Sensory Receptors Flashcards
What is the definition of sensory receptors?
They are nerve endings that act as transducers
What is the function of transducers?
They convert energy into frequency of APs
What is the function of sensory receptors?
They inform the CNS about the internal and external environments
What does sensory mobility mean?
A type of stimulus that activates a specific receptor
What is meant by adequate stimulus?
The type of energy a receptors responds to
What are receptive fields?
A specific area that activates a sensory neurone
What is neuronal convergence?
Many presynaptic neurones converging into a few postsynaptic membranes
What is lateral inhibition?
The process by which stimuli is located, which occurs in the spinal cord
What is cortical space?
The location of brain sensory receptors. The more sensitive the area, the larger the cortical space
What is meant be acuity?
How the sensitive areas of the skin detects 2 different points due to neuronal convergence and receptive fields
What are the properties of sensory receptors?
Very specific to one type of energy form, adaptive and can process receptive fields
When do sensory receptors generate a signal?
Due to change
What are mechanoreceptors?
Receptors that are stimulated by mechanical stimuli and can detect stimuli e.g. pacinian capsule
What is a proprioceptor?
A mechanoreceptor in the joints that provides information about the anatomical position e.g. muscle spindle and GTO
What is a nociceptor?
Receptors that respond to pain
What are thermoreceptors?
Receptors that respond to temperature changes
What are photoreceptors?
Receptors that respond to changes in wavelength of light
What are chemoreceptors?
Receptors that respond to changes in pH
What is transduction?
The opening or closing of ion channels
What are cutaneous receptors?
Nerve endings that are protected by a capsule and cause membrane deformation due to adequate stimulus
What does membrane deformation activate?
Stretch-sensitve ion channels which allow ions to flow across the membrane by voltage gated channels
What are ion channels?
Channels that exist in the distal tip on sensory neurones and release neurotransmitters to create a potential in the axons’s dendrites
What is a receptor potential?
Graded to stimulus intensity
What is the difference between mechanoreceptors and nociceptors?
Nociceptors can adapt
What is frequency coding?
The bigger the stimulus, the bigger the receptor potential and the bigger the AP frequency
What switches stimuli on and off?
Pacinian capsule
What happens when the pacinian capsule is removed?
Can no longer adapt so continues to produce a generator potential
When is a generator potential at its highest?
At the start and at the end
What is lateral inhibition?
The process by which the pathway closest to the stimulus inhibits neighbouring pathways ignorer to get a better idea of the stimulus
What is the function of a muscle spindle?
Monitor muscle length and the rate at which it changes, control reflex and voluntary movements and provide sensory information about your body’s position
What is Kinaesthesia?
Knowing your anatomical position
How is muscle length monitored?
When muscles contract after adequate stimuli which opens ion channels. This creates a local generator potential which releases APs who the muscle stretches and the ion channels open
What is the structure of a muscle spindles?
They lie in parallel with muscle fibres and are made of intrafusal fibres contained in a capsule
What are skeletal fibres made out of?
A mix of intrafusal and extrafusal fibres
What is contained within intrafusal fibres?
Contractile sarcomeres at both ends of the fibre, which can contract due to gamma motor neurones
How are APs released form muscle spindles?
When the sarcomeres contract the middle part is stretched which releases APs
What are the 2 types of intrafusal fibres?
Nuclear bag fibres and nuclear chain fibres
What is the mechanism for efferent control?
When agonists contract, antagonists relax and the joint moves
What happens to the spindle when agonists stretch?
Spindle discharge increases
What happens to the spindle when antagonists stretch?
Spindle discharge decreases
How can spindles allow signals to be sent to the brain?
Alpha motor fibres fibre which cause the extrafusal fibres to contract and then in order to not let the spindle slack, the gamma motor neurones are activated which contracts the sarcomeres so the spindle matches the contracting muscle, which allows signals to be sent to the brain
What is the function of alpha motor neurones?
Cause contraction when activated
What are the function of gamma motor neurones?
They are activated by alpha motor fibres and maintain spindle sensitivity to stretch
What does the co-avtivation of alpha and gamma motor neurones allow?
Voluntary movements
What is the function of the GTO?
It monitors muscle tension by monitoring stretch receptors in tendons
How is tension increased?
Isometric muscle contractions fire 1b sensory axons but muscles stay the same length as 1a sensory axons don’t fire
How can GTO monitor stretching in tendons?
Tedons are inelastic so the muscles must develop tension to stretch them, so this tension can be recored
What is the structure of GTO?
Nevre endings of GTO are mixed with the tendons at the ends of muscles and they are in series with muscle fibres
