Sensory Receptors Flashcards
What is the function of sensory receptors?
They inform your brain about external and internal environment.
What do sensory receptors turn stimuli into?
The frequency of action potentials.
Name three tyes of sensory receptor.
Mechanoreceptors, proprioceptors and nociceptors.
Describe mechanoreceptors.
Stimulated by mechanical stimuli - pressure, stretch, deformation - give us skin sensations of touch and pressure
What are proprioceptors?
Mechanoreceptors in joints and muscles. They signal information about body or limb position
Describe nociceptors.
Respond to painful stimuli
What receptors are found in the nose and tongue?
Chemical receptors.
What receptors are found in the ears?
Sound and position receptors
What receptors are found in the eyes?
Light receptors
What receptors are found in the skin?
Touch, pain, temperature and pressure receptors.
What is sensory modality?
The stimulus type that activates a particular receptor: eg. touch, pressure, joint angle, pain
What is an adequate stimulus?
The form of energy to which a receptor normally responds.
Minimum amount of energy required.
What does sensory receptor transduction involve?
The opening and closing of ion channels.
What is receptor potential/ generator potential?
When an adequate stimulus causes a graded membrane potential change (only a few mV) –
What is the adequate stimulus in cutaneous mechanoreceptors and proprioceptors?
Membrane deformation.
What does membrane deformation activate?
Activates stretch-sensitive ion channels – so ions flow across the membrane and change the membrane potential locally.
When do action potentials start firing?
When depolarisation reaches the area with voltage-gated ion channels (the first node of Ranvier)
How does stimulus intensity impact the production of action potentials?
Lowest stimuli intensity=no action potentials
Highest stimuli intensity= most action potentials
In a sensory nerve, a larger stimulus…?
Causes a larger receptor potential and a higher frequency of action potentials (frequency coding of stimulus intensity).
The info from the receptors on the skin depends on what?
The properties of nerve endings and of accessory, non-neuronal structures
Why do nociceptors not adapt?
As they detect pain due to the free nerve endings, it is important not to ignore pain generated.
Describe the Pacinian corpuscle.
Mechanoreceptor
It comprises a myelinated nerve with a naked nerve ending
enclosed by a connective tissue capsule of layered membrane lamellae
each layer is separated by fluid : (a bit like a spongy onion)
How does the Pacinian corpuscle respond?
- A mechanical stimulus deforms the capsule and the nerve ending
- This stretches the nerve ending and opens ion channels
- Na+ influx causes local depolarisation - a receptor/generator potential
- APs are generated and fire where myelination begins (because regenerative Na+ channels cluster at nodes of Ranvier)
What component of sensory receptors mean that you can feel an itch?
Receptive fields
->a somatic sensory neuron is activated by stimuli in a specific area called the receptive field
A touch-sensitive neuron in the skin responds to pressure within a defined receptive field (area of skin)
What is the Pacinian corpsule?
Sensory receptors for vibration and deep pressure and are essential for proprioception
Our ability to tell 2 points apart on the skin is measured by the…?
Two point discrimination test.
The ability for the two point discrimination test depnds on two things. Name them.
Receptive field size
Neuronal convergence.
What is the two point discrimination?
Two-point discrimination is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one.
WWhat is transduction?
Change from external energy into internal action potentials in known as transduction
What does the Pancinian corpusle sense?
Senses vibrations
What are proprioceptors?
Mechanoreceptors that signal body or limb position
Name three proprioceptors.
Muscle spindles
Golgi tendon organs
Joint receptors.
Name the three functions of receptors.
- Control voluntary movement
- Generate spinal reflex movement
- they provide sensory information to perceive limb and body position and movement in space = kinaesthesia.
What do muscle spindles monitor?
Monitor muscle length and rate of change of muscle length - they control reflexes and voluntary movements..
What do Golgi tendon organs monitor?
Tension on tendons
Discuss lateral inhibition.
Receptors at edge of a stimulus are more strongly inhibited than receptors near centre
enhances the contrast between relevant and irrelevant information.
Briefly describe the pathway of info from the body to the brain.
Info relayed by spinal cord -> thalamus -> somatosensory cortex
There are a few specialized muscle fibres have their own sensory and motor innervation…what are they called?
Intrafusal muscle fibres.
Name the two types of intrafusal fibre.
Nuclear bag fibres and nuclear chain fibres
Describe the structure of nuclear bag fibres and nuclear chain fibres.
Nuclear bag fibres- bag shaped w nuclei collected together
Nuclear chain fibres- nuclei lined up in a chain
Muscle fibres are multinucleated..what does this mean?
More than two nuclei.
What motor neurons have a smaller diameter- gamma or alpha?
Gamma
How does spindle information contribute to perception of body position and movement?
Joint movement is organized by groups of muscles working in opposition ie. agonists and antagonists (eg. biceps and triceps)
When agonist contracts, antagonist relaxes and the joint moves
Stretching the agonist joint…
Contracting the agonist joint…
…increases spinal discharge
…decreases spinal discharge
Stretching the antagonist joint…
Contracting the antagonist joint…
…decreases spinal discharge
…increases spinal discharge
How muscles develop tension?
Contracting to stretch the tendons as this stretches the nerve endings of the GTO and
initiates APs in the group 1b afferent fibre from the GTO (Golgi tendon organs).
How do muscle spindles lie and how to Golgi tendon organs lie?
Muscle spindles- in parallel.
GTOs- in series.
What is the significance of the gamma motor innervation to the contractile ends of muscle spindles?
Allows muscle fibres to change length and fire action potentials.
What would happen if an Alpha motor neuron fired without gamma?
What can joint receptors monitor?
Joint angle, rate of angular movement and tension on the joint
Which are more contractile- intrafusal or extrafusal muscle fibres?
Extrafusal
What kind of innervation can intrafusal muscle fibres provide?
Motor and sensory
How is joint movement organised?
By groups of muscles working in opposition- when the agonist contracts, the antagonist relaxes and the joint moves :)
Are tendons affected by passive stretch?
No as are inelastic
How do muscles develop tension?
By contracting to stretch the tendons
