- The Brain weighs 350 g in the newborn and 1400 g in the adult.
- The brain is classified into six postembryonic divisions:
- Telencephalon
- Diencephalon
- Mesencephalon
- Pons
- medulla oblongata
- cerebellum.
- Telencephalon
- consists of the cerebral hemispheres and the basal ganglia
- The cerebral hemispheres contain the lateral ventricles.
- Cerebral hemispheres consist of six lobes and the olfactory structures
- Frontal lobe contains the following gyri:
- Precentral gyrus - consists of the motor area (area 4). (MCQ)
- Superior frontal gyrus contains the supplementary motor cortex on the medial surface (area 6).
- Middle frontal gyrus contains the frontal eye field (area 8) (MCQ)
- Inferior frontal gyrus contains the Broca speech area in the dominant hemisphere (areas 44 and 45) (MCQ)
- Gyrus rectus and orbital gyri are separated by the olfactory sulcus.
- Anterior paracentral lobule
- is found on the medial surface between the superior frontal gyrus (paracentral sulcus) and the central sulcus.
- represents a continuation of the precentral gyrus on the medial hemispheric surface.
- Parietal lobe contains the following lobules and gyri:
- Postcentral gyrus is the primary somatosensory area of the cerebral cortex (areas 3, 1, and 2).
- Superior parietal lobule comprises association areas involved in somato sensory functions (areas 5 and 7 )
- Supramarginal gyrus interrelates somatosensory, auditory, and visual input (area 40)
- Temporal lobe contains the following gyri:
- Transverse temporal gyri of Heschl is the primary auditory areas of the cerebral cortex (areas 41 and 42).
- Superior temporal gyrus contains the Wernicke speech area in the dominant hemisphere (area 22).
- Occipital lobe contains two structures:
- Cuneus contains the visual cortex (areas 17, 18, and 19).
- Lingual gyrus (medial occipitotemporal gyrus) contains the visual cortex (areas 17, 18, and 19).
- Insular lobe (insula)
- Limbic lobe
- is a C-shaped structure of the medial hemispheric surface
- includes the following structures:
- Paraterminal gyrus and subcallosal area
- Cingulate gyrus
- Parahippocampal gyrus
- Hippocampal formation
- is connected to the hypothalamus and septal area via the fornix.
- includes the following three structures:
- Dentate gyrus
- Hippocampus
- Subiculum
- Olfactory structures
- are found on the orbital surface of the brain and include:
- Olfactory bulb and tract
- Olfactory bulb receives the olfactory nerve (cranial nerve [CN] I).
- Olfactory trigone and striae
- Anterior perforated substance is created by penetrating striate arteries
- Diagonal band of Broca interconnects the amygdaloid nucleus and the septal area.
- Basal ganglia
- are the subcortical nuclei of the telencephalon.
- Caudate nucleus
- Putamen
- Globus pallidus
- Amygdaloid nuclear complex (amygdala)
- What is striatum and lentiform nucleus (MCQ)
- Striatum = Caudate nucleus + Putamen
- lentiform nucleus = Globus pallidus + Putamen
- Lateral ventricles
- are ependyma-lined cavities of the cerebral hemispheres.
- contain CSF and choroid plexus.
- communicate with the third ventricle via the two interventricular foramina of Monro
- are separated from each other by the septa pellucida.
- Cerebral cortex
- consists of a thin layer or mantle of gray substance.
- is folded into gyri that are separated by sulci.
- White matter includes the cerebral commissures and the internal capsule
- Cerebral commissures
- interconnect the cerebral hemispheres
- Corpus callosum
- is the largest commissure of the brain.
- interconnects the two hemispheres.
- has four parts: Rostrum, Genu, Body ,Splenium
- Anterior commissure
- interconnects the olfactory bulbs and the middle and inferior temporal lobes.
- Hippocampal commissure (commissure of the fornix)
- Internal capsule
- consists of the white matter
- located between the basal ganglia and the thalamus.
- has three parts:
- Anterior limb
- located between the caudate nucleus and putamen.
- Genu
- located between the anterior and posterior limbs.
- contains corticobulbar fibers
- Posterior limb
- located between the thalamus and lentiform nucleus
- Contains corticospinal fibers.
