MIDTERM #2 Flashcards
tactile acuity
- found in cutaneous receptors
ability to distinguish between two points
small receptive field permit…
high resolution of spatial detail
- can tell difference between two point vs one point with little separation
- perceives touch well
superficial cutaneous receptors
meissners corpuscles
deep cutaneous receptors
pacinian corpuscles
What cutaneous mechanoreceptor would be most likely
responsible for tactile acuity?
merkel cells
what determines tactile acuity
- receptive field size
- density of receptors
- representation within somatosensory cortex
How do the 4 receptor types vary across the skin different regions
the relative densities of the 4 receptor types will vary
tip of finger has high concentrations of
- SA1s, FA1s
(merkel cells)
Palm of hand has concentration of equally distributed
SA2s and FA2s
merkel receptors densely packed on
fingertips
two point discrimination threshold
minimum distance at which a person can perceive two distinct points of contact on the skin rather than one
cutaneous receptors allow the body to have
- increased density of receptors
- smaller receptive fields
- lower two point discrimination thresholds
what correlates with tactile spatial acuity
receptive field sizes correlate
sensation physiology
occurs when the peripheral receptors are stimulated
perception physiology
occurs when the brain interprets the sensory stimulation
thalamus
relay information from the sensory receptors to areas of the cortex
thalamus relay physiology
somatosensory physiology
peripheral nerve fibres travel in bundles to the spinal cord
two major somatosensory physiology pathways
- medial lemniscal
- spinothalamic
Medial lemniscal pathway
consists of large fibers that carry proprioceptive and touch information
spinothalamic pathway
consists of smaller fibers that carry temperature and pain information
- cross over to the opposite side of the body and synapse in thalamus and then on to somatosensory cortex (S1)
somatosensory information
ascends in afferent tracts in spinal cord
- projects to primary somatosensory (S1) and parietal cortex
primary somatosensory cortex
located in a ridge of cortex (postcentral gyrus) which is found in the parietal love
homunculus
distorted visual representation of the human body based on the sensory or motor cortex in the brain
- lips, tongue, hands, feet, genitals: more sensitive than other parts of the body
somatosensory homunculus
visualizes the proportional sensory perception mapping of the body surfaces in the brain
amount of cortical tissue devoted to each body surface is proportional to
sensitivity of that part
Slowly adapting type 2 afferents (SAII) role
- code for finger position
- discharge rates correspond with finger movements (increased for flexion, decreased for extension)
primary somatosensory cortex
located in a ridge of cortex which is found in the parietal lobe
somatosensory homunculus
visualizes the proportional sensory perception mapping of the body surfaces in the brain
two methods of testing tactical acuity
- grating acuity test: (small groves on skin, ask participant to indicate orientation of grating
- spaces between the groves
Somatosensory of the fingers
tactile acuity decreases from index to the pinky but Merkel receptor density is the same across all fingers
Proprioception
perception of body movement/orientation in space
- reflexive or subconscious
kinesthesis
- SENSE OF MOVEMENTS
- conscious
- behavioural
4 major contributors to kinesthesis
- sense of position and movement of the limbs
- sense of tension or force
- sense of effort or heaviness
- sensations of body image and posture
Proprioceptive afference
afferent signals are generated by mechanoreceptors in response to stimulation produced as consequence of position, tension, and movements of body parts
ex afferent
external afference: generated from external source
- generated by proprioceptors in response to external stimulation
ex) an external object hitting you
re-afference
generated from your own movements
- generated by proprioceptors in response to internally-generated stimulation
ex) the sensory info you get from touching a pen you’re writing with
how can proprioception assessment be conducted
- matching tasks
- discrimination tasks
matching tasks can be
- simultaneous : both limbs compared to each other
- successive: single limb compared to itself (before vs after)
proprioception sources
- muscle spindles (length/velocity of muscle)
- Golgi tendon organs (tension/force of muscle)
- joint (pressure, force, position)
- cutaneous (length and velocity of skin stretch, onset and offset of movement)
cutaneous meaning
relating to or affecting the skin
what mechanoreceptors contribute to proprioception
all mechanoreceptors contribute to proprioception
- muscle, joint, and cutaneous receptors
ways to test proprioception
- tendon vibration: activates type 1as
=kinaesthetic illusion=Pinocchio effect
