Neuroscience Final Exam

What are association fibers?

are one of the three primary types of white matter pathways that make up the infrastructure of the brain.

Defining characteristics of associations fibers

interconnect different cortical areas within a single cerebral hemisphere

The sources identify several major association fiber bundles:

• Arcuate Fasciculus

• Cingulum

• Superior Longitudinal Fasciciulus

• Uncinate Fasciculus

• Inferior Longitudinal Fasciculus

• Superior and Inferior Occiptofrontal Fasciculi

What are commissural fibers?

Their primary role is to interconnect the left and right cerebral hemispheres, allowing for communication between similar areas across the midline

Example of a commissural fiber

corpus callosum

Commissural fibers inter-hemispheric connection:

Unlike association fibers, which stay within one hemisphere, commissural fibers cross the longitudinal cerebral fissure to link the two halves of the cerebrum

Commissural fibers Radial Distribution

These fibers radiate outward to reach different areas and lobes within both hemispheres

Commissural fibers structural composition

they are part of the brain's "infrastructure," made up of collections of axons that form a complex, interlocking "fabric" within the white matter

What are projection fibers?

Interconnect the cerebral cortex with deep structure of the brain, such as the diencephalon and brainstem, as well as the spinal cord

Projection fibers directional flow

transmit information to and from the brain

Projection fibers informational content

Descending motor pathways- carrying voluntary movement commands from the cortex to the muscles (corticospinal and corticobulbar tracts)

Ascending sensory pathways: Carrying sensory data from the body up to the perceptual processing regions of the cortex

Projection fibers travel

vertically

Arcuate fasciculus

is a critical white matter pathway in the brain, classified as a type of long association fiber. Its primary role is to interconnect different cortical areas within a single cerebral hemisphere, and it is considered especially vital for speech and language functions

Arcuate fasciculus key anatomical connection

• Wernicke’s area: Located in the posterior temporal lobe, responsible for language reception and comprehension.

• Broca’s area: Located in the frontal lobe, responsible for language production

What are the three meningeal layers?

1. Dura Mater (Outermost Layer)

2. Arachnoid Layer (Middle Layer)

3. Pia Mater (Deepest Layer)

1. Dura Mater (Outermost Layer)

is the thickest and most durable of the three layers. It surrounds the brain, brainstem, and spinal cord and is composed of two sub-layers: an external periosteal layer and an internal meningeal layer

epidural hematoma

between the skull and dura)

subdural hematoma

between the dura and arachnoid

arachnoid layer

is web-like in appearance and consists of two subcompartments

• Barrier layer: Attached directly to the dura mater.

• Subarachnoid space: cerebrospinal fluid

Pia Mater

is the deepest and thinnest of the meningeal layers. It is very delicate and attaches tightly to the surface of the CNS, following the various contours of the gyri and sulci of the brain

Cerebrospinal fluid (CSF)

is a clear fluid that circulates within and around the central nervous system (CNS) to provide a vital layer of protection

Cerebrospinal fluid (CSF) primary function

Protection: It acts as a shock absorber and cushion, protecting the brain and spinal cord from physical trauma

Biological Support: It contains necessary nutrients and immune cells to maintain the health of the CNS

Cerebrospinal Clinical Relevance

A major condition associated with this fluid is hydrocephalus. This occurs when there is an abnormal accumulation of CSF within the ventricles, typically due to a blockage or drainage issue. This leads to a pressure buildup that can displace brain tissue and cause neurological damage

Pathways of bloodflow

Arterial System: Supply

Venous System: Drainage

Arterial System: Supply

The arterial system is divided into anterior and posterior circulatory systems, which are interconnected at the base of the brain by a structure known as the Circle of Willis

Venous System: Drainage

The venous system is responsible for removing deoxygenated blood from the brain tissue.

Aneurysms

Weakened areas in artery walls that can rupture, leading to hemorrhagic strokes

Ischemic Strokes

Blockages in blood flow, often caused by a blood clot (thrombus) or a traveling fragment (embolism)

Arteriovenous Malformations (AVMs):

Tangles of blood vessels that can grow and potentially lead to hemorrhages

Anterior Cerebral Artery (ACA)

• Origin: It is one of the two main branches formed when the internal carotid artery bifurcates.

• Course and Supply: The ACA travels to the midline of the frontal lobe and branches out to supply critical midline frontal and parietal structures.

