Brain and Cranial - Lecture Flashcards
Name major divisions of brain + subsections
- Forebrain - cerebrum + diencephalon (thalamus, hypothalamus, epithalamus, third ventricle)
- Midbrain / Mesencephalon
- Hindbrain (cerebellum + pons + medulla oblongata)
brain stem -> midbrain (mesencephalon, pons, medulla oblongata).
Describe Cerebrum
Function
Higher-order processing (sensory perception, voluntary movement, cognition, language).
Landmarks
- Lobes: Frontal, Parietal, Temporal, Occipital, Insula
- precentral gyrus: primary motor cortex (frontal lobe)
- postcentral gyrus: primary somatosensory cortex (parietal lobe)
- central sulcus: separates precentral and postcentral gyrus
- Lateral sulcus / sylvian fissure: separates temporal lobe from frontal/parietal
- Longitudinal fissure: separates the two hemispheres
- Transverse fissure: separates the cerebellum from cerebrum
- lateral ventricles
- corpus callosum: major commissural fiber connecting hemispheres (white matter)
organization
Cortex: Outer layer of gray matter – neuronal cell bodies.
White matter: Internal region – myelinated axon tracts.
Basal nuclei: Deep masses of gray matter – subcortical neuron clusters.
we don’t call the cerebral cortex “nuclei” because it’s layered, not clustered.
Name primary, secondary brain vesicles and derived brain regions
Primary:
Prosencephalon,
Mesencephalon,
Rhombencephalon
Secondary:
Telencephalon, Diencephalon
Mesencephalon
Metencephalon, Mylencephalon
At Birth:
Cerebrum, Diencepyhalon
Midbrain
Cerebellum, Pons, Medulla oblongata
Describe Diencephalon
Function
Sensory relay, autonomic control, hormone regulation.
Landmarks
- Thalamus: relay center for sensory input (except smell)
- Hypothalamus: regulates autonomic and endocrine functions
- Epithalamus: includes pineal gland (melatonin) - involved in circadian rhythm
- Third ventricle: between left and right thalamus
Describe Physical layout of ventricular system
The ventricular system
is a continuous, interconnected network of cavities within the brain that are filled with cerebrospinal fluid (CSF) and lined with ependymal cells.
Lateral Ventricles: one in each cerebral hemisphere. Main portion in parietal lobe, each has an anterior horn extending into frontal lobe, a posterior horn extending into the occipital lobe, and inferior horn extending into the temporal lobe.
3rd ventricle: In the diencephalon (between thalami)
4th ventricle: In the hindbrain (between pons/medulla and cerebellum)
Lateral ventricles connect to the third ventricle via the interventricular foramen. Third ventricle connects to the 4th ventricle via the cerebral aqueduct. CSF exist the ventricular system via the median & lateral apertures
Define Septum pellucidum
- thin, vertical membrane made of neural tissue.
- separates the anterior horns of the left and right lateral ventricles.
- Located between the corpus callosum (above) and the fornix (below)
5 functions of CSF
The ventricular system’s main role is to support and protect the central nervous system through the production, circulation, and regulation of cerebrospinal fluid (CSF). Its functions include:
- Physical Protection
CSF acts as a cushion, absorbing shocks from impacts or sudden movements.
It creates a fluid buffer between the brain and the skull, reducing the risk of injury.
- Buoyancy
The brain weighs approximately 1,400 grams, but when suspended in CSF, its net weight is reduced to about 50 grams.
This buoyant support prevents the brain from compressing its own blood vessels or damaging lower structures due to its weight.
- Homeostasis and Chemical Stability
CSF helps regulate the chemical environment of the CNS by maintaining pH, electrolyte balance, and osmotic pressure.
It provides a stable environment necessary for proper neuronal function.
- Waste Removal
CSF removes metabolic waste, toxins, and excess neurotransmitters from the brain.
It facilitates exchange with the blood through structures like the arachnoid granulations and the glymphatic system.
- Nutrient Distribution
CSF helps distribute nutrients (such as glucose and ions) to brain tissues.
It also serves as a medium for the transport of hormones and signaling molecules.
Describe CSF production
- Blood enters fenestrated capillaries in the choroid plexus (within all four ventricles).
- Plasma leaks out of these permeable capillaries into the surrounding connective tissue stroma.
- This plasma is then filtered and modified by a layer of specialized ependymal cells (choroid plexus epithelium), with tight junction at apical ventricle facing surface (blood-csf barrier)
cells actively transport ions (e.g., Na⁺, Cl⁻) into the ventricular space.
Water follows osmotically via aquaporins.
Glucose and other essential solutes are selectively transported.
The result is CSF, a clear fluid low in protein and cells, but rich in specific ions, secreted directly into the ventricular system.
Define ependymal cells
A type of glial cell that lines the ventricles of the brain and the central canal of the spinal cord
Ciliated ependymal cells: help circulate cerebrospinal fluid (CSF)
Modified ependymal cells in the choroid plexus: produce CSF
Define choroid plexus
The choroid plexus consists of modified ependymal cells surrounding a core of fenestrated capillaries and loose connective tissue.
Functions:
Produces cerebrospinal fluid (CSF)
Forms the blood–CSF barrier
Location
Present in all four ventricles
Cells
Composed of ependymal-derived, cuboidal, epithelial-like cells. Glial in origin, but function as epithelial cells. Unlike other ependymal cells, have tight junctions at the apical surface. estricts substance exchange into the cerebrospinal fluid (CSF).
