Physiology Flashcards
What is the main role of dendrites in the neuron?
- Receive inputs from other neurones
- Give graded electrical signals to the soma
What is the main role of the cell body/soma of a neuron?
- Contains nucleus, ribosomes, mitochondria and endoplasmic reticulum (ER)
- Integrates incoming electrical signals that are passed to the axon hillock
What is the main role of the axon hillock/ initial segment?
site of initiation of the ‘all or none’ Action Potential (AP)
as all info has been integrated together by this point
What is the function of the axon?
- conducts output signals as APs to the presynaptic terminal.
What type of signal generates a positive change in membrane potential that could generate an AP?
Excitatory/ depolarixing stimulus
What type of signal prevents an AP from being generated?
Inhibitory stimulus (causes membrane to hyperpolarize - aka get more negative)
How are neurons classified based on neurite number?
Unipolar (one neurite)
Pseudounipolar (one neurite that immediately bifurcates)
Bipolar (two neurites)
Multipolar (multiple neurites)
Give an example of each type of neuron classified by neurite number
Unipolar = peripheral autonomic neuron Pseudounipolar = dorsal root ganglion neuron Bipolar = retina Multipolar = lower motor neuron
What are the 4 functional regions of neurons?
Input - what stimulates them (i.e. another neuron?)
Integrative - where all info is integrated (cell body)
Conductile - where integrated info is transmitted (axon)
Output - where nerve ending acts upon (secretions/ muscle/ other neuron)
What ion is responsible for the upstroke and downstroke in an action potential?
Upstroke = Na+ influx Downstroke = K+ efflux
these do NOT happen in sync, hence the up and down strokes
What is a projection neuron and how does this compare to an interneurone?
Projection = from one region of brain to another (e.g. cortex -> thalamus
Interneurone = found in particular areas of brain, integrate info and change it to suit this part of brain before it is passed to projection neuron
Why does the downstroke occur when the membrane potential reaches +40mV?
This is the equilibrium point of Na+
Why is there a brief period of undershoot where the membrane hyperpolarises, before it returns to a stable resting potential?
The membrane permeability to Na and K is constantly changing and therefore hasn’t quite settled by the time the downstroke reaches resting membrane potential
Why do passive signals at the peripheral terminal of the neuron not spread far from their site of origin?
They are not as strong as an AP therefore will diminish
ALSO - neurons are leaky and current is lost across the membrane
What factors within a neuron can be altered to promote faster conduction?
Increased membrane resistance (less leakage)
Decreased axial resistance of the axoplasm (current comes across no obstacles inside neuron)
How can membrane resistance be increased?
Myelinate axons
What is meant by Saltatory Conduction?
action potential ‘jumps’ from one node of Ranvier to the next for faster conduction
What conditions cause demyelination?
multiple sclerosis (CNS) Guillian-Barré syndrome (PNS
Briefly explain how APs cause release of neurotransmitter at a synapse
- Depolarization by AP
- Ca2+ influx
- Ca2+- induced release of transmitter (exocytosis from vesicles)
- Receptor activation on post synaptic membrane
How is neurotransmitter removed from the synaptic cleft before the next AP?
- Enzyme inactivation of transmitter
- Reuptake of transmitter into presynaptic neuron
Drugs which block enzymes from inactivating neurotransmitter in the synaptic cleft are used in what conditions?
Alzheimers
Where can an axon from the pre-synaptic neurone meet the post-synaptic neurone?
Dendrite (Axodendritic) VERY COMMON
Soma (Axosomatic) COMMON
Axon (Axoaxonic) UNCOMMON
What neurotransmitter is commonly released in the CNS by an excitatory signal?
Glutamate
What effect does glutamate have on post-synaptic receptors?
Activates ionotropic receptors Allows cations (+ve Na+, K+, Ca2+) into neuron
What neurotransmitter is released in the CNS in response to an inhibitory signal?
Gamma-aminobutyric acid (GABA)
OR Glycine
What is the difference between spatial and temporal summation of action potentials?
Spatial summation = Many presynaptic neurones release neurotransmitter to create one AP
Temporal summation = single neuron may release all the neurotransmitter for one AP
What are the main groups of substances used as neurotransmitters?
Amino acids (e.g. glutamate)
Amines (DopAMINE)
Peptides (cholecystokinin)
What is the difference in speed of transmission in Ligand Gated Ion Channel receptors and G-Protein coupled receptors?
