This document discusses different types of spinal reflexes and their components. It describes autonomic reflexes which control organs and glands, and somatic reflexes which control muscles. Specific examples of reflex tests are provided, including the patellar reflex test for somatic reflexes and pupillary light reflex test for autonomic reflexes. Sensory receptors like muscle spindles, Golgi tendon organs, and their roles in reflexes are also explained.

1. Spinal Reflexes
Dr Dr Oyaro

2. Learning objective
• Distinguish between the types of spinal
reflexes

3. Nervous System

4. Reflexes
• Reflexes are rapid, predictable involuntary
responses to stimuli.
• The pathway along which the electrical
signals travel is called a reflex arc
• Reflex arc: a pathway in which signals
travel over many synapses on their way
back to the muscle .

5. There are five parts to a reflex arc:
1. The receptor detects a stimulus.
2. The sensory (afferent) neuron sends an electrical signal to the CNS.
3. The integration center consists of one or more synapses in the CNS, and
processes the information.
4. The motor (efferent) neuron sends an electrical signal from the CNS to the
effector.
5. The effector, which may be muscle tissue or a gland, responds
appropriately.

6. Reflex Arc
There are two types of reflex arc:
1. autonomic reflex arc (affecting inner
organs).
2. somatic reflex arc (affecting muscles).

7. Autonomic Reflexes:
• Autonomic reflexes control and regulate smooth
muscle cells, cardiac muscle cells and glands.
In general these reflexes contain the same
basic components as somatic reflexes but a
key difference is that autonomic reflexes
have the ability to both stimulate or inhibit
the smooth muscle/gland.
• Examples of Autonomic Reflexes:
1. Pupillary-pupil constricts on both sides when
shine a light into the eye
2. Accomodation-focus on distant object then near
object-pupil constricts on both sides.

8. Somatic Reflexes
• Skeletal muscle reflex mediated by the
brainstem and spinal cord resulting in an
involuntary contraction of a muscle.
• Are involved in the reflex control of skeletal
muscles and as such there are many different
types of somatic reflexes including scratching
reflexes, withdrawal reflexes and stretch
reflexes and tendon reflexes.
• Examples of Somatic reflexes :
1. Corneal- blink reflex (respond to stimulus)
2. Pateller: knee jerk (tap patellar ligament-
stretches quads)

9. Purpose of the Reflexes tests:
• Reflex testing is an important diagnostic
tool for assessing the general health of the
nervous system.
• Distorted, exaggerated or absent reflexes
may indicate pathology. If the spinal cord
is damaged, reflex tests can help pinpoint
the level of damage

10. Example 1: Somatic Reflex :The Patellar
Reflex
• The patellar (or knee-jerk) reflex is called a
stretch reflex because it is initiated by tapping a
tendon, which stretches the muscle, stimulating
the muscle spindle (the proprioceptor inside the
muscle) and causing reflex contraction of the
quadriceps muscles. Stretch reflexes generally
act to maintain posture, balance and locomotion.

12. Purpose of testing:
• After the tap of a hammer, the leg is normally extended
once and comes to rest.
• The absence or decrease of this reflex is problematic,
and known as Westphal's sign. This reflex may be
diminished or absent in lower motor neuron lesions and
during sleep.
• On the other hand, multiple oscillation of the leg
(pendular reflex) following the tap may be a sign of a
cerebellar disease. Exaggerated (brisk) deep tendon
reflexes such as this can be found in upper motor neuron
lesions, hyperthyroidism, anxiety or nervousness. The
test itself assesses the nervous tissue between and
including the L2 and L4 segments of the spinal cord.

13. Example 2: Autonomic Reflexes
:Pupillary Reflexes test
• The pupillary light reflex (PLR) is a reflex that controls
the diameter of the pupil, in response to the intensity of
light that falls on the retinal ganglion cells of the eye,
thereby assisting in adaptation to various levels of
lightness/darkness.
• A greater intensity of light causes the pupil to constrict
(miosis) (allowing less light in), whereas a lower intensity
of light causes the pupil to dilate (mydriasis, expansion)
(allowing more light in). Thus, the pupillary light reflex
regulates the intensity of light entering the eye
• We will test the pupillary light reflex and the consensual
reflex. In both, the retina of the eye is the receptor, the
optic nerve holds the afferent fibers, the oculomotor
nerve contains the efferent fibers, and the smooth
muscle of the iris is the effector organ.

14. Procedure for activity 2:
• 1. For the pupillary light reflex, have the subject in a
relatively dim area (turn off lights in lab if helpful). The
subject should shield the right eye. Shine a penlight into
the subject's left eye. What happens to the pupil?
• 2. Also observe the right pupil. Does the same change
(called a consensual response) occur?
• When a reflex is observed on the same side of the body
that was stimulated, that is called an ipsilateral
response. When a reflex occurs on the opposite side of
the body that was stimulated, that is a contralateral
response.

