topic 6: control of heart rate and light receptors Flashcards
what is the CNS?
central nervous system
the brain and the spinal cord
what is the peripheral nervous system?
made up of pairs of nerves that originate from the brain of spinal cord
consists of the sensory neurone system and the motor neurone system
what can the motor neurone system be divided into?
voluntary nervous system and autonomic nervous system
what is the purpose of the sensory neurone system?
carry nerve impulses away from the receptors and towards the CNS
what is the purpose of the motor neurone system?
carries nerve impulses away from CNS to effectors
what is the voluntary nervous system?
carries nerve impulses to the body muscles and is under voluntary/conscious control
what is the autonomic nervous system?
carries nerve impulses to the glands,smooth muscle and cardiac muscle
it is involuntary
what is a reflex arc?
pathway of neurone that links receptors to effectors in a simple reflex
it is rapid involuntary response
it bypasses the CNS
how many neurones in a reflex arc?
3
why are reflex arcs important?
make survival more likely
they are involuntary and don’t require decision by the brain
to protect body from harmful stimuli
fast
effective from birth don’t need to be learned
stimulus in a reflex arc where a hot object is touched
heat from the hot object
receptor in a reflex arc where a hot object is touched
detect temperature on skin and generate a nervous impulse
neurones involved in a reflex arc when a hot object is touched?
sensory: passes nerve impulse to spinal cord
relay: links sensory neurone and motor
motor: carries nerve impulse from the spinal cord to a muscle in the upper arm
effector in a reflex arc when a hot object is touched?
muscles in the upper arm are stimulated to contract
does the nervous system have control in the heart?
cardiac muscle is myogenic so it contracts and relaxes on its own without nervous input
the nervous system does control rate of reaction
what is the sinoatrial node?
a group of cells in the right atrium known as the pacemaker
sets the pace that the heart will beat at
where is the atrioventricular node found?
between the right atrium and left ventricle
what is the bundle of His?
tissues running through the septum
where are the purkyne fibres found?
in ventricle walls
explain the events involved in the electrical coordination of the heartbeat
- initial stimulus for the heartbeat starts at the SAN and sets up a wave of electrical activity
2.the wave spreads out from the SAN across both atria causing them to contract and push blood into ventricles - wave of electrical activity reaches AVN
4.AVN delay electrical activity so atria can empty before ventricles contract
5.atria relax
6.wave of electrical activity is directed to purkyne fibres that form the bundle of His - bundle of His passes along the septum to the bottom of the ventricles then upwards
- blood is forced from the ventricles into the aorta and pulmonary artery
what happens in the electrical coordination of the heart after blood has been forced into the aorta and pulmonary artery?
- short delay before the next wave of excitation occurs. the atria and ventricles are relaxed during this time
- atria begin to fill with blood from pulmonary vein and vena cava and the process starts again
what is the role of the autonomic nervous system?
it controls the involuntary activities of internal muscles and glands
what are the 2 divisions of the autonomic nervous system?
sympathetic and parasympathetic
what does the sympathetic nervous system link?
acceleratory centre to the SAN to increase heart rate
what is the role of the sympathetic nervous system?
stimulates effectors
speeds up activities
prepares for stressful activities by increasing the rate of respiration-fight or flight
what does the parasympathetic nervous system link?
inhibitory centre to the SAN to decrease heart rate
what is the relationship between the sympathetic and parasympathetic nervous system?
they are antagonistic-actions oppose each other
what happens to heart rate if more impulses are sent via the sympathetic?
causes SAN to release waves of depolarisation more frequently and increase heart ratew
what happens to heart rate if more impulses are sent via the parasympathetic?
SAN releases waves of depolarisation less frequently decreasing heart ratewh
what controls the heart?
the cardio-regulatory centre in the medulla oblongata of the brain
located at the base of the brain
what are the 2 regions of the cardio-regulatory centre?
acceleratory and inhibitory
what does the acceleratory centre do?
increase the heart rate, is linked to the SAN of the heart by the sympathetic nervous system
what does the inhibitory centre do?
decrease the heart rate, linked to SAN by parasympathetic
what are chemoreceptors?
receptors are sensitive to change in PH
found in walls of carotid artery and walls of aorta
why are chemoreceptors necessary?
when exercising CO2 is produced
forms an acid that lowers PH
H+ concentration increases
how is heart rate increased?
- increase in muscular activity
2.increase in Co2 produced by tissues from respiraton
3.fall in blood PH
4.detected by chemoreceptors in carotid arteries
5.more nerve impulses sent to acceleratory centre of cardiac centre in medulla
6.more impulses along sympathetic to SAN
7.SAN stimulated by neurotransmitter noradrenaline
8.increased frequency waves of electrical activity across atria and ventricles, increases heart rate - increased blood flow, CO2 removed quicker
- CO2 returns to norma
how is heart rate decreased?
