Summaries Flashcards
*What is the primary muscle of inspiration?
The diaphragm, which contracts to expand the thoracic cavity and draw air into the lungs.
*Where is the respiratory rhythm generated?
In the medulla of the brainstem, which produces the rhythmic breathing cycle
*What is the primary regulated variable in the respiratory system?
PaCO2 (arterial carbon dioxide pressure), which is key for maintaining acid-base balance and proper gas exchange
How is breathing controlled?
Breathing is controlled both automatically and voluntarily.
The cortex can override automatic breathing processes, allowing voluntary actions like speech, singing, sniffing, coughing, spirometry tests, and breath-holding.
Deep-sea divers hyperventilate before breath-holding to lower PaCO2, which induces alkalosis. The urge to breathe during a breath-hold typically occurs at a PaCO2 of around 50 mmHg
Innervation of spinal respiratory motor neurons?
Insp -
Diaphragm - C3-C5
Scalenes - C2-C7
Exp -
Sterno - Accessory and C2-3
Intercostals - T1-T11
Abs especially Transversus abdominus - T7-L1
*PaCO2 regulation: feedforward and feedback control/adaptive control?
Feedforward Control:
Regulates PaCO₂ through goal-oriented commands that account for targets and disturbances, independent of chemoreception.
Feedback Control:
Uses closed-loop negative chemofeedback to adjust PaCO₂ based on detected changes.
Adaptive Control:
Involves long-term modifications (e.g., neuroplasticity) to the respiratory control system for sustained regulation.
Operates across multiple levels of respiratory control.
*Basic elements of the respiratory control system?
Central Controller (=pons,medulla, other parts of brain)
> Effectors (= resp muscles) > Sensors (= Chemoreceptors, lungs and other receptors)
CC > Eff = Output
S > CC = Input
*Respiratory control functions?
The respiratory control system must
be able to regulate:
1. Blood-gas tensions and acid-base
balance (alveolar ventilation)
2. Speech and breath-holding
3. Airway defence (cough, swallow)
*Golgi Tendon Organ (GTO) Reflex?
At rest: Negative feedback inhibits muscle activity.
During locomotion: Positive feedback enhances extensor activity, modulated by descending motor commands
*Flexion Withdrawal Reflex?
Polysynaptic reflex activating ipsilateral flexors and contralateral extensors in response to painful stimuli
What is the neural pathway of the flexion withdrawal reflex?
Stimulus: Painful stimulus detected by free nerve endings (nociceptors).
Afferent Pathway: Group III fibers transmit signals to the spinal cord.
Central Integration: Polysynaptic pathway with interneurons; coordinates ipsilateral flexion and contralateral extension.
Efferent Pathway:
Ipsilateral: Flexors activated, extensors inhibited for withdrawal.
Contralateral: Extensors activated for stabilization.
Function: Protective reflex for rapid withdrawal, independent of supraspinal inputs.
*What is the neural pathway of the stretch reflex?
Stimulus: Triggered by a stretch or tendon tap, detected by muscle spindles.
Afferent Pathway: Group Ia afferent fibers carry stretch signals to the spinal dorsal horn.
Central Integration:
Monosynaptic loop: Afferent neurons synapse directly with α-motor neurons.
Reciprocal inhibition: Group Ia interneurons inhibit antagonist muscles.
Efferent Pathway: α-motor neurons signal contraction of agonist/homonymous and synergist muscles.
Function: Maintains muscle length via negative feedback, compensating for unexpected load deviations.
H-Reflex: Elicited by electrical stimulation of Ia fibers, similar to stretch reflex with EMG-recorded muscle contractions.
*Types of Reflexes?
Stretch Reflex: Activated by muscle spindles, using a monosynaptic loop for rapid contraction and reciprocal inhibition to maintain muscle length.
Hoffman Reflex (H-Reflex): Laboratory test using electrical stimulation to assess reflex pathways and demonstrate plasticity in motor learning.
Flexion Withdrawal Reflex: Polysynaptic reflex triggered by painful stimuli, activating ipsilateral flexors and contralateral extensors for protective withdrawal.
Golgi Tendon Organ Reflex: Inhibits muscle contraction at rest (negative feedback) and enhances extensor activity during locomotion (positive feedback) based on gait phase.
*Definition of Reflex?
Automatic, involuntary motor response to a stimulus, modifiable by supraspinal inputs
*What is balance?
Quiet standing involves keeping the centre of
mass (COM) within the base of support (BOS)
*Centre of Mass & Pressure?
The Center of Pressure (COP) is the point where the ground reaction force acts on the body. It actively shifts forward and backward to help maintain the Center of Mass (COM) within the body’s limits of stability, ensuring balance. By adjusting the COP, the body compensates for any shifts in the COM to prevent falling
*What is sway? Why do we sway?
Sway is the natural oscillation of the body to maintain balance, typically occurring at the ankle joint.
Reasons for sway:
Imperfect sensory estimation due to sensor noise.
Imperfect motor output in executing movement.
External/internal perturbations like wind, breathing, or being pushed.
