Neural Pathways, Brain Structures, and Stroke Recovery in Neuroanatomy!

What is the composition of the cerebral cortex?

Cerebral cortex is composed of 6 layers stacked on top of each other, consisting of varying concentrations of different types of neurons

What type of neurons are found in Layer V of the cerebral cortex?

Layer V contains large pyramidal neurons that connect to the basal ganglia, brainstem, and spinal cord

What are the two types of neurons based on function?

Neurons can be classified as motor (efferent) or sensory (afferent)

What are upper motor neurons (UMNs)?

Upper motor neurons are located in the central nervous system

What are lower motor neurons (LMNs)?

Lower motor neurons are located in the peripheral nervous system

What is the primary function of the pyramidal pathway?

The pyramidal pathway is generally responsible for muscle strength

What is the primary function of the extrapyramidal pathway?

The extrapyramidal pathway regulates muscle tone and consists of various tracts that transmit motor signals

What happens when there is damage to upper motor neurons?

Damage to upper motor neurons results in spasticity or hypertonia due to muscle overactivity

What happens when there is damage to lower motor neurons?

Damage to lower motor neurons results in flaccidity or hypotonia, marked muscle atrophy, and weakness

What is the role of the primary motor cortex?

The primary motor cortex is influenced by the basal ganglia and cerebellum, which relay information to initiate movement

What does decussation refer to in the context of motor pathways?

Decussation refers to the crossing over of motor fibers, where the left motor cortex controls the right side of the body and vice versa

What are the two tracts that organize impulses traveling down the pyramidal pathway?

corticospinal tract and corticobulbar tract

What is the different between the corticospinal and corticobulbar tracts?

The corticospinal tract synapses primarily with spinal nerves, while the corticobulbar tract synapses with cranial nerves

How many pairs of cranial nerves are there?

12

What is the function of the autonomic nervous system?

The autonomic nervous system regulates involuntary functions such as digestion, heart rate, and respiratory rate

What are the two divisions of the autonomic nervous system?

sympathetic nervous system and the parasympathetic nervous system

What is the function of the sympathetic nervous system?

The sympathetic nervous system stimulates the fight-or-flight response

What is the function of the parasympathetic nervous system?

The parasympathetic nervous system is responsible for ‘rest and digest’ functions

What is the final common pathway in motor signaling?

The final common pathway refers to the last leg of the journey for all motor signals, where LMNs are the final pathway through which motor stimulation reaches the target muscle

What occurs if the LMN is completely destroyed?

If the LMN is completely destroyed, muscle activity will not occur, regardless of the condition of the CNS

What is the role of cranial nerves?

Cranial nerves may be motor, sensory, or both, and they exit the CNS at the brainstem

What is the different between spinal nerves and cranial nerves?

Spinal nerves - always both sensory and motor

Cranial nerves - motor, sensory, or both

Which cranial nerve is unilaterally innervated by the contralateral motor cortex?

The hypoglossal nerve (CN XII)

What is the significance of the decussation of corticospinal fibers?

90% of corticospinal fibers decussate at the medullospinal junction, meaning that a spinal nerve on the left side is innervated by neurons from the right side of the brain

What happens to muscle tone when UMN pathways are damaged?

When UMN pathways are damaged, LMNs may exhibit hypertonic or spastic muscle tone

What is the role of the hypothalamus in the autonomic nervous system?

The hypothalamus regulates body temperature, appetite, emotional responses, and acts as a link between the endocrine and nervous systems

What does ‘MESA’ stand for in relation to neurons?

Motor (efferent), Sensory (afferent)

What are upper motor neurons (UMN)?

Upper motor neurons are located in the central nervous system

What are lower motor neurons (LMN)?

Lower motor neurons are located in the peripheral nervous system

What is the difference between pyramidal and extrapyramidal pathways?

Pyramidal pathways directly connect to LMNs, while extrapyramidal pathways indirectly influence LMNs

What is the role of the extrapyramidal pathway?

