Responses to change in the enviroment

• What is a stimulus

  A detectable change in the enviroment
• What is taxes

  simple respones in which an organisms will move its entire body towards a favourable stimulus or away from an unfavourable stimulus
• What is Kinesis

  When an organism changes the speed of movement and the rate it changes direction
• What does the pacinian corpuscle respond to

  Pressure
• What is the structure of the Pacinian Corpuscle

  Single sensory nuerone wrapped with layers of tissue separated with gel called the lamellae
• What happens when pressure is applied to the Pacinian corpuscle?

  Deforms the layers

  stretch mediated sodium channels are opened

  sodium ions enter

  causes depolarisation and if generator potential produced a action potential can be produced
• Where are rods and cones found?

  Retina and they are photoreceptors
• Why do rods only processes imaged in black and white?

  Due to their shape they can’t distinguish between wavelengths of light
• Why can rods detect light of very low intensity?

  Many rods connected to one sensory nuerone
• How is the generator potential reached for rods?

  Rhosopsin which is the pigment of rod cells is broken down by light energy. There is enough energy from low-intensity lights to cause the breakdown
• Why can the threshold of rod cells be reached in low light intensity’s?

  Many rod cells connected to a single bipolar cell. This is an example of summation
• How can we perceive a range of different colours due to the cone cells?

  Different cone cells contain different pigments which absorb different wavelengths of light. Depending on the proportion of the diferent cone cells stimulated we perceive a range of colours
• Why is the action potential only reached in light for cone cells?

  Iodopsin is only broken down if there is a high light intensity
• Why can we not see colours in the dark?

  There is no spacial summation so only one cone cells connected to one bipolar cells.
• What is the distribution like in the the retina of rods and cone cells?

  Uneven distribution.

  Fovea recieve the highest intensity of ligt so most cone cells are near the fovea as they respond to high light intensity’s and rods cells further away.
• The fovea of the eye of an eagle has a high density of cones.An eagle focuses the image of its prey onto the fovea.

  Explain how the fovea enables an eagle to we its prey in detail

  High visual acuity as cone cells connected to single heron so sends severe impulses to the brain
• The retina of an owl has a high density of rod cells. Explain ow this enables an owl to hunt its prey at night

  High visual sensitivity as several rod cells connected to bipolar single neurone .

  Spatial summation allows it to reach threshold
• Explain how applying pressure to the pacinian corpuscle produces changes in the membrane potential

  High pressure disorts/deforms the membrane

  sodium ion. Channels open and sodium ions move in the greater the pressure ht more channels open
• What is the meaning of visual acuity

  Ability to tell two Points that are close together
• Define myogenic ?

  Contracted of the heart is initiated within the muscle itself rather than by nerve impulses
• State the name and location of the 2 nodes involved in heart contraction ?

  Sinoartrial node (SAN) : within the wall of the right atrium

  Atrioventricular Node (AVN) : lower end of right atrium in the wall that separates the 2 atria
• Describe how heartbeats are initiated and coordinated ?

  SAN initiates a wave of depolarisation

  Wave of depolarisation spreads across both atria = atrial systole

  Layer of fibrous non conducting tissue delays impulse while ventricles fill and the valves close

  AVN conveys the wave of depolarisation down the septum via bundle of his which branches into purkinje fibres along ventricles

  causes ventricles to contract form apex upwards
• State the difference between the sympathetic and parasympathetic nervous system?


  Sympathetic involved in ‘fight or flight’ repsonse : stimulates effectors to speed up activity

  Parasympathetic involved in resting conditions to slow down
• Name the receptors involved in changing heart rate and state their location?

  Baroreceptors : change in pressure located in artery wall and cartoid artery wall

  Chemoreceptos : Change in Ph carotid wall and aortic wall
• How does the body respone to an increase in blood pressure?

  Baroreceptos send more impulses to the medulla oblongata which then sends more impulses down the parasypathetic nervous system to the SAN which decreases teh frequency of electrical impulses
• How does the body respond to a decrease in blood pressure?

  Baroreceptors send more impulses to the medulla oblongata which then send more impulses down the sympathtic nervous system to the SAN which increases the frequency of electrical impulses
• How does the body respond to an increase in Co2 concentration?

  Chemoreceptors detect a drop in ph and send more impulses to the medulla oblongata

  more impulses send to the SAN via the sympathetic nervous system Increase in heart rate so the blood flow to the lungs increase for gaseous exchange to remove CO2
• Describe the general structure of a motor nuerone?

  Cell body, dendrites, axon, axon terminal.
• Describe the additional features of a myelinated motor nuerone?

  Schwann cell: wraps around the axon many times

  myelin sheath: made from myelin rich membranes of Schwann cell.

  nodes of ranvier: very short gaps between neighbouring Schwann cells where there is no myelin sheath.
• Name 3 processes Schwann cells are involved in?

  Electrical insulation

  phagocytosis

  nerve regeneration
• How does an action potentials pass along an unmyelinated nueron?

  Stimulus leads to influence of NA+ ions. First section of membrane depolarises

  Local electrical current sodium voltage gated channels further along the membrane

  the section begins to repolarise

  wave of depolarisation
• Explain why myelinated axons conduct impulses faster than unmylinated axons?

  Saltatory conduction : impulse jumps from one node of ranvier to another . Impulse does not travel along whole axon length
• How is resting potential established ?

  Membrane is more permeable to K+ then Na+

  Sodium potassium pump activley transports 3Na+ out and 2k+ into cell

  cell contents more negative than extracellular enviroment.
• Name the stages in generation an action potential?

  Depolaisation

  Repolarisation

  Hyperpolarisation

  Return to resting potential
• What happens during depolarisation?

  Stimulus -> facillitated diffusion of Na+ ions into cell down the electrochemical gradient

  Potential difference across membrane becomes more positive

  If membrane reaches threshold potential then voltage gated sodium channels open

  significant influx of Na+ ions reverses potential difference to +40
• What happens during repolarisation ?

  Voltage gated Na+ channels close and voltage gated K+ channels open

  Facilitated diffusion of K+ ions out of cell down their electrochemical gradient

  potential different cross membrane becomes more negative
• What happens during hyperpolarisation?

  Overshoot when K+ ions diffuse out = potential difference becomes more negative than resting potential

  Refractory period : no stimulus is large enough to raise membrane potential to threshold

  Voltage gated potassium channels close and sodium potassium pump established resting potential
• What is the al or nothing princple?

  Any stimulus that causes the membrane to reach threshold potential will generate an action potential
• Name the factors that affect the speed of conductance ?

  Myelin sheath

  axon diameter

  temperature
• How does axon diameter affects the speed of conductance?

  greater diameter = faster

  less resistance to flow of ions

  less leakage of ions