3. A baseball pitcher planning a pitch…
The mental body image seems to be generated by somatosensory, proprioceptive, and visial inputs to the posterior parietal cortex (area 5, area 7)

4. The motor control hierarchy have three levels
The highest level---strategy
Represented by the association areas of neocortex and basal ganglia of the forebrain
Is concerned with strategy:
The goal of the movement and the movement strategy that best achieves the goal.

5. The motor control hierarchy have three levels
The middle level---tactics
Represented by the motor cortex and cerebellum
Is concerned with tactics
The sequences of muscle contractions
Arranged in space and time
Required to smoothly and accurately achieve the strategic goal.

6. The motor control hierarchy have three levels
The lowest level—execution
Represented by the brain stem and spinal cord
Is concerned with execution
Action of the motor neuron and interneuron pools that generate the goal-directed movement and make any necessary adjustments of posture.

7. organization of motor subsystems

8. Spinal Control of Movement
Part 1
Spinal Control of Movement

9. Introduction
The rhythmic movements could be elicited in the hind legs of cats and dogs long after their spinal cords had been severed from the rest of the central nervous system
---Charles Sherington Graham Brown(English)
The importance of circuitry within the spinal cord for the coordinated control of movements

11. Spinal motor neurons Alpha motor neurons
Innervate skeletal muscle (extrafusal muscle)
Function: directly command muscle contract
Gamma motor neurons
Innervate muscle spindle (intrafusal muscle)
Function: regulating the muscle spindle
Interneurons
Allows coordinated motor programs to be generated
Final common pathway
Directly command muscle contract
Compare: Upper motor neurons
Lower motor neurons

13. Spinal interneurons
Most of the input to the alpha motor neurons comes from interneurons of the spinal cord.
Interneurons receive synaptic input from primary sensory axons, descending axons from the brain, and collaterals of lower motor neuron axons.
The interneurons are themselves networked together in a way that allows coordinated motor programs to be generated in response to their many inputs.

14. The Lower Motor Neurons
Alpha motor neurons are directly responsible for the generation of force by muscle
Motor unit: one alpha motor neuron and all of the muscle fibers it innervates collectively make up motor unit, the elementary component of motor control
Motor neuron pool: the collection of alpha motor neurons that innervates a single muslce.

15. α，β，γ I. Final Common Pathway and Motor Unit
Anterior motor neurons of the spinal cord
Anterior horns of the cord gray matter
α，β，γ

16. Muscle innervation by lower motor neurons
The ventral horn of the spinal cord contains motor neurons that innervate skeletal muscle fibers
30 mixed spinal nerves
Cervical 1-8
Thoracic 1-12
Lumbar 1-5
Sacral 1-5
Ventral roots+Dorsal root=Spinal nerve

17. Inputs to alpha motor neurons
This input may be excitatory or inhibitory and is part of the circuitry that generates the spinal motor programs
This input provides feedback about muscle length
This input is important for the initiation and control of voluntary movement

18. Alpha-motoneuron – final common pathway

19. organization of motor systems
Motor Cortex
Brain Stem
Spinal Cord
-motor neuron
Final common pathway
Skeletal muscle

20. motor neuron:
final common
pathway

21. Spinal control of Motor Function
Motor neurons in the spinal cord
–α motor neurons
Causes contraction of the innervated muscle.
Final common pathway.
– γ motor neurons
innervates intrafusal muscle to adjust the
sensitivity of muscle spindle to stretch.

