B10 Flashcards
The human nervous system
What is homeostasis ?
The regulation of a cell or organism’s internal conditions to maintain optimum conditions for function, in response to internal or external stimuli
Name 3 internal conditions regulated homeostatically
- blood glucose concentration
- water content of the body
- body temperature
What are the key components of a control system ?
- receptor
[] receptor cells are often found in sensory organs like the nose and eyes, as well as in the skin, the mouth and so on
[] detect stimuli (changes to the environment)
[] also found in the brain - coordination centre
[] receive and interpret information retrieved by receptor cells
[] send out signals to prompt responses from the body to the information retrieved
[] include brain, spinal cord and some organs like the pancreas - effector
[] responds to the signals (either electrical impulses or hormones) sent by the coordination centre
[] are either muscles or glands
[] restore body to optimum conditions
What is a control system ?
Automatic system in the body which helps to maintain homeostasis
What does a sensory neurone do ?
carries electrical impulse with information from receptor cells to a coordination centre
What does a motor neurone do ?
carries electrical impulse with instructions from coordination centre to an effector organ (muscle or gland)
Describe very simply how your nervous system works to respond to stimuli
stimulus -> receptor -> sensory neurone -> coordination centre (usually CNS) -> motor neurone -> effector
What is the CNS ?
central nervous system (brain and spinal cord)
Describe two methods of measuring reaction times and the effect of a stimulus (like caffeine, playing music etc.) on the reaction times
ruler drop test:
- sit on a stool with your arm resting on a table and your dominant hand overhanging the edge
- have someone else hold a ruler with the 0cm mark in line with the top of your hand between the thumb and finger
[] they randomly drop it
[] when they drop it, catch the ruler as quickly as possible between the thumb and forefinger
- other person records where you caught it (measuring from top of thumb)
- take a short break (5 minutes) then repeat 4 more times
- calculate a mean measurement
[] use a conversion table online to convert the mean distance into a reaction time
- THEN drink a set amount of coca cola/coffee/tea (anything with caffeine) (300 ml), wait 5 minutes and repeat whole test again
- compare mean reaction times (caffeine’s presence should mean a decrease in reaction time)
- make sure not to change the person catching the ruler, and for them to always use their dominant hand when catching
What is a reflex action ?
unconscious, rapid, involuntary response to a stimulus
[] present to facilitate survival - eg. jerking away from a hot surface or something sharp
What is a relay neurone ?
neurone in the spinal cord or unconscious parts of brain depending on distance to receptor connecting the sensory and motor neurones
[] allows impulse to bypass conscious part of CNS (brain) in order for response to be quicker than normal - if too slow, you could be dead or injured
Describe the reflex arc
stimulus -> receptor cells -> sensory neurone -> relay neurone (the coordination centre in this case) -> motor neurone -> effector (muscle or gland)
Describe how synapses work to pass electrical impulses from one neurone to another
- gaps between neurones (called synapses)
- at the end of the neurone, neurotransmitter chemicals released and diffuse across the gap
[] once these reach the next neurone, a new electrical impulse is stimulated and carried along with the same information from before
What is the cerebral cortex’s function in the brain ?
- conscious thought
- memory
- intelligence
- language
What is the medulla’s function in the brain ?
unconscious actions (reflexes like breathing, heartbeat etc.)
What is the cerebellum’s function in the brain ?
muscle coordination and balance
What is the hypothalamus and the pituitary gland’s function in the brain ?
hypothalamus = regulates body temp.
pituitary gland = secretes hormones and acts as a coordination centre
Why is it presently difficult to treat brain damage, disorders and disease ?
- drugs often fail to reach the brain due to thick membranes encasing the brain (meninges)
- easy to cause unintended damage to areas of the brain as it has very soft texture, and it is not fully known what all areas of the brain are responsible for
What are the main ways in which scientists can map the brain and its functions ?
- studying the brains of people with brain damage
[] can electrically stimulate regions of these brains (can also be done on healthy brains but there is risk of inadvertently damaging areas) - MRI scans
- CT scans
- EEGs (electroencephalography)
What is an MRI scan ?
