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Sunday, 30 July 2017



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* The reflex arc is made of:

1.Sense organ (Receptor). Receive the stimulus.
2.Afferent (Sensory) neuron.
3.Synapse (Center).
4.Efferent (Motor) neuron.
5.Effector (eg Skeletal muscle). 
it Give the response that opposes the stimulus.

* Classification of reflexes: 

A\ According to the site of receptors:
1. Superficial Rxs: have receptors on the skin or S/c tissues. 
2. Deep Rxs: Have receptors in the deep somatic structures ( Muscles, tendons)
3. Visceral Rxs: Have receptors in the viscera.

B\ According to the site of the center:
1. Simple spinal Rxs: centre in spinal cord.
2. More complicated brain stem Rxs: centre in brain stem.
3. Most complicated cortical Rxs: centre in the motor cortex.

C\ According to the number of synapses:
1. Monosynaptic Rxs: Have one synapse between the sensory & motor neuron.
2. polysynaptic Rxs: Have more than one synapse between the sensory & motor neuron.

* Stretch reflex:
> Contraction of skeletal muscle with intact nerve supply in response to stretch.
* Is a monosynaptic deep spinal reflex. 

Maintenance of muscle length & tone (stretch is lengthening & contraction is shortening of muscle fiber).
> Sense organ is muscle spindle located deeply in the muscle.   
> The muscle spindle contains specialized ( intrafusal muscle fibers)  IFFs  parallel  & to inside the contractile extrafusal musle fibers.
intrafusal muscle fibers have contractile terminals & a noncontractile centre (receptor site).

IFFs have 2 types :

1. nuclear bag fibers which contains many
nuclei in a dilated central area., 
2. Nuclear chain fibers contains many nuclei as a chain.
> The nuclear bag fibers are of dynamic & static types. 
> The nuclear chain fibers are static. 
* The afferent (sensory) nerves originating in the central portion of the intrafusal fibers.
*Efferent nerves supplying the polar contractile regions of the intrafusal fibers dynamic and static.

* Normally the muscle spindle is stimulated by stretch via:

1.Tapping the muscle tendon by a reflex hammer (Dynamic response).
2. Gamma (γ) motor neuron discharge to the muscle spindle.(static response) 
3. Both.

* Deep tendon reflexes (Tendon jerks): 

1\ Biceps tendon Rx: 
*Flexsion of the elbow due to contraction of    the biceps brachii, in response to tapping its  tendon by a reflex hammer.
2\ Triceps tendon Rx:
* Extension of the elbow due to contraction of the triceps brachii, in response to tapping the triceps brachii tendon by a reflex hammer. 
3\ knee jerk (Patellar tendon Rx:  
* Extension of the knee due to contraction of the quadriceps femoris, in response to tapping the patellar tendon by a reflex hammer.
4\ Achilles tendon Rx (Ankle Jerk):
* Tapping on the Achilles tendon causes contraction of gastrocnemius muscle with plantar flexion of ankle.
¤ Clinical importance (Significance) of Deep tendons reflex:  
* The normal response of a reflex indicate intact reflex arc of this reflex.
* Absence or reudction of the response of a reflex (Areflexia, Hyporeflexia) suggests:
1.Interruption of the sensory (Afferent) of the arc, as in Tabes dorsalis.
2. Interruption of the motor (Efferent) of the arc, as in poliomyelitis & other causes of lower motor neuron lesion.
3. Period of the neural shock in UMNL or spinal cord transection.
4. Others.

* Exaggerated response of Deep Tendon Reflexs (Hyperreflexia) occurs in :

1.Upper motor neuron lesion UMNL after passing the neural shock. 
5.Strychnine poisoning.
* Pendular reflex occur in cerebellar lesion. 
* Localization of lesions in the spinal cord by observing the differences in Deep Tendon reflexs responses
* In neurological exam the DTRs are graded by the following scale: 
0 (absent, Areflexia), 
1+ (hypoactive, Hyporeflexia ), 
2+ (brisk, normal),
3+ (hyperactive without clonus), 
4+ (hyperactive with mild clonus), 
5+ (hyperactive with sustained clonus).

* Inverse stretch reflex:  

> Is a relaxation of skeletal muscle with intact nerve supply in response to over tension.
* Function: Protection against over tension that can cause  tearing of muscle fibers.
*Sense organ is Golgi tendon organ.
* Sensory (afferent) Type 1b fibers,

Supra spinal control of γ motor neuron:
> Gamma (γ) motor neuron discharge to the muscle spindles is subjected to facilitatory & inhibitory impulses from the motor brain areas.

* Facilitatory areas include:
>Primary motor cortex (Area 4).
>Pontine reticular formation.
>Vestibular nuclei.
>Deep cerebellar nuclei.

* Inhibitory areas include:
>Area 4s (small suppressor strip) just in front of area 4. with stronger effect than area 4.
>Medullary reticular formation. 
>Basal ganglia.
>Some areas in cerebellar cortex.


> Rapid, rhythmic repeated contractions in response to sudden sustained stretch,  
Eg, Ankle clonus & knee clonus.
Results from increased sensitivity of 
muscle spindle (increased γ motor neuron 
discharge) & of Golgi tendon organ →Rapid
alternation between stretch & inverse 
stretch reflexes.
> It is a sign of UMNL.

Superficial reflexes:
> Clinically used  because they help to localize the lesions, they  Include:

1.Superficial abdominal reflexes: 
> Contraction of abdominal muscles when
their overlying skin is stroked by a blunt
object. Centres T7- T12.

2. Plantar reflex: 
>Plantar flexion of the toes in response to
lateral scratch of the soles by a blunt object.
Centres L5 &  S1.
* NOTE: In the first year of infancy & in the UMNL, the response of this reflex is a dorsiflexion of the big toes & fanning of other toes (Positive Babiniski`s sign)
3. Cremasteric reflex: 
> Elevation of the testicles by contraction of cremasteric muscle in response to stoke of the inner & upper aspect f the thigh.
Centres L1 &  L2.

4. Withdrawal (flexor) reflex:
> Is a contraction of a flexor limb muscle in response to a painful stimulus.
>A polysynaptic, superficial spinal reflex.
>Receptors: Pain receptors (Nociceptors) .
>Function: Withdrawal of a limb from a painful stimulus.
>The flexor response is accompanied by relaxation of the antagonist muscle (Extensor).

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