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
What sensation do free nerve endings in the skin convey?
pain, heat, cold
What sensation do merkels disks in the skin convey?
touch
What sensation do krause end bulbs in the skin convey?
touch
What sensation do root hair plexus in the skin convey?
touch
What sensation do Meissners corpuscles in the skin convey?
touch
What sensation to Pacinian corpuscles in the skin convey?
pressure
What sensation do Ruffini endings in the skin convey?
pressure
Meissner’s corpuscles are abundant in skin locations where ________________
two point discrimination is highest, not present in hairy skin
Merkel’s discs are abundant in skin locations where ___________
two point discrimination is highest, ARE present in hairy skin
Krause end bulbs are found _____________
at the border of dry skin and mucous membranes
Pacinian corpuscles are found __________
within dermis and fascia
Ruffini endings are found ____________
within dermis and also joint capsules
Describe the basic cellular structure of the retina?
Most posteriorly is the photoreceptors there is then bipolar cells and then ganglion cells which convey impulses to the optic nerve There is also horizontal and amacrine cells
Describe the direction of signal vs direction of light in the retina?
The light actually goes through the ganglion cells first but the direction of signal is from the photoreceptors up to the ganglion cells
Photoreceptors and bi-polar cells do not ______________
generate APs but generate graded potentials
_______ is released onto ganglion cells which respond by producing APs which will convey to the visual cortex
glutamate
Describe the role of horizontal and amacrine cells?
They exert influence in a horizontal manner causing lateral inhibition (neurons excitation can inhibit neuron excitation next to it). This helps the brain perceive visual contrast and localise images.
Each ganglion cell responds to changes in light intensity over a limited area of the retina which is called?
the receptive field of the cell
What does the receptive field of a ganglion cell correspond to?
the group of photoreceptors that has synaptic connections with that particular ganglion cell
Explain what on and off centre ganglion cells are?
Ganglion cells are usually spontaneously active.
Approximately half of the ganglion cells in the retina respond with decreased firing of their impulses when the periphery of their receptive field is stimulated by light and increase their firing when the centre of the receptive field is lit up. This is the ON centre cells.
The other half increase their firing rate when the periphery is illuminated and decrease their firing rate when the central receptors are stimulated. This is the OFF centre.
What does the on and off centre ganglion cells allow?
Allows the output of the retina to signal the relative brightness and darkness of each area being stimulated within the visual field
What are ganglion cells further subdivided into after on and off?
P and M cells
Describe P ganglion cells?
These receive the central parts of their receptive fields from 1 sometimes 2 types of colour specific cone. P cells are good at detecting colour form and selection
Describe M ganglion cells?
M cells receive from all 3 cones. They are good at detecting movement of images on the retina.
What is meant by the concept of the dark current?
Photoreceptors have a more positive RMP compared to other neurons. They are technically already depolarised and hyper polarise in the light. Sodium gated channels are open in the dark.
Describe the process of detecting light?
1) when a photon of light is absorbed by retinal it changes from cis-retinal to trans-retinal which causes a conformational change in the rhodopsin
2) this activates G protein transducer, which alpha subunit activates phosphodiesterase
3) phosphodiesterase hydrolyses cGMP from ligand gated sodium channels so these channels close and inward leakage of sodium ions stops
4) If there is a sufficient build up of sodium the membrane becomes hyper polarised and a nerve impulse is generated
Describe 5 differences between rods and cones?
RODS contains rhodopsin active in low light found in peripheries of retina greyscale high convergence system
CONES contains photopsin active in bright light found in centre of retina colour vision low convergence system
Cones have a ____1___ convergence system
Rods have a ___2_____ convergence system
1) low
2) high
What is meant by rods having a high convergence system? What are the benefits?
Many rods feed into one ganglion meaning objects aren’t seen as sharply but it allows better vision in the dark as greater activity is feeding into one ganglion
What is meant by cones having a low convergence system? What are the benefits?
Only a few cones to a single ganglion, this allows sharp vision, the receptor field of the ganglion cell is much smaller so things are seen in greater detail
Describe how cones allow us to see different colours and shades?
3 different opsin that detect long (red), middle (green) and short (blue) wavelengths
We see different shades due to wavelengths of light triggering multiple cones to different extents
Each lateral geniculate nucleus contains ___ cellular layers and the info from the 2 eyes _______
6
remains separate
In the lateral geniculate nucleus M ganglion cells terminate in the ___________
lower 2 layers called magnocellular layers
In the lateral geniculate nucleus P ganglion cells synapse in the ___________
upper 4 layers (2 for each eye) called the parvocellular layers
Each cortical cell in the primary visual cortex receives inputs from a limited number of cells in LGN and therefore _________
has its own receptive field or patch of retina to which it responds
The entire visual field is precisely mapped onto the primary visual cortex which is said to have _____1________
About half of the visual cortex is dedicated to Information from the ____2_____
1) visuotopic organisation
2) fovea
Describe what ocular dominance columns are?
stripes of neurons in the visual cortex that respond preferentially to inform from one eye or the other (it is thought eyes compete for these columns)
What is the major route for touch and conscious proprioception info to ascend to the cerebral cortex?
