recepetors

receptor (detects stimuli)

• responds only to a specific stimuli

• stimulation of receptor leads to establishment of a generator potential.

• which can cause a response.

pacinian corpuscle structure

• sensory neurone wrapped in layers of lamallae seperate by gel

• contains channel proteins in plasma membrane

how a generator potential is established in pacinian corpuscle

1. mechanical stimulus e.g. pressure deforms lamellae (and stretch mediated sodium ion channels)

2. so sodium ion channels open and sodium ions diffuse into sensory neurone

3. DEPOLARISED: leads to generator protection

• if threshold reached, action potential triggered

who does the pacinian corpuscle show

• receptors only respond to specific stimuli

→ pacinian corpuscle only responds to mechanical pressure

• stimulation of receptor leads to establishment of generator potential

→ threshold reached; action potential sent (all or nothing principle)

rod cells (dark blurry)

• rhodopsin (pigments) must be broken down by light energy in order for generator potential to be reached

• they detect lights of LOW light intensity

→ because of retinal convergence (many rod cells connect to one sensory neurone/bipolar cell)

• low visual acuity BECAUSE brain cannot distinguish between separate sources of light that stimulated it (because multiple rod cells attached to one bipolar cell)

cone cells (colour)

• 3 types of pigment iodopsin (red, green, blue)

• iodopsin is only broken down in high light intensity

• ACTION POTENTIONS ONLY GENERATED WITH LOTS OF LIGHT

• 1 cone cell connects to 1 sensory neurone DEPOLARISED → cones only respond to high light intensity can’t see colour dark

why are rods more sensitive to light and give lower visual acuity

• multiple rods connected to 1 neurone

• spatial summation to overcome threshold to generate an action potential

• and several rods send a single set of impulses to brain (can’t distinguish between seperate sources of light)

why are cones less sensitive to light and give higher visual acuity

• each cone connected to single neurone;

• no spatial summation

• cones send seperate impulses to brain (can distinguish between 2 separate light sources)

cones don’t sell signals to brain they do this?

THEY SEND IMPULSES TO BRAIN

differences in sensitivity for rods and cones

RODS: monochromatic vision 1 pigment

CONES: 3 types (red green blue) - sensitive

• different optical pigments absorb different wavelengths

• stimulating different combinations of cones gives range of colour perception

distribution of rods and cones in retina

fovea: where highest light intensity reaches

• lots if cone cells near fovea

• rod cells further (work at low light intensity)

SAN:

• right atrium (natural pacemaker)

• AVN (between right and left ventricle within atria)

• bundles of His: runs through septum

• purkyne fibres: branch into walls of ventricles

what do the nodes do? and the bundle of his and fibres?

emit electrical activity / transmit and conduct it through myogenic muscle

control of heart

1. SAN acts as pacemaker to send wave of electricity across atria, causing it to contract.

• non conductive layer between atria and ventricles prevent the electricity from travelling down into ventricles.

• prevents ventricles contracting

2. waves reach AVN, it delays impulse

• allows atria to fully contract and empty before ventricles contract

3. wave passed down Bundle of His, which conducts the wave between ventricles to apex where it branches into Purkyne tissue

• so ventricles contract

4. cells are repolarised and muscle relaxes

advantadge of the short delay

alllows atria to fully empty blood before ventricles contract, ventricles contract upwards to pump blood efficiently out,

Where are chemoreceptors and pressure receptors located?

Chemoreceptors and pressure receptors are located in the aorta and carotid arteries.

Describe the roles of chemoreceptors, pressure receptors, the autonomic

nervous system and effectors in controlling heart rate

1. Baroreceptors detect [fall / rise] in blood pressure and / or chemoreceptors detect blood [rise / fall] in blood CO2 conc. or [fall / rise] in blood pH

2. Send impulses to medulla

3. Which send more frequent impulses to SAN along [sympathetic / parasympathetic] neurones

4. So [more / less] frequent impulses sent from SAN and to / from AVN

5. So cardiac muscle contracts [more / less] frequently

6. So heart rate [increases / decreases]