Quiz 2 Flashcards
What are the fastest conducting afferent neurons
Proprioceptive afferent neurons
What do proprioceptive afferent neurons do
they take information that the motor system uses to perform rapid actions
What are among the slowest conducting afferent neurons
Nociceptive afferent neurons
The afferent Neuron: Somatosensory
What are mechanoreceptors in the somatosensory system
Specialized cells that project to an afferent neuron or are actually part of the afferent neuron itself
The afferent Neuron: Somatosensory
What affects how fast the afferent information reaches the CNS? (conduction speed)
- Amount of insulation (myelin)
- Diameter of axon
The afferent Neuron: Somatosensory
How does insulation impact conduction speed
The insulation prevents ions from leaking out of the axon and forces ions to move along the axon
(more insulation = faster)
A types are insulted
The afferent Neuron: Somatosensory
How does diameter impact conduction speed
larger diameter provides more room for ions to flow unobstructed along axon (larger = quicker)
(larger diameter = quicker)
Afferent fiber classification:
Classify Cutaneous mechanoreceptors
Group II (A - beta)
Afferent fiber clasification:
Classify Muscle spindles
2 types
Dynamic: Group Ia (A-alpha)
Static: Group II (A-beta)
Afferent fiber clasification:
Classify Golgi tendon organs (GTO)
Group 1b (A-alpha)
Afferent fiber clasification:
Classify Joint receptors
Group II (A-beta)
Afferent fiber clasification:
Classify Free Nerve endings
2 types
- Group III (A-delta)
- Group IV (C-fiber)
Afferent fiber clasification:
Rank Afferent fiber clasification from fastest to slowest
A-alpha -> A-beta -> A-delta -> C-fibres
Group Ia and Ib -> Group II -> Group III -> Group IV
The afferent Neuron: Somatosensory
Explain the afferent neuron
- receptors transform stimulus into AP
- afferent neuron = sensory neuron
- sensory neuron is pathway in PNS
- Synapse of sensory neuron and CNS is the pathway and processing in CNS
The afferent Neuron: Somatosensory
Afferent projections to CNS
(where do they project, where do they converge, what does this generate)
Afferent projections travel to specific grey matter regions in CNS that are specific for 1 sensory modality.
Sensory info from multiple modalities eventually converges in associated areas to generate unified percept of action
Where is somatosensory info
Parietal lobe
1st gyrus, very front
Where is auditory information
Temporal lobe
Where is visual information
Occipital lobe
what is used for action control
what cotex
Parietal cortex
What is used for perception
inferior temporal lobe
What is divergence
- Same input separates to multiple locations
- divides equally across all channels (like current)
- Most neurons will impact more than 1 neuron (divergence)
What is convergence
Multiple inputs project to a common location
What is topographic
ordered projection of a sensory surface (like retina or skin) within nuclei (neurons) in CNS
Found throughtout all levels of CNS
What is ipsilateral
Belonging to or occuring from the same side of the body
What is contralateral
Belonging to or occuring from the opposite side of the body
Peripheral and central pathways: Visual System
What are the 2 parallel pathways the optic nerve projects
- Geniculostriate Visual System
- Tectopulvinar Visual System
Peripheral and central pathways: Visual System
Describe the geniculostriate visual system (including pathway)
- 90 % of fibers
- Primary visual pathway
Retina -> Lateral geniculate (LGN) thalamic nucleus -> Primary visual (V1) cortex
Peripheral and central pathways: Visual System
Describe the tectopulvinar visual system (including pathway)
- 10% of fibres
- secondary visual pathway (vision for action)
Retina -> Superior Colliculus (midbrain) -> Pulvinar nucleus of thalamus
Superior Colliculus is involved in eye movement
Peripheral and central pathways: Visual System
When does the optic nerve become the optic tract and what happens here
After the optic chiasm
after which left side represents right visual field ad vice versa
Peripheral and central pathways: Visual System
What is on the fovea
The point of fixation (object directly in focus)
Peripheral and central pathways: Visual System
What is Retnotopic organization
- location of stimulus on retina is preserved with high affinity from retina to primary visual cortex (retinotopic maps)
