Chapter 11- Motor control and plasticity

Question 1

How does the skeletal system influence behavior?

Answer 1

Some properties of behavior arise from physical characteristics of the skeleton. The types of joints determine the types of movements that are allowed- some joints only allow movement in one direction, while others allow movements in multiple directions.

Question 2

How do muscles control the actions of the skeletal system?

Answer 2

Muscles work through contraction (shortening), so the skeletal connections of the muscle provides information about the types of movement it can cause. Properties of a muscle can influence the timing of behavior and the forces that are generated.

Question 3

Antagonists

Answer 3

When one muscle group contracts, it stretches the other group. Biceps and triceps- when the biceps contract, the triceps relax and vice versa.

Question 4

Synergists

Answer 4

Muscles that contract together. Act in a coordinated manner- speech requires the coordinated movement of muscles controlling the mouth/lips, tongue, and other structures

Question 5

How do muscles work on the molecular level?

Answer 5

A skeletal muscle is composed of thousands of voluntary muscle fibers. Skeletal muscles have a striated (striped) appearance due to thick and thin filaments actin and myosin overlapping. When the muscle contracts, the overlap increases, as the filaments slide past each other and the muscle fiber shortens.

Question 6

Motor end plate

Answer 6

Branches of an axon end at a specific part of the muscle- where it ends is called the motor end plate. This is where neurotransmitter is released from

Question 7

Neuromuscular junction

Answer 7

Where the branch of an axon synapses with a muscle.

Question 8

How do muscles contract at the neuromuscular junction? (3 steps)

Answer 8

1. Alpha motoneuron releases acetylcholine (ACh) from the motor end plates when an action potential arrives at the synapse
2. ACh binds nicotinic ACh receptors (nAChR) to allow sodium influx-ionotropic receptors
3. Creates EPP (end plate potential) which triggers muscle fiber contraction- EPP is most similar to a postsynaptic potential or receptor potential

Question 9

Crossed extensor system

Answer 9

Information crosses the spinal cord- left ventral side to right ventral side, back and forth as you’re walking. Allows you to maintain balance while walking or shifting your weight.

Question 10

Proprioception

Answer 10

Knowing the position and movement of the body- monitors muscle length and muscle tension/movement. If you need to react to something, you need to know where all of your body parts are in space.

Question 11

Primary motor cortex (M1)

Answer 11

Disproportionately large regions in the maps of M1 are devoted to the body parts involved in the most elaborate and complex movements, like the hands, similar to the somatosensory homunculus. The activity of most M1 neurons correspond to movement in a particular direction in space

Question 12

Which muscles are controlled directly by the brain?

Answer 12

The cranial motor nuclei of the brainstem send their axons to innervate muscles of the head and neck. These axons are part of the pyramidal system.

Question 13

The pyramidal system

Answer 13

The pyramidal system consists of neuronal cell bodies within the cerebral cortex and their axons, which pass through the brainstem and form the pyramidal tract to the spinal cord. The pyramidal tract can be seen as a wedge shape in a cross section of the medulla. Many axons of the pyramidal tract originate from neurons in M1.

Question 14

Where is M1 located?

Answer 14

Consists mainly of the precentral gyrus just anterior to the central sulcus. Located in the frontal lobe in front of the central cortex

Question 15

What happens if M1 is damaged?

Answer 15

In humans, brain damage to M1 results in partial paralysis on the contralateral side to the lesion.

Question 16

Spinal reflex

Answer 16

Simple, unvarying, and unlearned responses- don’t require brain inputs to the spinal cord

Question 17

Voluntary movements

Answer 17

Require brain inputs to the spinal cord. Motor plan, or motor program, is established before action occurs

Question 18

Levels of voluntary motor systems (6)

Answer 18

1. Primary motor cortex- initiate main commands
2. Non-primary motor cortex- additional motor commands
3. Cerebellum/basal ganglia- modulate motor control systems. Can add extra information
4. Brainstem- integrates motor commands from higher brain regions
5. Spinal cord- implements commands from brain
6. Skeletal muscle system- determine possible movements

Question 19

Purpose of voluntary motor systems

Answer 19

Allows us to react to the world- we approach reward/reinforcer or withdraw from negative

Question 20

Betz cells

Answer 20

M1 contains Betz cells (pyramidal neurons) that form homunculus. Similar conceptually to the primary somatosensory cortex

