distal joints (e.g hand) joint and cutaneous receptors contribute more.