- Diencephalon
- is located between interventricular foramen and the posterior commissure.
- receives the optic nerve (CN II).
- consists of the epithalamus, thalamus, hypothalamus, subthalamus, and the third ventricle and associated structures.
- Epithalamus
- Pineal body (epiphysis cerebri)
- Habenular trigone
- Medullary stria of the thalamus
- Posterior commissure
- mediates the consensual reaction of the pupillary light reflex.
- Tela choroidea and choroid plexus of the third ventricle
- Thalamus
- consists of the following surface structures:
- Pulvinar
- Metathalamus
- Medial geniculate body (auditory system)
- Lateral geniculate body (visual system)
- Hypothalamus
- Optic chiasm
- Mamillary body
- Infundibulum
- Tuber cinereum
- Subthalamus (ventral thalamus)
- Subthalamic nucleus
- Zona incerta and fields of Forel
- Third ventricle and associated structures
- Lamina terminalis results from closure of the anterior neuropore.
- Tela choroidea
- Choroid plexus
- Interventricular foramen of Monro
- interconnects the lateral ventricle and the third ventricle.
- Optic recess
- Infundibular recess g. Suprapineal recess
- Pineal recess
- Mesencephalon (midbrain)
- contains the cerebral aqueduct, which interconnects the third and fourth ventricles.
- Ventral surface
- Cerebral peduncle
- Interpeduncular fossa
- Oculomotor nerve (CN III)
- Posterior perforated substance is created by penetrating branches of the posterior cerebral and posterior communicating arteries.
- Dorsal surface
- Superior colliculus (visual system) (MCQ)
- Brachium of the superior colliculus
- Inferior colliculus (auditory system) (MCQ)
- Brachium of the inferior colliculus
- Trochlear nerve (CN IV)
- is the only cranial nerve to exit the brainstem from the dorsal aspect.
- Pons
- Ventral surface
- Base of the pons
- Cranial nerves (MCQ)
- Trigeminal nerve (CN V)
- Abducent nerve (CN VI)
- Facial nerve (CN VII)
- Vestibulocochlear nerve (CN VIII)
- Dorsal surface (rhomboid fossa)
- Locus ceruleus
- contains the largest collection of norepinephrinergic neurons in the CNS. (MCQ)
- Facial colliculus
- contains the abducent nucleus and internal genu of the facial nerve.
- Sulcus limitans (MCQ)
- separates the alar plate from the basal plate.
- Striae medullares of the rhomboid fossa
- divide the rhomboid fossa into the superior pontine portion and the inferior medullary portion.
- Medulla oblongata (myelencephalon)
- Ventral surface
- Pyramid contains the corticospinal tract.
- Olive contains the inferior olivary nucleus. (MCQ)
- Cranial nerves
- Glossopharyngeal nerve (CN IX)
- Vagal nerve (CN X)
- Accessory nerve (CN XI)
- Hypoglossal nerve (CN XII)
- Dorsal surface
- Gracile tubercle
- Cuneate tubercle
- Rhomboid fossa
- Striae medullares of the rhomboid fossa
- Vagal trigone
- Hypoglossal trigone
- Sulcus limitans
- Area postrema (vomiting center) (MCQ)
- Cerebellum
- is located in the posterior cranial fossa.
- is attached to the brainstem by three cerebellar peduncles.
- forms the roof of the fourth ventricle.
- is separated from the occipital and temporal lobes by the tentorium cerebelli.
- consists of folia and fissures on its surface.
- contains the following surface structures
- Hemispheres made up of two lateral lobes.
- Vermis is a midline structure.
- Tonsil
- may herniate, with increased intracranial pressure, through the foramen magnum.
- Superior cerebellar peduncle connects the cerebellum to the pons and midbrain.
- Middle cerebellar peduncle connects the cerebellum to the pons.
- Inferior cerebellar peduncle connects the cerebellum to the medulla.
- Anterior lobe
- Posterior lobe
- Flocculonodular lobe
Hemisphere Brain Functions
The brain is divided into two halves (hemispheres). Usually, the left half of the brain controls the right side of the body. The right half of the brain controls the left side of the body.