Question 21

M1 pyramidal neurons axon bundles- transmission of action potentials (5 steps)

Answer 21

1. Initiate action potentials which travel down the axons of pyramidal neurons
2. Crosses in the medulla- information only crosses once
3. Descends caudally in spinal cord via corticospinal tract
4. Synapse onto ventral spinal cord alpha-motoneurons
5. Muscle fiber contracts

Question 22

2 regions of the nonpyramidal motor cortex

Answer 22

1. Supplementary motor area (SMA)

2. Premotor cortex

Question 23

SMA function

Answer 23

Planning movement that is internally generated, rehearsing moving. Basic tasks like grabbing a glass of water requires many parts to occur and requires a lot of motor planning- SMA is responsible for this. SMA is activated when you mental rehearse motions- sports, playing instruments, etc

Question 24

Premotor cortex function

Answer 24

Directs movement based on external stimuli

Question 25

Mirror neurons definition

Answer 25

These neurons match the observed behavior with an internal motor representation of that behavior, as if the first individual is imagining doing the same thing as the individual it is watching. Plastic, can grow synapses

Question 26

Mirror neurons functions (2)

Answer 26

1. Understand/imitate another person’s actions- maybe for learning or cooperation
2. Could also be used for empathy, language, and be implicated in autism spectrum disorder

Question 27

What is the extrapyramidal system?

Answer 27

Many motor tracts run from the forebrain to the brainstem and spinal cord, and are located outside of the pyramid in the medulla. Connects with motor cortices to form a closed loop- cortex to EMS to cortex

Question 28

Important components of the extrapyramidal system (2)

Answer 28

1. Basal ganglia

2. Cerebellum

Question 29

Basal ganglia function

Answer 29

Initiation of motor action (related to motivational systems and cognition)

Question 30

Cerebellum function

Answer 30

Coordination, precision, and accurate timing

Question 31

2 basal ganglia circuits

Answer 31

1. Excitatory D1 receptors- go/direct pathway

2. Inhibitory D2 receptors- stop/indirect pathway

Question 32

How does dopamine affect the D1 go pathway?

Answer 32

Dopamine turns on the D1 go pathway, which leads to reward seeking and initiation of movement

Question 33

How does dopamine affect the D2 stop pathway?

Answer 33

Dopamine turns off the D2 stop pathway, which leads to reward seeking and initiation of movement

Question 34

2 types of dopamine receptors

Answer 34

D1 and D2

Question 35

How many types of each dopamine receptor does each neuron have?

Answer 35

Most neurons only have one type of dopamine receptor (either excitatory or inhibitory). The same dopamine molecule can have opposite functions (inhibitory/excitatory) depending on which receptors it binds

Question 36

Parkinson’s disease symptoms (3)

Answer 36

1. Tremors in limbs, especially hands
2. Difficulty with balance
3. Difficulty with initiating movement- once they’ve started moving they can maintain the movement, but have trouble getting started.

Question 37

What causes Parkinson’s disease?

Answer 37

Dopamine containing cells in the substantia nigra that project to the basal ganglia begin to degenerate progressively. Most cases are not inherited, it’s a combination of genetic and environmental influences.

Question 38

Parkinson’s disease treatment (2)

Answer 38

1. Pharmacological therapy involves dopamine replacement through L-dopa- this is a precursor molecule to dopamine, which will eventually stop working because too few dopamine containing neurons will remain in the substantia nigra. It enhances the dopamine levels of the remaining cells to relieve symptoms.
2. Deep brain stimulation- stimulating the thalamus or subthalamic nucleus, usually skipping the dopamine pathway so they can stimulate a part of the pathway that actually works

Question 39

Huntington’s disease

Answer 39

Caused by progressive destruction of the basal ganglia, especially the caudate nucleus and the putamen. The disease is transmitted by a single dominant gene- trinucleotide expansion in huntingtin gene (more than 40 repeats). Longer repeat sequences, earlier onset and more copies= earlier onset

Question 40

Huntington’s disease symptoms

Answer 40

Symptoms include clumsiness, twitches in the fingers and face, eventually causing involuntary jerking motions of the entire body (chorea) followed by intellectual deterioration and depression.

Question 41

How could Huntington’s disease potentially be treated?

Answer 41

Can be treated by reducing dopamine transmission