Unit 4: Plant and Animal Equilibrium

+ Neural Signalling

Gas Exchange as a vital function in all organisms

Intake of oxygen to metabolise energy

Removal of metabolic waste products i.e. CO₂

Why do challenges become greater in larger organisms?

SA:Vol ratio decreases with increasing size

• Increased distance from centre to exterior of organism

Properties of Gas Exchange Surfaces

Thin tissue layer

Permeable to respiratory gases

Moist (Gases are often dissolved; Exchange occurs in liquid medium)

Large SA

Maintenance of Concentration Gradients at Exchange Surfaces

Dense networks of blood vessels

Continuous blod flow

Continuous ventilation with air (lungs) / water (gills)

Adaptations of Mammalian Lungs for Gas Exchange

Alveolar lungs

• Presence of surfactant (phospholipid and protein film) → Reduce surface tension of moist inner surface of alveolus → Prevents alveolus from collapsing when air is expired (Low air pressure)

• Branched network of bronchioles + alveoli → Large SA of gas exchange tissue

• Extensive capillary beds surrounding alveoli → Close access to capillaries → Easy access to / from bloodstream

• High SA

Ventilation of Lungs (Mention Diaphragm, Intercostal muscles, Abdominal muscles, Ribcage)

Concentration gradient of O₂ and CO₂ is maintained by inhalation (intake of O₂ from environment into lungs) and exhalation (expulsion of CO₂ from lungs into environment)

Role of…

• Diaphragm → Change volume of thoracic cavity

  INHALATION: Contract → Flattening + Pushing down on abdomen

  EXHALATION: Relax → Moves up

• Intercostal muscles

  INHALATION: Externals contract; Internals relax

  EXHALATION: Internals contract; Externals relax

• Abdominal muscles

  INHALATION: Relax

  EXHALATION: Contract → Pressure pushes diaphragm into dome shape

• Rib cage

  INHALATION: Moves upward and outward (due to contraction of external intercostals and abdominal muscles)

  EXHALATION: Moves down and inward

Lungs & Thoracic Cavity

• INHALATION: Expand → Lower internal pressure → Air flows in

• Exhalation: Volume decrease → Raise internal pressure → Air flows out

Measurement of Lung Volume (Spirometer graph)

Tidal Volume: Volume of air breathed in / out in a cycle at rest

Vital Capacity: Sum of inspiratory, expiratory reserves and tidal volume

• Measure from maximum of inspiratory reserve to minimum of expiratory reserve

Inspiratory Reserve: Maximum volume of air that can be breathed in

• Measured ONLY from maximum of tidal volume

Expiratory Reserve: Maximum volume of air that can be breathed out

• Measured ONLY from minimum of tidal volume

Measurement of Lung Volume (How to use spirometer)

1. Ask subject to stand and breathe in and out using the device for ~15 seconds (Measure tidal volume)

2. Rest subject ≥1 minutes

3. Ask subject to breathe in maximum volume of air

4. Rest subject ≥1 minutes

5. Ask subject to breathe out maximum volume of air

Adaptations for Gas Exchange in Leaves

In leaf structure…

• Cells on upper epidermis secrete waxy cuticle → Prevents water evaporation (Affects transpiration)

• Air spaces in the spongy mesophyll (Main site of gas exchange) → Allow movement of gases + gas exchange

• Stomata are on underside of leaf → Prevent obstruction → Maintain open channel for gas exchange

• Stomatal Guard cells embedded on lower epidermis → Control opening and closing of stoma → Regulates amount of water lost; Responsible for gas exchange by diffusion → Controls transpiration rate

  • Turgid → Open // Flaccid → Closed

  • When plant wilts from water stress → Release of abscisic acid → Trigger efflux of potassium from guard cells → Decreased water pressure → Loss of turgor → Becomes flaccid and occlude opening

• Veins are located centrally → Optimal access by all leaf cells

Draw and label a plant diagram

Transpiration & Gas Exchange + Factors

Transpiration = Consequence of gas exchange in leaf; Evaporation of water through open stomata

Factors include…

• (Increased) Light → Increases rate

  Stimulates guard cells to open stomata + Increase rate of photosynthesis → Requires increased diffusion of CO₂ (in) and O₂ (out)

• (Increased) Temperature → Increases rate

  Increase molecular movement → Increased water evaporation

• (Increased) Wind speed → Increases rate

  Removes water vapour at entrance of stomata → Increase water concentration gradient between inside and outside of leaf

• (Increased) Humidity → Decreases rate

  Reduce water concentration gradient between inside and outside of leaf

Stomatal Density

Varies between species due to long-term environmental factors

To calculate based on image…

• Measure length and width of photograph

• Using magnification formula, determine actual length and width

• Count number of stomata

  (At least half of stomata should be seen to be counted)

• Express to nearest whole number as stomata per mm^-2

Adaptation of Foetal and Adult Haemoglobin for Oxygen Transport

Capable of reversibly binding to both oxygen and carbon dioxide molecules

Saturated = Capacity is full

• In HbF…

  • Quaternary structure – 2x alpha and 2x gamma polypeptide chains; Each contain haem group (Reversibly bind to oxygen)

  • Gamma polypeptides – Higher affinity for oxygen → Increased efficiency to obtain oxygen from mother’s blood across placenta

• In HbA…

  • Quaternary structure – 2x alpha and 2x beta polypeptide chains

Cooperative binding of oxygen to haem groups

• Binding of an oxygen molecule to a haemoglobin subunit alters its conformation → Increased affinity for oxygen; Easier for additional molecules to bind to remaining groups of haemoglobin

  
  

Allosteric binding of CO₂

• Forms carbaminohemoglobin

• Induces conformational change → Reduced affinity for oxygen → Facilitates release of oxygen in regions with low oxygen partial pressure (E.g. respiring tissues)

Bohr Shift

Increase in CO₂ → Increased dissociation of oxygen

• Carbaminohemoglobin has decreased affinity for oxygen → Greater tendency to give up oxygen

