1
Q
List the main classes of sensory receptor found in the body
A
Mechanoreceptors - tactile and position sensations
Thermoreceptors - detect heat and cold
Pain receptors - detect damage to the tissue
2
Q
What is glabrous skin ?
A
Skin that doesn’t have hair on it
e.g. palm of hand / sole of foot
3
Q
What is hairy skin ?
A
Skin that has hair on it
Touch from receptors in skin surface
4
Q
Name some structures found in the dermis
A
Pacinian corpuscle
Meissners corpuscle
Ruffini’s ending
Hair follicle receptor
Free nerve endings
5
Q
What do cutaneous mechanoreceptors respond to ?
A
Touch from receptors in skin surface
Pressure from receptors in deep tissue
6
Q
Spray endings
A
Ruffini’s ending (specialised nerve endings)
7
Q
Encapsulated endings
A
Pacinian corpuscles (receptor cells around nerve)
8
Q
Muscle endings
A
Muscle spindles
Golgi tendon organs
9
Q
Describe Pacini’s corpuscle
A
Largest mechanoreceptor in the skin (2mm long)
Onion like encapsulation of nerve ending
Found in deep layers of the dermis
10
Q
Explain the structure of Pacini’s corpuscle
A
1st part is unmyelinated
2nd part is myelinated (as it leaves receptor cell)
ABeta fibres (quick) - glabrous & hairy skin
11
Q
Function of Pacini’s corpuscle
A
Detects high frequency (40-500Hz) vibration
12
Q
State some features of Pacini’s corpuscle
A
Rapidly adapting due to a slick viscous fluid between layers.
Has a low activation threshold (i.e. it is sensitive)
13
Q
Describe Meissner’s corpuscle
A
Encapsulated nerve endings similar to Pacini’s but MUCH smaller
Found between dermal papillae
14
Q
Explain the structure of Meissner’s corpuscle
A
Stacks of discs interspersed with nerve branch endings
ABeta Fibres (quick) - Glabrous skin types
15
Q
Function of Meissner’s corpuscle
A
Detects touch, flutter and LOW frequency vibration
(2-40Hz)
16
Q
State some features of Meissner’s corpuscle
A
Rapidly adapting - low activation threshold
(sensitive )
17
Q
Describe Merkel’s discs
A
Non -encapsulated nerve endings
18
Q
Explain the structure of Merkel’s discs
A
Consist of a specialised epithelial cell + nerve fibre
ABeta fibres - all skin types
19
Q
Function of Merkel’s discs
Found just under the skin surface
e.g. fingertips : good discrimination :
- Detects static touch
- Light pressure
Work with Meissner’s corpuscles to help determine texture.
20
Q
State some features of Merkel’s discs
A
Slowly adapting - low activation threshold (sensitive)
21
Q
Describe hair follicles
A
Embedded in the skin
22
Q
Function of hair follicles
A
Detect muscular movements of the hair (erector muscle) and external displacements of hair
23
Q
What are hair follicles innervated by ?
A
Innervated by nerve endings wrapped around the follicle.
24
Q
Describe Ruffini corpuscle
A
Encapsulated nerve endings
25
Q
Function of Ruffini corpuscle
A
Responds to skin stretch and is located in the deeper layers of the skin as well as tendons and ligaments
26
Q
Structure of Ruffini corpuscle
A
Nerve endings weave between collagen fibres which activate the nerve when they are pulled longitudinally.
ABeta fibres - all skin, but especially abundant in hands and fingers as well as sole of feet
27
Q
Features of Ruffini corpuscle
A
Slow adapting - low threshold activation
(sensitive)
28
Q
Skeletal muscle receptor types
A
Muscle spindles
Golgi Tendon organs
29
Q
What are muscle spindles ?
A
Main proprioceptors that provide infrmaoin about the state of musculature.
30
Q
Where are muscle spindles found ?
A
Muscle spindles lie within muscles in parallel with skeletal muscle fibres.
Particularly numerous in fine motor control muscles (e.g. eyes, hands)
31
Q
What are muscle spindles innervated by ?
A
Innervated by gamma-motoneurons (efferents) and group Ia and II afferent fibres
32
Q
What are Golgi tendon organs ?
A
Main proprioceptors that provide information about the state of musculature.
33
Q
Where are Golgi Tendons Organs found ?
A
Liw within tendons in a series with contractile fibres.
34
Q
How do Golgi tendons act ?
A
Respond to a degree of tension within the muscle.
Group Ib afferent fibres relay information to CNS (particularly spinal cord and cerebellum)
35
Q
What is a generator potential ?
A
The potential caused by a stimulus to a nerve ending.
Generates action potentials in a sensory neuron.
36
Q
What is a receptor potential ?
A
Potential causes by a stimulus to a receptor cell.
Affects the amount of neurotransmitter released by a receptor cell onto sensory neuron.
37
Q
What can a receptor potential be caused by ?
