Lesson 21 - Receptors and Spinal Control of Somatosensory Feedback Flashcards
Importance of sensory feedback
Proprioception: where body is in space
Cuetaneous receptors: where we are touched
Sensory feedback from our body and the world around us to adjust to ongoing surroundings
Acute inflammatory demyelinating polyneuropathy: no proprioception feedback
A Complex System of Sensory Feedback
Muscle spindle: muscle length
Vestibular System: balance
Cutaneous Receptors: touch
Golgi Tendon Organs: muscle tension
Loss of Sensory Information Disrupts Normal Reaching Movements
Without vision, Patient GL makes inaccurate, jerky movements with large errors
Don’t have info from muscle spindle in terms of length of muscle and angle of joint
Need muscle spindle for proprioception without vision
Muscle spindle recap
Refer to older pages
Muscle spindle= joint angle and proprioception
How muscle spindles work and respond to stretch
Muscle stretch causes spindle receptors to increase their firing rates
Muscle shortening causes spindle receptors to reduce their firing rates
Stretch is sensed in sensory endings and in mechanoreceptors
Muscle stretch deforms and opens stretch-sensitive ion channels, exciting the spindle afferent and causing it to fire action potentials
Relationship between Muscle stretch and excitation
Larger, longer stimuli cause a greater change in membrane potential, more
action potentials and release of neurotransmitter, more ions travel in
More stretch, more ap, more glutamate in synapse
Basic Reflexes Mediated by Muscle Spindles Process
- Tendon tap rapidly lengthens the
quadriceps muscle. - Stretch of quadriceps muscle
lengthens intrafusal fibers, causing
spindle to fire action potentials. - Spindle afferents enter the spinal
cord via the dorsal horn. - Sensory neuron synapses on and
excites alpha motor neuron (AMN). - Excitation of AMN causes reflex
contraction of quadriceps - Sensory neuron also synapses on
inhibitory interneuron, which
inhibits AMN of antagonist muscle
(reciprocal inhibition). - Hamstring (antagonist) is inhibited.
- Information is sent to the brain
Basic Reflexes Mediated by Muscle Spindles information
When a stretch is applied, it activates
the spindle afferent. If the stretch is large enough, the afferent
depolarizes.
Motor neurons in the homonymous muscle begin to depolarize (EPSP).
The inhibitory interneurons (excitatory input) start firing
at the same time (EPSP).
Motor neurons in the antagonist are then inhibited (IPSP)
Gaba in dumped onto antagonist muscle. This mean chloride enters
More synapses means more time for contraction
Synergist muscles
Stretch of agonist muscle produces reflex contraction of agonist (homonymous; biceps brachii) and
synergist muscles (e.g., brachialis), and inhibition of its antagonist (e.g.,
triceps)
-Synergist is contraction of other muscle that has been diversified into surrounding motor units
-Antagonist synergist as well
Homonymous meaning
Homonymous muscle’ means ‘in the
same muscle stretched by the stimulus’
The point of gamma motor neurons
Gamma motor neurons are for the coactivation of muscle spindle.
Gamma MN maintains length of intrafusal fibers, make sure they don’t become loose.
GMNs stimulate intrafusal muscle fibers. This maintains the length of intrafusal fibres and spindle sensitivity during voluntary muscle contractions/movements
Changing length of muscle fibers
Take home message
Proprioceptive feedback provides
information about body position and motion and is critical for skilled voluntary actions