Beneficial for actively respiring tissues

• More CO₂ → More O₂ is released

• Greater concentration of CO₂ in muscles indicates that it is where oxygen is most needed for cellular respiration

Oxygen Dissociation Curve + Comparison between HbA and HbF

Represents affinity of haemoglobin for oxygen at different oxygen concentrations

• Sigmoidal

  • As partial pressure of oxygen initially increase, rate of oxygen uptake by haemoglobin rises quickly due to cooperative binding (lil like chain reaction ykyk)

  • Eventually levels (Haemglobin is fully saturated with oxygen in regions of high oxygen partial pressure i.e. lungs)

• Shifted left for HbF

  • Greater affinity for oxygen at almost every partial pressure of oxygen → More highly saturated with oxygen compared to mother (Due to gamma polypeptide chains)

  • Important in placenta where HbF and HbA must compete for oxygen in mother’s blood

Distinguishing Arteries and Veins in Micrographs

Structure of vessel wall + Thickness relative to diameter of lumen

• Arteries: Thick smooth muscle layer; Regular circular shape

  • To transport blood at high pressures

• Veins: Thin wall thickness; Wide lumens; Irregular shape

  • To transport blood at low pressures

Adaptations of Arteries for Transport of Blood Away From Heart

Layers of muscle and elastic tissue in walls of arteries

THREE LAYERS – Tunica adventitia, tunica media, tunica intima, endothelium

• Muscle fibers help arteries stay rigid + maintain high pressure without bursting + contract → Increase pressure between pulses → Steady blood pressure

  • Smooth muscle layer (Controlled by ANS) changes lumen diameter → Regulate blood pressure

• Elastin and collagen fibers allow arteries stretch / expand as blood flows + Elastic recoil helps push blood forward + Maintain pressure

Adaptations of Capillaries for Exchange of Materials Between Blood and Internal / External Environment

Blood from arterioles branch → Capillary beds → Venules

ONE LAYER – Only has tunica intima

Large SA + Narrow diameters due to branching

• Ensures every cell is near a capillary and can receive oxygen

• Slows down blood flow → More time for exchange (Only one cell is accommodated at a time)

Thin walls

• Reduces diffusion distance

Fenestrations (pores) in capillaries where exchange needs to occur rapidly

• Further enhances rapid exchange at intestines and kidneys

Adaptations of Veins for Return of Blood to Heart

THREE LAYERS – Tunica externa (elastin and collagen), tunica media (smooth muscle), tunica intimate (endothelium)

Presence of valves in areas where gravity is strong (e.g. legs)

• Prevents back flow; Blood flows in one direction

Flexible wall; Have elastin

• Allows to be compressed by muscle action (During activities like exercise where muscles contract) → Push blood towards heart

Coronary Heart Disease

Coronary arteries = Blood vessels at heart; Branched from aorta

• Crucial in supplying oxygen to heart since very active and muscle-dense

Occlusion = Blockage caused by fatty plaque built up in inner lining of coronary arteries; May be caused by…

• High blood cholesterol levels, smoking, hypertension, high blood sugar levels (Due to diabetes), genetic factors

Consequently…

• Restricted blood flow to cardiac muscle → Chest pains + Deposition of minerals in plaque → Hard and rough plaque

Transport of Water during Transpiration + Properties of Water Involved

• Loss of water by transpiration in leaf cells results in a negative water potential which draws water from xylem to the leaf. This generates a tension force known as a transpiration pull (a form of capillary action) which pulls water from roots, up the xylem, to the leaf.

• Cohesion (attraction between water molecules due to hydrogen bonding) ensures that this column of water is continuous.

• Adhesion (attraction to walls of xylem) allows water to counter gravity and travel upward by adhering to xylem walls

Adaptations for Xylem Vessels for Transport of Water

Lack of cell contents; Hollow dead cells + Incomplete / Absent end walls

• Allows for unimpeded flow of water

• Water movement is unidirectional (up)

Lignified walls

• Provide strength → Withstand tensions during water transport

• Prevent collapse under negative water potentials generated by transpiration

Pits (Microscopic holes in walls)

• Enable entry and exit of water / water transfer

Transverse Section of Stem in Dicotyledonous Plant (HINT: 5 main features + 2-3 extra)

• Vascular bundle

  Function: Around edge of stem for structural support

• Xylem

  Function: Water and minerals transportation

• Phloem

  Function: Carbohydrate transportation

• Cortex

  Cylinder of tissue around stem; Has cells with secondary thickening in cell walls

  Function: Provide support; Withstand bending and compression

• Epidermis

  Surface of stem made of cell layers; Embedded with stomata

  Function: Waxy cuticle → Reduce water loss + Aid in gas exchange

• Pith

  Tissue of thin walled, parenchymal cells in centre of stem

  Function: Storage of starch and oil + Secretion of resin

• Cambium

  Lateral meristem (cell growth region); Vertical cylinder in stem

  Function: Produces secondary xylem and phloem through cell division

• Fiber caps

Transverse Section of Roots in Dicotyledonous Plant (HINT: 5 features)

• Vascular bundle

  Contains xylem (inside), phloem (outside), and cambium tissue

  Function: Arranged in centre → Structural support; Withstand stretching roots

• Xylem

  Function: Water and minerals transportation

• Phloem

  Function: Carbohydrate transportation

• Cortex

  Cylinder of tissue around stem; Has cells with secondary thickening in cell walls

  Function: Storage of reserve food

• Epidermis

  Surface of stem made of cell layers; Embedded with stomata

  Function: has root hairs → Increased SA for substance exchange

Movement of Tissue Fluid in Capillaries

Tissue fluid = Aqueous portion of plasma including dissolved substrates; Formed by pressure filtration of plasma in capillaries

• Leak out through fenestrations

• Promoted by higher pressure of blood from arterioles

Lower pressure in venules allow tissue fluid to drain back into capillaries

Composition of Plasma and Tissue Fluid (HINT: 7 elements)

