Sensory Pathways 1 Flashcards
what are the 3 stages of senses
detection
transmission
recognition
what are the two main types of receptors
cutaneous
special senses
A alpha/ group 1
proprioceptors
A beta/ group 2
mechanoreceptors of skin
A delta/ group 3
pain temperature
C / group 4
temperature/ pain/ itch
free nerve endings
non specialist
pain
C and A delta
slowly adapting
merkel’s disks
static touch and pressure
A beta, epithelial cell and nerve fibre
slowly adapting
lips, extremities and genitals
meissner’s corpuscles
encapsulated nerve endings, dermal papillae, changes in touch and pressure, A beta
fingers, palmar and plantar surfaces
Pacini’s corpuscles
largest mechanoreceptors
onion like encapsulation of nerve endings
vibration
A beta
rapidly adapting
hands feet, nipples
hair follicle receptors
sensitive to hair movements
ruffini corpuscle
skin stretch
measures changes in length of muscle
muscle spindles
how do muscle spindles regulate muscle length
gamma reflex loop
describe the gamma reflex loop
when intrafusal fibres are stretched afferent fibres stimulate contraction of extrafusal fibres via alpha motor neurones
golgi tendon organs
detect tension in the muscle via type 1b sensory nerve endings which innervate a collagen matrixin the tendon
as the tendon stretches the endings depolaries and send information to the CNS
Where do first order neurons projects to (conscious sensory tracts)
spinal cord or brainstem
where do second order neurons project to (conscious sensory tracts)
thalamus
where do third order neurons projects to (conscious sensory tracts)
cortex (somatosensory)
intrafusal muscle fibres
proprioception
what is the function of the thalamus
conduit for all sensory information except for some olfaction
reciprocal connections to all cortical regions and can relay information, recieve feedback and modulate cortical activity
grey matter
cell bodies and dendrites
middle bit of spinal cord
information from lower body extremities
fasciculus gracilis
upper body extremities information
fasciculus cuneatus
dorsal spinocerebellar tracts
proprioceptive information from muscle spindles
ventral spinocerebellar (white matter)
proprioceptive information from golgi organs
pain transmission in white matter of spinal cord
spinothalamic tract
composed of A beta fibres fasc. gracilis fasciculus cuneatus ascend ipsilaterally synapse in the brainstem form the medial lemniscus and project to the ventral posterolateral lobe of the thalamus and then the cortex dorsal column nuclei
dorsal column medial lemniscus pathway
conveys information from the skin and joints
fasciculus cuneatus
above T6
fasciculus gracilis
below t6
what is lateral inhibition
the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction.
relies on reciprocal inhibition between two adjacent neurons
the purpose is to sharpen discrimination between two points
what can cause gait ataxia
gracile fasciculus lesion due to the brain being deprived of sensory information from lower body extremities
can be compensated with vision
what does a stamp and stick gait imply
gait or sensory ataxia
what could cause parasthesia in the distal extremities
dorsal column disease
may be from ectopic discharge in dorsal column
how can you test dorsal column function impairment
ability to feel changes in the position of toes and fingers or feel a tuning fork vibration
also Romberg’s sign- not a definitive sign
what are the cortical functions of the dorsal column medial lemniscus pathway
determine the shape of an object without sight
determine the texture of an object
requires the somatosensory association area in the parietal lobe
what is steriognosis
ability to detect 3D nature of an object and depth using touch
what does a lesion of one somatosensory association cortex cause
amorphosynthesis
patient is unaware of sensation on one side of the body, contralateral to the lesion
patient cannot localise pain and temperature but can feel it
