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Neurology > Ascending tracts, sensory receptors > Flashcards

Ascending tracts, sensory receptors Flashcards

1
Q

What are sensory receptors?

A
  • specialized cells which convert stimuli into AP via transduction which is then interpreted by CNS
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2
Q

What are the somatic senses?

A
  • temp
  • touch
  • pressure
  • vibration
  • proprioception
  • pain
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3
Q

What are the special senses?

A
  • vision
  • hearing
  • smell
  • taste
  • equilibrium
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4
Q

What is the mechanism of activation of mechanoreceptors?

A
  • receptor stretched or compressed

- (stretch-sensitive)

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5
Q

What is the mechanism of activation of thermoreceptors?

A
  • hot and cold receptors
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6
Q

What is the mechanism of activation of electromagnetic receptors?

A
  • light in retina (only in eyes)
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7
Q

What is the mechanism of activation of chemoreceptors?

A

respond to chemical stimulus:

  • O2
  • CO2
  • H+
  • osmolarity (hypothalamus)
  • taste
  • smell
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8
Q

How can receptors be classified?

A

1) mech of action (mechano- thermo- chemo- electro-)

2) purpose (nociceptors or proprioceptors)

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9
Q

What are nociceptors?

A
  • give rise to pain sensation

- usually mechano, thermo and chemo

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10
Q

What are proprioceptors?

A
  • give info about joint position

- usually mechano

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11
Q

What does a receptors modality refer to?

A
  • show high sensitivity to one type of stimulus

- can still respond to others

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12
Q

How does the level of sensitivity and the size of receptive field relate?

A
  • more sensitive the area the smaller the receptive field

- e.g. finger tips small receptive field

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13
Q

What is the structure of a pacinian corpuscle?

A
  • bare neurone ending

- surrounded by layers of tissue

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14
Q

How do pacinian corpuscles transmit a signal?

A
  • membrane surrounding receptor must be distended
  • this causes pressure from distension to pull apart the ion channels
  • allowing Na+ ions to enter down conc gradient
  • if enough sodium can result in threshold depolarisation where AP transmitted down axon
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15
Q

What does the strength of stimulus effect about the signal?

A
  • size of receptor potential

- sensory nerve frequency of AP

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16
Q

Describe a phasic receptor response?

A
  • adapts rapidly
  • receptor potential and resultant AP diminish
  • will deliver transient information
  • example pacinian corpuscle
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17
Q

Describe a tonic receptor response?

A
  • adapts slowly
  • receptor potential and resultant AP maintained
  • give constant sensation information
  • e.g. some proprioceptors
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18
Q

Give example of mechanoreceptors?

A
  • tactile receptors of skin and deep tissue
  • proprioceptors
  • baroreceptors (CV system)
  • inner ear receptors
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19
Q

What are the different types of tactile mechanoreceptors found in the skin?

A
  • free nerve ending receptors (bare dendrites), very sensitive
  • root hair plexus (sensory dendrites) surround hair follicles
  • Merkels receptors (surface of skin)
  • Meissners corpuscle (encapsulated nerve ending) very sensitive found in fingertips
  • Pacinian corpuscle
  • Ruffini corpuscle
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20
Q

What is the function of muscle spindles?

A

stretch receptors which sense muscle length and trigger muscle stretch reflexes

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21
Q

What is the structure of muscle spindle?

A

Intrafusal
- central region of fibre
- contains receptors with sensory afferents
- at either end have contractile regions with gamma motoneurones
Extrafusal
- alpha motorneurone supply
- (oustide muscle spindle)

22
Q

How do muscle spindles work?

A
  • muscle stretch causes intrafusal stretch
  • which sends this information to spine
  • spine synapses with alpha motor neurones to trigger muscle contraction which opposes the stretch
  • opposing muscle is also inhibited
  • intrafusal fibres contracted along with extrafusal to avoid distorsion of intrafusal fibres maintaining sensitivity
23
Q

What is the function of the Golgi tendon organs?

A
  • sense muscle tension
  • initiate muscles inhibitory reflex
  • located in tendons
  • help protect muscle from excessive tension
24
Q

What do proprioceptor joint receptors detect?

A

joint

  • pressure
  • movement
  • tension
25
Q

Where are the baroreceptors located?

A
  • glossopharyngeal nerve
  • carotid sinus (bifurcation of carotid arteries)
  • aortic arch
  • heart muscle
  • pulmonary artery
26
Q

Where would you find temperature receptors?

A
  • dermis
  • hypothalamus
  • spine
  • liver
  • skeletal muscle
    (all send info to hypothalamus which can respond)
27
Q

What type of receptors are temperature receptors (phasic or tonic?

A

Phasic

28
Q

What channels open in response to temperature changes?

A

TRPV1 > 43 degrees (also responds to capsaicin found in chillies)
TRPV2 > 52 degrees
TRPA1 < 18 degrees (also responds to menthol)

29
Q

What are examples of chemoreceptors?

A

sense changes in chemicals

  • carotid body sense O2, CO2 and PH changes
  • medulla oblongata sensitive to H2 and CO2 ions (function in respiration)
  • hypothalamic receptors help signal hunger and thirst, sense glucose and osmolarity
  • GI tract receptors, trigger gastric secretions in response to proteins
30
Q

What stimuli can trigger nociceptors?

A
  • mechanical damage
  • dissolved chemicals
  • temperature extremes
  • (often response due to chemicals released by damaged cells)
31
Q

What chemical mediator can sensitize nociceptors?

A
  • prostaglandins

- reduce sensitivity so reduce pain

32
Q

What are the types of primary afferent neurones?

A
  • A(alpha) (Fastest)
  • A(beta)
  • A(delta)
  • C (Slowest)
33
Q

What are examples of receptors which use C fibres?

A
  • pain and temp
34
Q

What are examples of receptors which use A(alpha) fibres?

A

muscle spindle
Golgi tendon organ
touch and pressure

35
Q

What factors effect the speed of conduction in a nerve fibre?

A

Faster

  • larger diameter
  • myelinated
36
Q

What is the difference between white and grey matter?

A

axons myelinated when white, unmyelinated when grey

37
Q

What is the pathway through which a signal passes from sensory receptors into the spinal cord?

A
  • From sensory receptor signal carried via primary afferent nerve
  • enters spinal cord via dorsal root ganglion
38
Q

Where will faster and slower fibres synapse within the spinal lamina?

A
  • slower fibres synapse more dorsally

- faster synapse more ventrally

39
Q

Give examples of sensory pathways ascending from the spinal cord to the cortex?

A
  • spinothalamic tract
  • dorsal column
  • spinocerebeller tract
40
Q

What receptors use the spinothalamic tract?

A
  • temp
  • pain
  • touch
41
Q

Describe the spinothalamic pathway?

A
  • receptor signal passes into SC via dorsal root ganglion and synapses in dorsal region in unilateral region
  • 2nd order neurone crosses over to contralateral side and ascends on that contralateral side to the thalamus
  • 3rd order neurone carries signal from thalamus to sensory cortex
42
Q

Describe speed of conduction and sensitivity of signal in spinothalamic tract?

A
  • slower
  • poor spatial discrimination
  • crude sensation
43
Q

What receptors use the dorsal column tract?

A
  • proprioceptor
  • touch
  • vibration
44
Q

Describe the speed and sensitivity of signals in dorsal column?

A
  • good spatial discrimination
  • fine sensation
  • faster
45
Q

Describe the dorsal column pathway?

A
  • enter SC via primary neurone
  • primary neurone ascends immediately via dorsal column and synapses at dorsal column nuclei
  • 2nd order neurone crosses within brainstem to thalamus and goes to sensory cortex
46
Q

What receptors use the spinocerebellar tract?

A

proprioceptors

47
Q

Describe the spinocerebellar pathway?

A
  • 1st order neurone carries proprioceptive information from spinal cord to cerebellum via different routes
  • some can cross at spinal cord and ascend contralaterally
  • all terminate at cerebellum
48
Q

Where will sensory signals from the CS synapse in the brain?

A

Sensory cortex in posterior central sulcus

49
Q

What are resulting symptoms of damage to the ascending tracts?

A

Bilateral spinal damage (common)
- sensory loss in all modalities below lesion level
Unilateral spinal damage (rare)
- ipsilateral loss of joint sensation
- contralateral loss of temp & pain sensation
- Brown-Sequard syndrome

50
Q

What is Brown-Sequard syndrome?

A
  • damage to one side of spinal cord resulting in paralysis and loss of proprioception on ipsilateral (same) side
  • and loss of pain and temperature on contralateral side

Neurology (53 decks)

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