CNS - Topic 2, 3, 4 - Spinal reflex arcs

Question 1

1. What are the 3 types of sensibility?

Answer 1

1/ Protopathic sensibility
- Crude touch, temperature, pressure, heat pain
- Crucial for SURVIVAL

2/ Proprioceptive sensibility
- Detection of movement and position of joints/ muscles (body in space)

3/ Epicritic sensibility
- Fine touch, vibration, two-point discrimination

Question 2

2. Spinal reflex
   a/ Definition of spinal reflex

Answer 2

1. Spinal reflex is an automatic, involuntary and rapid response to a particular stimulus
2. The basic unit of reflex is the reflex arc
3. Note: the reflex activity is shown in 3 types of reflex arcs
   - Stretch reflex arc (proprioceptive)
   - Withdrawal reflex arc
   - Autonomic reflex arc

Question 3

2. Spinal reflex
   b/ Components of a reflex arc

Answer 3

1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ

Question 4

2. Spinal reflex
   b1/ Characteristics of receptor in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 4

specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release

Question 5

2. Spinal reflex
   b5/ Characteristics of Effector organ in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 5

contracts/ relaxes in response to the efferent stimuli

Question 6

2. Spinal reflex
   b1/ Characteristics of receptor in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 6

specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release

Question 7

2. Spinal reflex
   b1/ Characteristics of receptor in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 7

specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release

Question 8

2. Spinal reflex
   b2/ Characteristics of Afferent/ sensory neuron in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 8

transmit AP into the CNS

Question 9

2. Spinal reflex
   b3/ Characteristics of Integration center in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 9

Location: cranial (brain) or spinal (SC)
- If the sensory afferent synapses directly on the motoneuron, the reflex is monosynaptic
- If the sensory neuron makes synaptic contact with an interneuron that activates other neurons or motoneurons, the reflex is polysynaptic

Question 10

2. Spinal reflex
   b4/ Characteristics of Efferent neuron in a spinal reflex arc

(1. Receptor
2. Afferent/ sensory neuron
3. Integration center
4. Efferent neuron
5. Effector organ)

Answer 10

motoneuron that innervates the effector

Question 11

2. Spinal reflex
   c/ What are the 5 Types or receptors in spinal reflexes

Answer 11

1/ Exteroreceptors
2/ Interoreceptors
3/ Proprioreceptors
4/ Muscle spindle
5/ Tendon spindle

Question 12

2. Spinal reflex
   c1/ 5 examples of exteroreceptors

Answer 12

1/ Meissner corpuscles
- Mainly in hands/finger = touch
2/ Ruffini endings (pressure)
3/ Free nerve endings (pain, heat, cold)
4/ Merkel disks (touch)
5/ Vater-Paccini’s lamellar body (pressure)

Question 13

2. Spinal reflex
   c2/ 5 examples of interoreceptors

Answer 13

1/ Golgi-Mazzoni-corpuscule (tendons, joints)
2/ Vasoceptors
3/ Internal nociceptors
4/ Chemoreceptors (carotid body)
5/ Stretch receptors (carotid sinus)

Question 14

2. Spinal reflex - Types or receptors in spinal reflexes
   c3/ Characteristics of Golgi tendon organ

Answer 14

encapsulated heavily branched sensory nerve ending running among collagen fibers in tendon
–> protects from overstretching

Question 15

2. Spinal reflex - Types or receptors in spinal reflexes
   c4/ Characteristics of muscle spindle

Answer 15

Muscle spindle: modified intrafusal muscle fibers wrapped around by sensory nerve endings and innervated by gamma-motoneurons. CT capsule separates them from the extrafusal muscle fibers
- Extrafusal muscle fiber – innervated by alpha- motoneurons (A⍺)
- Intrafusal muscle fiber – innervated by gamma- motoneurons (Aβ)

Question 16

3/ PROPRIOCEPTIVE REFLEX
a/ Definition of proprioceptive reflex?

Answer 16

Proprioceptive reflexes are reflexes that protect the muscles from the passive forces (elongate and stretch) to help body maintains its balance

Question 17

3/ PROPRIOCEPTIVE REFLEX
b/ 3 examples of proprioceptive reflex?

Answer 17

E.g, patella reflex – a sharp tap on the pattela tendon results in sudden kicking movement of the leg

E.g, brachioradial reflex, masseter-reflex

Question 18

3/ PROPRIOCEPTIVE REFLEX
c/ What is the aim of proprioceptive reflex? (give an example)

Answer 18

1/ To keep the length of a given muscle standard
2/ Any attempt to elongate muscle will activate the reflex arch to regain its original length
3/ E.g, the continuous contraction against the spontaneous flexion of hip/ knee/ ankle joint due to the weight of the body

Question 19

3/ PROPRIOCEPTIVE REFLEX
d/ What are the components of proprioceptive reflex?

Answer 19

1/ Receptor: annulospiral terminal on the muscle spindles
2/ Afferent nerve: Aβ (Ia), pseudounipolar
3/ Central process: 1 synapse on the Iα motor neuron
4/ Efferent nerve: Aα motoneuron in the ventral horn (lamina IX)
5/ Effector: motor end plate → extrafusal muscle fiber (located in the same muscle)

Question 20

3/ PROPRIOCEPTIVE REFLEX
e/ What is the Mechanism of proprioceptive reflexes?

