Lecture 1 Motor Pathways

Question 1

What are the divisions of the human nervous system?

Answer 1

1. Central nervous system which is composed of the brain and spinal cord
2. The peripheral nervous system is composed of the autonomic nervous system and peripheral nerves.
   The autonomic nervous system can be divided into the parasympathetic nervous system which is predominantly “rest and digest” and the sympathetic nervous system which is “fight or flight”
   Peripheral nerves are the cranial nerves (except for CN11). Cranial nerves are sets of paired nerves in the back of the brain.

Question 2

The neuron is the functional unit of the nervous system. Draw a neuron and describe the purpose of each part.

Answer 2

The soma (cell body) is the cell’s life support center. The primary function of the cell body is to organize and keep the cell functional.

Dendrites are tree branch-like structures of the neuron. Dendrites facilitate neuron communication. The primary function of dendrites is to receive and transmit electrical impulses toward the cell body. An increase in dendrites will increase the opportunity for information transmission. With the increased practice of a task, there is an increase in dendrites. Once practice comes to a halt, dendrites will begin to diminish.

The axon will arise from the axon hillock. This is the region where the plasma membrane generates nerve impulses in the neuron.

The axon transfers nerve impulses and signals away from the dendrites and soma toward other neurons.

The nodes of Ranvier are periodic gaps in the axon that are not covered by myelin sheath.

A protective insulation coating for the axon. The myelin sheath allows electrical impulses to transmit quickly and efficiently along nerve cells. Myelin sheath can reproduce itself and aerobic exercise can increase myelination.

At the synapse, there is a transmission of impulses. Neurotransmitters will cross from the presynaptic neuron, past the synaptic cleft, to the postsynaptic neuron to allow transmission of information (nerve impulses)

Question 3

what is a sensory neuron?

Answer 3

Nerve cells that are activated by sensory input from the environment. Most are unipolar neurons meaning that they have one axon that is split into two branches

Question 4

what is a motor neuron?

Answer 4

Motor neurons are part of the CNS and connect to muscles, glands, and organs of the body. These neurons transmit impulses from the spinal cord to the to skeletal and smooth muscles so they control all of our muscle movement. Most are multipolar meaning that they each have one axon with several dendrites.

Question 5

what is an interneuron?

Answer 5

Interneurons connect the spinal motor neurons and sensory neurons so they can transmit information from one another. These are multipolar, meaning that they have one axon with several dendrites.

Question 6

What is white matter? What is gray matter?

Answer 6

White matter and gray matter exist in the brain and spinal cord (CNS).
White matter is composed of highly myelinated axons. Groups of axons form pathways. In the brain, white matter is found closer to the center of the brain. White matter is the “wires” that transfer the impulse generated by gray matter to other parts of the CNS or body.
Fasciculi/fasciculus are white matter pathways or tracts
Commisures are a type of white matter that connects the R/L hemispheres.

Gray matter is composed of neuronal cell bodies. A group of cells is called nuclei or ganglia. In the brain, gray matter is found in the outer cortex. Gray matter is like the “generator” of impulses.
Nucleus: a group of functionally related nerve cells
Gangilia: a group of multiple nerve cells (lentiform nucleus or basal ganglia)

Question 7

What are columns or tracts?

Answer 7

Columns or tracts are groups of nerve cells bodies and axons that are related in function
The tracts are responsible for carrying sensory and motor stimuli to and from the periphery (respectively).

Question 8

What are glial cells? What happens when there is abnormal glial activity?

Answer 8

Glial cells are support cells that provide a critical support network for neurons. They are often involved in the pathogenesis of several diseases like Alzheimer’s and multiple sclerosis.
In Alzheimer’s and multiple sclerosis, there is abnormal glial activity. The microglia lose their protective control and will stimulate cell breakdown.
Neuroinflammation (inflammatory response within the CNS) is mediated by astrocytes and microglia.

Question 9

what are astrocytes?

