Lecture 15 - Spinal Cord + Motor Cortex Flashcards
Motor cortex
planning, initiating, directing voluntary movements
Brainstem Centers
basic movements, postural control
What is the basal ganglia?
gating proper initiation of movement
What is the cerebellum?
sensory motor coordination of ongoing movment
What are the spinal cord and brainstem circuits
- local circuit neurons
- motor neuronpools
What does SAME-DAVE stand for?
sensory-afferent
motor-efferent
dorsal-afferent
ventral-efferent
What is a motor unit?
group of muscle fibers that receive input from a single motor neuron
What are lower motor neurons?
-motor neurons that innervate proximal mucles
Smaller (S) alpha motor neurons
- conduct slowly
- innervate muscle fibers that generate small, lasting contractions (EX: postural muscles like soleus)
Larger (FF) alpha motor neurons?
- fast
- innervate larger groups of muscle that generate larger forces (EX muscles for jumping)
Intermediate (FR) alpha motor neurons
-innervate muscles with intermediate properties
What is the motor pool? What can it comprise?
- group of motor neurons that innervate a single muscle
- can comprise more thane one type of motor unit
What are golgi tendon organs?
capsules encasing group 1b afferents
-embedded in tendons that connect muscle to bone
What do golgi tendon organs signal?
- information about force
- afferent atvity is greatest when muscle contracts
What is the monosynaptic stretch reflex?
maintains muscle length(classical reflex induced with hammer to the knee)
What does the golgi tendon organ reflex do?
maintains tension via negative feedback
Where are upper motor neurons?
brainstem and cortex
Where are lower motor neurons?
in spinal cord or brain stem
Dorsal horn
inputs from sensory cells, somas of local circuit neurons
Dorsal roots
contain somas of sensory neurons who axons travel out to peripheral sensor receptors and to the cord (afferent)
ventral horn
somas of lower motor neurons
ventral roots
contains axons of lower motor neurons that travel out toward muscles (efferent)
medial white matter
carries fibers from brainstem
what are the 4 regions of the spinal cord?
- cervical
- thoracic
- lumbar
- sacral
What does each spindle contain? What are they called?
two types of special muscle fibers (intrafusal fibers)
How are intrafusal fibers arranged?
in parallel with extrafusal fibers
What are nuclear bag fibers?
sensitive to rate of change in muscle length (velocity)
What are nuclear chain fibers?
sensitive to muscle length
What are Group 1a sensory afferents? When are they most active?
- wrap around the bag and chain fibers
- most active when muscle length changes (EX stretching)
What are group II sensory afferents? When are they most active?
- wrap around chain fibers only
- most active when muscle is stretched
What are intrafusal fibers innervated by?
gama motor neurons
What do gama motor neurons do?
- regulate sensitivity of the muscle spindle
- pull at both ends of bag and chain fibers
- stretching regions where afferent endings are wrapped
What Betz cells?
- very large
- stout axons form most fibers in descending and corticobulbar tracts
- example of upper motor neuron
What are the 2 descending motor tracts that originate in the motor and premotor cortices?
- corticobublar (ends in brainstem)
2. corticospinal (ends in spinal cord)
The corticobulbar tract is ______ while the corticospinal tract _____ at the _____
- uncrossed
- crosses, midline
What is the lateral cortico-spinal tract?
- comprises most of corticospinal tract
- originates from premotor cortex + primary motor cortex
Where do most fibers cross?
- at the pyramidal decussation
- terminate on lateral motor neurons (those that move distal muscles like fingers and toes)
What is the anterior (ventral) corticospinal tract?
- crosses at the cord
- makes bilateral + polysynaptic connections with medial motor neurons that are used to maintain posture
supplementary and premotor cortex
movement planning
motor cortex
movement execution
How are cells organized in cortices?
arranged in columns that perform common functions
What are the 3 steps to the monosynaptic stretch reflex?
- agonist muscle is stretched, leads to increase in discharge by 1a afferents
- monosynaptic excitation of a-motoneuron in lateral horn
- disynaptic relaxation of antagonist, 1a afferent synapses with inhibitory interneuron in dorsal horn
What kind of diameters do the 1a fibers and a-fibers have? What does this mean?
- large diameters
- conduct quickly
- reflex is fast
What are the 3 steps of the Golgi tendon organ reflex?
- agonist contracts, muscle tension increases, 1b afferents fire hard
- 1b afferents synapses with inhibitory interneuron
- muscle relaxes, tension decreases
How are motor neurons (in ventral horn) arranged?
somatically
What does it mean that motor neurons (in ventral horn) are somatically arranged?
- motor neurons that innervate proximal muscles are medial
- those that innervate distal muscles are lateral
