central nervous system Flashcards
what is the corticospinal pathway involved with?wh
controlled and fine tuned movements. descending motor pathway from primary motor cortex.
crossing over of axons occurs in medulla or brainstem. this means left part of brain controls right side of the body, this is called contralateral control.
what is the brainstem pathway involed with
involved in coordinating large groups of muscle at once. generally used for posture and something we are not conciously thinking about.
!!doesnt cross over to the other side, ipsilateral.
what is a stretch reflex
maintains muscle length. initiated by stretch receptor (muscle spindle). causes contracting to resist further stretching and bringing muscle back to normal length.
monosynaptic arc vs polysynapitic arc
monosynaptic- sensory neurons can directly excite motor neurons
polysynaptic- to inhibit motor neurons an sensory neuron will activate an inhibitory interneuron.
what is a tension reflex
to regulate muscle force. initiated by golgi tendon organ. causes relaxation to prevent excessive force and potential injury.
what is a withdrawal reflex
to move away from painful stimulus. initiated by pain receptors, causes withdrawel of affected limb.
what are interneurons
they can be excitatory or inhibitory and are important for relaying information. they also innervate motor neurons and facilitate movement during a reflex:
- relax opposing muscle groups
-coordinate muscles on the contralateral side.
can the somatotopy map change?
yes, it is plastic and is able to change as sensory demands in the body may change.
larger area on the map= areas that require fine motor control.
what is transduction?
when a sensory stimulus is converted into a electrical signal in the nervous system
merkles corpuscle receptive field vs pacinian corpuscle receptive field
merkles- superfiscial receptors will a small receptive field
pacinian- more for heavy touch, large receptive field but this means that it doesnt have the ability to distinguish where the pain has come from.
what do free nerve endings detect?
pain
where are action potentials at mechanoreceptors transduced?
at the first node of ranvier.
what are rapidly adapting receptors and what are some examples of them?
only respond briefly to a stimulis, good for detecting movement and changing pressure
meissners and pacinian corpuscles
what are slowly adapting receptors and what are some examples of them?
respond slowly throughout a stimulus, good for signalling during the duration of the stimulus.
merkles disks and ruffini corpuscles
temperature gates ion channels
detect temperature but also touch and pain.
different receptors are activated at different temperatures, can also be activated by ligands.
very small receptors.
what is intensity coding?
stronger stimuli, more receptors are activated there is more depolarisation. therefore more action potentials and signals to the brain
what is lateral inhibiton?
a mechanism used to increase accuracy of sensory information
mediated by inhibitory neurons. neurons close together inhibiting action potentials around it so that only action potentials from the area of the stimulis are firing.
this means that the area of sensation will be localised at the area of the stimulis.
what is the dorsal column pathway for and where do the axons cross over?
fine touch and proprioception, crossing over occurs at the brain stem
what is the anterolateral pathway for and where do the axons cross over?
pain and temperature, crossing over occurs in the spinal cord.
where are noiceceptors (free nerve endings) not found?
in the brain
charactaristics of C nerve fibres
smallest diametre, unmyelinated axons
have a slow conduction velocity
they signal ongoing damage
dull throbbing pain
A delta fibre charactaristics
small diametre myelinated axon
faster conduction velocity
small receptive field
sharp pain
what do mast cells release and what does the release of this chemical cause?
they release histamines
histamines work in an inflammatory response which causes an area to become red and swollen
inhibition of pain pathway:gate control theory
inhibitory interneurons in the spinal cord can reduce transmission between neurons so less of the signal makes it to the brain therefore decreasing the sensation of pain.
