Topography of the brain Flashcards
Central nervous system (CNS)
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.
Peripheral nervous system (PNS)
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.
Somatic nervous system (SNS)
Responsible for voluntary movement via the contraction of skeletal muscles.
Autonomic nervous system (ANS)
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.
3 primary vesicles of the brain
- forebrain (prosencephalon)
- midbrain (mesencephalon)
- hindbrain (rhombencephalon)
5 secondary vesicles of the brain
- cerebrum (telencephalon)
- thalamic brain masses (diencephalon)
- midbrain (mesencephalon)
- pons and cerebellum (melencephalon)
- medulla oblongata (myelencephalon)
Regions of the adult neural canal
- 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
Cerebrum (telencephalon)
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.
Lobes of the cerebrum
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
Cerebral cortex
A continuous, highly folded layer of grey matter, located superficially within the cerebrum.
Gyri and sulci
Gyrus= a ridge in the cerebral cortex Sulcus= a groove in the cerebral cortex
Fissures and sulci
- 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
Thalamic masses (diencephalon)
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.
Thalamus
A bilaterally-symmetrical, egg-shaped structure sitting in the third ventricle. The thalamic nuclei are responsible for relaying sensory and motor information.
Hypothalamus
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.
Epithalamus
Located above the thalamus. Contains the pineal gland, which secretes melatonin to regulate circadian rhythms.
Brain stem
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).
Midbrain (mesencephalon)
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.
Pons
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.
Medulla
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.
Cerebellum
A highly folded, accordion-like structure split into two hemispheres. Involved in fine motor control and memory of motor skills.
Bones of the neurocranium (brain box)
- frontal bone
- parietal bones
- temporal bones
- occipital bone
- sphenoid bone
- ethmoid bone
Sutures of the cranium
- sagittal suture; between parietal bones
- coronal suture; between frontal and parietal bones
- lambdoid suture; between parietal and occipital bones
Bones of the viscerocranium (facial skeleton)
- nasal bones
- inferior nasal conchae
- lacrimal bones
- zygomatic bones
- palatine bones
- maxillae
- mandible
- vomer
- ethmoid bone
Meninges
Three connective tissue layers enveloping the CNS:
- dura mater
- arachnoid mater
- pia mater
Dura mater
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
Arachnoid mater
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.
Pia mater
The deepest layer of the meninges, composed of a thin fibrous membrane which adheres tightly to the brain and spinal cord.
Cerebrospinal fluid (CSF)
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.
Choroid plexus
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.
Flow of CSF
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.
Hydrocephalus
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.
Function of the blood brain barrier (BBB)
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.
Structure of the blood brain barrier (BBB)
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.
Exceptions to the blood brain barrier
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
Diseases of the blood brain barrier
The BBB may become leaky in certain diseases eg. epilepsy, brain trauma. It becomes more permeable as a result of inflammation.
Falx cerebri
A thick layer of fibrous tissue running between the two cerebral hemispheres, along the longitudinal fissure.
Tentorium cerebelli
A thick layer of fibrous tissue running between the occipital lobe and the cerebellum.
Corpus callosum
A white matter tract connecting the two cerebral hemispheres. Located inferiorly to the cingulate gyrus, from which it is separated by the callosal sulcus.
Divisions of the cranial cavity
The cranial cavity can be divided into:
- anterior cranial fossa
- middle cranial fossa
- posterior cranial fossa
Cranial foramina
- 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)