Extrapyramidal pathway regulates muscle tone and consists of various tracts that transmit motor signals

What is the primary motor cortex influenced by?

Primary motor cortex influenced by the basal ganglia and cerebellum

What is the significance of decussation in the pyramidal pathway?

Decussation means that the left motor cortex controls the right side of the body and vice versa

What are the two tracts organized in the pyramidal pathway?

Corticospinal tract and corticobulbar tract

What is the main function of the corticospinal tract?

Corticospinal tract primarily synapses with interneurons that connect to spinal nerves

What percentage of corticospinal fibers decussate at the medullospinal junction?

90% of corticospinal fibers decussate at the medullospinal junction

What is the main function of the corticobulbar tract?

The corticobulbar tract synapses with the cell bodies of cranial nerves

How are cranial nerves innervated by corticobulbar tracts?

Most cranial nerves are bilaterally innervated, but some, like the hypoglossal nerve, are unilaterally innervated

What is the role of the autonomic nervous system?

The autonomic nervous system regulates involuntary functions such as digestion, heart rate, and respiratory rate

What is the final common pathway in motor control?

The final common pathway refers to the last leg of the journey for all motor signals through the axons of lower motor neurons

What happens if a lower motor neuron is destroyed?

If an LMN is destroyed, it cannot control the muscles it innervates, regardless of the CNS condition

What are the components of the peripheral nervous system?

The peripheral nervous system consists of cranial nerves and spinal nerves

How many pairs of cranial and spinal nerves are there?

12 pairs of cranial nerves and 31 pairs of spinal nerves

What is the primary function of spinal nerves?

Spinal nerves are always both sensory and motor

What is the difference between upper motor neurons and lower motor neurons?

Upper motor neurons are contained in the CNS, while lower motor neurons exit the CNS to innervate muscles

What are intrafusal muscle fibers?

Smaller muscle fibers wrapped in a sheath of connective tissue, found deep in the center of the muscle, known as muscle spindles

Where are intrafusal muscle fibers present?

In the tongue, larynx, jaw, and some palatal muscles, but NOT in facial muscles or levator veli palatini

What is the role of sensory receptors in intrafusal muscle fibers?

They send information about muscle spindle length back to the central nervous system (CNS)

What are alpha motor neurons?

Motor neurons that synapse with extrafusal muscle fibers

What are gamma motor neurons?

Motor neurons that synapse with intrafusal muscle fibers

What is a motor unit?

A single motor neuron and all the muscle fibers it innervates

What is the innervation ratio?

Number of muscle cells innervated by one motor neuron

What characterizes motor neurons for fine motor control?

They are relatively small and do not synapse with many muscle fibers, resulting in a low innervation ratio

What characterizes motor neurons for gross motor control?

They have large motor units and a high innervation ratio

What is the gamma loop?

A feedback loop in the nervous system that regulates resting, active, and sustained muscle tone

How does the gamma loop function at rest?

It maintains a baseline level of activity (tone) in all skeletal muscles

What is the role of the stretch reflex?

It activates gamma motor neurons when the knee is tapped, causing intrafusal muscle fibers to contract

What happens during the stretch reflex?

Sensory nerves detect changes in intrafusal fiber length and send signals back to the CNS, which synapses with alpha motor neurons

What is the sequence of events in the stretch reflex?

1. CNS influences gamma motor neurons

2. Intrafusal fibers contract

3. Sensory nerves send signals to CNS

4. Alpha motor neurons fire

5. Extrafusal fibers contract

How does the gamma loop affect alpha motor activity?

It fine-tunes alpha motor activity based on sensory feedback during movement

How does the gamma loop affect alpha motor activity?

It fine-tunes alpha motor activity based on sensory feedback during movement

What is the significance of the gamma loop during movement?

It acts like a volume control for muscle tone and activity

What happens to the gamma loop after activation?