- Retinotopic maps are still present in secondary visual cortex and association cortec, just more abstract
Peripheral and central pathways: Visual System
What is the visual field
Part of the visual environment that can be detected by both eyes
Peripheral and central pathways: Visual System
What is a hemifield
Left or right half of visual field
* Left hemifield = right thalamus/V1
* Right hemifield = left thalamus/V1
Both eyes capture most of the visual field
V1 is a mirror is visual environment
Upper visual field is represented in the inferior part of the cortex
Peripheral and central pathways: Visual System
What is monocular hemianopia
Complete loss of vision in one eye due to damage of the ipsilateral optic nerve
Peripheral and central pathways: Visual System
What is the optic tract (where does it bring info)
the bundle of nerves relaying visual information from optic chiasm to LGN thalamic Nucleus
Peripheral and central pathways: Visual System
What are the 2 visual cortical pathways
- Dorsal stream
- Ventral stream
Peripheral and central pathways: Visual System
Exlpain the dorsal stream
- Visual areas relate the visual environment (spatial locomotion, motion) to the body
- Vision for action (where, how)
- Parietal lobe
Peripheral and central pathways: Visual System
Exlpain the ventral stream
- Visual areas emphasize object recognition and classification
- Vision forperception (what)
- Temporal lobe
Peripheral and central pathways: Visual System
What is Prospagnosia
A disorder characterized by the inability to recognize faces
Peripheral and central pathways: Vestibular System
What nerve do the vestibular axons form and where do they project to?
They form the vestibular nerve (cranial nerve VIII) and directly project to:
* Ipsilateral vestibular nuclei
* Ipsilateral cerebellum
Cranial nerves do not run through spinal cord
Peripheral and central pathways: Vestibular System
describe ipsilateral vestibular nuclei (where are they located)
- Located in pons and medulla
- 4 nuclei that make up vestibular nuclear complex
Peripheral and central pathways: Vestibular System
What do vestibular nuclei do
Relay vestibular signals to cerebellum, cortex (via thalamus) and brain stem nuclei that send efferent signals to eye muscles
Peripheral and central pathways: Somatosensory
Describe somatosensory nerves
- Somatosensory nerves (except from head) enter spinal cord via dorsal horn
- Somatosensory nerves layer to form ascending pathways but also have many divergent projections in spinal cord
- Divergent projections facilitate reflexes and coordination among muscle groups
Nerves from head form trigeminal nerve (cranial nerve V which does not entre through spinal cord)
Peripheral and central pathways: Somatosensory
Where are motor neuron cell bodies
inside spinal cord on ventral side
Peripheral and central pathways: Somatosensory
Where are sensory neuron cell bodies
outside spinal cord on dorsal side (dorsal root ganglion)
Peripheral and central pathways: Somatosensory
What are the 3 pathways/tracts in the somatosensory system
- Posterior column
- Spinothalamic
- Spinocerebellar
Peripheral and central pathways: Somatosensory
What does the Posterior Column pathway convey
Crosses midline?
- Fine touch
- Vibration
- Proprioceptive afferent info
Does not cross midline in spinal cord (crosses in medulla)
Peripheral and central pathways: Somatosensory
What are the different neurons in Posterior Column
- Third order neuron
- Second order neuron
- first order neuron
Peripheral and central pathways: Somatosensory
What is a third order neuron
Posterior column
axon that projects from thalamic nucleus to primary somatosensory cotrex
Peripheral and central pathways: Somatosensory
What is a second order neuron
Posterior column
axon that crosses body midline in medulla and projects to thalamic nucleus
Peripheral and central pathways: Somatosensory
What is a first order neuron
Posterior column
Axon that projects from receptor to medulla
Peripheral and central pathways: Somatosensory
What is the spinothalamic pathway divided into
- Anterior spinothalamic tract
- Lateral spinothalamic tract
Collectively these are nociceptor axons
Peripheral and central pathways: Somatosensory
What does the spinothalamic pathway convey
crosses midline?
