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Medicine Year 1 - Semester 2 - Part 1 > Reflexes > Flashcards

Reflexes Flashcards

1
Q

What is a reflex ?

A

A specific, involuntary, unpremeditated, “built in” response to a particular stimulus.

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2
Q

Give some examples of reflexes

A

Removing hand from a hot object.

Lifting a foot of a sharp object.

Shutting eyes as object rapidly approaches face.

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3
Q

Describe a learned / acquired reflex

A

Many operations involved in driving a car.

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4
Q

Homeostasis

A

A stimulus-response sequence.

Reflexes may be a component of homeostatic control systems.

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5
Q

State the reflexes involving special senses

A

Rotatory Nystagmus

Post Rotatory Nystagmus

Interpretation of movement within images

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6
Q

Rotatory Nystagmus

A

Eye movements driven by moving visual images.

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7
Q

Post Rotatory Nystagmus

A

Eye movements driven by the movement of fluid in the semi-circular canals of the inner ear.

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8
Q

Interpretation of movement with images on the retina

A

Used to make postural adjustments to preserve balance.

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9
Q

Describe Step 1 in the pathway mediating a reflex arc

A

A detectable change in internal/external environment, (stimulus).

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10
Q

Describe Step 2 in the pathway mediating a reflex arc

A

The receptor detects the change

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11
Q

Describe Step 3 in the pathway mediating a reflex arc

A

Signal received (along with those from other stimulus/receptor interactions)

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12
Q

Describe Step 4 in the pathway mediating a reflex arc

A

Sometimes the response gives negative feedback

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13
Q

State the classes of movement

A

Voluntary
Reflexes
Rhythmic motor patterns

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14
Q

Describe voluntary movement

A

Complex actions (reading, writing)
Purposeful goal directed
Learned

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15
Q

Describe reflex movement

A

Involuntary
Rapid
Stereotyped (knee jerk, eye blink)

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16
Q

Describe rhythmic motor patterns

A

Combines voluntary and reflexive acts (chewing, walking, running)

Initiation and termination voluntary

Once initiated repetitive and reflexive

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17
Q

Describe organisation of the spinal cord

A

Sensory information comes in through the dorsal root of the spinal cord.

Sensory (afferent nerve) will synapse with either an interneuron or directly with the alpha motor neurones that are situated in the ventral horn.

Ventral horn - front part of the spinal cord where alpha motor neurons come out and go to a skeletal muscle

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18
Q

Describe Lamina I-VI (dorsal horn)

A

Terminations for primary afferent sensory neurones and neurones of reflex circuits.

Sensory input from joints and muscles (lamina VI)

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19
Q

Describe Lamina VII (lateral horn)

A

Pre-ganglionic sympathetic (T1-L2) and parasympathetic (sacral)

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20
Q

Describe Lamina VIII and IX (ventral horn)

A

Cell bodies of motor neurones

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21
Q

Where are motor neurones supplying muscles of the trunk situated ?

A

Medially

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22
Q

Where are motor neurones supplying distal muscles situated ?

A

Laterally

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23
Q

Corticospinal tract

A

Information from the brain CNS going down towards the spinal cord

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24
Q

Spino thalamic tract

A

Information going from the spine and ending up in the thalamus

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25
Q

Describe the circular route for a simple reflex arc or spinal reflex

A

Information comes into the spinal cord via the dorsal root ganglia, that ultimately leads into the dorsal part of the dorsal horn of the spinal cord.

These neurones ultimately either innervate directly alpha motor neurones or to an interneuron that connects sensory information to an alpha motor neurone.

Alpha motor neurones come out of the ventral horn and essentially of to the muscle to bring out contraction.

26
Q

Describe the reflex connections of muscle spindles with alpha-motor neurones supplying the muscle

A

Alpha motor neurone cell bodies lie in clumps within the ventral horn of the spinal cord.

Each motor neurone activates a motor unit.

27
Q

Describe the connection between alpha motor neurones and Renshaw cells

A

The alpha motor neurone in the ventral horn thats going to a particular muscle has a collateral that comes off that.

That collateral stimulates a Renshaw cell (which is inhibitory).

The Renshaw cell goes back on to the alpha motor neurone and reduces the activity of the alpha motor neurone.

28
Q

What are Renshaw cells ?

A

Interneurons
(recurrent or feedback inhibition)

29
Q

Function of Renshaw cells

A

Helps to produce a refinement of muscle contraction.