• Coordination: The left and right ACAs must communicate with each other to ensure proper blood distribution

Middle Cerebral Artery (MCA)

• Origin: Like the ACA, the MCA originates from the bifurcation of the internal carotid artery.

• Course and Supply: It follows the lateral sulcus toward the temporal lobe, supplying the most lateral aspects of the cerebral hemispheres.

• Relevance to Communication: Because it supplies lateral areas including the temporal lobe and regions vital for speech and language, the MCA is highly relevant to communication sciences and disorders.

Posterior Cerebral Artery (PCA)

• Origin: Unlike the ACA and MCA, the PCAs originate from the posterior circulatory system. The vertebral arteries merge to form the basilar artery, which then divides into the left and right PCAs.

• Course and Supply: The PCAs provide blood to the ventral (bottom) and posterior (back) areas of the brain, including the occipital lobe.

• Interconnection: Each PCA is capable of communicating with the MCA

1. Strokes

occur when blood flow to the brain is interrupted and are the most common cause of neurogenic language conditions like aphasia. They are broadly categorized into two types:

Ischemic Stroke

Hemorrhagic Stroke:

Ischemic Stroke:

These are caused by a blockage in a blood vessel

Hemorrhagic Stroke

These involve a bleed into the brain tissue. This can occur when an arterial wall ruptures, often due to an aneurysm or an arteriovenous malformation

Aneurysms

A cerebral aneurysm is a weakened area in an artery wall that often balloons out

3. Arteriovenous Malformations (AVMs)

AVMs are "tangles" of small blood vessels

Sensation

is the process by which specialized neural structures called sensory receptors are activated by stimuli. It is a two-step process that involves the transduction of physical energy into electrochemical signals and the transmission of those signals to the central nervous system (CNS)

Perception

is the interpretation of these "raw" inputs once they reach the CNS. It is a cognitive event actively constructed by the brain, heavily dependent on memory and past experiences.

Modality

The general class of stimuli (e.g., taste, smell, vision) mediated by specialized receptors. These include chemoreceptors (taste/smell), mechanoreceptors (hearing/balance/touch), photoreceptors (vision), and thermoreceptors (temperature)

Location

The ability to map external space onto neural structures through receptive fields. The size and density of these fields can be measured by tests like two-point discrimination

Intensity

How the system encodes the physical strength of an event; the receptor potential encodes these intensity cues

Duration

The temporal properties of a stimulus. Through receptor adaptation, the brain can perceptually adjust to continuous sensory experiences

1. Somatosensory System

Somatosensory receptors are distributed widely throughout the body to detect touch, proprioception, pain, and temperature

1. Somatosensory System location

• Skin: For tactile sensations from the surface of the body.

• Face and Head: Receptors are located in the facial skin and the linings of the oral and nasal cavities, including the surface of the tongue.

• Musculoskeletal System: Receptors in muscles and joints provide proprioceptive information about body position.

• Internal Structures: Sensory endings are also found in the meninges, cardiovascular system, and visceral organs

2. Auditory System

The sensory receptors for hearing are specialized hair cells. These are located within the inner ear, specifically:

• Cochlea: The hair cells are housed in the Organ of Corti.

• Function: These receptors transduce mechanical-hydraulic energy into electrochemical signals that the brain can process as sound

3. Vestibular System

Like the auditory system, the vestibular system relies on hair cells as its primary sensory receptors. These are located in two main areas of the inner ear to maintain balance and equilibrium

Semicircular Canals: These receptors detect head rotation and angular acceleration

• Proprioception

is a sub-modality of the somatosensory system that provides the brain with a sense of where the body is located in space. It acts as a critical sensory complement to motor performance, allowing the nervous system to monitor and adjust movements in real-time

1st-Order Neuron (Afferent Neuron):

This neuron begins at the sensory receptors in the periphery. Its cell body is located outside the spinal cord or brainstem (e.g., in the dorsal root ganglion for the body or the trigeminal ganglion for the head). It transmits the signal to the spinal cord or brainstem, where it synapses with the next neuron

2nd-Order Neuron

This neuron starts in the spinal cord or brainstem and projects to the thalamus. A critical feature of the 2nd-order neuron is that it crosses the midline (decussates), ensuring that sensory information from one side of the body is processed by the opposite side of the brain

3rd-Order Neuron:

This neuron originates in the thalamus, which acts as a "gatekeeper," and transmits the information to the primary somatosensory cortex (S1) in the parietal lobe.

