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BIOMEDICAL ENGINEERING

SEMESTER 1

The Human Body: An Engineering Perspective
A system is a set of interdependent and related things
...
If even only one part of the system breaks the system is impaired
...


Human Body Subsystems








Nervous System: Brain and nerves
Cardiovascular System: Heart, vessels and blood
Respiratory System: Nose, trachea and lungs
Digestive System: Stomach – Duodenum (digestion) and Liver (absorption)
Urinary (Excretory) System
Lymphatic (Immune) System
Integumentary System (Skin)

Human Body: The level of Organization
1
...
Cellular level
3
...
Organ level
5
...
Organismal level

Anatomy and Physiology
Anatomy: Is the study of the entire body and its components with particular focus on their names,
structure and localization
...
Superficial markings

Physiology
Cell Physiology: Cellular level e
...
functioning of a neuron
Special Physiology: Organ level e
...
functioning of heart
System Physiology: Organ systems e
...
muscular physiology
Pathophysiology: The effect of disease on organs and systems

Directional References22

Homeostasis
The ability to survive in different environments and conditions is achieved through a process called
homeostasis
...

Negative Feedback:






To act in opposition to external disturbances
...

Equilibrium average
...

 The control system operated either from within the organ itself (autoregulation) or via a
superordinate organ such as the central nervous system or hormone glands
...
Within the body the set point is rarely
invariable, but can be shifted when requirements of higher priority make such a change necessary
...
Since the regulatory process is then triggered by variation of the
set point, this is called the servocontrol or servomechanism
...
The degree of deviation may be slight in some cases but substantial in others
...
However, this
extends the settling time
...
First sensors with differential characteristics ensure that the intensity of the sensor signal
increases in proportion with the rate of deviation of the controlled variable from the set point
...


Positive (reinforcing) feedback:
 Blood clot
 Instability
 Larsen effect (Different end product)

The Cell
Cells are the building block of every living individual and are divided via Prokaryotic and Eukaryotic
...

The cell is the smallest functional unit of a living organism
...
Growth,
reproduction and hereditary transmission can be achieved by cell division
...
The
genetic material of the cell is concentrated in the cell nucleus, whereas digestive enzymes are located in
the lysosomes
...

Need to interact with the external environment:
 Intake of nutrients
 Waste Disposal
 Signalling

Prokaryotic Cell

Eukaryotic Cell

Differences between Prokaryotic and Eukaryotic Cells

The Nucleus
Contains the genetic information
...
Chromatin carries the genetic information
...

It is surrounded by the nuclear envelope: It is a continuum of the endoplasmic reticulum (ER)
...

Chromatin contains deoxyribonucleic acids (DNA)
...

DNA is made up of a strand of three-part molecules called nucleotides, each of which consists of a
pentose (deoxyribose) molecule, a phosphate group and a base
...


DNA-Deoxyribonucleic acid
DNA is Digital

The Endoplasmic Reticulum (ER)





Substances synthesis
Storage and transport through the cell
Rough ER: Production site of proteins
Smooth ER: Production site of lipids and carbohydrates

Ribosomes and Golgi complex
Ribosomes:




Either floating in the cytosol or bound to the ER
Mae up of proteins
Biochemical machinery for protein synthesis

Golgi complex:



Further processing of substances and direction of molecules into finished products
Packaging of proteins

Lysosomes and Peroxisomes
Lysosomes:



Small Vesicles
Break down dying cells, organelles, and food particles

Peroxisomes:


Micro bodies involved in the oxidation of fatty acids, amino acids,
toxins and other substances

Mitochondria
Oxidation of carbohydrates and lipids
...


The Cytoskeleton
Protein structure that acts as a skeleton:




Determines the shape
Maintains or changes it
Motility

Made up of actin filaments
...
This involves the movements of substances inward and outward
the cell through the membrane
...
This homeothermy
applies only to the core temperatures of the body
...
e
...
In order to maintain a constant core
temperature, the body must balance the amount of heat it produces and absorbs with the amount it loses;
this is thermoregulation
...
Concentration,
temperature and density and uniformly distributed
...


