Sensory receptors Flashcards
what are sensory receptors
are nerve endings, often with specialized non-neural structures
What do sensory receptors induce
convert different forms of energy into frequency of Action Potentials (APs)
what is a sensory modality
a type of stimulus activating a particular receptor
what is the type of energy a receptor normally responds to called
an adequate stimulus
What are Mechanoreceptors
stimulated by mechanical stimuli
what are the mechanoreceptors in joints and muscles that signal information related to body or limb position called
Proprioceptors
What are the receptors that respond to pain
Nociceptors
Damage to the nerve by stimuli activates a generator potential which in turn opens
ion channels causing ion flow across the membrane
an adequate stimulus causes a graded membrane potential change called
receptor potential
For action potential to be fired what needs to happen
receptor potential reaches threshold
frequency coding of stimulus intensity means
the larger the receptor potential the higher the frequency of APs in sensory neurone
Merkel receptors senses
pressure and texture
Pacinanan corpuscle sense
vibration
meissners corpuscle senses
flutter and stroking movement
ruffini corpuscle senses
skin stretching
Adaption of sensory nerves is
stimulus is enough to trigger an AP, but as stimulus continues generator potential decreases so mechanoreceptor only responds to onset of stimulus
ie stimulus there but you are no longer consciously aware
Rapidly/Moderately-adapting receptors are
Pacinian corpuscles and Meissner’s corpuscles
Slowly-adapting receptors are
Merkel’s discs and Ruffini endings
Why don’t Nociceptors adapt
important not to ignore painful stimuli
Whats is the structure of Pacinian corpuscles
a myelinated nerve with a naked nerve ending,
naked nerve ending enclosed by a connective tissue capsule of layered lamella
Describe how Pacinian corpuscles respond to stimuli
mechanical stimulus deforms capsule nerve ending is stretched ion channels open Na+ enters local depolarisation generator potential reaches threshold APs fire at myelinated nerve detect stimulus ON
How does the Pacinian corpuscles show rapid adaptation
Due to fluid redistribution in the capsule, removes mechanical stretch of nerve ending, causing stimulus to disappear and AP stop firing
What can cause an AP to fire again in a Pacinian corpuscles after stimulus is applied
withdrawal of stimulus causes capsule to bring back and AP fired again
What is necessary for quick adaptation in Pacinian corpuscles and enhance sensory function
the lamella
what is the receptive field
a somatic sensory neuron is activated by stimuli in a specific area
What are the two things that tell parts of the skin apart
receptive field size
neuronal convergence
Neuronal convergence occurs when there is
sensory neutrons with neighbouring receptive fields
what can neuronal convergence stimulate
large secondary receptive field
relatively insensitive area indicated by
and example
So convergence and a large secondary receptive field
eg. fingers and lips
What is acuity
The ability to locate a stimulus on the skin and differentiate it from another close by
Example of low acuity is
two different points are stimulated but one signal is sent to the brain
What is lateral inhibition
Central neurone inhibits surrounding neighbour pathways this pinpoints where stimulus is
Inhibition of lateral neutrons enhances what
perception stimuli, awareness of where exactly stimuli is coming from
All sensory information goes to the brain then is relayed through what to what
relayed through thalamus to somatosensory cortex
What are the three things present and needed in proprioceptors
Muscle spindles
golgi tendon organs
joint receptors
What monitors muscle length and rate of change, controlling reflects and voluntary movement
Muscle spindes
Where are muscle spindles located
in the intrafusal of muscle fibres
What do golgi tendons do
tension on tendons
What is tension produced by
muscle contraction
What is the 3 functions of proprioceptors
Provide sensory information for:
Voluntary movement
spinal chord reflexes
kinaesthesia
What lies in parallel with muscle fibres
muscle spindles
What innervates end of intrafusal muscle spindle
gamma motor neurons
what innervates end of extrafusal muscle spindle
alpha motor neurons
How do afferent neurones position themselves around the muscle spindle
they spiral around
What motor neurone is smaller in diameter
gamma
How are golgi tendons arranged
in series with muscle fibres
When muscle contraction increases tension in golgi tendon sensory axon fires but why doesn’t sensory axon fire from muscle spindle
as activated muscle stays the same length therefore doesn’t activate muscle spindle
Gamma motor invasion of the muscle spindles allows
brain to be informed about muscle length
prevents spindle fibres flopping, allows them to contract
What happens to muscle spindles when muscles contracts and shortens
gamma motor neurons contract poles of muscle spindle, shortening to match the muscle fibre.
Why does the muscle spindle need to contract
to allow information to be transmitted to the brain
spindle sensitivity to stretch is maintained by
gamma motorneurons
the work of alpha and gamma is called
co-activation
What does co-activation allow
this restores tension and resets sensitivity of the central sensory part of intrafusal fibres, at a new muscle length
What are the two kinds of intrafusal fibre
nuclear bag fibres
nuclear chain fibres
Reflex contraction inhibited by
muscle spindles
Muscle contraction stretches golgi tendon organ but if excess load is applied what happens
Goligi tendon reflex causes relaxation due to motor neurone being inhibited, thus protecting muscle
