Basic definitions (all topics) Flashcards
define axonal transport
transport of proteins from where they are made in the nucleus/cell body, to the terminal boutons of the axon where they are needed - for example neurotransmitters. this is done by the molecule kinesin ‘walking’ down the cytoskeleton of the neuron.
define resting membrane potential
the relative charge across the membrane of a neuron (sits at -70mv)
define graded potential
a localised change in the membrane potential of a neuron. these can be hyperpolarisations or depolarisations and depend on the strength of the incoming stimuli (hence they are graded)
define action potential
a wave of negative electrical excitation (depolarisation) that travels down the axon of a neuron. they are unidirectional and are all or nothing events, unlike graded potentials which can vary in strength.
define depolarisation
a change in membrane potential that gets less negative (closer to 0)
define hyperpolarisation
a change in membrane potential that gets more negative (further away from 0)
define saltatory conduction
this is the way that an action potential travels down a myelinated axon, whereby depolarisation only occurs in non-myelinated gaps called nodes of Ranvier. this speeds up the conduction of an action potential as less voltage gated channels have to open along the length of the axon.
define synaptic delay
communication at a chemical synapse is slower than the propegation of action potentials as chemicals must diffuse across the synaptic cleft which takes time. this slows nervous communication down as synaptic transmission takes 0.3-5ms to happen.
define neuroglia
neuroglia or glial cells are the support cells of the nervous system. they perform many different roles, including providing neurons with nutrients and maintaining the chemical environment. they also create myelin sheaths etc.
define neuropraxia
a category of nerve damage whereby nerves are compressed or stretched but remain in tact. this type of injury may result in temporary loss of sensation or function but will return once the source of the compression or stretch is removed.
define axonotmesis
a category of nerve damage where individual axons within a nerve are broken but the nerve itself (connective tissues etc) remains in tact. this will cause temporary loss of function or sensation but will usually heal and this will be restored after time
define neurotmesis
a category of nerve damage where an entire nerve is severed. this is a severe injury, leads to distal loss of sensation and function that is likely to be permanent. some healing may occur but this can be complex and also lead to pain.
define ischemic damage
damage caused to a nerve due to lack of oxygen supply. this leads to cellular respiration stopping. no cellular respiration leads to the cell depolarising and an influx of calcium ions. these ions cause excitotoxicity.
define excitotoxicity
prolonged exposure to excitatory neurotransmitters such as glutamate can lead to a cascade of neurotoxicity which leads to loss of function or cell death
define myofibril
an organelle within a muscle cell that is made up of end to end sarcomeres which are the contractile elements of muscle cells.
define sarcomere
a contractile unit of a muscle cell, it is the space between two adjacent z discs. it consists primarily of thin filaments (actin) and thick filaments (myosin)
define sarcoplasmic reticulum
an elaborate smooth endoplasmic reticulum found only in muscle cells. it stores and releases calcium ions
define terminal cisterns
large sarcoplasmic reticulum channels at the junction of the I and A bands of a myofibril
define T tubules
at each I-A band junction the sarcolemma of the cell protrudes deep into the cell interior, forming an elongated tube called the T tubule. it is flanked by two terminal cisterns
define T tubule Triad
a t tubule flanked by two terminal cisterns
define end plate potential
the binding of ACh to a receptor on the sarcolemma at a neuromuscular junction causes a local depolarisation (like a graded potential) which in a muscle is called an end plate potential
define excitation-contraction coupling
the process just before muscle contraction can start. it involves ca2+ being released at the terminal cisterns. Ca2+ then binds to troponin, which shifts tropomyosin out of the way of the myosin binding site on actin. once this shift has occurred a myosin head can bind to actin.
define cross bridge cycling
the process of muscle contraction itself. myosin head binds to actin, it releases ADP and P as it shift back, bringing the actin filament closer to the M line of the sarcomere. ATP is then added, myosin head detaches. as it returns to its ‘ready’ position it hydrolyses ATP to ADP and P and is energised so it can re bind to the next section of actin.
define motor unit
all the muscle fibres innervated by one motor neuron. they can be small (and therefore engaged when small contraction is needed), medium or large (engaged when maximum effort is required)
define frequency coding
as the frequency of action potentials increases, the muscle doesn’t have time to relax in between stimuli and therefore it remains contracted
define decussation
crossing the midline of the body (in relation to spinal tracts)
define memory
the acquisition, encoding, storage and retrieval of information in the nervous system
define declarative memory
consciously accessible information such as facts and figures
define non-declarative memory
unconscious information including procedural memory (motor learning)
define anterograde amnesia
memory disorder characterised by a lack of ability to form new long term memories, but older memories are easily accessible
define retrograde amnesia
memory disorder characterised by a lack of ability to recall older long term memories but the ability to form new short term memory is in tact.
define long term potentiation
the process by which one time maximal stimulation of a neuron (in the hippocampus if to do with memory but also occurs at spinal level in spinal hyperexcitability) causes the neuron to become more sensitive to a normal level of stimulus. this is done through the activation of/unblocking of NMDA receptors, which allow calcium ions into the cell which start a complex intracellular cascade.
