Week 1 - neurons Flashcards
identify the components of the neuron and describe their functions
What is the function of neurons?
transmission of information
What is the function of glia cells?
- specialised support cells
- provide structural, metabolic and defensive support for nervous tissue
Recap of an action potential
stimulus reaches threshold of -55 mV -> depolarisation (Na+ ions in) -> depolarisation (K+ ions out) -> hyperpolarisation -> resting state
What is the function of a dendrite?
- sensory (afferent)
- receives information and relay it to the cell body in order to innervate it
What form of signals do dendrites relay?
electrical signals
What is the function of the cell body (soma)
- large nucleus, abundant rER,
- performs most synthetic and metabolic functions
- integrates information i.e electrical signals, at the axon hillock
What is the function of the nucleus?
- same as any other nuclei
- contains chromosomes, needed for DNA transcription
- production fo proteins
What is the function of the axon?
- effector portion (efferent) - propagates the action potential
- having a larger diameter and myelination increases conduction velocity
- axon terminals, expansions at the ends of the axon branches, are specialised for chemical neurotransmission
How many axons are there?
only one
How many dendrites can arise from a neuron?
multiple
What is the function of a myelin sheath?
- insulating layer that forms around nerves
- allows electrical impulses to transmit quickly and efficiently along the nerve cells
What is a myelin sheath made up of?
protein and fatty substances
What happens if myelin is damaged?
impulses slow down
What is the function of the nodes of ranvier?
- periodic gasps in the insulating sheath facilitate rapid conduction of nerve impulses - saltatory conduction
What are Schwann cell/ oligodendrocytes?
- glial support cells
- serve as myelinating cell of the PNS
- forms a myelin sheath by wrapping its plasma membrane concentrically around the inner axon
What is the function of the synapse/ axon terminal
- the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector)
- involves release of neurotransmitter across the gap
- innervates the dendrite at next neuron
- synapse splits to innervate multiple neurons
What happens at a synapse? (1-6)
- transmitter is synthesised and then stored in vesicles
- an action potential invades the presynaptic terminal
- depolarisation of presynaptic terminal causes opening of voltage gated Ca2+ channels
- influx of Ca2+ through channels
- Ca2+ causes vesicles to fuse with presynaptic membrane
- Transmitter is released into synaptic cleft via exocytosis
What happens at a synapse? (7-11)
- transmitter binds to receptor molecules in postsynaptic membrane
- opening or closing of postsynaptic channels
- postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell
- removal of neurotransmitter by glial uptake or enzymatic degradation
- retrieval of vesicular membrane form plasma membrane
Are there more neurons or more glial cells?
there are 10 times as many glial cells as neurons
Are there different types of glial cells?
yes - different types found in CNS and PNS
Name examples of glial cells
- Schwann cells
- oligoendocytes
- astrocytes
- microbial cells
- ependymal cells
Compare glial cell in CNS vs PNS
- PNS only contains satellite cells (support) and Schwann cells (myelinate)
- CNS glial cell types include astrocytes, microglial, oligodendrocytes, ependymal cells, stem cells
What are the functions of Oligodendrocytes?
- insulate axons preventing their spontaneous or accidental depolarisation
- produce myelin by wrapping around axons many times,
What does myelination of an axon do?
increases action potential conduction velocity
can a single oligodendrocyte insulate multiple axons?
Yes
What are ependymal cells and where are they found?
epithelia-like cells lining the ventricles of the brain and spina cord
Microglia
act as defensive cells of the CNS, perform the functions of macrophages
What are the 7 functions of astrocytes?
- development: form structural framework for migration of neurons eg. radial glia
- regulation of extracellular K+
- roles in neurotransmission eg. uptake of glutamate at synapses
- insulate neuronal cell bodies and dendrites at non-synaptic sites
- form continuous layer over blood vessels, part of the blood- brain- barrier, regulate local microcirculation and vascular permeability
- metabolic energy generation in neurons (transfer of substances form vasculature to neurons, provide lactate into extracellular fluid for neurons)
- form glial scars at sites of damage (gliosis) and have roles in a nr. of pathologies interacting with microglia and neurons
