WEEK 2 Flashcards
Overview of Nervous System
CNS/PNS->Afferent/Efferent System->Somatic/Autonomic NS
What is the Somatic Nervous System?
Voluntary division of NS
What defines the Central Nervous System?
Meningeal encasement-Brain and Spinal cord. Also encased by cranium and vertebral column.
What defines the Peripheral Nervous System?
Part of NS outside CNS, connecting CNS to target organs/tissues and sensory organs to CNS
What is a Neurone (nerve cell)?
The specialised functional unit (ie cell) of the NS
General Anatomy of a Neurone
Cell body (soma), Axon Hillock, Axon, Axon terminal, Myelin Sheath, Nodes of Ranvier, Internodal and Nodal membrane
What makes up the Somatic NS?
Efferent and Afferent
What is the job of the efferent system?
Conveys commands from the CNS to target organs/tissues via motor neurones
Where do somatic efferents act?
At skeletal muscles via muscle contraction to bring about displacement of limbs (movement) and set muscle tone
What is the job of the afferent system?
Carry sensory information from sensory receptors to the CNS via sensory neurones
What do somatic afferents do?
Cause sensations which give awareness to the sensory experience
Typical characteristics of Somatic NS
Bi-stable state (Active or Inactive)
Largely paralysed during REM sleep
Effector organ is skeletal muscle and is responsible for muscle/motor tone
Morphology of motor neurone is
Multipolar (soma at distal aspect of neurone in CNS)
Morphology of sensory neurone is
Pseudounipolar (soma found along neurone in PNS)
Features of somatic motor neurones
Cell bodies located in either: Ventral horn of spinal cord or cranial nerve motor nuclei of the brain
Largely myelinated: Aalpha (faster than Agamma) or Agamma classification
Features of somatic sensory neurones
Varying levels of myelination:
Heavily myelinated=Aalpha and Abeta
Lightly myelinated=Aalpha
Unmyelinated=C-fibres/free nerve endings
What other somatic neurone morphology is there?
Bipolar (soma found along neurone)
What is the ‘nerve entry point’ or neurovascular hilum?
The geographical centre of any given muscle
The site of entry of a motor neurone into the substance of the muscle (NMJ)
The site of entry/exit of arterial supply/venous drainage to/from the muscle
The site of aggregation of nicotinic receptors of healthy muscles
What is the thickness of the axon dependent on?
The level of myelination (thicker axon=more myelination)
Conduction velocity (CV)=
5.8xFibre diameter (FD)
What is the importance of myelination?
provide insulation of otherwise bare axonal membrane, increase axonal conduction velocity, reduce capacitance of neurones (easier activation), creates path of remyelination if nerve axon is cut
Characteristic Neuroglia of the PNS and their functions
Schwann cells-myelinate peripheral nerve axons (1SC myelinates 1 axon)
Satellite cells-provide physical support for neurones
Microglia-immune and inflammatory functions
Characteristic Neuroglia of the CNS and their functions
Oligodendrocytes-myelinates many axons at any one myelination segment
Membrane envelopes of cranial and spinal nerves (from out to in)
Epineurium-ensheaths entire nerve, interfascicular bands attach adjacent nerve fascicles
Perineurium-ensheaths a nerve fascicle (collection of axons)
Endoneurium-ensheaths a single cell’s axon
General functions of glia
guiding connections, physical support, metabolic support, electrical insulation, signalling
Neuronal specialisations for communication
Dendrites-input from other neurones
Axon Hillock-action potential generation
Axon-impulse conduction
Axon Terminal-release of neurotransmitter
What is the electrical synapse (gap junction)?
bidirectional transfer of information via a channel formed by pores in each membrane created by two connexons (composed of 6 connexins each), one in each membrane, allowing ions and small mol. to transfer, allowing synchronous activity between cells
Where is the electrical synapse important?
glia-neurone or glia-glia communication + cardiac myocytes are connected by gap junctions
What is the chemical synapse?
unidirectional transfer of information from pre-synaptic to post-synaptic neurone
Describe the process of the chemical synapse
AP arrives at axon terminal of Pre-S neurone, V-gated Ca2+ ion channels open, Ca2+ enters the Pre-S neurone, synaptotagmin (Ca2+ sensor) causes vesicle movement to and fusion with membrane, docked vesicles release neurotransmitter via exocytosis, neurotransmitter diffuses across synaptic cleft and binds to receptors on Post-S membrane, ligand-gated ion channels open (cause excitation/inhibition), enzymes hydrolyse neurotransmitter, ending Post-S stimulation, neurotransmitter diffuse back into Pre-S neurone and are repackaged into vesicles
What is the role of receptors in NS?
Membrane spanning protein recognition site for neurotransmitter, causing initiation of intracellular signal
What are ionotropic receptors?
ligand-gated channels
What is the process of ionotropic receptor signalling?
transmitter binds, conformational change, channel opening, ion movement
What is the electrical effect of ionotropic receptor excitation?
neurotransmitter binds, conformational change, Na+ ion channels open, Na+ influx, membrane depolarisation
What is the electrical effect of ionotropic receptor inhibition?
neurotransmitter binds, conformational change, Cl- ion channels open, Cl- influx, membrane hyperpolarisation
What does excitatory mean?
more likely to fire AP, promoting generation of Post-S electrical signal
What ion causes small excitatory post synaptic potentials (EPSPs)?
Na+
What ion causes small inhibitory post synaptic potentials (IPSPs)?
Cl-
What causes small excitatory/inhibitory post synaptic potentials?
individual synaptic input
What is the process of metabotropic receptor signalling?
transmitter binds, conformational change, G-protein activation, activates ‘effector systems’, indirect effects on excitability
What can G-protein activation cause?
Open/Close of ion channels or stimulation/inhibition of enzymes/secondary messenger systems
Examples of metabotropic receptors include
ACh muscarinic, GABA(B), monoamine receptors (except 5-HT)
Examples of excitatory ionotropic receptors include
glutamate AMPA, NMDA, ACh nicotinic receptors
Examples of inhibitory ionotropic receptors include
GABA(A), glycine receptors
What is needed to control neuronal firing?
Multiple synaptic inputs
Where are synaptic inputs more influencial?
To Cell body>To Dendrites
What is spatial summation?
summing of post synaptic potentials generated at separate synapses
What is temporal summation?
summing of post synaptic potentials generated at the same synapse if they occur in rapid succession
