Action Flashcards
How long did my guy Mike the headless chicken live and how was he fed?
Lived for 18 months from 1945- 1947 (RIP brother) and was fed with fluids and corn through a hole in his small intestine.
Also earned 4.5k (50k now) per month so he was all about the securing the bag even when headless.
In what way is the communication and translation of action in the brain the opposite of the visual system?
The hierarchical organisation of motor pathways go from ‘concept’ to muscle control
What is the final common pathway of all motor output?
The ventral horn Alpha motor neuron
What can be done to test the response of the alpha motor neuron? Describe this
The stretch reflex:
A hammer hits below the knee and stretches the quadriceps. The muscle spindles in the quadriceps femoris muscle acts as a stretch receptor and shoots a signal through the sensory neuron to the spinal cord. A signal is then sent through the alpha motor neuron causing the muscles to contract and you to kick out.
In which ‘root’ are each of these neurons located
sensory neuron- dorsal root
motor neuron- ventral root
Which parts of the spinal cord control 1) posture and 2) fine movements?
Dorsolateral part- distal muscles; fine movements
Ventromedial part; Proximal muscles; posture
Name and describe two diseases which affect the alpha motor neuron
Lou Gherig’s disease or ALS: Amyotrophic Lateral Sclerosis
Poliomyelitis: Viral infection that selectively attacks alpha motor neurons
Give an example of a constant requirement of the stretch reflex
keeping posture
What function does the gamma motor neuron carry out during voluntary movement and why?
Gamma motor neurons contracts muscle spindle during voluntary movement so that they stay ‘short enough’ to sense stretching when muscles are short
What brain area do these gamma motor neuron get input from when carrying out this function?
Pons
What two types of muscles fibres are involved in this reflex?
Larger extrafusal muscle fibres and smaller intrafusal muscle fibres within the muscle (see copy for diagrams)
What else happens when the the hammer hits the knee and stretches the quadriceps?
The reciprocal inhibition of antagonistic muscles. When extensor (quadriceps) contracts, Flexor relaxes.
Describe this reciprocal inhibition of the antagonistic muscle in 3 steps
1) Afferent impulses from stretch receptor to spinal cord via the sensory neuron. An interneuron then activates =>
2) Efferent impulses to motor neurons (serving quadriceps) cause contraction of the stretched muscle that resists/ reverse the stretch
3) Efferent impulses to antagonist muscles are damped (reciprocal inhibition) via the motor neuron serving antagonist muscle group (hamstrings)
What is meant by the crossed extensor reflex?
As one limb flexes, the other extends (walking, keeping balance when retracting your leg from standing on a pin)
However walking also utilises a different process to the crossed extensor reflex. Describe and name this process
Due to the central pattern generator, the spinal cord can do walking ‘all on its own.’ The central pattern generator ‘creates’ locomotion movements all on its pwn. The only thing that is requires in a high level ‘gait’ command (or it can be set in motion by proprioceptive feedback).
Give an example of an experiment which demonstrates this central pattern generator
A decerebrated cat (high level spinal cord cut) walks on a treadmill, in different tempos.
What other movements are fully automatic and highly coordinated in this manner? (3)
Swallowing, breathing orientating
Describe six steps which are involved in swallowing
1) When a person is not swallowing, the oesophageal sphincter muscle is contracted , the epiglottis is up and the glottis is open, allowing air to flow through the trachea into the lungs
2) The swallowing reflex is triggered when a bolus of food reaches the pharynx
2) the larynx , the upper part of the respiratory tract moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea
4) The oesophageal sphincter relaxes, Allowing the bolus to enter the oesophagus
5) after the food has entered the oesophagus, the larynx moves downward and opens the breathing passage
6) Waves of muscular contraction (peristalsis) move the bolus down the oesophagus to the stomach
What is the function of the withdrawal reflex
Protecting from damage
Describe the steps involved in the withdrawal reflex
Pain receptors in the skins send an impulse through the sensory nerve (afferent nerve) to the spinal cord, where it connects to the motor neuron through an interneuron. This neuron then causes the muscles to contract and withdraw the part being stimulated
What reflex protects from overload?
Golgi tendon reflex protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load
Explain the steps involved in the golgi tendon overload
=>Muscle contraction stretches the golgi tendon organ.
=>If excessive load is placed on muscle, the golgi tendon organ fires.
=> The motor neuron is then inhibited
=> The muscle relaxes
=> the load is dropped
What name is given to this type of motor control which is responsible for these reflexes, antagonistic relaxation, central pattern generators and others?