Answer 20

Stretch of muscles activates (anulo-spiral) sensory nerve endings in muscle spindle
-> sensory neurons
-> alpha-motoneurons activated
-> transmission back to the same muscle
-> contraction in the same muscle)

Question 21

3/ PROPRIOCEPTIVE REFLEX
f/ What are the 2 indirect mechanisms of proprioceptive reflex?

Answer 21

1/ Recurrent inhibition by Renshaw-cells
2/ γ-loop (the γ-motor neuron innervates the muscle spindle. By changing the sensitivity of the intrafusal fibers, γ-motor neurons can change the length of the muscle)

Question 22

3/ PROPRIOCEPTIVE REFLEX
f1/ Mechanism and characteristics of Recurrent inhibition by Renshaw-cells?

Answer 22

1/ Renshaw cells are inhibitory cells of ventral horn
2/ They are innervated by the collaterals of active α-motor neurons
3/ Depending on the situation, gamma-motoneurons can also be inhibited by Renshaw cells.
4/ The major function of the Renshaw cell is modulation of motor output and protection from over-excitation
5/ When the activity of a motor neuron decreases, the neighbouring cells are losing their previous inhibition

Question 23

3/ PROPRIOCEPTIVE REFLEX
f2/ Mechanism and characteristics of Gamma-loop?

Answer 23

1/ Descending pathways can stimulate gamma-motoneurons which innervate intrafusal muscle fibers.
2/ Contracting intrafusal fibers shorten the muscle spindle itself, which has a similar effect to that when the extrafusal fibers around the spindle are passively stretched.
4/ This stretch (-like) signal evokes the spinal proprioceptive reflex activating alpha-motoneurons, and finally contracting extrafusal fibers

Question 24

3/ PROPRIOCEPTIVE REFLEX
g1/ What is the Golgi tendon reflex?

Answer 24

(related to proprioceptive reflex but not proprioceptive reflex)

Definition: a polysynaptic (disynaptic) reflex that decreases the muscle tone to protect the muscle from tensing excessively; it inhibits α- and γ- motor neurons

Question 25

3/ PROPRIOCEPTIVE REFLEX g2/ What are the components of Golgi tendon reflex?

Answer 25

Receptor: golgi tendon organ (tension during muscle contraction) Sensory neurons: Ib thick myelinated axons Interneurons: Ib sensory afferents terminate on Ib inhibitory interneurons Efferent: alpha-motoneuron axon Effector: extrafusal fibers of skeletal muscle (relax)

Question 26

4. Nociceptive (withdrawal) reflex a/ Characteristics of Nociceptive (withdrawal) reflex

Answer 26

Withdrawal reflex (polysynaptic reflex, nociceptive reflex)

Question 27

4. Nociceptive (withdrawal) reflex b/ What are the components of Nociceptive (withdrawal) reflex?

Answer 27

1/ Receptor: skin receptor, probably nociceptive 2/ Afferent nerve: Aδ or C-fibers, pseudounipolar neuron 3/ Central process: one or more interneurons; funicular neurons over more segments 4/ Efferent nerve: Aα motor neuron, minimum the third 5/ Effector: motor end plate → extrafusal muscle fiber

Question 28

4. Nociceptive (withdrawal) reflex c/ What is the mechanism of Nociceptive (withdrawal) reflex?

Answer 28

Tissue damaging or stimuli threatening the integrity of the skin evokes a quick protective reaction = withdrawal of body / part of it from the dangerous stimuli. => Small stimuli only activates a few muscles, while a strong one may activate and withdraw the whole extremity. => Withdrawal of one extremity must be balanced by an increased extensor activity on the other side of the body (ipsilateral flexor and contralateral extensor reflex arc).

Question 29

4. Nociceptive (withdrawal) reflex d/ Examples of Nociceptive (withdrawal) reflex

Answer 29

cremaster-reflex, cough-reflex, sneeze-reflex, corneal-reflex

Question 30

4. Nociceptive (withdrawal) reflex e/ What is The relationship between crossed extensor-flexor reflexes and Nociceptive (withdrawal) reflexes?

Answer 30

Crossed extensor-flexor reflex is an additional component to nociceptive reflex. When the nociceptive reflex happen, flexor muscles ipsilaterally+ Extensor muscles contralaterally

Question 31

5. AUTONOMIC RELFEX a/ Characteristics of autonomic reflex

Answer 31

It is also known as a vegetative reflex arc

Question 32

5. AUTONOMIC RELFEX b/ What are the components of autonomic reflex

Answer 32

1/ Receptor: enteroceptor in the internal organ 2/ Afferent nerve: Aβ (Ia), or Aδ or C –fibers, pseudounipolar nerves 3/ Central process: at least one or several interneurons in the dorsal horn and intermediate zone 4/ Efferent nerve: B-fiber – preganglionic motor neuron → prevertebral sympathetic or intramural parasympathetic ganglion cell: C-fiber 5/ Effector: visceral organ: smooth muscle

Question 33

6. Give 3 Examples of „Mixed” reflexes?

Answer 33

Viscerocutan: From the organs to the skin (sudomotor, vasomotor function) Visceromotor: from the organs to a skelatal muscle Cutivisceral: somatosensory input to visceromotor efferent