Locomotor System Flashcards
what is meant by calcium activated calcium release
calcium channels opened at +35mV L-type channels, causes calcium to move into cytoplasm, calcium in the cytoplasm then generates release of more calcium from sacroplasmic reticulum
what activates calcium release from the SR
calcium binding to ryanodine receptors in skeletal, smooth and cardiac muscle, but also IP3 receptors in smooth muscle
how is calcium removed from the cytoplasm of the cell
re-uptake by the SR through serca receptors, or exchanging calcium out of the cell for sodium into the cell - NCX receptors
how does Calcium allow for contraction in skeletal and cardiac muscle
calcium binds to troponin C subunit, which changes the orientation and moves the tropomyosin away from the actin binding site, exposing this to myosin
how does calcium allow for contraction in smooth muscle
calcium binds to calmodulin, this complex this activates myosin light chain kinase, allowing it to phosphorylate myosin, allowing it to bind to actin
explain the cross bridge cycle in muscle contraction
myosin not bound to actin, bound to ATP molecule, muscle relaxed but myosin head cocked. myosin hydrolyses ATP to bind to actin, releases an inorganic phosphate. then generates a power stroke, shortening the sacromere and releasing ADP. muscle contracted but myosin head relaxed. then for muscle relaxation, ATP required to pull myosin head off of the actin
describe an abnormality of muscle physiology
when RyR are leaky, constantly releasing calcium into the cytoplasm, can get random contractions of muscle. also, Ca cytoplasm conc. increased so removal of Ca by NCX, SR levels of Ca constantly reduced, leads to inability to contract muscle due to lack of Ca - duchennes muscular dystrophy
describe the structure of a sensory neuron
pseudounipolar - has one cell body with 2 axons, one axon projects to periphery with nerve endings, one axon projects to central nervous system
what sensory information must be conveyed
quality, intensity, location and duration
how do we know the quality of a sensation
different receptors are activated for different types of sensation - nociception for pain, mechanoreceptors for touch
what is the receptive field
the area a neurone innervates, has nerve ending receptors in this location providing this area with sensory neurones
what is two point discrimination and how can this differ in different regions of the body
the minimum distance at which two points of touch can be felt as separate. areas with smaller two point discrimination have a higher density of neurones and a higher cortical representation, fingers, lips
how is an action potential generated in response to a sensation
mechanoreceptors - touch and pressure changes the membrane and opens a channel to allow influx of ions
chemoreceptors - either ligand gated which a ligand directly opens a channel or g-protein, ligand activates g protein which in turn opens a channel
how is the intensity of a stimuli detected
increased firing codes for a higher intensity, a lot of neurones recruited and increased frequency of action potential off the back of another means a higher intensity
how is the duration of a stimuli detected
the length of time an action potential is generated either slowly or rapidly adapting
what is the different types of axons and what are these used for
a alpha - motor neurones and sensory 1A fibres
a beta - mechanoreceptors
a delta - nociception and temperature
c fibres - pain temperature and itch
describe the pathway for mechanoreception from the body
the sensory afferents enter through the dorsal horn and immediately ascend through the medial lemniscal dorsal column pathway. first order neurons travel to the brainstem where they synapse to second order neurones. these then travel dessicate to the thalamus to synapse to 3rd order neurones which go to the cortex
describe the pathway for nociception from the body
these enter the dorsal horn of the spinal cord and synpase to 2nd order neurons. these then cross over to the other side and travel to the thalamus via the spinothalamic tract. at the thalamus, 3rd order neurones are activated and these travel to the cortex
how are the sensory pathways arranged
modality specific
what are the different types of pain
nociceptive, clinical - acute and chronic
describe nocicpetive pain
this is in response to tissue damage, a protective mechanism for us to remove ourselves from the stimulus, a delta or c fibres, high threshold and limited duration
describe acute pain
similar to nociceptive, in response to inflammation, prostaglandins and bradykinin activate receptors, protective function
describe chronic pain
serves no protective function, due to damage in a nerve, activated despite no stimuli or damage, spontaneously activates pathway, not responsive to treatment
how is pain located