touch, temp and pain (includes nociceptor axons)
Crosses midline immediately after entering spinal cord
Peripheral and central pathways: Somatosensory
Explain the Anterior spinothalamic tract
- Anterior-medial part of spinothalamic path
- Conveys crude, poorly localized info about touch
Explain Lateral spinothalamic tract
- Lateral part
- Info about noxious stimuli and temp
Peripheral and central pathways: Somatosensory
What does the spinocereballar pathway convey
crosses midline?
proprioceptive info from limbs
Only ventral spinocerebellar tract crosses midline in spinal cord, others don’t at all
Peripheral and central pathways: Somatosensory
What can the spinocerebellar be divided into
- Dorsal spinocerebellar tract (DSCT)
- Rostral spinocerebellar tract (RSCT
- Ventral spinocerebellar tract (VSCT)
Peripheral and central pathways: Somatosensory
Explain the dorsal spinocerebellar tract
- projects into inferior peduncle of cerebellum
- proprioceptive info from lower limbs (spindle fibres via Ia afferent neurons)
Peripheral and central pathways: Somatosensory
Explain the rostral spinocerebellar tract
- projects into inferior peduncle of cerebellum
- proprioceptive info from upper limbs
Peripheral and central pathways: Somatosensory
Explain the ventral spinocerebellar tract
- projects into to superior peduncle of cerebellum
- proprioceptive info from lower limbs (GTO via Ib afferent neurons)
- Crosses midline in spinal cord
Peripheral and central pathways: Somatosensory
What is a peduncle
Thick stock/bundle of axons
Where do Ia afferent fibres originate from
Primary endings of muscle spindles, originate from 1 axon
Stimulus evoked responses and simple reflexes
What is stimulus evoked behaviour
Behaviour evoked as an automatic and relatively immediate consequence of sensory stimulus
Many are examples of relfexes
- Involuntary meaning compulsory/without will (not correct term)
- Automatice meaning occuring spontaniously/without conscious though/intention
Stimulus evoked responses and simple reflexes
What are the types of stimulus evoked responses
- Stimulus driven
- Stimulus released
Stimulus evoked responses and simple reflexes
What does stimulus driven mean
The stimulus defines the characteristics of the response
Stimulus evoked responses and simple reflexes
What does stimulus released mean
The characteristics of response can be independant of the stimulus characteristics
Stimulus evoked responses and simple reflexes
What is a reflex
a reflex is produced as a direct, automatic and relatively immediate response to stimulation of specific sensory inputs
Stimulus evoked responses and simple reflexes
How can we measure different elements of stimulus/response
- Behavioural measures of stimulus response process (timing, accuracy, stimulus-response characteristic, response modifiability)
- Electrophysiology assessment of stimulus response pathways (H-reflex, evoked potentials, brain hemodynamics, non-invasive brain stimulation)
Stimulus evoked responses and simple reflexes
What is the time within the nervous system comprised of:
- Conduction time
- Synapse time
Stimulus evoked responses and simple reflexes
What is conduction time
Time to conduct along axons of afferent (and efferent) pathways
Stimulus evoked responses and simple reflexes
What is synapse time
Time for info to be exchanged by neurons (processing time)
More synapses = more delay
Stimulus evoked responses and simple reflexes
What is response time
time between stimulus onset and movement outcome (reaction time + movement time)
ex. lights turn red -> brakes get pushed
aka response reaction time
Stimulus evoked responses and simple reflexes
What is reaction time
Time between stimulus onset and onset motor system response
ex. light turns red -> Movement of muscle starts
aka premotor time or latency
Stimulus evoked responses and simple reflexes
What is movement time
time between onset of motor system response and movement outcome
ex. movement of muscle starting -> brakes get pushed
Stimulus evoked responses and simple reflexes
What are factors that influence reaction time
- Task complexity/difficulty
- Stimulus-response compatability
- Stimulus modality
- Stimulus intensity and predictability
Stimulus evoked responses and simple reflexes
How does task complexity influence reaction time
* More response choices = longer reaction time (Hick’s law)
* Hicks law is prevalent in life
* Keep it simple stupid (KISS) principle is a manifestation of Hick’s law
Stimulus evoked responses and simple reflexes
How does stimulus-response compatibility influence reaction time
Reaction time is quicker the more straightforward it is to relate to the stimulus (on avg)
ex click left button when screen says left vs click right button when screen says left
Stimulus evoked responses and simple reflexes
How does stimulus modality influence reaction time
Stimulus modalities take different amounts of time to be identified and associated to appropriate responce
(process time, conduction time (aud vs tactile) and movement time (#of synapses) not same
Visual is slowest?
