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Neuroanatomy > Peripheral Receptors > Flashcards

Peripheral Receptors Flashcards

1
Q

What are the components of peripheral nerves?

A
  • Axons
  • Supporting Schwann cells
  • Connective tissue (including fibroblasts)
  • Blood vessels
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2
Q

Describe the dimensions of a peripheral nerve

A
  • Range in diameter from ~0.2-20µm
  • Axons above ~1-1.5µm are myelinated
  • Those below this threshold remain unmyelinated (but not generally ‘naked’
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3
Q

Describe the characteristics of primary spindle endings and golgi tendon organs

A
  • 12-20µm diameter
  • Myelinated
  • Condcution velocity = 80-120 m/sec
  • Class - Aα
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4
Q

Describe the characteristics of secondary spindle endings, deep pressure receptors and cutaneous tactile receptors

A
  • 6-12µm diameter
  • Myelinated
  • Conduction speed = 35-75 m/sec
  • Class - Aβ
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5
Q

Describe the characteristics of crude touch fibres and pain and temperature receptors

A
  • 1-6µm diameter
  • Myelinated
  • Conduction speed = 5-30 m/sec
  • Class - A𝝳
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6
Q

Describe the characteristics of slow pain fibres

A
  • 0.5-1.5µm diameter
  • Unmyelinated
  • 0.5-2 m/sec
  • Class - C
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7
Q

Describe motor to extrafusal fibres in skeletal muscle

A
  • 12-20µm diameter
  • Myelinated
  • 80-120 m/sec
  • Class - Aα
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8
Q

Describe motor to intrafusal muscle fibres in skeletal muscle spindles

A
  • 3-6µm diameter
  • Myelinated
  • 15-30 m/sec conduction speed
  • Class - Aγ
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9
Q

Describe preganglionic autonomic efferents

A
  • 1-3µm diameter
  • Myelinated
  • 3-14 m/sec
  • Class - B
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10
Q

Describe postganglionic sympathetic efferents

A
  • 0.5-1.5µm diameter
  • Unmyelinated
  • 0.5-2 m/sec
  • Class - C
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11
Q

What is the sensory threshold?

A

The minimum strength of a stimulus which a receptor can detect

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12
Q

What is receptor adaptation?

A

In skin receptors (and some others) if a stimulus is continuous for a period of time, the neural response becomes diminished.

Some receptors adapt slowly, others adapt rapidly.

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13
Q

What controls the intensity of a stimulus?

A

Intensity of the stimulus is encoded for by the frequency of the action potentials.

This is frequency modulation.

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14
Q

What are tactile receptors associated with?

A

Touch, pressure and vibration

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15
Q

List the types of tactile receptors

A
  • Hair follicle receptors
  • Meissner’s corpuscles
  • Pacinian corpuscles
  • Ruffini endings
  • Merkel’s nerve endings
  • Free nerve endings
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16
Q

Which tactile receptors are encapsulated nerve endings?

A
  • Meissner’s corpuscles
  • Pacinian corpuscles
  • Ruffini endings
  • Surrounded by a connective tissue capsule
17
Q

Describe hair follicle receptors

A
  • Formed from axons that surround or run parallel to hair follicles.
  • These are rapidly adapting receptors that respond to the bending of the hair shaft and so serve as receptors for light touch.
18
Q

Describe Meissner’s corpuscles

A
  • Found in many areas, but concentrated in glabrous skin (fingers, toes, plantar surfaces of feet, palms).
  • Composed of a stack of epithelial cells with 1-2 unmyelinated axons spiralling through them.
  • They are surrounded by a connective tissue sheath.
  • They are low threshold and rapidly adapting.
  • Sensitive to touch and vibration.
19
Q

Where are Pacinian corpuscles found?