Lack of visual information, which increases sway by limiting sensory feedback.
*Active Modulation?
Passive ankle stiffness alone cannot maintain balance; active muscle control is required to adjust and stabilize the body during movement. Active modulation allows for dynamic adjustments to prevent falls and maintain posture.
*Perturbing visual input? What does it look like?
Perturbing visual input involves changing the visual scene, causing the brain to misinterpret motion.
Subjects sway in the direction of the visual scene movement, as the brain interprets forward scene motion as backward body motion, producing a compensatory forward response.
Response timeline:
Initial sway in the direction of visual motion (~1s).
Corrective sway after 2-3 seconds.
Best responses occur with slow, low-frequency motion (<0.1Hz, <5°/s).
Responses habituate quickly and are influenced by expectation and cognition.
The brain uses prior knowledge to distinguish between object motion and self-motion.
*Ground reaction forces - walking?
Large vertical force upon heel-strike
Accompanied by a decelerating (backward) shear force (dotted line)
Push-off includes an ACCelerating shear force, accompanied by a secondary vertical force
Swing-stance pattern?
Alternating pattern of swing-stance
Flexors active during swing (e.g. TA, hamstrings, Hip flexors)
Extensors active during stance (e.g. triceps surae, quadriceps, Gluteus)
*Muscle actions of locomotion?
Alternating eccentric and concentric contractions control locomotion.
Eccentric contraction (stance start) brakes motion, while concentric contraction (stance end) provides push-off
*How do central pattern generators (CPGs) contribute to locomotion?
Spinal networks: CPGs generate rhythmic locomotor patterns even without sensory input.
Half-center model: Flexor and extensor neurons alternate activity through mutual inhibition.
Sensory feedback: Modulates CPG activity, helping with phase transitions, such as initiating the swing phase of gait.
What parts of the brain contribute in locomotion?
Motor cortex: Adjusts for obstacles using visual inputs.
Mesencephalic locomotor region (MLR): Initiates and adjusts gait speed.
Cerebellum/brainstem: Fine-tunes patterns with real-time sensory input.
*Purpose of Eye Movements?
Maintain a clear image/bring points of interest on the fovea.
Avoid visual blur
Track objects effectively.
*Types of Eye Movements?
Fast movements:
Saccades: Quick jumps to reposition focus (up to 900°/s, ~3 per second).
Resetting movements: During Vestibulo-Ocular Reflex (VOR) and Optokinetic Reflex (OKR).
Slow movements:
VOR: Stabilizes vision during head movement.
OKR: Visual stabilization during prolonged motion.
Smooth pursuit: Tracks moving objects using predictive mechanisms.
Vergence: Aligns both eyes for depth perception
*Methods of Measurement of eye movements?
Electrooculography (EOG): Tracks electric potential changes.
Infrared reflectance: Monitors eye position using IR beams.
Scleral coil: Accurate but invasive.
Video-oculography (VOG): Tracks pupil and gaze with software
*What are the applications and observations of eye movements?
Saccades show motor prediction in activities like walking or sports (e.g., cricket).
Predictive gaze in tasks like tea-making or walking anticipates upcoming actions.
Action observation involves predictive gaze, aligning observed actions with motor representations.
*What does a locomotor pattern involve?
A locomotor pattern involves rhythmic muscle activity and characteristic ground reaction forces, enabling efficient propulsion, stability, and balance during movement
*Where does the basic locomotor pattern come from?
It comes from the spinal cord, where central pattern generators (CPGs) produce rhythmic muscle activity for movements like walking, even without brain input.
*What role do supraspinal areas play in locomotion?
Supraspinal areas:
initiate
stop
and fine-tune locomotion by modulating spinal cord activity for adaptive and goal-directed movements.
*How does sensory feedback influence locomotor patterns?
Sensory feedback adjusts locomotor patterns to:
maintain stability
adapt to changes
enhance movement efficiency
*How do saccades contribute to motor control?
Saccades provide predictive information, aiding in anticipation and adaptation during movements like locomotion.
*Components of the vestibular system?
Otoliths: Structures in the vestibular system that detect linear acceleration (e.g., moving forward in a car) and head tilt relative to gravity.
Semicircular canals: Fluid-filled structures that sense rotational movements of the head (e.g., turning or nodding).
Vestibular-ocular reflex (VOR): A reflex that stabilizes vision by moving the eyes in the opposite direction of head movement, ensuring a steady visual field.
*Vestibular ocular reflex?
The Vestibular-Ocular Reflex (VOR) stabilizes vision during head movements by moving the eyes in the opposite direction of the head. It uses vestibular system signals to ensure a steady gaze, preventing visual blur during motion
*Ways to test Vestibular function?
Real rotation: Assessing responses during head or body rotation.
Caloric stimulation: Introducing warm or cold water/air into the ear to stimulate the vestibular system.
Galvanic Vestibular Stimulation (GVS): Using electrical currents to activate vestibular nerves.
*What does the vestibular system measure?
