Test 3 (Lectures 17-25) Flashcards
The biggest and most important relay station in the CNS
Thalamus
These pathways travel from the periphery to the center
Ascending pathways
These pathways travel from the center to the periphery
Descending pathways
Ascending and descending pathways have 3 common features
- Presence of synaptic relays.
- Integration of information.
- Topographic organization
Information can be amplified or attenuated by
Synaptic relays
Topographic organization refers to
motor and sensory maps
First order neurons
Primary afferent neurons
Second-order neurons
Relays between first-order neurons and brain centers;
Typically in the spinal cord and the brain stem
Third-order neurons
Commonly in thalamic nuclei.
Afferent fibers enter the spinal cord through the
dorsal columns
Pathway of the dorsal column-medial lemniscus pathways
Dorsal columns-spinal ganglion-medulla-thalamus-cortex
The ascending fibers of the dorsal column pathways terminate in these medullary nuclei
Cuneate nucleus
Gracile nucleus
This tract consists of the axons of neurons that lie in the dorsal and intermediate parts of the gray matter. The axons decusate and travel along the contralateral side of the spinal cord.
The spinothalamic tract
Conveys the sensations of touch, pressure, temperature, and pain
The spinothalamic tract
Consists of the dorsal spinocerebellar tract (DSCT), ventral spinocerebellar tracts (VSCT), rostral spinocerebellar tract (RSCT), the cuneocerebellar tract, and the spino-olivary-cerebellar tract (SOCT).
The spinocerebellar tracts
Ascends in Clarke’s column. Carries proprioception information from the lower extremities. Projects onto nucleus Z and the VPL thalamus.
Dorsal spinocerebellar tract (DSCT)
Carries proprioceptive information from the upper extremities
Cuneocerebellar tract
Ascends laterally in the ventral horn. Carries flexor reflex afferent information from lower extremities and afferent signals.
Only active during active movements
Ventral spinocerebellar tract (VSCT)
Carries flexor reflexor afferent information from upper extremities and also afferent signals.
Only active during active movements.
Rostral spinocerebellar tract (RSCT)
Ascends in the ventrolateral fasciculus directly to the reticular formation
Spinoreticular tract
Plays a role in controlling the sense of pain
Spinoreticular tract
Consists of two major groups of axons which split into separate tracts
Pyramidal tract
These axons from the pyramidal tract go down the spinal cord
The corticospinal tract
These axons leave the pyramidal tract and innervate the motor nuclei of the cranial nerves
The corticobulbar tract
M1 stand for
primary motor area
30% from the primary motor area
30% from the premotor and supplementary motor areas
40% from the somatosensory areas
Pyramidal tract
Contains most of the fibers (80%) that decussate at the brain stem. Has direct projections to both interneurons and motoneurons.
Lateral corticospinal tract
Contains most of the fibers that do not decussate. Mostly controls axial trunk muscles.
Ventral corticospinal tract
Exits at the pyramids. Controls cranial nerves (facial muscles, articular, etc.)
Cotricobulbar tract
Originates in the red nucleus
The rubrospinal tract
Receives input from the motor cortex, the cerebellum, and the olives.
The rubrospinal tract
Decussates at the midbrain and descends adjacent to the lateral CST. Has projections onto the olives.
The rubrospinal tract
Is suspected of being of major importance for motor control
The rubrospinal tract
Is part of the cerebellum-red nucleus-olive-cerebellum loop
The rubrospinal tract
Receives inputs from the cerebellum and the labyrinth.
The vestibulospinal tracts
Rises from the neurons in Deiter’s (lateral vestibular) nucleus.
Lateral vestibulospinal tract
Originates in the medial vestibular nucleus
Medial vestibulospinal tract
Descends ipsilaterally to the lumbar level. Makes connections with interneurons.
Lateral VST
Plays a role in the control of posture
Lateral VST
Descends ipsilaterally to the mid-thoracic level. Makes connections with interneurons.
Medial VST
Plays a role in postural control through control of head position
Medial VST
Travels ipsilaterally to spinal interneurons. Has mostly inhibitory effects.
Medial reticulospinal tract
Travels to interneurons in the ventral spinal cord. Provides postural control of the proximal extensor muscles.
Lateral reticulospinal tract
Suspected of bringing about the startle reaction
The reticulospinal tract
Comes from neurons in the superior colliculus.
The tectospinal tract
Decussates and plays a role in motor reactions to visual stimuli by controlling head orientation to visual stimuli through control of the neck muscles.