Ionotropic ligand-gated ion channels mediate FAST neurotransmission
G-Protein Coupled Receptors mediate slow neurotransmission
Describe the structure of ionotropic LGIC receptors vs that of metabotropic receptors
Ionotropic receptor for neurotransmitter is ITSELF a CHANNEL
Metabotropic receptors bind neurotransmitter and then signal to other G Proteins etc to open a channel to let ions in
If glutamate has both ionotropic and metabotropic receptors on the post-synaptic membrane, what kind of respons does this create?
A fast and slow EPSP are generated from each of the channels respectively
What types of ionotropic receptors can Glutamate bind to and activate an ion channel?
AMPA
Kainic Acid
collectively non-NMDA
NMDA
How do the responses of each ionotropic glutamate receptor differ?
AMPA - large but transient AP
NMDA - smaller and slower AP
What sensations are picked up by the somatosensory system?
- Fine discriminatory touch [light touch, pressure, vibration, stretch]
- Joint and muscle position sense (proprioception)
- Temperature (thermosensation)
- Pain (nociception)
- Itch (pruriception)
What are the 3 divisions of the somatosensory system classified by where the sensation comes from?
Exteroceptive division (cutaneous senses => skin)
Proprioceptive division (muscle, tendons and joints)
Enteroceptive division (viscera and autonomic function)
How may neurons are usually found in series in a somatosensory pathway?
3
What parts of the 1st order sensory neuron are known collectively as a SENSORY UNIT?
Receptor, cell body and axon
Where are the 1st, 2nd and 3rd order neurones normally found?
1st = dorsal root ganglia /cranial ganglia 2nd = dorsal horn of spinal cord/ brainstem nuclei 3rd = thalamus
Describe how sensory stimulation at the peripheral terminal of the 1st order neuron creates an AP
- Stimulus (mechanical, thermal, or chemical)
- Opens cation channels
- Depolarizes receptor potential
- If over threshold triggers AP
- AP frequency goes up if membrane is depolarized more
Explain what is meant by the Adaptation rate of sensory units
Does the unit APs fire continuously or does it respond preferentially to a changing stimulus?
E.g. When going from brightly lit area to dim room, eyes take a while to adapt due to stimulus change
What is the stimulus of fine touch and what sensory unit does it act upon?
Stimulus: mechanical force on skin
Sensory unit: skin mechanoreceptors
What stimulates proprioception and what snesory unit does it act upon?
Stimulus: Mechanical forces acting on joint and muscles
Sensory Unit: Joint/ Muscle Mechanoreceptors
What sensory units detect changes in temperature?
Thermoreceptors
What are the potential stimuli that can induce pain in nociceptors?
Strong mechanical force on skin/viscera
Heat on skin, mucous membranes, viscera
What stimulates sensation of an itch at pruriceptors?
irritant (e.g. chemical) on skin or mucous membranes
What type of threshold unit responds to non-damaging stimuli?
Low threshold units
- fine discriminatory touch
- cold -> hot temperatures
What type of threshold unit responds to noxious and potentially damaging stimuli?
High threshold units
nociceptors, mechanoreceptors, thermal nociceptors and chemical nociceptors
Describe AP conduction in a Slowly adapting (SA) or tonic/static response
Continuous APs to CNS for entire length of stimulus
Describe AP conduction in a Fast adapting (FA) or phasic/dynamic response
- Detects changes in stimulus strength
- Number of impulses increases when rate of change of stimulus increases
Describe AP conduction in a Very fast adapting (very FA) or very phasic/dynamic response
- Responds only to very fast movement, such as rapid vibration
- One AP generated at beginning of mechanical stimulus
Which types of axon have the highest and lowest conduction velocities?
A-Alpha = highest (80-120ms-1)
**due to high axon diameter and myelin sheath
C = Lowest (0.5-2.0ms-1)
** due to no myelination and small axon diameter
What is a receptive field?
target territory from which ONE sensory unit can be excited
Areas of skin with small receptive fields have high acuity. TRUE/FALSE?
TRUE
skin on the fingertips = small receptive fields due to high innervation density
Where are pacinian corpuscles found and what sensation do they mediate?
FOUND: Dermis or subcutaneous fat
SENSATION: Vibration (mediated by capsule around nerve ending)
What do Ruffini nerve endings mediate?
