topic 7 rev notes

8/2/2019 Topic 7 Rev Notes

1/28

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

o Information is processes

Impulses are sent along parasympathetic motor neurones


2/28

EFFECTORS: circular muscles of iris are stimulated

o Circular muscles contract

o 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


3/28

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


4/28

Ensures the impulses are UNIDIRECTIONAL: travel in justone direction


5/28

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, initiatinganother action potential

Impulses jump from one node to the next by SALTATORYCONDUCTION


6/28

How do Synapses transmit an impulse?

An action potential arrives at the presynaptic membrane Membrane depolarises, causing:

o Calcium ion channels to open; calcium ions enterneurone

Increased calcium ion concentration causes synapticvesicles (containing neurotransmitter) to fuse with

presynaptic membrane Neurotransmitter released into synaptic cleft by

EXOCYTOSIS Neurotransmitter binds with receptor proteins on

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

channels


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Postsynaptic membrane depolarises, initiating an actionpotential

When released, the neurotransmitter is either:o Taken up across the presynaptic membraneo Or it can diffuse away and be broken down


8/28

List some differences between Rods and Cones

Rods Cones

Numbers inRetina

20:1

Where in Retina All over Retina butnot fovea

ONLY fovea

Light-sensitive

pigment

Rhodopsin Iodepsin

Vision Only black &white vision

Both dim & brightlight

Colour vision ONLY in bright

light

Sensitivity Intensity Wavelength


9/28

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

1. Light energy breaks rhodopsin opsin + retinal2. Opsin binds to the membrane of the outer segment

a. Causes Na+ channels to close3. Influx of Na+ ions into rod cell decreases while inner

segment continuously actively pumps out Na+ ions.4. So inside of cell is more negative that outside

a. Causing membrane to be hyperpolarised (-90 mv)5. Less inhibitory neurotransmitter is released6. In bipolar cell:

a. Cation channels openb. Membrane becomes depolarised

7. Generates an action potential in neurone of opticnervebrain


10/28

Explain what each lobe of the brain does.

FRONTAL LOBE:o Decision makingo Reasoningo Planningo Forming association:

infoideaso Includes primary

motor cortex: Movement Stores info

OCCIPTAL LOBE: (visualcortex)

o Processes info fromeyes

Vision, colour,

perspective PARIETAL LOBE

o Orientationo Movemento Sensationo Calculation

o Some types ofrecognition

o Memory

TEMPORAL LOBE:o Processes auditory

processes


11/28

Hearing,sound, speech


12/28

Define Habituation .

Type of learning

Reduced response to an unimportant stimulus afterrepeated exposure over time

Define homeostasis

The maintenance of a stable internal environment


13/28

How is habituation achieved?

With repeated stimulation, calcium ion channels become less

responsive:

Less calcium ions cross presynaptic membrane intopresynaptic 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


14/28

Less/ no action potential is triggered


15/28

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


16/28

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

o Temperature rises above normo Detected by:

Receptors in blood Thermoreceptors in skin

o Sends nerve impulseso

Heat loss centre is activated (in hypothalamus)o Hypothalamus sends nerve impulses effectors turn on/offo HEAT LOSS PROCESSESo Temperature falls back to Norm = 37.5C


17/28

Name processes in which the body does to lose orgain heat

HEAT GAIN PROCESSES HEAT LOSS PROCESSES

Vasoconstriction;stimulates the arteriolesin skin to constrict

Vasodilation; inhibits thecontraction of arterioles inskin

Hair erector muscles

contract

Hair erector muscles relax

Sweat glands areinhibited

Sweat glands are stimulatedto secrete sweat

Liver secretes

hormonesincreasesmetabolic rate

Liverdecreases metabolicrate


18/28

Skeletal musclescontract: shivering,increased respiration

Skeletal muscles relax; noshivering


19/28

How does the cardiac muscle control the regularbeating of the heart?

Electrical impulses from the SAN

Spread across atria walls contraction

Impulses pass to ventricles via AVN

o 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


20/28

Impulses spread through the ventricle walls, causing

contraction from the apex upwards

Blood is squeezed into arteries


21/28

Explain how the nervous system increases heart rate.

An increase in heart rate is caused by:

o an increase in carbon-dioxideo a decrease in oxygeno a decrease in blood PHo an increase in temperature

detected by chemoreceptor (in medulla, carotid artery,aorta)

o 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)


22/28

Compare slow-twitch and fast-twitch muscle fibres.

Slow-twitch Fast-twitch

Colour Dark red/ brown Pale whiteMyoglobin More LessMitochondria More LessCapillaries More LessKerb cycleenzyme content

High Low

Glycogen content Low HighResistance tofatigue

High Low

Type ofrespirationinvolved in

Aerobic Anaerobic

Creatinephosphate

Low High


23/28

Sarcoplasmicreticulum

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 towardsthe centre of sarcomere


24/28

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 itsupright position

enabling cycle to repeat


25/28

Explain the process of OXIDATIVE PHOSPHORYLATION.

1. Reduced coenzymes carry hydrogen ions and enzyme to Electron

Transport Chain on inner mitochondrial membrane.2. Electrons get passed along electron carriers, in a series of Redoxreactions.

3. Protons/ H+ ions move across inner mitochondrial membrane intointermembrane space, increasing its proton concentration.

4. Hydrogen ions diffuse down the electrochemical gradient backinto the mitochondrial matrix using ATPsynthase on a stalkedparticle (CHEMIOSMOSIS).

5. The hydrogen ion diffusion allows the synthesis of ATP (ADP +Pi).

6. Electrons and hydrogen ions recombine with the oxygen tocreate water.

(OXYGEN is called the FINAL ELECTRON ACCEPTOR.)


26/28

Explain how the nervous system decreases heart rate.

o 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.


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DEFINITIONS

TIDAL VOLUME The volume of air we breathe in and out ateach breathVITAL CAPACITY The maximum volume of air we can inhale

and exhaleVENTILATIONRATE

The volume of air taken into the lungs inone minute

= tidal volume x breathing rateAEROBICCAPACITY

Ability to take in, transport and useoxygen

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


28/28

During exercise, how is breathing rate and depthcontrolled?

During exercise, there is an increase in carbon-dioxide inblood

Carbon-dioxide dissolved in blood plasma, forming carbonicacid

Carbonic acid dissociateshydrogen ions and hydrogencarbonate ions

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

o Intercostals muscles

o Diaphragm Increasing breathing rate and depth

topic 7 rev notes

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