How is the pupil size controlled in BRIGHT light?

• STIMULUS: bright light• Detected by photoreceptors in the retina• Sends nerve impulses along optic nerve• Along sensory neurone• To CNS – Information is processes

• Impulses are sent along parasympathetic motor neurones• EFFECTORS: circular muscles of iris are stimulated– Circular muscles contract– Radial muscles relax

• Constrict pupils

How is the impulse propagated along a myelinated axon?

• Neurone is stimulated, causing voltage-dependent Na+ channels to open

• Na+ ions diffuse into axon• Depolarisation of membrane increases (to +40mv)• Action potential is generated at Node of Ranvier• Local circuit is produced• Second action potential is generated by the first• If potential difference threshold is reached, more Na+ channels open• Voltage-dependent Na+ channels close• Voltage-dependent K+ channels open• K+ ions move out of axon, repolarising membrane• Hyperpolarisation of membrane occurs• Voltage-dependent K+ channels close• K+ ions diffuse back into axon, recreating resting potential

What is the REFRACTORY PERIOD?

• A time delay between one action potential and the next

• Lasts until all voltage-dependent K+ and Na+ channels close, returning to normal resting potential state

• Ensures the impulses are UNIDIRECTIONAL: travel in just one direction

How are impulses passed along a MYELINATED neurone?

• Depolarisation occurs at Node of Ranvier• Local electric current occurs between nodes• Potential difference is reduced at the next

node, initiating another action potential• Impulses ‘jump’ from one node to the next by

SALTATORY CONDUCTION

How do Synapses transmit an impulse?• An action potential arrives at the presynaptic membrane• Membrane depolarises, causing:

– Calcium ion channels to open; calcium ions enter neurone• Increased calcium ion concentration causes synaptic vesicles

(containing neurotransmitter) to fuse with presynaptic membrane

• Neurotransmitter released into synaptic cleft by EXOCYTOSIS• Neurotransmitter binds with receptor proteins on postsynaptic

membrane, causing:– Cation channels to open; Na+ ions flow through channels

• Postsynaptic membrane depolarises, initiating an action potential• When released, the neurotransmitter is either:

– Taken up across the presynaptic membrane– Or it can diffuse away and be broken down

List some differences between Rods and Cones

Rods ConesNumbers in Retina

20:1

Where in Retina All over Retina but not fovea

ONLY fovea

Light-sensitive pigment

Rhodopsin Iodepsin

Vision Only black & white vision

Both dim & bright light

Colour vision ONLY in bright

light

Sensitivity Intensity Wavelength

How does light reaching a rod cell result in an action potential in the optic nerve to the brain?

• Light energy breaks rhodopsin opsin + retinal• Opsin binds to the membrane of the outer segment

– Causes Na+ channels to close• Influx of Na+ ions into rod cell decreases while inner segment

continuously actively pumps out Na+ ions.• So inside of cell is more negative that outside

– Causing membrane to be hyperpolarised (-90 mv)• Less inhibitory neurotransmitter is released• In bipolar cell:

– Cation channels open– Membrane becomes depolarised

• Generates an action potential in neurone of optic nervebrain

Explain what each lobe of the brain does.

• FRONTAL LOBE:– Decision making– Reasoning– Planning– Forming association:

infoideas– Includes primary motor

cortex:• Movement• Stores info

• OCCIPTAL LOBE: (visual cortex)– Processes info from eyes

• Vision, colour, perspective

• PARIETAL LOBE– Orientation– Movement– Sensation– Calculation– Some types of recognition– Memory

• • TEMPORAL LOBE:

– Processes auditory processes• Hearing, sound, speech

Define Habituation.

• Type of learning• Reduced response to an unimportant stimulus

after repeated exposure over time

Define homeostasis• The maintenance of a stable internal environment

How is habituation achieved?• With repeated stimulation, calcium ion channels become less

responsive:

• Less calcium ions cross presynaptic membrane into presynaptic neurone • Fewer synaptic vesicles fuse with presynaptic membrane

• Less neurotransmitter is released into synaptic cleft

• Less sodium ion channels on postsynaptic membrane open

• Less sodium ions flow into postsynaptic membrane

• Less/ no action potential is triggered

Explain negative feedback.

• Receptors are used to detect deviations from the norm

• And are connected to a control mechanism• turns on/ off effectors• To bring condition back to the norm

Explain how temperature is controlled in the body when it rises above norm.