The Dorsal Column Medial Lemniscal System
In the DCML as information is conveyed from one neuron to the next in a sensory pathway, differences in the activity of ___1______
Lateral inhibition ____2______
1) its neighbours are amplified producing contrast enhancement
2) sharpens stimulus perception and is one mechanism by which info is transformed at the synapses of the DCML pathway
General somatic info from the anterior head is mediated by the ________
trigeminal system
Soma of the sensory neurons of the trigeminal system are located in the ____________
trigeminal sensory ganglion
Central terminals of the trigeminal nerve synapse upon second order neurons in ____1_______ or ____2_____ or ___3_____ which in turn ____4______
1) mesencephalic nucleus (proprioception from chewing)
2) Spinal trigeminal nucleus (pain and temperature)
3) Pontine trigeminal nucleus (discriminative touch and vibration)
4) decussate to the ventroposteriomedial nucleus of the thalamus
In the trigeminal system third order neurons ________
relay info to the cortex via thalamocortical neurons
The primary somatosensory cortex (SI) is located in ________
the post central gyrus
The SI has __1__ cell layers, thalamic input terminates mainly on neurons within layer __2__ which in turn project to cells towards the surface of the cortex and also deeper layers. Vertical columns of neurons extend across the six layers and each column consists of ____3____
1) 6
2) 4
3) neurons with similar inputs and responses
Remapping of the primary somatosensory cortex can ________
occur and is a continuous process moulded by life experiences
What is the role of the posterior parietal cortex (SII)?
This receives and integrates info from SI and other cortical areas (visual, auditory) and sub cortical areas (thalamus). Basically deciphers the deeper meaning of the info in SI.
The neural element of the somatic motor system comprises of __________________
upper motor neurons within the brain and lower motor neurons with soma within the brainstem and ventral horn of the spinal cord
As well as input from upper motor neurons, lower motor neurons also receive ___________
input from proprioceptors and interneurons, LMNs command muscle contraction and form the final common pathway
LMNs comprise of alpha motor neurons that ______1_______ and gamma motor neurons that _____2_________
1) innervate the bulk of fibres within a muscle that generate force
2) innervate a sensory organ within the muscle known as the muscle spindle
Axons of LMNs exit the spinal cord in ____1_____ each ventral root joins with ____2____ to form ___3____
1) ventral roots (or via cranial nerves)
2) a dorsal root
3) mixed spinal nerve
Motor neurons are not distributed equally in the spinal cord, a greater no. are found ____________
in the cervical enlargement (C3-T1) supplying the arm and the lumbar enlargement (L1-S3) supplying the leg.
LMNs innervating the arms and legs are mainly found in __1____ but those innervating axial musculature occur ___2_____
1) cervical and lumbar enlargements
2) at all levels
Define a motor unit?
One alpha motor neuron and all the skeletal muscle fibres that it innervates
Define a motor pool?
The collection of alpha motor neurons that innervate a single muscle
The number of fibres per motor unit depends on the functions served by the muscle, muscles which serve fine movement __________
e.g. external eye have fewer fibres per motor unit
Describe what causes a muscle twitch vs a sustained contraction?
A single action potential causes a muscle fibre to twitch, summation of twitches causes a sustained contraction as the number of incoming APs increases.
What are the three types of muscle fibres?
Slow oxidative/ type 1 fibres
Fast oxidative/ type 2a fibres
Fast glycolytic/ type 2x or 2b fibres
Describe slow oxidative/ type 1 fibres?
ATP is largely derived from oxidative phosphorylation, used for prolonged, relatively low work activities e.g. walking, posture. They are red in colour.
What type of muscle fibre is being described?
ATP is largely derived from oxidative phosphorylation, used for prolonged, relatively low work activities e.g. walking, posture. They are red in colour.
slow oxidative/ type 1 fibres
Describe fast oxidative/ type 2a muscle fibres?
uses aerobic and anaerobic metabolism for prolonged moderate work e.g. jogging
What type of muscle fibre is being described?
Uses aerobic and anaerobic metabolism for prolonged moderate work e.g. jogging
fast oxidative/ Type 2a
Describe fast glycolytic/ type 2x/ 2b muscle fibres?
ATP mainly derived from glycolysis, fast contraction but not fatigue resistant, white fibres.
What type of muscle fibre is being described?