Lower motor control (because they all take place in the spinal cord)
To what extent is the actions we do carried out by the lower motor control?
They do all the ‘work.’ Only thing that is needed is a central ‘command.’ And some checks and balances…
What explanation can you give for Mike walking around as a headless chicken?
The incision was likely made near where the hindbrain and midbrain meet the forebrain
Of the several system which activate the neurons in the spinal cord, which is the most important in humans and most mammals? Describe where it passes through
The cortico-spinal pathway;
Motor cortex
Medulla
Spinal cord
It is dorsolateral
Two other originate in the midbrain, what are these systems and from where do they originate?
Rubro-spinal- Right red nucleus
Tecto-spinal- Superior nucleus
Where do the last two systems originate?
Vestibulo-spinal- Vestibular nucleus
Reticulo-spinal- reticular nucleus
Both of these are located in the medulla and go from there to the spinal cord
What name is given to separate the system originating from the motor cortex and the other systems?
Motor cortex- Pyramidal
Others- Extrapyramidal
Other than location of origin how else do the extrapyramidal systems differ from the Cortico-spinal system? (specifically location of tract in spinal cord and function)
Cortico-spinal; dorsolateral tract in spinal cord, responsible for distal, fine movements. The movements from this system also tend to be deliberate movements.
Extrapyramidal systems; ventromedial tract in spinal cord, responsible for proximal, coarse movements as well as posture, orientation and balance
What functions does the rubrospinal tract carry out?
Controls muscle tone and distal limb muscle that perform more precise movements
What functions does the tectospinal tract carry out and where does it originate?
upper motor neurons in superior and superior and inferior nuclei
They receive visual (superior) and auditory (inferior) info
Reflex-like orienting response: head, neck upper limbs move towards visual and auditory stimuli
Where does the vestibulospinal tract receive information and what functions does it carry out?
Info from the vestibulococlear nerve (inner ear)
Monitors position and movement of the head to maintain Posture and Balance
What functions are carried out by the reticulospinal tract?
controls many reflexes (excitability)
Where does the pyramidal start? (3)
upper motor neurons of primary motor cortex and other cortical areas (SMA, PMC). Axons descend into brain stem and spinal cord to synapse on lower (alpha) motor neurons.
What two tracts are there within the pyramidal system?
cortico-bulbar tract
Corticospinal tract
Where is the corticobulbar tract located and what functions does it carry out?
towards cranial nerve (nerves around the skull) nuclei that move eye, jaw, face, and some muscles of the neck and pharynx (throat)
Where can the corticospinal tract be seen?
Visible along ventral surface of medulla oblongata as pair of thick bands, the pyramids
What is the function of the corticospinal tract?
Control of all non-facial somatic muscles
Where does the corticospinal tract cross to the contralateral side of the body? (2)
Lateral CS tract crosses at pyramidal decussation at a higher level (around medulla)
Anterior CS tract cross to the opposite side of spinal cord at lower level in anterior white commissure (in the spinal cord)
What typically result in damage to the corticospinal tract? (3)
Paralysis/ paresis
Spasticity/ flaccidity
Changed reflexes: babinski sign
What is meant by spasticity/ flaccidity?
A pattern of weakness in the estensors (upper limbs) or flexors (lower limbs) known as ‘pyramidal weakness’
What is meant by the Babinski sign?
Instead of the normal reflex of you toes and foot curling (flexion) when your foot is stroked, your big toe extends and the rest fan out and throw up gang signs
What therapy works well for pyramidal weakness?
Constraint induced motor therapy: forcing the weak parts to work by tying up the strong half
What two environmental factors did the Boston dynamics robots struggled with?
Perturbations
- Outside forces
- Uneven terrain
Slopes
-Require different balance setting between agonist and antagonist
What kind of damage can present similar problems in humans? (struggling with motion, balance)
When they lack a functional cerebellum
How does the cerebellum help this movement?
It provides a subcortical-cortical loop. This assists in the fine tuning of movements (lesions or alcohol result in ataxia), timing of automated movement sequences, motor memory and also perhaps timing in general.
How does the arm positioning and EMG differ between a normal subject and cerebellar patient
There is a slight overshoot of arm positioning in normal people then they correct it to the right place. In a cerebellar person, there is a larger overshoot, before they overshoot in the opposite to correct their self before overshooting again a couple times in a waving motion to get to the right place.
This is reflected in the EMG with a bump of agonist activity then a bump of antagonist activity. In the cerebellar patient, a number of bumps in each is observed in the activity.
