NEU 201 Exam III Lecture Notes

What is the main pathway of motor command?

Brain → Spinal cord → Muscles.

Where do voluntary movements generally begin?

Voluntary movements generally begin in the brain, where the movement is planned and initiated before motor commands descend through the spinal cord to the muscles.

What are the three major cortical areas involved in performing a motor sequence?

1. Prefrontal cortex

2. Premotor cortex

3. Primary motor cortex (M1)

What is the general sequence of motor planning and execution in the brain?

Prefrontal cortex → Premotor cortex → Primary motor cortex (M1).

What is the function of the prefrontal cortex in motor behavior?

The prefrontal cortex is responsible for higher-order planning, decision-making, and volition (the conscious intention or desire to perform an action).

What is volition?

Volition is the conscious intention or willingness to perform an action.

What is an example of prefrontal cortex involvement in motor behavior?

Deciding that you should remember a fact for later and choosing to write it down as a way to remember it

What deficits can result from damage to the prefrontal cortex?

• Poor decision-making

• Impaired executive function

• Difficulty planning and organizing behavior

What is an executive function?

A group of higher-order cognitive processes that allow individuals to plan, organize, make decisions, regulate behavior, and accomplish goals

What is the function of the premotor cortex?

The premotor cortex helps coordinate movements involving multiple body parts and organizes movements before they are executed.

What is an example of premotor cortex involvement?

Coordinating multiple body parts to reach into a hole in a table and retrieve a piece of food

How does the premotor cortex differ from the prefrontal cortex?

The prefrontal cortex determines the intention and plan to perform an action, while the premotor cortex helps organize and coordinate the movements needed to accomplish it.

What is the primary motor cortex (M1)?

M1 is the cortical region responsible for sending motor commands down toward the spinal cord to execute voluntary movements

What types of movements are associated with the primary motor cortex?

Focused, skilled, and precise voluntary movements

What is the role of neurons in the primary motor cortex?

Neurons in M1 send descending motor commands through pathways that ultimately activate muscles.

How is the primary motor cortex organized?

Different regions of M1 correspond to muscles and movements involving specific body parts

What does it mean that the primary motor cortex has a somatotopic organization?

Different body parts are represented in an organized spatial arrangement within the motor cortex

What is the difference between motor planning and motor execution?

Motor planning involves deciding and organizing how an action will occur, while motor execution involves sending commands that produce the actual movement.

What is an example of the three cortical areas working together when picking up a pen?

• Prefrontal cortex: Decides to pick up the pen.

• Premotor cortex: Organizes the coordinated movements needed to reach and grasp it.

• Primary motor cortex: Sends commands to execute the movement.

What is the pyramidal tract?

A group of descending motor pathways that carry motor commands from the brain toward the spinal cord. The corticospinal tracts are major components of this system.

What are the corticospinal tracts?

Descending pathways that transmit motor commands from the cerebral cortex to spinal cord circuits involved in voluntary movement

What does contralateral mean?

Referring to the opposite side of the body

What does ipsilateral mean?

Referring to the same side of the body.

What are the two major corticospinal pathways?

1. Lateral corticospinal tract

2. Anterior corticospinal tract

What does the lateral corticospinal tract control?

Primarily voluntary movements of the contralateral distal limbs, especially skilled movements of the hands and fingers

What does the anterior corticospinal tract control?

Primarily muscles of the trunk and proximal limbs, contributing to posture and coordinated body movements

What is the difference between the lateral and anterior corticospinal tracts?

• Lateral corticospinal tract: Controls primarily contralateral distal limb movements.

• Anterior corticospinal tract: Controls primarily trunk and proximal limb muscles

Why is the lateral corticospinal tract important for skilled movements?

It contributes to precise voluntary control of distal muscles, especially those involved in fine hand and finger movements.

What is the neuromuscular junction (NMJ)?

The specialized communication site between a motor neuron and a skeletal muscle fiber where a nerve signal is transmitted to the muscle

What is the function of the neuromuscular junction?

It allows motor neurons to communicate with skeletal muscle fibers and initiate muscle contraction

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine (ACh).

What happens when acetylcholine is released at the neuromuscular junction?

Acetylcholine binds to receptors on the muscle membrane, producing an electrical response that can trigger a muscle action potential and contraction

What is the sequence of events from the brain to muscle contraction?

1. Motor commands are generated and organized in the brain.

2. Signals descend through motor pathways.

3. Signals reach spinal cord motor neurons.

4. Motor neurons send signals toward skeletal muscles.

5. Acetylcholine is released at the neuromuscular junction.

6. Muscle fibers are activated and contract.

What are antagonistic muscle pairs?

Pairs of muscles that produce opposite movements at a joint. When one muscle contracts, the opposing muscle generally relaxes.