Overall ascending pathway for hearing

1. Cochlea

2. Auditory Nerve

3. Cochlear Nucleus

4. Superior Olivary Complex

5. Inferior Colliculus

6. Medial Geniculate Body

7. Primary Auditory Cortex

Auditory processing

• Detection: The basic awareness of whether a sound is or is not present.

• Discrimination: The ability to determine whether two sounds are the same or different.

• Identification: The ability to understand what has been named or labeled.

• Comprehension: The highest level, referring to the ability to understand the meaning of spoken language

Auditory Discrimination:

Noticing, comparing, and distinguishing distinct and separate sounds within words

Auditory Figure-Ground Discrimination

The ability to pick out important sounds from a noisy background

Auditory Memory:

The ability to recall what was heard after a period of time, including both short-term and long-term memory

Auditory Sequencing:

The ability to understand and recall the specific order of words.

Neuroplasticity

refers to the changes to the structure and function of the brain in response to various experiences or conditions. It is a process of experience-dependent cortical reorganization where the brain adapts its circuitry based on the inputs it receives

Primary Motor Cortex (M1):

Located in the precentral gyrus of the frontal lobe, this area serves as the origin point for descending motor pathways. It is somatotopically organized, meaning different regions of the cortex correspond to specific discrete muscles in the body

Premotor Cortex

Divided into the Pre-motor area (PMA) and the Supplementary motor area (SMA), these regions are vital for motor planning and the development of complex, sequential actions

Broca’s Area:

Situated in the left frontal lobe, this area is critical for the motor aspects of language production and speech

Insula

Identified as a processing hub, the insula has known activity in motor control and swallowing

Basal Ganglia

These subcortical nuclei help the brain select the best action for a goal and are heavily involved in determining whether movements should be initiated or suppressed

Cerebellum

Often called "the comparator," the cerebellum is vital for motor coordination and learning. It receives the "intent of action" from the cortex and compares it with real-time feedback to update and refine performance

Thalamus

This structure acts as a key relay station in motor-related circuits, helping to refine movements so they are smooth and automatic

Hypothalamus

Responsible for regulating autonomic motor processes and maintaining the body's internal homeostasis

Corticospinal Tract:

Carries commands from the cortex to the spinal cord to move the limbs and trunk

Corticobulbar Tract:

Originates in the cortex and terminates in the brainstem to innervate the cranial nerves necessary for speech and swallowing

1. Pyramidal Tracts (Direct System)

This system is responsible for the voluntary control of muscles. The fibers originate as Upper Motor Neurons (UMN) in the primary motor cortex and descend through the corona radiata and internal capsule.

Corticospinal Tract:

Corticobulbar Tract:

2. Extrapyramidal Tracts (Indirect System)

These pathways provide involuntary and automatic control of muscles, primarily regulating posture, tone, and balance to modulate movement. These tracts largely originate from nuclei within the brainstem. The major extrapyramidal tracts include:

• Rubrospinal tract

• Vestibulospinal tract

• Reticulospinal tract

• Tectospinal tract

neuromuscular junction (NMJ)

is a specialized synapse that serves as the critical bridge between the nervous system and the musculoskeletal system. It is the site where the axon terminal of a lower motor neuron (LMN) meets a muscle fiber to initiate movement

Myasthenia Gravis

This is a condition specifically associated with an imbalance or disruption of acetylcholine at the NMJ. In this disorder, antibodies block or destroy ACh receptors, leading to weakened muscle contractions and characteristic symptoms like drooping eyelids or asymmetry of the facial muscles

cerebellum

is a critical structure of the central nervous system located inferior to the cerebrum and posterior to the pons and medulla. It is primarily responsible for regulating movement in an indirect way to facilitate motor learning and motor coordination

Functional Role: "The Comparator"

It receives the "intent of action" from the motor cortex and compares it with real-time sensory feedback from the spinal cord and brainstem regarding the body's actual position and movement. Based on this comparison, it sends signals to update both current and future motor performance to ensure movements are smooth and accurate.

While primarily a motor structure, the cerebellum also contributes to language processing, specifically in areas of cognitive and executive control, spoken language preparation, and language production and monitoring

Cerebellar Damage and Clinical Signs

• Intention Tremors: Involuntary tremors that occur during purposeful, goal-directed movement.

• Dysmetria: The inability to perform accurate movements, resulting in over-shooting (hypermetria) or under-shooting (hypometria) a target.

• Dysdiadochokinesia: Significant difficulty performing rapid alternating movements, such as flipping hands quickly or repeating speech syllables.

