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Questions and Answers
What is decerebrate rigidity primarily due to?
What characterizes paraplegia in flexion?
What is the likely cause of paraplegia in extension?
Which function is NOT typically associated with the limbic system?
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What might result from damage to the limbic system?
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What is the primary function of the cervical spine?
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Which of the following features characterizes normal spinal alignment?
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What is the role of the fovea dentis in the spine?
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What stabilizes the atlanto-occipital junction?
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How many paired nerve roots does the spine convey?
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What functions are primarily associated with the limbic system?
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Which part of the hippocampal formation is considered the transitional zone?
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What is the relationship between the hippocampus and short-term memory?
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Which condition is characterized by loss of recent memory and a tendency to fabricate stories?
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Which component of the limbic system is primarily involved in emotional behavior?
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What is a major function of the hypothalamus as part of the limbic system?
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What major change is observed after bilateral removal of the hippocampus?
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What best describes Kluver-Bucy Syndrome?
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Which area is NOT considered a part of the limbic lobe?
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What is the primary output pathway from the amygdala associated with pleasure?
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What best explains the initial center of the Papez circuit?
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Which structure is involved in transmitting signals from the hippocampus?
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What neurotransmitter's reduction is linked to cognitive deficits in dementia?
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Which element of emotional processing bypasses the thalamus?
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What function does the anterior longitudinal ligament (ALL) primarily serve?
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What describes the orientation of the lumbar vertebrae's spinous processes?
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How does the posterior longitudinal ligament (PLL) function when it ossifies?
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At which vertebral level does the spinal cord typically end in adults?
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What is the role of the ligamentum flavum?
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What articulations does the sacrum make with the spine?
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What is the effect of intervertebral fanning in the thoracic region?
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What is a characteristic load-sharing function of the sacrum?
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What is the composition of the sacrum?
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Which of the following describes the attachment behavior of the anterior longitudinal ligament?
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What occurs when the PLL ossifies?
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What unique characteristic do the thoracic vertebrae exhibit compared to lumbar vertebrae?
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What is a distinctive feature of the coccyx?
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Which of the following is true regarding the ligamentous anatomy of the spine?
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Where is the thinnest part of the spinal cord's ligament located?
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What structure holds the nerve poles in place?
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Which statement accurately describes the relationship of afferent and efferent pathways in the spinal cord?
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In which layers are first-order neuron cell bodies of the corticospinal tract predominantly located?
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What surrounds the small central canal filled with CSF in the transverse section of the spinal cord?
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Where does the conus medullaris terminate in adults?
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Which of the following statements about spinal cord width is true?
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Which part of the spinal cord is involved in the ascending sensory pathways?
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What is the primary role of the paired denticulate ligaments?
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Which ascending spinal tract is responsible for fine touch and proprioception?
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Which of the following describes the flow of CSF from the fourth ventricle?
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Where do the axons of upper motor neurons travel after leaving the cortex?
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What is the functional significance of the lumbosacral enlargement?
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What is a distinguishing feature of the spinal cord's white matter?
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Study Notes
Decerebrate Rigidity
- Also known as decerebrate posturing
- Caused by overactive gamma efferent nerve fibers to muscle spindles
- Results from the release of these neurons from higher centers
Paraplegia in Flexion
- Occurs when all descending tracts are severed
- Reflex responses are flexor in nature
- Tone of extensor muscles is diminished
Paraplegia in Extension
- Domination of increased tone of extensor muscles over flexor muscles
- Occurs due to incomplete severance of all descending tracts, with persistence of the vestibulospinal tract
