Neuroanatomy Basics Quiz

Introduction

• The human brain is incredibly complex.
• Brain function is clinically linked to the state of being alive or dead.
• The importance of the brain hasn't always been fully understood.
• Aristotle believed the brain simply cooled blood.
• Hippocrates had a more accurate understanding of the brain's importance.
• This chapter will study the brain and cranial nerves directly connected to it.

Major Landmarks

• Rostral refers to the forehead.
• Caudal refers to the spinal cord.
• The average human brain weighs 1,600 grams (3.5 lbs) in men and 1,450 grams (3.2 lbs) in women.
• The cerebrum comprises 83% of the brain's volume.
• The cerebellum is the second largest region, containing 50% of the neurons and located in the posterior cranial fossa.
• The brainstem is the remaining portion after removal of the cerebrum and cerebellum. It includes the diencephalon, midbrain, pons, and medulla oblongata.

Major Landmarks (Detailed)

• Longitudinal fissure: A deep groove separating the cerebral hemispheres.
• Gyri: Thick folds (ridges) in the brain.
• Sulci: Shallow grooves in the brain.
• Corpus callosum: A thick nerve bundle at the bottom of the longitudinal fissure, connecting the hemispheres.

Surface Anatomy of the Brain

• A visual representation of the brain labeled with its parts.

Gray and White Matter

• Gray matter contains cell bodies (neurons), dendrites, and synapses – it appears dull due to minimal myelin.
• Gray matter forms the surface cortex of the cerebrum and cerebellum, and nuclei deep within the brain.
• White matter consists of axons, appearing pearly white due to the myelin sheath.
• White matter is positioned below the cortical gray matter in a reversed relationship compared to the spinal cord.
• Tracts or bundles of axons connect different brain regions and the spinal cord.

Meninges

• The meninges are three connective tissue membranes enveloping the brain.
• They lie between the nervous tissue and bone.
• Composed of dura mater, arachnoid mater, and pia mater.
• Protects the brain and provides structural support for its blood vessels.
• No epidural space exists, except in a few locations.
• Dura mater is closely associated with the skull.
• Folds of dura mater extend between different parts of the brain (falx cerebri, tentorium cerebelli, falx cerebelli).
• Arachnoid and pia maters are similar to the ones in the spinal cord.
• Arachnoid mater is a transparent membrane on the brain surface.
• Subarachnoid space isolates it from the pia mater below.
• Subdural space isolates it from the dura mater above, in some places.
• Pia mater is a thin membrane that follows the contours of the brain, dipping into the sulci.

Ventricles of the Brain

• Within the cerebral hemispheres lie cavities known as ventricles, filled with cerebrospinal fluid.
• The lateral ventricles (1 & 2) are the largest, extending into the frontal, temporal, and occipital lobes; separated by the septum pellucidum.
• The third ventricle is a single vertical space beneath the corpus callosum; it communicates with the lateral ventricles through the interventricular foramen (foramen of Monro).
• The fourth ventricle is found within the brainstem, connecting with the third ventricle through the cerebral aqueduct.
• The fourth ventricle continues into the central canal of the spinal cord.

Cerebrospinal Fluid (CSF)

• Fills the ventricles and subarachnoid space.
• The brain produces and absorbs 500mL of CSF per day.
• CSF is produced by the choroid plexus through filtration of blood plasma, with modifications by ependymal cells.
• CSF functions include buoyancy for the brain, cushioning from skull impacts, providing chemical stability, and flushing out waste products.

Blood Supply and the Brain Barrier System

• The blood-brain barrier (BBB) isolates the CNS neural tissue from general circulation.
• Formed by tight junctions between endothelial cells of CNS capillaries.
• Lipid-soluble compounds, steroids, and prostaglandins can pass through.
• Astrocytes control the blood-brain barrier.

Blood Supply and the Brain

• Supplies nutrients and oxygen to the brain via internal carotid and vertebral arteries.
• Drained by the internal jugular veins.
• Cerebrovascular disease is any condition interfering with blood circulation to the brain (e.g., stroke or cerebrovascular accident [CVA]).
• Stroke interrupts blood flow to a brain area, leading to neuron death.

Brain Protection and Support

• Cranium (skull) protects the brain.
• Meninges stabilize the brain within the cranial cavity.
• Cerebrospinal fluid (CSF) protects the brain from sudden movement, provides nutrients, and removes waste.
• Blood-brain barrier (BBB) and blood-CSF barrier selectively isolate the brain from chemicals that may disrupt its functions.