Diffusion
Difference (gradient) in concentration
...

Simple diffusion is Oxygen diffusion inside and Carbon Diode diffusion outside
...
g
...
Solute cannot pass through the membrane
...


Electrical Gradient
Intracellular and extracellular fluids are also made of ions: Na+, Cl-, Ca2+ and organic ions
...
Requires energy expenditure (ATP) Has Na+ - K+
pump (3Na+ out and 2K+ in)
...
When the sodiumpotassium- ATPase enzyme points into the cell, it has a high affinity
for sodium ions and binds three of them, hydrolysing ATP and
changing shape
...

The enzymes new shape allows two potassium to bind and the
phosphate group to detach, and the carrier protein repositions itself
towards the interior of the cell
...
After potassium released into
the cell, the enzyme binds three sodium ions, which starts the process over again
...
A stable potential
difference between inside and outside of the cell
...

The 4 most important ions are sodium, chlorine, potassium and chlorine and are usually in the processes of
diffusion, active transport, facilitated diffusion and osmosis
They have membrane channels (proteins)
...

The tendency of ions is:





K+ outside
Has a natural tendency to go out
Na+ inside (strongly) Goes in cell due to 62mV as the difference is high
Cl- in equilibrium
It does move
Ca2+ inside (strongly) It is used in muscular contraction

Ion flow is a movement of charge across the membrane
...

Voltage across the membrane, current
...
It computes the equilibrium potential (Ex) of any species of ions
distributed inside and outside of the cells
...
The capacitor stores the charge (the plasma membrane)

Electrical Equivalent of the membrane
Cell membrane is a double layer of insulating material
...
It
can be modelled by a capacitor
...
These are current generators
...

Cell membrane can be hyperpolarized and depolarized
...
e
...
There is a fast influx of sodium ions
...


Sodium Protein Channels

Depolarization above the Threshold
This stimulus above the threshold causes:








gNa (Na+ entry)  further depolarization   gNa (etc
...
This is important is neurones and muscular cells
...

The action potential unit of power due to physical and chemical properties
...

When a particular voltage is received i
...
-40mV
...

It establishes the polarisation
...

Threshold: The Em where enough voltage gated Na channels pop open so that the permeability to Na+ ions
is greater than the K+ (gNa > gk)
Rising Phase: When inside of a cell is negative there is a large force driving Na ions in causing
depolarisation
...
Delayed opening of voltage gated K+ ions
...
Repolarisation
...
It is also very fast and the interval is longer
for the potassium
...
e
...
e
...


Nervous System
Extends throughout the body:





Skin
Muscle
Organs
Bone

The Nervous System is a complex system which provides:






Stimuli reception
Information processing
Generation of appropriate signals
Transmission of signals within the body
Peripheral level actions

Central (Processing and Control Unit)
Transmissive (Cables)
The anatomical division:



Central Nervous System (CNS)
Brain, spinal cord
Peripheral Nervous System (PNS)
Connections (Organs, muscles)
PNS is divided into Somatic and Autonomic

Function of Nervous System is to control and send messages
...
The afferent (sensory branch) and efferent (centre to external)
...
“A nerve is like an insulation
of copper wires
...
Shape reflects the function
...

From the anatomical point of view, the PNS is split into autonomic and somatic
...
Each of the cells has a specific function
...
Have a mass of electrical signals in the brain
...
The transmission part
of the nervous system consists of nerve fibres (Cables)
...
The receptors can receive information regarding the outside or the
inside of the body
...
The output units of the
Autonomic Nervous System (ANS)
Effector reflexes: Act as a result of internal or external stimuli
Voluntary effectors: e
...
skeletal muscles

10^10 – 10^12 cells (100-1000 billions)
The Elements are:





Brain
Cranial nerves
Spinal cord
Spinal nerves

Nervous Tissue: Neurons and neuroglia (also called glial cells)
...

 Information processing
 Communication with other cells as well as other neurones
...
There is white matter and grey matter
...
Dorsal and ventral can get information as there are a number of neurones
...

