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Flashcards in Hirsch - Spinal Motor Deck (57):
1

Eadweard Myubridge

Motion recording

2

Motor Pathways

Upper motor neurons in brainstem and cortex
Lower motor neurons in spinal cord

3

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)

4

Dorsal Horn

inputs from sensory cells, cell bodies of local circuit neurons

5

Dorsal Roots

somas of sensory neurons
axons travel into the cord and out to sensory receptors = afferent

6

Lateral white matter

carries fibers from motor cortex

7

Ventral Horn

cell bodies of motor neuron

8

Ventral roots

axons of lower motor neurons that travel out towards muscles = efferent

9

medial white matter

carries fiber from brainstem

10

SAME-DAVE

sensory-afferent, motor-efferent
dorsal-afferent, ventral-efferent

11

Levels of spinal cord

(from top )
cervical - arm movement
thoracic - information transfer
lumbar - leg movement
sacral

12

different types of fibers

Dorsal roots (sensory afferents)
Ventral roots (motor efferents)

SAME-DAVE

13

Dorsal Roots (sensory afferents)
SAME-DAVE

muscle spindles
golgi tendon organs
tactile
sharp pain/temp
dull pain

14

Ventral Roots (motor efferents)
SAME-DAVE

alpha-motorneuron -> larger
gamma-motorneuron -> small

15

Motor unit

group of muscle fiber that receive input from a single motor neuron
single action potential to many muscle fibers

16

Somatotopic arrangement of Lower Motor Neurons (Ventral horn)

motor neurons that innervate proximal muscles are central
motor neurons that innervate distal muscles are lateral

17

Different alpha- motor neurons

Smaller
Larger
Intermediate sized

18

Small alpha motor neuron

slow
muscle fibers that generate small but lasting contraction
180 muscle fibers per neuron (or smaller for eye movement)

19

larger alpha motor neuron

fast fatigue
generate larger forces - jumping
1-2K fibers; less precision, more power

20

Intermediate sized alpha motor neuron

fatigue resistant
intermediate properties

21

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 ...

22

Muscle spindle

each spindle contains intrafusal fibers arranged in parallel with the extrafusal muscle fibers

23

Nuclear bag

response to rate of change (velocity)

24

nuclear chain

track muscle length

25

sensory afferents

Group Ia
Group II

26

Group Ia

sensory afferent
wrap around the bag and chain fibers
most active when stretching

27

Group II

sensory afferent
wrap around the chain fiber only
most active when stretched

28

intrafusal fibers

innervated by gamma-motor neurons

29

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

30

Golgi tendon organs

1. capsules encasing Group Ib afferents
* organs are embedded in the tendons that connect muscle to bone
2. signal information about force

31

Group Ib

wrap around collagen fibrils

32

afferent activity is greatest when...

the muscle contracts

33

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

34

velocity and length of muscle

phasic - brief; velocity
tonic - longer; length

35

Monosynaptic stretch reflex

maintains muscle length
ex. classical reflex hammer to the knee

36

Know the picture of knee reflex in 13/22 slilde

agonist, antagonist, alpha motorneuron, inhibitory, Ia fiber

37

Knee reflex occuring steps

1. agonist muscle is stretched --> increase in discharge by Ia afferents

2.a. Discharge ---->> mono-synaptic excitation of alpha-motor neuron (white cell) in lateral horn which innervates same muscle to contract to restore muscle length
2.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

38

1a fibers and alpha fibers have

large diameters so conduct quickly; fast reflex

39

Golgi tendon organ reflex in knee reflex

it maintains tension via negative feedback
1. agonist contract
2. muscle tension increases
3. Ib afferents fire hard
*Ib afferent synapses with an inhibitory interneuron
4. reduces firing of the alpha motor neuron
5. muscle relaxes, tension decreases

40

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

41

Upper motor neurons reside where? 15/22

brainstem and cortex

42

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

43

premotor cortex in frontal lobe

supplemenatary and premotor cortex = movement planning
*more to the frontal lobe

44

motor cortex in frontal lobe

movement execution
* further from frontal lobe

45

motor movement planning and execution

1. frontal lobe = idea
2. premotor cortex = program
3. supplementary motor area = program
4. primary motor cortex = execution

46

motor homunculus

at primary motor cortex
corticobullbar tract = face
corticospinal tract = upper extremity, trunk, lower extremity

47

histology of motor cortex

in primary motor cortex; Betz cells (large, fast conduction) and non-Betz pyramidal neurons exist

48

Betz cells

big; fast conduction
axons form most fibers in descending tracts
* descending tract = corticospinal tract, corticobulbar tract

49

descending tract in primary motor cortex

corticospinal tract
corticobulbar tract

50

corticospinal tract

to the spinal cord
upper motor neuron

51

corticobulbar tract

to the brainstem
upper motor neuron

52

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)

53

corticobulbar tract

cortex-> midbrain-> middle ons-> middle edulla (brain stem)
uncrossed

54

subdivision of corticospinal tract

later corticospinal
anterior corticospinal

55

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

56

anterior corticospinal tract

anterior or ventral
crosses at the cord(?)
bilateral & polysynaptic with medial motorneurons (maintain posture)

57

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 *