What is an example of an antagonistic muscle pair?

The biceps and triceps:

• Biceps contraction flexes the elbow.

• Triceps contraction extends the elbow.

Why are muscles often organized in antagonistic pairs?

Because joints need opposing muscle actions to produce movements in different directions.

What is the difference between the central and peripheral portions of the motor pathway?

The central portion involves the brain and spinal cord, while the peripheral portion involves motor nerves communicating with muscles through neuromuscular junctions.

What are the basal ganglia?

A collection of interconnected subcortical brain regions that are important for regulating motor function, selecting actions, habit learning, and goal-directed behavior

Where are the basal ganglia located?

Deep within the brain, beneath the cerebral cortex; they are considered subcortical structures

How are the basal ganglia connected to the motor cortex?

The basal ganglia receive input from and project information back to the motor cortex through interconnected neural circuits

Do the basal ganglia contribute many neurons directly to descending motor pathways?

No. They contribute relatively few neurons directly to descending motor pathways. Instead, they modify motor signaling at higher levels through their connections with the motor cortex.

What is the primary role of the basal ganglia in motor function?

They help regulate and modify motor commands, including action selection, movement initiation, and the organization of appropriate movements.

What are three important functions of the basal ganglia?

1. Habit learning

2. Goal-directed actions

3. Action selection

What is habit learning?

The process of developing automatic, learned behaviors through repetition and practice.

What are goal-directed actions?

Behaviors performed intentionally to achieve a particular outcome or goal

What is action selection?

The process of selecting an appropriate action from multiple possible behaviors

What is the relationship between the basal ganglia and repetitive grooming behavior in rats?

The basal ganglia help organize repetitive, sequential grooming behaviors. Rat grooming can occur in a predictable sequence involving elliptical strokes, unilateral strokes, bilateral strokes, and body licking.

What happens when the dorsolateral striatum (DL) is lesioned in rats?

Lesions disrupt the normal organization of habitual, repetitive grooming sequences, demonstrating the dorsolateral striatum's role in habit learning.

What is the dorsolateral striatum (DL)?

A region of the striatum involved in habit learning and the organization of habitual behaviors

What is Parkinson's disease (PD)?

A neurodegenerative movement disorder associated with the loss of dopamine-producing neurons in the substantia nigra pars compacta, resulting in altered basal ganglia circuitry and impaired movement.

Who first characterized Parkinson's disease, and when?

Dr. James Parkinson in 1817 in his essay titled "An Essay on the Shaking Palsy."

What is the typical age of onset of Parkinson's disease?

Usually in the 60s.

Approximately what percentage of adults develop Parkinson's disease according to the lecture?

Approximately 1%

What are the classic motor symptoms of Parkinson's disease?

• Resting or involuntary tremor

• Stooped posture

• Shuffling gait

• Difficulty initiating and controlling movements

What is a shuffling gait?

A walking pattern characterized by short, dragging steps and difficulty producing normal walking movements

What is stooped posture?

A forward-flexed body posture commonly observed in Parkinson's disease.

 What brain region is primarily affected in Parkinson's disease?

The substantia nigra pars compacta (SNc)

What type of neurons are lost in the substantia nigra pars compacta in Parkinson's disease?

Dopamine-producing (dopaminergic) neurons.

What is dopamine?

A neurotransmitter that plays an important role in regulating basal ganglia circuits and modulating motor activity

What is the sequence of events that produces Parkinson's disease motor symptoms?

1. Dopamine-producing neurons in the substantia nigra pars compacta degenerate.

2. Dopamine levels decrease.

3. Basal ganglia circuitry becomes altered.

4. Motor control is disrupted.

5. Parkinsonian motor symptoms develop

Why does dopamine loss affect movement?

Dopamine normally modulates basal ganglia circuits involved in regulating movement. When dopamine is depleted, the balance of activity within these circuits is disrupted, impairing normal motor control.

Approximately how many dopamine-producing cells have been lost by the time Parkinson's symptoms appear, according to the lecture?

Approximately 80%.

Why is Parkinson's disease often diagnosed after substantial neuronal loss has already occurred?

Because noticeable motor symptoms generally emerge after substantial degeneration of dopamine-producing neurons has already taken place.

What is the difference between the substantia nigra in a healthy brain and in Parkinson's disease?

A healthy brain has functioning dopamine-producing neurons in the substantia nigra pars compacta. In Parkinson's disease, many of these neurons degenerate, resulting in reduced dopamine production.

How do the basal ganglia relate to Parkinson's disease?

he basal ganglia depend on dopamine input from the substantia nigra pars compacta to regulate motor circuits. Loss of this dopamine input alters basal ganglia signaling and causes impaired movement

What is the difference between the basal ganglia and the primary motor cortex?

