How nerves work Flashcards
What are the meninges?
The meninges are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater (from outer to inner skull).
What are the three different meninges called?
Dura mater (outer) - arachnoid mater - pia mater (inside)
What are the four lobes of the cerebrum, what are they responsible for and where are they located?
Cerebrum is a large part of the brain, comprising of:
– Frontal lobe (front) – reward, attention, short term memory etc
– Temporal lobe (sides) – memory, language, emotion
– Parietal lobe (top) – senses e.g. pain, temperature etc., language
– Occipital lobe (back) - vision
What is the parietal lobe responsible for?
Language and touch
What is the frontal lobe responsible for?
Memory, thought, behaviour, movement
What is the temporal lobe responsible for?
Hearing, learning, feelings
What is the occipital lobe responsible for?
Sight
What is found in the diencephalon located just above the brainstem?
Thalamus and hypothalamus
What are the functions of the thalamus and the hypothalamus?
– Thalamus - site of last relay for sensory information
– Hypothalamus - important neuroendocrine regulator – controls basic functions e.g. feeding, drinking, breathing, sleep, mating)
Whats are the sulcus and gyrus of the brain?
The sulcus is a depression or groove in the cerebral cortex. It surrounds a gyrus, creating the characteristic folded appearance of the brain in humans and other mammals.
Whats the difference between the cerebrum and the cerebellum?
Cerebrum - large bit of brain, contains lobes
Cerebellum - “little brain”, important in motor control
What is the primary function of the brainstem and what is it made up of?
Brainstem is in charge of controlling basic functions e.g. blood pressure, respiratory rate etc., and is made up of the:
– Midbrain
– Pons
– Medulla oblongata
How many pairs of spinal nerves are there, and how are they segmented based on their origin?
31 pairs
– 8 cervical (neck, shoulders & arms)
– 12 thoracic (chest & abdomen)
– 5 lumbar (hips & legs)
– 5 sacral (genitalia & gastrointestinal tract)
How many cranial nerves are there?
12 pairs
What type of information goes through ventral and dorsal roots?
Ventral - motor neurons, motor information
Dorsal - sensory information
What is the grey column in the spinal cord made up of
The grey column in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons.
What is the white matter of the spinal cord made up of?
The white matter is located outside of the grey matter and consists almost totally of myelinated motor and sensory axons. “Columns” of white matter carry information either up or down the spinal cord
Define a neuron
A neuron (also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information through electrical and chemical signals.
Describe the basic structure of a neuron
Cell body (soma(
Dendrites
Axon hillock/initial segment
Axon
What is a neurite?
Can be a dendrite or axon, usually termed this when neuron is in its undifferentiated stage
What is a fascicle?
Bundle of nerve fibres
Describe the three different types of neurones
- Afferent (sensory) neurones - Peripheral nervous system
- Interneurones - Central nervous system
- Efferent (motor) neurones - Peripheral nervous system
What are glial cells?
Glial cells, sometimes called neuroglia or simply glia are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central and peripheral nervous systems.
What percentage of cells in the CNS are made up of glial cells?
90%
Describe the 4 types of glial cells
Astrocytes
• Maintain the external environment for the neurones
• Surround blood vessels & produce the BBB
Oligodendrocytes
• Form myelin sheaths in the CNS
Microglia
• Phagocytic hoovers mopping up infection
Schwann cells
• Responsible for the myelination of neurons in PNS
What is the resting membrane potential?
The relatively static membrane potential of quiescent cells is called the resting membrane potential (or resting voltage). Usually around -70mV (-90mV in more excitable cells e.g. cardiac, striated muscle)
What is responsible for the resting membrane potential?
The resting membrane permeability to K+ (this is why the RMP is very similar to the K equilibrium potential)
What is the equilibrium potential?
The membrane potential at which the electrical gradient is exactly equal and opposite to the concentration gradient
What is the Nernst equation used for?
The Nernst equation predicts the equilibrium potential for a single ion species
What is the Goldman equation used for?
The Goldman equation predicts the equilibrium potential generated by several ions
What ion channels can be opened to hyperpolarise a cell?
Cl- (moves in) and K+ (moves out)
What ion channels can be opened to depolarise a cell?
Na+ (moves in) and Ca (moves in)
What are the major differences between graded potentials and action potentials?
Action - all or none, encoded by frequency, threshold and refractory period, always depolarising, self propagating, mediated by voltage gated channels, can signal over long distances
Graded - graded, coded by amplitude, can summate, no threshold or refractory period, hyper polarising or depolarising, decremental, voltage and ligand channels, operate locally
Give some examples of graded potentials
o Generator potentials - at sensory receptors
o Postsynaptic potentials - at synapses
o Endplate potentials - at neuromuscular junction
o Pacemaker potentials - in pace maker tissues
What are EPSPs and IPSPs?
EPSP = excitatory post-synaptic potential (makes cell more likely to reach threshold) IPSP = inhibitory post-synaptic potential (makes cell less likely to reach potential
What causes fast and slow inhibitory potentials?
GABA causes both, glycine only affects Cl-
Fast - opening of voltage gated Cl channels to let it in
Slow - opening of metabotropic channels to let K+ out
How do different GABA receptors affect the speed of inhibitory signalling?
GABAA in which the receptor is part of a ligand-gated ion channel complex = Cl- in very fast reaction
GABAB metabotropic receptors, which are G protein-coupled receptors that open or close ion channels via intermediaries (G proteins) = K+ out very slow reaction
What channels are responsible for the production of action potentials and post synaptic potentials?
Postsynaptic potentials are produced by a neurotransmitter ligands opening or closing ion channels = ligand-gated ion channels
Actions potentials are produced by depolarisation of the membrane potential opening ion channels = voltage-gated ion channels
What is synaptic integration?
Is the computational process by which an individual neuron processes all of its synaptic inputs in space and time to determine whether to convert them into an output signal.
What is the difference between temporal and spatial summation of nerve inputs?
- If you stimulate a cell again quickly at the same site, the next EPSP adds on to it. This is temporal summation.
- You can also summate stimulations from two different sites on the soma of the cell. This is spatial summation.
Define an action potential
- Defined as the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.
- RMP sits at -70mV, action potentials occur when cells reach threshold - usually about -55mV.
What can increase the velocity of action potentials?
Bigger axons - lowers axonal resistance (can have Na+ channels further apart)
Myelination - increases capacitance of vessels (can then only have Na channels at nodes of ranvier)
What is Guillain-Barre syndrome?
Demyelinating disease similar to MS but specific to PNS.
How does Tetrodotoxin affect action potential formation?
Toxin from puffer fish; blocks Na+ channels and so blocks the action potential
How does Joro spider toxin affect action potential formation?
Toxin blocks Ca2+ channels and prevents neurotransmitter release, causing paralysis
How does Botulinum toxin affect action potential formation?
It disrupts the release machinery proteins and so blocks transmitter release, mechanism behind botox (paralysis of facial muscles)
How does Curare affect action potential formation?
Toxin blocks Ach receptors and so prevents the end plate potential, plant extract used for poison darts
What are the differences in signalling between the NMJ and CNS synapses?
CNS - many transmitters, EPSPs and IPSPs, allows synaptic integration, variation in arrangement
NMJ - one primary transmitter (ACh), EPSPs only
Which cholinergic receptors are found on the post NMJ synaptic left?
Nicotinic
