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MSS > MSS32 Somatic And Autonomic Reflexes > Flashcards

MSS32 Somatic And Autonomic Reflexes Flashcards

1
Q

Reflex

A

Reaction to a specific stimulus

  • Rapid
  • Short neural pathway
  • Automatic / Involuntary
  • Predictable
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2
Q

Brain stem

A
  1. Midbrain
  2. Pons
  3. Medulla oblongata

–> continuous with spinal cord

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3
Q

Proprioceptors

A

sense of self-movement and body position

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4
Q

Reflex arc

A
  1. Receptor
    - detects stimulus
  2. Sensory (afferent) neuron
    - transmits sensory (afferent) impulse ***from receptor to CNS
  3. Integration centre
    - CNS interprets sensory information and coordinates the events in response to stimuli
  4. Motor (efferent) neuron
    - transmit motor (efferent) impulses ***from CNS to effector
  5. Effector
    - muscle / gland responds to instruction of motor neuron
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5
Q

Monosynpatic reflex vs Polysynaptic reflex

A

Monosynaptic: NO interneuron

Polysynaptic (>= 2 synapses): have interneuron

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6
Q

***Functions of reflexes

A
  1. Maintenance of balance and posture
    - Stretch reflex
    - Flexor and Crossed-extensor reflex
    - Vestibulo-spinal reflex
  2. Protection
    - Golgi tendon reflex
    - Withdrawal reflex
  3. Digestive and renal functions
    - Defecation reflex
    - Micturition reflex
  4. Automatic actions
    - Pupillary light reflex
    - Reflexes in deglutition (swallowing)
    - Cough reflex
    - Sneeze reflex
  5. Homeostasis
    - Chemoreceptor reflex
    - Baroreceptor reflex
  6. Coordination of complex movements
    - Vestibulo-ocular reflex
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7
Q

Classification of reflexes

A
  1. Innate (inborn) vs Acquired (learning-dependent)
  2. Spinal (process in spinal cord) vs Cranial (process in brain)
  3. Somatic (control skeletal muscles) vs Autonomic (control smooth / muscles / glands)
  4. Monosynaptic vs Polysynaptic
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8
Q

***Skeletal muscle

A

Extrafusal muscle:

  • Contractile
  • innervated by α motor neuron (efferent)

Intrafusal muscle (Muscle spindle):

  • Sensory + Contractile
  • Sensory (non-contractile, central): receptive surface, wrapped with type 1a (primary), 2 (secondary) sensory nerve fibres
  • Contractile region (peripheral): innervated by γ motor neuron (efferent)
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9
Q

***Muscle spindle

A

Stretching extrafusal muscle

  • -> Activates intrafusal muscle spindle (拉長左)
  • -> ↑ action potential firing rate in type 1a sensory fibres

Contracting muscle

  • -> Reduce tension muscle spindle (縮短左)
  • -> ↓ action potential firing rate in type 1a sensory fibres
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10
Q

Type 1a fibre vs Type 2 fibre

A

Type 1a:

  • Annulospiral ending
  • Detect muscle length during ***movement

Type 2:

  • Flower spray ending
  • Detect muscle length during ***static state
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11
Q

Spinal reflexes (somatic)

A
  1. Stretch reflex (e.g. knee-jerk, ankle-jerk, biceps, triceps reflex)
    - monosynaptic (except reciprocal inhibition)
  2. Golgi tendon reflex
    - polysynaptic
  3. Flexor reflex
    - polysynaptic
  4. Crossed extensor reflex
    - polysynaptic
  5. Superficial cord reflex
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12
Q
  1. Stretch reflex
A

Stretching muscle

  • -> **Muscle spindle activation (detecting change in muscle **length)
  • -> ↑ Firing rate in type 1a sensory fibres
  • -> Spinal cord (Monosynaptic)
  • -> ↑ Firing rate in α motor neuron
  • -> Muscle contraction

Reciprocal inhibition:

  • antagonist inhibited –> accommodate contraction of agonist
  • Excitatory signal from muscle spindle
  • -> Spinal cord
  • -> Stimulation of inhibitory ***interneuron
  • -> Inhibition of motor neuron that innervates antagonist

Alpha-Gamma co-activation:
maintains sensitivity of muscle spindles

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13
Q

Patellar reflex (knee-jerk)