Stimulus evoked responses and simple reflexes
How does stimulus intensity and predictability influence reaction time
- the more intense the stimulus energy, the quicker the reaction time
- Knowing when a specific response will be required (predictability) leads to quicker response times (can preload responses)
Stimulus evoked responses and simple reflexes
What is a monosynaptic arc
Sensory neuron synapses directly with motor neuron
Stimulus evoked responses and simple reflexes
What is a disynaptic arc
sensory neuron acts on motor neuron via interneuron
2 synapses: sesory to inter and inter to motor
Stimulus evoked responses and simple reflexes
What is a polysynaptic arc
Pathway involving multiple interneurons between sensory and motor
Can include a mix of mono, di and polysynaptic arcs
Stimulus evoked responses and simple reflexes
What is an interneuron
Neuron that transmitts impulses between other neurons
Can transmit or modify the nature of the incoming signal
Stimulus evoked responses and simple reflexes
What is an inhibitory neuron
Neuron that, when excited, exerts a suppressive effect on next neuron
Monosynaptic or simple reflexes
What are extrafusal muscle fibers
muscle fibers responsible for generating contractile force (movement)
Monosynaptic or simple reflexes
What are intrafusal muscle fibers
specialized muscle fibres that detect muscle stretch (sense)
Monosynaptic or simple reflexes
Why do the afferent nerves of a monosynaptic reflexe diverge to act on many motor neurons?
Because there are substantially more extrafusal compared to intrafusal fibres in a muscle. Therefore, the afferent nerves diverge, innervating different extrafusal fibres when muscle is stretched
1 intrafusal innervates many extrafusal
Monosynaptic or simple reflexes
What does agonist, synergist and antagonist mucsles mean
- Agonist: Main muscle that is excited (sensory neuron originates here)
- Synergist: secondary excited muscle
- Antagonist: main muscle that is inhibited
Monosynaptic or simple reflexes
Which pathways are monosynaptic and which are disynaptic
agonist, synergist and antagonist
Monosynaptic: Agonist and synergist
Disynaptic: antagonist
Monosynaptic or simple reflexes
Describe Homonymous reflex pathway
which muscle pathway is homonynous?
Afferent exitation os sensory neuron acts to excite a motor neuron that projects to the same muscle from which the sensory neuron originated
agonist monosynaptic pathway is homonymous
Monosynaptic or simple reflexes
Describe heteronymous reflex pathway
Afferent excitation of sensory neuron acts to excite/inhibit motor neuron that projects to a different muscle
Synergist monosynaptic pathway and antagonist disynaptic pathway is heteronymous
Monosynaptic or simple reflexes
Describe alpha motor neurons
alpha motor neurons innervate extrafusal fibers to shorthen (increase AP) or lengthen (decrease AP) the fiber
Alpha motor neurons are sometimes just referred to as motor neurons
Monosynaptic or simple reflexes
Describe Gamma Motor neurons
Gamma motor neurons innervate special segments at each end of intrafusal fibers to keep them taught (stretch endings out) as muscle contracts
Monosynaptic or simple reflexes
- What is the system of gamma motor neurons and spindle fibers called?
