Sensory and Proprioception Flashcards
What are the three types of sensory receptors?
Mechanoreceptors, proprioceptors, nociceptors
What is the role of mechanoreceptors?
Stimulated by mechanical stimuli on skin - e.g. touch and pressure
What is the role of proprioceptors?
Stimulated by mechanical stimuli in joints and muscles
What is the role of nociceptors?
Stimulated by painful stimuli - damage to tissue
How are sensory receptors triggered by stimuli?
An adequate stimulus will cause local stretch ion channels to open, causing a graded potential/ flow of ions which will reach a node of ranvier and cause depolarisation, leading to an action potential.
What determines if an Action potential will fire and how many
The level of stimulus. Low stimulus may not produce any action potentials, high stimulus may produce many.
How can we figure out duration and strength of stimulus?
Looking at the pattern of action potentials produced
What does ‘adaptation’ mean in relation to receptors?
Whether the receptor continues to produce action potentials in response to a stimulus, or adapts to a new ‘normal’ and stops producing action potentials. E.g. when we put socks on
What are the 4 skin touch receptors?
Pacinian corpuscle (fast), Merkel receptors (f), Ruffini corpuscle (s) and Meissner corpuscle (s)
Which type of receptor does not adjust?
Nociceptors - because it is important to feel painful stimuli
What is the structure of the pacinian corpuscle?
A naked myelinated nerve ending encapsulated by a lamellae capsule with several layers, and liquid between each layer
How does the pacinian corpuscle adapt to stimuli?
Mechanical stimulus deforms capsule and causes the nerve to stretch, so stretch ion channels open and cause Na+ to flow, which depolarises and causes AP at first node of ranvier. This tells brain about stimulus, and then the liquid redistributes in the lamellae to minimise deformation, so AP’s stop firing. When stimulus is removed, liquid flows and ions spread again, so AP’s occur again.
What is the importance of capsules in sensory receptors?
Cause AP’s to stop firing. Without them they wouldn’t.
What is a receptive field and what is its importance?
Its a area of skin which is associated with 1 sensory neuron, which synapses on 1 CNS neuron. Smaller receptive fields are found on more sensitive parts of the body, like lips and fingers, while large ones are found in less sensitive areas, like the back.
What its the 2-point discrimination test?
Tests 2 adjacent points until we perceive 2 separate neurons rather than 1. Closer points = more sensitive
What is convergence?
Neighbouring receptive fields may summate to 1 secondary neuron if they’re close together. High convergence = Less sensitive.
How do convergence and acuity relate?
High convergence = low acuity and vice versa. Acuity is ability to differentiate between close points skinned locate a stimulus
What is lateral inhibition?
When neuron closest to stimulus inhibits neighbouring neurons to allow us to identify exact point of stimuli
What happens to sensory info from receptors?
Relays from skin, so primary sensory neuron, to secondary CNS neuron in spinal cord, to the thalamus and finally to the somatosensory area in the parietal lobe
What are the main receptors involved in proprioception?
Muscle spindles, golgi tendon organs (GTO’s) and joint receptors
What do muscle spindles do?
Measure muscle length and rate of change of length
What do golgi tendon organs do?
Measure tension on tendons and muscles
Extrafusal vs Intrafusal muscle fibres?
Extrafusal innervated by alpha-motor neurons, Intrafusal innervated by gamma-motor neurone. Most are extrafusal, intrafusal ones have their own sensory receptors and contained in capsule called muscle spindles. Extrafusal and Intrafusal are parallel
What are the 2 types of intramural fibre?
Nuclear bag fibres (many nuclei collected together|) and nuclear chain fibres (many nuclei in chain).
What must be present for a contraction to occur and how is it related to muscle spindles?
Sarcomeres. These aren’t found in the centre of muscle swindles so it centre doesn’t contract - it stretches instead.
What are the 2 kinds of sensory nerve found in the centre of muscle spindles?
Ia - annulospiral and II - flower spray endings
What happens when a muscle is stimulated
The ends of intramural fibres with sarcomeres are contracted by gamma motor neurons. This causes central section to stretch, which opens stretch-sensitive ion channels and creates a local generator potential, and nervous impulse leaves from Ia annulospiral sensory neuron.
How do Golgi tendon organs communicate with the brain?
When muscle contracts, tendons are stretched, causing tension. This sends a message from II afferent fibres (flower spray endings) to the brain
What is the importance of gamma motor neurons?
Without them, we wouldn’t be able to tell the brain about the length of our muscles, or tension. Muscle would be useless
What is Frequency Coding?
The rate that action potentials is determined by the size of stimulus. Fast discharge of action potentials lead to more powerful muscle movement
