nervous communciation & receptors

define stimuli

changes to the internal or external environment of an organism,, resulting in a response

why do animals respond to stimuli?

it increases their chance of survival

eg external: avoiding harmful environments

eg internal: make sure that cinditions are always optimal for metabolism

define receptors

they are cells or proteins that can detect stimuli and are cells or proteins on cell-surface membranes

• many different types of receptors detect different stimuli

what are effectors?

cells that bring about a response to a stimulus to produce an effect

• effectors include muscle cells & cells bound in glands eg pancreas

how do receptors and effectors communicate?

via the nervous system or hormonal system, sometimes using both

what are the three main types of neurons?

• sensory

• motor

• relay

what is the role of sensory neurons?

transmit electrical impulses from receptors to CNS (brain & spinal cord)

what is the role of motor neurons?

transmit electrical impulses from CNS to effectors

what is the role of relay neurons?

transmit electrics, impulses between sensory neurons & motor neurons

what happens after a stimulus triggers the nervous system?

• describe and explain this process

1. stimulus is detected by receptor cells & electrical impulse is sent along a sensory neuron

2. when electrical impulse reaches end of the neuron, chemicals called neurotransmitters take info across to next neuron, sends electrical impulse

3. CNS processes the info & sends impulses along motor neurons to an effector

describe the structure of the nervous system

what is a reflex?

where the body responds to a stimulus without making a conscious decision to respond

How do you simple reflexes help organisms?

• they are rapid- fast response

• short-lived, can return to homeostasis

• localised response- neurotransmitters secreted directly onto target cells

what is a reflex arc?

pathway of neurons linking receptors to effectors in a reflex

the three neurons involved are sensory relay and motor

eg receptors detect stimuli

sensory neuron carries impulse to relay neuron

relay neuron connects to motor neuron

motor neuron sends impulses to effector

muscle contracts to move away or closer to stimulus

• if relay neuron involved, can override reflec

when is a nervous system receptor in resting state?

and how does this occur?

• when difference in charge between inside and outside of cell

• this is generated by ion pumps & ion channels

• so there’s a voltage across the membrane

• voltage aka potential difference

what is resting potential?

the potential difference when a cell is at rest (not stimulated)

what is generator potential? how can a bigger one be triggered?

• change in potential difference across cell-surface membrane of a receptor as a result of a stimulus

• bigger stimulus excites membrane more, causing a bigger movement of ions & bigger change in PD - so bigger generator potential is produced

how does potential difference become altered?

• when a stimulus detected, cell membrane is excited & more permeable, so more ions to move in & out of cell

how is an action potential triggered?

• generator potential is big enough it'll trigger an action potential

• only triggered if generator potential reaches a certain level called the threshold level

• action potentials are all one size, so strength of stimulus is measured by frequency of action potentials

label the diagram of the pacinian corpuscle

what kind of receptors are pacinian corpuscles?

they are mechanoreceptors

• detect mechanical stimuli, eg pressure & vibrations (found in skin)

describe what happens in a Pacinian Corpuscle to generate an action potential in the sensory neurone

• when pressure from touch/ pacinian corpuscle is stimulated, lamellae deformed & press on sensory nerve ending

• stretches sensory neuron cell membrane- deforms stretch-mediated Na ion channels

• channels widen & open, Na+ ions diffuse/flood into axon

• axon = depolarised, establishes generator potential

• if threshold reached- action potential triggered

Describe how the stimulation of a pacinian corpuscle

• stimulus occurs, deforming the lamellae

• stretch-mediated Na+ ion channels widen and open

• Na+ ions diffuse in via the Na+/K+ pump/ depolarisation occurs due to this

Explain how the resting potential of –70 mV is maintained in the sensory neurone when no pressure is applied in the pacinoan corpuscle.

• membrane is more permeable to potassium ions and less permeable to sodium ions

• sodium ions are actively transported/ pumped out and potassium ions in

what is the fovea?

area in the retina where many photoreceptors are found

ALSO WHERE CONE CELLS ARE IN THE EYE

what is the retina?

retina is the layer of photoreceptor cells found at the back of the eye

what are the two types of photoreceptors in the retina?

rods and cones

where are rod cells found in the eye?

in the periphery of the retina

where are cone cells found in the eye?

in the fovea

how do photoreceptors work?

light enters the eye, hitting the photoreceptors

absorbed by the light-sensitive optical pigments

light bleaches pigments

cussing chemical change & altering membrane permeability to sodium ions

generator potential created, if reaches threshold, nerve impulse sent along a bipolar neuron

bipolar neurons connect photoreceptors to optic nerve, takes impulse to brain

what kind of information can rods give?

monochromatic (black and white)

what kind of information can cones give?

• trichromatic vision- 3 colours

• 3 types of cones, red-sensitive, green-sensitive and blue-sensitive

• when stimulated in different proportions, you can see different colours

what is visual acuity?

ability to tell apart points close together

what is sensitivity?

how easily they reach action potential

what kind of sensitivity and visual acuity do rod cells have? and why?

• rod cells very sensitive to light (work well in dim light)- because many rods join 1 bipolar neuron, so many weaker generator potentials combine to reach threshold & trigger action potential

• rods have low visual acuity- because many rods join to same bipolar neuron, so light from 2 points close together cannot be told apart

what kind of sensitivity and visual acuity do cone cells have? and why?

• cones are less sensitive than rods (work best in bright light)- because one cone joins 1 bipolar neuron, so takes more light to reach the threshold & trigger action potential

• cones have high visual acuity- because cones are close together & one cone joins bipolar neuron

  • when light from 2 points hit 2 cones, 2 action potentials go to brain, so can distinguish 2 points close together as 2 separate points

give a summary of the similarities and differences between rods and cones

explain why an image formed at the fovea is perceived in more detail than an image formed at any other point on the retina (2)

• fovea has many / only cones / more cones than rest of the retina;

• each cone is synapse to a single neurone / bipolar cell / no retinal convergence;

OR

• the rest of the retina has mainly rods/more rods than cones;

• which share/converge on neurones/bipolar cells;

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 see its prey in detail. Do not refer to colour vision in your answer. (3)

1. high (visual) acuity;

2. (each) cone is connected to a single neurone;

3. (cones send) separate (sets of) impulses to brain;

retina of an owl has a high density of rod cells.

explain how this enables an owl to hunt its prey at night. do not refer to rhodopsin in your answer. (3)

1. high (visual) sensitivity;

2. several rods connected to a single neurone;

3. enough (neuro)transmitter to reach/overcome threshold

OR

spatial summation to reach/overcome threshold;

describe how a Pacinian corpuscle produces a generator potential when stimulated.

(increased pressure) deforms/changes stretch-mediated sodium ion channel;

(sodium channels open and) sodium ions flow in;

depolarisation (leading to generator potential);