Neuroanatomy I: The Cerebral Cortex: Gross and Functional Anatomy Flashcards
Three embryological regions of the brain
Forebrain [Cerebrum | Diencephalon]
Midbrain
Hindbrain [Pons | Medulla oblongata | Cerebellum]
Cerebrum (cerebral hemispheres)
- Largest area of brain
- Divided into two cerebral hemispheres
- Separated by the longitudinal fissure
- Connected by the corpus callosum
- Conscious thought processes & intellectual function
- Memory storage, processing & retrieval
- Conscious & subconscious regulation of skeletal muscle contraction
Cortex
- Surface layer
- Gray matter
Increases surface area:
- Thrown into folds - Gyri
- Separated by fissures - Sulci
- Subdivide surface into lobes
Lobes of the Cerebral Hemispheres
- Frontal lobe
- Parietal lobe
- Temporal lobe
- Occipital lobe
Lobes & Sulcus of the Cerebral Hemispheres
Precentral Gyrus
(anterior to central sulcus)
- Primary motor area
- Controls voluntary movement
Post-central gyrus
(posterior to central sulcus)
- Primary sensory area
- Receives & interprets sensations
Superior temporal gyrus
- Primary auditory area
- Reception and interpretation of sound
Motor speech (Broca’s) area
- Located just above lateral sulcus, usually on the left side of the brain
- Controls movements involved in speech
Wernicke’s area
- Located in the posterior section of the superior temporal gyrus on the left side of the brain
- Comprehension of speech
Calcarine sulcus & Primary visual area
- Located on the posterior pole of the occipital lobe around the calcarine sulcus
- Receives visual impressions
Cerebellum (cerebellar hemispheres)
- Co-ordinates complex somatic motor patterns
- Postural muscles-maintains balance
- Refines learned movement patterns
The Brainstem
[Medulla oblongata | Pons | Midbrain]
- Processing and relay centre for information passing to and from cerebrum & cerebellum
- Contains reflex centres associated with respiratory & cardiovascular functions
Diencephalon
- Region of the brain almost completely hidden from the surface
- Consists of dorsal thalamus & ventral hypothalamus
Diagram (back of skull)
The diencephalon consists of the following structures:
Thalamus: Relay & processing centre
Hypothalamus: Involved in hormone production & emotional control
The brain is supplied by…
[Arterial Supply of the Brain]
Two internal carotid arteries
Two vertebral arteries (a branch of subclavian artery
Four arteries anastomose on the inferior surface of the brain & form the circle of Willis
Internal Carotid Arteries
- Leaves neck by passing into cranial cavity through the carotid canal
- Passes upwards & forwards in the cavernous venous sinus (without communicating with it)
- Then leaves sinus, passes lateral to the optic chiasma
- Terminates by dividing into anterior & middle cerebral arteries
Vertebral Arteries
Ascend in the neck through the foramina in the transverse processes of the upper six cervical vertebrae
Enters cranial cavity through foramen magnum
Join together from either side to form the basilar artery
Circle of Willis
Function of the Circle of Willis
Allows for collateral circulation of blood if one or part of the circle becomes blocked or narrowed
Avoids ischemia
The left middle & anterior cerebral arteries are filled via the contralateral anterior & posterior communicating branches
Autoregulation of Cerebral Blood flow
The ability of the brain to maintain relatively constant blood flow
Due to the need for a constant blood supply & water homeostasis
§ Reductions in cerebral blood flow stimulate release of vasoactive substances from the brain that cause arterial dilatation
§ Cerebral smooth muscle in arterioles constricts in response to elevated pressure
Stroke
Interruption of blood supply to parts of the brain
Causes (two main):
Ischaemic - blood supply is blocked due to a blood clot (85% of all cases)
Haemorrhagic - where a weakened blood vessel supplying the brain bursts
Blood Supply in Brain Function
(Cerebral Vascular territories)
- Anterior cerebral
- Middle cerebral
- Posterior cerebral
Anterior Cerebral
Loss of blood supply effect primary motor cortex for lower limb & perineum of contralateral side
Can lead to incontinence (unintentional passing of urine) due to lack of control of pelvic floor muscles
Middle Cerebral
- Blockage will lead to loss of sensation & motor function of body except for lower limb & perineum
- Also supplies Broca’s motor speech area & Wernickes sensory speech area
- Loss of function can effect how someone speaks & the ability to understand speech
Posterior Cerebral
• Supplies primary visual cortex
§ Blockage can lead to visual field defects
• Supplies the hippocampus