• Ataxic Dysarthria: A motor speech disorder characterized by imprecise articulation, irregular speech breakdowns, and "drunken-sounding" or slurred speech. Prosody may also be affected, often presenting with excess or equal syllable stress

1. Upper Motor Neurons (UMN)

are located entirely within the Central Nervous System (CNS). They originate in the cerebral cortex or the brainstem and travel down descending tracts to synapse on lower motor neurons

2. Lower Motor Neurons (LMN)

Known as the "final common pathway," lower motor neurons are the last link in the chain that triggers muscle contraction.

• Location: Their cell bodies (somas) are located in the brainstem (for cranial nerves) or the ventral horn of the spinal cord (for spinal nerves).

• Path: Their axons exit the CNS to form the Peripheral Nervous System (PNS) and travel to specific muscles

basal ganglia

The primary role of the basal ganglia is "motor control"

What is dysarthria?

refers to a group of neurological speech disorders resulting from disturbances in muscular control over the speech mechanism due to damage to the central or peripheral nervous system

Site of damage Flaccid Dysarthria

Damage to the lower motor neurons (LMN)

Flaccid Dysarthria Key Features:

This type is characterized by muscle weakness, flaccidity, reduced muscle tone (hypotonia), absent or reduced reflexes, and significant muscle atrophy. Fasciculations (visible muscle twitches) may also be present

Flaccid Dysarthria Speech Impacts:

Common symptoms include breathiness (phonation), hypernasality (resonance), imprecise articulation, and audible inhalation or gasping for breath (respiration)

Spastic Dysarthria Site of Damage

Damage to the upper motor neurons (UMN), often resulting from strokes or traumatic brain injuries

Spastic Dysarthria Key Features

Muscles are weak but show increased tone (spasticity) and exaggerated reflexes

Spastic Dysarthria Speech Impacts:

It is characterized by a strained-strangled voice quality, a monotone pitch, hypernasality, and a slow, labored speech rate with imprecise articulation

Ataxic Dysarthria Site of Damage

Damage to the cerebellum

Ataxic Dysarthria Key Features

The primary feature is ataxia, which is a general incoordination of the rate, range, direction, force, and timing of movement. This includes dysmetria (over- or under-shooting targets) and dysdiadochokinesia (difficulty with rapid alternating movements)

Ataxic Dysarthria speech Impacts:

Speech often sounds slurred or "intoxicated" with irregular speech breakdowns. Prosodic features include loudness variations and excess and equal syllable stress

Hypokinetic Dysarthria Site of Damage

Damage to the basal ganglia, most commonly associated with the loss of dopaminergic neurons in Parkinson’s disease

Hypokinetic Dysarthria Key Features

Characterized by a reduced capacity for movement (akinesia), slowness of movement (bradykinesia), rigidity, and resting tremors

Hypokinetic Dysarthria Speech Impacts

Notable for low volume (monoloudness), a monotone voice, difficulty initiating speech, and rapidly increasing speech rates

Hyperkinetic Dysarthria Site of Damage:

Damage to the basal ganglia, leading to the intrusion of abnormal, involuntary patterns of action

Hyperkinetic Dysarthria Key Features

• Associated with involuntary movements such as chorea (rapid, jerky movements), athetosis, dystonia, myoclonus, tics, and essential tremors.

Hyperkinetic Dysarthria Speech Impacts:

Speech impacts vary by the type of movement but may include sudden, forced inspiration or expiration, a harsh or strained voice, transient breathiness, and voice tremors

Mixed Dysarthria

This occurs when damage affects multiple parts of the motor system simultaneously

Acquired Apraxia of Speech (AOS)

is a neurological speech disorder specifically characterized by a deficit in motor planning. It is distinct from dysarthria, which involves disturbances in muscular control such as weakness or spasticity

AOS is caused by ?

damage to the premotor areas of the brain, specifically frontal lobe

Unlike dysarthria, where speech errors are often consistent, AOS is associated with

irregular speech patterns

Aphasia

is an acquired neurogenic language condition characterized by varying degrees of difficulty in language expression, comprehension, and naming. It is most commonly associated with strokes, though it can result from other forms of brain injury

1. Nonfluent/Expressive Aphasia (Broca’s Aphasia)

• Damage to the anterior areas of the left frontal lobe, specifically Broca's area.

• Language production is typically agrammatic and effortful. While expression is significantly impaired, comprehension remains relatively intact