Physiology Flashcards
Describe the role of dendrites in the neuron?
receive inputs from other neurones and convey graded electrical signals passively to the soma (cell body of neuron)
Describe the role of the cell body (soma) in the neuron?
synthetic and metabolic centre. Contains the nucleus, ribosomes, mitochondria and endoplasmic reticulum (ER; rough ER is Nissl substance). Integrates incoming electrical signals that are conducted passively to the axon hillock
Describe the role of the axon hillock and initial segment in the neuron?
site of initiation of the ‘all or none’ action potential
Describe the role of the axon in the neuron?
conducts output signals as action potentials to the presynaptic terminal.
Describe the role of the synapse in the neuron?
point of chemical (usually) communication between neurones (or other cells)
Name and briefly describe four types of neuron?
Unipolar: single axon with lots of axon terminals
Pseudounipolar: Joined process that splits
Bipolar: 2 processes either side
Multipolar: gives rise to more than one set of dendrites
Define depolarisation and hyperpolarisation?
Hyperpolarization is when the membrane potential becomes more negative at a particular spot on the neuron’s membrane, while depolarization is when the membrane potential becomes less negative.
What is the resting membrane potential for a typical human nerve cell?
-70mV
What are the equilibrium potentials for sodium and potassium?
For potassium -90mV
For sodium +60mV
Explain why the resting membrane potential for a typical human nerve cell is -70 mV?
Greater movement of potassium as membrane is more permeable to it which will try and drive membrane potential towards its own. There is still a small but significant movement of sodium ions hence why it is -70 and not -90mV.
Describe the resting membrane potential of cells
Resting membrane potential is constant in non-excitable cells, and in excitable cells at rest. Usually inside negative, for typical human nerve cell is -70mV. the sign (+ or -) is the polarity of the excess charge on the inside of the membrane.)
Define a neurotransmitter
a chemical substance which is released at the end of a nerve fibre by the arrival of a nerve impulse and, by diffusing across the synapse or junction, effects the transfer of the impulse to another nerve fibre, a muscle fibre, or some other structure.
Explain what EPSP is?
An excitatory postsynaptic potential (EPSP) is the change in membrane voltage of a postsynaptic cell following the influx of positively charged ions into a cell (typically Na+) as a result of the activation of ligand-sensitive channel.
Explain the process of an action potential in a nerve cell?
- Sodium ions will diffuse into the neuron when channels are open (due to channel opening stimulus) and if the membrane potential reaches a threshold level all voltage gated sodium channels will open resulting in the upstroke and depolarisation.
- When depolarisation reaches a critical level the potassium channels will open resulting in repolarisation and the downstroke.
- The undershoot is due to delayed closure of voltage-activated K+ channels
Describe the refractory period and what absolute vs relative means?
Refractory period refers to the period in which it is impossible to generate another AP (as sodium voltage gated channels inactivate quickly after opening).
Absolute refractory period refers to when the channels are inactive so no AP can be generated
Relative refers to when there is a mixed population of active and inactive channels so need a stronger than normal stimulus
The nerve cell membrane is leaky and ___________
passive signals don’t spread far from their site of origin due to current loss across the membrane accompanied by a reduced change in potential
Describe what rm and ri refer to in terms of passive conduction?
rm = membrane resistance (higher resistance means less leakiness) ri = axial resistance (lower resistance means better flow of current)
What is the length constant?
denotated as lamda, distance current can travel before the current diminishes to zero
A __1___ rm
A ___2__ ri
will equal a good length constant
1) high
2) low
Passive conduction is a factor in the propagation of the ___1_____ the longer the length constant, the further ___2__ which increases ____3_____
1) the action potential
2) the local current spread
3) the AP conduction
Describe 2 strategies to increase local current spread and therefore AP velocity?
Decrease ri by increasing the axon diameter (as a smaller diameter means increased pressure so increased resistance)
Increase rm by adding insulating material myelin
Conduction in myelinated axons is much _____ than in non myelinated axons
faster
In the PNS ___1___ Schwan cells provide myelin for __2___ axon
In the CNS __3___ oligodendrocyte supplies myelin to __4___ axons
1) many
2) one
3) one
4) many
Explain saltatory conduction and why it helps increase speed of AP?
Propogation of action potentials along myelinated axons from 1 node of ranvier to the next. Voltage activated sodium channels are located in clusters at these nodes and the AP jumps from 1 node to the next instead of travelling the whole length.