(ex. touch nose but vibrate another muscle to make you think you’re no longer touching your nose)
does the body trust muscle spindle info or cutaneous info
body trusts muscle spindle info over cutaneous info
what is sensory dominance
conflict arises and brain chooses one sensation over other sensory information
sensory visual dominance
muscle spindles cause illusion with removal of vision (vision is dominant over the other senses)
in order for kinesthetics illusion to be effective
need to remove sight of limb
lignocaine
can decrease the joint receptor sensitivity lowering the proprioception
dextran
increases the joint receptor sensitivity increasing proprioception
do joint receptors have a role in proprioception
yes
Fast adapting type 1 afferents (FA1):
- innervate meissner corpuscles
- detect intial rapid change in skin stretch locally
- code for which joint is moving
Proprioception of cutaneous receptors
- remove feedback
- skin stretch (kin tape)
how is kinaesthetic information obtained
signal are ambiguous from one proprioceptor alone
- its the combination of multiple inputs necessary for accuracy
sources of proprioception
- muscle spindles/GTO’s
- joint receptors
- cutaneous receptors
sensory dominance
muscle spindles and vision
proprioceptive afference
re-afference
ex afferent
motor cortex 3 areas
- premotor cortex
- supplementary motor area
- primary motor cortex (M1)
premotor cortex role
- selection of appropriate motor plans for voluntary movements
- preparing complex tasks
- produces complex movement (at high level of current)
relays information to M1
when is the premotor cortex stimulated
at high level of current
what are motor-set neurons
- neurons located in the premotor cortex that signal preparation for movement
are there specific neuron’s for specific actions
yes
Mirror neurons
neuron’s that are active in response to sensory aspects with motor actions
- activates during the performance of an action and also when observing someone else performing the same action
respond to sight and sound of action performed by another individual
Supplementary motor area (SMA)
programming complex sequences of movements and coordinating bi-lateral movements
*based on remembered/previous sequences of movements
what part of the motor cortex bases movements on remembered/previous sequences of movements
supplementary motor area
what does the supplementary motor area respond to
- sequences of movements
- mental rehearsal of sequences of movements
primary motor cortex (M1) roles
relays motor commands to the alpha motor neurons via corticospinal motor neurons to the corticospinal pathway
(discharging/firing 5-100ms prior to movement)
motor homunculus
map of the primary motor cortex : size of each body part corresponds to the amount of motor cortex dedicated to controlling it
- elicits movements of individual body parts, involving multiple muscles
Primary motor cortex function
- encodes the force of movement
- encodes the direction of movement
- encodes the speed of movement
spatial resolution
high accuracy in determining WHERE something happens
temporal resolution
high accuracy in determining WHEN something happens
Electroencephalography (EEG)
description, pros, cons
electrodes placed over various positions on the scalp and record activity underneath each electrode
Pros: excellent temporal resolution
Cons: poor spatial resolution
functional magnetic resonance imaging (fMRI)
premiseL neuronal activity involves metabolic demand
neuronal activity is increased with increased in metabolism and increase in oxygen demand
what does an fMRI measure
measure blood flow within cortex
: comparison of deoxygenated blood versus oxygenated blood, can tell what regions are active
Functional magnetic resonance imaging (fMRI)
pros and cons
pro: excellent spatial resolution
con: poor temporal resolution
Transcranial Magnetic Stimulation (TMS)
selectively determine what region of motor cortex to investigate
transcranial magnetic stimulation magnetic filed causes
depolarization of motor cortical neurons which activates muscles innervated by cortical neurons
pre motor cortex
observing and planning movement
supplementary motor area (SMA)
active during mental rehearsal and movement planning
basal ganglia
sub-cortical structure (group of various distinct cell clusters)
function of basal ganglia
modulate voluntary movement through facilitation or inhibition of signals descending from the motor cortex
basal ganglia is part of
the extrapyramidal system
extrapyramidal system
functional, not anatomical, unit compromising of nuclei fibers that control and coordinate posture, locomotion, and static supporting voluntary movement
basal ganglia receives input from
the cortex (primary motor and frontal)
basal ganglia put output to
pre-motor area, supplementary motor area, primary motor cortex, frontal cortex (all via thalamus)
* no direct outputs to spinal cord.
