Post on 24-Dec-2015
SPINAL CORD REFLEXESLecture - 2Dr. Zahoor Ali Shaikh
1
Spinal Reflex
What is Reflex?
-- It is a response that occurs automatically without conscious effort.
2
Reflex
Components of reflex arc are Five:
1- Sensory Receptor2- Afferent pathway3- Center4- Efferent pathway5- Effector organ
3
Components of reflex arc
4
REFLEX
Receptor responds to the stimulus and produces action potential (AP)
AP is taken by afferent pathway to the integrating center (usually CNS)
Spinal cord and brain integrate basic (automatic) reflexes
5
REFLEX
Integrating center processes all the information and makes the decision about the response
Instruction from integrated center are sent via efferent pathway to the Effector organ (muscle or gland)
6
Classification of reflexes
Monosynaptic or stretch reflex or tendon jerkeg. Bicep jerk ,tricep jerk, supinator jerk
knee jerk, ankle jerk Polysynaptic reflexeg. Withdrawal reflex
Abdominal reflexPlantar reflex
Visceral reflexeg. Micturation, defecation reflex
Jendressik Phenomenon7
Stretch Reflex [monosynaptic] Sudden stretch to a muscle leads to
contraction of that muscle is known as stretch reflex.
8
9
Stretch Reflex [monosynaptic]
Stretch Reflex is basic (automatic) spinal reflex. We will take example Knee jerk
There are 5 components of Stretch Reflex
1- Sensory receptor – muscle spindle in skeletal muscle
2- Afferent pathway – 1a fibers 3- Center – spinal cord 4- Efferent fibers – α motor neuron 5- Effector organ – skeletal muscle
contraction
Types of muscle fibers
Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron)
Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by
γ - motor neuron)
10
11Fig 13.3 – Sensory receptors in muscle Silverthorn 2nd Ed
MUSCLE SPINDLE (INTRAFUSAL FIBERS)12
MUSCLE EXTRAFUSAL FIBERS
MUSCLE INTRAFUSAL FIBERS
13
Muscle spindle
Nuclear bag fiber Nuclear chain fiberSensory innervations of muscle
spindle Ia – nuclear bag & nuclear chain
fibers II – nuclear chain fibersMotor supply – γ motor neuron Dynamic & Static
14
Types of motor neuron
α – motor neuron (supply Extrafusal fibers )
γ - motor neuron (supply Intrafusal fibers)
15
Patellar Tendon Reflex
16
KNEE JERK – MONOSYNAPTIC REFLEX
17
Polysynaptic Reflex
In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway
We will study withdrawal reflex
18
POLYSYNAPTIC REFLEXESWithdrawal Reflex When a person touches a hot stove or pin
prick, a withdrawal reflex occurs from the painful stimulus
1. Receptor- pain and Temperature Receptors stimulated
2. Afferent impulse travels via Action potential
3. Center– Spinal cord.( Excitatory interneuron stimulated that stimulate efferent fibers).
19
POLY SYNAPTIC REFLEX
4 .Efferent fibers to Biceps to cotract ( flextion of arm ) and inhibitory neuron stimulated to inhibit contraction of Triceps.
This type of connection causing stimulation of nerve supply to one muscle and simultaneous inhibition of the nerve to its Antagonistic muscle is known as RECIPROCAL INNERVATION. 20
Withdrawal reflex – Polysynaptic reflex21
Poly synaptic reflex
Important Afferent neuron stimulate also interneuron
that carry signals to the Brain ( Ascending tracts in the spinal cord )
Therefore Brain can modify the with drawl reflex. How?
By sending impulses via descending pathways to the efferent motor neuron supplying the involved muscles and prevent contracting of biceps inspite of painful stimulus e.g. pin prick
22
DIFFERENT REFLEXES SHOWN
23
Jendressik Phenomenon
(Reinforcement)
24
25
Jendressik Phenomenon
(Reinforcement)
Superficial Reflexes
26
Summary
27
28
TRANSVERS SECTION OF SPINAL CORD
29
Dermatomes of Spinal roots and divisions of trigeminal nerve (V1 ,V2, V3)
30
Spinal Cord Reflexes
Cranial Nerve
Other Reflexes
1- Golgi tendon Reflex 2- Crossed Extensor Reflex
We will discuss first Golgi endon Reflex
31
Golgi Tendon Organs
Composed of: Nerve fiber endings that wind between
collagen fibers inside connective tissue capsule
If muscle is stretched: Free nerve endings are pinched and they
fire Activation of Golgi tendon organs:
Inhibits alpha motor neurons and decreases muscle contraction
32
The Golgi tendon reflex (inverse stretch reflex)
33
Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed34
Crossed Extensor Reflex
Extension of opposite limb
Flexion & withdrawal of stimulated limb
Painful Stimuli
35
36
POLYSYNAPTIC REFLEX37
Clinical Importance of reflexes
To test the integrity of reflex arc. Localization of neurological lesion. Identifying the type of lesion. Monitoring the progress of
neurological deficit.
38
Clinical Importance of reflexes
Deep tendon reflexes are absent in lower motor neuron lesion.
The become exaggerated in upper motor neuron lesions.
Pendular jerks are observed in cerebellar lesions.
39
Thank you
40