22. Every striated muscle has encapsulated muscle fibers scattered throughout the muscle called muscle spindles.
Extrafusal and intrafusal muscle fibers

23. regulate sensitivity of muscle spindle to stretch stimulation
The extrafusal muscle fibers are innervated by Alpha motor neuron
The intrafusal muscle fibers are innervated by Gamma motor neurons
skeletal muscle contraction
regulate sensitivity of muscle spindle to stretch stimulation

25. ※ Motor unit  A motor unit consists of a single α-motor
neuron and the group of muscle fibers
which it innervates. The elementary component of motor control. ※
For the refined motion
Innervation ratio
Fibers per motor neuron
Extraocular muscle 3:1
Gastrocnemius 2000:1
For the strength

26. The muscle cells of a motor unit are not grouped, but are interspersed among cells from other motor units
The coordinated movement needs the activation of several motors

27. organization of motor systems
Voluntary movements
Nociceptive stimulus
Stretch muscles
Posture maintenance
Motor Cortex
Reflex
Brain Stem
Spinal Cord
Final common pathway
-motor neuron
Effector
Skeletal muscle
Receptor
Skin Muscle Joint

28. Regulating Functions of the Spinal Cord
Spinal shock
Spinal Reflex
spinal animal:
is prepared by transecting the spinal cord at the fifth cervical segment

29. Spinal shock ※ Concept:
Complete transection of the spinal cord results in the immediate paralysis and loss of sensation in all body regions innervated by spinal cord segments below the lesion. All reflex in the isolated segments of the spinal cord are at once totally depressed. This is called spinal shock.

30. Symptoms of spinal shock
During spinal shock:
complete loss of all reflexes,
no tone, paralysis, complete anaesthesia,
no peristalsis, bladder and rectal reflexes absent (no defecation and micturition )(Feces is detained in rectum and urine in bladder )
no sweating (Sweating reflex is suppressed)
arterial blood Pressure decrease(40mmHg)
(BP drops down, peripheral blood vessels are dilated)

31. Spinal shock Facilitate Inhibit
The reason: Is result of the sudden withdrawal of descending control from suprasegmental centers in the brain.
The recovery of spinal neurons excitability.
The time course of recovery from spinal shock varies considerably with the species studied. It is increased with ascent of the phylogenetic scale.
Extensor reflex weaken Flexor reflex strengthen
Facilitate
Inhibit
High central ?

32. ※
Postural reflex

33. Flexion reflex and crossed extension reflex
-is a protective reflex and a polysynaptic reflex.
-results in flexion on the ipsilateral and extension on the contralateral.
-can be innervated by noxious stimulates.

34. Flexion reflex and crossed extension reflex
There is a rapid lifting of the affected foot (ipsilateral withdrawal reflex ),
while the contralateral response activates the extensor muscles of the opposite leg (contralateral extensor reflex)
support the weight shifted to it.

35. Flexion reflex and crossed extension reflex
Flexor reflex
A noxious stimulus to the spinal animal induces flexion upward and away from the stimulus.
Reflex response consists of facilitation of flexor muscles and inhibition of extensor muscle in the stimulated limb.
That can provide protection from the injury.
Crossed extensor reflex
If the stimulus sufficiently strong, flexion of ipsilateral limb and extension of the contra-lateral limb which serves to support the body weight and maintain the body balance.

36. ※

37. Stretch reflex includes:
Tendon reflex (Phasic stretch reflex ) ：
short lasting and relatively intense (Ⅰa), strong reflex contraction.(single synaptic reflex).
Muscle tonus (Tonic stretch reflex ) :
less intense but lasts longer, maintain the body posture.（polysynaptic reflex）

39. Tendon reflex—knee-jerk reflex;
 Caused by rapid stretch of the muscle,
 Transmitted from the Ia sensory ending of the M. S.
 Causes an instantaneous, strong reflex contraction of the same muscle;
 Opposing sudden changes in length of the M.S;
 A monosynaptic pathway:
being over within 0.7 ms;

40. elbow jerk
Achilles
tendon
reflex

42. Muscle tonus  Caused by a weaker and continues stretch of the muscle,
 Transmitted from the Ia and II sensory ending of the M. S.
 Multiple synaptic pathway, continues for a prolonged period.
 Non-synchronized contraction,
 for at least many seconds or minutes, maintaining the posture of the body.

