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Body sensation - proprioception - reflexes Flashcards

1
Q

What are the functions of sensory receptors

A
  • Inform your brain about the internal and external environment
  • Are nerve endings (many have specialised non-neural nendings)
  • Convert different stimuli into frequency of action potentials
    They are transducers
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2
Q

What are the 3 types of sensory receptors

A

Mechanoreceptors
Proprioceptors
Nociceptors

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3
Q

Describe mechanoreceptors

A

Stimulated by mechanical stimuli - pressure, stretch, deformation - Give us skin sensation of touch and pressure

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4
Q

Describe proprioceptors

A

Are mechanoreceptors in joints and muscles which signal information about the body or limb position

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5
Q

What do nociceptors respond to?

A

Pain

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6
Q

Define ‘sensory modality’

A

The stimulus type that activates a particular receptor

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7
Q

Describe what is meant by an ‘adequate stimulus’

A

Is the form of energy to which a receptor normally responds

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8
Q

What does sensory receptor transduction involve?

A

The opening and closing of ion channels

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9
Q

What does an adequate stimulus cause?

A

A graded membrane potential change

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10
Q

What are graded membrane potential changes called when caused by an adequate simulus?

A

Receptor potentials or generator potentials

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11
Q

What is the name of an adequate stimulus in cutaneous mechanoreceptors and proprioceptors?

A

MEMBRANE DEFORMATION

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12
Q

What does membrane deformation activate?

A

Stretch sensitive ion channels

so ions flow across the membrane and change the membrane potential locally

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13
Q

When do action potentials start firing in cutaneous mechanoreceptors?

A

When depolarisation reaches the area with voltage gated ion channels (the first of o Ranvier)

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14
Q

What is frequency coding of stimulus intensity?

A

When a larger stimulus causes:

  • A larger receptor potential
  • A higher frequency of action potentials
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15
Q

What do Pacinian corpuscles sense?

A

Vibration and pressure

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16
Q

What do merkel receptors sense?

A

Steady pressure and texture

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17
Q

What do meissner’s corpuscle’s do?

A

They respond to flutter and stroking movements

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18
Q

What do Ruffini corpuscles respond to?

A

Stretches in the skin

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19
Q

Describe what is meant by adaptation in relation to mechanoreceptors

A

When they adapt to a maintained stimulus and only signal change - eg. the onset of stimulation

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20
Q

Describe the mechanism of adaptation in mechanoreceptors

A

Generator potential declines rapidly blow threshold and AP’s cease

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21
Q

What types of receptors are rapidly to moderately adapting

A

Pacinian corpuscles and meissner’s corupscles

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22
Q

What types of receptors are slowly adapting receptors?

A

Merkels discs and ruffini endings

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23
Q

What types of receptors do not adapt?

A

Nociceptors

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24
Q

Describe the structure of pacinian corpuscles

A

It comprises a myelinated nerve with a naked nerve ending
It is enclosed by a connective tissue capsule of layered membrane lamellae
Each layer is separated by fluid