Limbic System
- A functional system of cortical and subcortical neurons
- Interconnections form complex circuits involved in memory, behavior, and emotions
- Damage to the limbic system can lead to anterograde amnesia, and inappropriate behavior and emotions
Limbic Lobe: The Limbus
- Means "to border, fringe or ring"
- Coined by Broca in 1878
- Found in the medial surface of the cerebral hemisphere
- Borders the corpus callosum and rostral brainstem
- Includes:
- Cingulate gyrus and Subcallosal gyrus (anterior extension)
- Cingulum
- Septal regions
- Parahippocampal gyrus and Hippocampal formation
Limbic System Functions
- Emotion activities
- Preservation of species
- Visceral activities
- Mechanisms for memory
Hippocampal Formation
- Involved in memory and learning
- Three parts:
- Dentate gyrus
- Hippocampus proper (Ammon’s Horn)
- Subiculum (transitional zone between hippocampus and entorhinal area)
- Resembles a seahorse
- 2 inches long
- Located on the floor of the temporal horn of the lateral ventricle
Hippocampal Connections
- Connect to:
- Cingulum to prefrontal, posterior parietal, and temporal association areas, and the entorhinal area of the parahippocampal gyrus
- Hippocampal formation via the cingulum from cerebral cortex
Hippocampal Function
- Formation of new memories and learning
- Bilateral removal can lead to loss of recent and short-term memory and the ability to learn
- Anterograde amnesia
- Signals are emitted to the hippocampal formation to rehearse memories until they are stored permanently for long-term memory
Alzheimer's Disease
- Progressive dementia under the age of 65
- Senile dementia over the age of 65
- Marked by increasing forgetfulness
- Loss of neurons in:
- Hippocampus (output to association cortices and diencephalon)
- Parahippocampal areas (input to hippocampus from association and limbic areas)
- Decreases cholinergic innervation of the cerebral cortex
- Reduction of hippocampal connections causes recent memory loss
- The reduction of cholinergic innervation is due to the degeneration of large cholinergic neurons in the Basal Nucleus of Meynert in the anterior perforated substance -Substantia innominata
- Absence of neocortical acetylcholine accounts for cognitive deficits
Korsakoff Syndrome
- Loss of recent memory and tendency to fabricate false accounts of recent events
- Caused by chronic alcoholism and nutritional deficiencies (Vitamin B deficiency)
- Affects the hippocampus, mammillary bodies, and medial dorsal thalamic nuclei
Papes Circuit
- Alveus of the hippocampus → Fimbria of the Fornix → Crux of the fornix→ Body of the fornix → Column of the fornix (anterior commissure) → Subiculum → Nuclei of the mamillary body → Mamillothalamic tract (bundle of Vicq d Azyr) → Anterior thalamic nucleus → Thalamocingulate radiation → Cingulate Gyrus
Emotion
- Any feeling state
- Includes: fear, anger, excitement, love, hate
- Components:
- Perception
- Feeling
- Autonomic
- Affect
- Reflex
Amygdaloid Nucleus
- The Amygdala
- Involved in behavior and emotions
- Almond-shaped, found beneath the uncus
- Divided into:
- Large basolateral group
- Small corticomedial group
- Central group
Amygdaloid Nucleus Connections
- Basolateral nuclei:
- Well-developed in humans
- Input from sensory areas of cerebral cortex and thalamus
- Corticomedial nucleus:
- Poorly developed
- Input directly from olfactory bulb
- Via lateral olfactory stria
- Central nucleus:
- Receives input from both basolateral and corticomedial nuclei
Amygdaloid Nucleus Functions
- Programs appropriate behavioral responses
- Animals: primarily corticomedial nuclei
- Humans: purely non-olfactory experiences, from all parts of the cerebral cortex via the cingulum to basolateral nuclei
- Assess the nature of input, pass to the hypothalamus, other limbic centers, and cerebral cortex to elicit a response
- Orbitofrontal and cingulum: perceive emotions
- Hypothalamus: expresses emotions
Kluver-Bucy Syndrome
- Absence of emotional response (fear, rage, aggression)
- Compulsion to be overly attentive to all sensory stimuli and examine objects visually, tactilely and orally
Septal Region
- Poorly developed in humans
- Includes:
- Paraterminal gyrus
- Subcallosal area in front of lamina terminalis
- Septal nuclei
- Receives input from the hippocampus
- Reciprocal connections with the hypothalamus, amygdala, and cingulate gyrus
Septal Region Connections
- Septal region and anterior hypothalamus to midbrain reticular system:
- Via medial forebrain bundle and stria medullaris
- Stria passes dorsomedial thalamus to habenular nucleus
- Habenulointerpeduncular tract (fasciculus retroflexus) to interpeduncular nuclei of the midbrain reticular formation
Septal Region Functions
- Input to:
- Respiratory
- Cardiovascular
- Salivatory
- Other centers to respond to emotional events
- Associated with reward or pleasure phenomenon
- Connections may be modified by anti-psychotic drugs
- May be involved in the euphoria associated with the use of narcotics
- Damage can lead to a marked increase in sexual activity in elderly males
Limbic System Summary
- Visceral brain
- Ring
- Crown
- Subdivisions:
- Cortical
- Limbic Lobe
- Hippocampus
- Subcortical
- Amygdaloid Nucleus
- Septal Region
- Fornix
- Hypothalamus (MB)
- Olfactory
- Thalamus
Thalamus: The Sensory Relay Station
- Relays sensory information for everything seen, heard, tasted, and touched to the cortex
- Relates experience for memory storage
Smell
- The only sense that bypasses the thalamus
- Relayed directly to near the emotion amygdala and mammillary bodies
Inferior Articulating Processes
- Lie medial to the superior processes
- Correspondingly face laterally and somewhat anteriorly
Lumbar Vertebrae
- Have the largest vertebral bodies
- Carry the largest axial bones
- Spinous process is oriented horizontally, compared to thoracic vertebrae where it faces downward
Adult Spinal Cord
- Ends at the level of T12-L1
Anterior Longitudinal Ligament
- Originates at the tubercle of the atlas’s anterior arch
- Extends ventrally along the entire spinal column to the sacrum
- Adherent to the periosteum of vertebral bodies and the ventral intervertebral anulus fibrosus ventrally
- Restrains extension
- Located anterior to the vertebral body
- Prevents anterior dislocation
Sacral Spine
- A triangular anteriorly concave bone
- Bridges and shares loads between the spine and the pelvis
- Articulates with:
- Superiorly: L5 (via facet articulations facing medially and posteriorly)
- Bilaterally: the ilium (via the synovial sacroiliac joints)
- Inferiorly: the non–load-bearing four-level coccyx
Sacral Spine (Continued)
- Composed of five vertebrae fused both anteriorly and ventrally by early adulthood.