What are the 4 components that protect the brain?
- Bones of skull: prietal, frontal, temporal occipital
- Cranial Meninges: three connective tissue layers - Dura, arachnoid, pia
- Cerebrospinal fluid (CSF)
- Blood-brain barrier
Describe the Cranial Meninges
Three connective tissue layers that surround and protect the brain, enclose the cerebrospinal fluid (CSF), and support blood vessels.
-
Dura layer: Thick, fibrous outer layer composed of two sublayers:
- periosteal layer: attaches to the skull
- meningeal layer: Lies adjacent to the arachnoid mater and continues into the spinal canal as spinal dura. - Arachnoid mater: Web-like middle layer. Separated from pia by subarachnoid space, which contains CSF and blood vessels. Connected to pia via arachnoid trabeculae. Anchors blood vessels. Continues into the spinal cord and maintains the subarachnoid space, which contains cerebrospinal fluid
- Pia matter: Thin, delicate inner layer. Adheres tightly to the brain surface, following contours (gyri and sulci). Helps anchor larger blood vessels of cerebrum. Also continues into the spinal cord.
Describe Dural Venous Sinuses
venous channels located within the dura mater, formed either
- between the periosteal and meningeal layers of the dura (e.g., superior sagittal sinus)
- within folds of the meningeal layer alone, where the meningeal dura separates and creates a channel (e.g., inferior sagittal sinus, straight sinus).
the majority of arachnoid granulations are in the superior sagittal sinus, some in transverse, straigt, and occipital as well.
Define and Name Dural Folds
Where the meningeal layer folds inward, away from the periosteal layer, it forms dural septa that partition and support the brain.
Falx cerebri – a vertical fold that separates the two cerebral hemispheres; attaches anteriorly to the crista galli and posteriorly merges with the tentorium cerebelli.
Tentorium cerebelli – a horizontal fold that separates the occipital lobes from the cerebellum.
Falx cerebelli – a small midline fold between the two cerebellar hemispheres.
Diaphragma sellae – a circular sheet covering the sella turcica, with a hole for the pituitary stalk (infundibulum).
Arachnoid Granulation
small, tufted projections of the arachnoid mater that extend through the dura mater into the dural venous sinuses, primarily the superior sagittal sinus.
one-way valves that allow cerebrospinal fluid (CSF) to pass from the subarachnoid space into the venous blood, but prevent backflow. This is the primary mechanism by which CSF is reabsorbed into the bloodstream, maintaining normal CSF pressure and volume.
Define Meningitis
Inflammation of the meninges
- caused by bacterial or viral invasion of the CNS by way of the nose and throat.
- Pia mater and arachnoid layer are most often affected
- Causes swelling of brain, enlargement of ventricles, hemorrhage
- signs include, high fever, stiff neck, drowsiness, headaches
- diagnosed by examining the CSF -> spinal tap
Describe CSF circulation
- CSF is produced in the choroid plexus of the lateral ventricles from plasma filtered through fenestrated capillaries and processed by ependymal (choroid epithelial) cells.
- CSF flows through the interventricular foramina (of Monro) into the third ventricle, where additional CSF is produced, then through the cerebral aqueduct into the fourth ventricle, where more CSF is produced.
- From the fourth ventricle, CSF exits via the median aperture (foramen of Magendie) and lateral apertures (foramina of Luschka) into the subarachnoid space. A small amount continues into the central canal of the spinal cord.
- CSF circulates in the subarachnoid space, bathing the brain and spinal cord, providing buoyancy, protection, nutrient transport, and waste removal.
- CSF is reabsorbed into venous blood through arachnoid granulations into the dural venous sinuses, mainly the superior sagittal sinus.
- It then drains from the venous sinuses into the internal jugular vein.
Blood Brain Barrier
The blood-brain barrier (BBB) is a selective, protective barrier that regulates the passage of substances from the blood into the brain’s extracellular fluid, maintaining a stable environment for neural function.
Function
1. Protects the brain from toxins, pathogens, and fluctuations in plasma composition
- Maintains ionic and neurotransmitter balance for proper neuronal activity
- Restricts access of immune cells and antibodies, limiting inflammation in CNS
Structure
Formed by endothelial cells of brain capillaries connected by tight junctions, which prevent paracellular diffusion of most substances. Astrocyte end-feet (perivascular feet) surround the capillaries and signal to endothelial cells to maintain the tight junctions and barrier properties, and provide additional layer.
Selective Permeability
Lipid-soluble substances (e.g. oxygen, CO₂, alcohol, nicotine, anesthetics)
→ Cross easily by diffusion through endothelial membranes.
Water-soluble substances (e.g. glucose, amino acids, ions)
→ Require specific transport proteins to cross the barrier.
Large or charged molecules (e.g. most drugs, proteins, pathogens)
→ Blocked unless actively transported or unless BBB is disrupted.
• Small • Lipid-soluble (lipophilic) • Non-polar or weakly polar • Uncharged at physiological pH ⸻ Examples • Gases: • Oxygen (O₂) • Carbon dioxide (CO₂) • Nitric oxide (NO) • Lipid-soluble molecules: • Ethanol • Nicotine • Anesthetics (e.g., diethyl ether) • Barbiturates • Some steroid hormones (e.g., cortisol
Circumventricular Organs
Specialized structures in the brain located around the third and fourth ventricles that lack a typical blood-brain barrier (BBB).
