CIE A Level Biology 9700 Topic 15: Control and Coordination Summary Notes

Topic 15: Control and coordination
Endocrine system
● all of endocrine glands in body + hormones they secrete
● endocrine gland
○ group of cells that prod. & releases hormone(s)
○ good blood supply → get hormones into bloodstream
○ no ducts
● hormone
○ chemical substance prod. by endocrine gland & carried by blood → transmit info. from 1
part of organism to another → alter activity of target organ(s)
○ only affect cells w/ complementary receptors → bind
○ types of hormones

Peptides/small proteins Steroids

water-soluble lipid-soluble

cannot cross phospholipid bilayer can cross phospholipid bilayer

bind to receptors on cell membrane of target cells bind to receptors in cyto./nucleus of target cells
→ activate 2nd messengers inside cyto.

eg. insulin, glucagon, ADH eg. testosterone, oestrogen, progesterone


Nervous system
● nervous vs endocrine systems

Nervous system Endocrine system

Parts of system CNS = brain, spinal cord glands
PNS = cranial & spinal nerves

Type of message electrical impulse chemical hormone

Method of transmission nerves/neurones bloodstream

Effectors muscles/glands target cells in specific tissues

Speed of transmission v. fast slower

Length of effect shorter (until impulses stop) longer (until hormone break down)


● neurones
○ features
■ axon – long fibre insulated by fatty sheath
■ myelin – fatty sheath made of Schwann cells
● ~⅔ motor & sensory neurones = unmyelinated
● encloses axon in many layers of cytoplasm
■ nodes of Ranvier – small uninsulated sections along axon
■ cell body – contains organelles & structure of neurones
■ dendrites – connect to other neurones

, ○ types of neurones
■ motor neurone
● CNS → effectors
● large cell body at 1 end w/in CNS
● nucleus in cell body
● many extensive RER in cell body
● many mito. in cell body, axon, axon terminals
● many highly-branched dendrites → large SA for axon terminals of other
neurones
■ sensory neurone
● receptors → CNS
● cell body branches off in middle of axon
● nucleus in cell body
● near source of stimuli/in swelling of spinal nerve = ganglion
■ intermediate/relay neurone
● connect sensory neurones & motor neurones
● entirely w/in CNS
● sensory receptor cells
○ features
■ respond to stimuli
■ = transducers – convert E. in 1 form → electrical impulse
■ often found in sense organs
■ some = specialised cells → detect specific type of stimulus, others = ends of
sensory neurones
○ example – chemoreceptors in taste bud for salt
1. Na+ from NaCl diffuse thru. highly-selective channel proteins in cell membranes of
microvilli of chemoreceptor cells → ↑ +tive charge → cell membrane depolarised
● ↑ +tive charge = receptor potential – change in resting pot. across
membrane of receptor cell
2. sufficient stimulation by Na+ → sufficient depolarisation → receptor pot. > threshold
potential → V-gated Ca2+ channels open
● if stimulus = weak → receptor pot. not as often > threshold pot. → ↓ freq. of
impulses
● if stimulus = v. weak → receptor pot. < threshold pot. → will not transmit
impulse
● eg. of all-or-nothing law – impulse only transmitted if initial stimulus
sufficient to ↑ membrane pot. > threshold pot.
● NB. threshold pot. often ↑ w/ continued stimulation → ↑ stimulus req. for
impulses
2+
3. Ca enter cyto. → stimulate exocytosis of vesicles containing neurotransmitters
from basal membrane of chemoreceptor
4. neurotransmitters stimulate action pot. in sensory neurone → transmits impulse to
brain
● nerve impulses
○ resting potential
■ inside of resting axon always has ~-70mV pot. diff. cf. outside
● ie. inside 70mV more negative cf. outside axon
■ factors maintaining resting pot.