The tectospinal tract
Comes from neurons in the midbrain.
Its function is a mystery.
The interstitiospinal tract
How many cranial nerves are there?
12
Sense of smell
Olfactory nerve (cranial nerve I)
Information from the retina
Optic nerve (cranial nerve II)
Motor control of the oculomotor muscles, pupillary reflexes
cranial nerve III
Oculomotor nerve (cranial nerve III)
Motor control of the oculomotor muscles
cranial nerve IV
Trochlear (cranial nerve IV)
Control of jaw movements during speech; sensory information from teeth
Trigeminal nerve (cranial nerve V)
Motor control of the oculomotor muscles
cranial nerve VI
Abducens (cranial nerve VI)
Control of facial muscles, including lip and eyelid movments; minimal sensory function.
Paralysis of the nerve is known as Bell’s palsy
Facial nerve (cranial nerve VII)
Hearing and balance
Vestibulocochlear nerve (cranial nerve VIII)
Motor control of the pharynx; control of speech
Glossopharyngeal nerve (cranial nerve IX)
Control of autonomic functions of the whole body
Wandering nerve
Vagus nerve (cranial nerve X)
Innervation of trapezius, helps control head movements
Spinal accessory nerve (cranial nerve XI)
Control of tongue movements; speech
Hypoglossal nerve (cranial nerve XII)
Soul is responsible for thinking (cognition); body obeys soul and laws of nature. Considered mind a uniquely human feature independent of the body. Theorized by Descartes.
Dualism
All features of human behavior are reflected in measurable physical properties of neurons and synapses (everything can be measured, including specific memory sites)
Reductionism
Function of a complex system is an emergent property of all the system elements and cannot be assigned to certain changes in neurons and synapses. The mind is an emergent part of the body. not a separate feature.
Neodualism
Semantic and episodic memories; facts and events
Declarative memories
Declarative memories are stored in
Hippocampus, medial temporal lobe, diencephalon
Procedural, non-associative, and associative memories
Nondeclarative memories
Habituation and sensitization
Non-associative learning
Skills, habits
Nondeclarative memories
Nondeclarative memories are stored in
Amygdala, cerebellum, basal ganglia, cortex
Learning not to respond to a stimulus following its multiple presentations (usually, when it is not very meaningful)
Habituation
The restoration or recovery of a habituated response (usually requires a new, strong stimulus)
Dishabituation
Learning to respond to smaller magnitudes of a stimulus (usually, if it is very meaningful)
Sensitization
Non-associative learning and associative learning
Implicit memory
Associative learning is a subtype of
Non-declarative memory
Involves creating a relationship between two stimuli
Associative learning
Generally studied in animals and involves food as a stimulus/reward
Associative learning
Example of associative learning
Conditioning
Associating a response with a stimulus based on repetitive presentations
Classical conditioning
Ringing a bell is associated with getting food; the animal has no initiative
Classical conditioning
Considered a conditional reflex, not an inborn reflex
Classical conditioning
Searching for an action that leads to a desired consequence; active exploration.
Operant conditioning
Even monosynaptic reflexes can show this
Operant conditioning
Requires thousands of repetitions
Operant conditioning
Example of non-declarative memory
Motor skills and motor learning
Typically involves a motor program
Motor skills and motor learning
Four stages of memory
Encoding
Storage
Consolidation
Retrieval
Putting an event into an internal code
Encoding
Maintaining the code over time
Storage
The process that makes the temporarily stored and still liable information more stable
Consolidation
Using a key (intrinsic or extrinsic) to recover the code/event
Retrieval
Typically an acoustic, visual, or somatosensory code
Encoding
Limited capacity (7 +/- 2 “pieces”); decay; followed by consolidation or loss of memory. Effectiveness is typically a few minutes or hour
Storage
Allocates attentional resources to the verbal and visuospatial subsystems, also monitors, manipulates, and updates stored memory representations.
Executive control process
Can be consolidated into long-term memory
Short-term memory
Processing a sensory stimulus may lead to creating a short-term memory trace in parallel with producing an effector (motor).
Memory consolidation
Pros for synapses serve as the site for memories
The phenomena of long term potentiation and long term depression in the cerebellum and hippocampus.
Cons against synapses serving as memory sites
Disposable synapses don’t exist
Long term potentiation is too short according to animal studies
Lashley says that
each neuron takes part in many memories
partial loss of memory
Amnesia
Causes of amnesia
Brian injury, stroke, encephalitis, electric shock, etc.