The Medulla Oblongata, Pons, and Midbrain

• Details of each structure and their functions
• The medulla oblongata is crucial for life-sustaining autonomic functions.
• The pons relays sensory information to different brain regions and plays a role in respiration.

The Cerebellum

• Largest part of the hindbrain and second largest part of the entire brain.
• Functions include adjusting postural muscles and fine-tuning conscious and subconscious movements.

The Cerebellum (Structures)

• Structures of the cerebellum include folia, highly folded neural cortex, anterior and posterior lobes separated by a primary fissure, cerebellar hemispheres separated by the vermis, and a narrow band of cortex called the vermis.

The Cerebellum (Structures II)

• The cerebellum includes specialized neurons like Purkinje cells in the cerebellar cortex and the arbor vitae (tree of life), the highly branched internal white matter.
• Cerebellar peduncles connect the cerebellum to brain stem, cerebrum, and spinal cord.

The Forebrain

• Divided into two parts: diencephalon and telencephalon.

Forebrain: Diencephalon

• Encloses the third ventricle, located at the most rostral part of the brainstem.
• Diencephalon comprises three parts: thalamus, hypothalamus, and epithalamus.

Forebrain: Telencephalon

• Primarily develops into the cerebrum.

The Diencephalon: Thalamus

• Acts as a sensory relay station transmitting sensory information to the cerebral cortex.
• Integrates and directs sensory information through the last relay site before it reaches the cerebral cortex.

The Diencephalon: Hypothalamus

• Forms part of the third ventricle walls and floor.
• Extends anteriorly to the optic chiasm and posteriorly to the mammillary bodies.
• Each mammillary body contains nuclei relaying signals from the limbic system to the thalamus.
• The infundibulum is the stalk attaching the pituitary to the hypothalamus.

The Diencephalon: Hypothalamus (II)

• A major control center for autonomic and endocrine systems regulating heart rate, blood pressure, and gastrointestinal activity.
• Responsible for hormone secretion, controlling anterior pituitary hormones (releasing and inhibiting) to regulate growth, metabolism, reproduction, and stress response (LH, FSH, TSH, ACTH, GH, MSH).
• Also produces posterior pituitary hormones for contractions, lactation, and water conservation.
• Regulates water, electrolyte balance, hunger, body weight, sleep, wakefulness, memory, and emotion.

The Diencephalon: Epithalamus

• Includes the pineal gland, which produces melatonin.
• The epithalamus also contains choroid plexus, a web of blood capillaries producing cerebrospinal fluid and lining the thin roof over the third ventricle.

The Cerebrum

• Largest and most prominent part of the human brain.
• Functional principles of the cerebrum:
  • Each hemisphere receives sensory info & sends motor commands to the opposite side of the body.
  • Hemispheres have different functions despite structural similarities.
  • Specific functions correspond to definite regions of the cerebral cortex.

The Cerebrum (Structures II)

• Contains gyri (ridges) and sulci (grooves).
• The insula is medial to the lateral sulcus.
• The longitudinal fissure separates the cerebral hemispheres.
• Lobes are named after the overlying cranial bones. (frontal, parietal, temporal, occipital).
• Sulci divide the frontal lobe from the posterior parietal lobe, the frontal lobe from the temporal lobe, and the parietal lobe from the occipital lobe.

The Cerebrum: Lobes

• Functions of each lobe: frontal (motor, higher thought, planning, etc.), parietal (sensory, integration), temporal (hearing, language), occipital (vision), insula (consciousness, empathy, etc.).

Primary Motor Cortex

• Controls voluntary motor functions.
• Different areas of the cortex correspond to different body parts.

The Primary Somatosensory Cortex

• Receives sensory information from different body parts.
• A specific area of this cortex corresponds to every part of the body.

The Cerebral White Matter

• Mostly consists of glial and myelinated nerve fibers for signal transmission.
• Organized in tracts involved in projection, commissural, and association.
• Projection: Connects cerebrum to lower CNS areas.
• Commissural: Crosses to the opposite hemisphere (e.g., corpus callosum).
• Association: Connects lobes and gyri within a hemisphere.

The Cerebral Cortex

• Located on the surface of the hemispheres, only 2-3mm thick.
• Is about 40% of the brain's mass.
• Contains 14-16 billion neurons.
• Neocortex is the 90% of the cerebral cortex involved with recent evolutionary development and is six layered.
• Basal nuclei and limbic system are also parts of the cerebral cortex.

