vestibular system, spinal reflexes and breathing Flashcards
1
Q
what are the 3 main contributors to orientation?
A
- vision (visual space)
- vestibular system (inertial space)
- proprioception (internal space)
2
Q
what does orientation mean?
A
ones position, direction and spatial relationship with the environment influenced by many sensory inputs and cognitive mechanisms
3
Q
how does the visual system contribute to orientation?
A
- provides info about surrounding environment
- give visual cues, and helps individuals determine position, heading and spatial relationship
- very good at detecting motion (optic flow)
4
Q
visual systems problems with detecting motion
A
- motion aftereffect - prolonged exposure to moving stimulus and then period of rest can course motion in a stationary object
- visual illusions - misinterpretations on motion and speed e.g., section when a train starts moving
5
Q
how does the vestibular system contribute to orientation?
A
- located in inner ear
- changes in head position
- balance, spatial orientation and motion
- balance when standing and head tilting
- coordinates eye movements when head rotates
6
Q
how does the proprioceptive system contribute to orientation?
A
- ones own body position and movement through sensory receptor feedback
- awareness of limb position, muscle tension and position of body parts
7
Q
what are the rogans of balance in the vestibular system?
A
- otolith organs
- semicircular canals
8
Q
otolith organs
A
- sense linear acceleration and affects of gravity
- perception of head position
- utricle and saccule containing small calcium carbonate crystals that responds to head movements and linear acceleration
9
Q
semicircular canals
A
- perpendicular to each other
- detect rotational movements of head in any direction
- info about changes in angular acceleration
- 3 of them
- anterior, posterior and lateral
- orientated in different planes to detect head rotation
10
Q
what do cilia hair cells do?
A
- what the otoliths and canals contain
- movement causes deflection on hairs
- motion towards stereocilium depolarises receptor and increases firing rate of afferent
11
Q
what is rotation and acceleration signalled by
A
- difference in firing rate between the different vestibular system in each ear
- when you move your head it will cause an increase of firing rate on one side and decrease on other
-different calculates how fast you are moving - in disease = if you lose info from one side of head quickly it is nauseating
12
Q
what is the structure of the utricle and saccule?
A
- contain endolymph
- receptors in macula
- respond to acceleration and gravity
- main role is postural stabilisation
13
Q
utricle in more detail
A
- within membranous labyrinth
- calcium crystals called otoliths embedded
- horizontal = sensitive to linear acceleration changes in horizontal plane
- stereocilia present
14
Q
utricle function
A
- head undergoes linear acceleration
- otoliths move causing its membrane to deform
- this stimulates hair cells
- signals transmitted to brain via vestibular nerve
- provides info about heads orientation
15
Q
saccule in more detail
A
- located in membranous labyrinth
- contains otoliths
- membrane positioned vertically
- stereocilia present
- senses linear acceleration on vertical plane
16
Q
saccule function
A
- head will undergo linear acceleration
- exactly the same just on the vertical plane
17
Q
what is the oticonia
A
- like a brick
- if head rotates the oticonia deflects hair cells due to gravity
- acceleration and tilt do exactly the same
18
Q
how do you differentiate between acceleration and tilt signals?
A
- different movement profiles
- canals tell you when tilting head you also get a rotation signal
19
Q
what is a somato-gravic illusion?
A
- illusion in aircraft
- high high acceleration
- people end up crashing into sea as soon as they take off as incorrect perception of pointing into sky, so pitch down but actually just crash
(false climb) - continuous and high acceleration = otolith organs have continuous tilt
20
Q
anatomy of the semicircular canals
A
- column of fluid
- swollen section at one end of canal = ampulla
- cupula = stretched across walls of Canal forming a seal
- rotate canal fluid will stay
- hair cells embedded in cupola = signal in rotation
- only responds to rotation
21
Q
cupula in more detail
A
- same density as surrounding endolymph fluid (neutrally buoyant)
- does not response to changes in orientation
22
Q
what happens to the cupolas buoyancy when drunk?
A
- becomes lighter so rises when lying down
- produces a left-beating nystagmus when lying on left ear
- after heavy water ingestion cupula becomes heavy so sinks when lying down producing a right beating nystagmus when lying on left ear
23
Q
what is caloric vestibular stimulation
A
- method of modulating firing rate of primary vestibular afferents by irrigation of ear canal with warm or cold water
24
Q
how does caloric vestibular stimulation work?
A
- irrigates external ear with cold or warm water using device to circulate water in to ear canal
- changes of temp in inner ear will induce nystagmus
- assesses VOR by observing induced nystagmus - eyes move in direction opposite to temp change
- important for diagnosing disorders within vestibular system
25
Q
what is galvanic vestibular stimulation?