Types of amnesia
Anterograde
Retrograde
Affects the ability to recollect events that occurred after an injury
Anterograde amnesia
Affects the ability to recollect events that occurred prior to an injury
Retrograde amnesia
Caused by chronic alcohol abuse or thiamine deficiency
Korsakoff’s syndrome
Characterized by defective retrieval of memories. Partial cues or prompts cause the brain to fill in the gaps in whatever way it can
Korsakoff’s syndrome
Type of progressive dementia that causes problems with memory, thinking, and behavior.
Alzheimer’s
Earliest sign is inability to remember newly learned things
Alzheimer’s
Patients with lesions in this brain structure will solve the same puzzle over and over as if it was a new puzzle every time
Hippocampus
Important in storing declarative memory
Hippocampus
Crucial for transferring short term memories to long term memories
Hippocampus and medial temporal lobe
Long hypothesized to store long-term effects of training, specifically motor memories
Cerebellum
Likely occurs in interneurons controlling reflex arcs
Spinal memory
An engineer would find human movements to be suboptimal. Why?
Because muscles fatigue, get injured, the electromechanical delay, etc.
Human movements are produced by force generating structures called
Muscle
Muscles are relatively ____ in their actions.
slow
Muscles interact with the nervous system in a _____ fashion.
non-linear
The body is highly
adaptable
The requirements of most everyday tasks
To move a limb or the whole body to a particular point in space
Movements requires two things:
Rotation at one or several joints
Force production using the muscular system
Finding a joint configuration corresponding to the location of the endpoint. Considers different joints, different joint actions, sequencing of actions, etc.
Inverse kinematics
Finding patterns of joint torques.
Inverse dynamics
The CNS produces active changes in _____ _____ by sending signals to the muscle
muscle force
Depends on neural signals sent to the muscles and external loading conditions
Force
Computes signals sent to spinal neurons and considers the activation of alpha motoneurons through reflex pathways
CNS
Developed by Schmidt in the 1970s
Generalized motor program
Brain stores “movement formulas” expressed as mechanical patterns associated with particular actions
Generalized motor program
Has support from experiments which demonstrate invariant timing patterns when movement is sped up or slowed down
Generalized motor program
These can be changed in a program
Parameters
Stay the same in the same motor program; is different in different programs
Invariant features
In this model, the CNS computes control signals that produce adequate force patterns
Internal models
The 2 factors the brain has to account for in the internal model:
1: All the steps involved in transforming neural signals into mechanical variables.
2: Time delays in information transmission from the brain to muscle and from peripheral receptors to the brain
These internal models is similar to feedback
Inverse models
These internal models is similar to feedforward
Direct models
Compute descending neural commands based on a desired mechanical effect
Inverse models
Computations are made from sensory signals that deliver some outdated information
Inverse models
Computed signals from the brain reach muscles after substantial time delay
Inverse models
Compute the effects of current neural commands on the state of the periphery
Direct models
Takes into account possible changes in muscles and limbs due to time delays in the neural pathways
Direct models
The common explanation for how internal models work is
The internal model is quickly updated (recomputed) based on feedback signals
The problem with internal models
The brain does not have an amazingly quick and accurate computational process.
One signal, one response
Simple reaction
Different signals with specific responses to each signal
Choice reaction
If an agonist-antagonist pair of muscles are relaxed, one will shorten and one will lengthen as the joint moves to a new position. This would require active force production to prevent the joint from moving back to the original position. However, neural structures can modify the spring like properties of muscles. This is known as the ______.
Equilibrium Point Hypothesis
The central control structures shift muscle activation thresholds and readdress posture stabilizing mechanisms to a new posture. These mechanisms turn from posture stabilizing into movement producing. This is an example of:
A dynamic system
Has the ability to resolve the posture-movement paradox
Equilibrium point hypothesis
During active movement, neural commands re-address afferent signals from proprioceptors to the new posture. These signals allow the movement to occur and are used to stabilize the new posture.
Central control structures shift physiological variables associated with muscle activation thresholds and re-address posture stabilizing mechanims to a new posture.
