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Year 1 Semester 2 > Sensation and reflexes > Flashcards

Sensation and reflexes Flashcards

1
Q

What are cutaneous mechanoreceptors?

A

Receptors in skin that relay sensory information, specifically touch from skin surface receptors and pressure from receptors in deep tissue

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2
Q

What is glabrous skin?

A

Skin surfaces that do not have hair

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3
Q

Describe pacini’s corpuscle

A
  • Largest mechanoreceptor - 2mm long
  • Onion like encapsulation of nerve endings
  • Found in deep layers of dermis
  • Detects high frequency (40-500Hz) vibration
  • A-beta fibres - glabrous & hairy skin
  • Rapidly adapting due to a slick viscous fluid between the layers
  • Has a low activation threshold i.e is sensitive
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4
Q

Describe meissner’s corpuscle

A
  • Encapsulated nerve endings similar to pacini’s but much smaller
  • Stacks of discs interspersed with nerve branch endings
  • Found between dermal papillae - detects touch, flutter & low frequency vibration (2-40Hz)
  • A-beta fibres - glabrous skin types
  • Rapidly adapting - low activation threshold (sensitive)
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5
Q

Describe merkel discs

A
  • Non-encapsulated nerve endings
  • Consist of a specialised epithelial cell + nerve fibre
  • Found just under the skin surface in, for example, the finger tips - good discrimination - detects static touch and light pressure
  • A-beta fibres - all skin types
  • Slowly adapting - low activation threshold (sensitive)
  • Work with meissner’s corpuscles to help determine texture
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6
Q

Describe hair follicles

A
  • Embedded in skin - innervated by nerve ending wrapped around its follicle
  • Detect muscular movements of the hair (erector muscle) and external displacements of hair
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7
Q

Describe ruffini corpuscles

A
  • Encapsulated nerve ending
  • Nerve ending weave between collagen fibres which activate the nerve when they are pulled longitudinally
  • Responds to skin stretch and is located in the deeper layers of the skin as well as tendons and ligaments
  • A-beta fibres - all skin types but especially abundant in hands and fingers as well as soles of feet
  • Slowly adapting - low threshold activation (sensitive)
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8
Q

Describe muscle spindles

A
  • Main proprioceptors that provide information about the state of musculature
  • Muscle spindles lie within muscles in parallel with skeletal muscle fibres
  • Innervated by gamma-motoneurons (efferents) and group Ia and II afferent fibres
  • Afferents respond to muscle stretch while gamma-efferent activity regulates the sensitivity of the spindle
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9
Q

Describe golgi tendon organs

A
  • Main proprioceptors that provide information about the state of musculature
  • Golgi tendon organs lie within tendons in series with contractile fibres
  • Respond to degree of tension within the muscle
  • Group Ib afferent fibres relay information to CNS (particularly spinal cord and cerebellum)
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10
Q

Describe generator potential

A
  • Potential caused by a stimulus to a nerve ending

- Generates action potentials in a sensory neuron

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11
Q

Describe receptor potential

A
  • Potential caused by a stimulus to a receptor cell

- Affects amount of neurotransmitter released by receptor cell onto sensory neuron

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12
Q

Receptor potential generation in a pacini corpuscle

A
  • Tip unmyelinated - nerve fibre myelinated before leaving corpuscle
  • Compression anywhere on outside of corpuscle elongates and indents/deforms central fibre
  • Receptor potential induces local current flow (Na+ current) which spreads along nerve fibre
  • At first node of ranvier local current flow depolarizes fiber membrane at this node which sets off action potentials to CNS
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13
Q

Explain the relationship between receptor potential and action potential generation

A
  • When receptor potential (from receptor) rises above threshold in nerve fibre - action potentials fire
  • Amplitude of receptor potential increases rapidly at first then less rapidly at high stimulus strength
  • The more receptor potential rises above threshold level, the greater the action potential frequency
  • APs generated in a sensory nerve at a frequency directly related to stimulus size
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14
Q

How is the precision localisation of a particular stimulus determined?

A
  • Size of individual nerve fibre receptive field
  • Density of sensory units
  • Amount of overlap in nearby receptive fields
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15
Q

What is two-point discrimination?

A
  • Minimum distance at which two points can be perceived as distinct
  • It is a result of receptive field size and receptor density in the are
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16
Q

Where is the somatosensory cortex located?

A

In a strip posterior to the post central sulcus of the brain

17
Q

What happens at the somatosensory cortex?

A
  • Sensory information projected in a topographical manor to this area
  • Areas of higher discrimination/senses have a larger proportion of the space
17
Q

What happens at the somatosensory cortex?

A
  • Sensory information projected in a topographical manor to this area
  • Areas of higher discrimination/senses have a larger proportion of the space
18
Q

What is a reflex?

A

A specific, involuntary, unpremeditated, built-in response to a particular stimulus

19
Q

What are some examples of reflexes?

