Receptors Flashcards
What is the role of a sensory receptor?
Reserve information from the environment and pass it to sensory neurons which transmit the information to the brain
What are stimulus modality?
The range of different sensory stimuli
What is adequate stimulus?
The sensory stimuli used by one receptor
What are the three types of sensory receptor?
Mechanoreceptors - touch and pressure
proprioceptors - Joints and muscles
Nociceptors- Pain
Describe the differences in response of mechanoreceptors to stimuli
- Adaptive. Only fire potentials when the stimuli starts and when it ends or when there is a change in stimuli. There ae rapidly and slowly adapting receptors.
- Non-adaptive. Continues firing APs as long as the stimuli is present.
How do Pacinian corpuscle work?
It is contains a myelinated nerve with a naked nerve endingIt is enclosed by a connective tissue capsule of layered membrane lamellae and each layer is separated by fluid ( it is a bit like a spongy onion).
Mechanical stimulus deforms (i.e. when pressure pushes down on the cell and changes its shape) the capsule and the nerve ending.
The nerve ending is stretched and opens ion channels.
Na+ influx causes local depolarisation (a receptor/generator potential ) which passes the threshold generating and firing and action potential.
Fluid rapidly redistributes within capsule lamellae, this spreads the stimulus impact out laterally minimizing downward deformation so APs stop firing. This gives Pacinian corpuscles a rapid adaption. If the capsule is lost then the adaptive power is lost which is not good.
As stimulus is withdrawn - capsule lamellae spring back which causes another AP to fire. This means that the start and end of the stimulus is detected.
What is acuity?
The ability to locate a stimulus on the skin and differentiate it from another.
Some parts of the body will have high acuity while others will have low acuity.
Low acuity is a result of high levels of convergence.
Can be tested using the 2 point discrimination test.
What is lateral inhibition?
Therefore we can say that lateral inhibition “sharpens or cleans up” sensory information
What are the different types of proprioceptors?
Muscle spindles - Monitor muscle length and rate of change
Golgi tendon organs - Monitor tension in tendons
joint receptors - Monitors joint angle
What is kinaesthesia?
The ability to perceive limb and body position and movement in space.
Describe muscle fibres ?
They contain extrafusal and intrafusal muscle fibres.
The extrafusal fibres are skeletal muscle and the intrafusal fibres are proprioceptors.
Muscles fibres can either be nuclear bag or nuclear chain.
Muscle fibres are innervated at there ends by gamma motors.
Ia innervates the middle and II innervates the ends of nuclear chain.
When muscles contract in order to retain tension in the intrafusal muscle fibres alpha (extrafusal) and gamma (intrafusal) muscle fibres must contract together.
What are golgi tendon organs ?
They have nerve endings that mingle with the tendons. Innervated by Ib.
What is a stretch reflex?
i.e. a hammer hits the knee. This causes a very fast contraction of the muscles in the knee including the intrafusal muscle fibres. It causes an afferent nerve to go to the spinal chord causing a signal to return to the intrafusal muscle fibres causing muscle activation and it will also feed to the antagonist muscle to cause inhabitation of it. This is known as reciprocal inhibition.
What is an inverse stretch reflex?
When the Golgi tendon organs send signals to the brain to stop agonist contraction as a way of protecting itself.
What are flexor or withdrawal reflexes?
Movement of the body away from painful stimuli.
How can reflexes be overridden?
Consciously by sending EPSPs which cancel out the IPSPs.
What is facilitation?
The enlargement of a response beyond the summation of the parts.
What are hydrophobic signals?
Signalling molecules which can go into the cells. They bind to intracellular receptors.
I.e. nitric oxide which binds to guanylyl cyclase and generate cGMP as a 2ns messenger. Or steroid hormones which bind to a transcription factor.
What are the four types of hydrophilic receptor?
Receptor-channels. Ionotropic i.e. nicotinic
G proteins coupled. metabotropic.
Receptor-enzyme. i.e. insulin receptors
Integrin receptors. Interact with the cytoskeleton.
What are the three ways in which G proteins work?
- Couples to ion channels
- Couples to adenylyl cyclase.
- Coupled to phospholipase C.
Describe the process of G protein coupled to adenylyl cyclase
Coupling with adenylyl cyclase causes the production of cAMP which regulates protein kinase A which phosphorylates target proteins.
Describe the process of G protein coupled to phospholipase C.
Activated PLC produced IP2 which releases Ca2+ which phosphorylase target protein. It also produces DAGs which activate PKC which phosphorylates proteins.
Where is Ca2+ coming from?
Internal stores
Outside
Inhibition of exit
What is Ca2+ used for?
Cross bridge cycle in smooth and skeletal muscle
Used to bind to targets protein
What is pharmacology?
The study of the way living systems are affected by chemical agents.
What are drugs made from?
Natural products
Synthetic
biotech
Gene therapy
What is a drug?
A chemical agent that affects the biological system
What is affinity?
The strength of a chemical attraction between a drug and a receptor
What is EC50 ?
The drug concentration at half the max response. Low EC50 high affinity.
What is efficacy?
How good a drug is at activating a receptor
What are the types of drug ?
Full agonist Partial agonist Antagonist Seelctive agonist Selective antagonist
