Topography of the brain

Question 1

Central nervous system (CNS)

Answer 1

Composed of the brain and spinal cord, which are surrounded by the meninges, and enclosed within the cranial cavity and vertebral column. Responsible for coordination and control.

Question 2

Peripheral nervous system (PNS)

Answer 2

The rest of the nervous tissues not enclosed by the meninges, responsible for carrying information to and from the CNS. Composed of sensory afferent neurones, which carry signals to the CNS, and motor efferent neurones, which carry signals away from the CNS.

Question 3

Somatic nervous system (SNS)

Answer 3

Responsible for voluntary movement via the contraction of skeletal muscles.

Question 4

Autonomic nervous system (ANS)

Answer 4

Responsible for involuntary responses via the contraction of smooth/cardiac muscle and secretion from glands. Can be sub-divided into sympathetic, parasympathetic and enteric divisions.

Question 5

3 primary vesicles of the brain

Answer 5

• forebrain (prosencephalon)
• midbrain (mesencephalon)
• hindbrain (rhombencephalon)

Question 6

5 secondary vesicles of the brain

Answer 6

• cerebrum (telencephalon)
• thalamic brain masses (diencephalon)
• midbrain (mesencephalon)
• pons and cerebellum (melencephalon)
• medulla oblongata (myelencephalon)

Question 7

Regions of the adult neural canal

Answer 7

• two lateral ventricles; houses telencephalon
• interventricular foramina; connect lateral ventricles to 3rd ventricle
• third ventricle; houses diencephalon
• cerebral aqueduct; links 3rd and 4th ventricles
• fourth ventricle; houses hindbrain
• central canal; houses spinal cord

Question 8

Cerebrum (telencephalon)

Answer 8

The largest part of the brain, divided into two bilaterally symmetrical hemispheres along the longitudinal fissure. Composed of the cerebral cortex and white matter. Responsible for higher neurological functions eg. memory, emotion and conciousness. Sensory and motor functions also occur in the cerebrum.

Question 9

Lobes of the cerebrum

Answer 9

4 superficial lobes:

• frontal lobe; motor function
• parietal lobe; somesthetic sensation
• temporal lobes; auditory sensation
• occipital lobe; visual sensation

2 deeper lobes:

• cingulate gyrus
• insular

Question 10

Cerebral cortex

Answer 10

A continuous, highly folded layer of grey matter, located superficially within the cerebrum.

Question 11

Gyri and sulci

Answer 11

Gyrus= a ridge in the cerebral cortex
Sulcus= a groove in the cerebral cortex

Question 12

Fissures and sulci

Answer 12

• longitudinal fissure; separates cerebral hemispheres
• lateral fissure; separates temporal lobe from frontal and parietal lobes
• central sulcus; separates frontal lobe from parietal lobe
• parieto-occipital sulcus; separates parietal lobe from occipital lobe

Question 13

Thalamic masses (diencephalon)

Answer 13

Composed of two major regions; the thalamus and hypothalamus, located deep to the cerebrum. Also includes the epithalamus, which contains the pineal gland. Acts as the connection between the cerebrum and the rest of the nervous system.

Question 14

Thalamus

Answer 14

A bilaterally-symmetrical, egg-shaped structure sitting in the third ventricle. The thalamic nuclei are responsible for relaying sensory and motor information.

Question 15

Hypothalamus

Answer 15

Located below the thalamus. Responsible for the control of homeostasis and the regulation of secretion by the pituitary gland. Extends inferiorly to form the posterior part of the pituitary gland, connected by the infundibulum.

Question 16

Epithalamus

Answer 16

Located above the thalamus. Contains the pineal gland, which secretes melatonin to regulate circadian rhythms.

Question 17

Brain stem

Answer 17

Composed of the midbrain, pons and medulla. Carries all motor and sensory pathways to/from the cerebral cortex, houses the nuclei of 10 of the cranial nerves, and the nuclei of neurones that regulate basic functions to sustain life (eg. breathing, heart rate).

Question 18

Midbrain (mesencephalon)

Answer 18

Superior part of the brainstem, connecting the forebrain to the hindbrain. Responsible for the coordination of visual, auditory and somatosensory perception. Surrounds the cerebral aqueduct.

Question 19

Pons

Answer 19

The ‘belly’ of the brainstem, connecting to the cerebellum and coordinating its activities via the cerebellar peduncles. Houses neurones that are important in regulating respiratory rhythm.

Question 20

Medulla

Answer 20

The inferior part of the brainstem, continuous caudally with the spinal cord. Contains neurones that regulate respiration, and autonomic functions such as heart rate and vomiting.

Question 21

Cerebellum

Answer 21

A highly folded, accordion-like structure split into two hemispheres. Involved in fine motor control and memory of motor skills.

