Responding to internal/external stimuli Flashcards
What is a reflex?
an involuntary response to a sensory stimulus
Why is a reflex arc important?
-protects body from harmful stimuli
-effective from birth/innate
-fast/immediate due to short neurone pathway
-invariable - always the same response
INNATE, IMMEDIATE, INVOLUNTARY, INVARIABLE
What makes up the central nervous system?
brain and spinal cord
What is a stimulus?
a change in the environment
What is a receptor?
detects the stimulus
What is an effector?
carries out a response - muscle or gland
What is a sensory neurone?
transmit electrical impulses from a receptor to the coordinator/CNS
What is a motor neurone?
transmit electrical impulses from the CNS to the effector
What is a nerve?
a bundle of neurones
What is a neurone?
a nerve cell
What are the spiky bits of the neurone?
dendrites
What are the bits between the myelin sheath called?
node of ranvier
What is the cell inside the myelin sheath called?
schwann cells
What is the autonomic nervous system?
part of the nervous system dealing with involuntary actions/responses
What is the difference between parasympathetic/sympathetic?
sympathetic - stimulates from normal level
parasympathetic - relaxes/reduces to normal level
What type of muscles make up the heart?
cardiac muscle
How would you describe cardiac muscle?
myogenic
What group of muscles beats at a higher frequency?
atrial
What is the small patch of tissue called in the right atrium that generates electrical
What is the muscle tissue that separates the two ventricles called?
non-conducting fibrous tissue
What is the tissue called that takes the excitation wave to the apex of the heart?
purkinje fibres
Where are the pacemaker cells?
SA node
Where is the Bundle of His?
in the middle, after the AVN node, splits into two branches
Describe the story of a heartbeat
-SA node emits spontaneous impulses and they spread rapidly across both atria
-this stimulates a wave of contraction within the atrial walls - atrial systole
-when electrical impulses reach the border between the atria and ventricles, they are blocked by non-conducting fibrous tissue
-to reach the ventricles, electrical ventricles must pass through the AV node, which slows down the speed of electrical transmission
-this delay allows the atria to complete their contraction before the ventricles begin to contract
-impulses are conducted from the AV node along the Bundle of His
-the bundle fibres divide into numerous purkinje fibres that permeate through the ventricle muscles
-the spread of electrical impulses throughout the ventricles triggers ventricular systole from the apex of the heart up
What is the order of the reflex arc?
stimulus, sensory neurone, synapse, relay/interneurone, motor neurone, effector, response
What does heartrate effect?
blood pressure
What can affect heartrate?
-adrenaline
-nerve input
How does adrenaline increase heartrate?
-secreted by the adrenal glands during stress
-diffuses into blood
-transported to target organs
-stimulates SAN to increase frequency of waves of excitation/strength of contraction
Which part of the brain holds the cardiovascular centre?
medulla oblongata
What are the antagonistic nerves that connect the medulla oblongata to the heart?
sympathetic - speeds up
parasympathetic - slows down
How do the nerves increase heartrate/stroke volume?
increase/decrease stimulation to the SAN and the frequency of the waves of excitation
What are chemoreceptors sensitive to?
changes in the pH of blood
What are baroreceptors sensitive to?
changes in blood pressure
Where are the chemo and baro receptors?
both in carotid artery, chemo also in medulla/aorta and baro also in vena cava/aorta
Describe the reflex arc for the chemoreceptors?
stimulus - increased CO2 in blood, causes a fall in pH
receptor - chemoreceptors in carotid artery detect this
coordinator - cardiovascular centre in medulla
effector - increased impulses along sympathetic nerve to SAN, more waves of excitation
response - increased heartrate, more blood moving, more CO2 removed
Describe the reflex arc for the baroreceptors?
stimulus - high blood pressure stretches the arteries
receptor - baroreceptors found in carotid artery detect this
coordinator - cardiovascular centre in medulla
effector - increased impulses along the parasympathetic nerve to SAN, less waves of excitation
response - decreased heartrate, decrease in blood pressure
What are photoreceptors?
light receptors that are found in the retina in the eye
What is the fovea?
an area in the eye where lots of photoreceptors are found
Why is there a blindspot?
where the optic nerve leaves the eye, so no photoreceptors
What are the two types of photoreceptors in the eye?
rods and cones
Describe rod cells?
(light sens, acuity, colour, number)
-very sensitive to light
-low visual acuity
-black and white only
-120 million in each eye
Describe cone cells?
(light sens, acuity, colour, number)
-less sensitive to light
-high visual acuity
-colour vision - red/green/blue
-7 million in each eye
Explain how we see very briefly
-light enters the eye and hits the photoreceptors
-the receptors are broken down (bleaching)
How does the breakdown of rhodopsin cause a nerve impulse to be transmitted?
-rhodopsin breaks down into opsin
-opsin causes a change in the permeability of the rod cell to sodium, which initiates a generator potential
-a nerve impulse is sent
What cells have dark adaption?
rod cells
What is the difference between bright and dim light for rods?
bright - rhodopsin is broken down faster than it is reformed so is of little use
dim - breakdown of rhodopsin is lower, so production keeps up with breakdown
What does acuity mean?
clearness/clarity
Why do rods have high light sensitivity?
-many rods join 1 bipolar neurone (retinal convergence)
-many weak generator potentials combine to reach threshold and trigger an action potential
Why do cone cells have low light sensitivity?
-only one cone cell connects to one bipolar neurone
-so more light is needed to reach threshold potential and trigger an action potential
Why do rods have low visual acuity?
-retinal convergence, many rods join 1 bipolar neurone
-so light from 2 points cannot be seen as separate as brain doesn’t know EXACTLY where it came from
Why do cones have high visual acuity?
-1:1 ratio of cone:bipolar neurone
-when light from two points hits two cones, both send an action potential to the brain, so it is able to distinguish between both points
How do we see different colours?
-we have three types of cone cell
-each have a different type of iodopsin that responds to a different wavelength of light
-colour seen depends on the relative degree of stimulation of the different types of cone cell
Compare the distributions of rod cells and cone cells?
rod cells - all over including peripheral
cone cells - mainly in fovea
Compare rod and cone cells with regards to retinal convergence?
rods - yes
cones - no
Compare the names of the pigments in rods and cones?
rods - rhodopsin
cones - iodopsin
