6 Nervous coordination and muscles Flashcards
What are the two main forms of coordination in animals?
The nervous system
The hormonal system
Give an example of nervous coordination
Reflex action e.g withdrawal of hand from an unpleasant stimulus
Give an example of hormonal coordination
The control of blood glucose concentration
What are neurones?
Specialised cells adapted to rapidly carrying nerve impulses from one part of the body to another
What is a mammalian motor neurone made up of?
Cell body, dendrons, Schwann cells, myelin sheath and nodes of Ranvier.
What do Schwann cells do?
They surround the axon, protecting it and provide electrical insulation
What are noses of Ranvier?
Constrictions between adjacent Schwann cellswhere there is no myelin sheath
What are the different types of neurones?
Sensory neurones, motor neurones and relay neurones
What is the function of the sensory neurone?
It transmits nerve impulses from a receptor to a motor or relay neurone
What is the function of a motor neurone?
It transmits nerve impulses from a relay neurone to an effector
What is the function of a relay neurone?
It transmits impulses between neurones
What is a nerve impulse?
A wave of electrical activity that travels along the axon membrane
What prevents the sodium and potassium ions from diffusing across the axon plasma membrane?
The phospholipid bilateral of the axon plasma membrane
By what process do sodium and potassium ions pass through ion gates channels?
Facilitated diffusion
What is the resting potential value in humans?
-65mV
What is the role of the sodium potassium pump?
Actively transport sodium ions out of the axon.
Actively transport potassium ions into the axon.
What is the threshold that needs to be reached in order to create an action potential?
+40mV
What is resting potential?
The difference in electrical charge maintained across the membrane of the axon of a neurone when not stimulated
What is repolarisation?
Return to the resting potential in the axon of a neurone after an action potential
Does the size of an action potential ever change?
No, it remains the same from one end of the axon to the other
Why does an action potential pass along a myelinated neurone faster than an unmyelinated neurone?
Because in an unmyelinated neurone, the events of depolarisation have to take place all the way along an axon and this takes more time.
What factors affect the speed at which an action potential travels?
Myelin sheath, diameter of the axon and temperature.
What is saltatory conduction?
When an action potential jumps from one node of Ranvier to another.
How can an organism perceive the size of a stimulus?
By the number of impulses passing in a given time.
By having different neurones with different threshold values
What is the refractory period?
The period during which the membrane of the axon of a neurone can’t be depolarised and no new action potential can be initiated.
What are the three purposes of the refractory period?
It ensures that action potentials are propagated in one direction only.
It produces discrete impulses.
It limits the number of action potentials.
What is a synapse?
A junction between neurones, in which they have a narrow gap, the synaptic cleft, which a neurotransmitter can pass.
What is a presynaptic neurone?
The neurone that releases the neurotransmitter
What organelles does the synaptic knob possess?
Many mitochondria and large amounts of endoplasmic reticulum
What are these organelles required for?
They are required in the manufacture of the neurotransmitter which takes place in the axon.
Where is the neurotransmitter stored?
In the synaptic vesicles
What are the features of the synapse?
Undirectionality - synapses can only pass information in one direction, from the presynaptic neurone to the postsynaptic neurone.
Summation - a rapid build up of neurotransmitter in the synapse.
What are the two types of summation?
Spatial summation
Temporal summation
What is spatial summation?
When a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the post synaptic neurone.
What is temporal summation?
When a single presynaptic neurone releases neurotransmitter many times over a short period of time in order to exceed the threshold value.
What are inhibitory synapses?
Synapses that make it less likely that a new action potential will be created on the post synaptic neurone.
What is a cholinergic synapse?
A synapse in which the neurotransmitter is a chemical called acetylcholine.
Where do cholinergic synapses occur?
Central nervous system
Neuromuscular junctions
What are the three types of muscle in the body?
Cardiac muscle
Smooth muscle
Skeletal muscle
What are myofibrils?
Tiny muscle fibres that individual muscles are made of
Which two types of protein filament are myofibrils made of?
Actin and Myosin
What is a sarcomere?
The distance between adjacent Z-lines
What is tropomyosin?
An important protein found in muscle, which forms a fibrous strand around the action filament.
What types of muscle fibre are there?
Slow-twitch fibres
Fast-twitch fibres
What is a neuromuscular junction?
The point where a motor neurone meets a skeletal muscle fibre
What is the sliding filament mechanism?
The process where actin and myosin filament slide past one another.
