Chapter 6 - Somatosensory Flashcards
muscle spindle
the sensory organ in muscle
- consists of muscle fibers, sensory endings, and motor endings
sensory endings of spindle
- respond to stretch(changes in muscle length)
- respond to velocity of length change
Type 1a afferents(primary endings) = quick and tonic stretch of the spindle- wrap around the central region of each intrafusal fiber
Type 2 afferents(secondary endings) = tonic stretch of the muscle - end on nuclear chain fibers
- wrap around the central region of each intrafusal fiber
intrafusal fibers
fibers inside the spindle
- contractile only at their ends
Types: 1) nuclear bag fibers 2) nuclear chain fibers
nuclear bag fibers
intrafusal fibers
- have a clump of nuclei in the central region
nuclear chain fibers
intrafusal fibers
- have nuclei arranged in single file
primary endings
type 1a
- wrap around the central region of the intrafusal fiber
- also called annulospiral endings
- discharge is phasic and tonic
secondary endings
type 2
- end mainly on nuclear chain fibers adjacent to the primary endings
- also called flower-spray endings
- respond only tonically
phasic discharge
maximal during quick stretch and fades quickly
tonic discharge
sustained during constant stretch
- rate of firing is proportional to the stretch of spindle fibers
Golgi tendon organs
encapsulated nerve endings woven among the collagen strands of the tendon
- relays tension in tendons(very sensitive)
- responds to tension exerted by active contraction and passive stretch
- type 1b afferents
joint receptors
- respond to mechanical deformation of the capsule and ligaments
Types:
1) ligament receptors(type 1b)
2) Ruffini’s and paciniform endings(type 2)
3) free nerve endings
Ruffini’s endings
in the joint capsule
- signal extremes of joint range
- respond more to passive than active movement
paciniform corpuscles
respond to movement, but not when joint position is constant
ligament receptors
signal tension
free nerve endings
stimulated by inflammation
discriminative touch
localization of touch and vibration
- ability to discriminate between two closely spaced points touching the skin
conscious proprioception
awareness of movements and of the relative position of body parts
stereognosis
ability to use touch and proprioception to identify an object
pathway for discriminative touch and conscious proprioception
- dorsal column/medial lemniscus system
1) 1st order = neuron conveys information from the receptors to the medulla
2) 2nd order = neuron conveys information from the medulla to the thalamus
3) 3rd order = neuron conveys information from the thalamus to the cerebral cortex
Discriminative touch and conscious proprioceptive information pathways from the body
1st order = dorsal root ganglion —–> 2nd order = nucleus cuneatus or gracilis —–> VPL(ventral posterolateral) nucleus of thalamus
Discriminative touch and conscious proprioceptive information pathways from the face
1st order = trigeminal ganglion —-> main sensory nucleus of trigeminal nerve ——> VPM(ventral posteromedial) nucleus of thalamus
SPG
Stepping Pattern generator
- adaptable networks of spinal interneurons that activate lower motor neurons to elicit alternating flexion and extension of the hips and knees
- for walking
H-reflex
monosynaptic reflex elicited by electrically stimulating a nerve
- testing substitutes cutaneous electrical stimulation of a peripheral nerve for tendon percussion of the myotatic reflex
- faster than the tendon tap reflex because it does not require activation of spindle receptors
UMNs
upper motor neurons
- provide all motor signals from the brain to the spinal cord and from the cerebrum to the cranial nerve lower motor neurons in the brainstem
- ones projecting to the spinal cord are classified according to where they synapse: medially, laterally, or throughout the ventral horn
Medial UMNs
signal lower motor neurons that innervate postural and girdle muscle 3 tracts from the brainstem: - reticulospinal - medial and lateral vestibulospinal - medial corticospinal
Lateral UMN’s
signal lower motor neurons that innervate muscle used for fractionated movement and muscles in face and neck
UMNs throughout the ventral horn
contributes to background levels of excitation in the cord and facilitates local reflex arcs
reticulospinal tract
begins in the reticular formation
- facilitate bilateral lower motor neurons innervating postural and gross limb movement muscles throughout the entire body
- involved in anticipatory postural adjustments and reaching
- for neck reflexes in response to visual and auditory input
medial vestibulospinal tract
receive information about head movement and position from the vestibular apparatus in the inner ear
- project to cervical and thoracic levels and affect activity in lower motor neurons controlling neck and upper back muscle
lateral vetibulospinal tract
respond to gravity information from the vestibular apparatus
- facilitate lower motor neurons to extensors while inhibiting lower motor neurons to flexors
- continuously active to maintain the center of gravity over the base of support, responding to destabilization
medial corticospinal tract
direct connection from cerebral cortex to the spinal cord
- project to the ipsilateral, contralateral, and bilateral spinal cord
- synapse with lower motor neurons that control neck, shoulder and trunk muscles
fractionation
the ability to activate individual muscles independently of other muscles
- lateral spinal cord
- 2 tracts: 1) rubrospinal(minimal contribution) 2) lateral corticospinal
lateral corticospinal tract
most important in controlling voluntary movement
- fractionates movement by activating inhibitory neurons to prevent unwanted muscles from contracting
- arise in the primary motor, premotor, and supplementary motor cortex
raphespinal tract
releases serotonin
- modulates the activity of spinal lower motor neurons
- part of the emotional motor system
ceruleospinal tract
releases norepinephrine
- produces tonic facilitation of spinal lower motor neurons
- part of the emotional motor system
