Peripheral Sensory Systems Flashcards
what is the overview of the CNS
what are the sensory systems
visual, auditory, vestibular, olfactory, taste, temperature, pain, touch/pressure/movement
some overlap between senses and stimuli (pain and temperature)
what are the types of sensory receptors
- mechanoreceptors
- chemoreceptors
- thermal receptors
- photoreceptors
- pain receptors
what do sensory sytems have
sensory fields –> cover a defined area (ex. skin)
stimuli passed by sensory afferent –> overlap of fields can assist in localization of stimuli
how is sensory information percieved with a primary afferent merge on a single secondary afferent
perceived as single point
good for sensitivity
graded potential
how are stimuli percieved with a primary afferent associated with several secondary afferent
two distinct stimuli felt and localized
poor sensitivity but good localization
what is lateral inhibition
five primary afferents and stringer stimuli to B
neuron B has a strong impulse onto the secondary neuron
secondary can have an inhibitory effect on its neighbours
this can suppress the impulse passing through A and C
produces a sharp response signal
improves localization and pattern recognition
what are the skin senses
cold, heat, pain, pressure, kinesthesia (move joint)
dorsal roots are organized in orderly way to different areas (strips) of skin
what are free nerve endings
mainly in hairy skin
not specific to a particular stimulus
what is terminal encapsulations
hairless skin (ex. palmar/plantar surfaces)
mostly mechanoreceptors –> pacinian (local pressure), ruffini (tension in collagen fibres), merkels (deformation of skin), meissners (sideways shearing)
not all specific (shearing of skin will also stimulate pacinian and meissners)
what are thermal receptors
free nerve ending encapsulated endings
two types –> hot and cold
two sensors required to differentiate temperature
at extreme temps activate pain receptors
also have paradoxical cold receptor
what is sensory adaptation
maintain stimulus, response declines
most senses show adaptation and will be complete (smell, touch) or partial (temperature)
prevents overload
what are the mechanism of adaptation in pacinian corpusle
most often adaptation is due to inactivation of ion channels
pacinian corpuscle and a little different
fluid within layers that surround the central neuron
pressure applied and passed to sensory neuron
redistribution of fluid to ease pressure and give adaption
what are the two types of receptors in the muscle
- muscle spindles –> in parallel with muscle fibres
- golgi tendon organs –> in series with muscle fibres
what are muscle receptors important for
proprioception
knowledge of position and movement of head/limbs and attitude and motion
through reflexes they are also important for posture
what are muscle spindles
resemble extrafusal fibres but –> 1. smaller 2. innervation is from gamma motor neurons (to ends of fibre) 3. importantly they have sensory type Ia and II fibres
sensitive to muscle stretch
what are the types of sensory fibres
type Ia fibres are adaptive
type II fibres are largely non-adaptive
muscle spindle important for postural reflexes so important not to have adaption
what will gamma motor stimulation cause
contract the ends of the muscle spindle
alters sensitivity of spindle to stretch
alpha and gamme fibres act together
what is alpha/gamma co-activation
important to maintain sensitivity to stretch if there is alpha motor stimulation
if alpha only spindle becomes flaccid and lose sensitivity
with both –> intra and extrafusal both contract and maintain sensitivity
what does gamma stimulation also activate
sensory afferents and changes sensitivity of the muscle spindle
activation of the gamma neurons contracts the muscle spindle
this leads to stretch of the intrafusal fibres and firing of sensory afferents
what is the myotatic reflex (stretch reflex)
muscle spindles also give rise to myotatic reflex
stretch muscle –> stretch spindle –> activates sensory afferent –> activates a motor neuron
simple but important postural reflex –> muscle stretch causes reflex contraction of that muscle
what is the golgi tendon organ
situated within the tendon
responds to tension in muscle –> stretch or contraction
free nerve ending lie within the tendons
gives rise to type 1b sensory fibre
gives rise to inverse myotatic reflex –> also postural
what are central projections
both the golgi and muscle spindle project in same way to CNS
enter at T1-T3 and synapse at Clarkes column
projects to cerebellum –> cerebellum is co-ordination centre for movement
sensory input to this pathway can originate from different levels of spinal cord
