Week 10: Decision Making

Question 1

What are the 3 types of muscles?

Answer 1

1) Smooth Muscles
2) Skeletal (striated) Muscles
3) Cardiac Muscle

Question 2

Where are smooth muscles usually found?

Answer 2

Found in intestines and other organs

Question 3

What do smooth muscles consist of? What are they controlled by?

Answer 3

Consist of long, thin cells

Generally not under conscious control; under control of autonomic nervous system

Question 4

What do skeletal (striated) muscles consist of? What are they controlled by?

Answer 4

Consist of long cylindrical fibres with stripes

Controlled by the central nervous system (CNS)

Question 5

Where are skeletal muscles usually found and what do they control?

Answer 5

Help control movement in relation to the environment

Eg. muscles in arms and legs

Question 6

Where is the cardiac muscle found?

Answer 6

Found in heart

Question 7

What does the cardiac muscle consist of?

Answer 7

Consists of fibres that fuse together at various points

Fusion causes cardiac muscles to contract together, instead of independently

Question 8

Each muscle is composed of many _____.

Answer 8

Muscle fibres

Question 9

Each muscle fibre receives information from ____ axon(s). 1 axon may innervate ____ muscle fibre(s).

Answer 9

Each fiber receives information from only one axon, but one axon may innervate more than one muscle fiber.

Question 10

What is the significance of the axon to muscle fibre ratio?

Answer 10

Axon to muscle fibre ratio:
Eg. Eye muscles – ratio of 1 to 3
Eg. bicep muscle – ratio of 1 to 100.
In eye muscles, 1 axon controls only 3 fibres. In bicep muscles, 1 axon controls 100 fibres. This means that the eye can move more precisely than the bicep.

Question 11

What is the neuromuscular junction found in skeletal muscles?

Answer 11

A synapse where motor neuron axon transmit information to muscle fibres

Question 12

At the neuromuscular junction, what neurotransmitter does the axon of the motor neuron release?

Answer 12

Every axon releases acetylcholine, which always excites the muscle to contract.

Question 13

What happens when there is a deficit of acetylcholine or acetylcholine receptors at the muscle fibres?

Answer 13

movement is impaired

Question 14

At the neuromuscular junction, depolarisation leads to the opening of _____.

Answer 14

voltage gated Ca2+ channels.

Question 15

What happens after the voltage-gated Ca2+ channels are opened?

Answer 15

Ca++ flows into the cell, since it is attracted by lower concentration, as well as the negative membrane potential (ie. cell is more negative inside presynaptic neuron).
Entrance of Ca++ leads to fusion of vesicles filled with acetylcholine. Vesicles filled with acetylcholine is released to the synaptic cleft.

Question 16

What happens after acetylcholine is released into the synaptic cleft?

Answer 16

Acetylcholine binds to a ligand-gated channel that is selective to positive charges. When this channel opens, Na+ flows in, and K+ flows out of the cell.
Inflow of Na+ leads to depolarisation of the membrane
Leads to opening of voltage-gated Na+ channels in the vicinity of the synapse. An action potential is hence generated in the muscle fibre, leading to its contraction.

Question 17

What is a proprioceptor?

Answer 17

a receptor that detects the position or movement of a part of the body. Muscle proprioceptors detect the stretch and tension of a muscle and send messages to spinal cord to adjust its signals. The spinal cord sends a signal to contract it reflexively.

Question 18

What are 2 types of proprioceptors?

Answer 18

1) Muscle spindle

2) Golgi tendon organ

Question 19

Where is the muscle spindle located and what does it do?

Answer 19

Parallel to the muscle that responds to a stretch
When muscle spindle is stretched, its sensory nerve sends a message to a motor neuron in the spinal cord, which in turn sends a message back to the muscles surrounding the spine, causing a contraction.

Question 20

How is the muscle spindle’s mechanism a negative feedback?

Answer 20

when a muscle and its spindle are stretched, the spindle sends a message that results in a muscle contraction that opposes the stretch.

Question 21

Where is the golgi tendon organ located and what does it do?

Answer 21

Located in tendons at opposite ends of a muscle
Act as a brake against excessively vigorous contraction
Some muscles are so strong they could damage themselves if too many fibres contracted at once
It detects the tension from a muscle contraction.
Impulses travel to the spinal cord, where they excite interneurons that inhibit motor neurons.

Question 22

What are the 2 different motor pathways?

Answer 22

1) Lateral Corticospinal Tract

2) Medial Corticospinal Tract

Question 23

What does the lateral corticospinal tract control?

Answer 23

Controls precise movements of extremities (ie. lateral parts of the body.) Eg. hands, fingers, feet

Question 24

What does the medial corticospinal tract control?

Answer 24

Controls muscles in the medial parts of the body muscles of the neck, shoulders, and trunk.

Question 25

Describe the lateral corticospinal tract.

Answer 25

Axons originate from upper motor neurons in primary motor cortex (M1) & the red nucleus of the midbrain
Large axonal tract generated by these neurons bundle up at the pyramids of medulla, and move towards final targets in the spinal cord.
Tract crosses to contralateral side to synapse onto lower motor neurons that control muscles in the opposite side of the body.
Right hemisphere controls left extremities, vice versa

Question 26

Describe the medial corticospinal tract.

Answer 26

Controls muscles of the neck, shoulders, and trunk.
Axons originate from neurons in multiple cortical areas:
Primary motor cortex, premotor cortex, temporal lobe
Axons also originate from subcortical structures in midbrain: Tectum, reticular formation, vestibular nuclei
Axons then go to both sides of the spinal cord

Question 27

_____ and _____ are important in modulating movement control

Answer 27

cerebellum

basal ganglia

Question 28

What are the effects of damage to cerebellum?