Most of the right hand body is controlled by the left hemisphere and vice versa
...

You can behave with just one hemisphere and influence your brain to do what you want
...
It is a reaction
...


Meninges:
Specialise membranes
 Dura Mater: Outermost thick and tough membrane






Arachnoid
Pia Mater
Maintain the cerebrospinal fluid
Provide mechanical protection
Act as barrier to toxins and other substances

The Brain
Exterior:
The brain stem – At the base of the brain and it regulates the reflexes and body’s basic involuntary
actions (heart rate, blood pressure, sleeping)
Cerebellum – Coordinates muscle movements and controls
balance
...

Adjustment of voluntary and involuntary activities based on
input and stored memories
...
Processing centre for
thought, memory, language, sensory information
...

Right Hemisphere – Controls most of the function of the right side of your body
...

Cerebral cortex – The outer surface
Lobes –
 Frontal: Complex mental activities (speech)
 Parietal: Pain, touch, temperature
 Temporal: Sounds, some memory function
 Occipital: Processing vision images
Interior:
Pons – Relay station and
sleep
...

Medulla oblongata – Some
involuntary activity, HR and
blood pressure
...

Relays sensory information to various brain centres; also
contains centres for autonomic regulation of heart rate,
digestion, blood pressure, respiration, etc
...
Part of the
brain stem which connects brain to spinal cord
...

Corpus Callosum – Communication between left and right hemispheres
...
Axons from the peripheral sensory organs synapse in the
thalamus
...
Relaying and processing sensory
information
...
Each of them is identified by a letter, which relates with the vertebral
segment
...
Its diameter generally decreases from top to bottom
...
Each segment contains a posterior
root (dorsal) through which sensory information arrives
...
Dorsal and ventral roots unite into a single spinal nerve
...
After this, nerves extend inferiorly without spinal cord protection
...

The PNS consists of:
 Nerves coming to or from the CNS
 Ganglia: groups of neuron cell bodies in the periphery
It also consists of afferent (sensory) and efferent (somatic, autonomic)
Nerves: Axons bundled together by connective tissue
...

Has connections between neurones
...
Have pre and post ganglionic neurones so
that they can join together
...

Consists of two branches:
 Sympathetic (fight or flight)
 Parasympathetic (rest & digest)
Functionally and anatomically distinct
...

Anatomical Distinctions:



Sympathetic – Thoracic-lumbar region from T1 to L2
Parasympathetic
 Cranio-sacral
 Cranial nerve components







III (oculomotor)
VII (facial)
IX (glossopharyngeal)
X (vagus)
S2 to S4

 An important differentiation of the ANS with respect to the somatic nervous system can be found in
the efferent components
...
The preganglionic and
postganglionic neurons located in ganglia (different from those of the afferent sensory neurons)
 A preganglionic neuron leaves the CNS via the ventral g=horn and exits through the ventral root as
we have seen in the somatic division
 However, it does not connect directly with organs or muscles but forms a synapse in another
ganglion (a collection of neurons’ bodies that are outside the CNS)
 This preganglionic neuron synapses onto the postganglionic neuron which then innervates the
target organ in example the smooth muscle walls of a blood vessel
 The cell bodies of the preganglionic neurons are located either in the spinal cord or in the brain
 The preganglionic neurons are myelinated meaning fast transmission velocity
 The postganglionic neurons are unmyelinated meaning slow transmission velocity

Sympathetic Division:
 Ganglia are located close to the vertebrae in the so called sympathetic chain are called
paravertebral ganglia
 Short axon for preganglionic neurons
 Long axon for postganglionic neurons
Parasympathetic Division:
 Ganglia are located either in or near to the target organs
 Long axon for preganglionic neurons
 Short axon for postganglionic neurons
Neurotransmitters:





