Cardiovascular system (cardiac and smooth muscle) Flashcards
what stops the myosin head from binding to actin ?
Tropomyosin
why are cardiac muscle cells striated ?
because of the alternating thick and thin myosin fliaments
what are intercalated disks?
made of three types of cell-cell junctions: 1. Fasica adherens
- Desmosomes
- Gap junctions
What are Fasica adherens?
They are anchoring sites for intracellular actin filaments which connect to integrins ( membrane bound proteins) which connect to fibronectin. Fibronectin can act acts as bridges connecting integrins to proteglycans complexes (collagen and carbohydrate). This anchors the cell to it’s extracellular matrix and plays and important role in cell signalling.
What are desmosomes ?
Stop the separation during contraction by binding intermediate filaments via cadherins( membrane bound proteins) , joining cells together.
What are gap junctions ?
From when 6 membrane proteins called connexins form an elongated, donut-like structure called a connexon. Allow for the transport of ions, water and other structures between cells without escaping to the extra cellular matrix. i.e action potentials spread between cardiac muscle cells, i.e depolarisation in sync.
Are pacemaker cells cardiac muscle cells ?
No
What is the sinus rhythm ?
Pacemaker cells in sino atrial node automatically depolarise resulting in a wave that results in the sinus rhythm
How does wave spread ?
SA in RA to LA then to AV node (delay) down the bundle of his to purkinji fibres to ventricles. Delay is to ensure atria have finished contracted before the ventricles contract.
What is meant by the contraction is myogenic in origin ?
originating in muscle tissue rather than from nerve impulses
Where is the origin of the nerve fibres ?
autonomic ganglia
what do the autonomic nerves do ?
they control the functions of internal organs like the heart, stomach and intestines.. specifically in the context of the heart, they act to modulate the rate and force of the contraction of cardiac muscle
which nervous system are the autonomic nerves part of?
peripheral nervous system
autonomic nervous system split into ?
sympathetic nerves (fight or flight) and parasympathetic nerves (at rest) both
Vagus nerve in association with what ?
parasympethetic nervous system..
What is the force of contraction regulated by ?
The degree of stretch of muscle fibres.. hormonal signals and autonomic nerves
Effect of increased stretching of cardiac myocytes on tension
directly proportional
Effect of Norepinephrine of tension ?
directly proportional
100 beats/min
heart rate of SA pacemaker cells without innervation by sympthetic nerves or parasympathetic nerves
60-70 beats/min
heart rate due to parasympathetic nerves innervating pacemaker cells in SA
What effect does acetylcholine have on the heart ?
acts by opening K+ channel via g protein, hence lowering heart rate - hence this is parasympethteic signal - think vagus nerve
what effect does noraepinephrine have on the heart’s pace maker cells ?
opens Ca2+ channels via G proteins. The inotropic response.
does epinephrine and norepinephrine have the same effect of the heart’s pace maker cells ? if so, why ?
yes, because the adrenegic receptors in the heart are all beta receptors. However, this is not the case in various other organs.
how do the depolarisation phases vary between pacemaker cells and non-pacemaker cells ?
in pacemaker cells, calcium ions are involved in the initial depolarisation of phase of the action potential.
but in non-pacemaker cells depolarisation is caused by an opening of sodium channels.
what is the depolarisation phase of skeletal muscle action potential caused by ?
an opening of sodium ligand gated channels which causes vg gated sodium channels to open .. depolarisation which causes ca2+ to be released from SR.. contraction
What modulates pacemaker activity ?
Autonomic nerves - chronotropic regulation
How is a muscle contraction initiated in skeletal muscle ?
Nevre action potential - ACh secretion by nerve ending - End-plate potential - Muscle Action potential - Depolarise T-tubules and open Ca2+ channels of SR - increased Ca2+ conc from SR - contraction - Pump Ca2+ into SR - Relaxtion
What is the shape of cardiac muscle cells ?
discrete rod shaped cells linked together by intercalated disks and connected electrically via gap junctions
what is the heart rate set by ?
the pacemaker activity of the sion-atrial node.
What is the long plateau of the cardiac action potential due to?
Ca2+ influx through voltage-gated calcium channels.
Why does the cardiac action potential coincide with the contractile response ?
So cardiac muscle cannot be tetanized
What is the force by which cardiac muscle is regulated by ?
The Frank-Starling mechanism (preload) and by its inotropic state (intrinsic contractility)
where are smooth muscle cells found ?
the walls of hollow organs of the body and the blood vessels. it is also found in the eye.
What are the two main types of smooth muscle ?
single unit smooth muscle and multi unit smooth muscle
Are the smooth muscle contractions in single unit smooth muscle myogenic or neurogenic in origin ?
myogenic
Are the smooth muscle contractions in multi unit smooth muscle myogenic or neurogenic in origin
largely initiated by autonomic nerve fibres and therefor neurogenic in origin
How are the contractile proteins of smooth muscle arranged ?
They are arranged in a loose matrix ?
How does the loose arrangement of smooth muscle matter ?
allows for a greater degree of shortening than seen in striated muscle
is there troponin, tropomyosin in smooth muscle?
no - think myosin light chain kinase reaction. Agonists can act via second messenger IP3 releasing Ca2+ from SR leading to contraction via activation of myosin light chain kinase
What is the shape of smooth Muscle ?
spindle shaped cells
Are the contractile proteins arranged in regular sarcomeres ?
no therefore no striations
How does smooth muscle maintain a steady level of tension known as tone ?
it is modulated by autonomic nerves, by local chemical factors (paracrine agents) and by circulating hormones
How does the myogenic activity of single unit smooth muscle behave ?
in syncytium
What is the shape of skeletal muscle cells ?
long cylindrical cells with many nuclei, striations
What is the shape of cardiac muscle ?
irregular rod shaped cells with many nuclei, striations
What is the shape of smooth muscle cells ?
spindle shaped with a single nucleus, no striations
30 cm (length) times 100 micrometers (diameter)
skeletal muscle cells
100 micrometres (length ) times 15 micrometers (diameter)
cardiac muscle
200 micrometres (length) times 5 micrometers (diameter)
smooth muscle
do skeletal muscle show myogenic activity ?
no, they exhibit neurogenic activity
innervation of skeletal muscle
somatic
innervation of cardiac and smooth muscle
autonomic
Contraction type of skeletal muscle ?
phasic
Contraction type of cardiac muscle ?
Rhythmic
Contraction type of smooth muscle ?
Mostly tonic
Basis of muscle tone for skeletal muscle
neural activity
Basis of muscle tone for cardiac muscle ?
None
Basis of muscle tone for smooth muscle ?
Intrinsic and extrinsic factors
Cells electrically coupled ?
skeletal no cardiac yes smooth - only single unit
T- system ?
skeletal muscle yes , cardiac muscle yes but only in ventricular muscle , smooth muscle no
Mechanism of e/c coupling in skeletal muscle ?
Action potential and T -system
Mechanism of e/c coupling in cardiac muscle ?
action potential and t system
Mechanism of e/c coupling in smooth muscle ?
action potential and second messengers(IP3)
Hormonal regulation ?
Skeletal muscle no, Cardiac muscle yes, smooth muscle yes
What is cardiac output ?
HR*SV
