Ch 13, communication Flashcards
Need for Coordination/Communication
Organisms must coordinate actions of different cells/organs to operate effectively.
Example of Plant need for Coordination
Flowering must coordinate with seasons.
Light-sensitive chemicals enable plants to coordinate the development of flower buds with lengthening days that signal the approach of summer.
Example of Animal need for Coordination
Muscles need energy to contract, so must constantly respire. Respiration requires oxygen, so cells must be consantly supplied with oxygen - depend on red blood cells (erythrocytes) for this.
Define Homeostasis
Maintainance of a stable equilibrium in the body’s internal environment
What is Cell Signaling?
Communication at a cellular level.
One cell releases a Chemical that has an effect on another cell (target cell).
Cell Signalling can:
Transfer signals locally, e.g. between neurones at synapses - neurotransmitter = signal
Transfer signals across large distances, using Hormones, e.g. ADH
Coordination in plants
Hormonal only - plants do not have nervous systems.
Reflex Arc
(stimulus is detected by) Receptor Sensory neurone Relay neurone Motor neurone Effector (carries out appropriate response)
Types of Muscle
Skeletal - responsible for movement
Cardiac - only in heart, myogenic (contract without need for nervous stimulus = heart beats in regular rhythm)
Involuntary - in walls of hollow organs and blood vessles
Structure & Function of Skeletal Muscles
Striated appearance Voluntary/Conscious control Regular arrangement = muscle contracts in one direction Rapid contraction speed Short length of contraction Fibres are tubular and multinucleated
Structure & Function of Cardiac Muscles
Specialised Striated appearance Involuntary Control Cells branch and interconnect = simultaneous contraction Intermediate contraction speed Intermediate length of contraction Fibres are Branched and Uninucleated
Structure & Function of Involuntary Muscle
Non-Striated
Involuntary Control
No regular arrangement - different cells can contract in different directions
Slow contraction speed
can remain contracted relatively long time
Fibres are Spindle Shaped and Uninucleated
What are Skeletal Muscle made up of?
Skeletal Muscles are made up of
bundles of Muscle Fibres, enclosed withing the Sarcolemma (membrane).
Muscle fibres contain a number of nuclei and are longer than normal cells = makes muscles stronger as fewer junctions (point of weakness).
Sarcoplasm = shared cytoplasm within a muscle fibre
What are T Tubles?
Transveres Tubles = inward folds of sarcolemma
Help to spread electrical impulses throughout the sarcoplasm, ensuring whole of the fibre recieves the impulse to contract at the same time.
What do Muscle Fibres have lots of?
Mitochondria to provide ATP for contraction.
Sarcoplasmic Reticulum - contains Ca ions required for mucle contraction; extends throughout the muscle fibre.
Make-up of Myofibrils?
Long Cylindrical Organelles made of Actin & Myosin, specialised for contraction.
Collectively very powerful - lined up in parallel to provide maximum force when all contract together.
Light-Bands / I-bands
region where actin and myosin filaments don’t overlap
Dark bands / A-bands
Dark due to presence of myosin. Actin overflaps myosin at edges
Z-line
line at centre of each light/I band
What is a Sarcomere?
Distance between each Z-line; the functional unit of the myofibril.
Shortens when muscle contracts
H-zone
Lighter coloured region found at centre of each dark/A band. Only Myosin filaments are present.
H-zone decreases when muscle contracts.
bands/zones when Muscle Contracts:
Myosin filaments pull the actin filaments inwards toward the centre of the sarcomere, resulting in:
Light bands/I-bands become narrower
Z-lines move closer togther = Sarcomere shortens
H-zone becomes narrower
The Simultaneous Contraction of many sarcomeres means the myofibrils and therefore muscle fibres contract, resulting in enough force to pull on a bone and cause movement - muscle relaxes when sarcomeres return to their origninal length.
Structure of Myosin
Globular heads have binding sites for actin & ATP, and are hinged to allow them to move forward and back.
The tails of several hundred myosin molecules are aligned together, forming the myosin filament.
Structure of Actin
Actin-Mysoin Binding Sites - blocked by tropomyosin, held in place by troponin when muscle is relaxed.
When muscle is stiumulated to contract, the myosin heads form bonds with actin filaments; actin-myosin cross-bridges. Myosin heads flex/change angle in unison, pulling the actin filament along the myosin filament. Myosin detatches from the actin and its head returns t its original angle using ATP. The Myosin reataches further along the actin filament.
Muscle contraction, starting at Neuromuscular Junction
muscle contraction is triggered when an action potential arrives at a NMJ
Ca2+ ion channels open and diffuse into the synaptic knob (from synapse) where they cause synaptic vesicles to fuse with the presynaptic membrane, releasing Acetylcholine into the synaptic cleft (exocytosis) & it diffuses across the synapse.
Acetylcholine binds to receptors on the postsynaptic membrane (sarcolemma), opening Na+ ion channels, resulting in depolarisation.
Acetylcholinesterase breaks acetylcholine into choline and ethanoic acid, preventing muscle being over stimulated - re-uptake.
Define Motor unit
Motor unit = all musce fibres supplied by a single motor neurone
Depolarisation of Sarcolemma
Depolarisation of sarcolemma travels deep into musclr fibre through T-tubules (in contact woth sarcoplasmic retculum, contaiing Ca2+ ions)
When action potential reaches S.R it stimulates Ca ion channels to open and diffuse out down cond. grad., flooding the sarcoplasm.
The Ca2+ ions bind to troponin causing it to change shape. this pulls tropomyosin away from the actin-myosin binding site. Myosin heads now form actin-myosin cross-bridges.
Myosin heads flex once attached, pulling the actin filament. The ADP bound to myosin is released and ATP replaces it = head detatches from actin.
Myosin hydrolyses ATP, releasing energy, used to move the mosin head back to original position, reattaching at another actin binding site.
Creatine Phosphate
stored in muscles; acts as reserve store of phosphate available immediately to combine with ADP = ATP. Stores are used up quickly so only used for short-bursts of vigorous exercise.
Sensors can be used to monitor the electrical activity in a muscle; to measure strenghth of muscle contraction or to track muscle fatigue.
Electromyography :
What is an Electromyogram? (EMG)
Use of Electrodes (which detect electrical currents created when muscles contract) to gain the signal trace (EMG).
Changes in this signal are used to identify fatigue:
increase in mean amplitude
decrease in frequency of the signal
disruption to overall pattern existing within the signal
An EMG is a record of the electrical activity in a muscle during contraction.