A
  1. Tap patellar tendon
  2. Quadriceps stretched
  3. Muscle spindle activated
  4. Impulse in 1a sensory neuron
  5. Monosynaptic (spinal cord) + Polysynaptic (Stimulation of inhibitory interneuron of antagonist muscle)
  6. Impulse in α motor neuron + Inhibition of antagonist muscle
  7. Muscle contract + Antagonist muscle relax

Reciprocal inhibition:
antagonistic pair of muscle (Hamstrings) must be inhibited / relax to prevent working against the agonist (Quadriceps)

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14
Q

Test for localisation of site of lesion / neuropathy

A

∵ different stretch reflexes are mediated by neural pathways at different segments of spinal cord
e.g. No knee-jerk reflex –> problem with L4 level
Biceps reflex: C5
Triceps reflex: C7
Brachioradialis reflex: C6
Ankle jerk: S1

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15
Q

***Alpha-Gamma Co-activation

A

When extrafusal muscle fibres actively shorten

  • -> intrafusal muscle fibres are NOT shortened accordingly
  • -> muscle spindle becomes slack
  • -> ↓ sensitivity of muscle spindles

Co-activate γ motor neuron by descending pathways

  • -> intrafusal muscle fibres now ALSO shortened
  • -> keeping muscle spindles taut
  • -> ↑ sensitivity of muscle spindles
  • -> Muscle spindles are still responsive during muscle contraction to detect further changes in muscle length
  • -> in turn ↑ α motor neuron discharge (enhance activity), allowing the continued firing of α motor neurons

–> Alpha-Gamma loop

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16
Q

Hyperreflexia and Hyporeflexia

A

Upper motor neuron lesion (cerebrum, brainstem, spinal cord)

  • -> loss of inhibition of γ motor neuron
  • -> ↑ activity of γ motor neuron
  • -> ↑ sensitivity of muscle spindles
  • -> ↑ muscle tone (Hypertonia)
  • -> Hyperactive stretch reflex (Hyperreflexia)
  • -> Spasticity

(damage to descending pathways –> increasing the total responsiveness of α motor neurons from muscle spindle 1a sensory input)

Lower motor neuron lesion (anterior horn, nerve roots, peripheral nerves, NMJ) / Impairment of reflex arc integrity

  • -> direct damage to α motor neurons / 1a afferents
  • -> ↓ muscle tone (Hypotonia)
  • -> Hypoactive stretch reflex (Hyporeflexia / Areflexia)
17
Q

Type 1b fibre

A
  • Innervate muscles of Golgi tendon organ (senses changes in muscle tension)
  • ***Contracting muscle (vs stretched muscle in 1a fibre)
  • -> activates Golgi tendon organ
  • -> ↑ firing rate of action potential in 1b fibres
18
Q
  1. Golgi tendon reflex
A

Contracting muscle
—> Golgi tendon organ activation (detecting ***tension)
—> ↑ Firing rate in 1b fibres
—> Spinal cord (polysynaptic):
—> Inhibitory interneuron to Agonist + Excitatory interneuron to Antagonist
—> ↓ Firing rate of α motor neuron (agonist)
—> Agonist muscle relaxation

e.g. Protect biceps from excessively heavy loads by causing muscle to relax and drop the load

19
Q
  1. Flexor reflex (withdrawl reflex)
A

Noxious stimulus

  • -> ***Pain receptor activation
  • -> Pain afferent impulse
  • -> Spinal cord (polysynaptic)
  • -> ↑ Firing rate of α motor neuron
  • -> Flexor muscle contraction (+ Extensor muscle relax)
20
Q
  1. Crossed extensor reflex
A

***Excitatory neurons (that cross spinal cord) stimulate motor neurons that innervate extensor of opposite leg

Ipsilateral side = Flexor reflex (***Flexor contract, Extensor relax)
–> move foot away from stimulus

Contralateral side = Opposite of Flexor reflex (Flexor relax, ***Extensor contract)
–> allow body weight shifts to non-stimulated leg

21
Q
  1. Superficial cord reflex
A

Mediated by neural pathway **locally organized at the spinal cord
- but requires descending activity from **Supraspinal level for normal manifestation (descending signals modulate reflex arc action)

Clinical significance: Test for ***Corticospinal tract lesion

Gentle cutaneous stimulation:
stroking sole (lateral aspect) of the foot

Positive Babinski reflex:

  • Extension of great toe
  • Fanning out of other toes
  • Infant: normal (corticospinal tract not fully myelinated / mature)
  • Adult: pathological

Normal plantar reflex (Negative Babinski reflex):

  • Flexion of all toes
  • Adult: normal
22
Q

Cranial reflexes (autonomic)