4 main nuclei of the basal ganglia
- striatum
- globus pallidus
(internal segment, external segment) - sub thalamic nucleus
- substantia nigra
where do the basal ganglia nuclei relay to
thalamus
how are the basal ganglia nuclei organized
- they are somatotopically organized: grouped by specificity of movement (direction, amplitude, velocity)
Basal ganglia neurotransmitters
- GABA
- Glutamate
- Dopamine
Gaba
GABAergic neurons (inhibitory)
Glutamate (glutamatergic neurons)
excitatory
Dopamine (dopaminergic neurons)
action depends on the receptor it binds with
D1 receptors: excitatory involved in the direct pathway
D2 receptors: inhibitory involved in the indirect pathway
Basal ganglia functional pathway types
direct pathway vs indirectpathway
direct pathway
neural pathway involving the basal ganglia vital to the initiation and facilitation of voluntary movement
indirect pathway
works in conjunction with the direct pathway, functions inhibit unwanted movement
Basal Ganglia- direct pathway (conceptual figure)
Which of the following nuclei within the Basal Ganglia can
act as an excitatory nucleus?
substantia nigra
Parkinsons disease
progressive neurodegenerative disorder:
- death of dopaminergic neurons causing reduced dopamine release causing issues with movement
Parkinson’s disease age frame and risk
- 1/100 individuals under the age of 60
- 1.5x higher in males then in females
parkinsons cure
no cure: treatments target symptom management
parkinsons life expectancy
10-20 years after diagnosis
Parkinson’s disease 4 main symptoms
- resting tremor
- rigidity
- bradykinesia (slowness of movements)
- parkinsonian gait (forward lean)
*cannot initiate movements properly
Parkinson’s disease pathophysiology
- death of dopaminergic neurons in the substantia nigra
- reduced dopamine release in the basal ganglia
- direct pathway cannot aid in initiation/facilitation of movement
- movement symptoms of Parkinson’s disease
lewy bodies
abnormal aggregates of protein that displace other cell component and disrupt cell function
- present within neuron’s in the substantial nigra
- leads to death of the neuron
substantia nigra
“black substance”: cells appear dark due to increased concentration of neuromelanin
parkinsons disease direct pathway diagram
What nucleus within the basal ganglia contains dopaminergic
neurons? Where does this nucleus project to within the basal ganglia?
substantia nigra projects to the striatum
cerebellum
“little brain”
- 10% of total brain volume but over 50% of total brain neurons
- is our comparator
comparator
- receives afferent (sensory) and efferent (motor) information
- compares intention vs what happened
cerebellum 3 functions
- maintenance of balance and posture: integrates sensory information relevant to balance and modulates information sent to motor neurons to control postural muscles
- coordination of voluntary movements: coordinates timing and force of different muscle groups, plan and produce movements
- motor learning: adapt and fine tune motor commands to make accurate movement: trial and error process
Cerebellum anatomy
- has two symmetrical hemispheres
- anatomy divided by function
4 symmetrical sections
cerebrum 4 symmetrical sections
- hemisphere
- vermis
- intermediate zone
- flocculonodular lobe
cerebellum pathways
- spinocerebellar
- cerebrocerebellar
- vestibulocerebellar
spinocerebellar pathway
- in vermis and intermediate zones
- integrates sensory and motor information
- motor coordination
cerebrocerebella pathways
- lateral hemisphere
- involves cortical input
- planning and timing of movements
vestibulocerebellar pathways
- flocculonodular lobe
- involves vestibular nuclei input
- posture and vestibular reflexes
Cerebellum is important for
planning
- smooth, coordinated movements (spinocerebellar and cerebrocerebellar pathways)
- balance control
how do we know there is damage to our cerebellum
- damage or loss of cerebellar tissue
cerebellum dysfunction symptoms
- Ataxia
- Dysmetria
- Hypotonia
- Large amounts of sway
ataxia
- lack of coordination
- decomposition of movement
- jerky movement
dysmetria
(dys=bad, metry=measure)
- inability to make accurate voluntary movements
- overshoot/undershoot of movement
Hypotonia
(hypo= under/less, Tonia= tension/stretching)
- decrease in muscle tone/resistancee
efferent
motor command sent from motor cortex to body
efferent copy
copy of motor command use to update other brain regions on the action about to be performed
ex-afference
sensory information from externally generated source, unexpected
re-afference
sensory information from a self-generate source, expected
corollary discharge
signal created within the cerebellum represents the re-afference we expect to get from a self generated movement