Strong mechanical pain
What sensation do Meissner’s corpuscles mediate and where are they found?
FOUND: Dermo-epidermal junction
SENSATION: touch (contributes to texture)
Merkel disks consist of a sensory axon and a merkel cell. What are the functions of these?
Sensitive to light touch
Merkel cells make neurotransmitter for sensory nerve terminal
Where are Krause end bulbs found and what do they mediate?
FOUND: border of dry skin and mucous membranes
SENSATION: touch
What sesnation can the root hair plexus detect?
Movement of hair in a particular direction
How can low threshold mechanoreceptors be classified?
Slow or Fast adapting? (SA or FA)
Small or large receptive field? (1 or 2)
=> SA1 or FA2 is a “physiological subclass” of an A-alpha receptor
Low threshold mechanoreceptors comprise of a receptor and what else?
A “Parent fibre type”
e.g. A-alpha, A-beta etc
Encapsulated nerve ending mechanoreceptors (e.g. meissners corpuscles, pacinian corpuscles, ruffini endings) have what parent fibre type?
Aβ
What Low threshold mechanoreceptors are associated with Aβ fibres?
- Follicular nerve endings
- Merkel cell-neurite complexes
- Encapsulated nerve endings
What parent fibres are associated with free nerve endings?
Aδ, or C
=> thin or no myelination
=> SLOW
Describe the difference in receptive field for pacinian corspuscles and meissner’s corspuscles
- Pacinian corpuscles = Large RF
- There is an area of MAX. sensitivity
- BUT corpuscle responds when the stimulus is strong enough anywhere within RF
- Meissner’s corpuscle = Small RF
What frequencies are pacinian and meissner’s corspuscles most likely to pick up?
Pacinian = 200Hz Meissners = 50Hz
Meissner’s corpuscles need the vibration to be indented further into the skin than pacinian corpuscles before becoming activated. TRUE/FALSE?
TRUE
If a single dorsal root is cut, why does the corresponding dermatome not lose all sensation?
- degree of overlap with the region of adjacent dorsal roots
- Therefore if T4 dorsal root was damaged, there would still be sensation in T4. To lose ALL sensation T4,5,6 would need to be damaged
What virus lies latent until reactivated in a dermatomal distribution?
Shingles
Lies in dorsal root ganglia until reactivated
Describe the changes in grey and white matter as you move up the spinal cord, and why this change is required?
More white matter and less grey matter as you move up from sacral -> cervical.
This is due to more afferent fibres joining further up and more white matter is needed to carry all these axons
How is the grey matter in the ventral and dorsal horns of the spinal cord divided?
Divided into 10 laminae of Rexed
What laminae are found in the dorsal horn and what afferent signals terminate here?
I and II most posterior in dorsal horn
- nociceptors found here
III to VI found in anterior of dorsal horn
- Low threshold mechanoceptors found here
VII to IX in ventral horn
- Proprioceptors found here
Using the Dorsal Column/Medial leminiscus tract and the Spinothalamic tract, explain what symptoms a patient with Brown-Sequard syndrome would experience if there was hemisection of the spinal cord.
Dorsal Column/ML Tract = touch, vibration
=> This would be lost on the ipsilateral side of the hemisection, as sensory input doesnt cross until brainstem
Spinothalamic Tract = Pain, temp
=> This would be lost on the contralateral side to the hemisection, as the sensory fibres cross segmentally in this tract
What are the two sections of the dorsal column called and what levels do they extend to/from in the spinal cord?
Gracile = Medial section
- extends whole way up spinal cord
Cuneate = Lateral section
- extends from T6 upwards (to deal with info from upper limbs)
What can the dorsal column/medial leminiscus pathway be used for?
- Stereognosis – recognise an object by feeling it
- Vibration
- Fine touch (two point discrimination)
- Conscious proprioception – awareness of body position and movements
- Weight discrimination
What is lateral inhibition and why/where does it occur?
- Active neurone inhibits the activity of its neighbours via stimulating inhibitory interneurons lateral to it
- This sharpens stimulus perception (eliminates background noise)
- This happens in synapses of the DCML pathway
The DCML pathway does not exist for sensory information from the anterior head. What picks up this information instead?
Trigeminal divisions which feedback to the trigeminal ganglion and different nuclei in the brainstem
Where is the primary somatosensory cortex located?
