Control and Coordination

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Cambridge International AS & A Level Biology (9700)

Control and Coordination

The big idea: Nerve impulses are waves of depolarisation made by ions moving through gated channels, passed across synapses by chemicals. Hormones travel more slowly in the blood. Plants coordinate too: with electrical signals in the Venus fly trap and with auxin and gibberellin for growth.

Summary — What This Chapter Covers

The endocrine system (ADH, glucagon, insulin) compared with the nervous system.
Sensory, motor and intermediate neurones; sensory receptor cells, with the taste bud chemoreceptor as the example.
Resting potential, action potential, refractory period, saltatory conduction and impulse frequency.
The cholinergic synapse and the role of calcium ions.
Neuromuscular junction, T-tubules, sarcoplasmic reticulum, sarcomere structure and the sliding filament model.
Plants: the Venus fly trap, auxin and elongation growth, gibberellin in barley germination.

1. Control and Coordination in Mammals

15.1

The endocrine system

The endocrine system is made of endocrine glands: ductless glands that secrete hormones directly into the blood. A hormone is a chemical messenger carried in the blood plasma to target cells, which have specific receptors complementary to it. Cells without the receptor do not respond.

Hormone	Made by / released from	Target	Effect
ADH (peptide)	Hypothalamus / posterior pituitary	Collecting duct cells	Aquaporins inserted; more water reabsorbed
Glucagon (peptide)	α cells, islets of Langerhans	Liver cells	Glycogen broken down; blood glucose rises
Insulin (protein)	β cells, islets of Langerhans	Liver and muscle cells	Glucose uptake and glycogen synthesis; blood glucose falls

These peptide hormones are water-soluble and cannot cross the membrane, so they bind to receptors on the cell surface and act through second messengers (see Homeostasis).

Nervous and endocrine systems compared

Nervous system	Endocrine system
Electrical impulses along neurones, chemical transmission at synapses	Chemical (hormones) only
Transmitted along neurones	Transported in the blood
Very fast	Slower
Short-lived effect	Often longer-lasting effect
Acts on a precise, localised target (one muscle or gland)	Can affect widespread target cells all over the body
Effectors: muscles and glands	Target cells in many tissues

Neurones

	Sensory neurone	Motor neurone
Function	Carries impulses from a receptor to the CNS	Carries impulses from the CNS to an effector (muscle or gland)
Cell body	In a ganglion (dorsal root ganglion) just outside the spinal cord, partway along the neurone	Inside the CNS (spinal cord or brain), at one end
Processes	Long dendron from the receptor to the cell body; short axon into the CNS	Many short dendrites; one long axon to the effector, ending in motor end plates

Both may be myelinated and contain mitochondria, Nissl bodies (rough ER) and vesicles of neurotransmitter at their terminals. Intermediate (relay) neurones, found within the CNS, connect sensory neurones to motor neurones.

Sensory receptor cells

transducers receptor potential frequency

Chemoreceptor in a taste bud: detecting salt

Resting potential and action potential

Maintaining the resting potential (about −70 mV)

Na⁺/K⁺ pumps

Memorise

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Also in the full note

Transmission along the neurone and saltatory conduction
Stimulating contraction in striated muscle
Ultrastructure of striated muscle
The Venus fly trap
Auxin and elongation growth
Gibberellin in the germination of barley

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Control and Coordination