A
  • Remove hand from hot object (spinal reflex)
  • Lift foot off sharp object (spinal reflex)
  • Shutting eyes as object rapidly approaches face (cranial nerve)
20
Q

Name and describe some reflexes involving special senses

A
  • Rotatory nystagmus - Eye movements driven by moving visual images
  • Port rotatory nystagmus - Eye movements driven by the movement of fluid in the semi-circular canals of the inner ear
  • Interpretation of movement within images on the retina - used to make postural adjustments to preserve balance
21
Q

What is an example of a baroreceptor reflex?

A

Blood pressure regulation

22
Q

Describe the reflex arc

A
  • Stimulus - a detectable change in internal/external environment
  • Receptor - detects the change
  • Integrating centre - signal received (along with those from other stimulus/receptor interactions)
  • Effector
  • Response
  • Sometimes response gives negative feedback
22
Q

Describe the reflex arc

A
  • Stimulus - a detectable change in internal/external environment
  • Receptor - detects the change
  • Integrating centre - signal received (along with those from other stimulus/receptor interactions)
  • Effector
  • Response
  • Sometimes response gives negative feedback
23
Q

What are the different classes of movement?

A

Voluntary:

  • complex actions (reading, writing)
  • purposeful goal directed
  • learned

Reflexes:
-involuntary, rapid, stereotyped (knee jerk, eye blink)

Rhythmic motor patterns:

  • combines voluntary and reflex acts (chewing, walking, running)
  • initiation and termination voluntary
  • once initiated repetitive and reflexive
24
Q

What spinal cord root do sensation neurons come in from?

A

Dorsal root

25
Q

Explain spinal cord laminae

A

Lamina I-VI (dorsal horn):

  • terminations for primary afferent sensory neurons & neurons of reflex circuits
  • sensory input from joints and muscle (lamina VI)
Lamina VII (lateral horn):
-preganglionic sympathetic (T1-L2) & parasympathetic (sacral)

Lamina VIII & IX (ventral horn):
-cell bodies of motor neurons

25
Q

Explain spinal cord laminae

A

Lamina I-VI (dorsal horn):

  • terminations for primary afferent sensory neurons & neurons of reflex circuits
  • sensory input from joints and muscle (lamina VI)
Lamina VII (lateral horn):
-preganglionic sympathetic (T1-L2) & parasympathetic (sacral)

Lamina VIII & IX (ventral horn):
-cell bodies of motor neurons

26
Q

Organisation of the spinal cord

A
  • Alpha-motor neuron cell bodies lie in clumps within ventral horn of spinal cord (lower motor neurons)
  • Each motor neuron activates a motor unit (6-1500 skeletal muscle fibres)
  • Some axons branch back into cord and synapse with interneurons called Renshaw cells (recurrent or feedback inhibition)
  • Suppresses weakly firing motor neurons and dampening strong firing ones
  • Produces economical movement
  • Importance reflected in strychine poisoning - disables Renshaw cell inhibition - leads to convulsions
27
Q

Explain a myotatic (knee jerk) reflex

A
  • Example of a monosynaptic stretch reflex
  • Tap of patellar tendon stretches quadriceps muscle
  • Stimulates dynamic nuclear bag receptors of muscle spindle
  • Increase in 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 knee joint
28
Q

Muscle spindles and voluntary activity

A
  • Muscle spindles play important role as comparators for maintenance of muscle length during foal directed voluntary movements
  • Voluntary changes in muscle length initiated by motor areas of brain, orders include changes to set-point of muscle spindle
  • Simultaneous activation of extrafusal fibres (alpha-motor neurons) and intrafusal fibres (gamma-motor neurons) is called alpha-gamma-co-activation
29
Q

Explain the inverse myotatic (golgi tendon) reflex

A
  • -Protective to prevent tearing of muscle/detachment of tendon
  • Contributes to maintenance of posture
  • GTO stimulated by increasing tension in muscle
  • Signals transmitted to spinal cord - reflex entirely inhibitory
  • Negative feedback mechanism which prevents development of excessive tension in muscle
  • Inhibitory effect from GTO can be so great leads to sudden unloading of muscle
30
Q

Explain the withdrawal reflex and crossed extensor 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
31
Q

Describe the process of the withdrawal reflex and crossed extensor reflex

A
  • In the leg that feels the pain, the reflex inhibits -in the spinal cord - the motor neurons to the extensor muscle and stimulates the motor neurons to the flexor muscle
  • In the opposite leg, the reflex stimulates - in the spinal cord - the motor neurons to the extensor muscle and inhibits the motor neurons to the flexor muscle
32
Q

What is the central pattern generator?

A
  • Located in spinal cord - capable of autonomous signals
  • Modulated by proprioception input
  • Thought to be inflated by mesencephalic locomotor region - output through reticular nuclei and reticulospinal tracts
33
Q

Central pattern generators for walking

A
  • 2 half centres which activate flexors and extensors respectively and which mutually inhibit each other
  • Can be modelled using inhibitory 1a interneurons and renshaw cells

Year 1 Semester 2 (26 decks)

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