Acetylcholine
Noradrenaline (UK) = Norepinephrine (USA)
Parasympathetic and sympathetic preganglionic neurons release acetylcholine
Sympathetic division
 Postganglionic neurons are Noradrenergic (i
...
release noradrenaline to the target organs)
 Except those which innervate sweat glands (acetylcholine)
 Parasympathetic Division
 In the parasympathetic division, the postganglionic neuron release acetylcholine to the
target organs (smooth muscle, glands)
 Adrenal Medulla
 Directly innervated by the preganglionic neuron of the sympathetic system
 Has the capacity to release adrenaline (epinephrine) or noradrenaline (norepinephrine)
directly into the circulation
Functions:
 ANS divisions:
 Fight or flight for the sympathetic system
 Rest and digest for the parasympathetic system
 Sympathetic: e
...
increases heart rate, dilates bronchioles, dilates blood vessels in muscle
 Parasympathetic: e
...
decreases heart rate, constricts bronchioles, constricts blood vessels in
muscle

Sensory Input

Afferent sensory receptors:
 A huge amount of stimuli comes from the environment
 Different form of energies (mechanical, thermal, electromagnetic)
 Specific sensors (e
...
taste)
 Bitter/sweet
 Transduction of the energy
 Action Potential

Skin Receptor:

Sensory Receptors
Coding:
 Stimulus frequency (impulses = Hz)
 Adaptation

CNS-PNS Integrated Functions
The reflex arc:
 Certain actions need to be made without or before entering cerebral cortex and conscious
awareness
 Autonomic motor responses: Arise from specific trigger
 In: Muscle spindles
 Transmission: Sensory neuron
 Out: Motor neuron
The withdrawal effect:






More complex response means more time
Polysynaptic
In: Nociceptors
Transmission: Sensory neuron and mono/polysynaptic
Out: Motor neurons

Levels of Organisation





Behavioural neuroscience
Systems neuroscience
Cellular neuroscience
Molecular neuroscience

Neuroglia Cells
Oligodendrocytes: Secret myelin
Astrocytes: Absorb nutrients from the capillary and pass it to the neuron
...
Have chemical synapse
which releases a substance through vesicles via
exocytosis
...
Have gap junctions which allow the movement
of ions through them
...
Excitatory
synapse is a processing strategy
Axon terminal gives rise to the synapse
...

Sites for the interneuronal communication that contain specific proteins essential for transmitter release
...

Receptors: A specialised protein that detects chemical
signals and initiates a cellular response
...

Axoaxonic: Axon terminal to axon of neighbouring cell
Chemical synapses:
 Occurs in brain, spinal cord, autonomic nervous system,
and skeletal muscle
...


Spatial Summation: Summation of PSPs generated at more than one synapse on the same cell
...
e
...
Conduction velocity 10m/sec
...
Velocity and
relation to a leaky hose
...


The ‘All or None’ Concept

The generated in spike initiation zone, numerous Na channels
...
A
stimulus can occur at different places
...
By diffusing they are reaching the action potential
...


Conduction Velocities
Diameter of axon
 The greater the diameter
 The faster the conduction
Myelination
 Unmyelinated-0
...


Salutatory Conduction
Myelin sheath (spirally wrapped glial cells) increases speed of AP conduction
...
These vesicles move towards the membrane
...

 The heart – the engine
 The circulatory system – a closed system of vessels:
 Arteries
 Capillaries
 Veins
 The blood – Essential for distributing oxygen, nutrients
 Closed loop system
 Dynamic system
 Modifies the blood flow to feed specific organs
 Functions can be described by the underlying engineering principles
 Blood flows cyclically
 Composed of branches which allow the blood to spread all over the body
 Tissues properties change depending on the specific branch (function)
 Diameter decreases
 Blood flow decreases (locally)

Blood is pumped from the left ventricle of the heart to capillaries in the periphery via the arterial vessels of
the systemic circulation and returns via the veins of the right heart
...

The total blood volume is about 4-5 L
...


A decrease in blood volume will be reflected almost entirely by a decrease in the blood stores in the low
pressure system
...

The cardiac output is calculated as heart rate (HR) times stroke volume (SV)
...
Maintaining adequate cerebral perfusion is the top priority, not only because
the brain is a major vital organ, but also because the brain is a major vital organ, but also because it is very
susceptible to hypoxic damage
...
During strenuous physical exercise, the CO increases
and is allotted mainly to the skeletal muscle
...