- Post central gyrus of the parietal cortex
immediately posterior to the central sulcus (SI) - Adjacent to the posterior parietal cortex (SII)
What areas are found in the Primary somatosenspry cortex
Brodmann areas (BA) 1, 2, 3a and 3b
What areas of the primary somatosensory cortex receive most info from the thalamus?
Areas 3a and b receive around 70%
What sensations do each of the Brodmann areas deal with?
3a - proprioception
3b - Touch (texture, shape, size)
1 - Texture (as this receives input from 3b)
2 - Pressure and Joint position, distinguishing objects
Describe the organisation of the body parts in the primary somatosensory cortex
The toes are at the top of the post central gyrus with the tongue at the lower end, but the hand separates the head from the face
Describe the organisation of the columns in the sensory cortex
alternating columns of cells with rapidly adapting and slowly adapting sensory responses
Are each of the Brodmann areas using the same somatotopic map?
Yes - Adjacent strips of cortex have the same parts of the body in parallel to each other
BUT - maps are not identical, they are mirror images of each other
An area of cortex responsible for a part of the body that has been amputated or damaged will be taken over by other parts of the body. TRUE/FALSE?
TRUE
areas next to it controlling other parts of the body will extend into the area
What happens if the sensory input from a particular area of the body increases?
- cortical space for that digit increases
relative to other inputs generating less activity
Describe a condition where cortical remapping can become an issue
Phantom limb pain
If a limb is amputated and other parts of the body take over that area of cortex, a pain stimulation in these areas can cause the brain to feel it as pain from the non-existent limb
What is the job of the posterior parietal cortex?
Receives and integrates information from SI and other cortical areas
- (visual, auditory)
- sub-cortical areas (thalamus)
What condition can arise due to damage of the posterior parietal cortex?
Neglect syndrome
- If damage is on RHS of posterior parietal cortex, then patients fail to acknowledge the left side of the world exists.
- No vision problems, Patients just disclaim the existence of things, including their own left leg!
The somatic motor system is responsible for what type of skeletal muscle movement?
Voluntary movement
And involuntary spinal reflexes
What two neurons make up the somatic motor system?
- upper motor neurones (UMNs) within the brain and
- lower motor neurones (LMNs) within the brainstem and ventral horn of the spinal cord
What is the main function of upper motor neurons (UMNs) in relations to lower motor neurons (LMNs)?
upper motor neurones (UMNs) modulate the activity of Lower motor neurons (LMNs)
LMNs receive input from UMNs and what other places?
proprioceptors and interneurons
LMNs command the ‘final common pathway’. What is the function of this?
To cause muscle contraction
What two types of muscle fibres are found in LMNs? One supplies the bulk of the muscle whilst the other supplies the muscle spindle.
alpha (α) motor neurones (α-MNs) - supply muscle bulk
Gamma (γ) motor neurones (γ-MNs) - supply spindle
What is meant by “synergistic muscles” such as biceps brachii and brachioradialis?
They both aim to complete the same movement (i.e. arm flexion)
What name is given to muscles which oppose each others action?
Antagonist
e.g. tricep is an antagonist of biceps brachii
What is the difference between axial and distal muscles?
Axial muscles control movements of the trunk (posture)
Distal muscles move the hands, feet and digits (allowing fine manipulation of objects by the hand)
Why are the ventral horns of the spinal cord larger at the cervical and lumbar enlargements?
More alpha motor neurons are found here for relay of motor info to the upper and lower limbs
What is encompassed in a motor unit?
α-MN and all of the skeletal muscle fibres that it innervates
What name is given to all of the alpha motor neurons innervating one muscle?
motor neurone pool
What does each AP cause in a muscle fibre?
A muscle twitch
Summation of twitches causes a sustained contraction
Describe the somatotopic map of the ventral horn of the spinal cord?
Axial muscles = medial
Distal muscles = lateral
Flexor muscles = more dorsal in the ventral horn
Extensor muscles = anterior of ventral horn
What 3 neurons can input to an alpha-motor neuron?
- dorsal root ganglion cells
- Upper Motor Neurons
- Spinal interneurones
Muscle force is dependent on what factors?
- Firing rates of the LMNs
- No. of LMNs that are all active (=> more motor units contributing)
- Co-ordination of the movement (agonist versus antagonist)
- Muscle fibre size (hypertrophy)
- Fibre Phenotype (fast/slow)
If the AP frequency is low, why does no prolonged contraction occur?