• Cells

  Plasma: Red + White blood cells, platelets

  Tissue fluid: Phagocytes

• Proteins

  Plasma: Higher concentration; Large proteins and hormones

  Tissue fluid: Lower concentration; Small proteins

• Glucose

  Plasma: Higher concentration; ~70-100 mg per 100 mL

  Tissue fluid: Lower concentration; Used by cells for respiration

• Fats

  Plasma: Lipoproteins

  Tissue fluid: N/A

• Amino acids

  Plasma: Higher concentration

  Tissue fluid: Lower concentration

• Oxygen

  Plasma: Arterioles - High concentration; Venules - Low concentration

  Tissue fluid: Lower concentration; Used by cells for respiration

• Carbon dioxide

  Plasma: Arterioles - Low concentration; Venules - High concentration

  Tissue fluid: Higher concentration; Released by cells from respiration

Drainage of Excess Tissue Fluid ~ Lymphatic system

Presence of valves + Thin walls with gaps in lymph ducts

• Lymphatic capillaries (small, gapped tubes with thin walls) facilitate easy movement of water and solute

  • Collection of lymph in lymphatic capillaries prevent build up and swelling around body cells

• Valves assist with movement of lymph + Prevent back flow

Return of lymph to blood circulation

• Through veins near heart

• Facilitated by lymph nodes (Contain phagocytes to filter cellular debris & micro-organisms + immune cells)

Single VS Double Circulation (Circuit diagrams)

FISH (& some invertebrates):

Heart → Artery → Gill capillaries → Systematic capillaries → Vein

• Blood flows once in one circuit

• One pathway

• Two heart chambers

• Low blood pressure → Low efficiency

MAMMALS (& birds):

Heart (Right atrium and ventricle) → (Pulmonary circuit) Lung capillaries → Heart (Left atrium and ventricle) → Artery → (Systemic circuit) Systemic capillaries → Vein

• Blood flows once in two circuits

• Two pathways; Pulmonary and systemic

• Four heart chambers

• High blood pressure → High efficiency

Adaptations of Mammalian Heart for Delivery of Pressurised Blood to Arteries (HINT: 8 features; Indicate direction of blood + Label)

Cardiac Muscle

• Striated, branched, interconnected by intercalated discs

• Allow for coordinated contraction and relaxation of heart

• Myogenic (Originate from muscle, not nerve impulses)

Pacemaker

• Specialised cells in right atrium

• Generate electrical impulses; Regulate heart rhythm + Initiate heartbeat

Atria

• Thin walls of cardiac muscles; At top chambers

• Receive blood returning to heart + Help transfer to ventricles

Ventricles

• Thicker walls; At bottom chambers

• Forcefully contract to pump blood out of heart to lung (right) / body (left)

Atrioventricular valves (Tricuspid & Mitral valves)

• Between atria and ventricles

• Prevent back flow of blood from ventricles back to atria

Semilunar valves (Pulmonary & Aortic valves)

• Located at exits of ventricles

• Ensure blood flows one-way from ventricles to arteries

Septum

• Thick muscular walls separating left and right parts of heart

• Prevent mixing of oxygenated and deoxygenated blood

Coronary arteries

• Small arteries and veins

• Supply heart with oxygen and nutrients to fulfil high metabolic demands

Stages in Cardiac Cycle

NOTE: Electrocardiogram (ECG)

• Atrial systole: Blood moves from atrium to ventricle through atrioventricular valves (tricuspid and mitral valves)

  P-wave: Depolarisation of atria; Electrical impulse spreads from sinoatrial node to walls of atria causing muscle contraction

  hey these are my flashcards so imma add whatever i want here hehe apparently the “sino-” prefix relates to “sinus” which in latin means hollow or curve so um thats cool 

  • PR-interval: Delay to reach atrioventricular node (causes ventricular systole); Time for impulse to travel is ~0.1 seconds

  Atrial pressure: Increases → Falls ; Rise → Decline on graph

  • Fall when atria stops contracting

  Aortic pressure: High; Flat on graph

  Ventricular volume: Increase; Bump on graph

  Ventricular pressure: Slight increase as blood flows in

• (Beginning of ventricular systole) Isovolumetric contraction: Interval between closing of AV valves and opening of SV (Both AV valves and semilunar valves are closed); Amount of blood in ventricle remains same

  • AV valves closes when ventricular pressure > atrial pressure

  QRS Complex: Polarisation of ventricles

  • Bundle branches and purkinje fibre carries signals from atrioventricular node to heart apex throughout ventricles

    ok bio is weird idk why it's called the apex but its the very bottom tip of the heart

  Atrial pressure: Increases; Bump on graph – c-wave

  • Blood in ventricles bulges against closed AV valves

  Aortic pressure: High; Flat on graph

  Ventricular volume: No difference; Flat line on graph

  Ventricular pressure: Significant increase; Sharp gradient on graph

• Ejection: Opening of semilunar valves (aortic and pulmonary valves) due to high ventricular pressure overcoming aortic pressure; Blood flows from ventricle into aorta and enters systemic / pulmonary circuit

  T-wave: Repolarisation of ventricles; Ventricles relax

  Atrial pressure: Decrease → Gradual increases; Decline → Slow rise on graph

  • Blood in ventricles are now exiting through SV → No longer pushing against AV

  • Since SV is closed and atria are relaxed, blood gradually flows back in → Atria becomes filled

  Aortic pressure: Increase → Decrease; Rise → Fall on graph

  Ventricular volume: Significant decrease; Decline on graph

  Ventricular pressure: Initially increase (Higher than aortic pressure) → Decrease; Parabola / Rise → Decline on graph

  • Decrease due to repolarization

• Isovolumetric relaxation: SV valves close, ventricles relax

  End of T-wave: Ventricular repolarisation → Relax

  Atrial pressure: Increases; Slight rise on graph

  Aortic pressure: Small increase; Bump in graph

  • Blood in aorta briefly flows backwards and hit closed SV

  Ventricular volume: No difference; Flat line on graph

  Ventricular pressure: Decrease significantly (Below atrial pressure); Steep drop on graph

• Ventricular filling: Since ventricular pressure is below atrial pressure, AV valves reopen, blood partially flows from atria to ventricles via passive filling

  Flat line

  Atrial pressure: No difference; Flat line on graph

  Aortic pressure: Decreasing; Gradual decline in graph

  Ventricular volume: Gradual increase; Rise on graph

  Ventricular pressure: No difference; Flat line on graph

NOTE: Ventricular systole is from Q to T

On phonocardiogram…

• “Lub” = AV closing

• “Dub” = SV closing

Other Mechanisms of Water Transport by Generation of Root Pressure

When transpiration pull is insufficient for transport in xylem, e.g.