The vestibular system measures linear acceleration, tilt, and rotation, playing a crucial role in balance, orientation, and eye movements
*What is phototransduction?
Bleaching: Light changes rhodopsin, separating retinal and opsin.
Hyperpolarization: Activated opsin reduces cGMP via PDE, closing Na+ channels.
Signal Transmission: Decreased neurotransmitter release alters bipolar and ganglion cell activity, transmitting signals to the brain.
*What is the role of the pupil in light adaptation?
The pupil adjusts from 2 to 8 mm, controlling light intake by up to 16 times. While it is the primary response to changing light, it plays a small part in overall light adaptation, with retinal adaptation providing significant contribution.
*Benefits of smaller pupil size?
Less light reaching retina
Greater depth of field (more focus)
Reduced spherical abberation
Reduced glare (scattering of light)
Infinite depth of field
Compensates for myopia
*Retina cell types?
Photoreceptors, horizontal,
amacrine, bipolar and ganglion cells
*Structure of Retina?
Consists of layers: photoreceptors (rods and cones), bipolar cells, and ganglion cells
Rods and cones?
Rods - Responsible for vision in low light (scotopic vision) and are highly sensitive to light but do not detect color.
Rods are most densely packed in the periphery of the retina, with the highest concentration around the fovea’s outer region, but they are absent in the central fovea
Cones - Cones are responsible for color vision and detailed vision (photopic vision) in bright light.
Cones are concentrated in the fovea, the central part of the retina, providing high visual acuity. The fovea contains almost exclusively cones, with the density decreasing in the periphery.
What is rhodopsin and its role in vision?
Rhodopsin is a light-sensitive pigment found in rod cells of the retina, essential for vision in low-light conditions.
It consists of two components: opsin (a protein) and retinal (a light-absorbing molecule).
When light strikes rhodopsin, it causes a shape change in retinal, activating opsin and triggering electrical signals sent to the brain. For continued function in dim light, rhodopsin must regenerate after each use.
*Visible range of luminance?
Human vision functions across ~ 10^15 units of luminance
*Scotopic versus Photopic vision?
Scotopic
low light vision
Rods only
High sensitivity/low acuity
Non-foveal
Photopic
Suited for high luminance
Cones only
Lows sensitivity/high acuity
Foveal & peripheral
Mesopic
Intermediate luminance (e.g. Dusk)
Rods & cones
Intermediate sensitivity/acuity
Foveal & peripheral
*Adaptation of eye?
Pupil Size: Adjusts to control light intake; smaller pupils enhance depth of field and reduce scatter, larger pupils improve low-light vision.
Rod/Cone Switch:
Low light: Rods dominate for high sensitivity (scotopic vision) but low acuity.
Bright light: Cones dominate for high acuity and color vision (photopic vision) and high acuity.
Intermediate light: Both rods and cones work together (mesopic vision).
Photopigment Regeneration: Photopigments are bleached(broken down) by light and regenerate in darkness, essential for maintaining vision.
*Color Vision?
Human vision relies on three types of cones, each sensitive to different wavelengths:
S-Cones: Short wavelengths (blue).
M-Cones: Medium wavelengths (green).
L-Cones: Long wavelengths (red).
These cones work together to perceive a wide range of colors.
Colors are processed in opposing pairs:
Red-Green, Blue-Yellow, and Black-White.
Color blindness results from cone defects or absence
*Visual Pathways?
Retina: Light is detected and converted into neural signals.
Optic Nerve: Carries visual information from the eye.
Optic Chiasm: Some fibers cross to the opposite hemisphere.
Optic Tract: Transmits information to the thalamus.
Lateral Geniculate Nucleus (LGN): Processes and relays signals.
Primary Visual Cortex (V1): Interprets visual data in the occipital lobe.
Higher Visual Areas: Dorsal stream for motion, ventral stream for object recognition.
*Definition of Proprioception?
Proprioception is the sense of body position and movement, involving muscle spindles and Golgi tendon organs. It is highly sensitive for balance and integrates with vision and vestibular input.
*Muscle Spindles?
Muscle spindles, lying parallel to extrafusal fibers, detect muscle stretch and velocity. Through alpha-gamma coactivation, they maintain sensitivity during muscle contraction, ensuring accurate feedback for posture, movement, and reflexes
*Golgi Tendon Organs?
Golgi tendon organs detect muscle tension and help prevent overload by signaling the nervous system through group Ib afferents. When excessive tension is detected, they trigger an inhibitory response to reduce muscle activity, preventing injury or damage from overloading.
*How are sensory feedback and force production interlinked?
Muscle spindles detect changes in muscle length and velocity, while Golgi tendon organs sense muscle tension. Both provide feedback that fine-tunes force production, ensuring muscles generate the right amount of force for a task while preventing injury and optimizing performance
*Structure of cerebellum?
3 lobes: Anterior, posterior, and flocculonodular.
3 functional subdivisions.
3 pairs of peduncles (superior, middle, inferior).
3 pairs of deep nuclei (dentate, interposed, fastigial).
