BIO-375 Exam #3

Cerebellum

This structure compares the intended movement with the actual movement performed.

1. Ventral horns of the spinal cord

2. Brainstem

What are the two main locations where lower motor neurons are found?

Motor Unit

One motor neuron that innervates several muscle fibers

Motor Pool

The collection of lower motor neurons that control a specific muscle.

• contains different types of motor units

1. Recruitment

2. Firing Rate (AP Frequency)

What are the two components of generating force?

1. Slow (S)

2. Fatigue-Resistant (FR)

3. Fast Fatigable (FF)

What are the three different types of motor units that can be recruited to generate force?

Slow (S) Motor Units

What motor unit type is this?

• Smallest size

• Slow twitch

• Synapse with red muscle fibers (Type 1)

• Many mitochondria

• High myoglobin content

• Extensive capillary beds

Fatigue-Resistant (FR) Motor Units

What motor unit type is this?

• Medium size

• Fast twitch

• Innervate white muscle fibers (Type 2a)

• Has 2x the force of S fibers

• Less mitochondria and capillaries

• More likely to fatigue than S units

Fast Fatigable (FF) Motor Units

What motor unit type is this?

• Largest size

• Fast twitch

• Innervate white muscle fibers (Type 2b)

• Large force

• Very few mitochondria (very fatigable)

• Important for burst-type motion (ex. sprinting)

1. Higher

2. Calcium

Does a higher or lower rate of action potential frequency/firing rate allow for more force to be generated? What ion is important for this?

Muscle Spindle

Type of sensory receptor that:

• Detects the length and stretch of a muscle

• Stretch reflex

• Detects static information

• Reciprocal inhibition

Reciprocal Inhibition

A neuromuscular process where the agonist muscle is excited and the antagonist muscle is inhibited

• Hold something, add more weight, quick adjustments made to continue holding object in the same position

• Myotatic Reflex

Gamma Motor Neuron

Type of lower motor neuron that regulates muscle spindle sensitivity (gain) by modulating the levels of excitability

• Passive stretch- turn gain down, decrease excitability and reactiveness, allowing muscle to relax into a deeper stretch

Golgi Tendon

Type of sensory receptor that:

• Detects the tension and force on a muscle

• Located in the musculotendinous junction

• Reciprocal Excitation

Reciprocal Excitation

A neuromuscular process where the agonist muscle is inhibited and the antagonist muscle is excited.

• Golgi tendon reflex

• Autogenic inhibition reflex

• Inverse myotatic reflex

The Flexion Reflex

An automatic, protective spinal reflex often triggered by nociceptors that causes a rapid withdrawal of a limb from a painful/harmful stimulus through contraction of flexor muscles and inhibition of extensor muscles.

Central Pattern Generators

Neural circuits that produce rhythmic outputs, controlling repetitive motor movements, without requiring sensory input.

• Ex. Walking and breathing

• A cat’s walking is less complicated than that of humans because they have 4 legs versus just 2

Lower Motor Neuron Syndrome

Neurological disorders resulting from damage to the motor neurons in the brainstem and spinal cord

• Characterized by

  • Flaccid paralysis

  • Hypotonia/atonia

  • Hyporeflexia

  • Atrophy

Upper Motor Neuron Syndrome

Neurological disorders resulting from damage to the motor neurons in the brain

• Characterized by

  • Spasticity

  • Hypertonia- muscle more resistant

  • Hyperreflexia

1. Primary Motor Cortex

2. Premotor Cortex

3. Supplementary Motor Cortex

4. Brainstem

What are the four main locations where upper motor neurons are found?

Primary Motor Cortex

Part of the motor cortex that encodes the parameters of specific movements.

Premotor Cortex

Part of the motor cortex that plans movements and selects appropriate motor plans for voluntary movements

• Extensive sensory input

Supplementary Motor Cortex

Part of the motor cortex that selects movements based on remembered sequences, contains internally generated actions, and utilizes bimanual coordination (ex. walking)

1. Reticular formation - travel through central part of brainstme

2. Superior Colliculus- eye movements, hand eye coordination

3. Vestibular Complex

What are the three important components of the brainstem?

Postural Neurons

Rapidly adapting neurons that play a crucial role in maintaining balance and stability during movements.

Feedforward Postural Regulation

The activation of postural muscles before a voluntary movement begins in anticipation of the destabilizing forces caused by the movement.

Feedbackward Postural Regulation

Having to adjust and activate postural muscles while performing a movement due to destabilization caused by the movement.

Fritsch and Hitzig

These two people did a study on monkeys in the 1800s where they stimulated the left cortex and found there to be movement on the right side of the body (contralateral)

John Hughlings Jackson

This neurologist studied epilepsy and seizure progression

Wilder Penfield

This scientist created a spatial map of the human motor cortex

• Part of the surgical process

Microelectrodes

Invented in the 1960s and were used to stimulate small/pinpoint areas of the brain.

Ed Evarts

This scientist implanted microelectrodes in monkeys and trained them to perform specific tasks and found the correlation of upper motor neuron activity to voluntary movements

• Increased firing rate in UMN = increase in muscle force

• UMN firing rate changes prior to a movement (anticipatory)

• UMNs are important for the bidirectionality of muscles

Spike-Triggered Averaging

In the 1970s it was determined that there are specific muscle fibers correlated with specific upper motor neurons.

