Hirsch - Spinal Motor Flashcards
Eadweard Myubridge
Motion recording
Motor Pathways
Upper motor neurons in brainstem and cortex
Lower motor neurons in spinal cord
Spinal cord - know the locations in the picture
Dorsal Horn Dorsal roots Lateral white matter Ventral Horn Ventral roots Medial white matter
- grey matter (inside)
- white matter (outside)
Dorsal Horn
inputs from sensory cells, cell bodies of local circuit neurons
Dorsal Roots
somas of sensory neurons
axons travel into the cord and out to sensory receptors = afferent
Lateral white matter
carries fibers from motor cortex
Ventral Horn
cell bodies of motor neuron
Ventral roots
axons of lower motor neurons that travel out towards muscles = efferent
medial white matter
carries fiber from brainstem
SAME-DAVE
sensory-afferent, motor-efferent
dorsal-afferent, ventral-efferent
Levels of spinal cord
(from top ) cervical - arm movement thoracic - information transfer lumbar - leg movement sacral
different types of fibers
Dorsal roots (sensory afferents) Ventral roots (motor efferents)
SAME-DAVE
Dorsal Roots (sensory afferents) SAME-DAVE
muscle spindles golgi tendon organs tactile sharp pain/temp dull pain
Ventral Roots (motor efferents) SAME-DAVE
alpha-motorneuron -> larger
gamma-motorneuron -> small
Motor unit
group of muscle fiber that receive input from a single motor neuron
single action potential to many muscle fibers
Somatotopic arrangement of Lower Motor Neurons (Ventral horn)
motor neurons that innervate proximal muscles are central
motor neurons that innervate distal muscles are lateral
Different alpha- motor neurons
Smaller
Larger
Intermediate sized
Small alpha motor neuron
slow
muscle fibers that generate small but lasting contraction
180 muscle fibers per neuron (or smaller for eye movement)
larger alpha motor neuron
fast fatigue
generate larger forces - jumping
1-2K fibers; less precision, more power
Intermediate sized alpha motor neuron
fatigue resistant
intermediate properties
Motor pool
group of motor neurons that innervate a single muscle
can comprise more than one type of motor unit (slow, fast, intermediate..)
ex) calf muscle used for standing, jumping, walking …
Muscle spindle
each spindle contains intrafusal fibers arranged in parallel with the extrafusal muscle fibers
Nuclear bag
response to rate of change (velocity)
nuclear chain
track muscle length
sensory afferents
Group Ia
Group II
Group Ia
sensory afferent
wrap around the bag and chain fibers
most active when stretching
Group II
sensory afferent
wrap around the chain fiber only
most active when stretched
intrafusal fibers
innervated by gamma-motor neurons
gamma-motor neuron
regulate the sensitivity of the muscle spindle
pulling at both ends of bag and chain fibers; stretching the regions where afferent endings are wrapped
Golgi tendon organs
- capsules encasing Group Ib afferents
* organs are embedded in the tendons that connect muscle to bone - signal information about force
Group Ib
wrap around collagen fibrils
afferent activity is greatest when…
the muscle contracts
muscle spindles and golgi tendon organs
(passive stretch) from short to long
II sensitive to length
Ia sensitive to velocity and length
Ib not sensitive
(passive stretch) from long to short
II less sensitive to length
Ia less sensitive to length; AP recorded from afferent
Ib very sensitive
velocity and length of muscle
phasic - brief; velocity
tonic - longer; length
Monosynaptic stretch reflex
maintains muscle length
ex. classical reflex hammer to the knee
Know the picture of knee reflex in 13/22 slilde
agonist, antagonist, alpha motorneuron, inhibitory, Ia fiber
Knee reflex occuring steps
- agonist muscle is stretched –> increase in discharge by Ia afferents
- a. Discharge —-» mono-synaptic excitation of alpha-motor neuron (white cell) in lateral horn which innervates same muscle to contract to restore muscle length
- b. Discharge —» di-synaptic relaxation of the antagonist; Ia afferent synapses with an inhibitory inter neuron in the dorsal horn –> suppresses activity in the alpha-motor neuron that innervates the antagonist
1a fibers and alpha fibers have
large diameters so conduct quickly; fast reflex
Golgi tendon organ reflex in knee reflex
it maintains tension via negative feedback
- agonist contract
- muscle tension increases
- Ib afferents fire hard
* Ib afferent synapses with an inhibitory interneuron - reduces firing of the alpha motor neuron
- muscle relaxes, tension decreases
Top down control of spinal cord from cortex and brainstem
1. lateral white matter
medial white matter
lateral white matter (know location) = axons from motor cortex
medial white matter (know location) = axons from brainstem
Upper motor neurons reside where? 15/22
brainstem and cortex
Brainstem to spinal cord
- many things happen, but simply remember…
brainstem nuclei provide upper motor neurons that project to the cord - there are many tracts such as… (study their pictures 16/22)
1. lateral and medial vestibulospinal tracts
2. reticulospinal tract
3. colliculospinal tract
- there are many tracts such as… (study their pictures 16/22)
premotor cortex in frontal lobe
supplemenatary and premotor cortex = movement planning
*more to the frontal lobe
motor cortex in frontal lobe
movement execution
* further from frontal lobe
motor movement planning and execution
- frontal lobe = idea
- premotor cortex = program
- supplementary motor area = program
- primary motor cortex = execution
motor homunculus
at primary motor cortex
corticobullbar tract = face
corticospinal tract = upper extremity, trunk, lower extremity
histology of motor cortex
in primary motor cortex; Betz cells (large, fast conduction) and non-Betz pyramidal neurons exist
Betz cells
big; fast conduction
axons form most fibers in descending tracts
* descending tract = corticospinal tract, corticobulbar tract
descending tract in primary motor cortex
corticospinal tract
corticobulbar tract
corticospinal tract
to the spinal cord
upper motor neuron
corticobulbar tract
to the brainstem
upper motor neuron
Corticospinal tract
cortex -> midbrain -> middle pons -> middle medulla -> caudal medulla (pyramidal decussation; nerve crosses to opposite side) -> spinal cord
* subdivision: lateral corticospinal (cross), anterior corticospinal (do not cross)
corticobulbar tract
cortex-> midbrain-> middle ons-> middle edulla (brain stem)
uncrossed
subdivision of corticospinal tract
later corticospinal
anterior corticospinal
later corticospinal tract
80% of cortico-spinal tract; distal muscles (fingers and toes)
most fibers cross at pyramidal decussation in caudal medulla
controls detailed/fine movement
anterior corticospinal tract
anterior or ventral
crosses at the cord(?)
bilateral & polysynaptic with medial motorneurons (maintain posture)
cells in motorcortex arranged in colums that perform common functions
motor cortex are believed to be organized according to movements (functions carried by muscles) rather than target muscle *