- What is the effect of gamma motor neurons on spindle fibers called?
- Fusimotor system
- Fusimotor drive
Monosynaptic or simple reflexes
How is receptor potential generated
in context of motor neurons and spindle fibers
By stretching forces that pull ion channels open.
no receptor potential will occur if spindle fiber folds in on itself, even if muscle is lengthening, until after it becomes taught again (this is why gamma motor neurons are important)
Monosynaptic or simple reflexes
What is Alpha-gamma coactivation
coordinated action of alpha and gamma motor neurons during muscle contraction
Monosynaptic or simple reflexes
What is tonic or fusimotor bias
the increase in spindle fiber tension through coordinated action of alpha and gamma motor neurons
Monosynaptic or simple reflexes
How can the stimulus-response relationship of simple reflexes be modified
- Change in gamma motor activity (changes in spindle sensitivity; changing alpha-gamma relationship will alter taughtness [same stretch result in weaker afferent response])
- Inhibit reflex (decrease strength effect of sensory afferent motor neuron [gain])
- Facilitate reflex (increase gain at the sensory motor synapse)
What is the Hoffman (H-) reflex
a common neurophysiological tool to assess stimulus-response characteristics on the myotactic reflex pathway.
The H-reflex amplitude is sensitive to intensity of elec. stimulus
H-reflex vs. M-wave
H-reflex: motor response elicited by electrical stimulation of afferent sensory nerve
M-wave: motor response elicited by electrical stimulation of efferent motor nerve (skipping sensory nerve, therefore faster)
Waves will cancel each other out, as M gets bigger and bigger, H is cancelled
Simple reflexes
What is the Inverse myotatic reflex
strong excitation of Ib afferent (gamma motor) due to extreme muscle tension overrides alpha motor neuron excitation [less excitation] of muscles (via inhibitory interneuron)
aka Golgi tendon organ (GTO) reflex
simple reflexes
Is the inverse myotatic reflex always inhibitory?
No, it is state dependant.
* inhibitory when at rest
* facilitory when muscle is contracted
Simple reflexes
What is the withdrawal reflex
- a polysynaptic spinal reflex that requires ipsilateral and contralateral muscle coordination
- Ipsilateral contracts to withdraw, contralateral extends to stabalize/balance
- Nociceptor pathway (somatosensory)
- movement is faster than nociceptor so reflex will occur before perception of pain
Stimulus evoked behaviours: Eye movements
Describe foval vision/fovea
- Fovea is responsible for high-accuity (sharpness of vision)
- Portion of retina with highest desity of cones
- Foval vision is middle 5 degrees around point of fixation
- point of foval vision can be changed by moving eyes
Stimulus evoked behaviours: Eye movements
What is the visual axis
The straight line path from the light that is directed to fovea
Stimulus evoked behaviours: Eye movements
What is the optical axis
The straight line path through geometrical centre of lens
Stimulus evoked behaviours: Eye movements
What is direction of gaze
Direction of visual axis relative to environment
Stimulus evoked behaviours: Eye movements
What is gaze angle
Angular measurement of direction of gaze in horizontal or vertical plane
Stimulus evoked behaviours: Eye movements
What are eye movement effectors
Extraocular muscles that control horizontal, vertical and rotational movement of eyes
Stimulus evoked behaviours: Eye movements
What are the 3 cranial nerves that innervate eye movement effectors
- Abducens nerve (VI)
- Oculomotor nerve (III)
- Trochlear nerve (IV)
Stimulus evoked behaviours: Eye movements
Which muscles/effectors does the Abducens innervate
Lateral rectus muscle
Stimulus evoked behaviours: Eye movements
which muscles/effectors does the oculomotor nerve innervate
- Medial rectus
- superior rectus