Enough time is given for the muscle to relax
“relaxation phase” involves calcium reuptake into the sarcoplasmic reticulum (SR) and the reversal of troponin cross-bridges
Give an example of muscles in the body which require small motor units to carry out their function
extraocular eye muscles as fine movements are required
Give an example of muscles in the body requiring large motor units to carry out their function?
large postural (antigravity) muscles e.g. leg muscles
Motor units only contain fibres of one type i.e. fast or slow. TRUE/FALSE?
TRUE
slow and fast twitch fibres are interspersed throughout a full muscle but are specific in each individual motor unit
Each muscle fibre is innervated by a single motor axon at endplate (neuromuscular junction). Where along the fibre are these found?
midway along the fibre, usually in the centre
Why are muscle fibres divided into slow and fast twitch types?
They differ in how quickly myosin ATPase splits ATP
to provide energy for cross bridges
What are the main types of slow and fast twitch muscle fibres?
Slow-oxidative (Type I)
Fast (Type IIa,IIb,IIx)
What makes a muscle fibre Slow Type I?
- Get ATP oxidative phosphorylation
- Slow contraction and relaxation
- Fatigue resistant.
- Red fibres as high myoglobin content.
What is the difference between Fast Twitch Type II muscle fibres?
IIa - ATP from oxidative phosphorylation
- Fast contraction and relaxation
- resistant to fatigue
- well vascularised => relatively red in colour
IIb,IIx - ATP from glycolysis
- fast contraction
- NOT fatigue resistant
- white in colour
What is the Henneman size principle?
Smaller α-MNs (part of slow motor units) have a lower threshold => are recruited FIRST
THEN larger ones are recruited
=> LMNs are recruited in an order appropriate to the physical task that is being performed
Describe the recruitment of LMNs from standing to running
Standing - Slow Type I
Walking - Fast Type IIa
Run - Fast Type IIx (IIb doesnt exist in many mammals including humans)
Describe the Myotatic reflex
When a muscle is stretched, it pulls back
e.g. knee jerk response from quads
What structure is responsible for the myotatic reflex?
Muscle spindle (sensory organ)
This is stretched with the muscle as it is parallel to the fibres
What is found inside the fibrous capsule of the muscle spindle?
- intrafusal muscle fibres
- sensory afferents (very fast conducting)
Describe how the myotatic reflex is initiated?
- Stretch of muscle spindle
- Activation of Ia afferent (these are like Aα sensory fibres)
- Excitatory synaptic transmission in spinal cord
- Activate α-MN back to muscle
- Contraction of muscle
What manoeuvre can be attempted if a spinal reflex is deemed to be absent?
Jendrassik manoeuvre
- patient interlocks fingers and tries to pull hands apart strongly when instructed
- reflex is usually exaggerated
What spinal levels are tested in the biceps, supinator, triceps, knee and ankle jerks?
Biceps C5/6 Supinator C5/6 Triceps C7 Knee L3/4 Ankle S1
Why are α- and γ-MNs normally co-activated
to make the intrafusal muscle fibres in the muscle spindle contract in parallel with the extrafusal fibres?
To prevent the intrafusal muscle spindle fibres getting slack and not firing any APs
What different named fibres are found in the muscle spindle?
Nuclear bag fibres:
- Bag 1 or dynamic
- Bag 2 or static
Chain fibres
What sensory afferents wrap around the intrafusal fibres in the muscle spindle?
Ia afferents
- wind around the centre of all intrafusal fibres.
II fibres
- wrap around endings on all intrafusal fibres except the bag 1 dynamic type
When are dynamic and static muscle fibres activated respectively?
Dynamic - γ-MNs are active when muscle length changes rapidly and unpredictably
Static - active when muscle length changes slowly and predictably only static γ-MNs
Where are golgi tendon organs found and what are they involved in?
Found at junction of muscle and tendon
Involved in Inverse Myotatic Reflex
Golgi tendon organs lie in series with muscle fibres rather than in parallel. TRUE/FALSE?
TRUE
What is the function of the golgi tendon organs and the inverse myotatic reflex?
- regulate muscle tension => protect muscle from overload
Describe the neurone pathway in the reverse myotatic reflex?