They contain fenestrated capillaries, allowing for free exchange between blood and brain tissue.
Function
1. Monitor the composition of the blood (e.g., osmolarity, hormones, toxins)
2. Secrete hormones directly into the bloodstream - neuroendocrine function
3. Initiate responses to systemic changes (e.g., vomiting, thirst, endocrine regulation)
Location, Function, Major structures of Medulla Oblongata
- Location: Inferior part of brainstem, continuous with spinal cord; below the pons, anterior to the cerebellum.
-
Function:
- All ascending sensory and descending motor tracts pass through
- Regulates autonomic functions: BP, heart rate, respiration
- Contains relay nuclei for sensory and motor pathways
- Associated with visceral/autonomic control
-
Major Structures:
- Decussation of pyramids: Anterior motor tracts (corticospinal); site of motor fiber crossing
- Gracile & cuneate nuclei: Relay touch/proprioception via DCML pathway
-
Olive: Lateral swelling
- Inferior olive: Cerebellar motor learning
- Superior olive: Auditory processing
- Cranial nerve nuclei: CN VIII–XII
First-Order Neuron
The first neuron in a sensory pathway.
Carries sensory information from the periphery to the CNS.
Cell body: in a dorsal root ganglion (for body) or cranial nerve ganglion (for head).
Synapses in the spinal cord or brainstem, depending on the pathway.
Second-Order Neuron
Receives input from the first-order neuron.
Located in the spinal cord (for pain/temp) or brainstem nuclei (for fine touch, proprioception).
Axons of second-order neurons cross (decussate) to the opposite side.
Most ascend to the thalamus and synapse in a thalamic nucleus.
Third-Order Neuron
Located in the thalamus.
Projects from the thalamus to the primary somatosensory cortex of the cerebrum (postcentral gyrus).
Responsible for conscious perception of the sensation.
gracile fasciculus cuneate fasciculus
-
Gracile fasciculus
→ Carries fine touch, vibration, proprioception from the lower body (below T6) -
Cuneate fasciculus
→ Carries same modalities from the upper body (above T6) - Both ascend in the dorsal columns of the spinal cord
- Synapse in the gracile and cuneate nuclei in the medulla oblongata
→ Together, they are part of the dorsal column–medial lemniscus (DCML) pathway.
Medial lemniscus
The medial lemniscus is an ascending sensory tract that carries fine touch, vibration, and conscious proprioception from the contralateral side of the body to the thalamus.
It is formed by the second-order neurons that originate in the gracile and cuneate nuclei of the medulla oblongata.
These axons decussate in the medullaand then ascend through the brainstem (medulla, pons, midbrain) to the ventral posterolateral (VPL) nucleus of the thalamus.
gracile and cuneate fasciculus caryy sensory information to the gracile and cuneate nuclei
Reflex centers of medulla oblongata
- cardiovascular centerers: heart rate, force, vessel diameter
- respiratory centers: breathing rate and depth
- coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head
Location, Function of Pons
Location
Prominent bulge superior to medulla oblongata and anterior to cerebellum
Major structures
- reticular formation: contains nuclei concerned with sleep and posture
- sensory and motor nuclei of cranial nerves, V, VI, VII, and VIII (VII has nuclei in both pons and medulla - pontomedullary junction)
- Nuclei involved with involuntary control of breathing - antagonistic apneustic and pneumotaxic centers
- ascending sensory tracts (from the spinal cord to the brain), descending motor tracts (from the cerebral cortex to the spinal cord), and transverse fibers that originate from the pontine nuclei
List Midbrain primary structures
-
Corpora Quadrigemina (posterior/dorsal)
- Superior colliculi – visual reflexes (tracking, quick eye reflexes, blinking, turning head and eye)
- Inferior colliculi – auditory reflexes (hearing and sound reflexes, flinching from sound, turning to sound) -
Substantia Nigra (between tegmentum and peduncle)
- relays inhibitory signals to thalamus and basal nuclei. Prevents unwanted body movement, degeneration leads to Parkinson’s. -
Superior Cerebral Peduncles
- ascending fibers that synapse in thalamus
- descending fibers of corticospinal pathway -
Cerebral Aqueduct / Aqueduct of Sylvius
- Narrow channel connecting the third and fourth ventricles; runs through the midbrain
Reticular Formation
6
- Diffuse network of neurons (gray matter) extending through the entire brainstem:
-
Regulation of consciousness & arousal
- Maintains alertness via the reticular activating system (RAS)
- Involves midbrain and upper pons
-
Filtering of sensory input
- Prevents sensory overload by filtering irrelevant stimuli
- Allows focus and attention (RAS function)
-
Autonomic control
- Regulates heart rate, blood pressure, and respiration
- Centered in the medulla and lower pons
-
Somatic motor coordination
- Helps control muscle tone, posture, and reflexes
- Integrates motor signals with balance and gaze
- Distributed through pons and medulla
-
Pain modulation
- Inhibits or facilitates pain signals via descending analgesic pathways
- Originates primarily in the medulla
-
Habituation
- Suppresses repeated, non-meaningful stimuli (e.g., ignoring background noise)
- Involves midbrain circuitry
La formación reticular
Epithalamus
Location
- Single midline structure in posterior diencephalon
- composed of paired components: pineal gland, habenular nuclei
- Forms the roof of the third ventricle
Function Pineal glands
- Produces melatonin in response to absence of light, signaling the body to prepare for sleep.