Principle of reafference
The central controller finds a unique solution each time a problem emerges
Redundancy
Central controller facilitates groups of equally acceptable solutions rather than unique solutions
Abundancy
A common approach to the problem of motor redundancy
Optimization
Allows selection of a unique solution to a problem
Optimization
Particular function of a system’s performance the controller tries to keep optimized, commonly at a minimum or maximum value
Cost function
Time derivative of acceleration
Jerk
Leads to smooth trajectories with a bell shaped velocity profile and a symmetrical double-peaked acceleration
Minimum jerk criterion
Bernstein’s kinematic study of professional blacksmiths found more variability in the _____ than in the _______.
joints; trajectory of the hammer
Multiple possibilities
Abundancy
Instead of searching for unique solutions, the controller can facilitate similar solutions that can solve the task
Abundancy
A task specific organization of elements, while each element within a structural unit is itself a structural unit at a different level of the analysis
Structural unit
Purposes of structural units
Synergies
Extrinsic patterns reflecting a synergy under particular external conditions
Behaviors
Based on a structural unit that consists of a neural network uniting different extremities.
Locomotion
Motion of the arms or legs is based on a structural unit comprising
individual joint rotations
Each joint rotation is based on a structural unit involving
muscle actions as elements
Each muscle is a structural unit of it
motor units
What would happen if the far motor neuron in a muscle stopped firing?
Muscle force drops, the muscle lengthens.
As the muscle lengthens, muscle force increases due to an increased activation of the remaining motor neurons due to the tonic stretch reflex.
If two fingers work in parallel to produce 20 N of force, the could accomplish this in three different ways
25/75%
50/50%
75/25%
Controller do not prescribe what each element should do in a synergy, they only set the overall task and organize feedback loops to assure task stability. This is opposite of an internal mode.
Hierarchy of a structural unit
According to the uncontrolled manifold hypothesis, the controller acts in
a space of elemental variables
In the uncontrolled manifold hypothesis, a subspace is termed
the uncontrolled manifold
These variables do not have to be controlled within the sub-space
Elemental variables
Within space, the controller selects a subspace corresponding to a desired value of a performance variable of the whole system.
The controller then tries to limit variability of elemental variables outside the subspace while allowing relatively large variability within the subspace
Uncontrolled manifold hypothesis
This is within the uncontrolled manifold. Does not affect performance variables and therefore may be relatively large
Good variability
This is outside the uncontrolled manifold. Changes important performance variables and needs to be kept low
Bad variability
An inverted pendulum in the field of gravity
Posture
Maintenance of body alignment and spatial orientation in order to put the body in a position to enable effective movement
Postural control
A position that is resistant to disturbance or returns to its normal state after disturbance
Stability
Sources of problems with postural control
High center of mass/center of gravity
Multiple joints
Small support area (1 square foot)
The location of the center of gravity of a human being in the normal standing position varies with
body build, age, and sex
Female’s center of gravity is ___ of standing height.
55%
Male’s center of gravity is ___ of standing height.
57%
The center of gravity can be considered to be almost directly over the center of pressure when
in quiet standing
The point at which the force vector for ground reaction force is applied
Center of pressure
Sway increases under these conditions:
Closed eyes
Standing on a narrow support
Age, disorder
Sway decreases under these conditions:
Light finger touch (to virtually any part of the body)
Holding an object connected to the external world
Center of gravity must remain within the base of support in order to maintain
equilibrium
It is easier to maintain center of gravity with a
larger base of support
Migration of the reference point, with respect to which equilibrium is instantly maintained
Rambling
Likely a reflection of a central search process (supraspinal process)
Rambling
Likely a reflection of the mechanical properties of the effectors and reflex loops (subspinal process)
Trembling
The body oscillates about a reference point, while
the reference point migrates for reasons that are not well understood.
One of the least prominent senses
Sense of balance
Are innvervated by the peripheral ends of bipolar sensory neurons in the ampullary nerve
Vestibular hair cells
The ampullary crest is covered by a gelatinous, diaphragm-like mass called the
cupula
The structure that aids in balance
Vestibular apparatus
Sensitive to angular acceleration of the head
Semicircular canals
The fluid in the semicircular canals move when the head
rotates
Action potentials are generated when fluid acts on the ____ and displace hair cells.
cupula
Sensitive to linear acceleration of the head
Otoliths
The zone in the utricle where the floor is thickened and contains hair receptors
Macula
Is covered with a gelatinous substance containing crystals of calcium carbonate (otoliths)
Macula
Otoliths deform the floor and bend the hair cells which generate action potentials when
The head is tilted or accelerated in a certain direction
Vestibular nuclei occupy a large part of the
medulla
Innervated by the 8th cranial nerve via Scarpa’s ganglion. Neurons here are bipolar.
Vestibular apparatus