Answer 9

Astrocytes are star-shaped glia that have a direct role in signaling a clean-up crew in the extracellular space.
They maintain the blood-brain barrier, provide structural support, regulate nutrition, absorb and recycle neurotransmitters, and form scar tissue after an injury. They are also involved in memory and mediate neuroinflammation. Astrocytes make up 30-65% of glial cells.

Question 10

what are oligodendrocytes?

Answer 10

Oligodendrocytes are a type of glia. They are the myelinating cells of the CNS. They provide a structural framework.

Question 11

what are ependymal cells?

Answer 11

Ependymal cells are a type of glia. They produce cerebrospinal fluid and are in charge of waste clearance.
They line the ventricles in the brain and spinal cord. They assist in producing, circulating, and monitoring CSF.

Question 12

what are microglial cells?

Answer 12

Microglial cells make up 10% of brain cells. They function as immune cells in the NS.
They remove cell debris, wastes, and pathogens by phagocytosis.
These cells become activated in diseases of the NS, infection, or injury. Dying neurons will secrete proteins that attract microglial cells.
Microglial cells mediate neuroinflammation.

Question 13

What occurs with glia in Multiple Sclerosis?

Answer 13

Microglia is involved in the demyelination and remyelination phases in multiple sclerosis.
Microglia will attack oligodendrocytes which destroys myelin which over time can result in plaques.
Degeneration occurs in both the brain and spinal cord

Question 14

What occurs with glia in Alzheimer’s Disease?

Answer 14

Microglia will increase neuroinflammation (inflammatory response of the CNS). There is an increased release of cytokines and free radicals which lead to amyloid plaques.
Microglia also play a role in reducing neuroinflammation.

Question 15

what is the central sulcus?

Answer 15

the central sulcus separates the frontal and parietal lobe.

Question 16

what is the lateral fissure?

Answer 16

defines the temporal lobe

Question 17

what structures are in the frontal lobe and what are their purpose?

Answer 17

The frontal lobe is the activation center. Its primary job is to generate signals to direct the movement of the body. It contains the primary motor cortex, the supplementary motor area, and the premotor cortex.
The supplementary motor area and the premotor cortex are the “set up crew” for the primary motor cortex. They will arrange activation patterns for movement.

Question 18

what structures are in the parietal lobe and what are their purpose?

Answer 18

The parietal lobe contains the primary somatosensory cortex, parietal association cortex, and second somatosensory area.
The primary somatosensory cortex interprets input fro other areas of the body. It receives and processes sensory information like touch, temperature, and pain.
the parietal association cortex and the secondary somatosensory area are the “Set up crew” from the primary somatosensory cortex.
the parietal lobe is vital for sensory perception and integration. It manages taste, hearing, sight, touch, and smell.

Question 19

What is the corpus callosum?

Answer 19

the corpus callosum is the structure that connects both hemispheres. It is composed of white matter.

Question 20

what is the homunculus?

Answer 20

The homunculus is a representation of the sensory and motor distribution of the human body.
The gyrus in front of the central sulcus (precentral gyrus) in the frontal lobe is the primary motor cortex which is responsible for initiation of voluntary movement.
The gyrus behind the central sulcus (postcentral gyrus) in the parietal lobe is the primary somatosensory cortex which is the main sensory receptive area for touch.
In both regions, the hands, face, mouth are neurologically large.

Question 21

What is lamina?

Answer 21

Neurons have a laminar alignment. Neurons are organized in layers (laminas), parallel to the surface of the brain. Each layer can be differentiated by the size and shape of neuronal bodies.
The motor cortex can be divided into 6 layers of lamina.

Question 22

what are betz cells?

Answer 22

Betz cells are a type of pyramidal neuron (upper motor neuron) that send their axons down the spinal cord via the corticospinal tract where they synapse directly with anterior horn cells which in turn synapse directly with their target muscle.
Betz cells originate from lamina V and lamina VI
50% of bets cells originate from the primary motor cortex

Question 23

What is the pathway for motor impulses?