- Regulates sleep-wake (day-night) cycles by increasing melatonin secretion at night.
- Light exposure suppresses melatonin production, reducing drowsiness during the day.
Function habenular nuclei
act as a relay between the limbic system and midbrain
el epitálamo
Thalamus Function
> The thalamus is the brain’s central relay station for sensory, motor, emotional, and cognitive processing.
Function
1. Sensory relay – Receives all sensory input (except smell) and sends it to the appropriate cortical areas for conscious perception
- Filters and modulates input, deciding what reaches awareness
- Motor relay – Receives modulatory motor signals from the cerebellum and basal nuclei, relays them to the motor cortex to help coordinate movement
- Emotion & memory – Involved in emotional processing and memory through connections with the limbic system
smell: Olfactory tract → Primary olfactory cortex
el tálamo
List nuclei of thalamus and functions
- Anterior nuclei – Part of limbic system → involved in memory and emotion
- Medial nuclei – Relay to prefrontal cortex → modulate awareness and emotion
- Ventral nuclei – Relay somatosensory input to parietal lobe (3rs oeswe nwueona -> postcentral gyrus); also carry motor-related signals to motor cortex
- Posterior nuclei – Relay to occipital lobe → contribute to visual processing
- Lateral nuclei – Modulate activity in cingulate gyrus → involved in emotional tone and pain perception
Somesthetic output: Motor responses generated in reaction to somatic sensory input such as touch, pain, temperature, or body position; involves activation of skeletal muscles based on processed sensory information.
"All My Very Powerful Lessons"
núcleos del tálamo
Hypothalamus Function
> The hypothalamus is the brain’s autonomic and endocrine control center, linking the nervous and hormonal systems while regulating survival behaviors.
- Regulates autonomic functions: heart rate, BP, respiration, digestion, body temperature
- Produces ADH and oxytocin → stored/released by posterior pituitary
- Controls thirst and hunger drives
- Coordinates voluntary and autonomic motor responses (When you’re nervous and decide to stand up (voluntary), your body also raises heart rate and blood pressure (autonomic)
- Controls circadian rhythms (biological clock)
- Modulates emotional and behavioral drives (via limbic system)
- Influences subconscious skeletal muscle activity (e.g., facial expression)
El hipotálamo
Cerebellum - Function
The cerebellum refines movement, supports balance, and contributes to motor learning, timing, and limited cognitive and sensory evaluation.
Structure
- Two hemispheres connected by vermis
- gyri of cerebellar cortex know as folia cerebelli
Function
1. Coordinates voluntary movement – smooths and refines motor output
2. Maintains balance & posture – regulates equilibrium and muscle tone
3. Motor learning – adapts and fine-tunes skilled movements
4. Timing & rhythm – regulates precise timing of motor activity
5. Cognitive roles (minor) – involved in attention, language, and planning
6. Evaluates sensory input – compares textures, processes different views of same object
- (Sensory input primarily processed by somatosensory cortex; cerebellum assists)
el cerebelo
cerebellar cortex
3 Layers (Superficial to Deep):
1. Molecular layer – Stellate & basket cells, Purkinje dendrites, parallel fibers
2. Purkinje cell layer – Single row of large Purkinje cells; axons inhibit deep nuclei via GABA
3. Granule layer – Receives input from mossy fibers; sends signals to molecular layer via parallel fibers
Cerebellar Input:
- Mossy fibers: From spinal cord/brainstem → synapse on granule cells
- Climbing fibers: From inferior olivary nucleus → synapse directly on Purkinje cells
Pyramidal cells in motor cortex initiate voluntary movement Send collateral signal -main signal goes to muscles to initiate movement, copy goes to the cerebellum (pons -> middle cerebellar peduncle). Signal copy enter as mossy fibers → processed by Purkinje cells Cerebellum compares intended movement with sensory input Sends inhibitory signals to deep cerebellar nuclei Cerebellar output pathways: To motor cortex (via superior cerebellar peduncle → thalamus) → refines voluntary motor commands To brainstem motor centers (red nucleus, vestibular nuclei, reticular formation) → adjusts posture, balance, reflexes
Arbor vitae
White matter of cerebellum
Function
- Connects cerebellar cortex with deep cerebellar nuclei and cerebellar peduncles
- Carries Purkinje cell output to deep nuclei
- Carries afferent input (from brainstem/spinal cord) to cerebellar cortex
Signals transmitted via Peduncles:
- Superior: Sends cerebellar output to midbrain/thalamus
- Middle: Brings input from cerebral cortex (via pons)
- Inferior: Brings input from spinal cord and medulla
Cerebellar peduncles
superior
connect cerebellum with the mesencephalon, diencephalon, and cerebrum.
Pathway by which most cerebelar output travles
middle
communicate between cerebellum and pons.
Pathway by which most input from the rest of the brain enters
inferior
connect cerebellum with medulla oblongata.
Pathway by which most most spinal input enters cerebellum
> Superior = output, Middle = brain input, Inferior = spinal/brainstem input
Cerebral Peduncles
Location
Midbrain of brain stem
Function
contain descending motor tracts from the cerebral cortex to the brainstem and spinal cord.