Describe the 7 steps involved in the subcortical-cortical feedback loop
1) The motor cortex sends action potentials to lower motor neurons in the spinal cord
2) Action potentials from the motor cortex inform the cerebellum of the intended movement
3) Lower motor neurons in the spinal cord send action potentials to skeletal muscles, causing them to contract
4) proprioceptive signals from the skeletal muscles and joints to the cerebellum convey information concerning the status of the muscles and the structure being moved during contraction
5) The cerebellum compares the information from the motor cortex with the proprioceptive information from the skeletal muscle joints
6) Action potentials from the cerebellum to the spinal cord modify the stimulation from the motor cortex to the lower motor neurons.
7) Action potentials from the cerebellum are sent to the motor cortex to modify its motor activity
What three parts make up the cerebellum? Name their associated function
Spinocerebellum- balance, walking
Neocerebellum- Control of fine movements
Vetibulocerebellum- coordination of eye movements
(see copybook for diagram)
Which of these areas is most affected by alcohol use?
Spinocerebellum
How is damage to the neocerebellum tested?
Finger to nose test as well as their speech
What reflex is the vestibulocerebellum responsible for?
VOR (vestibulo-occular reflex) (looking at one object while, moving rotating head etc)
What is the name given to the symptoms of cerebellum damage and what are these symptoms
Cerebellar ataxia; endpoint tremor, slurred speech (pointing nose task, or pointing anywhere)
What four main structures are there to the basal ganglia?
Striatum,
Globus Pallidus,
substantia nigra,
Subthalamic nucleus
(diagram in copy)
How is the globus pallidus divided?
Externa and Interna
How is the striatum divided?
Caudate nucleus
Putamen
What neurotransmitter is the substantia nigra associated with?
Dopamine
What is the basal ganglia important for?
The control of movement- whether you move or not
What two systems does it use to do this?
Direct and indirect pathway
Describe the direct pathway
Cortex =(+)=> striatum =(-)=> Globus pallidus i/ Substantia nigra (reticular)
It therefore inhibits the Globus pallidus i/ Subcortical nucleus r
Think of or draw the pathways of the basal ganglia
Check copybook/ 7.29 of pt 2 lecture 8 for answer
From the globus pallidus and substantia nigra r, how does this effect the cortex?
They have a tendency to inhibit the thalamus, and only the thalamus excites the cortex, and only the cortex excites the brainstem/ spinal cord so if you increase activation of the cortex by stimulation of the thalamus you get more movement, if you inhibit activation of the thalamus you get less movement.
With this knowledge, what happens when there is activation of the direct pathway?
There is more movement
The striatum inhibits the globus pallidus i/ Substantia nigra r which causes less inhibition to the thalamus which means more activation of the cortex and brainstem
Describe the indirect pathway
The striatum inhibits Globus Pallidus e
Globus Pallidus e inhibits GPi/SNr, therefore this inhibitioned is lessened
GPi/ SNr activity increases, more inhibition of thalamus
Less activity of thalamus, less movements
What is meant by the dam metaphor of the basal ganglia
You can only execute one motor response or movement at a time mostly so the basal ganglia holds back the other movements and only allow for the most active response
Name two diseases which affect this communication in the basal ganglia and where they affects it
Huntington’s disease
Parkinsons diseas
Where does Huntington’s disease affect the basal ganglia and what affect does this have on a person?
Affects the inhibition of the globus pallidus by the striatum, this means more inhibition of the GPi/ SNr and therefore less inhibition of the thalamus= more movement.
How does Parkinson’s disease affect the basal ganglia (2) and what affect does this have on a person?
It prevents the inhibitory and excitatory effects of the Substantia nigra c.
The substantia nigra c activates the D1 receptor in the striatum which is responsible for the inhibition of the GPi/SNr in the direct pathway. This means less activation of the thalamus and therefore less movement.
The substantia nigra c also inhibits the D2 receptor in the striatum which is responsible for inhibiting the Globus Pallidus e in the indirect pathway. As well as inhibiting the GPi/ SNr, the GPe inhibits the STN which activates the GPi. This means, while the inhibitory effects of the GPe on the GPi/ SNr are inhibited more, the greater activation of STN means more excitatory signals to GPi/SNr. This means even less movement.
This makes it difficult for the patient to move at all
What are the names given to the symptoms of huntingtons disease? (2)
Chorea, hyperkinesia
How is huntingtons disease contracted?
Hereditary (quite rare, one in 10,000)
What is the cause of parkinsons disease?