• During high humidity which prevents transpiration

• In spring, before leaves on deciduous plants have opened

Root pressure generates positive pressure potential

• Active transport of minerals and ions from soil to root cells creates accumulation of solutes in cells

• Lowers water potential inside cells → Causes water to move into cells by osmosis → Increases pressure inside cells → Positive pressure helps push water up the xylem

Phloem Translocation of Sap + Adaptations

Active loading of sucrose into sieve tubes at source creates positive pressure potential + Water pressure created by entry of water by osmosis at source (Due to high solute concentration) → Translocation; Mass flow of phloem sap forward towards sink

Living tissue → Active transport + Response to environmental changes

Sieve tube elements

• Sieve plates with pores → Allow sap to pass from one cell to another

• Reduced cytoplasm and organelles + No nucleus → Ease flow of sap which travels within the tube like area of elements (Translocation)

Companion cells

• Presence of many mitochondria → Actively load sucrose into phloem

• Plasmodesmata between them → Allown cytoplasm of tube cell to be shared + Origin of proteins and ATP needed by sieve tube elements

Ease flow of sap

Enhance loading of carbon compounds into phloem sieve tubes at sources (leaves) and unloading of them at sinks (roots)

Importance of POSITIVE Pressure Potentials in Xylem

Aids in water uptake, counteracts transpiration pull, and structural support?

System Integration

Necessary process in living systems

Coordination = Needed for component parts of a system to collectively perform an overall function

Hierarchy of Body Systems

Cells → Tissues → Organs → Organ systems

• Integrated in a multicellular living organism

System Integration & Emergent Properties + Example

System Integration = Responsible for emergent properties

• Emergent properties – Properties that result from various interactions in system + Do not exist in individual components of the system

For example, for the cheetah…

• Cellular level

  Cheetah DNA → Controls body shape + Pigmentation of the fur → Creates spots for camouflage → Advantage in hunting and hiding

• Tissue level

  Loose hips and shoulder joints + Flexible spine → Flexes to store potential energy & springs back to release → Running

  Smaller teeth → Larger nasal passage → Quick air intake

• Organ level

  Enlarged heart → Effective delivery of glucose & oxygen to muscles → Rapid physical response

  Position of eyes → Maximum binocular vision → Assess distances to prey accurately

• Organ system

  Breathing system → Rapid delivery of oxygen to muscles + Circulatory system → Delivers blood to muscles + body ⇒ Run at high speeds

• Organism level

  Narrow paws → Minimal contact with ground + Blunt claws → Increase traction + Long tail → Counterbalance ⇒ Run at high speeds & Fast acceleration for chasing prey

Integration of Organs in Animals (Role of Endocrine)

Regulate homeostasis within body; Widespread response

• Slow but long-lasting

• Controls longevity, growth, and homeostasis (Involuntary factors)

• Hormones = Chemical messengers; Manufactured by glands

  • Relies on circulatory system to be transported

  • From endocrine cell → Bloodstream → Target cell

Integration of Organs in Animals (Role of Nervous)

Receive information from various sensory inputs; Localised effects

• Integrate information and trigger electrical impulses to send out signals

  • Neurons transmit and receive impulses

• May be result from hormones released by glands in endocrine system

• Quick but short-lived → For survival

Integration of Organs in Animals (Role of Circulatory System)

Helps transport…

• Glucose and oxygen to the nerves and endocrine glands for energy

  • More generally, transport oxygen from lungs → legs

• Hormones throughout body (endocrine signalling)

• Waste products like CO₂ and ammonia out of body

  • Urea produced by liver as waste from protein metabolism → Kidneys for filtration → Urine

Integration of Organs in Animals (Example)

Epinephrine

• Sensory organs transmit information

• Nervous system to trigger fight-or-flight response → Signal release

• Adrenaline is released from adrenal glands → Body responses

Organisation of Nervous System

Central nervous system

• Brain

• Spinal chord

Peripheral nervous system

• Somatic

• Autonomic

  • Sympathetic

  • Parasympathetic

Role of Brain in Nervous System (HINT: 6 Parts)

Brain = Central information integration organ

• Processes information combined from several inputs

• Learning & memory

Three main areas:

1. Cerebrum

   Divided into cerebral hemispheres consisting of four lobes

   MAIN ONES TO KNOW:

   • Frontal Lobe: Learning new information

     Reasoning, motor control, emotion, language

   • Temporal Lobe: Storing and retrieving memories

     Managing emotions

     Processing information from sense; Understanding language

   • Occipital Lobe: Memory formation

     Visuospatial processing; Distance & depth perception

     Color determination

     Object and face recognition

     
     

2. Cerebellum

   Coordinates voluntary movements; Balance and equilibrium

3. Brainstem

   Connects cerebrum, spinal chord and cerebellum

   Controls involuntary impulses + ANS

Sensory Neural Pathway (Neural Pathway Pt. 1)

Input to spinal cord and cerebral hemispheres through sensory neurones

1. Sensory receptor is stimulated

2. (Transduction) Physical signal is converted into electrical impulse down axon to spinal cord and brain

3. Sensory neurons convey messages from receptor cells to CNS

4. Electrical signal causes release of neurotransmitter at a synapse between sensory neuron and interneurone

5. Neurotransmitter stimulates interneuron to form action potential which travels along its axon

6. Action potential is transmitted until activates interneurones in higher parts of brain → Perception; Conscious awareness of touching happens

Neural Motor Pathway (Neural Pathway Pt. 2)

Output from cerebral hemispheres to muscles through motor neurons

1. Stimulus in brain → Forms action potential in upper motor neurone

2. Action potential stimulates release of neurotransmitter in synapse between upper and lower motor neurons

3. Forms action potential in lower motor neurons which stimulates release of neurotransmitter at neuromuscular junctions

   • Connected to skeletal muscle fibers

4. Neurotransmitters stimulate muscle fibers → Form muscle action potentials → Muscle contraction (movement)

Role of Cerebellum in Skeletal Muscle Coordination

Receive feedback impulses from moving area of body & sensory organs → Sends out impulses to motor neurons → Coordinate & Fine-tuning movement; Smooth and balanced muscular activity

• Note initiation of muscle contractions is from motor cortex of cerebrum

  • Cerebellum does NOT initiate muscle contractions

• Coordinates posture, balance, etc.

