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Dr.HINA SIKANDAR
 2 types:
 A) Alpha motor neurons
It give rise to large alpha type nerve fibers
Size: 14um
Velocity: 70-120 m/s
Motor unit:
3 to several hundred nerve fibers are
innervated by a single alpha neuron
 B) Gamma motor neuron:
They transmit impulses through A gama
motor nerve fiber.It helps to maintain tone of
muscle spindle.
Size – 5 um
Velocity – 15 – 40 m/s
 All horns of spinal cord.
 Highly excitable, signals converge on
interneurons from different tracts.
 Inhibitory signals to surrounding motor
neurons – provides lateral inhibition
 Propriospinal fibers: involves in
multisegmental reflexes
 Structure
 3 – 12 tiny intrafusal fibers – attached to
extrafusal fibers by glycocalyx
 Excitation of muscle
spindle
1. Lengthening of whole
muscle
2. Contraction of end
portions of spindles
intrafusal fibers.
Sensory endings:
2 types :
Primary ending: 1a
fibers. 17 um dia
70 – 120 m/s
Secondary ending: 2
fibers 8 um
 Static response
By both primary and secondary endings when
muscle is stretched slowly
 Dynamic response
Only primary ending Is involved
When muscle shortens opposite occurs:
Gamma dynamic fibers – nuclear bag fibers
Gamma static fiber – nuclear chain fiber +
static bag fiber
 Muscle stretch
reflex
 Static reflex maintains the degree of muscle
contraction to remain constant.
 Functions of muscle spindle ( stretch
reflexes)
1. Damping mechanism
Helps in smooth muscle contraction (signal
averaging)
2. Voluntary motor activity
Co-activation of alpha and gamma efferent
neurons.
3. Stabilizes body position during tense action
By increase gamma efferent discharge by
bulboreticular area of brain stem.
4. Monitor muscle condition and provide a
detailed input to spinal, cerebellar,
extrapyramidal and cortical centers.
Concerning state of locomotion appratus.
5. Maintain of muscle tone.
Damage to motor cortex cause greatly
aggregated muscle reflex on opposite side
of body.
 It is an encapsulated sensory receptor
through which muscle tendon fibers pass.
 It helps to detect muscle tension
10 – 15 muscle fibers are usually connected
to each golgi tendon organ and it is
stimulated when the fibers are tensed by
contracton or stretching the muscle.
It has both dynamic and static response.
 Function:
It helps to provide the nervous system with
instantaneous information on the degree of
tension in each small segment of muscle.
 Innervation:
It is innervated by 1b nerve fiber having dia
16um.
they transmit information into local
areas of cord and then to cerebellum by
spinocerebellar tract by other tracts of
cerebellar cortex
 Mechanism
In spinal cord it activates an inhibitory
interneuron and inhibit anterior motor
neuron.
 Lengthening Reaction
When tension on the muscle becomes
extreme the inhibitory effect from the
tendon can be so great that it leads to
sudden reaction in spinal cord and relaxation
of entire muscle.
 Withdrawal reflex
Polysynaptic: Any cutaneous sensory stimulus
from a limb is likely to cause the flexor
muscle of limb to contract thereby
withdrawing the limb from stimulating
object.
 Neural mechanism
It involves the
following basic type
of circuits
1: Diverging circuits to
spread the reflex to
the necessary muscle
for withdrawal
2: Circuits to inhibit
antagonist muscle
called reciprocal
inhibition
3: Circuits to cause
after discharge.
 Crossed extensor reflex
About 0.2 – 0.5 sec after stimulus elicits a
flexor reflex in one limb, the opposite limb
begins to extend. This is called crossed
extensor reflex.
 Mass reflex
Excessive spinal cord discharge due to strong
pain stimulus or excessive viscous filling
1. Flexor spasm
2. Colon bladder evacuate
3. Increase B.P
4. Sweating
 Spinal cord transection
Spinal shock then regain their natural degree
of excitability
1. B.P falls
2. Skeletal muscle reflexes are blocked
(Recover after 2 weeks with stretch flexes
first to recover)
3. Sacral reflexes for bladder and colon
evacuation is suppressed.