Drugs/ Genes (pretty common 1:100)
Age of onset is usually over 50
What names are the symptoms of parkinsons? (3)
Tremor of hands
Rigidity
Bradykinesia (slow and small movements)
What medication is available for parkinsons?
L-dopa (artificially providing brain with dopamine since brain can no longer do this)
Stem-cells
DBS
Describe the unified parkinsons disease rating scale
0- normal
1- walks slowly, may shuffle with short steps, no festination ( involuntary gait in which stride length is shortened and steps become progressively more rapid) or propulsion
2- walks with difficulty, little or no assistance, some festination, short steps or propulsion
3- severe disturbance, frequent assistance
4- cannot walk
Name three cortical areas with cortico-spinal fibers and their respective functions
M1- direct motor control
PMC ( with PPC): externally guided , stimulus driving action (e.g. catching ball)
SMA (with PFC): internally guided action (e.g. deciding which object to pick up)
PMC: Premotor cortex
PPC: post parietal cortex
SMA: supplementary motor area
PFC: prefrontal cortex
Check copy for diagram
Name two syndromes which arise from lesions to these areas
Hemiplegia
Apraxia
What lesions cause Hemiplegia and what are the symptoms?
Half sided paralysis due to lesions of upper motor neurons coming from M1
How is apraxia defined by the symptoms
Loss of motor skill (which is not due to muscular, upper (M1) or lower motor (spinal cord) neuron deficit)
What lesions can cause apraxia?
SMA
PMC
PPC
Name and describe two types of apraxia
Ideomotor Apraxia: rough idea of movement can be executed (SMA, PMC)
Ideational Apraxia: No idea what to do, uses wrong tools (PPC)
How is ideomotor apraxia selective?
Many movements can be roughly executed, some totally not
What do these reveal about the post parietal cortex?
Very important for control of movement
Which brain areas encode movement direction (2)
In M1 (and PMC) neurons encode movement direction
What do individual motor neurons incode for ?
Vector of movement i.e are tuned for the direction of limb movement
Tuning is fairly broad in individual M1 cells, how is actual movement executed?
Actual movement is encoded by the vector sum of population of M1 cells.
What is meant by the affordance competition hypothesis?
Sensory inputs create many potential motor responses (affordances). Depending on needs and potential payoffs, one of these has to be selected
What brain area could play the biggest role in this affordance competition?
Bonus: What previously mentioned area also plays a considerable role in this?
The premotor cortex encodes population vectors of multiple potential actions.
( Basal ganglia decide which signal is most activated and allow that one ‘through.’)
Describe a study which provides evidence for this activity in the PMC
A task where monkeys are shown two red and blue spatial cue, before disappearing in a memory period. A colour cue is then shown and the monkey is trained to reach for the previous position of the colour shown.
The premotor cortex encodes population vectors of multiple potential actions (go to red or blue) until colour cue is given to perform one action and not another.
A surge in activity for ‘Go to red’, suppression of activity for ‘go to blue’ after cue is observed.
PMC also has neurons for performing other functions, what are these functions? (2)
Different types of movements regardless of where and where to
e.g precision grip vs power grip (reach, hold, tear….)
Mirror neurons: neurons that encode an action, yet are also activated by seeing (or hearing the same action performed by others)
Where else are mirror neurons found?
Widespread in motor cortex and parietal cortex (particularly PMC and PPC)
What possible result of mirror neurons is taking advantage of in marketing?
Contagious behaviour (yawning etc)
If typing a word, you can look at the keyboard and judge the distance between your finger and the relevant letter before executing the movement. How is this possible? (name relevant brain area)
The posterior parietal cortex (PPC) translates movement from retinal (eye centred) to hand-, head-, or body-centred reference frames.
Describe an experiment which examines ‘mind reading’ of potential movements is possible and the neural mechanisms measured
As previously mention individual M1 cells are broadly tuned. Actual movement is encoded by vector sum of M1 cells. This is used to ‘read’ the planned movement from the motor cortex. Rats can be trained to use a lever to control a robot arm that delivers them droplets of water. In the second stage, however, the signal from the primary motor cortex is used to move the robot arm when the rat pushes the lever, not the actual lever.
What practical applications does this finding have. Describe how this works
This can be used to ‘read’ the planned movement from the motor cortex and use this in prosthetics. A computer algorithm is trained to ‘recognise’ specific patterns of neural activity (combinations of activity increases and decreases of specific intentions to move).
Name some tasks required in the making of these devices (4)
- Training a subject to turn a motor cortex on and off (biofeedback)
- Training the classifier to recognise specific commands
- Testing the interface with online movements
- decoding intentions from the brain