Answer 23

A signal will travel from the primary motor cortex, through the brain, to the brainstem (midbrain, pons, medulla), through the spinal cord

Question 24

What is the lateral and anterior corticospinal tract?

Answer 24

The lateral corticospinal tract will cross over at the lower medulla cervicomedually junction (pyramidal decussation).

The anterior corticospinal tract stays unilaterally and crosses over at the spinal cord level to innervate bilateral sides. It will end at the mid-thoracic area. It is one long axon from the precentral gyrus to the medial motor nuclei. Contains motor tracts for cervical and upper thoracic cord (trunk). Will primarily innervate bilateral axial and shoulder girdle muscles.

Question 25

How do neurons travel through the corticospinal tract?

Answer 25

Motor axons pass through the internal capsule, the cerebral peduncles, the anterior pons, the pyramids of the medulla, and the lateral spinal cord to synapse with motor neurons that control distal limb movements and fine movements.
The corticospinal tracts in the lower medulla form the pyramids where at the junction of the medulla and spinal cord, 10% of neurons in the lateral corticospinal tract travel ipsilateral in the lateral corticospinal tract while most terminate in the ipsilateral spinal cord.

Question 26

What are the jobs of the posterior sensory cortex, prefrontal cortex, premotor cortex, and motor cortex?

Answer 26

The posterior sensory cortex provides sensory information to the prefrontal cortex. It sends goals.
The prefrontal cortex plans movements
The premotor cortex organizes the movement sequences
The motor cortex executes specific movements/ actions

Question 27

What are the steps involved in voluntary motor activation?

Answer 27

1. A decision is made in the frontal lobe
2. The signal is sent to motor planning areas and command centers (premotor and vision V1)
3. Signals go down the motor tract and deliver signals to alpha motor neurons (AMN)
4. The AMN transmits signals directly to skeletal muscles which elicits the contraction of skeletal muscle fibers
5. There is feedback and correction of activity made in the cerebellum and the sensory cortex which regulates activity in the descending motor tracts.

Question 28

What is an upper motor neuron?

Answer 28

An upper motor neuron is one long axon from the primary motor cortex to the anterior horn cell.
An upper motor neuron involves the brain and spinal cord and CNS

Question 29

What is a lower motor neuron?

Answer 29

A lower motor neuron is the connection between the anterior horn cell (AHC) and skeletal muscles. Involves the peripheral nerves.

Question 30

what are motor neuron pools and how do they relate to NS muscle activation?

Answer 30

Motor neuron pools are groups of muscles that cluster into discrete neurons (AHCs) with a common target (muscle).
They link across several spinal nerves and receive sensory
feedback (proprioception) from muscle spindles. They
coordinate with patterns of muscles by segments (sensory and cortical)
More motor neuron pools means more strength! You should do functional tasks that work different muscle groups to increase motor neuron pools.

Question 31

what is the henneman size principle and how does it relate to NS muscle activation?

Answer 31

The size principle states that motor units will receive common neural input and will be recruited in order of size from smallest to largest depending upon the intensity.
For any given task, you will gather small fibers first, medium fibers second, and large fibers are recruited last
S type are small and slow. They are “highly excitable” and are recruited first.
FR type are big, fast, and fatigue resistant. They are “average excitable” and atrophy quickly. They are recruited second.
FF type are very, fast, and fatigueable. They are of “low excitability” and are recruited last.

Question 32

Besides motor neuron pools and henneman size principle, what is another method of NS muscle activation?

Answer 32

increase the rate of stimulation
Increase firing speed (stimulation of motor unit)
Increase the number of motor units to increase active tension

Question 33

what are the two ways the NS can increase force production ?

Answer 33

Recruitment of new motor units
Increasing stimulation frequency

Question 34

Compare one motor neuron recruited vs many motor neurons recruited

Answer 34

Activation of one motor neuron will result in a weak muscle contraction. Activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction.