#FUND
T8. Polysynaptic reflexes
Prepared by :
Prof. Dr. Marwa Nagy Emam
Professor of physiology
ILOs
By the end of this lecture, students should
be able to:
1. Differentiate
between
monosynaptic
and
polysynaptic reflexes
2. Classify types of spinal polysynaptic reflex
3. Explain physiological functions and clinical
importance of polysynaptic spinal reflexes
Classification of spinal reflexes
I.
Acc. to number of synapses:
a) Monosynaptic reflexes ( Stretch reflex is the only monosynaptic reflex)
-1
>
b) Polysynaptic reflexes.
II. According to site of receptors:
a) Superficial reflexes: receptors are in the skin as planter reflex, abdominal reflex,
cremasteric reflex
b) Deep reflexes: stretch reflex
- muscles or
>
tendons
c) Visceral reflexes: micturition and defecation reflex.
Spinal Polysynaptic reflexes
• Polysynaptic reflex occurs
Between offerent and efferent
↑
>
-
when there are more than
one synapses between the
-
Stimulus - turn into AP-
Carry
on
offerent
-
S
afferents and motor neurons.
• One or more interneurons
connect the afferent to the
motor
(efferent)
(alpha AHCs)
neurons
&
Examples of spinal polysynaptic reflexes
Inverse stretch reflex
banother
Golgi
names :
Lengthening
,
❑Definition:
.
-S0 S
Reflex relaxation (lengthening) of the muscle in response to excessive stretch of that muscle.
·mig , d
❑Pathway: (it is Polysynaptic reflex)
Reflex relaxation
↑
o Stimulus: increased tension in the muscle caused by:
·
o Overstretch the muscle
o Severe strong contraction (isometric contraction) as during lifting a heavy weight
o Receptors: Golgi tendon organs (Tension receptors)
o Site: tendons of skeletal ms in series with ms fibers.↳
o Afferent:
↑
o A alpha (Ib fibers) · d i
&is Ne
o Afferent stimulates inhibitory interneuron and excitatory interneuron
Agonist
&.
o Inhibitory interneuron: inhibit the α -MNs supplying the same muscle -Min 40Apo
o Excitatory interneurons: excite the αMNs supplying the antagonistic muscle &
o Response:
>
o Relaxation of the same muscle o Contraction of antagonistic muscle
·iJ
jjs
&
..
·,j-
An
It have I action on Interneuron : Inhibitors
2
-
Stimulant
1
-
H
%
[
-
-
Significance of inverse stretch reflex
I. Physiological Significance:
Inverse Stretch Reflex is a protective reaction which prevents tearing of
the muscle or avulsion of its tendon from its bony attachment when muscle
is overstretched. ↳ 6%
Significance of inverse stretch reflex
> testing muscle toune
II. Clinical Significance: Clasp knife effect Demonstrated clinically by passive extension of a spastic upper limb (e. g. in
upper motor neuron lesions)
·
-
. • As the limb is passively extended, an initial resistance occurs due to contraction
of this muscle as a result of activation of stretch reflex.
• With persistent passive extension , at a certain point, Golgi tendon organ is
stimulated causing activation of inverse stretch reflex.
%
• Relaxation of the muscle and sudden disappearance of the initial resistance and the
limb extended easily, as occurs due to closing of a clasp knife
• Clasp knife effect is alteration between Stretch reflex-inverse stretch
reflex
si
-
·
Jigs
:
· sjjb g as
J
Significance of inverse stretch reflex
i Toune 1
081st
II. Clinical Significance: Clonus
&
❑Def: This is alternating rhythmic contractions and relaxations of a muscle in response to
sudden maintained stretch. Si
❑Mechanism:
• Clonus is the result of a stretch reflex-inverse stretch reflex sequence.
• Sudden stretch of the muscle results in its contraction through the stretch reflex.
• This is followed by relaxation due initiation of inverse stretch reflex due to stimulation
of Golgi tendons organs due to maintained stretch.
❑Cause: it occurs in upper motor neuron lesion ·Site
❑Types:
1. Knee (patellar) clonus
2. Ankle clonus.
.
j
&
8 Is
jiji,+ :
--
di, i.-
Tremor 11,
i
Knee clonus
Ankle clonus
2. Planter reflex
❑Definition:
-
Scratching the lateral (outer) margin of
the sole by a blunt object (key) starting
from the heal towards the toes
causing planter flexion of all toes. & N
Big
--
A
❑Center: sacral segments 1 and 2 (S1,S2)
mainly S1 segment.
❑Normal response: planter flexion of all
toes.
-i
❑N.B:
❑Normal response of this reflex (planter
flexion) needs intact descending tracts from
y
the cerebral cortex (pyramidal and
jio
p
extrapyramidal tracts).
I
n
>
-
&
%
--
-2 56i
&
(Abnormal response)
Babinski Sign (‫ٮﺔ‬,‫ٮﻌ‬,‫ٮﺮ ﻃ&ٮ‬,‫ﻋ‬+ ‫ٮ&ﺤﺎ&ٮﺔ‬$‫)اﺳ‬:
• Dorsiflexion (‫ڡﻊ‬#‫ٮﺮ )ر‬0‫ڡﺪم اﻟﻜ(ٮ‬,‫ﻹﺻ(ٮﻊ اﻟ‬
• ‫ﺣرى‬.‫ٮﻊ اﻷ‬$‫ٮﺎُﻋﺪ اﻷﺻﺎ‬$"‫( وٮ‬Fanning)
:
--
‫ى اﻟﺮﺿﻊ‬
6 ‫ڡ‬. ‫ى‬
6 ‫ٮع‬1‫ٮ‬$‫ ﻟﻜﻦ ﻃ‬،‫ٮﻦ‬1‫ٮﺎﻟ;ﻌ‬$‫ى اﻟ‬
6 ‫ڡ‬. ‫ى‬
6 ‫ٮع‬1‫ٮ‬$‫ٮﺮ ﻃ‬1‫ﻋ‬. ‫ﻫﺬا‬
ً.‫ڡري(ٮا‬,,‫ٮﺺ ٮ‬#‫ٮﺔ و‬#‫ﺣﱴ ﻋﻤﺮ ﺳ‬
Positive Babinski’s sign
❑Abnormal response: +ve Babinski's
&
Another name
sign (Extensor planter response).
❑In this case, there is dorsiflexion of the
big toe with or without fanning
(spreading apart) of the other toes.
❑Causes:
1. Physiological. >
-
2. Pathological.
: *
&
Positive Babinski’s sign
Physiological Causes:
Pathological Causes:
1. Newly born infants: during the first few months
1. UMNL ( cutting of pyramidal
tracts)
of life due to non-functioning pyramidal tracts
(incomplete myelination of pyramidal tracts)
2. Adults:
a. During sleep
b. During anesthesia.
• 1. Enumerate 2 physiological causes of extensor planter response
• 2. Enumerate 2 pathological causes of positive Babinski's sign.
2. During Coma (due to depressed
cortical function)
3. Flexor withdrawal reflex
❑Definition:
-
- They are reflexes that move the affected portion of the body away from a source
>
of painful stimulation. -
"
❑Stimulus:
- a painful stimulus is applied to the skin of one limb
❑Response:
- Contraction of the flexor muscles of that limb
- Withdrawal of the limb away form painful stimulus
- Relaxation of the extensor muscles of the stimulated limb.
as in
❑It is a protective reflex (inhibits all other reflexes occurring at the same time).
3. Flexor withdrawal reflex
- The pathways for eliciting the flexor reflex
do not pass directly to the anterior motor
neurons but instead pass first into the spinal
cord interneuron pool of neurons and then
to the motor neurons.
- The shortest possible circuit is a three- or
four-neuron pathway.
-i
&
]
Direct to
4. Crossed extensor reflex
j
·: - (2) -
Flexor Withdrawal I &
:Jes.
❑Definition:
S is is
·ji die:g ja
❑Application of noxious
stimulus to one lower limb
causes flexor withdrawal
reflex of the same limb
and extension of the
opposite limb to support
the body.
antagonise
>
-
Action of
muscles
:‫ٮﻂ‬,‫ٮﺎل &ٮﺴ‬1‫ﻣ‬
:‫ٮﻦ‬0‫ٮﻤ‬0‫دﻋﺴﺖ ﻋﲆ ﻣﺴﻤﺎر (ٮﺮ(ﺣﻠﻚ اﻟ‬
(‫ٮﺔ‬0‫ٮ‬#‫ٮ‬P‫ڡ(ٮﺾ اﻟﻌﻀﻼت اﻟﻤ‬,‫ٮ‬#,‫ٮﺴﺮﻋﺔ )ٮ‬$ ‫ٮﺴﺤﺐ‬."‫ٮﻦ ٮ‬0‫ٮﻤ‬0‫• ر(ﺣﻠﻚ اﻟ‬
‫ڡ(ٮﺾ اﻟﻌﻀﻼت اﻟ(ٮﺎﺳﻄﺔ( ﻋﺸﺎن ﻣﺎ ٮ"ﻄيﺢ‬,‫ٮ‬#,‫ڡﺴﻬﺎ )ٮ‬.‫ٮ‬. ‫ٮﺖ‬$‫ٮﺴﺎر ٮ"ث‬0‫• ر(ﺣﻠﻚ اﻟ‬
5. Cremasteric reflex
❑Definition:
-j
❑Scratching of the skin of
the upper medial aspect of
the thigh results in reflex
contraction of cremasteric
*
muscle and elevation of
the testes.
❑Center: L1,2
-ji, i
ji
6. Abdominal reflex
❑Definition:
❑Scratching of the skin of four
quadrants of the abdomen
results in contraction of the
underlying
muscles
and
deviation of the umbilicus to the
direction of the stimulus.
❑Center: T7-12
THANK
YOU.