3 cortical layers (molecular, Purkinje, granule).
*Functions of the cerebellum?
Coordinates movement, maintains posture and balance, and enables motor learning.
Integrates sensory and motor information for smooth execution of movements.
*Gross anatomy of the cerebellum?
Cerebellar peduncles - Superior, Middle, Inferior
Cerebellar cortex -Cerebrocerebellum, Spinocerebellum, Vestibulocerebellum
Deep cerebellar nuclei -
Dentate nucleus, Interposed nucleus, Fastigial nucleus
*What are the cerebellar peduncles and their functions / in/outputs?
The cerebellum is connected to the brainstem by 3 symmetrical pairs of peduncles:
Superior Peduncle:
- No inputs
- Outputs to motor cortex (via thalamus) and red nucleus.
Middle Peduncle:
- Inputs from motor cortex (via pons)
- No outputs.
Inferior Peduncle:
- Inputs from inferior olivary nucleus, spinal cord, and vestibular nuclei
- Outputs to reticular formation (brainstem), spinal cord, and vestibular nuclei.
*Dentate Deep cerebellar nuclei ?
Most lateral nucleus - Located in cerebrocerebellum
Output is to motor cortex via superior peduncle and thalamus
*Interposed Deep cerebellar nuclei ?
Located in intermediate cortex
(spinocerebellum)
Output is to red nucleus via superior peduncle
*Fastigial Deep cerebellar nuclei ?
Most medial nucleus - Located in vermis (spinocerebellum)
Output is to reticular formation and vestibular
nucleus via inferior peduncle
*What are the key elements of cerebellar circuitry?
Mossy Fibres (Granule Layer): Carry information into the cerebellum, activating granule cells and cerebellar nuclei.
Granule Cells (Granule Layer): Connect to parallel fibres, which synapse with Purkinje cell dendrites.
Climbing Fibres (Granule Layer): Excite Purkinje cells directly, originating from the inferior olive, and are involved in error signal processing for learning.
Purkinje Cells (Purkinje Cell Layer): Have a vast dendritic tree, provide inhibitory signals to cerebellar nuclei, modulating motor output.
Parallel Fibres (Molecular Layer): Arise from granule cells and synapse with Purkinje cells.
*Overall Function of the Basal Ganglia?
Modulates movement by influencing initiation, termination, and scaling of motor activity.
They affect premotor cortical activity through the cortico-basal ganglia-thalamic loop, integrating cortical input and motor planning without direct spinal cord connections.
*Cerebellum Connections?
Connections only to sensorimotor
areas of cerebral cortex (via
thalamus)
Receives input from brainstem and
spinal cord
Involved almost exclusively with movement
*Basal Ganglia Connections?
Widespread reciprocal connections to cerebral cortex (via thalamus)
Not just involved in movement
Behaviour and emotion
*Basal Ganglia internal connections?
Striatum Projects To:
Globus Pallidus (Striato-pallidal pathway)
Substantia Nigra (Striato-nigral pathway)
Subthalamic Nucleus (STN): Forms the indirect pathway between the Globus Pallidus Externa (GPe) and Substantia Nigra Reticulata (SNr).
Globus Pallidus Interna (GPi) and Substantia Nigra Reticulata (SNr): Act as the output centers of the basal ganglia, sending inhibitory signals to the thalamus.
*Direct motor pathway?
The direct motor pathway facilitates movement by involving two inhibitory synapses. It begins with the striatum inhibiting the Globus Pallidus Interna (GPi) and Substantia Nigra Reticulata (SNr), which normally inhibit the thalamus. This disinhibition of the thalamus allows it to excite the motor cortex, promoting the initiation of voluntary movements.
*Indirect motor pathway?
The indirect motor pathway suppresses movement through a series of excitatory and inhibitory signals. It starts with the striatum inhibiting the Globus Pallidus Externa (GPe), which reduces its inhibition on the Subthalamic Nucleus (STN). The STN then excites the Globus Pallidus Interna (GPi) and Substantia Nigra Reticulata (SNr), which increase their inhibition of the thalamus, thereby suppressing motor activity and reducing movement.
*What are the key features of the direct and indirect motor pathways?
Tonic Inhibition: The basal ganglia maintain a constant inhibitory output to the thalamus.
Neurotransmitters:
Glutamate: Excitatory neurotransmitter
GABA: Inhibitory neurotransmitter
Dopamine: Has mixed effects, modulating activity in both pathways.
Direct Pathway: Facilitates movement by reducing inhibition of the thalamus, leading to increased motor activity through the disinhibition of the thalamic output to the motor cortex.
Indirect Pathway: Suppresses movement through the Subthalamic Nucleus (STN) relay, increasing inhibition of the thalamus via the Globus Pallidus Interna (GPi) and Substantia Nigra Reticulata (SNr).
*Differences Between Basal Ganglia Diseases?
Parkinson’s Disease: Hypokinetic
Caused by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNc).
Overactive indirect pathway suppresses movement.
Symptoms: Bradykinesia, rigidity, tremor, postural instability.