Question 22

Bones of the neurocranium (brain box)

Answer 22

• frontal bone
• parietal bones
• temporal bones
• occipital bone
• sphenoid bone
• ethmoid bone

Question 23

Sutures of the cranium

Answer 23

• sagittal suture; between parietal bones
• coronal suture; between frontal and parietal bones
• lambdoid suture; between parietal and occipital bones

Question 24

Bones of the viscerocranium (facial skeleton)

Answer 24

• nasal bones
• inferior nasal conchae
• lacrimal bones
• zygomatic bones
• palatine bones
• maxillae
• mandible
• vomer
• ethmoid bone

Question 25

Meninges

Answer 25

Three connective tissue layers enveloping the CNS: - dura mater - arachnoid mater - pia mater

Question 26

Dura mater

Answer 26

The most superficial layer of the meninges, which is tough, fibrous and strong to protect the brain. Composed of two layers, which separate at dural venous sinuses: - periosteal/endosteal layer (found only within the cranium) - meningeal layer

Question 27

Arachnoid mater

Answer 27

A thin, web-like layer of tissue deep to the dura mater, forming a loose sac which does not extend into the sulci. Holds cerebrospinal fluid in the subarachnoid space, as well as cerebral blood vessels. Emerges into dural venous sinuses at arachnoid granulations, allowing CSF to drain into the bloodstream.

Question 28

Pia mater

Answer 28

The deepest layer of the meninges, composed of a thin fibrous membrane which adheres tightly to the brain and spinal cord.

Question 29

Cerebrospinal fluid (CSF)

Answer 29

A clear solution containing water, small molecules and electrolytes, which circulates throughout the CNS within the ventricular system and subarachnoid space. Removes metabolic waste from interstitial fluid. Provides cushioning and buoyancy to protect the brain from impact.

Question 30

Choroid plexus

Answer 30

A specialised membrane located in the ventricles of the brain, which filters the blood to produce CSF. Formed by vascularised invaginations of the pia mater lined with ependymal cells.

Question 31

Flow of CSF

Answer 31

As CSF circulates it picks up metabolic waste from nervous tissues, and removes it from the CNS. It enters the dural sinuses at arachnoid granulations, where it is reabsorbed into the blood.

Question 32

Hydrocephalus

Answer 32

A build up of CSF, which can increase pressure and cause damage to the brain. It can occur if too much CSF is produced, if there is a blockage in the circulation, or if there is a problem with the arachnoid granulations which stops it being reabsorbed.

Question 33

Function of the blood brain barrier (BBB)

Answer 33

Restricts and regulates the passage of materials between the blood and nervous tissues, helping to create the highly exclusive and specialised environment of the CNS. Essential nutrients may still pass through via simple diffusion (oxygen, CO2) or active transport (glucose, amino acids). The passage of large, hydrophilic molecules or pathogen is restricted.

Question 34

Structure of the blood brain barrier (BBB)

Answer 34

The endothelium of the capillaries in the brain is continuous, with tight junctions. Astrocyte end feet ensheath the capillary, while pericytes are embedded in the basement membrane.

Question 35

Exceptions to the blood brain barrier

Answer 35

Certain areas of the brain do not possess the BBB, and have highly permeable capillaries: - circumventricular organs eg. hypothalamus, pituitary; allows for detection of circulating signals and secretion of hormones - choroid plexus; blood is filtered to produce CSF

Question 36

Diseases of the blood brain barrier

Answer 36

The BBB may become leaky in certain diseases eg. epilepsy, brain trauma. It becomes more permeable as a result of inflammation.

Question 37

Falx cerebri

Answer 37

A thick layer of fibrous tissue running between the two cerebral hemispheres, along the longitudinal fissure.

Question 38

Tentorium cerebelli

Answer 38

A thick layer of fibrous tissue running between the occipital lobe and the cerebellum.

Question 39

Corpus callosum

Answer 39

A white matter tract connecting the two cerebral hemispheres. Located inferiorly to the cingulate gyrus, from which it is separated by the callosal sulcus.

Question 40

Divisions of the cranial cavity

Answer 40

The cranial cavity can be divided into: - anterior cranial fossa - middle cranial fossa - posterior cranial fossa

Question 41

Cranial foramina

Answer 41

- cribriform foramina; CN I - optic canal; CN II - superior orbital fissure; CN III, CNIV, CNV1, CNVI - foramen rotundum; CNV2 - foramen ovale; CNV3 - foramen spinosum; CNV3 (meningeal branch) - internal acoustic meatus; CNVII, CNVIII - jugular foramen; CNIX, CNX, CNXI - hypoglossal canal; CNXII - foramen magnum; CNXI (spinal division)