• Influence of a single cortical UMN on a population of LMNs

• UMNs encode movement rather than individual muscles

Muscle Fields

A group of muscles influenced by one upper motor neuron

Michael Graziano

A scientist who determined that the somatosensory cortex maps movements and not specific body parts.

Population Coding

A specific group of neurons required for a specific movement

Directionality

A study forced monkeys to move their arms in a certain direction found that a single motor neuron can move in a few different directions, and the combination of several neurons will give the correct direction (population vector)

Population Vector

The combination of several neurons will give the correct direction.

Glutamate

What chemical do upper motor neurons secrete into the synaptic cleft that is excitatory and can be toxic at high levels

• Needs to be recycled/reuptake from extracellular fluid

Excitotoxicity

Occurs when neurons are damaged and killed by excessive stimulation/depolarization by neurotransmitters, specifically glutamate.

• Leads to excessive amounts of calcium in the brain

• Key factors in stroke, TBI, and neurodegenerative diseases

Primary Motor Cortex

Part of the motor cortex known as Area 4 that contains betz cells which specialize in fine movements of distal limbs.

• Makes up 10% of the motor neurons in the lateral corticospinal tract

1. Caudate Nucleus

2. Putamen

3. Globus Pallidus (internal and external)

4. Substantial Nigra (pars reticulata and pars compacta)

What are the four main structures of the basal ganglia?

Basal Ganglia

Part of motor control that

• Regulates and modulates the activity of upper motor neurons

  • Inhibits or disinhibits

• Anticipation of and during movements

  • Important for initiation of a movement

  • Important for switching between movements

  • Important for terminating a movement

• Part of a loop with the cerebral cortex

Striatum

The input zone comprised of the putamen and caudate nucleus

• Contains medium spiny neurons

• Can get direct input from everywhere in the cerebral cortex except the primary auditory and visual cortices

Caudate Nucleus

This part of the striatum gets information primarily from

• Frontal eye field

• Multi-modal association cortex

  • Frontal, temporal, and parietal lobes

Putamen

This part of the striatum gets information primarily from

• Primary motor cortex

• Premotor cortex

• Prefrontal cortex

• Primary somatosensory cortex

• Secondary somatosensory cortex

• Secondary visual cortex

• Auditory association

Inward Rectifying K⁺ Currents

What do medium spiny neurons have that stop the excitatory/depolarizing current that comes from the cortex by pulling the signal back to resting potential making it more difficult to reach threshold?

Summation from several cortical neurons

What does a medium spiny neuron require of the signal for the signal to be delivered?

• Signal must be strong to reach threshold

• Prevent spontaneous activity/errors

1. Caudate Nucleus

2. Putamen

What are the two input nuclei of the basal ganglia?

1. Global Pallidus (internal* and external)

2. Substantia Nigra pars reticulata*

What are the two output nuclei of the basal ganglia?

Pallidum

The output cells (globus pallidus and substantia nigra pars reticulata-SNr) make up the ________.

Medium Spiny Neurons

Basal ganglia output cells get the information from the _____.

• >100 _____ synapse on a single pallidum neuron meaning the signal is strong and deliberate.

Globus Pallidus Internal Segment

What is the “main” output of the basal ganglia?

Corticostriatal Pathway

A motor pathway that consists of a network of neurons that project from nearly all regions of the cerebral cortex to the striatum (part of the basal ganglia).

True

T or F: Both the indirect and direct pathways must be activated for a movement to occur?

Direct Pathway

Which Corticostriatal pathway is this?

• The net effect of this pathway is to disinhibit the thalamus, allowing for movement

• Facilitate the initiation of voluntary movement

• Projections from the medium spiny neurons of the caudate and putamen to the globus pallidus internal segment (GPi)

Indirect Pathway

Which Corticostriatal pathway is this?

• Increase the tonic inhibition of GPi

• Prevent unwanted movements

• A population of medium spiny neurons project into globus pallidus external segment (GPe) and inhibit the GPe

• Inhibition of the GPe disinhibits the GPi and Subthalamic nuclei

• Disinhibition of the GPi allows for further inhibition of the thalamus

Eye Movements

Which movements are produced by this pathway?

• Cerebral Cortex —(glutamate(+)—> Caudate Nucleus —(GABA (-)—> Substantia Nigra pars reticulate —(disinhibits)—> Superior Colliculus

Substantia Nigra Pars Compacta

Where is the dopamine source in the basal ganglia?

Hypokinetic Diseases

Diseases characterized by a decreased ability to move

• Ex. Parkinsons Disease

Parkinson’s Disease

A hypokinetic disease characterized by the death of dopamine-producing cells in the substantia nigra

• Initially lose dopamine input

• Dr. James Parkinson first described this disease as “The Shaking Palsy”

• Lewy Bodies- accumulation of misfolded α-synuclein protein leads to apoptosis

• Increased inhibitory output from the basal ganglia

Hypokinetic/Parkinson’s Disease

Which disease do these symptoms represent?

• Difficulty with fine motor movements (ex. writing)

• Mood or behavioral changes

• Executive dysfunction

• Pill-rolling movements or resting hand tremors

• Rigidity

• Shuffling gait/stooped posture

• Trouble initiating/planning movements

• Limited or complete lack of associated movements

• Minimal facial expressions

• Medication: L-DOPA

• Deep Brain Stimulation

What are the two most common treatments for Parkinson’s disease?

Hyperkinetic Disease

Diseases characterized by increased movement of the body without control.

• Ex. Huntington’s Disease

Huntington’s Disease

A hyperkinetic disease characterized by e