Huntington’s Disease: Hyperkinetic
Results from striatal atrophy, reducing activity in the indirect pathway.
Underactive indirect pathway facilitates excessive movement.
Symptoms: Uncontrolled, jerky movements (chorea).
*Cerebellum functional subdivisions?
Vestibulocerebellum: Maintains balance and controls eye movements.
Inputs: Vestibular system.
Outputs: Vestibular nuclei.
Spinocerebellum: Regulates posture and coordinates limb movements.
Inputs: Spinal cord (proprioceptive signals).
Outputs: Motor cortex and brainstem.
Cerebrocerebellum: Plans and fine-tunes voluntary movements.
Inputs: Cerebral cortex.
Outputs: Premotor and motor cortices.
Each subdivision ensures smooth and precise motor control by integrating specific inputs and outputs.
*Main functions of the motor cortex?
Initiates and controls voluntary movement
Corticospinal Tract originates from the motor cortex, so signals are sent through contributing significantly to precise and skilled motor control.
Somatotopy organizes specific regions of the cortex to correspond to different body parts, as illustrated by the homunculus.
*Evidence for somatotopy?
Jacksonian March:
Observed in patients with focal epilepsy where seizures spread sequentially across body parts (e.g., hand to arm to neck).
Demonstrates the spatial organization of motor control within the motor cortex.
*Movements of motor cortex cells?
Kinematics: Encode the direction and trajectory of movement (how it moves)
Kinetics: Encode the force required for movement (how much to move)
Directional Tuning: Neurons exhibit a “preferred direction” of movement.
Population Coding: Collective activity of neuron populations predicts movement direction and force.
*Basic Principles of Transcranial Magnetic Stimulation (TMS)?
Technique: Uses magnetic pulses to non-invasively stimulate the motor cortex.
Applications: Maps motor cortical regions and assesses corticospinal pathway integrity.
Insights: Measures cortical excitability and plasticity, aiding in understanding motor function and rehabilitation.
*Role of the spinal cord ?
The spinal cord is crucial for motor control, with α-motor neurons acting as the final common pathway. These neurons receive input from local circuit neurons (interneurons) within the spinal cord, as well as direct signals from the brainstem and motor cortex, facilitating precise and coordinated movement.
*What is the role of the thalamus in motor control?
The thalamus acts as a relay station for sensory and motor signals, integrating inputs from the cerebellum and basal ganglia to adjust motor activity. It relays sensory information (except smell) to the appropriate cortical areas and facilitates communication between motor control centers, ensuring coordinated motor output.
*What are the descending tracts of the spinal cord?
Corticospinal Tract
Rubrospinal Tract
Reticulospinal Tract
Vestibulospinal tract
*Corticospinal Tract ?
Largest descending tract, critical for voluntary movement.
Lateral tract (90%) crosses at the medullary pyramids and controls distal muscles.
Ventral tract (10%) remains uncrossed and controls trunk and proximal muscles.
*Rubrospinal Tract?
Origin: Starts in the red nucleus of the midbrain.
Primary function: Voluntary control of muscles. Stimulation of the red nucleus produces contralateral flexion and inhibition of extension, controlling flexor motor neurons.
Compensation: Provides compensation for corticospinal damage.
*Reticulospinal Tract?
Originates from the reticular formation and is involved in posture, autonomic functions(heart/kidneys), and respiratory control(somatic).
Medial (Pontine): Facilitates extensor spinal reflexes. Projects ipsilaterally to entire spinal cord
Lateral (Medullary): Suppresses extensor activity. Projects bilaterally to entire spinal cord
*Vestibulospinal Tract?
Originates in vestibular nuclei in the pons-medulla junction
Overall maintains balance and posture.
Medial tract: Controls neck muscles.
Lateral tract: Controls body posture and muscle tone.
*General roles of integrated motor systems?
Motor Cortex: Initiates and plans voluntary movements.
Basal Ganglia and Cerebellum: Refine movements
Basal Ganglia: Manage movement initiation and suppression.
Cerebellum: Ensures coordination and accuracy of movements.
Thalamus: Relays motor signals between the motor cortex and other regions, facilitating communication.
Brainstem and Spinal Cord: Execute motor commands, integrate sensory feedback, and control reflexes and basic movements.
*What are passive electrical properties?
Neurons conduct current through ions, unlikes wires that use electricity
Voltage decays over distance, described using space constant - distance travelled, and time constant - speed of travel
*Describe Action Potentials (AP) in terms of conduction ?
APs amplify signals because passive conduction is insufficient for long-distance signal transmission.
Generated by Na+ and K+ voltage-gated channels:
Na+ influx causes depolarization.
K+ efflux causes repolarization.
Unidirectional travel due to the refractory period, preventing the AP from traveling backward.
*Factors of Conduction velocity?
Depends on Space and time constant, Velocity∝λ/τ.
Increased axon diameter (less axial resistance) and myelination (enables saltatory conduction) enhances velocity
*Effect of Myelination?
