1. Spinal Cord-Reflex Action
Motor functions of
Spinal Cord-Reflex Action
The Pattern Generator

2. Objectives At the end of this lecture you must be able to:
Define a reflex action& know components of Reflex arc.
Types of reflexes & their level of integration
Physiological Significance of these reflexes.
Stretch Reflex and its practical Imporatnce

3. Connections of Peripheral Sensory fibers & Corticospinal fibers with Interneurons & Ant. Motor N (α & γ + Renshaw Cells)

4. Reflex
Is a quick, involuntary stereotype reaction of the body in response to stimulus.
All reflexes functions through a Reflex Arc.
Reflex Arc: is comprised of
-Receptor ->
-Afferent Nerve ->
-Interneuron( + ) ->(integration
Centre)
-Efferent Nerve
-Effector

5. Classification of Reflexes
On the basis of Innate or Acquired:
Unconditioned Reflexes.- Present since birth
Conditioned Reflexes: Learned after birth
On the basis of Number of Synapses:
- Asynaptic – e.g. Axon Reflex
- Monosynaptic – e.g. Stretch Reflex
-Polysynaptic – e.g. Withdrawal Reflex,
Crossed Extensor Reflex

6. Classification of Reflexes
Clinically:
- Superficial – Abdominal Reflex
- Deep Knee jerk
-Visceral from any viscera
-Pathological – Babinski Sign
PROPEERTIES of reflexes:
Already discussed in properties of synapses

7. Stretch Reflex Defnition. Whenever a muscle is stretched,
it responds in the form of contraction. (Monosynaptic)
TYPES:
1. Static ( Tonic )
2. Dynamic ( Phasic)
Stretch Receptor:
Muscle Spindle
To understand these types
muscle spindle ?

8. Muscle Spindle . 3-10 u Long Comprised of Two types of Fibers.
Is a type of Stretch
Receptor present in
Muscles lying Parallel to
Extrafusal muscle fibers
u Long
. Attached to Glycocalyx of surrounding Extrafusal fibers
Comprised of
Two types of Fibers.
1.Nuclear chain Fibers
2.Nuclear Bag Fibers
(Intrafusal fibers)
in number

9. Innervations of Muscle Spindle

10. Innervation of Intrafusal Fibers of Muscle Spindle
Afferent: Primary- Annulospiral endings ( group- I a)
Secondary-Flower spray endings (group- II )
Efferent: Dynamic -- (Gamma-1) - Plate endings
Static - (Gamma-2) - Trail endings a

11. Excitation of Muscle Spindle
Can be Excited by TWO ways;
1. Stretching the who muscle > Stretching of mid portion of the spindle >Excitation
2. Contraction of the end portion of the Spindle without stretching the muscle will also lead to Stretching the central part > Excitation

12. Functions of Muscle Spindle
Maintenance of Muscle Length by feedback:
- Stretching of muscle > Reflex Shortening of muscle
Opposite if Muscle contracts
Hence Detects Change in length &
Rate of change in length.
2. Damping (smoothing) of Oscillations by Primary Endings.
3. Excitation of Alpha Motor Neurons.

13. Functions of Muscle Spindle contd.
4. Maintenance of ά- motor Neuron discharge throughout the muscle contraction
5. Stabilizes body Position during Tense action
(Bulboreticular facilitatory area send excitatory signals to Gamma motor Neuron)
6. Tendon Reflexes
7. Muscle Tone

14. Clinical Example of Stretch Reflex 1. (Knee Jerk) 2. Clonus