43. tendon reflex and the tonic stretch reflex
Type
Tendon reflex
Tonic stretch reflex
stimulation
suddenly stretched
Weaker, continuous stretch
Afferent fiber
Ia sensory ending
Ia and Ⅱ sensory ending
Synapse
Monosynaptic reflex
Polysynaptic reflex
Significance
Determine the lesion areas
maintenance of posture

45. Stretch reflex Muscle sensors
Types of muscle fibers
a.  Extrafusal fibers
-make up the bulk of
muscle
-are innervated by
α-motoneurons.
-provide the force for
muscle contraction.

46. Stretch reflex Muscle sensors
b.  Intrafusal fibers
-are smaller than
extrafusal fibers
-are innervated by γ-motoneurons.
-are encapsulated in
sheaths to form
muscle spindles

47. Stretch reflex Muscle sensors
Muscle spindles:
-are distributed
throughout muscle
-intrafusal fibers is in
parallel with extrafusal
fibers.
-Nuclear bag fibers and
Nuclear chain fibers.

49. Stretch reflex How the muscle spindle works
-When a muscle is
stretched → the muscle
spindle is also stretched
→ stimulates group Ⅰa
and Ⅱ afferent fibers.
→α-motoneurons →
Innervates the extrafusal fibers → the muscle contracts

50. Stretch reflex How the muscle spindle works
γ-motoneurons
-innervate intrafusal
muscle fibers.
-adjust the sensitivity
of the muscle spindle.
-receive control of
high center .

51. Activation of the γ-loop
WHAT IS THE γ-LOOP?
Descending influence
Muscle spindle Ⅰa γ
Activation of the γ-loop
results in increased
muscle tone
MUSCLE α

52. The Gamma loop
Changing the activity of the gamma motor neurons changes the set point of the myotatic feedback loop
The Gamma loop
Gamma motor neuron—intrafusal muscle fiber---Ⅰa afferent---alpha motor neuron—extrafusal muscle fibers
Alpha and gamma motor neurons are simultaneously activated by descending commands from the brain.

53. Tendon organ and inverse stretch reflex
Change of tension
Ⅰb afferent fiber
Tendon
organ

55. Action of Tendon Organ
Tendon organ embedded in the tendon at the end of the muscle measure the tension of muscles can be activated by isometric contraction of extrafusal fibers. Tendon organ is innervated by Ib afferent fibers, which synapses with inhibitory interneurons and inhibit α motor neurons .

56. Proprioception from Golgi tendon organs
Acts like a strain gauge, it monitors muscle tension, or the force of contraction.
Located at the junction of the muscle and the tendon and are innervated by group Ⅰb sensory axons that are slightly smaller than the Ⅰa axons innervating the muscle spindles.

57. Tendon organ

59. Mechanism of stretch reflex
A skeletal muscle is stretched→ spindle is stretched →the impulses are conducted to the spinal cord by Ⅰa/Ⅱfibers to activate the α-motor neurons→which supply the same muscle → the muscle contracts to oppose the stretch (the antagonist muscle relaxes ).
if stronger stretch applied on muscle, it changes the muscle tone → stretch the tendon organ → in turn to inhibit αmotoneurons by inhibitory interneurons → to inhibits stretch reflex to prevent the stretched muscles from injury.

61. Summary
Spinal shock
Stretch reflex

62. Question
Describe the neuronal circuit and function of the skeletal muscle stretch reflexes in detail, and difference in the different types of the reflexes.

63. (1) The basic circuit:
Sudden stretch of a muscle excites the muscle spindle, and Ia proprioceptor nerve fiber sends signals to the spinal cord, synapses directly with anterior motor neurons that send nerve fiber back to the extrafusal muscle fibers of the same muscle, causing reflex contraction of the muscle.

64. (2) tendon reflex and the tonic stretch reflex
Type
Tendon reflex
Tonic stretch reflex
stimulation
suddenly stretched
Weaker, continuous stretch
Afferent fiber
Ia sensory ending
Ia and Ⅱ sensory ending
Synapse
Monosynaptic reflex
Polysynaptic reflex
Significance
Determine the lesion areas
maintenance of posture

65. (3)Functions:
Tendon reflex causes an instantaneous, strong reflex contraction of the same muscle; Muscle tonus is good for maintaining the posture of the body.