Motor pathway Starts: Primary motor cortex Passes through: Internal capsule Then: Cerebral peduncles (midbrain) Descends: Through pons → medulla Decussation: At pyramids of medulla Continues as: Lateral corticospinal tract in spinal cord Terminates: Anterior horn of spinal cord (synapses with lower motor neurons)
Major Functions Frontal Lobe
-
Motor control:
- Primary motor cortex → conscious control of skeletal muscles
- Broca’s area → speech production (usually left hemisphere)
-
Higher cognition:
- Abstract thought
- Foresight and planning
- Decision making
- Social judgment
- Motivation and mood regulation
-
Memory:
- Involved in explicit (declarative) memory retrieval
- Works with hippocampus during event replay and memory consolidation
Major 5 Functions Insula
- Taste perception (gustatory cortex)
- Pain processing – integrates sensory and emotional aspects of pain
- Visceral sensation – awareness of internal organ states (e.g., heartbeat, stomach)
- Emotion and empathy – involved in emotional awareness, especially disgust, empathy, and self-awareness -> connected to amygdala
- Autonomic regulation – contributes to cardiovascular homeostasis and other autonomic responses
Major Functions Parietal Lobe
-
Somatic Sensory Processing
- Somatic sensation – touch, pressure, pain, temperature (primary somatosensory cortex)
- Taste perception – integrates gustatory input
- Sensory integration – combines sensory info for perception (somatosensory association area)
-
Spatial Awareness & Visual Processing - think integrating visual input with somatosensory input
- Spatial perception – body position, depth, navigation
- Visual processing – contributes to spatial and motion aspects of vision
-
Higher Cognitive Functions
- Language comprehension – integrates input for understanding speech (Wernicke’s area, especially in left hemisphere)
- Numerical awareness – involved in quantity recognition, estimation, and calculation
Wernicke's area: Primarily: Posterior part of the superior temporal gyrus (STG) Extends into: Inferior part of the supramarginal gyrus and angular gyrus in the inferior parietal lobule
Major Function Occipital Lobe
- Visual awareness – conscious perception of visual stimuli
- Visual processing – analysis of visual input (color, shape, motion, depth, etc.)
Major functions temporal lobe
-
Sensory Processing
- Hearing – Conscious perception of sound (→ primary auditory cortex). Auditory association cortex.
- Smell – Involved in olfactory processing (via connections to olfactory cortex). Processing of smell occurs in frontal lobe
-
Language & Communication
- Language comprehension – Interpretation of spoken and written language (→ Wernicke’s area, typically in left hemisphere)
-
Emotion & Learning
- Emotion – Processes emotional content via connections to the amygdala
- Learning – Involved in encoding new information
-
Memory
- Memory consolidation – Transfers short-term to long-term memory (→ hippocampus)
- Verbal memory – Especially in dominant (usually left) hemisphere
- Visual & auditory memory – Recognizing and recalling sounds and images
Key structures of limbic system in temporal lobe: Hippocampus Amygdala Parahippocampal gyrus
Wernicke’s area spans both the temporal and parietal lobes: It is located at the posterior part of the superior temporal gyrus Often extends into the inferior parietal lobule This overlap is why it’s often described as at the temporo-parietal junction, especially in the dominant (usually left) hemisphere
Define Higher-order functions
- cognition, memory, emotion, sleep, sensation, motor control, language etc
- involve interactions between cerebral cortex and all other areas of the brain
- involve conscious and unconscious information processing
- subject to modifications and adjustments
Define cognition
The range of mental processes by which we acquire and use knowledge - sensory perception, thought, reasoning, judgement memory, imagination and intuition
Cognition “occurs” in the association areas of the cerebral cortex. Association areas
- constitute about 75% of all brain tissue
- build on what you already know -> more complex association areas pull from many different association areas to make complex pictures.
Much of what we know about cognition come from studies of patients with brain lesions, cancer, stroke and trauma.
Function of Parietal lobe association areas
Clinical Syndromes:
Parietal Lobe: Association Functions
-
Integrates sensory input (visual, somatosensory, proprioceptive) to support:
→ Spatial awareness, body position, and attention to surroundings - Helps determine which stimuli are relevant and builds a map of the body in space
Key Clinical Syndromes:
-
Contralateral neglect syndrome:
→ Ignores stimuli on side opposite lesion (usually left side of space)
→ Caused by damage to the posterior parietal association cortex -
Astereognosis:
→ Inability to identify objects by touch despite normal sensation
→ Caused by damage to somatosensory association area
Frontal Lobe Association areas
Frontal Lobe: Association Functions
- Coordinates complex behavior and movement planning
- Involved in decision-making, judgment, emotion, personality, and social behavior
- Regulates emotional expression and inhibits inappropriate actions
Damage Effects:
- Impaired movement planning
- Poor judgment, impulsivity, inappropriate behavior
- Personality changes
Example:
- Phineas Gage – damage led to disinhibition and personality shift
Temporal Lobe association areas
Clinical
Think identifying stimuli
Functions:
1. Auditory Processing: The temporal lobe is crucial for hearing and sound interpretation, including distinguishing different sounds and understanding speech.
- Memory: The temporal lobe, particularly the hippocampus, plays a vital role in forming new memories and retrieving stored ones.
- Language: Areas like Wernicke’s area (in the dominant hemisphere) are involved in understanding language.