The loop is inactivated, and the process repeats

What is a reflex arc?

A neural pathway that responds quickly to stimuli by sending signals to the spinal cord instead of the brain

What is the role of the spinal cord in a reflex arc?

The spinal cord responds by sending the signal back to the muscle

What are involuntary reflexes?

Primitive reflexes present at birth that indicate a typically functioning CNS

When should primitive reflexes disappear in children?

Most should disappear by 6 months, but some, like Babinski’s reflex, can be seen up to 2 years

What are postural reflexes?

Reflexes that help individuals cope with gravity, becoming active as a child matures

What is the rooting reflex?

A newborn’s instinct to turn their head toward anything that strokes their cheek or mouth

What is the sucking reflex?

An instinctive action where a newborn sucks at anything touching the roof of their mouth

What is the snout reflex?

Pouting or pushing of the lips elicited by tapping or stroking the closed lips

What is the jaw jerk reflex?

A quick closing movement of the jaw when tapped

What is the palmomental reflex?

Twitching of the chin when the base of the thumb is stroked

What is the gag reflex?

Constriction of the larynx and pharynx when the back of the tongue is stroked

What is the palmer grasp reflex?

An infant’s fingers close around anything placed in their hand that stimulates the palm

What happens to primitive reflexes after neurological injury?

They may return, indicating neurological dysfunction

What is the purpose of spinal reflexes?

To protect the body against harmful stimuli, mostly involuntary but can be suppressed

What is the purpose of spinal reflexes?

To protect the body against harmful stimuli, mostly involuntary but can be suppressed

What is the limbic system?

The brain’s emotional system located between the thalamus and the medial walls of the cerebral hemispheres

What structures are included in the limbic system?

Hippocampus, cingulate gyrus, amygdala, olfactory bulb, and limbic cortex

What is the function of the amygdala?

Involved in fear and aggression, it helps preserve self and respond to environmental danger

What can damage to the amygdala cause?

Flattened emotions and difficulty recognizing facial emotions

What is the cingulate cortex associated with?

Conditions like depression, schizophrenia, and bipolar disorder

What role does the insular cortex play?

Involved in expressing negative emotions and emotional awareness

What happens when the prefrontal cortex is damaged?

Impaired social emotions, absent physiological reactions, or explosive emotions

What is the hippocampus responsible for?

Storing and retrieving declarative memory, including facts and events

What are the three primary functions of the thalamus?

1. Send sensory information to the cortex

2. Integrate sensory and motor information

3. Act as a relay station

What is the primary function of the hypothalamus?

It regulates autonomic and endocrine functions, including behavior, body temperature, food and water intake, and sexual and sleep behaviors

What role does the hypothalamus play in relation to the pituitary gland?

It controls the pituitary gland, which releases hormones involved in many body functions

What is emotional lability?

Involuntary display of emotion that can be caused by neurological damage, leading to sudden outbursts of crying or laughing

What is pseudobular affect?

A condition where emotional expressions do not reflect true emotions, often resulting in inappropriate emotional outbursts

What is flat affect?

A condition where a person appears apathetic, speaks in a monotone voice, and does not change emotions in response to varying situations

What is the function of Wernicke’s area?

It is involved in language comprehension

What is the primary function of the right hemisphere of the brain?

It processes non-verbal auditory information, such as prosody and environmental sounds

What is the primary function of the left hemisphere of the brain?

It is responsible for language, reading, writing, and verbal memory

What are the functions of the parietal lobe?

It processes body sensory information, attention, and visual-spatial functions

What are the executive functions associated with the frontal lobe?

They include decision-making, problem-solving, and motor functions

What are the three layers of the meninges?

Dura mater, arachnoid mater, and pia mater

What is the dura mater?

The tough outer layer of the meninges that adheres to the skull and has two layers

What is a subdural hematoma?

Bleeding in the subdural space, which can increase intracranial pressure and damage brain tissue