The Brain Mechanisms of Action and Decision Flashcards
What is the role of the basal ganglia in movement?
Gating proper initiation of movement - planning, initiating, and directing voluntary movements.
What is the role of the cerebellum in movement?
Sensory motor coordination.
Basic movements and postural control.
Where do sensory inputs go?
Into the spinal cord and brainstem circuits
What do the upper motor neurones consist of?
Motor cortex and Brainstem centres
What are upper motor neurones?
Confined to the central nervous system - responsible for the initiation of voluntary movements.
What are local circuit neurones?
involved in short non-complex processes locally - short neurones that do not extend very far.
What are lower motor neurones?
The peripheral nervous system that connects the CNS with the muscle to be innervated.
Where do simple reflexes occur?
They are mediated at the level of the spinal cord?
Give an example of posture and postural change
Standing, balancing
Give an example of locomotion
Walking, running
Give an example of sensory orientation
Head turning, eye fixation
Give an example of species specific action patterns
Ingestion, courtship, escape/defence, grooming, gestures
Give an example of acquired skills
Dressing, painting, driving, sports, guitar hero, texting, etc
What is leprosy and how does it affect the PNS? (4)
- Caused by a bacterial infection
- Peripheral nerves thicken, disrupting afferent and efferent signals
- Thermal sensation usually goes first, followed by pain and touch
- Inability to feel pain can result in severe limb damage
What is the difference between afferent and efferent signals?
Efferent pathways carry signals AWAY from the CNS - signals that your brain sends to tell your body to do something.
Afferent signals come from outside stimuli and tell your body what they are sensing e.g. temperature.
What are fasciculations?
Spontaneous contractions
How are all voluntary and reflex movements defined?
By making striated muscles contract
How do we define a skeletal muscle?
When at least one end of a striated muscle is connected to a bone through a tendon
Why are muscle fibres striated?
Because of regular bands composed of proteins actin and myosin.
A sarcomere is the basic unit of striated muscle tissue.
How do we distinguish between actin and myosin?
Actin = thin Myosin = thick
What is a motor unit?
The motor neuron and all the fibres it controls
How do motor neurones control muscles?
It sends efferent signals and voluntary muscle contraction is initiated by nerve impulse via the PNS. A single motor neurone then controls several muscle fibres.
How does Curare toxin affect the nervous system? (4)
- Acetylcholine receptor blocked in muscle tissue
- inhibits muscles within 25 mins
- inability of the muscle to respond to motor nerve stimulus
- no contraction of muscle fibres
How does Myasethenia Gravis affect the nervous system?
- Abnormality in acetylcholine receptors
- People with this condition are very weak as they can only activate a few of their striated muscle fibres
- Trouble smiling
How do we make a sustained movement? (3)
- single action potential travels to a lower motor neurone and leads to a single muscle twitch
- a train of action potentials give rise to a sequence of twitches
- if they arrive within 10-100ms of each other, the contractions add up and give rise to large and prolonged contractions.
What are tetanic contractions?
Large and prolonged contractions
How can lower motor neurones be damaged? (4)
- Motor neurone disease
- Trauma where a peripheral nerve is cut
- Polio
- Alcohol
What are the symptoms of lower motor neurone syndrome? (4)
- Paralysis
- Muscle wasting
- No reflexes
- Fasciculation
What is a motor program?
An abstract representation of movements that centrally organise and control the many degrees of freedom involved in performing an action
What is the role of the SMA?
Supplementary Motor Area - well-learned actions that do not place strong demands on monitoring the environament.
What is the role of the PMC?
Primary Motor Cortex - responsible for the execution of all voluntary movements of the body
- the ‘doing’ area
What is the role of the PPC in decision making?
Posterior Parietal Cortex - the ‘planning’ area.
Also involved in spatial reasoning and attention.
What is the role of the PMA?
Premotor Area - links action with visual objects.
Selects sequences of appropriate movements.
Modulates primary motor cortex.
An ‘intention’ area.
What is somatotopic organisation?
The point-for-point correspondence of an area of the body to a specific point on the nervous system.
What is apraxia?
The inability to carry out movements in response to commands
- damage to the posterior parietal cortex
- difficulty in motor planning to perform tasks or movements when asked
- this is despite understanding the command and being motivated
How would we describe the organisation of our motor areas?
Hierarchical
What is special about a sea squirt?
- The larva is relatively complex
- Contains a primitive spinal cord, a tail for swimming, brain-like ganglion
- This is because once a sea squirt finds somewhere to live, it doesn’t need to move
Why does cerebellum mean little brain?
- Takes up 10% of the brain
- Packs a high number of neurones
Which parts of the brain are involved in the ‘reaching’ action?
Transforming visual info about the location of objects in extrapersonal space into the direction of a reaching movement - path connects the parieto-occipital extriate area (PO) and the dorsal premotor area (PMd)
Give examples of sensorimotor transformations
Reaching, grasping
What parts of the brain are involved in the ‘grasping’ action?
Transforming visual info about the properties of objects such as shape and size, into commands for effective grasping - path connects the dorsal extriate (ES) cortex and the ventral premotor area (PMv)
Why is the parietal cortex important for object manipulation?
Supports our sense of spatial awareness and helps us to direct eye movements and reaching and grasping and point in object manipulation, and also our sense of touch.
Also has strong connections with the frontal lobe.
What is optic ataxia? (3)
- Inability to reach accurately under visual guidance
- Reaching accurately involved reaching in the right direction, with the correct grip scaling and grip orientation
- visual guidance means being able to see both the target and the hand throughout
What type of deficit is optic ataxia?
- Not just due to a single basic sensory or motor deficit
- Can affect one limb or both hemispheres - so it’s not purely physical or spatial disorder
- Can also affect both or one limb in only one hemisphere - so it’s not purely a motor disorder
- It’s a problem of converting visual feedback into actionable motor content
What are linking sequences?
Movements that are chained together to satisfy goals
What does deactivation of the SMA produce?
Severe disruption of learned sequences (SMA)
Why can the cerebellum be called ‘the silent area’?
Because the electrical signals in the cerebellum don’t seem to cause any conscious sensation and rarely causes any motor movement
What is the cerebellum used for in advanced movement? (4)
- Coordination of voluntary motor movement
- Helps maintain balance and equilibrium
- Helps with muscle tone
- Helps with rapid movements