Biology Topic 8- Grey Matter

Topic 8 key definitions and functions of the nervous system's structures.

neurone/ nerve fibre

a single cell that transmits an impulse

sensory neurone

function: dendrites synapse with receptor cells to conduct an impulse to the CNS

location: dendrites and dendron outside CNS but cell body in the dorsal root ganglia at the entrance to the spinal cord

structure: cell body between axon and dendron above the plane. short axon but long dendron

relay neurone

function: dendrites synapse with sensory neurones, terminal branches synapse with motor neurones

location: whole neurone within the CNS

structure: cell body between axon and dendron

motor neurone

function: dendrites synapse with relay neurones, terminal branches synapse with effector cells

location: cell body within the CNS, axon leaves the CNS

structure: dendrites lead into cell body (no dendron), long axon

function of myelin sheath and the advantages of it structure

the myelin sheath is formed of Schwann cells, and wraps around the axon to provide protection from damage. it is composed of a predominantly lipid membrane which allows it to act as an electrical insulator preventing depolarisation of the neurone where it is present.

nodes of Ranvier

gaps between cells that provide an area along the axon where depolarisation can occur. transmission is therefore faster as the impulse jumps from node to node (saltatory conduction)

axon

carries impulses away from the cell body

dendron

carries impulses towards the cell body

the pupil reflex

the autonomic nervouse system controls the antagonistic pair of muscles in the iris:

• to increase the diameter of the pupil (sympathetic nervous system), the radical muscles contract, and the circular muscles relax

• to decrease the diameter of the pupil (parasympathetic nervous system), the circular muscles contract, and the radical muscles relax

the resting potential

the potential difference across the cell membrane of a neurone at rest, usually -70mV.

to conduct an impulse the inside of the membrane must initially be more negative on the inside- the membrane must be polarised

depolarisation

the rapid influx of sodium ions into the neurone which cause an increase in the charge inside the cell membrane and the membrane potential to increase- usually +40mV

hyperpolarisation

the drop in membrane potential below the resting potential due to open K+ channel- usually -80mV

threshold potential

the point at which a sufficient amount of sodium ion channels open for the influx of Na+ into the axon is greater than the outflow of K+ ions- usually -55mV

all-or-nothing response

any generator potential that reaches the threshold level will produce an action potential of equal magnitude

primary photoreceptor: rod cell

provides black and white vision and is specialised to work in dim light. contains rhodopsin

primary photoreceptor: cone cell

colour vision

rhodopsin structure and function

photochemical pigment located in the membranes of vesicles in the outer segment of rod cells. upon absorption of light, it breaks down into retinal and opsin

retinal

non-protein that converts from cis-retinal to trans-retinal

opsin

protein that activates a series of membrane bound reactions ending in the hydrolysis of a cyclic nucleotide to result in the closure of non-specific cation channels in the membrane of the outer segment

glutamate

neurotransmitter that is released from rod cell in the dark and binds to bipolar cell and causes its membrane to becomes hyperpolarised, preventing an action potential

dark adaptation

enables the eye to transition from a high light setting to a low light setting to restore retinal sensitivity. involves the conversion of trans-retinal to cis-retinal to recombine with opsin to form rhodopsin- requires ATP and can take upto 50 minutes

structure of the cortex/ cerebrum

grey matter- highly folded outer layer composed of nerve cell bodies, synapses and dendrites.

white matter- underneath the grey matter, composed of millions of myelinated axons connecting neurones in different areas

the cortex is divided into two cerebral hemispheres

frontal lobe

decision making, reasoning, planning, emotion, forming associations

temporal lobe

process of auditory information, hearing, sound recognition, speech, memory

occipital lobe/ visual cortex

processes information from the eyes: vision; colour; shape; perspective

parietal lobe

orientation, sensation, calculation, recognition, memory

motor cortex

connects to spinal cord, brain stem and muscles via motor neurones. stores informtaion about how to carry out movement

corpus callosum

white matter composed of axons: allows connection between the two hemispheres and the brain structures

medulla oblongata

regulates heart rate (cardiovascular control centre), breathing rate (ventilation centre), and blood pressure

