PHYS20008 Lecture Notes - Lecture 12: Skeletal Muscle, Myocyte, Autonomic Nervous System
12 Jun 2018
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Lecture 12
PHYS20008 - HUMAN PHYSIOLOGY
LECTURE 12
CARDIAC & SMOOTH MUSCLE
•If muscle can be moved voluntary, it is skeletal. If not, it is
smooth (if it’s not cardiac heart muscle).
•Autonomic nervous system controls cardiac and smooth
muscle.
•They are different in appearance;
•Striated means stripy basically, due to the way our
Sarcomeres line up in our thick and thin filaments, which
are slightly different colours and organised in parallel.
•Thus there are similarities between cardiac and skeletal
muscle in terms of cross bridge cycle and structure
(filaments etc).
•Smooth muscle has no striations, because the myosin and
actin filaments go in all different directions.
•There are two times of cardiac muscle: cardiac
contractile cells, in the walls of the ventricles and atrium, and nodal/
auto rhythmic/pacemaker cells, which are technically muscle fibres,
but these cells can spontaneously depolarise rhythmically.
•Cardiac contractile cells are also called myocytes, the ones in the
walls are called ventricular myocytes or myocardial cells. They look
a little different to skeletal muscle fibres, but have same set up with
thick and thin filaments. However the difference is that the AP is
begun somewhere (in the pacemaker), and then it spreads across the
heart from cell to cell, not by individual nerves between cells, but
directly between cells. This is different to skeletal muscle APs. So it
flows through the heart as a conjoined unit.
•Why do we like it to be set up this way? Because all of the cells are
contracting as a team. If we had individual neurons going to
individual cells, the cells would contract at different times and it
wouldn’t beat properly.
•Q. Ca2+ ions, which are more concentrated in the ECF, would have
a ___ equilibrium potential?
•A. Positive.
CARDIAC MUSCLE
ACTION POTENTIALS IN
CONTRACTILE CELLS
•The AP uses about 12 or 14 types of
channels. There are 2 types of Na+
channels and 3 or 4 types of K+
channel and 2 ish types of Ca2+
channels.
•The rising phase of this AP is
through voltage gated Na+ channels.
•The falling phase is through a type of
voltage gated K+ channel. The
plateau phase, delaying the
repolarisation, is due to a specific
type of Ca2+ channel, which opens !
Lecture 12
PHYS20008 - HUMAN PHYSIOLOGY
!
and Ca2+ moves in, which maintains the
plateau in the AP, until the Ca2+
channels close and it is allowed to
repolarise.
•So 250 msec is almost a 100 fold
increase in duration of its action
potential.
•We don’t want them to be too quick
anyway because it probably wouldn’t
work. So the refractory period ensures
that the cells can’t be re-stimulated for
250 msec.
•This implies that our maximum heart
rate would be 4*60 beats per minute. 240
beats per minute.
•If you put human heart stem cells in a
hamster heart, they can beat at 350 bmp
as hamsters’ usually do.
•We begin with a high K+ permeability, which is
reduced during the AP then rises at the end during
the phase.
•Plateau phase due to Ca2+, rising phase due to
Na+, falling phase due to K+. Learn shapes of the
graph."
Document Summary
Cardiac & smooth muscle: if muscle can be moved voluntary, it is skeletal. If not, it is smooth (if it"s not cardiac heart muscle): autonomic nervous system controls cardiac and smooth muscle, they are different in appearance, striated means stripy basically, due to the way our. They look a little different to skeletal muscle fibres, but have same set up with thick and thin filaments. However the difference is that the ap is begun somewhere (in the pacemaker), and then it spreads across the heart from cell to cell, not by individual nerves between cells, but directly between cells. Because all of the cells are contracting as a team. If we had individual neurons going to individual cells, the cells would contract at different times and it wouldn"t beat properly: q. Ca2+ ions, which are more concentrated in the ecf, would have a ___ equilibrium potential: a. Contractile cells: the ap uses about 12 or 14 types of channels.