• Overall control of movements of body including skeletal muscle contraction and balance

Nerve Bundles + Transverse section of Nerve

In cross section diagram of brain…

• Gray matter = Neuronal cell bodies

• White matter = Myelinated axons

  
  

Nerves = Bundles of sensory and motor neurones; Covered by layers of protective sheath (Made of connective tissue)

• Endoreneurium = Tissue surrounding each individual nerve fiber

• Perineurium = Smooth connective tissue surrounding each fiber bundle

• Epineureum = Fibrous tissue surrounding many bundles of nerve fiber; Covers most large nerves

Neurones can be unmyelinated or myelinated…

• Schwann cells wrapped around axon

• Nodes of Ranvier = Intervening areas between Schwann cells

  • Action potentials can skip from one node to another → Faster transmission compared to unmyelinated axons

Spinal Cord and Unconscious Processes

Spinal cord = Integrating center for unconscious processes

• Receptors in the body receive stimulation information and pass it to spinal cords and onto cerebral hemispheres

  • Receptors for unconscious processes:

    Osmoreceptors
    Change in osmotic pressure / Concentration of bodily fluids

    Baroreceptors
    Blood pressure and help with its regulation

    Proprioceptors
    In muscles, tendons, and joints; Body position and movement

  • Receptors for conscious processes:

    Proprioceptors

    Photoreceptors
    In eyes; Respond to light + Allow sight

    Thermoreceptors
    Changes in temperature

    Mechanoreceptors
    Respond to mechanical stimuli (touch, pressure, vibration)

    Chemoreceptors
    Detect chemical stimuli (taste, smell)

• White matter = Carry information to / from CNS & body

• Grey matter = Integration & processing of information

Conscious VS Unconscious processes

• Conscious = Deliberate and voluntary

• Unconscious = Automatic and involuntary

Example of Involuntary Response

Pain reflex arc = Involuntary response; Skeletal muscle as effector

Evoluntary advantage to limit damage to body tissue by generating quick reaction involving minimal (three) neurons

• Free sensory neuron (Pain receptor i.e. nocireceptor in hand) is stimulated → Initiate afferent (sensory) action potentials → Travel through hand → Joins a spinal nerve

• Afferent neuron forms a synapse with a short interneuron in grey matter of spinal cord

• Interneuron synapses with a motor neuron → Forms action potential → Travel to effector (arm muscles) → Movement (pull away)

• Sensation of pain must travel to cerebrum

Circadian Rhythm

Circadian rhythm = Controlled by biological clock; 24 hour cycle

Modulation of sleep patterns by melatonin secretion

• Regulated by pineal gland, hypothalamus, and pituitary gland

• Melatonin = Amine hormone

Diurnal pattern of melatonin secretion by pineal gland → Helps establish cycle of sleeping and waking

• When awake, LOW melatonin, HIGH cortisol

• When asleep, HIGH melatonin, LOW cortisol

• Exposure to light in retina inhibits melatonin production → Wakefulness during day / light period

Epinephrine and Vigorous Activity

Medulla of adrenal glands (located at upper side of kidneys) secrete epinephrine to prepare body for vigorous activity

• During times of stress; Fight-or-flight response

• Epinephrine = Peptide hormone

Widespread effects of epinephrine in the body

• Increased heart rate → Increased delivery of oxygen to tissues

• Increased breathing rate

• Stimulates glycogenolysis in liver cells → Increased blood glucose

Enables increased rates of aerobic respiration → Increased ATP production in muscle tissues → Facilitates intense muscle contraction

Hypothalamus, Pituitary Gland, and Endocrine System + Example

Hypothalamus and pituitary gland controls endocrine system

• Hypothalamus = Has receptors that detect changes in blood + Receives signals from neurons

  Signals stimulates neurosecretory / glandular cells to produce and secrete hormones that stimulate / inhibit hormone release in pituitary gland

  • Anterior and posterior lobes secrete their own hormones

For ADH…

• Hypothalamus produces ADH and sends to posterior pituitary

• Osmoreceptors in hypothalamus sense water content of blood

• If necessary, transmits action potential to cells in posterior pituitary gland

• Signals posterior pituitary gland to secrete hormone into bloodstream

• ADH reaches target tissue (collecting tubules in nephrons) → Higher water reabsorption

Maintain homeostasis by negative feedback

Feedback Control of Heart Rate

Feedback control of heart rate following sensory input from baroreceptors and chemoreceptors

• Baroreceptors = Monitor stretch in arteries → Indirect measurement of blood pressure + Volume of blood pumped by heart

  • Distension of arterial wall → Increased rate of action potentials sent to medulla

  • Carotid sinuses / Arch of aorta

• Chemoreceptors = Detect oxygen, carbon dioxide and pH levels in capillaries

  • When cellular respiration is increase, O₂ ↓ CO₂ ↑ pH ↓ (CO₂ combines with water in blood; forms carbonic acid) → Increased rate of action potentials to the medulla

  • Carotid sinuses / Arch of aorta

    
    

Role of medulla in controlling heart rate

• Sends nerve impulses to SA node to…

  • Adjust heart rate

  • Regulate stroke volume

Feedback Control of Ventilation Rate

Feedback control of ventilation rate following sensory input from chemoreceptors

• Changes in pH levels of blood are monitored by chemoreceptors in the brainstem; Caused by…