15. Clinical signification
• Under normal conditions, the
pupils of both eyes respond
identically to a light stimulus,
regardless of which eye is
being stimulated. Light
entering one eye produces a
constriction of the pupil of that
eye, the direct response, as
well as a constriction of the
pupil of the un stimulated eye,
the consensual response.
Comparing these two
responses in both eyes is
helpful in locating a lesion

16. B ) General Sensation and Sensory
Receptor Physiology:

17. Example 3: Cutaneous Senses :Two-
point Discrimination Test
1. Using calipers, test the ability of the subject to differentiate two
distinct sensations when the skin is touched simultaneously at two
points
2. Start with the points right together, then gradually increase the
distance apart. Record the distance at which the subject first
reports feeling two distinct points of contact with the skin (the two-
point threshold).
3. If the two stimulated points belong to the same receptive field, the
sensation is felt as one stimulus. If the points belong to separate
receptive fields, the subject feels two stimuli. The distance
between the points, at which the subject loses the ability to feel
two points is the diameter of the receptive field. The two point
discrimination threshold is less than 5 mm at the finger tips and is
about 40 mm at the thigh.

18. Example 4: Adaptation of Touch
Receptors
• The number of signals sent by the sensory
receptors may change with the intensity of the
stimulus and the length of time the stimulus is
applied.
• When the awareness of a stimulus decreases, it
is called adaptation.
• Some receptors adapt rapidly, such as certain
types of touch receptors, and others, such a pain
receptors, may not adapt at all.

19. The Golgi tendon reflex
• The Golgi tendon reflex is a normal component of the
reflex arc of the peripheral nervous system. The tendon
reflex operates as a feedback mechanism to control
muscle tension by causing muscle relaxation before
muscle force becomes so great that tendons might be
torn
• Although the tendon reflex is less sensitive than the
stretch reflex, it can override the stretch reflex when
tension is great, making you drop a very heavy weight,
for example. Like the stretch reflex, the tendon reflex is
ipsilateral.

20. • The sensory receptors for this reflex are
called Golgi tendon receptors, and lie
within a tendon near its junction with a
muscle.
• In contrast to muscle spindles, which are
sensitive to changes in muscle length,
tendon receptors detect and respond to
changes in muscle tension that are caused
by a passive stretch or muscular
contraction.

21. Withdrawal Reflex (WR)
• WR is a spinal reflex intended to protect the
body from damaging stimuli. It is polysynaptic,
and causes the stimulation of sensory,
association, and motor neurons.
• When a person touches a hot object and
withdraws his hand from it without thinking about
it, the heat stimulates temperature and danger
receptors in the skin, triggering a sensory
impulse that travels to the central nervous
system

22. • The sensory neuron then synapses with
interneurons that connect to motor neurons.
Some of these send motor impulses to the
flexors to allow withdrawal
• Some motor neurons send inhibitory impulses to
the extensors so flexion is not inhibited—this is
referred to as reciprocal innervation. Although
this is a reflex, there are two interesting aspects
to it:
1.The body can be trained to override that reflex.
2.An unconscious body (or even drunk or drugged
bodies) will not exhibit the reflex.

23. • The tendon organ is a stretch receptor that
signals the amount of force on the muscle
and protects the muscle from excessively
heavy loads by causing the muscle to
relax and drop the load.

24. The crossed extensor reflex
• The crossed extensor reflex is contralateral, meaning the
reflex occurs on the opposite side of the body from the
stimulus.
• To produce this reflex, branches of the afferent nerve
fibers cross from the stimulated side of the body to the
contralateral side of the spinal cord.
• There, they synapse with interneurons, which in turn,
excite or inhibit alpha motor neurons to the muscles of
the contralateral limb (e.g when one foot steps on a nail,
the crossed extensor reflex shifts the body’s weight onto
the other foot, protecting and withdrawing the foot on the
nail)

25. Muscle spindles
• When a skeletal muscle with an intact nerve
supply is stretched, it contracts. This response is
called the stretch reflex or myotatic reflex
• The stimulus that initiates this reflex is stretch of
the muscle, and the response is contraction of
the muscle being stretched
• The sense organ is a small encapsulated
spindlelike or fusiform-shaped structure called
the muscle spindle, located within the fleshy
part of the muscle.

26. • The neurotransmitter at the central synapse is
glutamate. The stretch reflex - monosynaptic reflex of
the knee jerk reflex
• Each muscle spindle has three essential elements:
(1) a group of specialized intrafusal muscle fibers with
contractile polar ends and a noncontractile center,
(2) large diameter myelinated afferent nerves (types Ia and
II) originating in the central portion of the intrafusal fibers,
and
(3) small diameter myelinated efferent nerves supplying the
polar contractile regions of the intrafusal fibers

27.  There are two types of intrafusal fibers in
mammalian muscle spindles.
1.The first type contains many nuclei in a
dilated central area and is called
a nuclear bag fiber. Two subtypes of
nuclear bag fibers, dynamic and static.
2.The second intrafusal fiber type,
the nuclear chain fiber, is thinner and
shorter and lacks a definite bag. Typically,
each muscle spindle contains two or three
nuclear bag fibers and about five nuclear
chain fibers

29. FUNCTION OF MUSCLE SPINDLES
• When the whole muscle is stretched, the
muscle spindle is also stretched and its
sensory endings are activated at a
frequency proportional to the degree of
stretching (“loading the spindle”).
• Spindle afferents stop firing when the
muscle contracts (“unloading the spindle”)

30. • Stimulation of γ-motor neurons cause the
contractile ends of the intrafusal fibers to
shorten. This stretches the nuclear bag region,
initiating impulses in sensory fibers
• The muscle spindle and its reflex connections
constitute a feedback device that operates to
maintain muscle length
• Dynamic and static responses of muscle spindle
afferents influence physiologic tremor