- The mature sacrum encases its respective nerve roots in a central canal terminating around S4.
- The sacral hiatus is found below the termination of the central canal.
- Also known as the tail bone
- Tip of sacral spine is the coccyx
Posterior Longitudinal Ligament
- Restrains spinal flexion
- Courses along the vertebral bodies dorsally from the axis (with its extension to the intracranial basion termed the tectorial membrane) to the sacrum
- Primarily a stabilizer of adjacent levels
- Its deep layers are wider and thinner than its superficial layers.
- Located over the annulus fibrosus.
- Superficial layer spans longer intervertebral intervals.
- Ossification potentially:
- Thickens and expands in diameter
- Reduces space and narrows the spinal canal
- Compresses the spinal cord and nerves
- Increases risk of spinal injury
Ligamentum Flavum
- Courses dorsal to the spinal cord.
- Prevents hyperflexion.
- Attaches the laminae of adjacent levels.
- Thickness increases from the rostral most ligament at C2 toward the caudal ligament at L5–S1.
- Thickest at its insertion in the posterosuperior caudal lamina and medially.
- Thinnest superiorly and laterally at each level.
- Has a deep, thin midline component that runs continuously throughout the spine in many people.
Spinal Cord and Spinal Nerves
- Ensheathed in leptomeninges: -pia, arachnoid, and dura
- Paired denticulate ligaments attach the spinal cord to the arachnoid and dural sheath.
- 20-22 pairs
- The spinal cord is bathed in CSF which is in continuity with the intracranial subarachnoid compartment.
- 31 pairs of ventral and dorsal roots emerge from the spinal cord on each side per level.
- Dorsal and ventral components combine into a mixed spinal nerve.
- These components exit the spinal canal below their correspondingly named levels.
Spinal Cord and Spinal Nerves (Continued)
- Due to the developmental ascent of the spinal cord relative to the vertebral column, there is a discrepancy in functional spinal cord segments relative to bony exit points in the vertebral column.
- The conus medullaris is the termination of the spinal cord at L1-L2 in adults before fanning into the cauda equina.
- It is attached to the sacrum via the filum terminale.
Spinal Cord Structure in Transverse Section
- A small central CSF-filled canal, which is lined with ependyma.
- Gray matter, which is butterfly-shaped and surrounds the CSF.
- White matter, which surrounds the gray matter.
Spinal Cord: Width
- Widest in the cervical region, due to the combination of its substantial dorsal horns serving the upper extremities and the afferent white matter dorsal fasciculi innervated at all inferior levels.
- Lumbosacral enlargement is present from L2 to S3 because of this region's motor functions.
Filum Terminale
- Holds nerve poles in place.
- The central canal is filled with CSF; from the fourth ventricle, some CSF flows through a narrow passage called the obex and enters the central canal of the spinal cord.
Spinal Cord Tracts
- Follow a medial-lateral topographic principle:
- Afferent pathways enter at higher levels and remain lateral than lower levels.
- Descending efferent tracts innervating lower levels remain lateral, whereas more proximal groups synapse medially onto gray matter more proximally.
Corticospinal Tract
- Cortico (cortex) and Spinal (spine) “from cortex to spine,” meaning it’s a descending motor pathway.
- The corticospinal tract or pyramidal motor tract has first-order neuron cell bodies predominantly in layer V of the primary motor (Brodmann area 4), premotor, and supplementary motor cortices of the brain.
- The axons of these upper motor neurons travel through the corona radiata and posterior limb of the internal capsule, cerebral peduncle, and upper brainstem before decussating in the medullary pyramids and traveling in the contralateral lateral corticospinal tract dorsolaterally in the spinal cord.
- A minority of axons descends instead as the ipsilateral anterior corticospinal tract, which lies just lateral to the anterior median fissure before crossing in the anterior white commissure at their level of termination.
Dorsal Column-Lemniscus
- The cell bodies of sensory neurons reside in the dorsal root ganglia.
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Description
Test your knowledge on motor disorders such as decerebrate rigidity and various forms of paraplegia, alongside the functions of the limbic system. Discover how these conditions affect muscle tone and emotional behavior. This quiz covers important concepts in neurology related to the nervous system.