The primary motor cortex generates descending commands for voluntary movement, while the basal ganglia modulate motor circuits and help select and regulate appropriate actions.

What does the word cerebellum mean?

Little brain.

Where is the cerebellum located?

Behind the brainstem, in the posterior portion of the brain

 Approximately what percentage of neurons in the nervous system are found in the cerebellum?

Approximately three-quarters (75%) of all neurons in the nervous system

What are the three major functions of the cerebellum?

1. Balance and equilibrium

2. Fine motor control and coordination

3. Posture and regulation of muscle tone

What is the cerebellum's role in balance?

It integrates sensory information and helps coordinate movements that maintain balance and equilibrium

What is the cerebellum's role in fine motor control?

It helps coordinate precise, smooth, and accurate movements

What is the cerebellum's role in posture?

It helps regulate posture and muscle tone to maintain body stability and appropriate positioning

What is an example of a movement that requires cerebellar function?

Touching your finger to your nose accurately and smoothly

What happens when the cerebellum is dysfunctional?

Individuals may experience impaired coordination, poor balance, abnormal posture, and difficulty performing precise movements.

What is ataxia?

A neurological condition characterized by impaired coordination of voluntary movements, often associated with cerebellar dysfunction

What are common manifestations of cerebellar ataxia?

• Poor coordination

• Unsteady movements

• Difficulty with fine motor tasks

• Impaired balance

• Difficulty performing coordinated movements

Why might someone with cerebellar dysfunction have difficulty touching their finger to their nose?

Because the cerebellum is necessary for coordinating and fine-tuning movements. Dysfunction interferes with accurate movement execution.

What sensory information does the cerebellum integrate to help maintain balance?

Proprioceptive, visual, and vestibular information

What is vestibular information?

Sensory information from the vestibular system of the inner ear that helps detect head position and movement and contributes to balance

How does the cerebellum differ from the basal ganglia?

 The basal ganglia are particularly important for action selection, habit learning, and modulating motor signaling. The cerebellum is particularly important for coordination, balance, posture, and fine-tuning movements

What is the difference between Parkinson's disease and cerebellar ataxia?

Parkinson's disease is associated with dopamine-producing neuron degeneration in the substantia nigra pars compacta and altered basal ganglia circuitry. Cerebellar ataxia involves impaired cerebellar function and is characterized by poor coordination and balance.

How does the cerebellum contribute to motor responses?

It contributes to the coordination and refinement of both coarse and fine motor responses, helping movements become smooth, accurate, and appropriately timed

What is the relationship between dopamine and the motor cortex?

Dopaminergic neurons in the basal ganglia circuitry modulate motor cortex activity. Degeneration of dopamine-producing neurons can disrupt motor control and contribute to Parkinson's disease

What is somatosensation?

The sensory system responsible for detecting information from the body, including touch, pressure, temperature, pain, and body position

What are cutaneous receptors?

Specialized sensory receptors located in the skin that detect different types of stimuli, such as touch, pressure, vibration, temperature, and pain

What are the five major types of cutaneous receptors covered in this lecture?

1. Pacinian corpuscles

2. Meissner's corpuscles

3. Merkel's disks

4. Ruffini endings

5. Free nerve endings

What is a sensory modality?

The specific type of sensory information detected by a receptor, such as pressure, vibration, temperature, or pain

What are Pacinian corpuscles responsible for detecting?

Deep pressure and high-frequency vibration

What are Meissner's corpuscles responsible for detecting?

Light touch and low-frequency vibration; they are particularly important for detecting changes in surface contact

What are Merkel's disks responsible for detecting?

Sustained light touch, pressure, texture, and fine spatial details

What are Ruffini endings responsible for detecting?

Skin stretch and sustained pressure; they contribute to information about hand shape and finger position

What are free nerve endings?

Simple sensory nerve endings distributed throughout the body that detect stimuli including pain and temperature

What are the primary sensory functions of free nerve endings?

Detecting pain and temperature.

What is the most common type of cutaneous receptor according to the lecture?

Free nerve endings

What are nociceptors?

Specialized sensory receptors, commonly associated with free nerve endings, that detect potentially damaging or painful stimuli.

What types of stimuli activate nociceptors?

Potentially harmful mechanical, thermal, and chemical stimuli.

What are the two major types of nerve fibers that carry nociceptive information to the CNS?

1. A-delta (Aδ) fibers

2. C fibers

What is the difference between A-delta and C fibers?

A-delta fibers are thinly myelinated and conduct signals relatively quickly, commonly carrying sharp, well-localized pain. C fibers are unmyelinated and conduct signals more slowly, commonly carrying dull, aching, or burning pain.

What are mechanoreceptors?

Sensory receptors that respond to mechanical changes, such as touch, pressure, vibration, and stretch.