- Group Ib afferents (not Ia like in normal myotatic)
- enter spinal cord
- synapse upon INHIBITORY interneurones
- these synapse upon the alpha motor neurones of the muscle to prevent contraction
What types of nerve endings contribute to proprioception, and where are they found?
free nerve endings (in capsule and CT) Golgi-type endings (found only in ligaments) Paciniform endings (found in periosteum) Ruffini endings (found mainly in joint capsule)
A loss of proprioception leads to what type of movement?
Vision guided movement
i.e. must look at limb before moving it OR must focus on an object in the distance to sit/stand without falling over
What is meant by reciprocal inhibition?
The antagonist of a muscle must relax for the other to perform its function.
i.e. for the biceps to contract and flex the arm, the triceps must relax
Excitatory interneurons mediate the flexor reflex and the crossed extensor reflex. Explain how these occur if a patient were to stand on a damaging stimulus, such as a drawing pin?
- Sensory afferents detect damage by pin
- Neuron sent back to spinal cord which diverges into 4 pathways
- 1 excitatory pathway to flexor muscle and 1 inhibitory pathway to extensor muscle on AFFECTED side
- 1 excitatory pathway to extensor muscle and inhibitory to flexor on OPPOSITE side (this is to provide stability whilst affected leg flexes upwards)
What ion causes depolarisation to occur in the hair cells of the ear?
K+ influx from endolymph
Explain how the hair cells cause sensory afferent signals to be produced?
Cilia move towards kinocilum K+ channels open due to tip link Hair cell depolarises Ca2+ channels open Vesicles of glutamate released to synapse with sensory afferent neuron
More APs are generated when cilia move towards the kinocilum. TRUE/FALSE?
TRUE
What are the ganglia of scarpa and where are they located?
Located in vestibular nerve just after CN VIII splits
- contain cell bodies of sensory neurons
Explain how sound is produced and how we hear it
- object (e.g. vocal cords) vibrate
- air pressure changes
- air vibrates in 3 dimensions towards ear
- Causes eardrum, incus, malleus and stapes to vibrate
- Stapes footplate vibration causes fluid in cochlea to move over hair cells
=> transduction
What properties of the middle ear make it useful at amplifying sound?
Area ratio of tympanic membrane to stapes footplate = 20:1 => decreasing area over which the noise is exerted increases the pressure of the noise
Lever action of the ossicles (malleus higher than incus)
=> increases pressure of noise
Buckling of ear drum - middle is attached to malleus therefore moves less and preserves force
What membrane separates the scala vestibuli and media?
Reissner’s membrane
What membrane separates Scala Media and tympani?
Basilar membrane
Which of scala vestibuli, media and tympani regress at the apex of the cochlea?
Media no longer exists
=> fluid in scala vestbibuli and tympani mix
What is meant by the tonotopy of the basilar membrane?
particular spatial arrangement of frequencies detected
The basilar membrane vibrates within the fluid of the cochlea. TRUE/FALSE?
TRUE
- it is flexible and therefore can move with the fluid
- It is widest and floppiest at the apex
Do we have more inner or outer hair cells?
OUTER
15000-20000 compared to 3500 inner
What is the role of the tectorial membrane?
vibrates and brushes against hair cells, making them move and release neurotransmitter
What ganglion is located near the organ of corti, containing sensory neuron cell bodies?
Spiral ganglion
Why must potassium be redistributed into the endolymph?
Causes problems such as deafness otherwise
=> mutations in any genes coding for K channels or transporters have the potential to cause deafness
How do the outer hair cells amplify sound?
- Have motor proteins on their sides which get compressed and change the length of the overall hair cell
- this moves the basilar membrane more, and the inner cell moves with this membrane
- inner hair cell then fires more sensory afferent transduction signals
Describe the pathway from the cochlea to the primary auditory cortex
Cochlea -> cochlear nucleii -> superior olivary nuclei -> nucleus of lateral leminiscus -> Inferior colliculus -> Medial geniculate nucleus -> primary auditory cortex
Which nuclei in the brainstem is important for the localisation of sound in space, and how does it do this?
Superior Olivary Nuclei
- senses time at which sound reaches each ear => intra-aural time difference
What is the Calyx of Held?
Large nerve terminal ending with lots of vesicle active zones ready to discharge upon signal
- they usually react to High frequency sounds
What 2 questions does the vestibular system function to answer?
1) Where am i going?
2) Which way is up?
What do the semicircular canals sense?
Head angular acceleration (rotation)
What do the utricle and saccule detect?
