Sensory receptors

Question 1

what are sensory receptors

Answer 1

are nerve endings that inform your brain about the internal and external environment. convert different stimuli into frequency of action potentials so are transducers

Question 2

3 types of sensory receptors

Answer 2

proprioceptors, mechanoreceptors, nociceptors

Question 3

sensory modality

Answer 3

stimulus type that activates a particular receptor eg touch, pressure, joint angle, pain

Question 4

adequate stimulus

Answer 4

form of energy to which a receptor normally responds

Question 5

what is a mechanoreceptor

Answer 5

stimulated by mechanical stimuli, pressure, strength, deformation, give us skin sensations of touch and pressure

Question 6

what are proprioceptors

Answer 6

mechanoreceptors in joints and muscles. they signal information about body or limb position

Question 7

what are nociceptors

Answer 7

respond to painful stimuli

Question 8

how are sensory receptors specific

Answer 8

highly sensitive to one specific energy form but they can be activated by other intense stimuli

Question 9

what is a receptor potential

Answer 9

adequate stimulus causing a graded membrane potential change

Question 10

what is the adequate stimulus in cutaneous mechanoreceptors and proprioceptors

Answer 10

membrane deformation- activates stretch sensitive ion channels. ions flow across the membrane and change the membrane potential locally

Question 11

how is receptor potential graded

Answer 11

by stimulus intensity. stimulus triggers ions to flow through membrane locally and when depolarisation reaches the area with voltage gated ion channels (first node of Ranvier), action potentials start firing

Question 12

what electrodes measure change in membrane potential

Answer 12

those at receptor membrane and first node of ranvier

Question 13

why is it important that some mechanoreceptors experience a drop off in APs if stimulus persists

Answer 13

the brain can process new or changing events eg taking off or putting on clothes. some receptors only signal the onset of a stimulus

Question 14

which receptors do not adapt

Answer 14

nocireceptors

Question 15

pacinian corpuscle

Answer 15

senses pressure and vibration. mechanoreceptor comprised of a myelinated nerve and a naked nerve ending. mechanical stimulus deforms the capsule and nerve ending, stretches and opens ion channels, sodium influx causes depolarisation, APs generated and myelination begins.

Question 16

how can pacinian corpuscle adapt

Answer 16

depends on capsule surrounding. can rapidly adapt by fluid between lamellae distributes, spreading stimulus impact out, minimising deformation which causes the stop of nerve endings stretching so APs stop firing. if stimulus withdrawn, the capsule lamellae spring back like suction force and Ap fire again

Question 17

receptive field

Answer 17

a specific area where a somatic sensory neurone is activated by stimuli

Question 18

ability to tell 2 points apart on the skin is measured by

Answer 18

two points discrimination test- the receptive field size and neuronal convergence

Question 19

neuronal convergence

Answer 19

if there is a single path to the brain or more than one that merge

Question 20

simultaneous sub threshold stimuli effect

Answer 20

can merge together and sum together at the secondary neuron, forming a larger secondary receptive field and initiating APs (two pencils test)

Question 21

acuity

Answer 21

ability to locate a stimulus on the skin and differentiate it from another close. low acuity means one signal goes to brain instead of two when there is two stimuli- caused by high convergence

Question 22

lateral inhibition

Answer 22

enhances perception of stimulus and means you can localise the central point of a stimulus precisely by receptors at edge of stimulus being more strongly inhibited than receptors near centre

Question 23

where does sensory information go

Answer 23

to the brain, relayed via the spinal cord to the thalamus and on to the somatosensory cortex

Question 24

proprioceptors include

Answer 24

muscle spindles, Golgi tendon organs, joint receptors

Question 25

3 things that proprioceptors do

Answer 25

control our voluntary movements, generate spinal reflex movements, perceive limb and body position and movement in space= kinaesthesia

Question 26

muscle spindles

Answer 26

intrafusal muscle fibres that have their own sensory and motor innervation. contained within a capsule. lie in parallel with muscle fibres

Question 27

two types of intrafusal fibre

Answer 27

nuclear bag fibres, nuclear chain fibres

Question 28

what part of intrafusal fibres contain contractile sarcomeres

Answer 28

ends not central area so when they fire the two ends contract and shorten but the central area does not so it therefore gets stretched out

Question 29

what motoneurones cause contraction of intrafusal fibres

Answer 29

gamma

Question 30

annulospiral endings

Answer 30

formed by primary endings of 1a afferent nerves wrapped around centre of intrafusal fibres

Question 31

how is the brain informed by joint position

Answer 31

spindle and joint receptors. muscle stretch stimulates spindle stretch receptors. stretch sensitive ion channels open, create a local generator potential which causes regenerative action potentials in the 1a afferent fibres

Question 32

what does Golgi tendon organ do

Answer 32

lie in series with extrafusal muscle fibres. monitors muscles tension by using stretch receptors and monitoring stretch of tendon. muscles have to develop tension by contracting to stretch the tendons. if contraction, the nerve endings of GTO stretch and initiate APs in group 1b afferent fibres from the GTO

Question 33

what happens if an alpha motor neurone fires without gamma

Answer 33

extrafusal muscle contracts and shortened but intrafusal muscle stays the same length so spindles go slack so 1a spindle sensory firing would decrease

Question 34

alpha-gamma coactivation

Answer 34

alpha motoneurons are activated causing contraction, gamma motoneurons are activated in parallel to maintain spindle sensitivity. makes sure brain is informed on movements and position of our body in space