201-L38-actpsyntran-2009ND slides

201-L38-actpsyntran-2009ND slides - Objectives 1 . C o m p...

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Unformatted text preview: Objectives 1 . C o m p a r e a n d c o n tr a s t th e c h a r a c te r is tic s o f le a k c h a n n e ls a n d g a te d c h a n n e ls . C o m p a r e a n d c o n tr a s t th e c h a r a c te r is tic s o f v o lta g e g a te d , lig a n d - g a te d , a n d m e c h a n ic a lly - g a te d c h a n n e ls 2 . L is t in o r d e r th e p r in c ip a l e v e n ts a s s o c ia te d w ith a n a c tio n p o te n tia l 3 . D e f in e th e p h r a s e ‘ a ll- o r - n o n e ’ in th e c o n te x t o f th e n e u r o n a l a c tio n p o te n tia l. Objectives 4 . C o m p a r e a n d c o n tr a s t th e c h a r a c te r is tic s o f g r a d e d v s . a c tio n p o te n tia ls 5 . D is c u s s th e b a s is o f a b s o lu te a n d r e la tiv e r e f r a c to r y p e r io d s Propagation of the Action Potential 1 . E n tr y o f N a + p r o d u c e s a ‘ l o c a l c u r r e n t ’ s p r e a d s la te r a lly to d e p o la r iz e a d ja c e n t a rea s o f m em b ra n e I f t h e a d j a c e n t m e m b r a n e a r e a is d e p o la r iz e d t o ‘ t h r e s h o ld ’ it s t a r t s a n e w c y c le o f a c t io n potential in this ‘new’ region of membrane 2 . E n t r y o f N a + i n t h e ‘ n e w’ r e g i o n o f m e m b r a n e p r o d u c e s a lo c a l c u r r e n t t h a t s p r e a d s t o a d j a c e n t a r e a s… I f t h e ‘ n e w ’ a d j a c e n t m e m b r a n e a r e a is d e p o la r iz e d t o ‘ t h r e s h o ld ’ it s t a r t s a n e w c y c le o f a c t io n p o t e n t ia l in t h is ‘ n e w ’ n e w region of membrane… Na+ out in+ + local depolarization opens channels + + + + + + + + + + + electrotonic spread of depolarizing current PD these channels are ‘recruited’ these are not Na+ out in+ local depolarization opens channels + + + + + + + + + + + electrotonic spread of depolarizing current PD now these are ‘recruited’ then these Velocity of Propagation T w o F a c to r s : 1 . S iz e ( d ia m e te r o f a x o n ) 2 . ‘ M y e lin a tio n ’ Size: Bigger is Faster R e s is ta n c e to c u r r e n t flo w in ‘ a x o p la s m ’ d e c r e a s e s a s d ia m e te r in c r e a s e s Squid giant axon S p e c ie s lik e s q u id h a v e g ia n t a x o n s u s e d to tr ig g e r c o n tr a c tio n s in th e m a n tle m u s c le s , d r iv in g th e je t- p r o p e lle d e s c a p e r e s p o n s e . G ia n t a x o n s h a v e b e e n u s e d b y p h y s io lo g is ts to s tu d y a c tio n p o te n tia ls . s te lla te n e r v e m a n tle s te lla te g a n g lio n P a rt 2 : s q u id a x o n Myelination C e r ta in g lia l c e lls (oligodendrocytes a n d S c h w a n n c e lls ) fo r m in s u la tin g layer (‘sheath’) a ro u n d a xo n s 1. Na channels at node open Na+ 3. Channels at next node open myelin sheath Na+ S a lta to r y C o n d u c tio n 2. Electrotonic conduction Na+ node of Ranvier 5. Next node begins to activate channels are refractory Na+ 4. Electrotonic conduction Demyelination Demyelination e.g., Multiple Sclerosis (central) Guillan-Barre (peripheral) Demyelination Demyelination e.g., Multiple Sclerosis (central) Guillan-Barre (peripheral) Disruption of myelin sheath Demyelination Demyelination e.g., Multiple Sclerosis (central) Guillan-Barre (peripheral) Disruption of myelin sheath conduction because Na channels slowed/blocked are restricted to nodal regions In absence of myelin ‘insulation’, electrotonic conduction fails to reach and depolarize next node - AP fails! H o w is a n e le c tr ic a l s ig n a l ( A c tio n P o te n tia l) tr a n s m itte d f r o m o n e e x c ita b le c e ll to a n o th e r ? Synaptic Transmission s a m e g e n e r a l e v e n ts th a t o c c u r d u r in g N e u r o m u s c u la r T r a n s m is s io n post-synaptic cell pre-synaptic cell T h e s e ‘ p o s t - s y n a p t ic ’ e le c t r ic a l e v e n t s a r e : 1. Depolarizing (if Na+ enters) E x c ita to r y P o s t- S y n a p tic P o te n tia l: E P S P or: 2. Hyperpolarizing (if K+ leaves; or Cl- enters) I n h ib ito r y P o s t- S y n a p tic P o te n tia l: I P S P ...
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