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25
Describe how the mechanism of a pacinian corpuscle
A mechanical stimulus deforms the capsule and the nerve ending This stretches the nerve ending and opens ion channels Na influx causes local depolarisation (receptor/generator potential) AP's are generated and fire where myelination begins (because regenerative Na channels cluster at nodes of ranvier)
26
How do pacinian corpuscles rapidly adapt?
Fluid rapidly redistributes within capsule lamellae, this spreads the stimulus impact out laterally - minimising downward deformation. As stimulus is withdrawn - capsule lamellae spring back and fire AP again
27
What is the capsules effect on the sensory function of the pacinian corpuscle
It enhances sensory function
28
What two things determine our ability to tell 2 points apart on the skin and by what test is this measured?
1. Receptive field size 2. Neuronal convergence Measured by the two point convergence test
29
What are the 2 types of neuronal convergence - describe them?
- Convergence - Divergence Convergence - sensory neurons converge on one 2ndary neuron Divergence - one sensory neuron diverges into many branches
30
What does neuronal convergence allow for?
The simultaneous sub-threshold stimuli to sum at the secondary neuron forming a larger secondary receptive field
31
Describe what is meant by 'acuity'
The ability to locate a stimulus on the skin and differentiate it from another closeby Low acuity is caused by high convergence
32
What process allows us to locate stimulus so precisely
Lateral inhibition
33
What are the 3 prorprioceptos?
Muscle spindles Golgi tendon organs Joint receptors
34
What is the function of muscle spindles?
They monitor muscle length and the rate of change of muscle length They also control reflexes and voluntary movements
35
What is the function of golgi tendon organs?
Monitor tension on tendons
36
What is the function of joint receptors?
Monitor joint angle, rate of angular movement and tension on the joint
37
What type of muscle fibre are most skeletal muscle fibres?
Extrafusal
38
What are Intrafusal muscle fibres? and where are they contained?
Muscle fibres which have their own sensory and motor innervation. They are contained within a capsule and called MUSCLE SPINDLES
39
Muscle spindles lie in ______ with muscle fibres
As DJ chorn says: PARALELL
40
What are the two kinds of intrafusal muscle fibre?
Nuclear bag fibres - Bag shaped with nuclei collected together Nuclear chain fibres - Nuclei lined up in a cha
41
What is the function of Gamma motorneurons?
They innervate and cause contraction of the contractile ends of the intrafusal fibres
42
What do the primary endings from type I afferent nerves form?
Annulospiral endings around the centre of intrafusal fibres
43
What do secondary ending from type II afferent nerves form?
flower spray endings
44
Does the central area of the muscle spindle contain contractile elements?
NO - dumbass
45
What happens when Gamma motorneurons fire?
They contract the two ends of the muscle spindle and shorten. HOWEVER the central area does not contract - therefore it gets stretched out
46
What do GTO's monitor?
They are stretch receptors and hence monitor the stretch of a tendon. Muscles have to develop tension by contracting to stretch the tendons
47
Do GTO's lie in series or in parallel with muscle fibres?
Series
48
Define isometric contraction
Same length - changing tension
49
Define isotonic contraction
Changing length - same tension
50
What is the result of alpha-gamma coactivation
Restores tension in the spindle and resets the sensitive of the central sensory part of the spindle to match a new muscle length
51
What happens when alpha motorneurons are activated?
Contraction of muscle
52
What type of reflex is found in all muscles?
Stretch reflex
53
Give an example of a stretch reflex
Patellar tendon/knee jerk reflex
54
Explain the mechanism of a stretch reflex
- Knee jerk follows a sharp tap to an inelastic tendon - Force is transmitted to the muscle fibres (they are more elastic than tendons and so are more able to stretch) - Stretch activates 1a afferent sensory nerves in the muscle spindle - This increases the number of AP's in 1a afferent sensory nerves projecting through the dorsal horn into the spinal cord
55
What is a monosynaptic reflex
reflex that only contains one space for an action potential to travel between a sensory and motor neuron
56
Describe reciprocal inhibition
Reciprocal inhibition describes the relaxation of muscles on one side of a joint to accommodate contraction on the other side. aka; when agonist contracts antagonist relaxes
57
Afferent Spindle firing travels up what colummns to what two structures?
Travels up the dorsal columns to the thalamus and the somatosensory cortex
58
What is the effect of spindle afferent firing traveling up up the dorsal columns to the thalamus and the somatosensory cortex
To tell the brain about the length of muscles
59
Describe what happens after the initial muscle stretch
1. Afferent impulses fire from stretch receptor to spinal cord (dorsal root) 2. Efferent impulses fire from the ventral horn to the alpha motor neurons, causing contraction of the stretched muscle that resists/reverses the stretch 3. Efferent impulses to antagonist muscles are damped (reciprocal inhibition)
60
What is the inverse stretch reflex caused by?
afferent nerve from the golgi tendon organs - which monitor muscle tension
61
What happens to the golgi tendon organ when a muscle contracts/shortens
This pulls on the tendon and the sensory 1b afferent nerves from the GTO's increase the firing of action potentials
62
What 3 things does increased firing of action potentials from the GTO cause
1. Activation of inhibitory interneurons to the agonist muscle and a decrease in contraction strength 2. Activation of excitatory interneurons to antagonist muscles 3. Information about muscle tension ascends in the dorsal columns to the somatosensory cortex
63
What is the function of the 'clasp-knife' reflex? why does it happen?
- Acts a protective mechanism to prevent muscle damage | - Happens because greatly increasing tension in tendon leads to a collapse of resistance
64
Describe the function of the flexor reflex?
They withdraw part of the body away from the painful stimulus and in towards the body - so flex the affected part
65
Describe the circuitry of the flexor relfex
- Small diameter Aδ nocieptive fibres triggering pain enter spinal cord. - They branch and activate interneurons in several spinal segments above entry points - These activate α motorneurons controlling all the flexor muscles of the affected limb
66
Describe how an upright posture is maintained during a flexor reflex?
The contralateral limb extends to bear the shift in body weight

My own anatomy (34 decks)

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