Myelin increases conduction efficiency and speed, due to saltatory conduction = jumping
Demyelination (e.g., in Multiple Sclerosis) reduces signal amplitude and increases latency.
*Points about Sodium-Potassium Pump?
Maintains resting membrane potential (-70 mV) by exchanging Na⁺ (out) and K⁺ (in) ensuring the electrochemical gradient required for APs.
Na⁺ channels open rapidly, initiating APs.
K⁺ channels open slower, restoring the resting potential.
This timing difference ensures AP propagation.
*Process of Sodium-Potassium Pump?
Ion Transport:
Actively transports 3 Na⁺ out and 2 K⁺ in using ATP.
Maintains high Na⁺ concentration outside and high K⁺ inside the cell.
Creates a negative resting membrane potential (~-70 mV).
Depolarization:
A stimulus depolarizes the membrane, reducing the negative resting potential.
Once the threshold (~-55 mV) is reached, voltage-gated Na⁺ channels open.
Na⁺ rushes in, making the inside positive and generating the action potential (AP).
Repolarization:
Voltage-gated K⁺ channels open, allowing K⁺ to leave the cell.
This restores the negative membrane potential.
Refractory Period:
Na⁺ channels close and deactivate, ensuring the AP travels in one direction.
K⁺ outflow continues briefly, causing temporary hyperpolarization.
Resetting Gradients:
The Na⁺/K⁺ pump restores ion concentrations to their resting state, preparing the neuron for the next AP.
*What are motor units and how do they affect muscle control and force output?
Motor Unit Composition: Made of an alpha motor neuron and its associated muscle fibers.
Force Output: Depends on motor unit recruitment and firing frequency.
Precision: Influenced by the number of motor units; smaller motor units offer better control (e.g., eye muscles), while larger units are used for more powerful movements.
**Muscle contraction mechanism ?
Excitation: Action potential reaches the neuromuscular junction, triggering acetylcholine release, which depolarizes the muscle fiber membrane (sarcolemma).
Calcium Release: Depolarization spreads through T-tubules, prompting the sarcoplasmic reticulum to release calcium ions (Ca²⁺) into the cytoplasm.
Troponin-Tropomyosin Shift: Calcium binds to troponin, causing a conformational change that moves tropomyosin away from actin’s binding sites.
Cross-Bridge Formation: Myosin heads attach to the exposed binding sites on actin, forming cross-bridges.
Power Stroke: ADP and phosphate are released from myosin, causing the myosin head to pivot and pull the actin filament toward the center of the sarcomere.
Detachment: A new ATP molecule binds to myosin, causing it to release actin.
Re-cocking of Myosin Head: ATP is hydrolyzed to ADP and phosphate, re-energizing the myosin head to its original position.
Relaxation: When the stimulation ends, calcium is pumped back into the sarcoplasmic reticulum, tropomyosin covers the binding sites on actin, and the muscle fiber relaxes.
*Measurement methods for muscle contraction?
Electromyography(EMG):
Measures electrical activity in muscles via surface or needle electrodes, vary with fiber type and contraction type.
Acoustomyography (AMG): Tracks sound from muscle contractions, sensitive to fatigue.
Ultrasound: Monitors muscle length changes during contraction.
*Motor unit fusion and modulation?
Muscles and their mechanisms adjust force appropriately to the task, by controlling the activity of motor units, which is why they are the fundamental units of muscle function. This adjustment happens in two main ways:
Motor Unit Fusion: A single motor unit generates a twitch when it fires once, but when multiple twitches overlap through frequent firing (known as twitch fusion), they produce a smooth, continuous contraction. This is how muscles create sustained force.
Modulation: 2 Parts
Recruitment: More motor units are activated to generate higher force. Small motor units are recruited first for fine control, and larger ones are added as needed.
Firing Frequency: The frequency at which motor units fire action potentials increases, resulting in stronger and steadier force output.
*Chain of Events in Muscle Contraction?
- Action potential (AP) stimulates the release of a neurotransmitter across the neuromuscular junction.
- AP spreads across sarcolemma/muscle membrane and into fiber along the T-tubules (Links to EMG signal)
- Causes release of Calcium from the Sarcoplasmic Reticulum
- Calcium binds to muscle and causes cross-bridge cycling
*Muscle wisdom
Muscle wisdom is the nervous system’s adaptive mechanism that adjusts motor unit firing rates in response to the muscle’s slower contractile properties during fatigue. This optimization helps sustain force output while conserving energy and mitigating the effects of fatigue.
*Neural control of muscle changes during fatigue?
During fatigue, neural control of muscles adapts to maintain performance. This involves increased motor unit recruitment, higher firing rates, or altered coordination to compensate for reduced muscle force and efficiency. These adjustments help sustain movement despite fatigue
*What is passive neuronal electrical conductance and its limitations?
Passive electrical conductance refers to the passive spread of electrical signals along the nerve.
Its limitations include signal weakening and slower transmission over long distances, which can reduce efficiency in activating muscles, making active mechanisms like action potentials a necessity ensures reliable signal delivery
*Describe the look up table model?