• Temperature rises above norm• Detected by:– Receptors in blood– Thermoreceptors in skin

• Sends nerve impulses• Heat loss centre is activated (in hypothalamus)• Hypothalamus sends nerve impulses effectors turn

on/off• HEAT LOSS PROCESSES• Temperature falls back to Norm = 37.5˚C

Name processes in which the body does to lose or gain heat

HEAT GAIN PROCESSES HEAT LOSS PROCESSES

Vasoconstriction; stimulates the arterioles in skin to constrict

Vasodilation; inhibits the contraction of arterioles in skin

Hair erector muscles contract Hair erector muscles relax

Sweat glands are inhibited Sweat glands are stimulated to secrete sweat

Liver secretes hormonesincreases metabolic rate

Liverdecreases metabolic rate

Skeletal muscles contract: shivering, increased respiration

Skeletal muscles relax; no shivering

How does the cardiac muscle control the regular beating of the heart?

• Electrical impulses from the SAN• Spread across atria walls contraction• Impulses pass to ventricles via AVN– Delay: ensures atria have finished contracting and

ventricles are filled with blood before they contract• Impulses pass down the purkyne fibres to the

heart apex• Impulses spread through the ventricle walls,

causing contraction from the apex upwards• Blood is squeezed into arteries

Explain how the nervous system increases heart rate.

• An increase in heart rate is caused by:– an increase in carbon-dioxide– a decrease in oxygen– a decrease in blood PH– an increase in temperature

• detected by chemoreceptor (in medulla, carotid artery, aorta)– an increase in blood pressure

• detected by pressure receptors in aorta wall and carotid artery• sends nerve impulses cardiovascular control centre in medulla• sends nerve impulses SAN• to increase heart rate (by sympathetic nerve)

Compare slow-twitch and fast-twitch muscle fibres.Slow-twitch Fast-twitch

Colour Dark red/ brown Pale whiteMyoglobin More LessMitochondria More LessCapillaries More Less Kerb cycle enzyme content

High Low

Glycogen content Low High Resistance to fatigue High Low Type of respiration involved in

Aerobic Anaerobic

Creatine phosphate Low High Sarcoplasmic reticulum

Little Extensive

Explain muscle contraction using the SLIDING FILAMENT THEORY.

• nerve impulse arrives at neuromuscular junction• depolarises the sarcolemma• calcium ions released out of sarcoplasmic reticulum and diffuse through

sarcoplasm• calcium ions bind to troponin, causing troponin to move exposing myosin-

binding site on actin filament• myosin head binds to myosin binding site = myosin-actin cross-bridges• activates enzyme ATPase, which is released from myosin head• provides energy to move the myosin head: causes myosin head to change

shape, causing it to nod forward, pulling actin towards the centre of sarcomere

• ATP molecule provides energy to break the actin-myosin cross-bridges, by binding to myosin head, causing it to detach

• ATPase on myosin head causes ATP hydrolysis: ATP ADP + Pi• causing a change in shape of myosin head, returning it to its upright position• enabling cycle to repeat

Explain the process of OXIDATIVE PHOSPHORYLATION.

• Reduced coenzymes carry hydrogen ions and enzyme to Electron Transport Chain on inner mitochondrial membrane.

• Electrons get passed along electron carriers, in a series of Redox reactions.

• Protons/ H+ ions move across inner mitochondrial membrane into intermembrane space, increasing its proton concentration.

• Hydrogen ions diffuse down the electrochemical gradient back into the mitochondrial matrix using ATPsynthase on a stalked particle (CHEMIOSMOSIS).

• The hydrogen ion diffusion allows the synthesis of ATP (ADP + Pi).• Electrons and hydrogen ions recombine with the oxygen to create

water.• • (‘OXYGEN’ is called the FINAL ELECTRON ACCEPTOR.)

Explain how the nervous system decreases heart rate.

– Blood pressure• Detected by pressure receptors in the aorta

wall, carotid artery• Send nerve impulses to the cardiovascular

control centre in medulla• If pressure is too high: cardiovascular control

centre sends inhibitory nerve impulses (via parasympathetic nerve) to the SAN

• To decrease heart rate.

DEFINITIONS

TIDAL VOLUMEThe volume of air we breathe in and out at each breath

VITAL CAPACITY The maximum volume of air we can inhale and exhale

VENTILATION RATE

The volume of air taken into the lungs in one minute= tidal volume x breathing rate

AEROBIC CAPACITY

Ability to take in, transport and use oxygen

CARDIAC OUTPUT Volume of blood pumped by the heart in one minute= stroke volume x heart rate

During exercise, how is breathing rate and depth controlled?

• During exercise, there is an increase in carbon-dioxide in blood

• Carbon-dioxide dissolved in blood plasma, forming carbonic acid

• Carbonic acid dissociateshydrogen ions and hydrogen carbonate ions

• PH falls• Detected by chemoreceptor• Sends nerve impulses to ventilation centre in medulla• Sends frequent nerve impulses to:

– Intercostals muscles– Diaphragm

• Increasing breathing rate and depth