Peripheral resistance: Flow resistance in the pulmonary circulation is about 10% of the total peripheral
resistance (TPR) in the systemic circulation
...
Since the resistance in the lesser arteries and arterioles
amounts to nearly 50% of TPR they are called resistance vessels
...
As a result, the mean blood pressure drops from around 100mmHg in the aorta
to 2-4 mmHg in the aorta to 2-4 mmHg in the vena cava
...

System Circulation:
 Heart
 Brain
 Organs
Pulmonary Circulation:
 Lungs
 Driving force
 Pressure
 How is it measure?
 MmHg (1/760 atm)
 Range (80-120 mmHg)
 Drops from the heart to the periphery
 It can be varied locally
 Cardiac output (CO)
 Measure in L/min
 Heart rate (HR)
 Stroke volume (SV)
𝐶𝑂 = 𝐻𝑅 ∙ 𝑆𝑉
𝐻𝑅 = 70 𝑏𝑝𝑚
𝑆𝑉 = 0
...
6 𝐿/𝑚𝑖𝑛

The Circulatory System
 Blood flow rhythmically from the heart
 The aorta and greater arteries distribute the blood to the
periphery
 They also convert the intermittent flow to nearly steady
through the capillaries
- High compliance (decreases with age)
- High diameter
 In the arteries the blood flows due to the pressure gradient
(ventricles to arteries)
 Two factors help maintain a pressure gradient also between
the veins and the heart
- Skeletal muscle pump: muscle contraction + veins internal
valves
- Respiration pump

The respiration pump aids blood flow through the veins of
the thorax and abdomen
...
The elevation of the chest caused by the
contraction of the external intercostal muscles also
contributes to the increased volume of the thorax
...
Additionally, as air pressure
within the thorax drops, blood pressure in the thoracic veins
also decreases, falling below the pressure in the abdominal
veins
...
This in turn
promotes he return of blood from the thoracic veins to the
atria
...


Driving Force
 The circulation driving force is the pressure difference
 Pressure measured in mmHg
[𝐿]
 𝑄̇ represents the blood flow
[𝑚𝑖𝑛]



𝑅 flow resistance

[𝑚𝑚𝐻𝑔]∙[𝑚𝑖𝑛]
[𝐿]

 Organ/vessel/entire system

Vessels

The exchange of nutrients and gasses takes place in the capillaries

Arteries:
 Thick walls to withstand high pressures
 Maintain the blood flow during the heart cycle
 They stretch during ejection phase (systole - high pressure)
 Store blood (and energy)
 Release the blood when the ventricles release (diastole) and their valves (semilunar) are
close (low pressure)

Capillaries:
 Microscopic channels 5-10 µm (10-6m)
 Provide blood to tissues (perfusion)
 Exchange of gases and other substances

Veins:

 Thin-walled vessels with large and irregular lumens
 Often equipped with internal valves (unidirectional flow)
 Blood reservoir

Peripheral Resistance
 Resistance to flow:
8∙ 𝑙∙ 𝜂
𝑅=
(𝜋 ∙ 𝑟 4 )
 Dependant on:
- L length

-

N viscosity of the fluid
1
𝑟4

inversely proportional to the 4th power of the inner radius

 Lesser arteries and arterioles account for almost the 50% of the total peripheral resistance
 They determine with the pre capillary sphincter the amount of blood that is distributed to the
capillary beds
 Parallel and series resistors
 Pressure regulation is achieved by:
 Temperature drop
 Release of chemicals in response to trauma (shock)
 Localized activities (digestions vs exercise, etc
...
Response is a direct effect of
conditions within local environment
...
in length, 8 to 9 cm
...
in thickness
...
The heart continues to increase in weight and size up to an advanced period of life; this increase is
more marked in men than in women
...


