Sensory receptors Flashcards
Sensory receptors are described as transducers, why?
Convert external energy to a number/frequency of AP
A certain amount of energy is needed to make a sensory receptor respond.
What is the term used to describe this?
Adequate stimulus
What is sensory modality used to describe?
The type of stimulus that the receptor responds to
ie touch, temperature etc
What are mechanoreceptors used for?
Stimulated by pressure, stretch, deformation
Used for hearing, balance, pain, blood pressure, touch etc
What is the name given to mechanoreceptors that are found in bones and joints, and signal the body about limb position?
Proprioceptors
proprioception - sense of bodily position
Nociceptors respond to what type of stimulus?
Pain, heat and tissue damage
Sensory receptors are often described as cutaneous. What does cutaneous mean?
Skin
These receptors sense stimuli acting on the skin
Cutaneous mechanoreceptors and proprioceptors sense stimulus using a specific type of ion channel. Describe what it is and how it works.
Stretch sensitive ion channels
Adequate stimulus causes membrane deformation ∴ ion channels open ∴ ion flow causes change to local membrane potential
Explain what is wrong with this statement.
An adequate stimulus causes graded potentials to travel along the receptor to the first node. At the first node, Voltage gated ion channels exist. Provided the depolarisation reaches the VG channel, action potentials will fire.
First part correct
However, APs will only fire if the depolarisation is strong enough to reach threshold
Aside from frequency of action potentials, what reflects the intensity of a stimulus?
Number of receptors activated per unit area
Free nerves are often wrapped around the roots of hair. These attach to what type of receptor, and what is the system used to sense?
Pacinian corpuscle
Senses vibrations
Nerves at hair root sense movement of hair
The Ruffini corpuscle is a type of sensory receptor, used to respond to what?
Stretches in the skin
Merkel receptors are present in the epidermis. What is their function?
Steady pressure
Texture
What type of receptors are used to detect ‘stroking and fluttering movements’?
Meissner’s courpuscles
True or false
All mechanoreceptors are designed so that if a stimulus persists, they basically ignore the stimulus unless there is a change.
False
Only some mechanoreceptors do this
What is adaption of mechanoreceptors?
Mechanoreceptors only responding to onset of stimulus
Then will only respond to change or a novel event
Why is it important that nociceptors do not show adaptation to stimulus?
Nociceptors respond to painful stimulus
Important not to ignore painful stimuli
Receptors can be categorised as rapidly adapting or slowly adapting.
Pacinian corpuscles and meissner’s corpuscles are classed as what type?
Rapidly adapting
Describe the structure of Pacinian corpuscles.
Capsule made of connective tissue
Layered membrane lamellae with fluid between
How does the pacinian corpuscle respond to stimulus?
Mechanical stimulus deforms capsule
Stretch ion channels opened ∴ Na+ flow
Depolarisation ∴ generator potential
If threshold, AP fired where the myelination begins
Why does the structure of pacinian corpuscles allow rapid adaptation?
Stimulus = deformation due to vertical force
Redistribution of internal fluid dissipates force
Vertical force effectively gone ∴ ion channels close
No GP ∴ no AP ∴ no feeling
In terms of the pacinian corpuscle, the non-neural component refers to what?
The CT capsule
Anything that isn’t the nerve
Presynaptic neurons often exhibit neuronal convergence. Why is this useful in terms of summation?
Multiple sub-threshold stimuli can synapse onto a secondary neuron and cause APs
large receptive field
What does lots of convergence and a large secondary receptive field indicate about the sensitivity of an area?
Insensitive
What is the 2-point discrimination test?
Distance between points adjusted until two points can be felt, not one
What is acuity?
The ability to locate a stimulus on the skin, and differentiate it from another closeby
What is the relationship between neuronal convergence and acuity?
High convergence = low acuity
In lateral inhibition, what happens to the surrounding sensory neurons to where the stimulus is applied?
Stimulated sensory neuron inhibits the surrounding neurons to stop them firing despite being slightly stimulated
Why is it important that inhibitory interneurons use a different neurotransmitter from the other neurons?
Specific to inhibition
Otherwise signals would be confused
Where does most lateral inhibition take place?
Spinal cord
What do muscle spindles do?
Monitor muscle length and rate of change of muscle length
Reflexes + voluntary movements
What organs are used to monitor the tension on tendons?
Golgi tendon organs
What do joint receptors monitor?
Joint angle
Rate of angular movement
Tension on the joint
Which receptors are involved with spinal cord reflexes?
Muscle spindles
Golgi tendon organs
Where would you find intrafusal muscle fibres?
Muscle spindle
The capsule encasing muscle spindles is made out of what tissue?
Connective tissue
What is the difference between alpha and gamma neurones in terms of the muscle fibres they link to?
Alpha = extrafusal
Gamma = intrafusal
In the muscle spindles, there are two types of nuclear fibres. What are they?
Nuclear bag fibre
Nuclear chain fibre
Which is thicker, alpha axons or gamma axons?
Alpha
What are annulospiral endings?
Primary endings from 1a afferent nerves wrap around the intrafusal fibres
What is the arrangement of contractile sarcomeres in intrafusal fibres?
Sarcomeres contained in ends of intrafusal fibres
Not in centre
What type of ion channels are in the type 1A afferents that surround the fibres in the muscle spindle?
Stretch sensitive
Describe the relationship between the velocity of spindle stretching, and frequency of generated potentials.
Proportional
The faster the stretch - the higher the frequency of APs
True or false
The difference between the initial length and final length of spindle informs about the muscle length.
True
Example
How would the AP frequency look from the afferent neurones surrounding nuclear bag fibre during contraction, when compared to relaxed?
Frequency is lower when contracted
Less stretched ∴ lower frequency
Describe what happens to the AP frequency in the neurones in the golgi tendon organs during contraction.
AP frequency increases with load
Tendons stretched more ∴ more APs
What type of afferent neurones innervate tendons?
1B
A muscle contracts but it’s length stays the same. What happens to the 1A and 1B neurones, in terms of Action potentials?
1B fires because tendons stretched
1A does not fire because muscle length unchanged
Why is it important that gamma motoneurons fire to contract the intrafusal fibres at the same time as alpha motoneurons fire?
So that intrafusal fibres shorten to match the shortening of the extrafusal fibres.
This means the sensory gamma neurones stay active