MOTOR FUNCTIONS OF SPINAL CORD.pptx

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MOTOR FUNCTIONS OF SPINAL CORD.pptx

  • 2.  2 types:  A) Alpha motor neurons It give rise to large alpha type nerve fibers Size: 14um Velocity: 70-120 m/s Motor unit: 3 to several hundred nerve fibers are innervated by a single alpha neuron
  • 3.  B) Gamma motor neuron: They transmit impulses through A gama motor nerve fiber.It helps to maintain tone of muscle spindle. Size – 5 um Velocity – 15 – 40 m/s
  • 4.  All horns of spinal cord.  Highly excitable, signals converge on interneurons from different tracts.
  • 5.  Inhibitory signals to surrounding motor neurons – provides lateral inhibition  Propriospinal fibers: involves in multisegmental reflexes
  • 6.  Structure  3 – 12 tiny intrafusal fibers – attached to extrafusal fibers by glycocalyx
  • 7.  Excitation of muscle spindle 1. Lengthening of whole muscle 2. Contraction of end portions of spindles intrafusal fibers. Sensory endings: 2 types : Primary ending: 1a fibers. 17 um dia 70 – 120 m/s Secondary ending: 2 fibers 8 um
  • 8.  Static response By both primary and secondary endings when muscle is stretched slowly  Dynamic response Only primary ending Is involved When muscle shortens opposite occurs: Gamma dynamic fibers – nuclear bag fibers Gamma static fiber – nuclear chain fiber + static bag fiber
  • 10.  Static reflex maintains the degree of muscle contraction to remain constant.  Functions of muscle spindle ( stretch reflexes) 1. Damping mechanism Helps in smooth muscle contraction (signal averaging) 2. Voluntary motor activity Co-activation of alpha and gamma efferent neurons.
  • 11. 3. Stabilizes body position during tense action By increase gamma efferent discharge by bulboreticular area of brain stem. 4. Monitor muscle condition and provide a detailed input to spinal, cerebellar, extrapyramidal and cortical centers. Concerning state of locomotion appratus. 5. Maintain of muscle tone. Damage to motor cortex cause greatly aggregated muscle reflex on opposite side of body.
  • 12.  It is an encapsulated sensory receptor through which muscle tendon fibers pass.  It helps to detect muscle tension 10 – 15 muscle fibers are usually connected to each golgi tendon organ and it is stimulated when the fibers are tensed by contracton or stretching the muscle. It has both dynamic and static response.
  • 13.  Function: It helps to provide the nervous system with instantaneous information on the degree of tension in each small segment of muscle.  Innervation: It is innervated by 1b nerve fiber having dia 16um. they transmit information into local areas of cord and then to cerebellum by spinocerebellar tract by other tracts of cerebellar cortex
  • 14.  Mechanism In spinal cord it activates an inhibitory interneuron and inhibit anterior motor neuron.  Lengthening Reaction When tension on the muscle becomes extreme the inhibitory effect from the tendon can be so great that it leads to sudden reaction in spinal cord and relaxation of entire muscle.
  • 15.  Withdrawal reflex Polysynaptic: Any cutaneous sensory stimulus from a limb is likely to cause the flexor muscle of limb to contract thereby withdrawing the limb from stimulating object.
  • 16.  Neural mechanism It involves the following basic type of circuits 1: Diverging circuits to spread the reflex to the necessary muscle for withdrawal 2: Circuits to inhibit antagonist muscle called reciprocal inhibition 3: Circuits to cause after discharge.
  • 17.  Crossed extensor reflex About 0.2 – 0.5 sec after stimulus elicits a flexor reflex in one limb, the opposite limb begins to extend. This is called crossed extensor reflex.  Mass reflex Excessive spinal cord discharge due to strong pain stimulus or excessive viscous filling
  • 18. 1. Flexor spasm 2. Colon bladder evacuate 3. Increase B.P 4. Sweating
  • 19.  Spinal cord transection Spinal shock then regain their natural degree of excitability 1. B.P falls 2. Skeletal muscle reflexes are blocked (Recover after 2 weeks with stretch flexes first to recover) 3. Sacral reflexes for bladder and colon evacuation is suppressed.