D4 The heart Flashcards
what is cardiac muscle?
striated muscle found in the wall of the heart
what is the structure of the cardiac muscle
- thick and thin muscle fibres with myofibrils
- cell nuclei in centre
- rich in mitochondria and glycogen granules
- “all or none” effect – once activated, max contraction
- long refractory period (cannot contract again)
- intercalated discs
how does the cardiac muscle structure ensure that the contraction/systole of the heart is seperated by a rest/diastole
long refractory period of cardiac muscle = cannot contract for a second time
in cardiac muscle structure: what are intercalated discs?
- transverse cross-bands
- attachment site between cardiac muscle cells
- contain adhering junctions (gap junctions – arrays of densely packed protein channels that permit intercellular passage of ions and small molecules)
what do intercalated discs do? (cardiac muscle)
- allows communication between cells
- allows electrical impulses to pass rapidly from cell to cell, so the linked cells contract almost simultaneously
what are gap junctions (cardiac muscle)
- arrays of densely packed protein channels that permit intercellular passage of ions and small molecules
- electrical activation of the heart requires cell-cell transfer of current thru these
4 similarities between cardiac muscle and skeletal muscle
- SARCOLEMMA (a membrane that surrounds and encloses muscle fibres) + from which transverse tubules tunnel in and around sarcomeres
- SARCOPLASMIC RECTICULUM – modified form of ER
- STRIATED in appearance + similar arrangement of actin and myosin filaments
- all muscle tissue consists of FIBRES that can SHORTEN by a HALF to a THIRD of their length
differences between cardiac muscles and skeletal muscle 7
- C much shorter and wider than S
*2. C have a single nucleus, S multicellular - C are branching and joined end to end in a complex 3D network, ?
*4.C many mitochondria, makes up more of cell vol vs S - C have transverse tubular system consistings of wider invaginations of the cell surface than S (C more abundant branching sarcoplasmic recticulum)
*6. C contract even in absence of stimulation by a nerve, not voluntary (unlike S) - C is unique to heart (unlike S)
how does the structure of cardiac muslce cells (CMC) allow for propogation of stimuli throughout the heart wall 4
- intercalated discs at junctions between CMC
- direct electrical coupling between cells – allows waves of depolarisation to pass thru – syncing contraction of the muscle (As if in a single cell)
- cardiac muscle fibres form an interconnected network
- CSC network of walls of atria – seperate from that of ventricles = transmission delay
define the cardiac cycle
The sequence of events of a heartbeat, by which blood is pumped around the body.
two stages of cardiac cycle
- systole – contraction of heart muscle
- diastole – relaxation of heart muscle
what is a myogenic activity, and how is the heart an example
- no need for nerve stimulus
- heart beats rhythmically throughout life without need to be stimulated by and external nerve
what triggers heartbeats in hearts (they are myogenic!) and how
the sinoatrial node/’pacemaker’
- a network of specialised, self-excitable cardiac muscle fibres
- located in the right atrial wall
- each elec charge is propped thru the network of muscle fibres in both atria walls (via gap junctions in the intercalated discs)
- muscle of both atrial walls contract simultaneously (atrial systole)
what is the function of the atrioventricular node
picks up the signal originating from the SAN (it cannot pass directly from the atria to the ventricles)
- at the base of right atrium
why is there a delay at the atriovetricular node (Essentially AV node structure vs SA node structure)
- cells of AV node take longer to get excited than the SA node
- smaller diameter of AV cells = slowing conduction results
- fewer sodium ion channels in membranes of AV + more negative resting potential
- fewer gap junctions in intercalated discs in AV
what is the purpose of the delay of transmission in the AV node
- gives atria time to contract fully (= more blood to ventricles)
- prevents atria and ventricles from contracting simultaneously
very long but coordination of the heartbeat full prose
- The beat of the heart is initiated in the sinoatrial node (SA)
- Signals from the SA that cause contraction cannot pass directly from A to V –> Instead the impulse spreads along the A to the atrioventricular node (AV), from where it spreads to the V. There is a DELAY between the arrival and passing on of a stimulus at the AV. This delay allows time for atrial systole before the atrioventricular (tricuspid and bicuspid or mitral) valves close. The blood therefore leaves the atria to the ventricles when the atrial systole occurs.
- The blood is now in the ventricles and the atrioventricular valves are closed. In the interventricular walls there are specialised fibres grouped to form a bundle called Bundle of His. This bundle splits into two branches that go to the left and right ventricles, leading to other specialised cells called Purkinje fibres.
- Conducting fibres ensure coordinated contraction of the entire ventricle wall. The ventricules contract. Blood then flows out of the heart as the semilunar (pulmonary and aortic) valves open and give access to the aorta and pulmonary artery.
- The heart is now relaxed.
outline contraction of ventricle wall (involving conducting fibres)
- From the atrioventricular node, a bundle of fibres (the AV bundle) conducts the signal into the ventricles
to a point where it splits into right and left branches. - Purkinje fibres deliver the signal to the base of each ventricle via conducting fibres – these ensure coordinated contraction of entire ventricle walls (ventricular systole)
how do conducting fibres speed up contraction of ventricular walls
○ large diameter
○ numerous voltage-gated sodium ion channels
○ well supplied with mitochondria + glycogen store – provides direct source of glucose for respiration
when do heart valves close
when theres a tendency for blood to flow in the opposite direction
- determined by relative pressures
what instrument is used to hear heart sound
stethoscope
what causes the lub sound
the simultaneous closure of AV valves
what causes the dub sound
closure of semilunar valves in ventricular diastole
who invented the stethoscope?
RENE LANNECIN IN 1819
how was the stethoscope revoluntaionary
gave access for the first time to body noises eg breathing, heart valves
- learning normal and abnormal breathing sounds = diagnosis of pulmonary ailments
why are the rhythms of pacemaker cells considered myogenic (of muscle origin) and not neurogenic (of neural origin)
pacemaker cells have their own intrinsic rhythms of activity – as one action potential is completed, immediately after another is generated in the membrane (even without nerve impulse)
define heart rate
the number of times the heart contracts in one minute (beats per minute)
how can a pulse be felt
ventricular contractions = wave of blood thru arteries = expansion of artieries = pulse
normal heartbreat ranges between ___ and ____ beats per minute
50 and 100
what controls the heartbeat?
Sinoatrial node (SA node)
- but can be affected by nervous, hormonal, etc factors
process for measuring heart rate in the neck
- press on one side of the neck with the index and middle fingers
- hence measuring the cartoid artery
- count number of beats per minute
process of measuring heart rate inside of wrist
- using index and middle finger from other hand
- count number of beats in one minute
name 10 factors that increase heart rate
gender
physical activity
body size
temperature
altitude
posture
stress
eating
sodium and calcium ions in blood
drugs
2 factors that decrease heart rate + how?
- age: heart muscles cant pump as efficiently
- potassium ions: decrease action potentials (hyperkalemia)
how does gender increase heart rate
women have slightly smaller hearts = needs to beat at a faster rate than male heart
how does physical activity increase heart rate
more blood required in muscles for oxygen supply