A
Mechanical deformation of receptor
Chemical application to membrane
Temperature change of membrane
Effects of electromagnetic radiation
38
Q
Mechanical deformation of receptor
A
[causes a receptor potential]
Stretch receptor membrane and open ion channels
39
Q
Chemical application to membrane
A
[causes a receptor potential]
Opens ion channels
40
Q
Temperature change of membrane
A
[causes a receptor potential]
Changes the permeability of membrane
41
Q
Effects of electrochemical radiation
A
[causes a receptor potential]
e.g. light on retinal receptor
42
Q
Explain receptor potential generation in a Pacini Corpuscle
A
Tip unmyelinated - nerve fibre myelinated before leaving corpuscle
Compression anywhere on outside of corpuscle elongates, indents/deforms central fibre
Receptor potential induces local current flow (Na+ current) which spreads along the nerve fibre
At the 1st Node of Ranvier local current flow depolarises fibre membrane at this node, which sets off action potentials to CNS
43
Q
Function of the 1st Node of Ranvier in the Pacini Corpuscle
A
At the 1st Node of Ranvier local current flow depolarises fibre membrane at this node, which sets off action potentials to CNS.
44
Q
Describe the relationship between receptor potential and action potential generation
A
When receptor potential rises above the threshold in nerve fibre - action potentials fire.
The more the receptor potential rises above the threshold level, the greater the action potential frequency.
45
Q
Describe how the receptor potential rises ?
A
Amplitude of receptor potential increases rapidly at first, then less rapidly at high stimulus strength.
46
Q
How is action potential related to stimulus size ?
A
APs generated in a sensory nerve at a frequency directly related to stimulus size.
47
Q
Describe adaptation of sensory receptors
A
Some sensory receptors adapt rapidly to constant stimulus so their generator potentials do too.
48
Q
What are tonic receptors ?
A
Slowly adapting receptors which detect continuous stimulus strength.
49
Q
What are rate/movement/phasic receptors ?
A
Rapidly adapting receptors which detect a change in stimulus strength.
50
Q
C fibres
A
Unmyelinated
Slow
Sensation of dull pain (generalised)
51
Q
A Delta
A
Myelinated
Fast
Sharp localised pain
52
Q
State some myelinated nerve fibre types
A
A alpha (Ia)
A alpha (Ib)
A beta (II)
A gamma (II)
A delta (III)
B
53
Q
State the order of magnitude of the axon diameters (from largest to smallest)
A
A alpha (Ia)
A alpha (Ib)
A beta (II)
A gamma (II)
A delta (III)
B
C (IV)
54
Q
State the order of magnitude of axon conduction velocities
(from largest to smallest)
A
A alpha (Ia)
A alpha (Ib)
A beta (II) : 35-75
A gamma (II) : 15-30
A delta (III) : 5-30
B : 3-15
C (IV)
55
Q
State the quickest nerve fibres in the body
A
A alpha
80-120 m/s
56
Q
State the widest nerve fibres in the body
A
A alpha
12-20
57
Q
State the slowest nerve fibres in the body
A
C nerve fibres
0.5 - 2
58
Q
State the thinnest nerve fibres in the body
A
C nerve fibres
0.2 - 1.5
59
Q
Describe A alpha (Ia)
A
Somatic motor
(Annulospiral endings of muscle spindle)
60
Q
Describe A alpha (Ib)
A
Golgi tendon organs
61
Q
Describe A beta (II)
A
Cutaneous tactile receptors (touch, pressure)
Flower spray endings of muscle spindle
62
Q
Describe A gamma (II)
A
Motor to spindle
63
Q
Describe A delta (III)
A
Crude touch
Temperature
Pain sensation
64
Q
Describe B
A
Preganglonic autonomic
65
Q
Describe C (IV)
A
Pain and temperature sensation
Postganglionic sympathetic
66
Q
What is precisions localisation of a particular stimulus determined by ?
A
Size of individual nerve fibre receptive field
Density of sensory units
Amount of overlap in nearby receptive fields
67
Q
Describe receptive field distribution
A
Higher the resolution, higher the number of modalities for a given situation, the better the understanding.
68
Q
Describe the receptive field of Pacini’s corpuscle
A
Pacini’s corpuscle have broad receptive field
69
Q
Describe the receptive field of Meissner’s corpuscle
A
Meissner’s corpuscle and Merkel’s discs are very small
Note : Small receptive fields allow high spatial resolution.
70
Q
What is 2 point discrimination ?
A
Horizontal bars represent minimum distance at which 2 points can be perceived at a distinct.
71
Q
How does 2 point discrimination work ?
A
It is a result of receptive field size and receptor density in an area.
Does NOT represent sensitivity to stimulus.
72
Q
What is the function of lateral inhibition ?
A
Aids in enabling localisation of stimulus
73
Q
Where does the information from touch receptors go to ?
A
The dorsal column which exists at all levels of the spinal cord
74
Q
Describe the spinothalamic tract
A
Information crosses over at the spinal cord level (e.g. pain), and goes up the spinothalamic tract to the opposite side of the brain.
You can use this information to determine where lesion may occur in the spinal cord.
75
Q
What is the somatosensory cortex ?
A
Sensory information passes through the thalamus to the primary sensory cortex.
Sensory information projected in a topographical manor to this area.
Areas of higher discrimination/senses having a larger proportion of the space.
76
Q
Where is the somatosensory cortex located ?
A
Located in a strip posterior to the post central sulcus of the brain