§ Blockage can lead to memory loss
The Meninges
Three protective membranes
Dura mater
§ Tough, fibrous outermost covering
Arachnoid mater
§ Consists of arachnoid membrane & the arachnoid trabeculae which extends to the surface of the Pia Mater
Pia mater
§ Blood vessels run along the surface of the pia mater within subarachnoid space
Cranial Dura Mater
Conventionally described as a double layer:
- Endosteal (or periosteal) layer - (actually periosteum covering the skull)
- Meningeal layer (Dura mater proper)
§ Covers the brain
§ Continuous through foramen magnum with the dura mater of the spinal cord
Cranial Dura Mater – Meningeal Layer
Sends inward four septa that divide the cranial cavity into freely communicating spaces, lodging the subdivisions of the brain
Function of the septa:
• Restrict rotatory displacement of the brain
Reflections of Dura Mater
Falx cerebri
Diaphragma sellae
Falx cerebelli
Tentorium cerebelli
Tentorial notch
Venous Sinuses
- Situated between periosteal & meningeal layers of dura mater
Receive tributaries (a vein that empties into a larger vein) from the brain, skull bones, the orbit & the internal ear
Extradural (between periostreal dura mater & the meningeal dura mater – dura mater proper)
[Intracranial Haemorrhages]
May result from trauma or cerebral vascular lesions (raises intracranial pressure)
Subdural (between dura & arachnoid mater)
[Intracranial Haemorrhages]
Due to mainly head trauma (displacement to skull - realtively slow build up of intracranial pressure)
Tearing of veins as they enter superior sagittal sinus
Blood accumulates in potential space between dura & arachnoid mater
Subarachnoid (between the arachnoid mater externally and pia mater internally)
[Intracranial Haemorrhages]
- Leakage or rupture of circle of Willis
- Severe headache | loss of consciousness
Diagnosed by withdrawing heavily blood-stained cerebrospinal fluid through a lumbar puncture
Ventricular System & Central Canal
Ventricular System: CSF filled central passageway - (Passageway -> Ventricles)
- Extends along spinal cord (Central Canal) & brain
- Filled with cerebrospinal fluid (CSF)
- Continuously circulated fluid which also surrounds the brain & spinal cord
- Provides a protective cushion
- Transports nutrients & waste
Ventricular System of the Brain
Cerebrospinal Fluid (CSF)
- Clear, colourless fluid formed by the choroid plexus (coloured red)
- Circulates through the ventricular system
- Enters the subarachnoid space through three foramina in the roof of the fourth ventricle
- Circulates both upwards over the surface of the cerebral hemispheres & downwards over the spinal cord
- Eventually enters bloodstream by passing through arachnoid villi into the dural venous sinuses, in particular the superior sagittal sinus
Cerebrospinal Fluid (CSF) function
- Removes waste products of neuronal activity
- Fluid cushion for protection
Hydrocephalus
Overproduction of CSF or blockage of the ventricular system leading to accumulation of CSF
§ In a neonatal skull the increase in pressure will force unfused cranial bones apart leading to cranial abnormalities as well as neurological complications
§ In a fused adult skull leads to a dangerous rise in intracranial pressure
How can Hydrocephalus be treated?
A shunt that drains the CSF from the ventricular system into a body cavity where it can be reabsorbed
Ventral Surface of the Brain
Cranial Nerves
Cranial Nerve Table
Way to Remember Cranial Nerves:
On Occasion Our Trusty Truck Acts Funny Very Good Vehicle Any How
Sensory | Motor | Both:
Some Say Marry Money But My Brother Says Big Brains Matter More
Olfactory Nerve
Cribriform Plate with foramina
It supports the olfactory bulb, and is perforated by olfactory foramina for the passage of the olfactory nerves to the roof of the nasal cavity to convey smell to the brain
Olfactory Nerve
Optic Nerve
II - Optic - Sensory - Vision
Optic Nerve
Vagus Nerve
X - Vagus - Mixed - Taste | sensory to thoracic & abdominal viscera; Movement & secretion
The vagus nerve travels through the middle portion of the jugular foramen
Vagus Nerve Features
- Longest cranial nerve in the body
- Innervates the skin of the external acoustic meatus & the internal surfaces of the laryngopharynx & larynx
- Provides visceral sensation to the heart & abdominal viscera
- Provides taste sensation to the epiglottis & root of the tongue
- Provides motor innervation to the majority of the muscles of the pharynx, soft palate & larynx.
- Parasympathetic innervation the smooth muscle of the trachea, bronchi and gastro-intestinal tract & regulates heart rhythm
What is the longest cranial nerve in the body?
Vagus Nerve