 Four chambers
 2 atria
 2 ventricles
 Separated by septum
 Interatrial
 Interventricular
 Right side veins
 Inferior and superior
 Left side arteries
 Aorta and pulmonary trunk

 Muscular tissue arrangement
 Different for atria and ventricles
 Reflects mechanical functions
 Different pressure regimes
 Four valves
 Two regulate internal blood flow
 Two regulate in  out blood flow
Thin on atria and thick tight on ventricles

 Internal Valves
 Tricuspid
 Bicuspid (Mitral)
 In too out valves
 Semilunar valves
The Coronary Circulation:

Coronary Angiogram (X-Ray):





The dye makes visible two occluded coronary arteries
Decreased blood flow (ischemia)
Insufficient oxygen (hypoxia)
Lead to cardiac muscle death (myocardial infarction)

Conduction and Contraction:



Smaller fibres
Joined end to end
 Syncytium

The fibres of the heart differ very remarkably
from those of other striped muscles
...
They show
faint longitudinal striation
...
Each cell
contains a clear oval nucleus, situated near its
centre
...
The
connective tissue between the bundles of fibres
is much less than in ordinary striped muscle, and
no sarcolemma has been proved to exist
...

Impulse moves through atrial walls via specialized conduction pathways
...

Specialized conduction pathways (Bundle of His) carry impulse toward the ventricular apex
...

Impulse spreads throughout ventricular myocardium
...
Cardiac
impulses are generated within the heart (automacity)
...
Myocardial tissue compromises a functional syncytium because the cell are
connected by gap junction
...

Cardiac contraction is normally stimulated by impulses from the sinoatrial node, which is called the
primary pacemaker
...
The bundle of His is the
beginning of the specialized conduction system, including the left and right bundle branches and the
Purkinje fibres, which transmit impulses to the ventricular myocardium, where they travel from inside to
outside and from apex to base of the heart
...
Cells don’t have constant
resting potential
...
The potential is subject to
various changes in ion conductance and ionic flow through the plasma membrane
...
When the TP is reached gca increases quickly and the slope of the pacemaker
potential rises
...


All components of the conduction system can depolarize spontaneously, but the SA node is the natural or
nomotopic pacemaker in cardiac excitation
...


 Pacemaker system consists of cells that do not have a resting potential
 They slowly depolarize until the threshold potential is reached and an action potential is generated
The Aps spontaneous depolarization normally does not occur in the myocardium
...
A cardiac cyles therefore takes 1 second
...

Phases I and II take place at systole and III, IV ake place at diastole
...
Electrica excitation of the atria and ventricles presedes their contraction
...
This results in atrial contraction and is followed by ventricular excitation
...
This the end of diastole
...
The semilunar valves open becuase the pressure in the left ventricle exceeds that in the
aorta at about 80 mmHg, and the pressure in the right ventricle exceeds that in the pulmonary artery
about 10 mmHg
...
A
large portion of the stroke colume is rapidly expelled and the maximum blood flow rate reaches a
maximum
...

The first phase of ventricular diastole or isovolumetric relxation now begins
...
The central venous pressure
decreases
...

The filling phase begins and blood passes rapidly from the atria into the ventricle, resulting in a drop in
CVP
...
Quadriceps
Ultrastructure of skeletal muscle fibres:








Muscle cells are often referred as muscle fibres
Nuclei can supply the large amount of proteins and enzymes to contract
Sarcolemma (membrane)
Sarcoplasm
Sarcoplasmic reticulum
Myofibrils
Sarcomere (µm)

Sarcomere Structure





M disk
Z disk
Actin filaments (thin)
Myosin filaments (thick)
 Hundreds myosin II molecules







Functional unit of contraction
Thousands each fibre
M-disc (line)
Z-disc (line)
Tropomyosin molecules
 Lie adjacent to the actin

Neuromuscular Junction
 Connects nervous system with muscle fibres
 Motor unit
 α Motor neuron
 Innervated fibres
 Motor end plate
 Innervation site






Resting potential (-90mV)
Motor neuron action potential
Acetylcholine release
Postsynaptic membrane depolarization
 Excitatory postsynaptic potential
 Action potential along the muscle fibre
 2 m/s