- Object / Face Recognition: The fusiform gyrus in the temporal lobe is involved in recognizing faces.
- Emotional Processing: The temporal lobe integrates emotional responses with sensory inputs.
Visual agnosia
cannot recognize objects -> lesions Inferior temporal cortex
Auditory agnosia
Can’t recognize or interpret sounds -> superior temporal gyrus
visual object agnosia
Inability to recognize objects by sight, despite normal vision. -> Lesion in the inferior temporal cortex
astereognosis -> inability to recognize objects by touch
anomic aphasia
Damage to Wernick’s area -> can recognize object but cannot recall the word.
prosopagnosia
- person cannot remember familiar faces -> lesion to right fusiform gyrus (temporal lobe)
Limbic system
- A network of interconnected brain structures that regulate emotion, motivation, memory, and behavior
- Links higher cognitive functions with emotional and autonomic responses
Core Structures & Their Roles:
- Cingulate gyrus – Emotion regulation, attention, pain processing, motivation
- Medial prefrontal cortex – Decision-making, social behavior, emotional control, self-awareness
- Basal nuclei – Motor control, habit formation, reward processing, some emotional influence
- Amygdala – Emotional memory, especially fear/aversion; links conscious thought to autonomic responses. Temporal lobe.
- Fornix – White matter tract connecting hippocampus to hypothalamus (memory relay)
- Hippocampus – Learning and memory formation (in temporal lobe)
Patient HM
- H.M. underwent surgery for epilepsy → bilateral removal of medial temporal lobes:
→ Nearly entire hippocampus removed
→ Partial amygdala removal
Clinical Findings:
1. Severe anterograde amnesia – Could not form new long-term declarative (explicit) memories
2. Partial retrograde amnesia – Lost some recent past memories; older childhood memories intact
3. Preserved procedural memory – Could learn motor skills (e.g., mirror drawing) without remembering the learning itself
4. Normal intelligence, language, attention, and perception
5. Short-term (working) memory remained intact
Conclusion:
> The hippocampus is essential for forming new long-term declarative memories, but not needed for short-term memory or procedural learning.
Function of Hippocampus
- Essential for forming new long-term declarative (explicit) memories
- Consolidates sensory and cognitive information into unified memories
- During an experience:
→ Hippocampus actively processes input while sensory events are happening - After the experience:
→ It “replays” memory traces to the cerebral cortex, which gradually encodes them into long-term storage
→ This process is called memory consolidation
Note:
> The hippocampus is crucial for forming and organizing new memories, but long-term storage occurs in the cerebral cortex
Type of Memory | Primary Storage Area |
Where are long term memories stored?
-
Temporal lobe (primary site for declarative memory storage):
- Left temporal lobe → Verbal, language-based memories
- Right temporal lobe → Visual and spatial memories
- Medial/anterior temporal regions → Semantic memory (facts, concepts)
-
Frontal lobe:
→ Involved in retrieval, organization, and executive control of memory
→ Stores some episodic memory details, especially sequencing and context -
Parietal lobe:
→ Supports attention to memory, spatial context, and numerical memory -
Occipital lobe:
→ Stores visual elements of long-term memories -
Procedural memory (skills, habits):
→ Stored in basal nuclei, cerebellum, and premotor cortex
→ Does not depend on the hippocampus
Amygdala role in emotion
- Receives input from multiple sensory systems (visual, auditory, olfactory, somatosensory)
- Integrates sensory signals and generates emotional responses (e.g., to a threatening face, pleasant music, or disgusting odor)
Key Functions:
1. Fear & Threat Detection – Detects danger; triggers defensive behaviors (e.g., freezing, fleeing)
2. Food Intake & Aversion – Assigns emotional value to food; can cause aversions after trauma
3. Sexual Behavior & Social Emotion – Guides emotional learning in social and reproductive contexts
4. Emotional Attention – Prioritizes emotionally significant stimuli in perception
Output Pathways:
-
To Hypothalamus
→ Regulates autonomic and endocrine responses (e.g., heart rate, BP, nausea)
→ Key role in the fight-or-flight response -
To Prefrontal Cortex
→ Supports regulation and expression of emotion
→ Helps balance instinctive feelings with socially appropriate behavior
Parts of Brain involved in controlling sleep rhythm
-
Cerebral cortex
→ Final target of sleep-related signaling; involved in conscious awareness and enters reduced activity during sleep -
Thalamus
→ Acts as a sensory gate during sleep; reduces sensory input to allow sleep
→ Helps regulate sleep spindles during non-REM sleep -
Hypothalamus
→ Contains the suprachiasmatic nucleus (SCN) – the body’s master circadian clock
→ Also regulates melatonin release, body temperature, and hormone rhythms -
Reticular formation (brainstem)
→ Contains the reticular activating system (RAS)
→ Promotes wakefulness and arousal by activating the cortex
Summary:
> Sleep-wake rhythms are coordinated by the SCN in the hypothalamus, gated by the thalamus, and promoted or suppressed via the reticular formation and cortical activity.