cerebellum

balance: coordinates movement as it is being carried out

hypothalumus

controls thermoregulation (thermoregulatory centre), thirst, hunger, circadian rhythms, and sleep- acts as an endocrine gland and stimulates the pituitary gland

thalamus

routes all incoming sensory information to the correct lobes

basal ganglia

selects and initiates stored programmes for movement

hippocampus

involved in laying down long-term memory

pituitary gland

endocrine gland responsible for secreting hormones hat control growth, blood pressure, energy management, sex organs, thyroid gland, metabolism, pregnancy, childbirth, nursing, water/ salt concentration at the kidneys, temperature, pain relief

midbrain

relays information to the cerebral hemispheres

pons

relays information from the forebrain to the cerebellum and the medulla. involved in sleep, breathing, respiration, swallowing, bladder control, hearing, taste, eye movement, facial expressions and sensations. implicated in sleep paralysis and dreaming.

MRI (magnetic resonance imaging)

combination of a magnetic field and radio waves that cause hydrogen nuclei to change orientation and release energy that is detected and converted into an image.

can be used for identifying soft tissues, tumour location and size, stroke damage, injuries to brain, spinal cord and joints

advantages- does not use X-rays, thin slices of image are created to produce a 3D image, better resolution that CT

disadvantages- loud noise, small imaging space- not good for small children or people with claustrophobia or special needs, cannot be used on people with metal implants.

fMRI (functional magnetic resonance imaging)

areas of high neural activity can be seen as ‘lighting up’ - these areas have a high demand for oxygen and so blood flow to them increases. oxyhameoglobin in the blood does not absord fMRI signals (radio waves) and so the areas with high activity will absorb less radio wave. must comapre with brain activity at rest

able to study the brain in action and determine different areas of the brain associated with human activities

advantages: no X-rays, very high resolution and 4 images produced per second so a process can be followed over a short period of time

disadvantages: expensive, patient must lie completely still, only measures blood flow and not how individual neurones are behaving

CT scans (computerised axial tomography)

narrow beam X-rays are fired at different angles around the patient where the beam is reduced in strength depending on the density of the tissue. X-rays are then detected and slices of tissue are created

used for investigating soft tissues ie. brain, tumour growth

advantages: more resolution than broad beam X-ray, soft tissues can be imaged

disadvantages: X-rays not good for pregnant women, pixture is frozen, looks at structure rather than function, limited resolution so small structures cannot be distinguished

PET scans (positron emission tomography)

radiotracers (isotopes with short half-lives) are incorporated into compounds such as water, glucose, or molecules that bind to receptors. the radiotracers are injected into the patient’s bloodstream. blood flow will increase to areas of activity in the brain due to greater oxygen and glucose demand. the radiotracers moved to these areas wil emitt positrons as they decay, which will collide with electrons in the tissue, producing gamma rays which are then picked up by detectors and converted to a signal, and an image is produced. the brighter the area the more the neural activity.

can be used in the diagnosis and monitoring of heart disease, cancer, and brain disorders

advantages: can follow changes in disease progression or treatment if video images are played in succession

disadvantages: expensive, radioactive tracers mean it can only be carried out once or twice a year, after a scan the patient cannot travel by public transport due to potentially coming into contact with a pregnant person

critical period

period during visual cortex development where exposure to many different visual stimuli is required for full development of neural connections

link from retina to the occipital lobe

axons leaving the retina arrive at the thalumus

the axons then leave and each connect up with a specific occular dominance olumn cell in the visual cortex in the occipital lobe

perception

creation of an image, involving knowledge and experience to interpret sensory information from the retina- has to be learnt (not innate)

examples of depth perception studies

cross cultural studies (carpented world hypothesis), crawling babies (visual cliff experiment)

Hubel and Weisel experiment

newborn kittens and monkeys exposed to monocular deprivation for different lengths of time during their critical period. when exposed to light, the column cells in the visual cortex corresponding with the light deprived eye did not respond.

