CNS - Topic 2, 3, 4 - Spinal reflex arcs Flashcards
- What are the 3 types of sensibility?
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
- Spinal reflex
a/ Definition of spinal reflex
- Spinal reflex is an automatic, involuntary and rapid response to a particular stimulus
- The basic unit of reflex is the reflex arc
- Note: the reflex activity is shown in 3 types of reflex arcs
- Stretch reflex arc (proprioceptive)
- Withdrawal reflex arc
- Autonomic reflex arc
- Spinal reflex
b/ Components of a reflex arc
- Receptor
- Afferent/ sensory neuron
- Integration center
- Efferent neuron
- Effector organ
- 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)
specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release
- 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)
contracts/ relaxes in response to the efferent stimuli
- 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)
specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release
- 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)
specific stimuli into receptor potential that upon reaching its threshold -> triggers AP/ transmitter release
- 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)
transmit AP into the CNS
- 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)
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
- 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)
motoneuron that innervates the effector
- Spinal reflex
c/ What are the 5 Types or receptors in spinal reflexes
1/ Exteroreceptors
2/ Interoreceptors
3/ Proprioreceptors
4/ Muscle spindle
5/ Tendon spindle
- Spinal reflex
c1/ 5 examples of exteroreceptors
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)
- Spinal reflex
c2/ 5 examples of interoreceptors
1/ Golgi-Mazzoni-corpuscule (tendons, joints)
2/ Vasoceptors
3/ Internal nociceptors
4/ Chemoreceptors (carotid body)
5/ Stretch receptors (carotid sinus)
- Spinal reflex - Types or receptors in spinal reflexes
c3/ Characteristics of Golgi tendon organ
encapsulated heavily branched sensory nerve ending running among collagen fibers in tendon
–> protects from overstretching
- Spinal reflex - Types or receptors in spinal reflexes
c4/ Characteristics of muscle spindle
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)
3/ PROPRIOCEPTIVE REFLEX
a/ Definition of proprioceptive reflex?
Proprioceptive reflexes are reflexes that protect the muscles from the passive forces (elongate and stretch) to help body maintains its balance
3/ PROPRIOCEPTIVE REFLEX
b/ 3 examples of proprioceptive reflex?
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
3/ PROPRIOCEPTIVE REFLEX
c/ What is the aim of proprioceptive reflex? (give an example)
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
3/ PROPRIOCEPTIVE REFLEX
d/ What are the components of proprioceptive reflex?
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)
3/ PROPRIOCEPTIVE REFLEX
e/ What is the Mechanism of proprioceptive reflexes?
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)
3/ PROPRIOCEPTIVE REFLEX
f/ What are the 2 indirect mechanisms of proprioceptive reflex?
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)
3/ PROPRIOCEPTIVE REFLEX
f1/ Mechanism and characteristics of Recurrent inhibition by Renshaw-cells?
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
3/ PROPRIOCEPTIVE REFLEX
f2/ Mechanism and characteristics of Gamma-loop?
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
3/ PROPRIOCEPTIVE REFLEX
g1/ What is the Golgi tendon reflex?
(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
3/ PROPRIOCEPTIVE REFLEX
g2/ What are the components of Golgi tendon reflex?
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)
- Nociceptive (withdrawal) reflex
a/ Characteristics of Nociceptive (withdrawal) reflex
Withdrawal reflex (polysynaptic reflex, nociceptive reflex)
- Nociceptive (withdrawal) reflex
b/ What are the components of Nociceptive (withdrawal) reflex?
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
- Nociceptive (withdrawal) reflex
c/ What is the mechanism of Nociceptive (withdrawal) reflex?
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).
- Nociceptive (withdrawal) reflex
d/ Examples of Nociceptive (withdrawal) reflex
cremaster-reflex, cough-reflex, sneeze-reflex, corneal-reflex
- Nociceptive (withdrawal) reflex
e/ What is The relationship between crossed extensor-flexor reflexes and Nociceptive (withdrawal) reflexes?
Crossed extensor-flexor reflex is an additional component to nociceptive reflex.
When the nociceptive reflex happen, flexor muscles ipsilaterally+ Extensor muscles contralaterally
- AUTONOMIC RELFEX
a/ Characteristics of autonomic reflex
It is also known as a vegetative reflex arc
- AUTONOMIC RELFEX
b/ What are the components of autonomic reflex
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
- Give 3 Examples of „Mixed” reflexes?
Viscerocutan: From the organs to the skin (sudomotor, vasomotor function)
Visceromotor: from the organs to a skelatal muscle
Cutivisceral: somatosensory input to visceromotor efferent