- used to inhibit expected feedback from self generated movement (frees up cortical resources)
what happens if there is unexpected afferent information from a voluntary movement
does not get inhibited, and gets sent to the cortex to update on unexpected information
cerebellum- feedforward model explained
- movement goal is sent to motor cortex
* SELECT an appropriate motor plan based on previous experience
(force, speed, direction of movement, correction of MU recruitment)
Efferent (motor command) sent ot effector muscles in the body
* EXECUTE appropriate motor plan based on pervious experience
(force, speed, direction of movement, MU recruitment)
Efferent copy (copy of motor command) sent to cerebellum to update on what is about to happen
- Corollary discharge is produced by the cerebellum
*created by efferent copy
*represents the expected sensory feedback we should get from executed movements
*used to inhibit any response to self-generated movement that may interfere with execution of motor task
Reafference is produced from the body
*actual sensory feedback, we get from the executed movement
- comparison of corollary discharge and reference occurs in cerebellum
- expected vs actual sensory info
if the expected and actual match=its successful movement
if they don’t match= unsuccessful execution and don’t need to update cortex
- cerebellum updates motor cortex about reference information that didn’t match
- adjust motor plan until desired movement is achieved
titi for tat experiment
two people alternate replicating force applied back and forth, increasing force dramatically
- sensory information from external source= info perceived
- try to replicate force
- re-afference inhibited by corollary discharge: so push much harder
- other person perceives higher force and replicates, same phenomenon occurs
Divided attention (multitasking)
ability to focus on multiple forms of sensory information
- can be investigated in an experimental condition
Dual task paradigm
- primary and secondary tasks
*can be manipulated with different interventions
selective attention
ability to focus attention on one specific task
exogenous
external, reflexive
- focus on objects/stimuli that stand out
endogenous
internal, voluntary
- incorporates intention, goal orientation, previous knowledge
blindness
due to attentional demand can experience types of blindness to your environment
intentional blindness
miss something
change blindness
dont notice something has changed
V1 (primary visual cortex) where is it located
- located within the occipital lobe
Retinotopically definition
- specific groups of neuron’s represent/respond to specific parts of our visual field
how is the primary visual cortex (V1) arranged
- arranged retinotopically
specific groups respond to specific parts of visual field
where does all visual info pass through in the primary visual cortex
- all passes through the lateral geniculate nucleus and relayed to cortical areas (V1 and visual association areas)
where is the lateral geniculate nucleus located
within the thalamus
theories to explain how we process and understand our visual world
- two stream hypothesis
two stream hypothesis important areas
- secondary somatosensory cortex
- inferotemporal lobe
- V1
V1
- receives visual signals from eyes
- passes through visual association areas
- relays information to two primary areas
secondary somatosensory cortex
- located in posterior parietal love
- complex movement sequences: confirm which movements have already taken place
- deciding what movements come next
*INVOLVED IN DORSAL STREAM
Inferotemporal lobe
- involved in visual memory
- role in object recognition
- helps understand complex stimuli like faces and scenes
*INVOLVED IN VENTRAL STREAM
two stream hypothesis: Dorsal stream
- V1secondary somatosensory cortex
object location and motion
detecting and analyzing movements and spatial awareness and guidance of action
Apraxia
Damage to the secondary somatosensory cortex
- doesn’t impair ability to plan or execute movements but
- movement disorder which impairs the how the movements are performed
two stream hypothesis: ventral stream
V1-> inferotemporal lobe
- object recognition and form representation
visual agnosia
damage to inferotemporal lobe
- impairs ability to recognize objects (doesn’t impair ability to see object but instead process and understand what the object is)
complex voluntary movements consist of
ventral and dorsal streams projecting to the prefrontal cortex
prefrontal cortex
decision making centre of the brain
- decide what response you want to have to your environment
Prefrontal cortex projects to the
premotor cortex
premotor cortex will
help plan movement and project to other motor areas to carry out desired movement
