A-Level CIE Biology: 15 Coordination & Control

what is a hormone

chemical substance produced by an endocrine gland and carried by the blood.

• chemicals which transmit information from one part of the organism to another and bring about a change.

• they alter the activity of one or more specific target organs

what do hormones control

functions that don’t need instant responses 

what is the endocrine system

endocrine glands that produce hormones in animals collectively

gland

group of cells that produces and releases one or more substances (secretion)

examples of cell-signalling molecules/hormones in blood

• insulin

• glucagon

• ADH

• adrenaline

why do endocrine glands have a good blood supply

when they make hormones, they need to get the hormones into the bloodstream/blood plasma asap so they can travel around body to target organs and bring about response

what is needed for hormones

cells with receptors that the hormone can bind to either found on the csm or inside cells. they must be complementary to have an effect

what hormones are peptides

insulin, glucagon and ADH

features of peptide hormones

• water-soluble so can’t cross pbl of csm 

• bind to receptors on csm of target cells which activates second msngers to transfer signal thru cyto

what hormones are steroids

testosterone, oestrogen, and progesterone

features of steroid hormones

• lipid-soluble and can cross pbl

• bind to receptors in cyto of nucleus of target cells

human nervous system: 2

• central nervous system/cns - brain and spinal cord

• peripheral nervous system/pns - all nerves in body

what does the nervous system allow us to do and how

• make sense of our surroundings nad respond to them and to coordinate and regulate body functions

• info sent thru nervous system as nerve impulses which are electrical signals passing along nerve cells (neurones)

nerve

bundle of neurones

neurones function

coordinate the activity of sensory receptors (e.g. eye), decision making centres in the cns, and effectors such as muscles and glands.

nervous system: parts, message, method, effectors, speed, duration

• brains, spinal cord, nerves/neurones

• electrical impulse

• neurones

• muscles or glands

• very fast

• short until electrical impulses stop

endocrine system: parts, message, method, effectors, speed, duration

• glands

• chemical/hormone

• bloodstream

• target cells in specific tissues

• slower

• longer until hormone broken down

axon

neurone’s long fibre

how is an axon insulated

fatty sheath with small uninsulated sections along its length (nodes of Ranvier)

what is the fatty sheath made of

myelin, substance made by specialised cells (schwann cells) when they wrap themselves around axon along its length

what is the effect of the axon

electrical impulse doesn’t travel down whole axon but jumps from one node to the next

why do electrical impulses jump

less time wasted transferring impulse from one cell to another 

dendrites

cell bodies contain many extensions/dendrites that allow them to connect to many other neurones and receive impules from them forming a network for easy communication

3 main types of neurone

sensory, relay, motor

sensory function

carry impulses from receptors to cns/brainorspinalcord

intermediate/relay neurone function

found entirely within cns and connect sensory and motor

motor function

carry impulses from cns to effectors/muscles or glands

are all neurones the same

no, each has slightly diff structure

motor neurone structure: 3

• large cell body at one end, that lies within spinal cord or brain

• nucleus that is always in its cell body

• many highly-branched dendrites extend from cell body, providing large sa for axon terminals of other neurones

sensory neurones structure

• same basic as motor but have cell body that branches off in middle of cell = may be near source of stimuli or in swelling of spinal nerve known as ganglion

receptor cell

cell that responds to a stimulus. transducers. convert energy in one form (e.g. light/heat/sound) into energy in electrical impulse within sensory neurone

where are receptor cells found

in sense organs (e.g. light receptor cells found in eye, chemoreceptors in taste buds)

what are some receptors

specialised cells that detect a specific tyep of stimulus and infleunce the elcetrical activity of a sensory neurone (light and chemo eye and tongue)

others (e.g. touch) are just ends of sensory neurones themself

what happens when receptor cells are stimulated. what if its weak/strong

depolarised

weak= not sufficiently depolarised and sensory neurone is not actviated to send impulses

strong=sensory neurone activated and transmits impulses to cns

tongue surface. 

many small bumps called papillae covering surface of tongue, each covered in many taste buds which contain many chemoreceptors that are sensitive to chemicals in food and drinks bc covered with receptor proteins to detect diff chemis

what do chemoreceptors in taste buds that detect salt (sodium chloride) respond directly to

sodium ions.

if salt is present in food (dissolved in saliva) being eaten:

• na+ diffuse thru highly selective channel proteins in csm of microvilli of chemoreceptor cells

• leads to depolarisation of chemoreceptor cell memb

• increase in + charge inside cell = receptor potential

• if sufficient stimulation by na+ and sufficient depolarisation of membrane, the receptor potential becomes large enough to stimulate voltage-gated calcium ion channel proteins to open

• as result, calcium ions enter the cyto of chemoreceptor cell and stimulate exocytosis of vesicles containing neurotransmitters from the basal membrane of the chemoreceptor

• neurotransmitter stimulates an action potential in sensory neurone

• sensory neurone then transmits an impulse to the brain

action potential page