B1.2 Flashcards
What is homeostasis?
maintaining a stable environment
What 3 things does homeostasis control?
osmoregulation- regulating water content
need balance between water gained (e.g food and drink) and lost (e.g in sweat)
thermoregulation - regulating body temperature
need to get rid of excess body heat when cold but retain heat when cold
blood glucose regulation -
need to keep glucose in blood at steady level
How does homeostasis work?
negative feedback keeps all things steady
changes in environment trigger response to counteract the changes
internal environment stays at the level cells work best
only works within certain limits - if too much change, may not be possible to counteract it
How is body temperature controlled?
enzymes work best at around 37oc
hypothalamus in brain controls it
when change detected, response in dermis
if too hot:
erector muscles relax, hairs lie flat
sweat produced in sweat glands - when it evaporates, transfers skin heat to environment and cools you down
blood vessels close to skin dilate (vasodilation) - more blood flow near surface and more heat lost through radiation
if too cold:
erector muscles contract, hairs on end - traps insulating layer of air to keep you warm
very little sweat produced - no heat lost through evaporation
blood vessels close to skin contract (vasoconstriction)- less blood flow near surface, less heat lost through radiation
What are hormones?
Where are they produced?
chemical messengers which travel in blood to activate target cells
produced in endocrine glands
travel all over body but only effect certain cells in certain places (target cells)
target cells have right receptors to respond to hormones
organ containing target cells is target organ
travel at speed of blood
What are neurones?
nerve cells that transmit information as electrical impulses around body
have branched endings (dendrons) to connect with other neurones
electrical impulse passed along axon of cell
myelin sheath- acts as electrical insulator, stops impulse getting lost and speeds it up
neurones long- speeds up impulse, one long neurone quicker than lots of small ones)
synapse (gap) - connection between two neurones
nerve impulse transmitted by neurotransmitters, diffuse across gap and start impulse in next neurone
What is the difference between hormones and nerves?
nerves: very fast act for short time act on very precise area electrical message
hormones: slower message act for long time act in more general way chemical message
What are chromosomes and genes?
chromosomes- long lengths of coiled up DNA
23 pairs in nucleus of human cells
carry genes
genes- short section of DNA
control development of different characteristics e.g hair colour
different versions of same gene - give different versions of characteristic. called alleles
two copies of each chromosome so two of each gene- two alleles same or two different
What are sense organs and stimuli?
sense organs detect stimuli
stimulus- change in environment you may have to respond to
5 sense organs - eyes, ears, nose, tongue, skin
all contain different receptors (group of cells sensitive to stimulus) that change stimulus energy (e.g light energy) into electrical impulses
stimulus can be: light, sound, touch, pressure, chemical or change in pressure/ temperature
What receptors do the sense organs contain?
eyes- light receptors
ears- sound and “balance” receptors
nose - smell receptors, sensitive to chemical stimuli
tongue - taste receptors sensitive to chemical stimuli, bitter, sweet, sour, savoury, salt
skin- sensitive to touch (pressure) and temperature change
What is the CNS and how does it work?
central nervous system- consists of brain and spinal chord
coordinates a response
when stimulus detected by receptors in sense organ, information sent as electrical impulses along sensory neurone
CNS then coordinates a response- decides what to do about stimulus and tells something to do it
CNS sends information to effector along motor neurone, effector responds accordingly
What are the different types of neurone and what do they do?
sensory neurone- long dendrons and short axons
carry nerve impulses from receptor in sense organs to CNS
relay neurones- short dendrons and axons
carry nerve impulses from sensory neurones to motor neurones
motor neurones - many short dendrons, one long axon
carry nerve impulses from CNS to effectors
effectors- muscles and glands, respond in different ways
muscles contract in response to a nervous impulse, glands secrete substances e.g hormones
What are reflexes?
automatic responses to certain stimuli to reduce chances of being injured
example: if light shone in your eye, pupils automatically get smaller so less light gets in eye
What is a reflex arc and how does it work?
passage of information in a reflex from receptor to effector
neurones go through spinal chord or unconscious part of brain
when stimulus detected by receptors, impulses sent along sensory neurone to CNS
in CNS, sensory neurone, passes on message to relay neurone
relay neurones relay impulse to motor neurone
impulses travel along motor neurone to effector
effector responds (e.g muscle moves hand)
you don’t have to think about it, quicker than normal responses
What practical can investigate external stimuli?
one person blindfolded, other person uses two points of paperclip fixed distance apart to touch the blindfolded person’s skin
how many points felt depends on area of skin and how sensitive
really sensitive places, both points felt when closer together as more touch receptors
less sensitive area, both points felt when further apart as fewer touch receptors