Head linear acceleration
saccule = vertical movement
utricle = horizontal movement
Which of the semicircular canals share a plane?
Left anterior and Right posterior (and vice versa)
Both horizontal are also in the same plane
What is the otoconia?
CaCO3 bio-crystals which help mechanical forces to reach the sensory hair cells in the utricle and saccule
What are the 3 vestibular reflexes and what do they do?
Vestibulo-ocular - moves eyes in opposite direction of head moving so that vision remains still.
Vestibulo-colic - keeps head on level playing field when you walk
Vestibular-spinal - adjusts posture when rapidly changing position
No input is needed from the motor cortex to rhythmically coordinate walking. TRUE/FALSE?
TRUE
Neuronal circuits causing flexion/extension of the legs can control this at spinal level
Describe the 3 levels of motor control
Strategy – aim of the movement? How can it best be achieved?
Tactics – what sequence of muscle contractions and relaxations will fulfil the strategic aim?
Execution – activation of neurons which command the desired movement
What areas of the brain are involved in producing a “strategy” for movement?
Neocortical association area and Basal Ganglia
What areas of the brain are responsible for the “tactics” of a motor movement?
Motor cortex
Cerebellum
What parts of the CNS cause execution of the planned movement?
Brain stem
Spinal cord
What Brodmann areas make up the motor cortex in the pre-central gyrus?
Brodmann areas 4+6
Name the two LATERAL descending motor tracts and their shared function
Lateral Corticospinal Tract + Rubrospinal Tract
Function:
- voluntary control of distal musculature
- particularly discrete, skilled, movements
- involved in fractionated movement (lots of different muscles making different movements at the same time)
There are various ventromedial pathways which descend the brainstem. Name some examples and their main function.
Ventral Corticospinal
Tectospinal
Recticulospinal
Vestibulospinal
Function:
control of posture and locomotion
The ventromedial pathways are under cerebral cortex control. TRUE/FALSE?
FALSE
The lateral pathways are under cerebral cortex control, whereas the ventromedial pathways are under brainstem control
Where in the corticospinal tract does decussation of fibres occur?
Medullary pyramids
Where do axons of the corticospinal tract terminate in the ventral horn of the spinal cord, and what muscles does this associate them with?
Terminate in dorsolateral region of the ventral horn
=> associated with distal muscles, particularly flexors
Where are cell bodies of the rubrospinal tract located, and where does this nucleus receive input from?
Red nucleus
- receives input from the motor cortex and the cerebellum
Where do fibres from the rubrospinal ract decussate?
decussate at the ventral tegmental decussation
What muscles does the rubrospinal tract control?
Exerts control over limb flexor muscle
If there is damage to only the Corticospinal tract, then the rubrospinal tract has the potential to compensate for the damage. TRUE/FALSE?
TRUE
If both lateral tracts are damaged, explain the characteristics of patients movement?
Less fractionated
=> all muscles are trying to do same thing at same time
=> movement is larger and less accurate
=> also slower
What are the two nuclei of the vestibulospinal tract?
Medial (goes to cervical region) and lateral ( goes to lumbar region)
What is the function of signals descending via the lateral vestibular nucleus?
- helps to hold upright and balance posture
- causes extension in antigravity muscles espeiclaly in lower limb
What is the function of the medial vestibular nucleus
- activate cervical spinal circuits (neck muscles etc)
=> guiding head movements
Where are cell bodies of the tectospinal tract found?
superior colliculus
Where does the superior colliculus receive input from?
- retina
- visual cortex
- sensory and auditory afferents
=> e.g. helps to guide eyes to new important visual stimulus
Where do axons of the tectospinal tract decussate?
Decussate in the dorsal tegmental decussation and descend close to the midline
What are the two parts of the reticulospinal tract and where do they arise from?
Pontine (Medial) and Medullary (Lateral)
- arise from the reticular formation (diffuse mesh of neurones at the core of the brainstem)
What are the functions of the Medial/Pontine Reticulospinal tract?
- enhances antigravity reflexes of the spinal cord
- maintain standing posture by helping contract extensor muscles in the lower limbs
What are the functions of the Lateral/Medullary Reticulospinal tract?
- opposes the action of the medial tract
- releases antigravity muscles from reflex control
Both of the reticulospinal tracts descend bilaterally. TRUE/FALSE?