  • Increased physical activity → Increased respiration rates → Higher concentration of CO₂ → Increased H^₊ ions → Increased action potentials to medulla

  • In blood, CO₂ combines with water to form of carbonic acid which later becomes bicarbonate and hydrogen ions

• Control of ventilation rate using signals to the diaphragm and intercostal muscles

Control of Peristalsis by Enteric Nervous System

Enteric nervous system = Controls digestive system

CNS + ENS → Control of peristalsis in digestive system

• Initiation of swallowing of food

  • Food forms into boluses in alimentary canal

• Peristalsis (Under involuntary control of ENS)

  • Contraction and relaxation of circular and longitudinal muscles

  • Keep food moving in one direction
    (From oesophagus → intestines → rectum)

• Egestion of faeces (Under voluntary control of CNS)

Peristaltic reflex works by…

• Triggered by boluses (food formed in alimentary canal); Bolus causes distension in surrounding area → Activates stretch receptors in ENS

• Receptors connect with relay neurons

• Relay neurons connect with motor neurons

  Contract smooth muscle behind bolus + Relaxes smooth muscle ahead → Push forward + Create space for food to pass through

ENS ensures passage of material through gut is coordinated

Phototropism

Positive phototropism = Directional growth response to lateral light in plant shoots

Phytohormones + Examples

Phytohormones = Signalling chemicals which control growth, development, and response to stimuli in plants

Examples include…

• Auxin → Plant cell elongation

• Cytokinin → Increased rate of cell division

• Ethylene → Promote fruit ripening

• Gibberellin → Control stem elongation, seed germination, flowering, and dormancy

Auxin & Auxin Efflux Carriers

Auxin = Phytohormone produced in growing regions of plants (Tips of shoots, roots, and growth buds)

• In growing areas where evenly concentrated, cell elongation is uniform

  • When concentrated on certain areas → Differential growth

• Can enter cells easily by diffusion but require efflux carriers to exit cell

  
  

Auxin efflux carriers = Maintaining concentration gradients of phytohormone

• Can be positioned in a cell membrane on one side of cell

• If all cells coordinate to concentrate efflux carriers on same side of cell, auxin can be actively transported from cell to cell through plants tissue → become concentrated in specific part of plant

Promotion of Cell Growth by Auxin

Cell elongation is facilitated by…

• Auxin stimulates synthesis of proton pumps

• Promotes secretion of hydrogen ions into apoplast

  • Apoplast = Area including cell wall and intercellular spaces

• Acidfies cell wall and activate expansin

• Loosen hydrogen bond cross links between cellulose molecules

• Absorption of water generates high turgor internal pressure + Loosened cellulose fibers are allowed to slide past each other and reposition themselves

• Forms new hydrogen bonds as elongated cell (walls)

Concentration gradients of auxin → Differences in growth rate needed for phototropism

• Elongation of cell on shaded side for new growth and turn towards the sun

Auxin and Cytokinin in Regulating Growth

Root tips produce cytokinin (promotes cell division) → Transported to shoots

• Transported via xylem fluid

Shoot tips produce auxin (promotes cell elongation) → Transported to roots

• Transported via phloem sap

Interactions between them ensure root and shoot growth are integrated

• HIGH auxin, LOW cytokinin → Rooting

• LOW auxin, High cytokinin → Shooting

• At certain concentrations, they works synergistically with each other

Feedback Control of Fruit Ripening

Positive feedback in fruit ripening and ethylene production

• Ethylene = Stimulates changes in fruits for ripening which in turn increases production of ethylene

Benefits of positive feedback mechanism

• Ensuring fruit ripening is rapid and synchronised

  • Due to its gaseous nature, also transmits to adjacent fruits

• Rapid ripening in large volume → Effectively attracts herbivores to consume fruit and disperse seeds (propagation)

Homeostasis & Homeostatic Variables

Maintenance of internal environment of organism

• Variables are kept within preset limits despite fluctuations in external environment

• Homeostatic variables in humans may include

  • Body temperature, blood pH, blood glucose concentration, and blood osmotic concentration

Negative Feedback Loops in Homeostasis

Negative feedback loops are…

• Used to return homeostatic variable from higher or lower values to a set point and keeps values within a narrow range

• Positive feedback loops would amplify responses which is less applicable

Example of Role of Hormones in Homeostasis

Regulation of blood glucose by secretion of insulin and glucagon

• By pancreatic endocrine cells

  • α-cells secrete glucagon

  • β-cells secrete insulin

• Transported through blood stream

Insulin works by…

• Opening protein channels in cell membranes → Allow facilitated diffusion for glucose uptake

• Stimulate muscles to take in more glucose / store as glycogen → Reduce blood glucose levels

Glucagon works by…

• Acts on stored glycogen in liver and muscles

• Glycogen is hydrolysed to glucose → Enters bloodstream; Increased blood glucose level

Type 1 Diabetes

• Physiological changes
  Autoimmune condition; β-cells are destroyed → Insulin can’t be produced

• Risk factors
  Family history, age

• Methods of prevention
  N/A

• Treatment
  Insulin injections, blood glucose monitoring, diet control

Type 2 Diabetes

• Physiological changes
  Insulin resistance; Body receptors don’t respond properly to insulin and cells cannot take in glucose

• Risk factors
  Family history, obesity, lack of exercise

• Methods of prevention
  Good eating habits, regular exercise

• Treatment
  Diet control, exercise, and medication

Example of Negative Feedback Control

In thermoregulation…

• Thermoreceptors in hypothalamus and skin (peripheral) sense temperature of blood

  • Peripheral thermoreceptors send impulses to the hypothalamus

• Hypothalamus responds by initiating cooling or heating mechanisms through stimulating pituitary gland

  • HEATING MECHANISM: Hypothalamus stimulates the pituitary gland to release hormones to activate the thyroid gland → Thyroid gland releases thyroxin to increase metabolic rate of body → Generate heat