Histology of the Neocortex

• Contains stellate and pyramidal cells.
• Stellate cells have dendrites projecting in all directions.
• Pyramidal cells have axons going away from the area.

The Limbic System

• Often termed the "emotional brain," it governs emotional experience, expression, and visceral responses.
• Key components include the hippocampus (memory), amygdala (emotion).

The Basal Nuclei

• Masses of cerebral gray matter deep within the white matter, lateral to the thalamus.
• Receive input from the substantia nigra, and the motor areas of the cortex.
• Send signals back to the motor areas and substantia nigra.
• Play a role in motor control.

Language

• The brain processes language with specific regions and association areas.

The Electroencephalogram (EEG)

• Monitors the electrical activity in the brain (brain waves).
• Used to study brain functions during sleep, wakefulness, and to diagnose diseases.
• Lack of brain waves is a sign of brain death.

Alpha Waves, Beta Waves, Theta Waves, Delta Waves

• Different types of brain waves associated with specific states of consciousness or brain activity.

Sleep

• Cycles of sleep occur in circadian rhythms, repeating approximately every 24 hours.
• Sleep is controlled by interactions among the cerebral cortex, thalamus, hypothalamus, and reticular formation.
• Sleep proceeds through four stages of increasing depth of sleep, marked by changes in EEG patterns (alpha, beta, theta, delta).

Memory

• Fact memories: Specific bits of information.
• Skill memories: Learned motor behaviors.
• Short-term memories: Information immediately recalled; includes primary memories.
• Long-term memories: Enduring memories, with secondary and tertiary types.

Cranial Nerves

• 12 pairs of cranial nerves originate at the brain base for communication to the body.
• Exit the cranium and innervate muscles and sense organs (primarily head and neck).
• Cranial nerves are classified as motor, sensory, or mixed.

Cranial Nerves Classification

• Some are purely sensory (e.g., olfactory, optic).
• Some are purely motor (e.g., oculomotor).
• Many are mixed (e.g., trigeminal, facial).

Olfactory Nerve (I)

• Sensory nerve for smell.
• Comprises olfactory bulbs and tracts.

Optic Nerve (II)

• Sensory nerve for vision.
• Composed of optic chiasm and tracts.

Oculomotor Nerve (III)

• Motor nerve controlling eye movement, eyelid opening, pupil constriction, and focusing.
• Damage leads to drooping eyelid, dilated pupils, and vision problems.

Trochlear Nerve (IV)

• Motor nerve responsible for eye movement; specifically rotating the eye.
• Damage can cause double vision.

Trigeminal Nerve (V)

• Largest cranial nerve with mixed functions.
• Provides sensation to the face (touch, temperature, pain).
• Controls chewing muscles.

Abducens Nerve (VI)

• Controls eye movement, specifically lateral eye rotation.
• Damage leads to difficulties in lateral eye movement.

Facial Nerve (VII)

• Mixed nerve controlling facial expressions.
• Involved in salivary gland and tear secretion.
• Sensory branch enables taste on anterior tongue.
• Damage leads to facial sagging and taste problems.

Vestibulocochlear Nerve (VIII)

• Sensory nerve important for hearing and balance.
• Cochlear branch conveys hearing information.
• Vestibular branch provides equilibrium.
• Damage results in hearing loss or balance issues (dizziness).

Glossopharyngeal Nerve (IX)

• Mixed nerve involved in swallowing, salivation, gagging, blood pressure regulation, and taste.
• Taste (bitter/sour) is transmitted via this nerve; damage affects this ability.

Vagus Nerve (X)

• Most extensive cranial nerve.
• Controls swallowing, voice, and regulation of visceral organs.
• Damage can cause problems with voice, swallowing, and regulation of visceral functions.

Accessory Nerve (XI)

• Primarily motor nerve controlling neck and shoulder movement.
• Stimulates shoulder, head, neck, and upper back movement.

Hypoglossal Nerve (XII)

• Motor nerve controlling tongue movement for speech, food manipulation, and swallowing.
• Damage affects tongue movements.

Test your knowledge of basic neuroanatomy with this quiz covering key structures and functions of the brain. Questions range from the corpus callosum to the meninges and cerebrospinal fluid. Perfect for students of neuroscience or anyone interested in brain anatomy.