Frontal Lobes
Functions:
- How we know what we are doing within our environment (Consciousness).
- How we initiate activity in response to our environment.
- Judgments we make about what occurs in our daily activities.
- Controls our emotional response.
- Controls our expressive language.
- Assigns meaning to the words we choose.
- Involves word associations.
- Memory for habits and motor activities
Observed Problems:
- Loss of simple movement of various body parts (Paralysis).
- Inability to plan a sequence of complex movements needed to complete multi-stepped tasks, such as making coffee (Sequencing).
- Loss of spontaneity in interacting with others.
- Loss of flexibility in thinking.
- Persistence of a single thought (Perseveration).
- Inability to focus on task (Attending).
- Mood changes (Emotionally Labile).
- Changes in social behavior.
- Changes in personality.
- Difficulty with problem solving.
- Inablility to express language (Broca's Aphasia).
Parietal Lobes
Functions:
- Location for visual attention.
- Location for touch perception.
- Goal directed voluntary movements.
- Manipulation of objects.
- Integration of different senses that allows for understanding a single concept.
Observed Problems:
- Inability to attend to more than one object at a time.
- Inability to name an object (Anomia).
- Inability to locate the words for writing (Agraphia).
- Problems with reading (Alexia).
- Difficulty with drawing objects.
- Difficulty in distinguishing left from right.
- Difficulty with doing mathematics (Dyscalculia).
- Lack of awareness of certain body parts and/or surrounding space (Apraxia) that leads to difficulties in self-care.
- Inability to focus visual attention.
- Difficulties with eye and hand coordination.
Temporal Lobes
Functions:
- Hearing ability
- Memory aquisition
- Some visual perceptions
- Catagorization of objects.
Observed Problems:
- Difficulty in recognizing faces (Prosopagnosia).
- Difficulty in understanding spoken words (Wernicke's Aphasia).
- Disturbance with selective attention to what we see and hear.
- Difficulty with identification of, and verbalization about objects.
- Short-term memory loss.
- Interference with long-term memory
- Increased or decreased interest in sexual behavior.
- Inability to catagorize objects (Catagorization).
- Right lobe damage can cause persistant talking.
- Increased aggressive behavior.
Occipital Lobes
Functions:
Observed Problems:
- Defects in vision (Visual Field Cuts).
- Difficulty with locating objects in environment.
- Difficulty with identifying colors (Color Agnosia).
- Production of hallucinations
- Visual illusions - inaccurately seeing objects.
- Word blindness - inability to recognize words.
- Difficulty in recognizing drawn objects.
- Inability to recognize the movement of an object (Movement Agnosia).
- Difficulties with reading and writing.
Cerebellum
The cerebellum is involved in the coordination of voluntary motor movement, balance and equilibrium and muscle tone. It is located just above the brain stem and toward the back of the brain. It is relatively well protected from trauma compared to the frontal and temporal lobes and brain stem.
Functions:
- Coordination of voluntary movement
- Balance and equilibrium
- Some memory for reflex motor acts.
Observed Problems:
- Loss of ability to coordinate fine movements.
- Loss of ability to walk.
- Inability to reach out and grab objects.
- Tremors.
- Dizziness (Vertigo).
- Slurred Speech (Scanning Speech).
- Inability to make rapid movements.
Brain Stem
The brain stem plays a vital role in basic attention, arousal, and consciousness. All information to and from our body passes through the brain stem on the way to or from the brain. Like the frontal and temporal lobes, the brain stem is located in an area near bony protrusions making it vulnerable to damage during trauma.
Functions:
- Breathing
- Heart Rate
- Swallowing
- Reflexes to seeing and hearing (Startle Response).
- Controls sweating, blood pressure, digestion, temperature (Autonomic Nervous System).
- Affects level of alertness.
- Ability to sleep.
- Sense of balance (Vestibular Function).
Observed Problems:
- Decreased vital capacity in breathing, important for speech.
- Swallowing food and water (Dysphagia).
- Difficulty with organization/perception of the environment.
- Problems with balance and movement.
- Dizziness and nausea (Vertigo).
- Sleeping difficulties (Insomnia, sleep apnea).
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