  • COOLING MECHANISM: Hypothalamus stimulates the pituitary gland to release hormones that inhibit the release of thyroxin → Decrease metabolic rate of body → Reduce heat production

  
  

Example of effectors of temperature change: Muscle and adipose tissue

• Hypothalamus initiates shivering

  • Generate heat by muscle movement

• Marine mammals also have layer of blubber (adipose tissue) for insulation

  • Helps retain warmth generated by internal metabolic activities

Thermoregulation Mechanisms

Ectotherms = Animals that don’t control their internal body temperatures

Endotherms = Maintain steady internal temperature

• Birds and mammals maintain body temperature through behavioural and physiological means

  Cerebrum initiates conscious behaviours

  E.g. Move around more to generate muscle heat, dress warmer, stay inside / Seek shade, use air conditioning, wear light clothing, stop exercising

Thermoregulation in humans

HEATING MECHANISM

• Vasoconstriction

  Arterioles near skin become smaller → More blood is shunted to internal organs / Capillaries receive less blood → Preserve vital internal organs + Prevent heat loss to surroundings

• Shivering

  Muscle movement → Generate heat

• Uncoupled respiration in brown adipose tissue (Lots of mitochondria)

  Undergo cell respiration uncoupled from ATP production / Oxidise glucose → Generate heat

• Hair erection

  Release of epinephrine → Goosebumps on skin + Raised hairs → Create insulating layer of air between fur and skin → Protect body from cold air

COOLING MECHANISM

• Vasodilation

  Hypothalamus sends impulses to arterioles near skin → More blood travel through capillaries in skin → Release of more heat to surrounding air

• Sweating

  Hypothalamus initiate perspiration → Heat from body is transferred to water in sweat → Evaporation of sweat from skin → Evaporative cooling

Role of Kidneys in Osmoregulation and Excretion (HINT: 5 parts)

Excretion VS Osmoregulation

• Osmoregulation = Regulation of osmotic concentration (osmoses per L)

• Excretion = Production of urine for leaving body

Nephron = Filtering unit in kidney; ~1.25 million in each kidney

• Thin tubules → Increased SA:V ratio

• Capillaries wrapped around → Movement of substances to bloodstream

Within the nephron…

• Glomerulus = Capillary bed

  Ultrafiltration of substances from blood under hydrostatic pressure

• Bowman’s capsule

  Collect filtrate from glomerulus

• Proximal / Distal convoluted tubule & Loop of Henle

  Pathway for filtrate to travel; Adjust water and salt concentrations

• (Peritubular) Capillary bed

  Surrounds tubules for reabsorption into blood

• Collecting duct

  Collect final urine to send out of kidney

Role of Glomerulus, Bowman’s Capsule, and Proximal Convoluted Tubules in Excretion

Ultrafiltration (In bowman’s capsule) remove solutes from blood plasma under high pressure

• Blood enters via afferent (wide) arteriole → Branches out to glomerulus → Exit through efferent arteriole (narrow diameter → high hydrostatic pressure)

• Fenestration in walls of glomerulus → Substances move into Bowman’s capsule (Becomes part of filtrate)

  • Water, glucose, Na⁺, Cl^-, amino acids, urea'

Useful substances (H₂O, Na⁺, Cl^- and glucose) are then reabsorbed into peritubular capillaries

• Filtrate travels into proximal convoluted tubule for selective reabsorption (All glucose, amino acids, vitamins, hormones, water, and most mineral ions are reabsorbed)

  • Tubule has microvilli → Increased SA for reabsorption

  • Mineral ions and vitamins are actively transported by protein pumps and carrier proteins

  • Glucose and amino acids are cotransported via symporters across apical membrane with sodium

  • Water follows movement of mineral ions (passive diffusion via osmosis)

Toxins and unwanted solutes are left in filtrate → Excreted in urine

Role of Loop of Henle

Descending limb = Permeable to WATER / Impermeable to SODIUM IONS

• High osmotic concentration in medulla creates osmotic gradient

• Water leaves filtrate by osmosis

• Solute concentration in filtrate increase as loop descends

Ascending limb = Permeable to SODIUM IONS / Impermeable to WATER

• Active transport of sodium ions into medulla, followed by Cl^- ions

• Solute concentration in filtrate decreases as loop ascends

  • Maintains high osmotic concentrations in medulla

• Facilitates water reabsorption in collecting ducts

Remaining liquid enters distal convoluted tubule

• Output of urine is more dilute than input

• Large amounts of salts are removed

Osmoregulation in Collecting Ducts (ADH)

Role of osmoreceptors in the hypothalamus

• Monitors water content of blood → Control release of ADH

Changes to the rate of antidiuretic hormone secretion by the pituitary gland

• ADH changes permeability of collecting duct

• ADH switches location of aquaporins between cell membranes and intracellular vesicles in cells of collecting ducts

  • When ADH present, aquaporins (where water move OUT of collecting duct) are inserted into membranes to allow water reabsorption

Changes in Blood Supply in Response to Activity

Controlled by vasodilation and vasoconstriction

To…

• Skeletal muscles

  Can withstand large volume changes

  Vasodilation in muscle arterioles to increase blood during exercise

• Gut

  Can withstand large volume changes

  Vasoconstriction in gut arterioles to decrease blood during exercise

• Brain

  Maximum blood flow during REM sleep

• Kidneys

  Maximum blood flow during sleep and wakeful rest

Neurons + Structure

Cells within nervous system that carry electrical impulses along their fibers

• Cell body = Cytoplasm and nucleus; Elongated nerve fibres project from it

• Axon = Long, single fiber

• Dendrites = Multiple shorter fibers

Nerve Signals / Impulses

Action potentials propagated along nerve fibers

• Impulses = Electrical; Involves movement of positively charged potassium and sodium ions

Generation of Resting Potential by Sodium-Potassium Pumps (HINT: 3? Nah. 2? Ok)

BTW: Potential difference ~ Voltage

Pumping establish and maintains concentration gradient of potassium and sodium ions

• Energy from ATP drives pumping of sodium and potassium ions AGAINST concentration gradient through sodium-potassium pumps across plasma membrane of neurones

