NAS W3 - sensory & motor neuron Flashcards
EXTEROCEPTORS
receive info from world around us (our senses)
INTEROCEPTORS
receive stimuli from world inside us
RECEPTIVE FIELD
- area innervated by a single neuron
- sensitive ares = smaller receptive field
RECEPTING STIMULUS TYPES
each sensory receptor responds to only one type of stimulus (e.g. firm/soft touch) but at a range of different intensities (labeled line - one nerve always ends in one effector and all its branches end there too)
RECEPTOR ADAPTATION
- when receptors stop continuously triggering AP even though stimulus is constant
- frees up our attention & resources to attend to other stimuli
PHASIC RECEPTORS
receptors that adapt rapidly (changing quickly helps give us instant updates on rate of change of stimulus/stimulus intensity)
TONIC RECEPTORS
receptors that adapt slowly & inform about duration & strength of stimulus
ADEQUATE STIMULUS
type of energy to which a stimulus is most sensitive
SENSE ORGANS
structure containing sensory receptors (to receive stimulus) & sensory nerve fibres (convey specific impulses to CNS)
TYPES OF MECHANORECEPTORS OF SOMATIC SENSORY SYSTEM
- Meissner receptor - transmit sensations of light, fine touches (rapidly adapting)
- Merkel receptor - slowly adapting & are between epithelial cells & respond to maintained stimulation
HOW SENSORY RECEPTORS IN PERIPHERY (side) INFORM BRAIN ON WAG1 IN/OUT BODY
action potentials conveyed from periphery to brain via sensory neurones
PACINIAN CORPUSCLE (PC)
- normally, stretch mediated sodium ion channels around neurone too narrow for sodium ions to pass through
- when pressure applied to PC, it is deformed & membrane around neurone stretches which widens sodium channel so ions can now diffuse into neurone
- influx of sodium ions leads to generator potential which creates nerve impulse that goes to CNS
- if stimulus is maintained, rings slide over each other, effectively damping energy of stimulus
MAJOR UNIT
single somatic efferent (motor-neurone) & all muscle fibres it supplies
USES OF SKELETAL MUSCLE
- movement (when one muscle contracts, other relaxes)
- heat genesis (as 80% wasted as heat energy)
MYOCYTE
single cell of muscle
TISSUE ENVELOPES OF SKELETAL MUSCLE
- ENDOMYSIUM (surrounds myocyte) PERIMYSIUM (surrounds fascicle) EPIMYSIUM (surrounds all fascicles & also the neurovascular bundle)
- neurovascular bundle binds nerves & veins with connective tissue
APONEUROSIS
tissue sheet that takes place of tendon in flat muscles
TENDON
tough band of fibrous connective tissue that brings together single contractions of myocytes to produce combined action at single point
MYOFIBRILS
- myocytes are made of myofibrils
DARK V LIGHT BANDS
light bands are only actin but dark bands are overlap of actin & myosin
PROCESS OF MUSCLE CONTRACTION IN MYOFIBRILS
- Neurotransmitter released from neuron & binds to receptors which depolarises membrane of muscle fibre in SR
- AP travels down T-tubules & opens calcium stores so CA2+ diffuses to myofibrils from reticulum (SR)
- CA2+ bind to troponin which causes tropomyosin molecule to move & expose myosin binding sites so myosin binds to actin on binding sites
- ATP hydrolysed to cause myosin heads to bend so actin pulled along & myosin remains attached until we attach ATP to each myosin head so it detaches from actin site
CHARACTERISTICS OF MOTOR UNIT
- each muscle cell supplied by only 1 motoneuron
- muscle cells of motor unit randomly distributed throughout muscle so if certain number of muscle cells are active & contracts, the whole muscle does not just one side of it
TETANIC CONTRACTION
muscles activated with very high frequency of stimuli to form tetanic (smooth) contraction not a jerking one like in single twitch or summation
INTRAFUSAL MUSCLE FIBRE
- Myocyte inside muscle spindle
- contract to change signalling of afferent nerves (update brain on muscle movement)
EXTRAFUSAL MUSCLE FIBRE
- myocyte outside of muscle spindle
- contract for movement
TEST TO SEE RELATIONSHIP BETWEEN MOTOR NEURONE (A-NEURONE) & MUSCLE FIBRE
type S motoneuron was connected to type FF muscle fibre vice versa & the result was that FF changed biochem properties & became type S vice versa
HOW WE HAVE PROPRIOCEPTION & KNOW LOCATION OF STIMULI
we code location and code where our receptors are to make maps of sensory space in our brain
NMJ
- synapse between motor neuron & muscle cell (NMJ is tuned for rapid transmission
- many synaptic vesicles in active zone of presynaptic terminal (way more than usual)
- junctional folds & lots of receptors in postsynaptic for more SA
WHY NMJ ALWAYS WORKS
- so many quanta (vesicles each containing hundreds of AcH molecules) released in presynaptic
- junctional folds & lots of nACH receptors
ROLE OF CA2+ IN EXCITATION-CONTRACTION COUPLING
- Ca2+ conc outside cell > inside so AP happens in presynaptic & depolarisation opens volatge gated Ca2+ channels
- Ca2+ enters presynaptic terminal & triggers vesicles to fuse with presynaptic membrane & release AcH in quota to synaptic cleft
- AcH binds to ionotropic nAcH receptors on postsynaptic (receptor has 2 AcH binding sites so 2 bind at a time)
END PLATE POTENTIAL (EPP)
- achieved when many EPSP collect together & depolarisation reaches threshold
- initiates AP in muscle (regularly passes threshold as so many Na+ channels)
- EPP decays as it moves away from end-plate (as nAcHR absent away from synapse)
MYASTHENIA GRAVIS
- autoimmune disease on nAcHR (so less of them at NMJ) identified by rolled back eyes (as leads to flaccid weakness of affected muscles (resp. failure is resp. muscles)
- seen on graph as decreased muscle firing (as not enough receptors activated)
- treated by giving AcH esterase inhibitors to prolong signal
thin/thick filaments
- thin filament made of actin (anchored to Z-line)
- thick filament made of myosin (anchored at M-line (centre of sarcomere))
- (sarcomere shortens from both sides when actin filaments slide along myosin filaments)