(What is it, experiment causing rejection, hypothesis on results, actual results and why it was rejected?)
Proposes the brain stores precomputed muscle force patterns for specific movements and retrieves them when needed.
No experiment, just issues/rejection based off computational and storage impracticality.
The hypothesis states the brain can store and retrieve vast numbers of precomputed movements
Rejected due to complexity, storing all movements, velocities and adjustments is beyond the brain capacity, it also cant adapt to changes
*Describe Reflex based model (Sherringtons hypothesis) model?
(What is it, experiment causing rejection, hypothesis on results, actual results and why it was rejected?)
Movements arise from combining reflexes like the stretch reflex, controlled by sensory feedback.
Taub and Berman (1968): Deafferented monkeys (with sensory feedback disabled) could still reach visual targets.
Movements are generated by reflexes driven by sensory feedback. Gamma motor neurons initiate movement before alpha motor neurons.
Deafferented monkeys could reach accurately, indicating movement is not entirely reflex-driven. No gamma motor neuron lead observed in Vallbo’s (1970) study of voluntary contractions.
*Describe the Equilibrium Point Hypothesis (EPH) model?
(What is it, experiment causing rejection, hypothesis on results, actual results and why it was rejected?)
Proposes the brain controls a virtual equilibrium point (desired position) to guide movements, not caring about intermediate forces.
Lackner and DiZio (1994): Coriolis force experiments showed that trajectories mattered and were affected by forces during movement.
The brain only cares about the final equilibrium point, not the trajectory or forces during movement. Movements should remain straight under perturbations, with accurate final positions.
Subjects showed curved trajectories during Coriolis force application, contrary to predictions. Endpoint accuracy errors persisted, refuting the claim that only final positions matter.
*Describe the Direct Cortical Control model?
(What is it, experiment causing rejection, hypothesis on results, actual results and why it was rejected?)
Suggests that the brain plans entire movement trajectories instead of just specifying an endpoint.
Validation - Emerged as a response to failures of EPH in explaining trajectory planning and adaptation.
The brain computes and controls the entire movement trajectory in advance.
This model has not yet been explicitly rejected and is supported by trajectory-sensitive experiments.
*What is optimal control and how the cost is defined?
Optimal Control: A mathematical framework that seeks the most efficient movement strategy by minimizing a “cost” function and highlighting a trade off.. The brain, acting as a controller, adjusts motor commands to balance efficiency, accuracy, and effort, ensuring smooth and effective movements.
Cost Definition: Cost is defined as the penalty related to a movement, including energy expenditure, time taken, or errors made. The goal is to reduce this cost, optimizing performance by achieving the desired outcome with minimal resource use and maximal precision.
*Key concepts of the Optimal Control Model of Reaching and its properties?
The brain minimizes or maximizes a specific cost/benefit associated with movement.
Minimum jerk model = smoothness: The brain minimizes jerk (rate of change of acceleration) to produce smooth, bell-shaped velocity profiles.
Minimum torque/force = energy: The brain minimizes changes in torque or energy expenditure during movement, accommodating forces like inertia
SIgnal dependent noise = uncertainty: Movements are optimized to minimize noise generated by larger or faster control signals, reducing variability and ensuring accuracy.
Optimal Feedback Control: The brain stores policies (rules for action based on the body’s state) rather than precomputed commands, allowing for robustness, real time adjustments and no planning. Flexible based on the task.
*What is optimal feedback control and how the feedback system works?
Optimal feedback control adjusts control inputs based on the system’s current state to minimize a cost function over time. It uses feedback to correct actions, guiding the system toward the desired goal while handling disturbances.
The feedback system measures the current state, compares it to the desired state, and adjusts control inputs to optimize performance and reduce errors in real-time
*What is signal-dependent noise and how that is related to the uncertainty / variability of movement?
Signal-dependent noise is a type of noise that increases with the strength or intensity of a signal. In movement, this means that as the force or effort behind a movement increases, the variability or uncertainty in the movement’s outcome also rises. Stronger or more forceful actions are more prone to greater variability, leading to increased uncertainty or error in the movement.
What are the two empirical observations? Describe them in short?
Fitt’s Law - If you need accuracy you become slow.
Movement and accuracy are inversely related
Two-Third Power Law - If you are making a curved movement you become slow. Curvature and velocity have a proportional relationship.
Two types of dynamics / kinetics ?
Forward - Kinetics to kinematics
Inverse - kinematics to kinetics
How are kinematics and dynamics related?
Kinematics describes motion, while dynamics links motion to forces using Newton’s second law (F = ma).
What is redundancy in kinematics?
Redundancy in kinematics occurs when a system has more joints or degrees of freedom (DOF) than are necessary to perform a given task.
This means there are multiple ways to achieve the same movement or end position, allowing for flexibility and adaptability in motion.
What is localisation and planning? in terms of reaching.
Localisation: Representation of where the object is
Planning: Strategy to reach object based off of the representation
How are voluntary movements hierarchically planned?
Higher brain areas plan broad movements
Lower areas refine and execute specific commands.