  • Three Na⁺ OUT

  • Two K⁺ IN

• Negative resting potential (-70 mV) due to imbalance of positive and negative charges across membrane

Stages of Nerve Impulse (Membrane Potential and Polarisation)

Membrane potential = Difference in charge across membrane of neurons; Allows creation of electrical signals

• Resting potential = Difference in charge when neuron is NOT firing

• Action potential = Difference in charge when neuron is FIRING; Rapid change resulting in nerve impulse

Stages:

1. Resting potential

   • Outside is relatively more positive; Na⁺ are concentrated OUTSIDE / K⁺ = INSIDE

2. Depolarisation = Change from resting to action potential

   • Opening of Na⁺ channels in response to signal initiated at dendrite (Inside becomes positive) → Passive influx of Na⁺ ions

3. Repolarisation = Restoration from action to resting potential

   • Opening of K⁺ channels (Inside becomes negative) → Passive efflux of K⁺ ions

4. Refractory period = Between action potentials

   • Since concentration of K⁺ is OUTSIDE / Na⁺ = INSIDE, sodium potassium pump restores concentrations to resting potential via anti porter action

   • Leakage channels allow for back flow of ions

Variation in Speed of Nerve Impulse

Myelinated VS Non-myelinated: Myelinated axons conduct faster

• Skin temperature receptor axon: 5 μm; 20 ms^-1

  Schwann cells around the axons provide insulation

  Electrical signals can jump between nodes of Ranvier and travel fast

Giant axons of Squid VS Non-myelinated: Axons with greater diameter conduct faster

• Squid: 500 μm; 25 ms^-1

• Internal organ axon: 1 μm; 2 ms^-1

(Chemical) Synapses

Junction between neurons / between neurons and receptor / effector cells

• Where signals are transferred through neurotransmitters

A signal can only pass in ONE DIRECTION across a typical synapse

Presynaptic cell = Neuron transmitting a signal and releasing neurotransmitters into synaptic cleft

Postsynaptic cell = Neuron receiving the signal by detecting presence of neurotransmitters

Processes in Synapses (Release of Neurotransmitter from presynaptic membrane)

Uptake of calcium in response to depolarisation of presynaptic membrane

Action as signalling chemical inside neurone

Steps:

1. Action potential arrives

2. Depolarisation of presynpatic membrane → Uptake of calcium

   • Calcium ions = Signalling chemicals → Trigger movement of vesicles through cell

3. Vesicles fuses with plasma membrane

4. Neurotransmitter is release into synaptic cleft

5. Neurotransmitter binds to receptors on postsynaptic neuron

Processes in Synapses (Generation of Excitatory Postsynaptic Potential)

Diffusion of neurotransmitters across synaptic cleft

Binding to transmembrane receptors

Processes in Synapses (Depolarisation and Depolarisation During Action Potential)

Action of voltage-gated sodium and potassium channels (See before)

• Stimulus causes their opening and subsequent diffusion of ions along concentration gradient

Need for threshold potential to be reached for sodium channels to open

• Action potential must reach minimum threshold potential in order to be self-propagated

Propagation of Action Potential Along Nerve Fibre

Due to local currents

Diffusion of sodium ions inside and outside axon cause threshold potential to be reached

• Depolarised area is initially localised

• Na⁺ ions that have entered diffuse to nearby areas → Raise axon voltage high enough to overcome threshold potential

Saltatory Conduction in Myelinated Fibers

Saltatory conduction = “Jumping” of impulses between nodes (depolarised region) → Achieve faster impulses

Ion pumps and channels are clustered at nodes of Ranvier

• Ion movement only occurs at nodes instead of whole axon → Less energy to fuel sodium-potassium pump + instantaneous response

Action potential is propagated from node to node

Effects of Exogenous Chemicals on Synaptic Transmission + Example

Exogenous chemicals = Chemical from outside cell / body

Neonicotinoids = Pesticide that blocks synaptic transmission

• Binds to acetylcholine receptors

• Cannot be broken down by acdtylcholinesterase (Irreversible binding) → Block cholinergic synapse

Cocaine = Drug that blocks reuptake of transmitter

• Affects dopamine, serotonin, and norepinephrine

• Binds to transporters that remove excess neurotransmitters from synaptic cleft

• Prevent reabsorption of neurotransmitters → Increased concentration → Enhances effects on postsynaptic neurons + Increased production of receptors → Increased sensitivity → Addiction / Depression

Excitatory VS Inhibitory Neurotransmitters + Generation of Excitatory VS Inhibitory Postsynaptic Potentials

EXCITATORY –

Acetylcholine

• Exists in many types of synapse including neuromuscular junctions

  Excitatory within neuromuscular junction

  Inhibitory within heart

• Acetylinecholinesterase breaks it down for recycling → Prevent sustained activation

• Generate action potential by increasing permeability of postsynaptic membrane to positive ions

  • Na⁺ ions in synaptic cleft diffuse into postsynaptic neuron

INHIBITORY – 

GABA

• Hyperpolarization inhibits action potentials

  • Binds to specific receptor causing Cl^- to move into / K⁺ move out of postsynaptic neuron

  • Postsynaptic membrane becomes hyperpolarized (More negative than normal) → Hard to overcome threshold potential

Summation of Effects of Excitatory and Inhibitory Neurotransmitters in Postsynaptic Neuron

Multiple presynaptic neurons interact with all or nothing consequences in terms of postsynaptic depolarisation

• EPSP → Depolarisation

• IPSP → Hyperpolarisation

• EPSPs combine via temporal or spatial summation → Threshold is reached → Action potential

  • Accumulation of EPSPs over time / in certain area

• EPSP + IPSP → NO Action potential

Perception of Pain

By neurons with free nerve endings in skin

Nerve endings have channels for positively charged ions

• Open in response to stimulus

  E.g. High temperature, acid, or certain chemicals like capaiscin

Entry of positively charged ions causes threshold potential to be reached

Nerve impulses pass through neurons to brain → Perception of pain

Consciousness

Emergent property from interaction of individual neurons in brain