Suprachiasmatic nucleus
Location:
In the hypothalamus, directly above the optic chiasm
Function:
Acts as the master biological clock
Synchronizes circadian rhythms with the light–dark cycle (external cues)
Pathway
1. Retinal ganglion cells activated by light -> active SCN
2. SCN inhibits pineal gland suppressing melatonin secretion -> promotes wakefulness and alertness
3. When light is absent SCN is not active, does not suppress pineal gland -> melatonin secreted.
Orexins
Location:
- neuropeptides
- Produced by neurons in the lateral hypothalamus
Key Roles:
1. Regulate arousal and wakefulness
2. Promote appetite and feeding behavior
3. Stabilize sleep-wake cycles by activating arousal systems
Adenosine
- A neuromodulator and byproduct of ATP metabolism
- Builds up in the brain during wakefulness as a result of cellular activity
Functions:
1. Promotes sleep pressure – increases the drive to sleep the longer you’re awake
2. Binds to adenosine receptors (A1, A2A), especially in the basal forebrain
3. Inhibits arousal systems and activates sleep-promoting regions
4. Cleared during sleep – adenosine levels fall, helping restore alertness
Clinical Insight:
- Caffeine is an adenosine receptor antagonist
→ Blocks adenosine’s action, preventing inhibition of wake-promoting neurons
→ Temporarily promotes alertness
Cerebral White Matter Tracts
-
Projection tracts
- Extend vertically between the cerebral cortex and lower brain regions, brainstem, or spinal cord
- Only tracts that leave or enter the cortex
- Involved in motor output (e.g., corticospinal tract) and sensory input
- Neurons: Primarily pyramidal neurons in the motor cortex and ascending sensory neurons -
Commissural tracts
- Connect left and right hemispheres to allow interhemispheric communication
- Cross through structures like the corpus callosum (largest), anterior and posterior commissures
- Neurons: Pyramidal neurons -
Association tracts
- Connect different regions within the same hemisphere
- Pyramidal neurons (long fibers) + stellate/interneurons (short fibers)
-
- Support intra-hemispheric integration of sensory, motor, and cognitive information
- Neurons: Interneurons coordinating signals within one hemisphere
Sites of neural integration in cerebrum
- All neural integration occurs in gray matter
- Gray matter in the cerebrum is found in three main locations:
-
Cerebral cortex
→ The outer layer of the cerebrum
→ 90% is neocortex – a six-layered structure with a relatively recent evolutionary origin
→ Primary site for conscious perception, thought, and decision-making -
Basal nuclei
→ Deep gray matter involved in motor control, habit formation, and emotional regulation -
Limbic system
→ Involved in emotion, memory, and motivation
→ Includes structures like the hippocampus and amygdala
Principle cells in cerebral cortex
-
Stellate cells
- Small, star-shaped cells with dendrites projecting in all directions
- Function: Receive and process sensory input locally
- Do not send signals out of the cortex
- Important in association tracts (within the same hemisphere) -
Pyramidal cells
- Large, cone-shaped neurons with long apical dendrites and many spiny branches
- Function: Serve as output neurons of the cerebral cortex
- The only cortical neurons that send axons to other parts of the CNS
- Involved in projection tracts (to brainstem/spinal cord) and commissural tracts (to opposite hemisphere)
Sematotopy
There is a point-for-point correspondence between an area of body and an area of CNS
Sensory Relay Through Spinal Cord
- Sensory information from the body travels to the brain via ascending tracts in the spinal cord. Also called somatosensory tracts
- Different tracts carry specific types of sensation
Examples of Afferent Tracts:
- Posterior column (gracile & cuneate fasciculi): fine touch, vibration, proprioception
- Anterolateral system (spinothalamic tract): pain, temperature, crude touch
- Spinocerebellar tracts: unconscious proprioception → cerebellum
Decussation (Crossing Over):
- Most sensory axons cross sides in the CNS
- Posterior column: decussates in the medulla oblongata
- Spinothalamic tract: decussates in the spinal cord
→ Explains why lesions often cause contralateral sensory loss
Three-Order Neuron Pathway:
1. First-order: receptor → spinal cord or brainstem
2. Second-order: crosses midline → thalamus
3. Third-order: thalamus → primary somatosensory cortex
Motor Output
- Motor intention begins in the motor association areas of the frontal lobe
- These regions generate a motor plan
→ Specifies the sequence and strength of muscle contractions - The motor plan is sent to pyramidal cells in the primary motor cortex (precentral gyrus)
→ These are upper motor neurons
→ Axons descend through the brainstem; most decussate in the medulla and form the lateral corticospinal tracts - Upper motor neurons synapse with lower motor neurons in the anterior horn of the spinal cord
- Lower motor neurons send axons to skeletal muscles, producing voluntary movement
Modulation of Movement:
- The basal nuclei and cerebellum fine-tune motor signals
→ Ensure movements are smooth, coordinated, and appropriately scaled
Role of Basal nuclei in movement
- Basal nuclei are deep gray matter structures located below the lateral ventricles, adjacent to the thalamus
Key Functions:
1. Initiate and terminate intentional movements
2. Involved in automatic, learned motor patterns (e.g., walking, typing)
3. Part of a feedback loop: cerebrum → basal nuclei → thalamus → back to cerebrum