FALSE
Medial/Pontine descends IPSILATERALLY
Lateral/Medullary decends BILATERALLY
What are the three main types of pain?
- nociceptive pain (immediate protective response, short-lived)
- inflammatory pain (assists in healing, persists over days, possibly weeks)
- pathological pain (no physiological purpose, persists over months -> years)
Describe the difference in sensation of cutaneous, muscular and visceral pain
Skin = Well localised, pricking/stabbing Muscle = Poorly localised, aching, tender, cramp, Viscera = Poorly localised (referred to a somatic structure), dull, vague, associated with nausea
What potential stimuli can activate nociceptors?
thermal, mechanical, chemical
Nociceptors are 1st order neurons. TRUE/FALSE?
TRUE
Relay info to second order neurons in CNS
What type of nerve fibres are nociceptors?
Aδ and C fibres
Explain the difference in pain response from Aδ and C fibres
Aδ = respond to noxious mechanical and thermal stimuli
NOT CHEMICAL. Mediate ‘first’, or fast, pain
C fibres = respond to all noxious stimuli (e.g. they are polymodal). Mediate ‘second’, or slow pain as they wait for inflammatory mediators to activate them.
Describe the difference in sensation between first “fast” pain from Aδ fibres and slow pain from C fibres.
First “fast” pain = stabbing, pricking sensations
Second “slow” pain = burning, throbbing, cramping, aching sensations
What receptors can pick up noxious thermal stimuli?
members of the transient receptor potential (TRP) family: => TRPA1, TRPC3 and TRPV1
**TRPV1 also active at normal body temp, but when inflammation is present
What receptors do noxious chemical stimuli activate?
H+ = Acid Sensing Ion Channels (ASICs) ATP = P2X and P2Y receptors Bradykinin = B2 receptors
What temperatures activate Aδ Type I fibres?
Aδ Type I = 53 degrees
whereas Aδ Type II/ or C = 43 degrees
What do efferent signals to nociceptor nerve endings cause?
Release of pro-inflammatory mediators
- calcitonin gene-related peptide (CGRP)
- substance P
These contribute to neurogenic inflammation
What can noxious stimulation cause in the long term?
- Increases spinal excitability
- More efferent signals causing pro-inflammatory mediators at peripheral nerve terminal
=> can cause hyperalgesia (amplified pain)
and allodynia (pain without a noxious input)
Explain the synaptic connection between the 1st and 2nd order neuron in nociception.
- AP opens voltage-gated Ca2+ channels
- Ca2+ influx
- Glutamate release from vesicles
- Activation of glutamate receptors
- Membrane depolarization (e.p.s.p.) (Mg2+ moves out of way in NDMA receptors)
- Opening of voltage-gated Na+ channels
- New AP
Where in the dorsal horn of the spinal cord do Aδ and C fibres terminate?
Laminae of Rexed I and II
Laminae I contains Nociceptive specific (NS) cells which synapse only with C- and Aδ-fibres
- then go on to interact with WDR neuron
What other type of nerve fibre (aside from Aδ and C) terminates in the laminae of rexed and has input to the Wide dynamic range (WDR) neuron?
Aβ
Where does visceral pain come from?
Coverings of organs - e.g. pleura/peritoneum
When these are stretched/twisted/ischaemic = PAIN
NO PAIN if cut/burnt
What nerve pathways are followed by visceral afferents from nociceptors before entering the dorsal horn of the spinal cord?
Follows sympathetic pathways
What is viscerosomatic pain and how does it present?
- sharp and well localised pain
- occurs when inflammatory exudate from diseased organ contacts body wall structure
- May present with diffuse visceral pain that progresses to sharp viscerosomatic pain (e.g. appendicitis)
Pain evoked by activity in nociceptors (C- and Aδ- fibres) can be reduced by activity in Aβ-fibres. TRUE/FALSE?
TRUE - this details the “Gate Control Theory”
patients often find that focussing on low threshold activity involveing Aβ fibres distracts them from the pain
What is the “Gate Control Theory”?
Firing of Aβ> Aδ and C fibres = GATE CLOSED
Firing of Aβ< Aδ and C fibres = GATE OPEN
if the gate is CLOSED then no 2nd order nociceptive signals fire to the brain
How do Aβ fibres cause no projection from the 2nd order neuron?
They excite an inhibitory interneurone, which then inhibits the projection of any signal
