Unit 3-Nervous System
Excitable Tissue
electrical/ionic properties of
·
cell membrane
=
membrane potential (resting) negative (potassium) electrical potential (voltage) associated with the cell membrane of an excitable
cell at rest ,
changes in this membrane potential influence conduction or action
·
higher intracellular potassium (cation) phosphate/protein Canions
-
the K
+
concen .
gradient favors movement of+out of cell
-
diffusion of +down its concen . becomes opposed by the charge on the outside of membrane
-
anionic molecules such as proteinssphosphates (nucleotides) cannot cross the membrane
sodium chloride outside cell
high
·
relatively impermeable to Nat
-
Gated on channel proteins induce changes in the membrane potential
-
Types of changes
·
-
depolarization : membrane potential becomes ⑪
hyperpolarization membrane potential becomes
-
:
·
Gated Channels ->
open : /or close in response to specific stimuli
-
Chemically :
chemical stimuli /hormones neurotransmitters
,
or certain ions
voltage changes in regional membrane potential
-
:
-
mechanically : mechanical stimuli (vibration , pressure)
Ungated Channels (leakage channels
·
Signal propagation in excitable tissue
·
-
Graded potentials >
-
changes in membrane potential caused by a stimulus (electrical, mechanical ,
or chemical
·
Mum
can be stimulatory (depolarizing) inhibitory (hyperpolarizing
·
or
mem
vary in magnitude
·
·
travel short distances with
dissipating magnitude
·
display summation
-
temporal :
freg of stimuli is
higher
spatial more than one stimulant act nearly simultaneously
-
:
sources
Action potential
-
characteristics >
-
self-propagating changes in mem potential transmitted long distance "all-or-none"
·
.
,
over ,
sequence of events
·
Dynamic nervous system
Mmmmmmmmm
, Positive Feedback in action potential
·
·
Nat entry during an action potential creates G feedback loop
the loop stops when the Nat channel inactivation
gates close
·
Voltage-gated Nat channel
·
there activation that
is an
gate rapidly open
: an inactivation
gate that is slower to close
Propagation
⑳
Me
Voltage-Gated Potassium Channel Refractory periods following an action potential
spec
I
·
a
Graded Potential vs Action Potential in Neurons
Mum
mem
I
Graded Potential
regenerationPotentiagnal
↓
in put signal
Typesofsignaa usually dendrites? cell body trigger zone thro axon
mechanically chem, or vot, are voltage-gated channels
Gatedion channels
involved , ,
Nat, K +, Caz sk +
+
Na+
Types of signal Depolarizing (Nat) depolarizing
I
peds on stimulus can he somma all or none" ; cannot be summed
a stengthofsigna
,
entry of ions thru channels above threshold to open channels
characteristics No min reg to initiate initial stimulus threshold stim reg to initiate
unique
. .
,
-
strength indicated by fregof series of
action potential
Excitable Tissue
electrical/ionic properties of
·
cell membrane
=
membrane potential (resting) negative (potassium) electrical potential (voltage) associated with the cell membrane of an excitable
cell at rest ,
changes in this membrane potential influence conduction or action
·
higher intracellular potassium (cation) phosphate/protein Canions
-
the K
+
concen .
gradient favors movement of+out of cell
-
diffusion of +down its concen . becomes opposed by the charge on the outside of membrane
-
anionic molecules such as proteinssphosphates (nucleotides) cannot cross the membrane
sodium chloride outside cell
high
·
relatively impermeable to Nat
-
Gated on channel proteins induce changes in the membrane potential
-
Types of changes
·
-
depolarization : membrane potential becomes ⑪
hyperpolarization membrane potential becomes
-
:
·
Gated Channels ->
open : /or close in response to specific stimuli
-
Chemically :
chemical stimuli /hormones neurotransmitters
,
or certain ions
voltage changes in regional membrane potential
-
:
-
mechanically : mechanical stimuli (vibration , pressure)
Ungated Channels (leakage channels
·
Signal propagation in excitable tissue
·
-
Graded potentials >
-
changes in membrane potential caused by a stimulus (electrical, mechanical ,
or chemical
·
Mum
can be stimulatory (depolarizing) inhibitory (hyperpolarizing
·
or
mem
vary in magnitude
·
·
travel short distances with
dissipating magnitude
·
display summation
-
temporal :
freg of stimuli is
higher
spatial more than one stimulant act nearly simultaneously
-
:
sources
Action potential
-
characteristics >
-
self-propagating changes in mem potential transmitted long distance "all-or-none"
·
.
,
over ,
sequence of events
·
Dynamic nervous system
Mmmmmmmmm
, Positive Feedback in action potential
·
·
Nat entry during an action potential creates G feedback loop
the loop stops when the Nat channel inactivation
gates close
·
Voltage-gated Nat channel
·
there activation that
is an
gate rapidly open
: an inactivation
gate that is slower to close
Propagation
⑳
Me
Voltage-Gated Potassium Channel Refractory periods following an action potential
spec
I
·
a
Graded Potential vs Action Potential in Neurons
Mum
mem
I
Graded Potential
regenerationPotentiagnal
↓
in put signal
Typesofsignaa usually dendrites? cell body trigger zone thro axon
mechanically chem, or vot, are voltage-gated channels
Gatedion channels
involved , ,
Nat, K +, Caz sk +
+
Na+
Types of signal Depolarizing (Nat) depolarizing
I
peds on stimulus can he somma all or none" ; cannot be summed
a stengthofsigna
,
entry of ions thru channels above threshold to open channels
characteristics No min reg to initiate initial stimulus threshold stim reg to initiate
unique
. .
,
-
strength indicated by fregof series of
action potential