What is a node of ranvier?
a gap in the myelin sheath of a nerve, between adjacent Schwann cells
Describe pre and post synaptic membranes?
Pre synaptic membranes have active zones around which vesicles cluster
Post synaptic membranes have neurotransmitter receptors
3 types of synapses?
Axodendritic (axon synapses onto dendrite)
Axosomatic (axon synapses onto cell body)
Axoaxonic (axon synapses onto an axon)
Two functions of synapses?
Excitatory
Inhibitory
The excitatory neurotransmitter in the CNS is often __1___
The inhibitory neurotransmitter in the CNS is often ___2___
1) Glutamate
2) GABA
In excitatory synapses the neurotransmitter typically causes ____
sodium to enter the cell making it more positive so more likely to cross threshold
In inhibitory synapses the neurotransmitter typically causes ______
influx of chloride which hyper polarises the cell making it less likely to reach threshold
What are the two categories of neurotransmitter receptors?
ionotropic
metabotropic
Explain what ionotropic receptors are?
These receptors form an ion channel pore, the receptor is an integral component of the molecule that forms the ion channel it controls, the gating of the channel is rapid
e.g. fast EPSP in activation of nicotinic receptors
Explain what metabotropic receptors are?
These receptors are indirectly linked with ion channels on the plasma membrane of the cell through signal transduction mechanisms often G proteins, gating of the channel is slower (10ms)
e.g. slow EPSP in activation of muscarinic receptors
Hair cells contain __1____ and ___2______ Deflection of the stereocilia ___3____ the kinocilium leads to ___4___ as the tilt opens ____5___ This results in release of neurotransmitter ___6_____ which _______7___
1) stereocilia
2) kinocilium
3) towards
4) depolarisation
5) channels for K+ and Ca2+ to enter the cells
6) glutamate
7) activates nerve fibres
Why does sound need amplified in the middle ear?
The vibration is going to be converted from air to fluid in the inner ear, fluid is denser so for the vibration to be maintained it needs to be amplified.
Explain 3 things that allows the middle ear to amplify sound?
20: 1 ratio of the tympanic membrane to the oval window
Force generation of the lever action of the ossicles
Force generation by movement of the tympanic membrane
The cochlea is made up of 3 coiled tubular canals which are? What do they contain?
The scala vestibuli and scala tympani contain perilymph
The scala media contains endolymph
At the base of the scala vestibuli is the ______1_______ and at the base of the scala tympani is the ______2______
The scala media lies between and the boundary between it and the scala tympani is called the ____3______
1) oval window
2) round window
3) basilar membrane
On top of the basilar membrane sits the ____
organ of corti where the hair cells are situated
Where are the hair cells of the cochlea situated?
in the organ of corti which is on top of the basilar membrane
The width of the basilar membrane __1___ as you get closer to the round window. High frequency sounds displace at the ___2__ and low frequency sounds at the___3______
1) decreases
2) base
3) apex (near the helicotrema)
think low frequency has less energy so doesn’t travel as far
What are the 2 types of hair cell in the ear? What are they separated by? Which ones are more frequent?
Inner (less frequent)
Outer (more frequent)
Separated by rods of corti
Describe the main role of the outer hair cells?
Amplify membrane vibration
They primarily receive efferent inputs
What hair cells primarily receive efferent signals?
Outer hair cells
Describe the main role of the inner hair cells?
Transduce the sound energy into a nervous signal
They’re primarily involved in afferent signals
What hair cells are primarily involved in afferent signals?
Inner hair cells
Semicircular canals detect __1___
The otolith organs detect ___2__
1) angular motion (where your head is in space)
2) linear acceleration and gravity
Describe the semicircular canals and what plane each detects motion?
3 canals in each ear
anterior (sagittal plane)
posterior (coronal plane)
lateral (axial plane)
Each canal contains a bulge along the canal called an ______ which contains ______
ampulla
crista
Crista is __________
the sheet of cells where the hair cells are clustered, the cilia project into the gelatinous cupola
In the canals the kinocilia are all oriented in the same direction so _______
they are all excited or inhibited together
In the canals movement causes fluid to circulate and displace ________
Movement in one direction causes _______ and in another ______
cupola which will move hair cells
increased firing
decreased firing
The posterior canal shares a plane with the __1______ and the horizontal canals __2______
1) contralateral anterior canal
2) share a plane
What are the two otolith organs and what do they do?
Saccule - detects movement in the vertical/ sagittal plane
Utricle- detects movement in the horizontal plane
In the otolith organs hair cells lie in the _____ and the ______ divides the hair cells into 2 populations with opposing polarities
macula
striola
What are otoconia?