- inferior rectus
- inferior oblique
Stimulus evoked behaviours: Eye movements
What are the 2 classifiactions of eye movement
- Conjugate (or version)
- Disconjugate (or vergence)
Stimulus evoked behaviours: Eye movements
What is conjugate/version eye movement
Coordintated eye movement in the same direction through the same angle
Stimulus evoked behaviours: Eye movements
What is disconjugate/vergence eye movement
Coordinated eye movement in the opposite direction through the mirrored angles
ex going cross-eyed. looking down towards nose
Stimulus evoked behaviours: Eye movements
What are the 5 classes of eye movement
- Vestibulo-ocular reflex (VOR)
- Optokinetic reflex
- Saccades
- Smooth pursuit
- Vergence
Stimulus evoked behaviours: Eye movements
What is Vestibulo-ocular reflex (VOR)
Stabalizes gaze in response to head rotation
Stimulus evoked behaviours: Eye movements
What is optokinetic reflex
Combination of slow and fast eye movements to keep a moving scene stationary on retina
Stimulus evoked behaviours: Eye movements
What are saccedes
Rapid ballistic eye movements of both eyes that change point of fixation
900 degrees/second, ~175 miles/hour
Stimulus evoked behaviours: Eye movements
What is smooth persuit
eye movements to keep eyes fixated on moving object
Stimulus evoked behaviours: Eye movements
What is vergence
Coordinated movement of both eyes to obtain or maintain binocular vision
Stimulus evoked behaviours: Eye movements
VOR (head moving with fixed vision example)
- eyes move in opposite direction of head, gaze is constant
- since eyes move with head, they counterrotate to cancel out rotation (rotate same amount in opposite direction)
- Hair cells in semicircular canals signal head movements
- One nucleus moves eye 1 in lateral direction and coordinates with another nucleus to move eye 2 in medial direction
ex: head turns left. therefore eyes move right. Agonist muscles are active/contracting (left medial rectus, right lateral rectus to move eyes to the right). Antagonist muscles inhibited/relaxing to prevent leftward rotation (left lateral rectus and right medial are inhibited)
[contraction = more excitable motor nucleus]
Eye movements: Saccades
What are the 2 types of saccades
- Exogenously driven (external stimulus) [ex. light flashing and you subconciously look]
- Endogenously driven (consiously doing it/ internal stimulus) [ex. scanning a crowd]
Eye movements: Saccades
What are the 2 types of exogenously driven saccades
- Express saccades
- Prosaccades (reflex) saccades
Eye movements: Saccades
What are express saccades
- eye movement for function (like balance; less common)
- Stimulus-response pathway Bypass cortex
- very quick to initiate (70 - 100 ms)
Eye movements: Saccades
What are prosaccades (reflex saccades)
- Stimulus response pathway traverses cortex
- still quick but route through cortex slows it (150 - 200 ms)
- Looking in response to visual stimulus such as light flashes in peripheral vision
Eye movements: Saccades
What is true about all endogenously driven saccades
- they involve the parietal and prefrontal cortecies
- More complex behaviour = more complex cortical pathway
- self directed/conscious/by choice
Eye movements: Saccades
What are the 4 types of endogenously driven saccades
- Predictive saccades
- Memory guided saccades
- Anti-saccades
- Saccade sequence
Eye movements: Saccades
What are Predictive saccades
Eye movement to point in space where stimulus is expected but isn’t yet
Eye movements: Saccades
What are memory guided saccades
eye movement to a point in space where Stimulus was but isnt anymore
Eye movements: Saccades
What are Anti-saccades
Eye movement on opposite direction of stimulus (requires inhibition of reflexive saccades)
Eye movements: Saccades
What are Saccade sequences
learned order of eye movements to fixate on series of points in space
