ML1 General Properties of Sense Organs Flashcards by blue sky

Charge

imbalance between positive and negative particles

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Current

flow of eletrically charged particles

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Voltage

potential difference between two points

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Electric potential

work required to move a charge (charged particle) from a reference point to a specified point

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Membrane potential

voltage of the cell i.e. the difference between charges inside and outside the cell (difference in charge across the membrane)

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Stimulus

change detectable by the body

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Modality

energy form of the stimulus

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Classes of nerve fibres

Aα, Aβ, Aγ, A𝛿, B and C

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Group IA and IB afferents are which class?

Aα

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Group II afferents are which class?

Aβ

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Group III afferents are which class?

A𝛿

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What size are Aα fibres?

15 microms

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What size are Aβ fibres?

12-14 microms

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What size are Aγ fibres?

8-10 microms

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What size are A𝛿 fibres?

6-8 microms

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What size are B fibres?

2-5 microms

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What size are C fibres?

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At what speed do Aα fibres conduct?

60-100 m/s

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At what speed do Aβ fibres conduct?

30-60 m/s

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At what speed do Aγ fibres conduct?

15-20 m/s

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At what speed do A𝛿 fibres conduct?

10-15 m/s

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At what speed do B fibres conduct?

3-10 m/s

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At what speed do C fibres conduct?

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What are the functions of Aα fibres?

the large motor axons - muscle stretch and tension sensory axons

What are the functions of Aβ fibres?

touch, pressure, vibration, joint position

What are the functions of Aγ fibres?

gamma motor neurons - muscle contraction

What are the functions of A𝛿 fibres?

sharp pain, very light touch, temperature

What are the functions of B fibres?

sympathetic preganglionic motor axons (sometimes sensory visceral)

What are the functions of C fibres?

temperature and dull, aching, burning pain

Which nerve fibre classes are myelinated?

(usually) all except group C

Two factors that affect conduction velocity

axon diameter (wider = faster) and myelination (myelinated = 50x faster)

Myelin

membrane component from glia (mixture of phospholipids & proteins) which surrounds and insulates axons of the CNS and PNS

Nodes of Ranvier

gaps in myelin where the membrane is uninsulated | this is where sodium channels are and where the AP can be propagated

Which cells provide myelination?

CNS - oligodendrocytes | PNS - Schwann cells

Sensory info comes in through the _ root

dorsal

Motor info goes out through the _ root

ventral

Five sensory modalities

vision, hearing, olfaction, gustation, somatosensation

Four somatosensory submodalities

touch, proprioception, temperature, pain

Five receptor types

mechanoreceptors, chemoreceptors, thermoreceptors, nociceptors, photoreceptors

Receptive field

particular region of a sensory space that will trigger firing of the neuron

Tactile acuity

distance between receptive fields

Factors affecting receptive field

connectivity (convergence, divergence or inhibition)

Special senses

senses detected by a specialised organ i.e. vision, olfaction, hearing/balance, gustation

General senses

senses that aren't sensed by a specialised organ i.e. touch, pain, temperature, proprioception, pressure, vibration

Special sense receptors

receptors of the special senses that use receptor potentials

Free nerve endings

modified endings of afferent neurons that act as receptors for the general senses by using generator potentials

Receptor potential

Stimulus activates the receptor. The receptor transmit a chemical messenger which opens the LGICs of the afferent neuron which then transmits an AP.

Generator potential

Stimulus activates the modified nerve ending of the afferent neuron which then activates the VGICs of the afferent neurons causing it to transmit an AP.

Transduction

Conversion of energy forms to electrical signals via a generator potential

Adaptation

Change in sensitivity to a long-lasting stimulus | Tonic or phasic

Tonic receptors (def, e.g., receptor type)

Slowly adapt (or don't at all) Pain, body position, chemical composition of blood and CSF Proportional receptors

Phasic receptors (def, e.g., receptor type)

Quickly adapt Pressure, touch, sound, smell Differential receptors

How is quality of stimulus determined?

Number of APs transmitted | Number of sensory receptors activated

Adaptation mechanisms

Chemical - inactivation of channels | Mechanical - slipping of layers of specialised nerve ending

In the DCML pathway the first order neuron synapses on the second order neuron in the _

medulla

In the DCML pathway the second order neuron synapses on the third order neuron in the _

thalamus

In the ST pathway the first order neuron synapses on the second order neuron in the _

spinal cord

In the ST pathway the second order neuron synapses on the third order neuron in the _

thalamus

Tactile acuity can be measured by...

two-point touch discrimination (minimum distance at which two points are perceived as separate)