Answer 28

Damage leads to trouble with rapid movements that require aim, timing, and alternation of movements
Eg. tapping a rhythm
Recently discovered that it is implicated in modulating other non-motor processes (eg. keeping track of time)

Question 29

The basal ganglia is primarily composed of: (3 structures)

Answer 29

Dorsal striatum (caudate & putamen), ventral striatum, and globus pallidus

Question 30

The ______ form the main component of the ventral striatum.

Answer 30

Nucleus accumbens

Question 31

Describe the cortico basal ganglia loop.

Answer 31

input from cerebral cortex –> caudate & putamen –> globus pallidus –> midbrain & thalamus –> motor & prefrontal cortex
Basically, cortical information passes through basal ganglia, only to go back to the cortex

Question 32

How is the cortico basal ganglia loop different from that of thalamic nuclei?

Answer 32

Thalamic nuclei receive sensory inputs from the periphery and project to cortex. (eg. transmit auditory of visual information to cortex). But in the cortico basal ganglia loop, input comes from cortex, goes through basal ganglia, and go back to cortex

Question 33

What does the basal ganglia do? What happens if there’s a damage to the basal ganglia?

Answer 33

Basal ganglia inhibits movements. Damage to this area (eg. Huntington’s disease) results in decreased inhibition, and therefore leads to involuntary, jerky movements.

Question 34

Which 3 areas in the cortex are important for movement planning?

Answer 34

Posterior parietal cortex
Premotor cortex (PMC)
Supplementary motor cortex (SMA)

Question 35

What does stimulation of the posterior parietal cortex do?

Answer 35

Patients reported intention to move. Stronger stimulation led some to report that they did move even though they haven’t moved. This happens in absence of visual feedback.

Question 36

When is the posterior parietal cortex active?

Answer 36

Active during movement planning.

Question 37

When is the premotor cortex most active?

Answer 37

Most active immediately before a movement

Question 38

What do neurons in the premotor cortex do?

Answer 38

Neurons in this area have sustained activation to specific movements, even if the plan precedes the execution of the movement by many seconds. Eg. If I ask you to raise your hand, but only after I say the word peanut. … “‘peanut”
During waiting period, cells in premotor cortex were with selectivity to right arm and selectivity to raising the arm were active. (same for direction selectivity)

Question 39

What is the supplementary motor cortex (SMA) involved in?

Answer 39

Involved in motor imagery, biannual motor tasks and sequential motor action. Important in initiating actions based on self-generated time estimates. (eg. Neurons in SMA will be activated when subject plays a complicated sequence on the piano)

Question 40

Where are mirror neurons found?

Answer 40

Premotor cortex.

Question 41

Briefly describe what mirror neurons do and their possible significance.

Answer 41

Seeing someone angry, frustrated, happy or sad, activates mirror neurons as if you are having the same experience yourself. We are soft wired to experience another person’s plight.
Suggests that humans are soft wired for sociability, attachment, affection, companionship

Question 42

When are mirror neurons active?

Answer 42

Mirror neurons are active both during preparation for a movement and while watching someone else perform the same or similar movement.

Question 43

In Libet’s study about cconscious decision, what does the readiness potential EEG signal show and what did it suggest?

Answer 43

Brain activity preceded even the decision to make the decision by as much as 300ms
Suggests that brain activity began before the person’s conscious decision. Hence, it suggests that your conscious decision does not cause your action, but rather, you become conscious of the decision after the process leading to action has already been underway for about 300ms.

Question 44

What is value-based decision making?

Answer 44

Involves the selection of action based on the value assigned to their outcomes

Question 45

What are the 3 types of factors that influence decisions?

Answer 45

1) Hedonic factors
2) Homeostatic factors
2) Cognitive factors

Question 46

What are the 3 forms of reward discounting?

Answer 46

Probability Discounting
Delay (temporal) discounting
Effort Discounting

Question 47

What is the key brain region involved in decision making?

Answer 47

medial prefrontal cortex (MPC)

and also Posterior Cingulate Cortex (PCC)

Question 48

Motor symptoms in Parkinson’s disease is due to the degeneration of which part of the midbrain?

Answer 48

Degeneration of dopaminergic neurons in the substantia nigra that produce dopamine

Question 49

The midbrain is involved in what functions?

Answer 49

Generated of eye movements (premotor nuclei)
Processing of visual information related to visual reflexes (superior colliculus)
Processing of auditory information (inferior colliculus)
Ascending modulatory source of Dopamine (substantia nigra and ventral tegmental area)

Question 50

What is Parkinson’s Disease characterised by?

Answer 50

Characterised by rigidity, muscle tremors, slow movements, and difficulty initiating physical and mental activity. Have difficulty with spontaneous movements in the absence of stimuli to guide their actions.

Question 51

Explain how environmental influences can lead to Parkinson’s disease.

Answer 51

MPTP destroyed all dopaminergic neurons. Led to the discovery that environmental influences could affect dopaminergic neurons selectively. Hazardous chemicals in herbicides and pesticides resemble MPTP. May explain why Parkinson’s disease is more common among farmers who have had years of exposure to these compounds.

Question 52

Describe 2 types of treatment for Parkinson’s disease.

Answer 52

1) L-DOPA: Used instead of dopamine itself because it can cross the blood-brain barrier, while dopamine cannot. But unpleasant side effects and does not prevent further loss of neurons
2) Deep brain stimulation

Question 53

Huntington’s disease is associated with gradual, extensive brain damage in the _______.

Answer 53

Primarily in the basal ganglia and cortex. (caused by genetic abnormality)