1.decrease in CO2 or H+, decrease the stimulation of chemoreceptors
2.inhibitory centre in the medulla sends more impulses via the parasympathetic nerves
3.SAN is stimulated by the neurotransmitter acetylcholine
4.reduces frequency of waves of electrical activity and heart rate decreases
what are pressure receptors known as?
baroreceptors
explain how heart rate is controlled by pressure receptors?
1.they are found in the walls of carotid arteries and aorta
2.when blood pressure is higher than normal, impulses sent to the medulla
3.more impulses are sent via the parasympathetic nervous system to SAN
4.decreases heart rate
5,when BP lower than normal, fewer impulses to medulla, more impulses via sympathetic to SAN to increase heart rate
what are sensory receptors?
they respond to only one type of stimulus
e.g. light, heat,sound,pressure
what do sensory receptors act as?
transducers
all receptors convert energy of stimulus into a nerve impulse called a generator potential
what is a generator potential?
the potential difference due to a stimulus
what happens when a stimulus is detected?
membrane of neurone is excited
it becomes more permeable to ions, changing the potential difference
bigger the stimulus, the bigger the pd change and generator potential
If the GP is big enough, it will reach threshold and an AP generated
structure of the pacinian corpuscle
found deep in the skin
especially fingers,soles of feet, also ligaments and tendons
function of the pacinian corpuscle
responds to mechanical stimuli like pressure
chances mechanical energy to generator potential
explain how the pacinian corpuscle works
- it consists of several layers surrounding the end of the fibre of the sensory neurone
2.plasma membrane has special stretch-mediated sodium channels
3.channels change permeability to sodium ions when they change shape by stretching
4.in resting state, they are too narrow to allow sodium ions through
so the neurone in the pacinian corpuscle is said to have resting potential
what happens when pressure is applied to the pacininan corpuscle?
5.it changes shape/is deformed so becomes stretched
6.sodium channels widen and sodium ions diffuse into the neurone
7.influx of sodium ions changes the potential of the membrane and produces generator potential
8.generator potential reaches threshold to trigger AP that passes neurone to the CNS
how many rods are in each eye
120 million
how are rods distributed in the eye?
widely across the retina
few at the fovea
none at the blind spot
what is the sensivity of rods?
high sensitivity-sensitve to low intensity light
enable animals to distinguish light from dark in low intensity light
what don’t rods do
distinguish different colours
what do rods contain?
rhodopsin
what is the role of rhodopsin
it is broken down by low intensity Light
what happens to rhodopsin at low intensity light or high intensity light?
absorbs light
gets broken down(bleaching)
changes the membrane potential, Na diffuses in and creates generator potential
threshold reached
AP generated
how much light is needed to break down rhodopsin?
one photon
allows night vision
how many cones are in each eye?
6 million
where are cones In the eye?
fovea
none at the blind spot
why are cones important?
they are sensitive to different WLs of light so colour can be distinguished
3 types responding to:red, blue,green
when stimulated in combination, range of colours on the visible spectrum are seen
what pigment is found in cones?
iodopsin
what is needed to break down iodopsin
a high light intensity
to break It down and create a GP
Define sensitivity
how much light is needed to stimulate the receptors
are rods or cones more sensitive?
rods are stimulated in light of lower intensity than cones so are more sensitivity
why do rods have a higher sensitivity?
several rods converge on one bipolar neurone and one ganglion cell=retinal convergence
one rod alone cannot produce enough neurotransmitter for GP to reach threshold in bipolar neurone to produce AP
groups of rods are stimulated by low intensity light at the same time, so combine to generate AP because threshold for neurotransmitter transmission reached- summation
image is less defined
define visual acuity
how far apart 2 spots of light can be seen as seperate
what affects visual acuity
affected by the way receptors are connected to optic nerves
enables sharp images to be seen
do rods or cones have better visual acuity?
cones have good visual acuity
rods have low
why do cone cells have high visual acuity?
they each have a single connection to a single bipolar neurone
so if 2 adjacent cone cells are stimulated, the brainrecieves 2 seperate nerve impulses
so brain can distinguish between 2 dots of light close together so cone cells give accurate vision
light id focused on the fovea by the lens, which is where the highest number of cone cells are found
why do rods have a low visual acuity?
because many rod cells link with one bipolar neurone
so several dots of light would only generate one nerve impulse
dots would appear as a single point of light