Crystals of calcium carbonate which help couple mechanic forces to the sensory hair cells in the utricle and saccule
The somatosensory system has different types of receptors distributed ________
throughout the body
The somatosensory system mediates the sensory modalities of _______
fine discriminatory touch [light touch, pressure, vibration, flutter and stretch (mechanosensation)]
joint and muscle position sense (proprioception)
temperature (thermosensation)
pain (nociception)
itch (pruriception)
Somatosensory pathways most often comprise of a ________ chain
3 neurone
Give a brief overview of the 3 neurone chain in the somatosensory pathway?
1st order neuron is pseudo unipolar and cell body is located in the PNS
2nd order neuron is located in the dorsal horn of the spinal cord or in the brainstem and is multipolar
The 3rd order neuron is located in thalamic nuclei and is multipolar
From here the impulse goes to the somatosensory cortex
Name 5 properties of sensory units?
Modality Threshold Adaption Rate Conduction Velocity Site and extent of peripheral termination
In the somatosensory system what does threshold relate to?
relates to the intensity of a stimulus required to excite a sensory unit
Describe what low threshold units are and give some examples?
Low threshold units: respond to low intensity (non-damaging) stimuli
Low threshold mechanoreceptors (LTMs): mediate fine discriminatory touch
Low threshold thermoreceptors: mediate cold through to hot
Describe what high threshold units are and give some examples?
High threshold (HT) units (nociceptors): respond to high (noxious, potentially damaging), but not (normally) low, intensity stimuli
High threshold mechanoreceptors (HTMs) (mechanical nociceptors) respond to high intensity mechanical stimuli
Thermal nociceptors respond to extreme degrees of heat (>45°C), or cold < 10-15°C)
Chemical nociceptors respond to substances in tissue [e.g. as in inflammation: prostaglandins, bradykinin, serotonin (5-HT), histamine, K+, H+ and ATP and many others]
Describe what adaption means when referring to sensory units?
is a feature of sensory units that determines whether they change their firing rate only in response to a stimulus of changing intensity, or fire continuously throughout a constant stimulus
Explain the difference between fast adapting and slow adapting units?
Slow acting: units that discharge action potentials at a constant or very gradually reducing frequency throughout the period of a suprathreshold stimulus. These produce a tonic or static response.
Fast acting: action potentials are discharged initially, but then the unit becomes become ‘silent’ despite the stimulus persisting and they are classed as fast adapting (FA), or at the extreme, very fast adapting (very FA) units
What is conduction velocity?
Conduction velocity is simply the rate at which an action potential is conducted along an axon and for any particular axon is constant.
What would increase conduction velocity?
thickest myelin and widest axon diameter
What are the four groups of axons?
Which is fastest conduction velocity? Which is slowest?
A alpha (group 1) fastest A beta (group 2) A delta (group 3) C (group 4) slowest
What type of sensory receptors are group 1/ a alpha?
Proprioreceptors of skeletal muscle
What type of sensory receptors are group 2/ a beta?
mechanoreceptors of the skin
What type of sensory receptors are group 3/ a delta?
pain and temperature
What type of sensory receptors are group 4/ C?
temperature pain and itch
The peripheral terminal of cutaneous afferent fibres branch into many fine processes the tips of which can be
_______________ or ________________
free nerve endings (partially naked)
associated with specialized structures
Receptive field (RF) is the ________1_________
RF size varies greatly over the body surface and is ________2_____________
Sensory acuity (‘fineness of discrimination’) correlates _____3________
1) target territory from which a sensory unit can be excited
2) inversely related to innervation density (ie if innervation density is very large then receptive field will be small because nerves close by will pick it up instead)
3) inversely with RF size (as RF size decrease sensory acuity increases, if you have smaller fields you can more easily pick up where the stimulation is)
Explain what two point discrimination is?
Two point discrimination is a simple measure of spatial acuity and somatosensory function. The basic idea is to present two stimuli as separate points and to ask the subject if he, or she, perceives the stimuli as just one point, or is able to tell the difference between them and respond that two points are being applied. This is repeated with the points separated by varying distances upon the skin. This allows a minimum distance, or threshold, for two point discrimination to be determined. Two point discrimination varies massively over the body surface.
Give seven examples of types of sensory receptors in the skin?
Free nerve endings Meissners corpuscles Merkels discs Pacinian corpuscles Krause end bulbs Hair end organs Ruffini endings
