Section 6 - Organisms respond to changes in their environments
14 Response to stimuli
15 Nervous coordination and muscles
16 Homeostasis
Internal and external stimuli
Receptors
Nervous coordination
Skeletal muscle
Homeostasis
Homeostasis
Heart rate
External stimuli
Myogenic - contraction is initiated from within heart itself
Autonomic nervous system
Chemoreceptors and baroreceptors
Sino-atrial node
Electrical wave is transmitted throughout heart
CO2, pH, and pressure changes
Parasympathetic - decreases heart rate
Sympathetic - increases heart rate
Pacinian corpuscle
Rods and cones in retina
Distribution in retina (periphery and fovea)
Cone cells are sensitive to wavelength and colour
Retinal convergence with rods
Different light sensitives
Visual activity
Layers of connective tissue surrounding a neurone ending
Specific to detecting mechanical pressure
Converts mechanical energy into a generator potential
Stretch-mediated sodium channels are deformed when pressure is applied
Influx of sodium ions depolarises the membrane of the neurone
Responses
Plants
Stimulus - a change that is detected and leads to a response
Motile organisms
Kinesis
Change in speed of movement or rate of turning
Taxis
Movement (not growth) of an organism in response to a stimulus
Increases chance of survival
Three neurone reflex
Stimulus - receptor - sensory neurone - intermediate neurone - motor neurone - effector - response
IAA, an auxin, controls plant cell elongation
Gravitropism
Phototropism
Negative gravitropism in shoots - grow away from force of gravity
Positive gravitropism in roots
IAA is produced in tip of root an moves to the lower side of the root
IAA inhibits cell elongation in roots
Negative phototropism in roots
IAA synthesised in the tip moves down to the shaded side of the shoot
Shoots grow and bend towards light - positive phototropism
Nerve impulses
Synaptic transmission
Synapse
Neuromuscular junction - between motor neurone and muscle end plate
Junction between 2 neurons
Inhibitory synapses
Chloride ion enter postsynaptic neurone
Hyperpolarisation
Summation
Spatial - multiple presynaptic neurones
Temporal - one presynaptic neurone firing many times
Undirectionality
Always from presynaptic neurone to postsynaptic neurone
Action potential
Resting membrane potential
Neuron = nerve cell
Stimulus opens voltage-gated sodium channels
Influx of sodium ions cause depolarisation of axon, which reaches a threshold
All-or-nothing principle
Action potential - wave of depolarisation
At +40mV, sodium channels close and potassium channels open
Repolarisation
Hyperpolarisation - temporary overshoot of outward potassium ions
Sodium-potassium channel returns membrane potential to -65mV
Refractory period
Discrete impulses
Limits number of impulses
Unidirectionality
Around - 65mV, in a polarised state
Sodium-potassium pump in axon membrane
3 sodium ions out, 2 potassium ions in
Protein channels allow ions to diffuse in and out
Membrane is more permeable to K+ ions, so some K+ ions diffuse back out
Structure
Adapted to carry rapid nerve impulses
Schwann cells
Cell body
Dendrites - carry nerve impulses towards cell body
Axon - single fibre that carries impulses away from cell body
Axons can be myelinated
Myelin sheath and nodes of Ranvier between
Muscle fibres
Muscle contraction
Structure
Fast twitch
Slow twitch
Calf and back muscles
Slow, sustained contractions
Store of myoglobin to provide oxygen
Aerobic respiration
Mitochondria
e.g. bicep
Thicker myosin filaments
Glycogen
Strong, fast contractions for a short period of time
Phosphocreatine to generate ATP rapidly
Sliding filament mechanism
Sarcomeres shorten
Neuromuscular junction
Motor unit = group of muscle fibres supplied by a single motor neurone
Action potential enters T-tubules
Release of calcium ions into sarcoplasm
Calcium binds to tropomyosin
Uncovers actin binding sites
Myosin heads bind to actin
Cross-bridge formaation
Myosin heads pull on actin
ADP released
ATP molecule attaches to myosin head
Myosin head detaches from actin
ATPase hydrolyses ATP to ADP
Calcium ions activate ATPase
Releases energy
Myosin head returns to original position, cycle repeats
Actin slides past myosin
Sarcomere - unit of muscle
Muscle contains bundles of muscle fibres
Actin (thin) and myosin (thick) protein filaments
Skeletal muscle is responsible for voluntary movement of the skeleton
Sarcoplasm around muscle fubres
Contains mitochondria and endoplasmic reticulum
Muscle fibres contain many myofibrils
Myofibrils consist of sarcomeres
Z-line - boundary of sarcomere
I-band - length of actin filament
Lighter than the A-band
A-band - length of myosin filament
Darker due to overlap of filaments
H-zone - in the centre of the A-band
Myosin heads
Blood glucose
Osmoregulation
Liver
Insulin
Diabetes
Glycogenesis
Type 1 and type 2
Insulin-dependent or insulin independent
Gluconeogenesis
Glycogenolysis
Regulates channel proteins and glucose uptake in cells
Pancreas
Activates enzymes to convert glucose into glycogen
Decreases blood glucose concentration
Glucagon
Activates enzymes to convert amino acids and glycerol into glucose
Increases blood glucose concentration
Activates enzymes to convert glycogen into glucose
Adrenaline
Second-messenger model of hormone action
Blood glucose is controlled to ensure the cells have enough respiratory substrates
Kidney
Cortex and medulla
Water potential of blood detected in hypothalamus
Nephron = functional unit of kidney
Glomerular filtrate - forms in Bowman's capsule
Glucose and water are reabsorbed in the proximal convoluted tubule
Loop of Henle - maintenance of sodium ion gradient
Counter-current multiplier
Water is reabsorbed in the distal convoluted tubule and collecting duct
ADH from posterior pituitary
Maintaining an internal environment within set limits
Temperature
Detected by hypothalamus
Too hot - vasodilation, sweating, seeking shade
Too cold - shivering, vasoconstriction, raising hairs on skin
pH
Need to control to maintain enzyme activity
Changes in water potential in blood and cells can lead to shrinkage or bursting
Need to control to maintain enzyme activity
Negative feedback
Positive feeback
The change detected leads to a further deviation away from the normal value
The change detected leads to a reduction in the stimulus, turning the system off or restoring to original level
Example - control of blood glucose