ATP mainly derived from glycolysis, fast contraction but not fatigue resistant, white fibres.
fast glycolytic/ type 2x/ 2b
Motor units are recruited in order of ____1___ Activation in such an order allows for a ____2______
1) their size (small before large)
2) fine control of muscle force across a wide range of tensions
Purpose of the myotatic reflex?
Helps maintain muscle at constant length
In the myotatic reflex the change in length and rate of change of the muscle is registered by a sensory organ within the muscle called the ___________ which contributes to_____________
muscle spindle
non-conscious proprioception
Four things muscle spindles consist of?
A fibrous capsule
Intrafusal muscle fibres
Sensory afferents 1a that innervate the intrafusal fibres
Gamma motor neuron that innervates the intrafusal fibres
Describe the difference between intrafusal and extrafusal muscle fibres?
Intrafusal fibres are those found in muscle spindles
Extrafusal fibres are those that generate force
What do intrafusal fibres consist of?
a non-contractile equatorial region innervated by the Ia sensory neurones
contractile polar ends that receive efferent input from γ-MNs with cell bodies in the ventral horn of the spinal cord
Intrafusal fibres can be further subdivided on the basis of morphology and function into ___________
nuclear bag fibres (bag 1 and 2)
chain fibres
bag 1 are dynamic, bag 2 and chain fibres are static
Activation of gamma MNs along with alpha MNs during voluntary movement prevents _____1________ which allows _____2_________
1) the muscle spindle from slackening as the body of the muscle contracts
2) continued signalling by the spindle
Give a brief overview of the myotatic reflex arc?
1) stretch of muscle spindle
2) activation of 1a afferent
3) excitatory synaptic transmission in spinal cord (mediated by glutamate release)
4) activation of alpha motor neuron
5) contraction of homonymous muscle
What is the only monosynaptic reflex arc in humans?
myotatic reflex arc
In activities in which muscle length changes slowly and predictably only _____1_________
___2____ gamma motor neurons are active during behaviours which muscle length changes rapidly and unpredictably
1) static gamma motor neurons
2) dynamic
Purpose of the golgi tendon reflex/ inverse myotatic reflex?
This operates a protective feedback mechanism to control the tension of an active muscle by causing relaxation before the tendon tension becomes high enough to cause damage. It basically keeps muscle tension within the optimum range.
Where are golgi tendon organs located?
At the junction of muscle and tendon
What are golgi tendon organs innervated by?
group 1b sensory afferents
Describe the inverse myotatic reflex pathway
polysynaptic pathway in which an inhibitory interneuron is interposed between the 1b afferent and alpha motor neuron
Proprioceptive information arises from what 3 places?
muscle spindles
golgi tendon organs
joint receptors
What does reciprocal inhibition describe?
The process of muscles on one side of a joint relaxing to accommodate contraction on the other side of that joint
What are central pattern generators?
These are neuronal circuits that when activated can produce rhythmic motor patterns such as walking, breathing and swimming in the absence of sensory or descending inputs that carry specific timing information.
Describe what is at the top of the motor control hierarchy?
Strategy
What is the aim of the movement, how is this best achieved?
Involved is the neocortical association areas which processes sensory input and decides behaviour
The Basal ganglia is also involved
What is in the middle of the motor control hierarchy?
Tactics
What sequence of contractions and relaxations will allow the aim?
Involved is the motor cortex (this generates impulses that will be sent down descending tracts) and the cerebellum which coordinates movement so it is balanced and smooth.
What is at the bottom of the motor control hierarchy?
Execution
Activation of motor pools that command the desired movement
This is achieved by the brainstem and spinal cord
Descending tracts arise from the _________ and _________
cerebral cortex
brainstem
What are the 2 important types of descending tracts and what are the differences?
Lateral > under control from the cerebral cortex and important for voluntary movement > e.g. corticospinal and rubrospinal
Ventromedial > under control from the brainstem and important for control of posture > e.g. tectospinal, vestibulospinal, reticulospinal
What is the longest and one of the largest CNS tracts?
The corticospinal tract
Cell bodies from the corticospinal tract are located in ___________
the motor cortex and somatosensory areas of the parietal cortex
The rubrospinal tract is a minor pathway and is __________ than the corticospinal tract
phylogenetically older
Cell bodies for the rubrospinal tract are located in the ___1___ and receive inputs from the _____2____
1) red nucleus
2) motor cortex and cerebellum
Why is the rubrospinal tract considered an indirect pathway?
When compared to the corticospinal it is indirect because the cell bodies aren’t in the motor cortex but a red nucleus (so basically there is an extra step in the path!)
Describe what functions more corticospinal or rubrospinal and if compensation can take place?
In higher mammals the direct corticospinal tract has largely replaced the functions of the rubrospinal tract but clinical experiences suggest that the rubrospinal tract is capable of compensating for the corticospinal tract if damage occurs.
