Lp 8 Flashcards
(24 cards)
-Corticospinal
-origin: pyramidal cells of 1* cortex & basal nuclei cells
-UMNs: pyramidal cells & their myelinated axons
-also known as lateral tracts
-major motor pathways control voluntary movement
Descending tracts (Pyramidal- direct tracts)
-origin: sub-cortical nuclei of brain stem
-control:
*balance & posture
*coarse movements of proximal portions of limbs
*head,neck & eye movements tracking objects in a visual field
*autonomic fxns
Extra-pyramid- indirect tracts
Origin: motor cortex & sub-cortical motor nuclei?
UMNs
Origin: anterior horn of SC segments?
LMNs
Transmission of impulses: brain to SC segments?
UMNs
Transmission of impulses: skeletal m fibres?
LMNs
Injury results in; spastic paralysis?
UMNs
Injury results in: flaccid paralysis?
LMNs
-innervate m fibres
-axons exit SC segmentally & extend to mm
-branch extensively & single neutron can innervate large no. Of myofibres
-single branch of LMN usually innervate a single m fibre in its middle
LMNs (a-motor neutrons)
-LMNs release ACh into synaptic cleft
-NT generates AP on sacrolemma of myofibres
*propagates along membrane, Down T-tubules & stimulates release of Ca2+ from SR
-Ca2+ initiates m contraction
-removal of Ca2+= m relaxation
Neurotransmission
Levels of reflex action?
-segmental
-intersegmental
-suprasegmental
-reflexes
-circuits confined to single Sc segment
-limited motor response
Segmental
-circuits in several segments
-several m groups/limbs
Intersegmental
-Sc segment & brain circuitry
-mediated by brain stem
-complex reflex activity
Suprasegmental
-stimulus
-integration
-motor response
Reflexes
-monosynaptic
-causes m contraction decrease stretch
-initiated by m spindle response to stretch
-direct afferent-to-efferent neuron reflex
Myotatic/stretch reflex
Specific reflexes
Myotatic/stretch reflex
Inverse Myotatic/tendon reflex
-polysynptic
-decrease force of mm contraction
-++ complex Han stretch reflex
-initiated by GTO sensory neurons & nociceptive afferents from CT of m
-activates multi-synaptic pathways & involves contractural component
Inverse Myotatic/tendon reflex
-modified myofibre
-non-contractile central portion
-repetitive surface of spindle
Intrafusal muscle fibre (IFF)
-innervate spindle centre
-activated by rate & degree of stretch on EFFs
1* sensory n fibre (type Ia)
Innervate EFFs of skeletal mm?
A motor neurons
-special class of LMN
-innervate IFFs of mm spindle
-y efferent firing decrease length of IFF contractile end, directly affecting Ia afferents & a motor neurons
Y motor neurons
When a muscle is stretched:
-excessive load on skeletal mm
-EFFs stretch (mm proper) & IFFs stretch (mm spindle)
-firing of primary (Ia) neurons increases
-Ia neurons synapse on…
-a-motor neurons (in ventral horn)
-excite EFFs
-mm contracts
-stretch resisted
=
Stretch reflex- Agonist
-high m spindle firing in agonist mm
-inhibits a-motor neuron discharge to antagonist mm
-antagonist relaxes
-less resistance to agonist contraction
=
Stretch reflex- antagonist
