Receptors Flashcards
importance of reflex arc
-involuntary: doesn’t require a decision, frees brain from executing more complex decision
-protection: protects from potentially dangerous stimuli
-rapid response: neuron pathway short, very few synapses
features of sensory receptors
-is specific to a single stimulus
-produces a generator potential by acting as a transducer
structure of pacinian corpuscle
-single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule.
-stretch-mediated Na+ channels on plasma membrane
-capillary runs along base layer of tissue
function of pacinian corpuscle
-pressure deforms membrane, causing stretch-mediated Na+ ion channels to open, allowing Na+ions to diffuse into neuron
- influx of sodium ions changes the potential of membrane, depolarising it-produces a generator potential
-in turn produces action potential which moves along sensory neuron to CNS.
2 photoreceptors located in retina and where
rods: evenly distributed in periphery but NOT in central fovea
cones: mainly central fovea
no photoreceptors in blindspot
pathway of light from photoreceptor to brain
photoreceptor->bipolar neuron->ganglion cell of optic nerve->brain
difference between rods and cones
-rod shaped/cone shaped
-greater number rod cells
-rods give poor visual acuity
-rods sensitive to low-light intensity, cones not sensitive
-rods only one type, cones-3 types each responding to different wavelengths of light
rod cells
-certain threshold value has to exceeded for generator potential to be created in bipolar cells to which the are connected
-as a summation of low light intensity needed to reach threshold value, it therefore allows us to see in low light intensities
-activation of rhedopsin (pigment in photosensitive region) by a photon results in cation channels to close, transmembrane potential becomes more negative.
-generates single impulse to brain
retinal convergence and its importance
a number of rod cells connecting to a single bipolar neuron
-greater chance that the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell.
why do rod cells give low visual acuity
-single impulses generated to brain as result of retinal convergence
-so brain cannot distinguish between separate sources of light. two dots together therefore cannot be resolved, will appear as single blob
cone cells
-often connected to their own bipolar cell subsequently connected to optic nerve
-means that the stimulation of a no. of cone cells cannot summate to help exceed the threshold value to create generator potential
-iodopsin (photosensitive pigment in cone) requires higher light intensity to hydrolyse and alter transmembrane potential
how do cone cells give high visual acuity
-cone cells have on connection to single bipolar cell
-so brain can distinguish separate sources of light.
-two dots of light can therefore be resolved and appear as 2 dots
therefore have high visual acuity
autonomic nervous system
system that controls all involuntary activities of internal muscles and glands.
has 2 subdivisions: parasympathetic & sympathetic
difference between parasympathetic and sympathetic
parasympathetic: inhibits effectors so slows down activity, controls activity in normal resting conditions.
-concerned with conserving energy & replenishing body’s reserve
sympathetic: stimulates effectors so speeds up activity, involved in ‘fight or flight’ response.
-heightens awareness, helps cope in stressful conditions.
medulla oblongata and its function
located in brainstem and controls involuntary functions
function is transmitting signals between spinal cord and higher parts of brain-controls autonomic activities.
events that control basic heart rate
-SAN initiates wave of electrical energy- spreads across both atria, causes the to contract= atrial systole
-wave of excitation enters AVN-between atria
-AVN, after a short delay, conveys wave of electrical excitation between the ventricles along Purkyne tissue (bundle of His)
-Bundle of His conducts wave through atrioventricular septum to base of the ventricles, where bundle branches into smaller Purkyne fibres
-wave of excitation released quickly from Purkyne fibres, contracts quickly from apex upwards.
centres in medulla oblongata to mediate heart rate
-1 centre causes sympathetic nerve to release neurotransmitter noradrenaline-connects to SAN, increases heart rate
-2nd centre causes parasympathetic (vagus) nerve to release neurotransmitter acetylcholine, connects to SAN-decreases heart rate.
receptors involved in changing heart rate and their location
chemoreceptors: sensitive to changes in pH of the blood as a result of CO2 concentration
-found in wall of carotid artery and aortic body
baroreceptors: detects changes in blood pressure
-carotid body
how does body respond to increase in CO2 concentration
-higher CO2 concentration=production of carbonic acid-lowers pH of blood
-chemoreceptors detect & increase frequency of impulses to centre of medulla oblongata that increases heart rate + respiration rate
-centre increases impulses to SAN via sympathetic nervous system
-heart rate increases-rate of blood flow increases-rate of gas exchange increase so more CO2 removed
-pH of blood rises to normal , chemoreceptors reduce frequency, medulla oblongata reduces impulses to SAN=reduction in heart rate