A
  1. Pupillary light reflex
  2. Chemoreceptor reflex
  3. Baroreceptor reflex
23
Q
  1. Pupillary light reflex
A

Light

  • -> Photoreceptor activation (from intrinsically photosensitive retinal ganglion cells)
  • -> ***Optic nerve
  • -> Midbrain (**Pretectal nucleus (unilateral) –> Accessory oculomotor nucleus / **Edinger-Westphal nucleus (bilateral))
  • -> ***2 Oculomotor nerves CN3 (Parasympathetic)
  • -> ***Direct response + Consensual response
  • -> Pre-ganglionic parasympatheic fibre –> ***Ciliary ganglion –> Post-ganglionic parasympatheic fibre
  • -> Pupillary constrictor muscle (Circular muscle) contraction
  • -> ↓ pupil size
  • radial muscle (control by sympathetic division) –> Superior cervical ganglion
24
Q

Clinical significance: Defect in Pupillary light reflex

A 
Motor defect (一隻有, 一隻無反應):
- impaired pupillary constriction of one eye REGARDLESS which eye stimulated
Sensory defect (兩隻都無反應):
- Impaired pupillary constriction of both eyes when ONE eye is stimulated
25
Q
  1. Chemoreceptor reflex
A

Blood CO2↑ / O2↓ / pH↓

  • -> Chemoreceptor activation (carotid, aortic bodies, medulla oblongata)
  • -> **Vagus nerve, **Glossopharyngeal nerve CN9
  • -> Medulla
  • -> Cardiovascular centre (medulla)
  • -> Vasomotor centre (medulla)
  1. ↑ Sympathetic nerve
    - -> ↑ Heart rate, ↑ Force of contraction, Vasoconstriction
  2. ↓ Parasympathetic nerve
    - -> ↑ Heart rate
26
Q

Chemoreceptors

A

Carotid, Aortic bodies: monitor O2, CO2, pH

Medulla oblongata: monitor CO2, pH

27
Q
  1. Baroreceptor reflex
A

↑ Blood pressure

  • -> Baroreceptor activation (Aortic bodies, Carotid sinuses)
  • -> **Vagus nerve, **Glossopharyngeal nerve CN9
  • -> Medulla
  • -> ↓ Sympathetic nerve + ↑ Parasympathetic nerve
  • -> ↓ Heart rate + ↓ Force of contraction + Vasodilation
28
Q 
Spinal reflexes (with autonomic component: autonomic ganglion)
--> involves 2 neuron: pre-, post-ganglionic neuron
A 
1. Defecation reflex
Feces in rectum
--> ***Stretch receptor activation
--> Sensory nerve
--> Spinal cord
--> ***Parasympathetic nerve
--> Contraction: Rectum, Sigmoid colon + Relaxation: Internal anal sphincter
2. Micturition reflex
Urine in bladder
--> ***Stretch receptor activation
--> Sensory nerve
--> Spinal cord
--> ***Parasympathetic nerve
--> Contraction: Bladder + Relaxation: Internal urethral sphincter
29
Q

Short reflex (in enteric nervous system ENS)

A

Processing at peripheral ganglia of local nerve plexus without involving CNS
Sensory fibres directly synapse onto ganglion (post-ganglionic cell)
–> Post-ganglionic fibre (skipped Pre-ganglionic fibre)
–> effector

Characteristics:

  • Skip pre-ganglionic cell
  • NO spinal cord / CNS processing
  • NOT considered autonomic (since no CNS involved)

Example:
Internal GI stimuli
–> Chemoreceptor, Osmoreceptor, Mechanoreceptor (visceral afferent)
–> Short reflex via local nerve plexus (ENS)
–> Smooth muscle / Gland
–> Contractile / Secretory activity to help digestion

30
Q

***Summary

A

Location of reflex arc:

  • Spinal vs Cranial
  • Somatic vs Autonomic

Spinal reflexes

  1. Stretch (somatic) (muscle spindle: type 1a sensory fibres as receptor)
  2. Golgi tendon (somatic) (golgi tendon organ: type 1b sensory fibres as receptor)
  3. Flexor, Cross extensor (somatic) (pain receptor)
  4. Superficial cord (somatic)
  5. Defecation (autonomic)
  6. Micturition (autonomic)

Cranial reflex:

  1. Pupillary (autonomic)
  2. Chemoreceptors (autonomic)
  3. Baroreceptor (autonomic)

MSS (32 decks)

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