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Title: Nervous System notes
Description: These notes are of a university standard and go into depth on the nervous system. They include details on autonomic and somatic nervous system; and transmitters and receptors involved in the system. They also go into depth about how action potentials are used and many more details about the nervous system
Description: These notes are of a university standard and go into depth on the nervous system. They include details on autonomic and somatic nervous system; and transmitters and receptors involved in the system. They also go into depth about how action potentials are used and many more details about the nervous system
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The Nervous System
Afferent – towards the CNS
Efferent – away from CNS
Divided into somatic and autonomic
Somatic Nervous system
From the sense organs and skin to the skeletal muscles
Under conscious control
Single neurone pathway
Autonomic Nervous system
connects smooth muscle, glands and heart
Involuntary processes – digestion
2 neurones connected in series
Can be either parasympathetic (output of craniosacral origin) or sympathetic
(output of thoracolumbar origin)
Heart rate
Blood pressure
Saliva production
Sweating
peristalsis
Sympathetic
Increase
Increase
supressed
increase
slows
Sympathetic using energy – preparation for activity
Parasympathetic conserves energy – calming
Parasympathetic
Decrease
Decrease
stimulated
Decrease
Speeds up
Transmitter and receptors
sympathetic
Transmitters:
Preganglionic
Postganglionic
Receptors:
Preganglionic
Postganglionic
Parasympathetic
Acetylcholine
noradrenaline
Acetylcholine
Acetylcholine
Nicotinic
Alpha or beta receptors
Nicotinic
muscarinic
Excitable Cells
Cells which are able to transmit electrical impulses
Cell type – neurones, skeletal muscle, cardiac muscle, smooth muscle
Ion concentration:
Na+
K+
Extracellular fluid (mM)
145
4
Intracellular fluid
12
155
And so a concentration gradient exists (K+ tends to move out of the cell, whilst
Na+ tends to move into the cell)
Movement of charge sets up an electrical gradient
Equilibrium potential – point where forces are balanced
Neurons conduct information in two ways:
one end of the neuron to the other – via action potentials
across the minute space separating one neuron from anther – via
neurotransmitters
Action Potentials
Stimulus
Small increase in permeability to Na+
Na+ influx (moves into cell)
Depolarisation of cell
Triggers opening of Na+ channels
Large increase in permeability to Na+
Large influx of Na+
Reversal of potential
Na+ permeability decreases, K+ permeability increases
K+ efflux (moves out of cell)
Repolarisation of cell
Cell has gained some Na+ and lost some K+
Absolute refractory period – time interval between the opening of the Na+
channel activation gate and the opening of the inactivation gate – Na+ channel
cannot be stimulated
Relative refractory period – takes a much stronger stimulus to generate an AP
during the undershoot
Continuous conduction
Occurs in unmyelinated axons
Wave of de and repolarisation travels in a wave from one patch of membrane to
the next adjacent patch
Aps move in this fashion along a muscle fibre too
Saltatory conduction
Occurs in myelinated axons
“to leap”
The myelin sheath is not completed and so an AP has to be regenerated
AP conduction is faster in myelinated axons with large diameters
Types of Nerve fibres
1
...
large diameters and thick myelin sheaths
2
...
Type C are unmyelinated and have the smallest diameter
ANS fibres serving the visceral organs, sensory fibres and small sensory
fibres
Synaptic Transmission
One neuron will transmit information to anther neuron or muscle or gland by
releasing chemicals called neurotransmitters
The site of chemical interplay is called a synapse
An AP reaches the axon terminal – Ca2+ channels open – Ca2+ rushes in and
binds to regulatory proteins – initiates neurotransmitter exocytosis –
neurotransmitter diffuses across synaptic cleft – binds to receptors on
postsynaptic membrane – initiates a response in the postsynaptic cell
Effects of neurotransmitters:
cation channels to open – depolarisation
anion channels to open – hyperpolarisation
EPSP and IPSP
A graded depolarisation will bring the neuronal membrane potential closer to
the threshold - excitatory postsynaptic potential
A graded hyperpolarisation will bring the neuronal membrane potential farther
away from the threshold and thus referred to as an inhibitory postsynaptic
potential
An EPSP is not strong enough to cause an AP, however EPSPs may be
summed:
Temporal summation – the same presynaptic neuron stimulates the postsynaptic
neuron multiple times in a brief period – depolarisation from the combination of
all the EPSPs may be able to cause an AP
Spatial summation – multiple neurons all stimulate a postsynaptic neuron
resulting in a combination of EPSPs which may yield an AP
Acetylcholine
site
Neuromuscular junction
action
excitatory
Parasympathetic/sympathetic excitatory
ganglion
Parasympathetic
Excitatory/inhibitory
neuroeffector junction
Central nervous system
Excitatory/inhibitory
Effect
Skeletal muscle
contraction
Ganglionic
neurotransmission
Smooth cardiac
muscle and glands
Learning, short-term
memory
Acetylcholine receptors – nicotinic (nAChR) and muscarinic (mAChR)
nAChR is directly coupled to cation channels and mediate fast excitatory
synaptic transmission – differences occur between muscle and neuronal nAChR
mAChR are G-protein coupled receptors and effects are mediated by
phospholipase C activation, Adenylate Cyclase inhibition and K+ activation/
Ca2+ inhibition
affect heart, smooth muscle and glands
3 main types:
1
...
M2 – cardiac, reduced cAMP, reduced Ca2+ and increased K+
conductance
3
Title: Nervous System notes
Description: These notes are of a university standard and go into depth on the nervous system. They include details on autonomic and somatic nervous system; and transmitters and receptors involved in the system. They also go into depth about how action potentials are used and many more details about the nervous system
Description: These notes are of a university standard and go into depth on the nervous system. They include details on autonomic and somatic nervous system; and transmitters and receptors involved in the system. They also go into depth about how action potentials are used and many more details about the nervous system