→ Helps refine motor output and suppress unwanted movement
Substantia Nigra (Midbrain) -> functionally part of basal nuclei circuitry
Clinical Note – Dyskinesias:
- Movement disorders from basal nuclei damage
→ Involuntary movements, tremors, or impaired initiation
Role of Cerebellum in movement
- Maintains motor coordination and timing
- Aids in learning motor skills (e.g., playing an instrument, riding a bike)
- Regulates muscle tone and posture
- Smooths muscle contractions for fluid motion
- Coordinates eye and body movements
- Synchronizes movements across multiple joints
Ataxia
- Poor coordination, balance, and timing of movements
- Movements are clumsy, unsteady, or inaccurate
Association Areas for language
-
Wernicke’s area – Left temporal and parietal lobes
- Permits recognition of spoken and written language
- Creates a plan of speech -
Broca’s area – Left lateral frontal lobe
- Generates motor program for speech muscles
- Sends instructions to primary motor cortex for execution -
Right hemisphere counterparts
- Mirror Wernicke’s and Broca’s areas
- Process emotional tone and affective meaning of speech
Clinical Notes:
- Wernicke’s aphasia: Fluent but meaningless speech; poor comprehension
- Broca’s aphasia: Slow, effortful speech; difficulty forming words. comprehension is generally preserved. Difficulty with complex grammar, especially syntactically demanding sentences
- Anomic aphasia: Normal comprehension and speech; impaired object naming. Anomic aphasia is usually caused by damage to the left temporal or parietal lobes, especially areas involved in word retrieval like the angular gyrus -> associated with Wernicke’s area
Cerebral Lateralization
Difference in the structure and function of the cerebral hemispheres
Left Hemisphere
- usually the categorical hemisphere: specializes in spoken and written language, sequential and analytical reasoning, breaks information into fragments and analyzes it
Right Hemisphere
- Usually the representational hemisphere. Perceives information in a more integrated way. Seat of imagination and insight, musical and artistic skill, perception of patterns and spatial relationships, comparison of sights, sounds, smells and taste
Cranial Nerve 1
- olfactory
- sensory
- Origin: Olfactory epithelium
- Function: Smell
- Damage: Loss of smell
Cranial Nerve 2
Optic Nerve
El nervio óptico
- Sensory
- Origin: Retina
- Function: Vision
- Damage: blindness in part or all of visual field
Cranial Nerve 3
Oculomotor
El nervio oculomotor
- Motor
- Origin: Midbrain
- Function: Controls muscles of the eye - inferior rectus, inferior oblique
- Damage: Dropping eyelid, dilated pupil, double vision, difficulty focusing, inability to move eye in certain directions
Cranial Nerve 4
Trochlear Nerve
El nervio troclear
- Motor
- Origin: Midbrain
- Function: Controls muscles of the eyeball - superior oblique
- Damage: double vision and inability to rotate eye inferolaterally - move the eye downward and outward (toward the lower outer corner).
Cranial Nerve 5
Trigeminal Nerve
El nervio trigémino
- Mixed
- Origin: Pons, Mouth
- Function:
Sensory: touch, temperature, pain on face
Motor: muscles of jaw
Most important sensory nerve of the face. Has three divisions
Cranial Nerve 6
Abducens
El nervio abducens
- Motor
- Origin: Pons
- Function: Muscles of the eyeball - lateral rectus
- Damage - inability to rotate eye laterally, and at rest, eye rotate medially
The abducens nerve emerges from the brainstem at the junction of the pons and medulla oblongata, specifically: Medially, between the pyramids (medial) and the pons (superior)
Cranial Nerve 7
Facial Nerve
El nervio facial
- Mixed
- Origin: Taste buds, pons
Sensory Function: Taste (anterior 2/3rds of tongue)
Motor Function: Facial muscles, facial expressions, salivary, tear, nasal and palatine glands - Damage: saggy muscles and disturbed sense of taste - no sweet and salty
Cranial Nerve 8
Vestibulocochlear
El nervio vestibulococlear
- Sensory
- Origin: Inner ear
- Function: Hearing and equilibrium
- Damage: Deafness, dizziness, nausea, loss of balance, nystagmus (involuntary rhythmic oscillation of eyes)
cochlear -> cóclea -> caracol
Cranial Nerve 9
Glossopharyngeal
- Mixed
- Origin: Tongue, medulla
- Sensory Function: Tongue sensations, including taste buds (posterior 1/3 of tongue)
- Motor: Swallowing, salivary glands
- Damage results in loss of bitter and sour taste, impaired swallowing
"Glosso-" means tongue (from Greek glossa) "Pharyngeal" refers to the pharynx (throat)
Cranial Nerve 10
Vagus Nerve
el nervios vago
- Mixed
- Origin: Medulla
- Sensory Function: pharynx, internal viscera
- Motor function: Involuntary motor functions of heart, lungs, digestive tract etc.
- Major role in autonomic nervous system -> control of cardiac, pulmonary, digestive and urinary function. Swallowing, speech, regulation of viscera
- Damage: hoarseness of loss of voice, impaired swallowing. Fatal if damage to both
Cranial Nerve 11
Accessory Nerve
El nervio accesorio / el undécimo par craneal
- Motor
- Origin: Upper spinal cord
- Function: Swallowing head, neck, and shoulder movement
- Damage: impaired head, neck and shoulder movement - head will turn towards injured side
Cranial Nerve 12
Hypoglossal
- Motor
- Origin: Medulla
- Function: Tongue movements for speech, food manipulation, and swallowing
-Damage: if one side is damaged, tongue deviates towards injured side. If both are damaged, then cannot protrude tongue.
The hypoglossal nerve (CN XII) emerges anterior to the vagus nerve (CN X) in relation to the olive.