- magnetic resonance imaging
- uses strong magnetic fields and radio waves to produce detailed images of regions in the body - very useful in mapping the brain
[] can also be used to detect cancer, clots and abnormal blood flow - very safe compared to CT scans because:
[] doesn’t use ionising radiation
[] non-invasive
What is a CT scan ?
- computed tomography scan
- uses x-ray to create detailed images of regions in the body
[] can be used to map brain activity in real time - good for investigating brain responses to (electrical) stimulation
[] can also be used to map the location of tumours before cancer treatment or surgery, diagnose conditions and monitor conditions of the brain after surgery/procedures - some risk due to use of ionising radiation and the injection of dye into the brain to better map activity
What is an EEG ?
- electroencephalograph
- small sensors attached all over the scalp to detect electrical signals produced by the nerves in the brain
- can be used to diagnose epilepsy, fits and memory problems
- no electricity or radiation put into body, so is non-invasive and safe
- cannot be used to detect cancer
Describe the functions of the main structures of the eye
- sclera
[] tough white outer layer of the eye - protects eye - cornea
[] transparent region of the sclera to let light through to the eye whilst still protecting it - pupil
[] hole in iris that allows light through to the lens - iris
[] muscly circle that controls the shape and size of the pupil based on light levels, emotion etc. - suspensory ligaments and ciliary muscles
[] control shape and thickness of lens to properly focus light on the retina via contractions/relaxing - retina
[] layer of light sensitive cells in the back of the eye
[] receive stimulus from environment and start an electrical impulse along the optic nerve to the brain - optic nerve
- blind spot where the optic nerve leaves the eye
- lens
[] focuses light on the retina to form an image
Describe how the muscles in the iris contract/relax to dilate/constrict the pupil
dilation:
- circular muscles relax
- radial muscles contract, pulling the iris open
[] USUALLY HAPPENS IN DIM LIGHTING AS NEED MORE LIGHT TO SEE BETTER IN DARK
constriction:
- radial muscles relax
- circular muscles contract, narrowing the pupil
[] USUALLY HAPPENS IN BRIGHT LIGHT TO PREVENT DAMAGE TO THE RETINA
Describe how the ciliary muscles and suspensory ligaments change the shape of the lens to properly focus light on the retina when looking at a distant vs nearby object
distant:
- lens has to be less convex, as needs to converge incident light rays via refraction only slightly
[] lens made long + thin for less refraction
- suspensory ligaments contract
[] lengthens lens
- ciliary muscles relax
[] thins lens
nearby:
- lens has to be more convex as needs to converge incident light rays via refraction a lot
[] lens made thick + short
- suspensory ligaments relax
[] shortens lens
- ciliary muscles contract
[] thickens lens
What is myopia, its causes and treatment ?
- inability of eye to focus light correctly on the retina to see distant objects
- caused by particularly long eye or a lens that is naturally too convex/thick
[] as a result, light focuses in front of the retina, not on it - treated by wearing glasses with concave lenses that spread out light more before it enters the eye and is converged to focus on the retina
What is hyperopia, its causes and treatment ?
- inability of the eye to focus light correctly to see nearby objects
- caused by a lens that is naturally too long and thin, or a particularly short eyeball
[] means that light is converged less than it needs to be and focuses behind the retina - treated by wearing glasses with convex lenses that converge the light a bit before it enters the eye so that it focuses on the retina instead of behind it
Describe 3 new ways that hyperopia and myopia can be treated
- laser eye surgery
[] for myopia, lasers used to thin cornea and make it refract light less before it reaches the lens
[] for hyperopia, lasers used to change curve of cornea to make it refract light more before it reaches the lens
[] only offered to adults once eyes have stopped growing
[] relatively low success rates - replacement lenses
[] a second lens is inserted into the eye to correct the defect whilst the natural lens is left in place, or the faulty lens is replaced entirely by an artificial lens
[] risks of developing cataracts, damage to retina (if natural lens left in place) and infections are increased by the surgery - contact lenses
[] do same job as glasses but are more convenient for sports etc.
[] two types: hard and soft
[] hard lenses must be kept in sterile solution overnight and last a long time - are also a little uncomfortable to wear
[] soft lenses may be disposable (daily) or can be worn for a month or so (kept in sterile solution overnight) before being thrown away - more comfortable to wear but more expensive long-term