A
- non-invasive methods for altering vestibular nerve activity
- cathode - increase afferent firing rate and on other side you decrease
- measure perceived rotation (maximal effect when head is tilted up or down)
- signals head roll towards cathode
- can also evoke torsional eye movements as modulating firing rate activates VOR
- also evokes balance response
26
Q
what are spinal reflexes
A
- automatic response to a change in the environment
- they are coordinated, involuntary motor responses initiated by a stimulus applied to peripheral receptors
- some reflexes are complex involving supra-spinal components
- highly modifiable by input from brain
27
Q
what is the stretch reflex - sensorimotor loop
A
- evoked by tendon tap
- abolished by cutting dorsal roots
not just a mechanical response but relies on sensory afferent feedback
28
Q
what is the stretch reflex - muscle spindle
A
- spindles detect changes in muscle length during contraction
- stretch evokes increase in spindle firing rate = signal sent to dorsal horn by afferent neurons
- alpha motor neurons activated in spinal ventral horn = contraction on agonist and synergist muscles
29
Q
what does a muscle spindle consist of?
A
- bundle of thin muscle fibres (intrafusal) containing capsule
- situated in parallel with main extrafusal muscle fibres but generates no force
- wrapped round pair of sensory axons
- y motor neurons cause active contraction of spindle
- detects position and velocity
30
Q
what are intrafusal fibres
A
- innervated by y-motor neurons
- both types respond to stretch
31
Q
what are the two main types of intrfausal fibres?
A
- nuclear bag fibres
- nuclear chain fibres
32
Q
nuclear bag fibres
A
- innervated by type Ia afferents, annulospiral endings
- Ia fibres repsond to velocity
- larger due to nuclei being bunched together
33
Q
nuclear chain fibres
A
- innervated by type Ia and II afferents, flower spray endings
- Ia responds to velocity
- have nuclei in series
34
Q
monosynaptic loop
A
- you can infer how many neurons are involved in a reflex by its latency
- faster response = fewer neurons and synapses
35
Q
what is the earliest onset response
A
- less than 1ms after stimulus. speed consistent with only 2 neurons (monosynaptic)
- disynaptic when antagonists inhibited for more than 1ms and speed is consistent with 3 neurons
36
Q
what is reciprocal inhibition?
A
- simultaneous contraction of muscles on one side of a joint and relaxation of muscles on opposing side
- facilitates smooth and coordinated movement around joint
37
Q
how does reciprocal inhibition work?
A
- muscles round joint work in antagonistic pairs
- NS controls muscle contractions through motor neurons. the activation of motor neurons to muscles on one side of joint is accompanied with inhibition of them on other side
- part of the reflex arc. this stretch reflex works by sensory neuron detecting stretch in muscle and sends signals to spinal cord. spinal cord activates motor neurons to contracting muscle and inhibit opposing ones
- mediated by Ia inhibitory interneurons
38
Q
what is a co-contraction?
A
- when we want to activate agonists and antagonists at the same time
- this means reciprocal inhibition is modulated by descending inputs from brain
39
Q
what is Klippel-Feil syndrome of the stretch reflex
A
- rare condition where premotor neurons from cortex bifurcate to innervate both sides of body
- moving one hand leads to mirror movements from other side
40
Q
explain hyperreflexia (spasticity)
A
- descending input fro brain normally regulates reflex gain in spinal cord
- spin al cord injury, stroke and other conditions can abolish the input
- results in increase in reflex gain
41
Q
what is the purpose of a stretch reflex?
A
- maintain muscle tone
- prevent overstretching
- control and coordination of voluntary movements
42
Q
feedback loop stretch reflex
A
- operates in negative feedback loop
- prevents major disturbances to the regulation of muscle length
43
Q
what is servo-assistance
A
- maintain accuracy of movement
- voluntary commands from motor cortex drive the reflex and corrects small deviations from desired trajectory
- a disturbance could be an unpredictable increase in load muscle spindles can detect.
44
Q
what is the Hoffman reflex?
A
- activation of type Ia sensory nerves
- causes muscle contraction via monosynaptic spinal reflex recorded by EMG
- sensory type Ia fibres activated at lower stimulation thresholds versus motor fibres due to their greater diameter axons
- high stimulation intensities, motor axons are activated abolishing the H-reflex due to antidromic signals
45
Q
how can the H-reflex’s amplitude be altered?
A
- conditioning its stimulus
46
Q
what is the flexion withdrawal reflex?