30
Q

Describe the action of Renshaw cells

A

They :

  • Suppress weakly firing motor neurons and dampening strongly firing ones
  • Produces economical movement
31
Q

Describe strychnine poisoning

A

Disables Renshaw cell inhibition - leads to convulsions

32
Q

Give an example of myotatic stretch reflex

A

Knee Jerk reflex - an example of a monosynaptic stretch reflex

33
Q

Describe the myotatic knee jerk reflex

A

Tap of patellar tendon stretches the quadricpes muscle.

This stimulates dynamic nuclear bag receptors of the muscle spindle.

34
Q

Describe how myotatic reflex jerks work

A

An increase in the rate of firing of group Ia afferents, leads to contraction of quadriceps muscle.

Ia fibres also stimulate inhibitory interneurons which inhibit antagonistic (flexor) muscle of the knee joint.

35
Q

When is myotatic reflex lost ?

A

Reflex is lost if lower lumbar dorsal roots of spinal cord are damaged.

36
Q

What are muscle spindles ?

A

Main proprioceptors that provide information about the state of musculature.

37
Q

Where are muscle spindles located ?

A

Muscle spindles lie within muscles in parallel with skeletal muscle fibres.

They are particularly numerous in fine motor control muscles (eyes, hands)

38
Q

What innervates muscle spindles ?

A

Gamma-motorneurons (efferents) and group Ia and II afferent fibres

39
Q

Function of muscle spindle afferents

A

Responds to muscle stretch

40
Q

Function of muscle spindle gamma-efferents

A

Regulates the sensitivity of the muscle spindle

41
Q

Function of muscle spindles

A

They play an important role as comparators for maintenance of muscle length, during goal directed voluntary movements.

42
Q

Describe voluntary activity of muscle spindles

A

Voluntary changes in muscle length initiated by motor area of the brain, orders include changes to set-point of muscle spindles.

43
Q

Describe alpha-gamma co-activation

A

Simultaneous activation of extrafusal fibres and intrafusal fibres is called alpha-gamma co-activation.

44
Q

Function of alpha-gamma co-activation

A

The process readjusts sensitivity of muscle spindles continuously as muscle shortens.

45
Q
A
46
Q

Function of the Golgi tendon reflex

A

Protective to prevent tearing of muscle/ detachment of tendon.

Contributes to maintenance of posture.

47
Q

What is another name for Golgi Tendon reflex ?

A

Inverse Myotatic Reflex

48
Q

How is the Golgi Tendon Organ stimulated ?

A

GTO is stimulated by increasing tension in muscle

Signals transmitted to the spinal cord - reflex is entirely inhibitory

Negative feedback mechanism which prevents development of excessive tension in muscle.

49
Q

Difference between muscle spindles and Golgi tendon organs

A

Muscle spindles monitor muscle length
Golgi Tendon organ monitors muscle tension

50
Q

What does the inhibitory effect from the Golgi tendon organ lead to ?

A

Inhibitory effect from GTO can be so great that it leads to sudden unloading of muscle.

51
Q

Describe the Golgi Tendon Organ

A

Main proprioceptors that provide information about the state of musculature.

52
Q

Where are Golgi Tendon Organs located ?

A

They lie within tendons in series with contractile fibres.

53
Q

Function of the Golgi tendon organ

A

Responds to a degree of tension within the muscle

Group Ib afferent fibres relay information to the CNS

54
Q

Function of the withdrawal reflex

A

Protective reflex of rapidly removing limb from damaging stimuli

Stimulation of withdrawal reflex, frequently elicits extension of the contralateral limb 250ms later.

Helps maintain posture and balance

55
Q

Describe locomotion step cycle

A

Stance phase
Swing phase

56
Q

Stance phase

A

Foot touching the ground, flexion of knee and ankle

Finishes with extension about all joints for forward movement.

57
Q

Swing phase

A

Bending (flexion) of hip, knee and ankle followed by knee and ankle straightening (extension)

58
Q

Central Pattern Generator

Location
Modulation
Initiation

A

Located in the spinal cord

Modulated by proprioception unit

Thought to be initiated by mesencephalic locomotor region - output through reticular nuclei and reticulospinal tracts

59
Q

Describe the structure of the CPG

A

2 half centres which activate flexors and extensors respectively and mutually inhibit each other

60
Q

What system is involved in reflexes ?

A

Central Pattern Generator

Medicine Year 1 - Semester 2 - Part 1 (51 decks)

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