nervous system L21-26 Flashcards
3 sub-divisions of the somatosensory system
cutaneous
visceral
proprioception
function of touch sense
recognition and properties of things
control of movement
communication
steps in converting stimulus energy into action potentials
- sensory transduction
- action potential generation
sensory transduction
stimulus converted into a graded electrical potential/ receptor potential
depends on stimulus strength
action potential initiation
receptor potential exceeding threshold> action potential of nerve fibres
stimulus strength coded by firing rate
cutaneous receptors
superficial (merkel’s disc/ epidermal-dermal border/ free nerve ending/ meissner’s corpuscle)
deep (pacinian corpuscle/ ruffini’s corpuscle)
skin receptors defined by
location
size and structure
rapid/slow adaptation
size of receptive field
types of nerve fibres connecting to skin receptors
A-beta large diameter myelinated fibres
A-delta small diameter myelinated
C fibres small diamter unmyelinated
receptive field
area over which stimulus activates receptor associated w single neurone/ nerve fibre
rapidly adapting receptors
firing at stimulus onset
highlights appearance of new stimuli/ stimulus change
slowly adapting receptors
nerve continues firing action potentials throughout stimulus
pacinian corpuscle mechanical property changes
capsule present> rapid adaptation of receptor potential
capsule not present> less adaptation of receptor potential
pacinian corpuscle capsule
onion-like layers w fluid in between
rapid adaptation
allows for v rapid vibration
temp receptors
warm > C fibres
cold > A-delta fibres
nociceptors
noxious/ painful stimuli
mechanical/ thermal
sharp pain A delta followed by C fibre burn following
somatosensory system in rodents
modifiable (one-to-one anatomical relationship)
accessible (easy to perform targeted functional measurement)
2 pathways transmit cutaneous signals to the brain
dorsal column pathway
spinothalamic tract pathway
dorsal root ganglion
cell bodies of primary sensory nerve fibres
fibres enter spinal chord at root
nucleus
cluster of neurones in CNS w shared properties
dorsal column pathway
first synapse in dorsal column nuclei in medulla
decussation at medulla level L to R cortex / R to L cortex
dorsal column info carried
fine-discrimination touch
stimuli moving over skin surface
recognition of objects by touch
lateral inhibition in dorsal column
^stimulus contrast and therefore edges and form of tactile objects
fibres from neighbouring receptive fields inhibit one another
spinothalamic tract functions
coarse touch
temp
nociception
flexion/ extension
flexion> contract flexors and relax extensors
extension> relax flexors and contract extensors
synergists / antagonists
synergists> muscles pulling in same direction
antagonists> muscles pulling in opposite directions
neurones innervating muscle
large neurones
alpha motoneurones
in ventral horn of spinal chord
motor unit
motoneurone and muscle fibres it innervates
large motor unit
innervates many muscle fibres
strong force and little precision
lifting/ holding weight
small motor unit
innervates only a few muscle fibres
fine control more precision
finger muscles for manipulating objects
upper motoneurones
cerebral motor cortex/ brain stem
command and control
basis of voluntary control for movement
interneurones in spinal chord
excitatory and inhibitory
important for spinal movement programmes
muscle spindle
receptor type
intrafusal fibres in parallel w extrafusal fibres
innervated by 1a afferents going to spinal chord
extrafusal muscle fibres
do work of contraction
golgi tendon organ
receptor type in series w extrafusal fibres
1a afferent fibre of muscle spindle receptor
carries output signal of receptor to spinal chord
gamma motorneurones in controlling muscle spindles
alpha-gamma coactivation
keeps spindle firing constant and in operating range even though muscle contracts
golgi tendon organs
activated by muscle tension
innervated by 1b nerve afferents
types of movement
reflex (simple movement)
voluntary (complex/ may be learned)
rythmic (initiated and terminated by conscious control, automatic pattern in spinal chord)
reflexes
one sensory and one motor neurone reflex arc
spinal/ cranial origin
monosynaptic/ polynaptic
stretch reflex
monosynaptic> maintains contraction w increased load
golgi tendon reflex
protection against excessive load for control of posture