Cell bodies for the vestibulospinal tract are located in __1____ that receive input from _____2______
Axons from the lateral vestibular nucleus descend ipsilaterally as far as the ___3____ and involved in ___4_____
Axons from the medial vestibular nucleus descend as far as the ____5____ and involved in ___6____
1) vestibular nuclei
2) CNVIII from the vestibular labyrinths, cerebellar input is also important
3) lumbar spinal cord
4) holding posture
5) cervicospinal cord
6) activating cervical spinal circuits that control neck and back muscles, guiding head movement
Cell bodies for the tectospinal tract reside in the _____1___ which receives input from _____2______ It influences ______3______
1) superior colliculus (aka optic tectum)
2) the retina and also from the visual cortex and afferents conveying somatosensory and auditory information
3) the muscles of the neck, upper trunk and shoulders
The reticulospinal is split into two tracts
____1____ enhances antigravity reflexes of the spinal cord and helps maintain a standing posture by facilitating contraction of the extensors of the lower limbs
____2_______ opposes the action of the tract above and releases antigravity muscles from reflex control
1) Pontine/ Medial Tract
2) Medullary/ Lateral Tract
What are three classifications of pain?
nociceptive
inflammatory
pathological
Describe nociceptive pain?
This is adaptive, it is an immediate protective response that is short lived
Describe inflammatory pain?
This is adaptive, it is assists in healing, persists over days possibly weeks.
Describe pathological pain?
This is maladaptive, there is no physiological purpose, it persists over months, years or even a lifetime.
Nociceptors are specific peripheral primary sensory afferent neurons normally activated by ____1______ They are __2_ order neurons. Transduction begins in ___3____
1) intense stimuli that is noxious
2) 1st order
3) free nerve endings
Two types of nociceptor fibres?
A delta
or C fibres
Describe a delta fibre nociceptors?
These are mechanical or thermal nociceptors that are thinly myelinated. They respond to noxious or thermal stimuli and mediate first or fast pain ie. when you have just hurt yourself. Usually causes a stabbing or prickling sensation.
Describe C fibre nociceptors?
These are unmyelinated and collectively they respond to all noxious stimuli. They mediate second or slow pain. Gives burning, throbbing, cramping, aching sensation.
Give a brief overview of the nociceptive pathway?
Noxious stimulus is picked up by a free nerve ending
travels down axon of nociceptor which has its soma within a dorsal root ganglion
Synapses in the dorsal horn onto second order neurons and decussates
Second order neuron has axon that form the spinothalamic or spinoreticular tract which takes this signal to the brain to be processed
Inflammatory pain after an injury causes ___1___ and __2___ which discourages ___3___ promoting healing
1) hyperalgesia (heightened pain sensitivity to noxious stimuli)
2) allodynia (pain sensitivity to innocuous stimuli e.g. touching)
3) physical contact and movement with the affected part
What is the neurotransmitter between primary afferent and second order neurons in the nociceptive pathway?
Glutamate
Visceral pain originates from nociceptors ________1_________ and is _____2______
1) covering tissues (e.g. peritoneum or pleura) or walls of hollow organs
2) poorly localised and dull and achy
Visceral afferents from nociceptors follow _____1_____
Some visceral and skin afferents converge upon the same _______2_______ so all cells with a visceral receptive field also have a ___3_____
1) sympathetic pathways before entering the dorsal horn
2) spinothalamic neurons
3) separate cutaneous receptive field
Describe what happens in referred pain?
The brain interprets nociceptive info arising from viscera as originating from the area of skin that may be distant to that organ. It will match up with the cutaneous RF of that cell that supplies the viscera.
Unlike visceral pain, viscerosomatic pain is ___1_______ It occurs when ____2__________
1) sharp and well localised
2) inflammatory exudate from a diseased organ contacts a somatic structure e.g. in appendicitis dull pain progresses to sharp pain when the appendix irritates the parietal peritoneum
Describe why pain and nociception are not identical?
Pain is awareness of suffering, nociception may occur in the absence of pain and vice versa.
Describe the gate control theory of pain?
Asserts that non-painful input closes the nerve “gates” to painful input, which prevents pain sensation from travelling to the CNS. Basically non-painful sensations can override and reduce painful sensations.
What are the two major nociceptive tracts?
spinothalamic and spinoreticular tract
What type of nociceptors give information to the spinothalamic tract? What type of pain is it involved in?
From fast alpha delta fibres, important in pain perception, location and intensity.
What type of nociceptors give information to the spinoreticular tract? What type of pain is it involved in?
Largely transmits slow C fibre pain, makes extensive connections with the reticular nuclei in the brainstem and parabrachial nucleus, involved in automatic responses to pain, arousal, emotional responses, fear of pain.
Thermoreceptors can perceive differences as small as ____ in temperature
0.01 ‘C
Temperature sensitivity is ____________
not uniform across the body, hot sensitive and cold sensitive spots do exist