habituation and its importance

the effect seen when animals gradually stop responding to a stimulus after repeated exposure

allows animals to ignore and prevent wasting energy on unimportant stimuli to concentrate on more threatening or rewarding stimuli

morality

concepts concerned with the code of behaviour considered right or acceptable for the norm of a particular society

ethics

concepts concerned with what is right and what is wrong regardless of moral concerns

absolutism

the view that something should not be done for any reason

relativism

view that there may be circumstances where something is justified normally when the benefits of a research outweighs the harm to the animals

arguments for animal research

• benefits of the research may outweigh the harm to the animals

• invertebrates have less complex/no nervouse systems so will feel less/no pain

• many mammals have the same organs performing the same functions

• non-animal methods do not provide enough information

• all research involving animals is approved by the home office and inspectors check animal welfare

• regulation is underpinned by the three R’s

arguments against animal research

• use of any animal is wrong or unethical

• vertebrates have complex nervous systems- can feel pain

• animals cannot give consent- they have rights

• animal coukd die or be permenantly affected

• significant species differences mean that it is not possible to extrapolate data for human accurately

• alternatives such as tissue culture can be used

• some research could be viewed and not essential

phototropism

plants can detect the quantity, direction, wavelength, and duration of light

detected by photoreceptors

plant cues

• heliotropism- directional movement of the sun

• hydrotropism- water

• chemitropism- chemicals

• geotropism- gravity

• thermotrapism- temperature

• thigmotropism- sense of touch

• electrotropism- electric current

• aerotropism- oxygen concentration

• hygrotropism- humidity

what happen when a plant is exposed to red light

Pr absorbs the red lightand converts to Pfr

Pfr accumulation initiates developmental processes in long day plants

what happen when a plant is exposed to far-red light

Pfr absorbs light and converts back to Pr

can also occur during the night

what determines flowering

ratio of Pr to Pfr- indicates to the plant the photoperiod and night

long day plants

only flower when period of uninterrupted darkness is less than 12 hours- Pfr stimulates flowering

short day plants

only flower when period of uninterrupted darkness is more than 12 hours- Pfr inhibits flowering

greening

once the shoot has broken the surface of the soil phytochromes promote primary leaf development unrolling and production of photosynthetic pigments , inhibition of cell elongation in the internodes

activation of Pfr

activated phytochrome interacts with other proteins to initiate a signal transduction pathways. signal proteins are or navigate transcription factors to bring about transcription of light-regulated genes

plant hormone (auxin)

IAA (indoleacetic acid)

candidate gene

gene that causes a disease

DNA sequencing- analysis of DNA to find candidate genes

any mutations that are specifically different to the population

DNA of affected people is compared to that of unaffected people

SNP- single nucleotide polymorphism

variation when one nuleotide is substituted and must occur in at least 1% of the population as a particular SNP could predispose people to disease

use of a candidate gene

The whole population, or affected individuals in the population, can be screened for mutations in the gene

drug target

A specific molecule (a protein) that a drug interacts with to bring about an effect

pharmacogenics

prescribing drugs based on a person’s genome

ethical dilemmas of genetic testing and personalised medicine

• discrimination of people with genes for diseases in insurance

• decision making on who should have the tests

• records and access to data

• maintaining confidentiality

• availability privately for people who can pay

• treatments will be expensive at first

• who is eligible

antibiotic resistance in genetic modification

gene could be transferred to pathogen bacteria

risks of animal modification

• risk of protein made by GMO being a health hazard

• virus as vectors

• people chosing wether to eat GMO food

risks of plant modification

• transfer of gene to non target species by cross pollination, allowing other species to outcompete eg creation of superweed- can ensure outcrosses are infertile or develop technology to prevent pollen from containing the DNA

• use of herbicides or pesticides can act as a selection pressure to weeds which may become resistant

• crop ownership- some farmers can afford the technology but some cant

nature and nurture in the critical period

nature- volumn cells present at birth

nurture- development during critical period results in less overlap between territories of different axons

neural plasticity

the changes occurring in our network of network of neurones by modification of synapses that underpin learning and memory

critical window

synapses made, maintained, and pruned for correct development of visual cortex so the neurones can respond to information from the retina

cross cultural studies

carpented worth hypothesis and depth clues and linear perspective

crawling babies

visual cliff experiment