What are the key sensorimotor transformations for motor planning?
Converting sensory inputs into motor outputs and translating desired movements into specific muscle commands to execute the action.
What brain area is involved in planning reaching movements?
The posterior parietal cortex
It plays a key role in planning reaching movements by integrating sensory information (such as visual and proprioceptive inputs) to guide the movement toward a target.
What is the evidence for eye-centered planning of reaching?
Bastia et al. (1999) found that the brain represents reaching targets relative to the eyes, not the body.
What did Raibert (1977) and Morasso (1981) show about kinematic planning?
They showed that kinematic planning occurs in end-effector space, focusing on the movement of the hand or tool rather than individual joints.
Why is variability of movement important in motor control studies?
It shows the system’s adaptability in balancing stability and flexibility.
It allows the body to adjust to different conditions, reduces repetitive strain risk, and promotes efficient, resilient motor control.
How does the brain solve kinematics and dynamics problems?
The brain uses internal models to predict and plan spatial relationships (kinematics) and calculate necessary forces (dynamics).
What is an internal model?
An internal model is a neural mechanism that aids in predicting and planning movements by compensating for sensory delays and errors. It allows the brain to anticipate the outcomes of actions, enabling smoother and more accurate motor control.
What are forward and inverse models?
Forward models predict the outcome of movements, while inverse models calculate the motor commands to achieve a desired outcome.
What is a reference copy?
A copy of the motor command sent to an internal model, allowing prediction and comparison with actual movement outcomes.
What brain area is mainly involved in movement execution and control?
The motor cortex is primarily responsible for movement execution and control.
What is the main observation of Graziano 2005’s experiment?
Graziano (2005) found that neurons in the motor cortex encode not just movements but also the perception of body parts in space
What is the directional tuning of motor neurons (Georgopoulos et al 1986)?
Motor neurons in the motor cortex exhibit directional tuning, meaning they fire more strongly for movements in specific directions. This tuning reflects the neurons’ preference for certain movement orientations, contributing to the precise control of movement direction.
What kinds of human movement are controlled by feedforward control?
Feedforward control is used for rapid, well-learned movements, like throwing or catching.
What are the two main strategies of feedback controllers to deal with sensorimotor delays?
1) Delay compensation – anticipating delays.
2) Posture adjustments – correcting movement after a delay.
How is the forward internal model used for anticipatory feedback control?
The forward internal model predicts the sensory consequences of movements, allowing anticipatory adjustments before feedback is available.
When are feedforward and feedback controllers used together?
They are used together in tasks requiring both fast, predictive control (feedforward) and real-time error correction (feedback).
What is the observer model?
The observer model is a system that estimates unmeasured variables (like forces) from available sensory information to guide movement control.
How does optimal feedback control differ from the optimal control model?
The Optimal Control Model focuses on planning the best strategy to minimize a cost function before movement, often using feedforward control.
Optimal Feedback Control adjusts control inputs in real-time based on feedback, making it more adaptive to changes and disturbances during movement.
While both aim to optimize performance, feedback control continuously refines the movement as it happens.
Sensory Info required for localisation and planning?
Extrinsic information: spatial location of target gathered by visual and auditory info.
Intrinsic information: Bodies state (kinetic and kinematic info) provided by -
muscle spindles - length and velocity of each muscle
golgi tendon organs - force produced by each muscle mechanoreceptors - force exerted/received on skin
Coordinate systems during planning?
Extrinsic - Allo/Egocentric, relative to body or external space, eye centered or hand
Intrinsic: Internal representations such as joint angles and muscles lengths
Sources of Variability?
Input variability: Sensory noise affects the estimation of object location and movement goals.
Intrinsic variability: Neural noise = fluctuating membrane potentials, limits accuracy and precision.
Output variability: Increased motor neuron and muscle contraction/excitability, this is known as signal dependent noise
Types of models
Internal/Forward - Predicts the outcomes of motor commands by simulating how the body and environment will respond.
Inverse - Translates desired outcomes (behavioral goals) into specific motor commands
Process of movement planning as a whole?
- Extrinsic Planning: Defines the goal in external space (e.g., “grab the apple”) using sensory input like vision or hearing.
- Coordinate Transformations: Converts the goal from external coordinates (eye/hand-centered) to internal body coordinates (joint angles/muscle lengths).
- Intrinsic Planning: Translates the transformed goal into specific motor commands for muscles and joints.
- Forward & Inverse Models:
Inverse Model: Determines the motor commands needed for the goal.
Forward Model: Predicts the outcome of those commands for error correction.
- Feedback Integration: Real-time sensory feedback adjusts movements, ensuring accuracy and adaptability.
Flow: High-level goals → Spatial transformations → Motor commands → Real-time adjustment.
Role of primary motor cortex in terms of movement planning?
Executes movements by encoding direction and location
Neurons tuned for final reach position
Observer model?
Combines predictions and actual sensory feedback.
Balances “expected” and “unexpected” feedback based on uncertainty, crediting improvement.