A
- a painful sensory stimulus activates ipsilateral flexor muscles whilst extensors are inhibited
- contralateral extensors are simultaneously activated
- causes extension in contralateral limb to compensate for unloading in ipsilateral limb
47
Q
how do u reverse the Golgi tendon organ reflex
A
- GTO input inhibits ongoing muscle activity via negative feedback at rest
- locomotion - GTO increases extensor muscle activity to produce positive feedback
- helps tov produce sufficient force during stance phase of locomotion
- caused by descending control motor commands
- GTO reflex contributes to transition between stance and swing (positive during stance and negative during swing)
48
Q
pulmonary stretch receptors
A
- cough and lung inflation reflexes mediated by these
- rapidly adapting receptors lie between airway epithelial cells and trigger cough reflex
- slowly adapting receptors lie within airway smooth muscle cells and trigger long inflation reflex
49
Q
what is the cough reflex work?
A
- an airway defence mechanisms against aspiration
- irritant receptors trigger the cough felx
- first order afferent travels to NTS of medulla
- second order afferent travels to respiratory central pattern generators in brainstem
- effects are activated
50
Q
3 phases of a cough
A
- inspiratory = deep inspiration with glottis open. diagram, external intercostals
- compression = expiratory muscles contract against closed glottis, generating large subglottic pressures. trunk and upper airway
- expiratory = glottis opens causing rapid ejection of airflow
51
Q
what does the respiratory control system regulate?
A
- blood-gas tensions and acid-base balance (alveolar ventilation)
- speech and breath-holding
- airway defence (cough, swallow)
52
Q
what is the basic elements of the respiratory control system
A
- sensors (chemoreceptors, lung and others) input»
- central controller (pons, medulla, other brain parts) output»_space;
- effectors (respiratory muscles
53
Q
what is the primary regulated variable?
A
arterial CO2 pressure (PaCO2)
54
Q
what is the CO2 mass balance equation explaining how the respiratory control system operates
A
PaCO2 = R . T . VCO2 / Va
55
Q
what type of loop is PaCO2 regulation?
A
- feedback is closed-loop negative chemofeedback
- feedforward is PaCO2 regulation by commands that translate goals, targets and info about disturbances, independent of chemoreception
56
Q
what is adaptive control of PaCO2 regulation
A
- by long-lasting modifications to the control system
- occurs at multiple levels of respiratory control
57
Q
respiratory neuroplasticity
A
- a persistent change in neural control system based on experience
- change in neural control behavi0our is essential to ensure PaCO2 homeostasis in face of recurrent or enduring perturbations
58
Q
what are ponto-medullary control pattern generators?
A
- neural circuits in the CNS that generate rhythmic patterns of motor activity without need for continuous sensory input
- circuits are involved in generation of rhythmic behaviours e.g., walking, swimming, or flying
- CPGs are found in various regions of the nervous system like the spinal cord, brainstem and other subcortical structures.
59
Q
what is the pre=botzinger complex?
A
- recordings directly from thin sections of medulla demonstrate presence of pacemaker cells known as this
60
Q
ventral respiratory group
A
- split into rental (rVRG) snd caudal (cVRG) aspects
- rVRG = inspiratory
- cVRG = expiratory
61
Q
dorsal respiratory group
A
small collection of inspiratory premotor neurons located in caudal NTS
62
Q
pontine respiratory group
A
- contains KF nucleus and PB nucleus
- inhibit inspiration and prolong expiration
- responsbile for hering-bruer long inflation reflex
63
Q
list the inspiratory pump muscles
A
- sternocleidomastoids
- scalenes
- external intercostals
- diaphragm
64
Q
list the expiratory pump muscles
A
- internal intercostals
- external obliques
- rectus abdominis
- transverse abdominis
- internal obliques
65
Q
voluntary breathing vs automatic
A
- breathing is not automatic. it is somatic process with automatic behaviour
- phrenic motor herons receive input from primary motor cortex and from brainstem
- direct inputs from cortex allow voluntary control of breathing and direct inputs from brainstem allow automatic control of breathing
- relay from cortex to brainstem allows cortex to override automatic breathing
66
Q
what voluntary behaviours can override automatic breathing?
A
- speech, swallow
- singing
- sniffing
- coughing
- spirometry tests
- breath-holding
67
Q
what are the central chemoreceptors (PCO2 sensors) in breathing
A
- located in ventral surface of medulla = retrotrapezoid muscles
- H+ doesn’t cross blood-brain-barrier (BBB) - CO2 diffuses through into cerebral spinal fluid
- CO2 binds with H2O forming carbonic acid
- carbonic acid dissociates into bicarbonate and H+
- changes in css CO2?pH activates central chemoreceptors
68
Q
what about the peripheral chemoreceptors (Po2 sensors)
A
- low PaO2 detected by receptors on glomus cells
- K+ channels close
- cell depolarised opening CA2+ channels
- enters cells causing release of ATP and ACh
- afferent neuron is activated
- activated respiratory control centres to increase breathing
69
Q
central and peripheral chemoreceptor interdependence
A
- do not work independently
- isolate carotid body from systemic and cerebral circulation
- CB stimulation = increased controller gain
- CB inhibition = decreased controller gain