Sarcoplasmic Reticulum:
 The EPP reaches the sarcoplasmic reticulum (via T-tubules)
 Voltage gated Ca2+ channels open
 Ca2+ is released into the cytoplasm of the depolarized muscle fibre

Skeletal and Cardiac Muscle:
 Dihydropyridine receptors (DHPR)
 Skeletal muscle: act as receptor for the Ca2+ channels in the sarcoplasmic reticulum
 Cardiac muscle: act as part of Ca2+ channels in the T-tubules
 Trigger the opening of Ca2+ channels in the SR

Actin, troponin and tropomyosin:
 Myosin heads tend to bind actin filaments
 Tropomyosin prevent this binding
 Action potential (End Plate Potential)
 Electrochemical coupling
 The Ca2+ attaches to the troponin
 This slides away the tropomyosin
 Myosin heads bind the actin filament
 Myosin heads tilt down (ATP)
 Sarcomere is shortened (contraction)

Working Cycle:
 Myosin binds ATP and hydrolyses it to ADP and Pi
 Myosin binds to actin
 Myosin undergoes a conformational change in which the actin
is pulled forward
 ADP is released, ATP binds and myosin dissociates from actin

Muscle Contraction:

Contractility Control:
 In skeletal muscle gradation of force is achieved by
 Action potential frequency
 Recruitment
 AP leads to the release of Ca2+
 A single stimulus however is too brief to allow the maximum shortening of sarcomeres
 If a second stimulus arrives before the muscle has completely relaxed, then the muscle
shortening can continue
 Mechanical summation or superposition

Twitch vs
...
It may be oxidative or anaerobic, in which
case lactic acid is produced and the muscle goes into oxygen debt
...


Cardiac Muscle





Main differences from skeletal muscles
Source of Ca2+ (external)
Single unit (Syncytium)
Force-length curve

Action Potential:
 Influx of Na+
 Out flux of K+
 Slow Ca2+ channels

Contractility Control:
 Calcium for contraction enters during the action potential
 as long as the contraction
 The subsequent refractory period occurs when the muscle is at rest
 Thus it is not possible to produce a tetanus (important for a pump!)
 Can get facilitation with increased frequency of stimulation
Role of Nerves:
 Gap junctions ensure the spread of Ca2+ from cell to cell so that the muscle behaves as a single unit
 Contraction is initiated spontaneously
 Nerves act to increase or decrease calcium entry
Force-length (muscle):






Less extensible than skeletal muscle
Greater tension force at rest
Cardiac muscle operates below Lmax
Maximum force at higher length
The ventricle response:
 Increased filling loads
 Increased force development
 Stretching results in a greater force of contraction (Frank-Starling mechanism

Smooth Muscle
 Main differences from skeletal muscles
 Source of Ca2+ (external)
 Single and multi-unit
 No tropomyosin/troponin
 Structure and force-length curve

 Actin and myosin contractile proteins
 Thick and thin filaments anchored by an analogous to the Z-discs of skeletal and cardiac muscle
fibres the dense body
 Non striated
 The actin-myosin filaments arrangement causes the muscle fibre to contract in a corkscrew motion

 Ca2+ influx
 Ca2+ binds with calmodulin
 Active calmodulin binds
 myosin light chains kinase (MLCK)
 MLCK enables the myosin to interact with actin
2+ binds with caldesmon
 Ca
 Myosin to interact with actin
 Muscle contraction

Force-Length:
 The less regular organisation of actin and myosin means that smooth muscle cells "round up" when
contracting
 Due to the irregular arrangement of the actin and myosin, the muscle has a much broader working
range over which the maximum tension can be developed

Relaxation and ATP consumption:
 Low rat of cross-bridge cycling
 Low ATP use

Postural and Skeletal Muscle Control
 Continuous coordination of hundreds of muscles
 Proprioception: sensing the muscle strength, position and movements of the body
 Muscle spindles
 Muscle sensors for position and movement
 Intrafusal muscle fibre
 Skeletal muscle
 Extrafusal muscle fibre
 Golgi organs
 Muscle tension sensor
 Inhibitory effect
 γ motor neurons (efferent)

Servo Control:



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