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Neurology > How reflexes keep us safe > Flashcards

How reflexes keep us safe Flashcards

1
Q

What is a reflex?

A

A reflex is a simple, stereotyped response that couples sensory input to motor output. It relies on functional connections between a-motor neurons and muscle receptors. Such reflexes are examples of involuntary movements that kirap us safe from harm

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2
Q

What is the spinal reflex

A

Sensory input detected by sensory receptors

Peripheral nerve Synapse onto alpha-motor (lower motor) neurons in the spinal cord ventral horn

Innervate muscle to cause movement
Avoid damage to muscle to keep us safe

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3
Q

What is divergence spinal cord

A

Information from the periphery comes into the spinal cord and have segregation of message
message spreads out

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4
Q

Why is divergence of the spinal cord important

A

amplifies sensory input and coordinates muscle

contractions = movement

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5
Q

What is convergence spinal cord

A

Different areas of the periphery will come together onto one neuron

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6
Q

Why is convergence of the spinal cord important

A

interneurons increase flexibility of response

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7
Q

How is stretching of the muscles detected

A

Sensory neurons in muscle spindle (intrafusal muscle fibre) encode information on muscle length

Specialised muscle cells that detect stretch- 1a and 11 sensory afferents

monitor the extent of stretch and the rate of change of length
Synapse in spinal cord onto a motor neurons
Intrafusal muscle fibres in parallel
- surrounded by extrafusal muscle fibres
-associated with afferent and efferent neurons

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8
Q

How does tapping of the knee activate the stretch monysynaptic reflex?

A

Sretches Patellar ligament and so the intrafusal muscle
Action poteential across la affernent neurone and synapses to efferent neurone which restores muscle length of same muscle while maintaining muscle tone

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9
Q

What are the lower motor neurons

A

Alpha motor neurones

Gamma motor neurons

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10
Q

Where are the lower motor neuron cell bodies located

A

Ventral horn

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11
Q

What is the polysynaptic reflex

A 
Two (or more) synapses
Stimulus is muscle stretch
Instead of one efferent neuron afferent neuron synapses on Inhibitory interneurons which synapse onto another alpha motor neuron and this acts on antagonistic muscle
ANTAGONISTIC muscle relaxes
RECIPROCAL INNERVATION
Coordination of antagonistic muscles
Movement of entire limb
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12
Q

Why is the polysynaptic reflex important

A

Protective

it relaxes the antagonistic muscle and prevents it from tearing

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13
Q

What is more common polysynaptic or monosynaptic

A

Polysynaptic as to innervate antagonistic pairs

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14
Q

What is the role of gamma motor neurons

A

Innervate specialised striated muscle (intrafusal muscle fibres)
Adjust sensitivity of muscle spindles & increase range of function

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15
Q

How do Golgi tendon organs detect stretch?

A

Sensory neurons in tendon encode information on muscle tension and contraction
1b afferent sensory neurons associated with collagen fibres within the tendon
Located within tendons each end of a muscle
Monitor and maintain muscle tension
Inhibit further muscle contraction

Funnel-like capsule containing collagen fibre bundle and nerve fibres

Arranged in series with extrafusal muscle fibres

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16
Q

What is the golgi tendon reflex also known as ?

A

Reverse monosynaptic reflex

17
Q

What is the golgli tendon reflex?

A

Muscle tension reflex

Golgi tendon body stretch

Disynaptic reflex = TWO synapses

Prevents overstretching of tendon

Muscle contraction stretches tendon

Sensory neurons (lb afferent) activate interneurons

Inhibit a neurons innervating muscle of origin

Opposite to myotatic reflex

Controls muscle tension

Inhibits muscle contraction

Protects muscle from causing damage to tendons

Fine control of tension for grasping fragile objects

18
Q

What are the different sources inputting in the motor neuron

A

sensory input form Muscles (reflex)
Descending input form upper motor neurons
Interneurons from neuronal coircuts that produce cooirdinated movement

19
Q

What lesion would it be if there is weak or absent reflex?

A

Llwer motor neuron lesion

20
Q

What lesion would it be if there is exaggerated reflex?

A

Upper motor neuron lesion

21
Q

How do you purposefully exagerrate lower limb tendon reflex?

A

Jendrassick manoeuvre

22
Q

What happens to purposefully exagerrate lower limb tendon reflex?

A

Voluntary Upper Motor Neuron innervation
‘overflows to increase the excitability of the lower
motor neuron pool of the lower extremities

Increases fusimotor (y motoneuron) drive

Increases amplitude of reflex

Counteracts (removes) descending inhibition of
the reflex arc.

Modulates interneuron excitability

Removes inhibitory action on the late component 
of the stretch reflex (Group II afferents)
23
Q

What does the flexion withdrawal reflex do?

A

Rapidly removes limb from harmful (noxious) stimuli

24
Q

What is the flexion withdrawal reflex

A

Cutaneous receptors in the skin

Activation of primary afferent neurons (flexor reflex afferents)

Disynaptic reflex — inhibitory interneurons excite flexor motor neurons and inhibit extensor motor neurons

25
Q

What does the crossed extensors reflex do ?

A

Maintains balance during flexion withdrawal reflex

Simultaneous extension (strengthening contraction) of contralateral limb

26
Q

What is the crossed extensor reflex?

A

PAIN activates sensory neuron that
synapse with spinal cord interneurons
Interneurons activate
CONTRALATERAL extensor motor neurons and inhibit CONTRALATERAL flexor motor neurons
Extensor muscles contract (and flexor muscles relax) and LEG STRENTHENS to support weight

27
Q

What is the jaw jerk reflex?

A

Downward tap on jaw stretches muscle
Activation of trigeminal nerve (CNV)
Contraction of masseter muscle

28
Q

What is jaw unloading reflex

A

Initiated by sudden unloading of the jaw
Activation of trigeminal nerve (CNV)
Inhibition and activation of jaw muscles
Stops jaw movement, protects teeth

29
Q

Pupillary light reflex

A

Pupil constriction (both eyes) in response to bright light

Activation of optic nerve (CNII) 4 constriction via oculomotor nerve (CNIII)

Protective = adaptation to light levels

30
Q

Accommodation reflex

A

Adduction of eyes initiated by change in focus

Activation of optic nerve (CNII) 4 change in lens shape (CNIII)

Protective = prevents blurred vision

31
Q

Corneal (blink reflex)

A

Closure of both eyes initiated by foreign object touching one eye

Activation of trigeminal nerve (CNV) innervates eyelid by facial nerve (CNVI I)

Protective = protects eyes from foreign bodies

32
Q

Gag reflex

A

Initiated by object touching posterior wall of pharynx
Activation of glossopharyngeal nerve (CN IX)
Contraction of soft palate and pharynx

Protects the airway

33
Q

Swallowing reflex

A

Initiated by food bolus created by chewing

Causes closure of glottis, elevation of larynx, and transient cessation of respiration

Protects the airway •

34
Q

Tectospinal and vestibulospinal reflex

A

Initiated by visual or audio stimuli

Coordinates head and eye movement, maintains posture

Protective = responsive to changes in surrounding environment

Neurology (14 decks)

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