A
  • Deep in the dermis or in the hypodermis
  • Can also be found in the:
    • Joint capsules
    • Mesentery
    • Periosteum surrounding bone
20
Q

Describe the characteristics of Pacinian corpuscles

A
  • More than 1000µm long
  • Concentric layers of flat cells with fluid and connective tissue between the layers.
  • The innervating fibre is myelinated, but loses its myelination once it enters the Pacinian corpuscle and lies at its centre.
  • Respond to pressure and vibration
  • Low threshold and very rapidly adapting
21
Q

Describe Ruffini endings

A
  • Small receptors (1-2µm)
  • Widely distributed and found in the dermis
  • Myelinated axon enters the capsule (loses its myelin as it does so) and ramifies amongst the collagen fibrils.
  • Low threshold, slowly adapting
  • Respond to the stretch of the collagen fibres and thus the skin
22
Q

Describe Merkel’s discs

A
  • Found in:
    • Lips
    • Fingers
    • Toes
    • Genitalia
  • Specialised large epithelial cell in the basal layer of the epidermis which is on contact with a disc-like ending of an axon.
  • Sensitive to pressure
  • Slowly adapting
  • Low threshold
23
Q

Where are free nerve endings found?

A
  • Skin (dermis, hypodermis, epidermis)
  • Organ capsules
  • Ligaments
  • Meninges
  • Perichondrium
  • Parietal peritoneum
  • Endomysium of muscle
  • Cornea
24
Q

Describe free nerve endings

A
  • Can be myelinated or unmyelinated
  • Respond to several sitimuli:
    • Light touch
    • Heat / cold
    • Tissue damage
    • Many act as nociceptors
25
Q

Which receptors are responsible for proprioceptive information?

A
  • Free nerve endings
  • Muscle spindles
  • Golgi tendon organs
26
Q

Describe muscle spindles

A
  • Special sense organs in muscle which provide information on the amount of stretch in the muscle and velocity of change of length in the muscle.
  • Contain special muscle fibres - intrafusal fibres
  • Normal contractile muscle fibres are termed extrafusal fibres
27
Q

What are the 2 types of intrafusal muscle fibres?

A
  • Nuclear chain fibres
  • Nuclear bag fibres
28
Q

Describe nuclear chain fibres

A

Homogeneous diameter and have their nuclei in a line

29
Q

Describe nuclear bag fibres

A

Have a swelling in the middle where their nuclei congregate

30
Q

Compare the innervation of the intrafusal muscle fibres to the extrafusal fibres

A
  • Intrafusal fibres are contractile and are innervated by smaller motor neurons (AƔ fibres or ‘gamma motor neurons).
  • Extrafusal fibres are innervated by Aα fibres (or ‘alpha’ motor neurons)
31
Q

What are the 2 types of sensory axons within the spindle?

A
  • Annulospiral endings
  • Flower spray endings
32
Q

Describe the golgi tendon organ

A
  • Spindle shaped, found in tendons near the myotendinous junction.
  • Thin capsule with a sensory axon that enters, ramifies and becomes interwoven between collagen fibres.
  • Golgi tendon organ fibres are slowly adapting and are stimulated by tension in the collagen fibres (which reflects the tension in the tendon and therefore the attached muscle).
33
Q

Which 3 cells are involved in forming the neuromuscular junction?

A
  • Motor neuron
  • Muscle fibres
  • Schwann cell
34
Q

Describe the motor neuron at the neuromuscular junction

A

The terminal of the motor neuron axon is the presynaptic element in the synapse. It contains vesicles of neurotransmitter - termed synaptic vesicles.

35
Q

Describe the muscle fibres at the neuromuscular junction

A

Specialised region of the muscle fibre that receives the nerve terminal is called the sole plate, and forms the postsynaptic element of the synapse.

Each terminal sits in a depression in the muscle fibre surface called the primary synaptic cleft.

36
Q

Describe the Schwann cell at the neuromuscular junction

A
  • Schwann cells are the main glial (support) cells of the peripheral nervous system.
  • Perisynaptic - covers over the cell process forming the synapse.
37
Q

Describe the neuromuscular junction

A
  • Almost all skeletal muscle fibres have a single neuromuscular junction.
  • Here, motor axons terminate at a motor end plate and action potentials arriving in the axon cause release of acetylcholine and initiate an action potential in the sarcolemma.
38
Q

What is the motor plate?

A

A slightly raised complex at the site where the motor axon terminal meets the muscle fibre.

Neuroanatomy (15 decks)

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