Since sections share property names eg. a length called :data:`L` it is always necessary to specify which section is being discussed; this is done using dot notation, e.g.
dendrite[2].L = dendrite[1].L + dendrite[0].L
axon.v = soma.v
print(soma.gnabar)
axon.nseg *= 3
This notation is necessary when one needs to refer to more than one section within a single statement.
Many NEURON functions refer to a specific Section. In recent versions of NEURON,
most of these either are available as section methods or take a section or segment
directly. For older code or for the remaining exceptions, the active section may
be specified using a sec=
keyword argument.
For example:
my_iclamp = h.IClamp(0.25, sec=soma) # better to use h.IClamp(soma(0.25)) though
num_pts_3d = h.n3d(sec=apical) # could get the same value as an int via apical.n3d()
If no sec=
keyword argument is specified, the functions will use NEURON's
default Section (sometimes called the currently accessed section),
which can be identified via h.cas()
.
The default Section is controlled by a stack; it is initially
the first Section created but entries may be pushed onto or popped off of the
stack by the following commands. Use this only as a last resort.
.. function:: pop_section Syntax: ``h.pop_section()`` Description: Take the currently accessed section off the section stack. This can only be used after a function which pushes a section on the section stack such as ``point_process.getloc()``. Example: .. code-block:: python from neuron import h soma = h.Section(name='soma') apical = h.Section(name='apical') stims = [h.IClamp(soma(i / 4.)) for i in range(5)] + [h.IClamp(apical(0.5))] for stim in stims: x = stim.get_loc() print("location of %s is %s(%g)" % (stim, h.secname(), x)) h.pop_section() (Note: in this example as ``nseg=1``, the current clamps will either be at position 0, 0.5, or 1.) (Note: a more Pythonic way to get the location of the point-process ``stim`` is to use ``seg = stim.get_segment()``, but this is shown as an example of using ``h.pop_section()``.)
.. function:: push_section Syntax: ``h.push_section(number)`` ``h.push_section(section_name)`` Description: This function, along with ``h.pop_section()`` should only be used as a last resort. It will place a specified section on the top of the section stack, becoming the current section to which all operations apply. It is probably always better to use :class:`SectionRef` or :class:`SectionList` . :samp:`push_section({number})` Push the section identified by the number returned by ``h.this_section()``, etc. which you desire to be the currently accessed section. Any section pushed must have a corresponding ``h.pop_section()`` later or else the section stack will be corrupted. The number is not guaranteed to be the same across separate invocations of NEURON. :samp:`push_section({section_name})` Push the section identified by the name obtained from sectionname(*strdef*). Note: at this time the implementation iterates over all sections to find the proper one; so do not use in loops. Example: .. code-block:: python from neuron import h soma = h.Section(name='soma') apical = h.Section(name='apical') # get a number to allow pushing by number soma_id = h.this_section(sec=soma) # push by name h.push_section('apical') # push by number h.push_section(soma_id) # RuntimeError -- no such section h.push_section('basal') .. seealso:: :class:`SectionRef`