each spinal nerve gives rise to a dermatome, an area of the body that it innervates, when this nerve is activated it travels to a specific area of the cortex in the sensory homunculous so the location can be noted
what is referred pain
when the damage is at one area of the body but the pain is felt elsewhere, due to embryological development
what are the different peaks in the pain activation
first peak - activation of a beta in response to touch
second peak - activation of a delta fibres in response to pain - sharp pain
third peak - activation of c fibres, dull pain - different latencys due to different myelination and diameter
How can perception of pain be dampened down
by rubbing the effected area, this activates mechanoreceptors and a beta fibres, this then travels to spinal cord where most travel up DCML pathway, but some come off and activate inhibitory interneurones, to inhibit the STT tract - reduced pain
what are the cardinal signs of inflammation
redness, heat, swelling, pain, loss of function
what are the 3 things in the triple response
red line, wheal and redness
what is the wheal in the triple response
this area is white and is swollen, due to oedema, inflammatory exudate moving in to deal with the trauma
what is the red area in the triple response
this area is not swollen or raised, just red due to dilation of blood vessels
what are the main features of the reflex movements
stereotyped response, short latency, no cortical in put even with conscious control, monosynaptic circuit involving peripheral nerve and spinal cord/brainstem
what is required for a reflex movement
stimuli, receptor, sensory nerve, motor nerve, effector organ, response
what nerve fibres are involved in the reflex response
A alpha fibres for both sensory and motor
how is posture maintained
stretch in muscle is detected by proprioceptors, this then activates muscle 1A afferents, enters dorsal horn, synapses to motor neurone, causes contraction of muscle
describe the tendon jerk reflex
tapping the tendon causes stretch of the muscle, activating muscle spindle receptors which activates muscle 1A afferent fibres, enter dorsal horn and synapse to efferent to cause contraction
how does the ankle tendon and jaw tendon reflex differ
the same mechanism but the jaw has a much shorter latency, as it is closer to the brainstem, the circuit is shorter so happens much faster. but the ankle has a bigger response as the muscles recruited are stronger
describe the gag reflex
sensory receptors on soft palate are activated, this activates glossopharyngeal nerve which travels to spinal trigeminal nucleus, then synapse and activate vagal nerve to cause contraction of pharyngeal constrictors on both sides
how does the reflex movement prevent muscle overloading
muscle overloading is detected by golgi tendon receptors, activates IB muscle afferents, this are inhibitory neurones and inhibit the motor neurones at the spinal cord, stops muscle contraction
how is overloading of the jaw detected and controlled
in jaw, no golgi tendon receptors, instead, PDL detects the loading of the jaw muscles and feeds back to the muscles of mastication and trigeminal nerve to control force of biting
what is the jendrasik manoeuvre
clasping the hands, this activates the corticospinal tract, meaning motor neurones are closer to their action potential even if theyre not being used, so when the reflex loop comes in to synapse, more neurones are recruited meaning more muscle fibres can be contracted - higher magnitude of response
what controls semi-automatic movements
central pattern generator - generates a rhythm
what provides feedback for semi-automatic movements
environment, effector organ, conscious control from cortex
how many neurones are involved in motor pathways
2 - one upper, from cortex, one lower from brainstem or spinal cord
describe the corticobulbar pathway
motor cortex activates upper motor neurone, travels to the brainstem, synpases at trigeminal nucleus, vagal, glossopharyngeal, hypoglossal, facial, this then activates the lower motor neurone which travels to the muscle to generate contraction
describe the corticospinal pathway
motor cortex generates upper motor neurone, these travel to the medullary pyramids where they decussate - 85% do, 15% do not - stay on same side. those decussated form the lateral pathway, the others form the anterior pathway. then travel to the correct level of the spinal cord for activating the lower motor neurones
how might the upper motor neurones be damaged
stroke
what would be the result of upper motor neurone damage
not able to generate voluntary movements but still have reflexes, often more reinforced
how might the lower motor neurones be damaged
nerve damage, trauma
what would be the result of lower motor neurone damage
unable to generate any type of movement, even reflexes, muscle atrophy
