Case 19- Brain anatomy Flashcards
Primary development divisions of the brain- based on embryological structures
- Forebrain (Prosencephalon)- forms the Telencephalon and Diencephalon
- Midbrain (Mesencephalon)- forms the Mesencephalon
- Hindbrain (Rhombencephalon)- forms the Metencephalon and Myelencephalon
Secondary developmental divisions of the brain- what do the primary developmental divisions give rise to
- Telencephalon- forms the Cerebral hemispheres, deep structures
- Diencephalon- forms the Diencephalon (Hypothalamus, Thalamus, Subthalamus, Epithalamus)
- Mesencephalon- forms the Midbrain
- Metencephalon- forms the Pons, Cerebellum
- Myelencephalon- forms the Medulla (Oblangata)
Structural development divisions of the brain- what do the secondary developmental divisions develop into:
- Cerebrum- made of Cerebral hemispheres and deep structures
- Diencephalon- made of Hypothalamus, Thalamus, Subthalamus, Epithalamus
- Brainstem- made of Midbrain, Pons and Medulla
- Cerebellum
Corpus callosum
Connects the two cerebral hemispheres. It function is to communicate between the right and left cerebral hemispheres of the brain.
Septum pellucidum
Thin membrane which separates the two lateral ventricles of the brain, extends down from the corpus callosum
Hypothalamus
Its function is homeostasis, regulation of metabolic processes. It links the nervous system and the endocrine system via the pituitary gland.
Thalamus
The inter thalamic adhesion connects the halves of the thalamus. The thalamus functions as a relay system. Site either side of the third ventricle
Subthalamus
Below the thalamis. It contains the subthalmic nucleus which is associated with the basal ganglia and controls motor control and learning, behaviour and emotions.
Epithalamus
Links the limbic system to other parts of the brain. The Limbic system is involved in emotion, behaviour and long term memory.
Midbrain
First part of the brainstem, involved in motor control, alertness, auditory processing and visual processing. The cerebral aqueduct runs through the midbrain.
Superior and inferior Colliculi
In the posterior part of the midbrain, there are two Superior and two Inferior Colliculi, its involved in visual and auditory processing.
Pons
Closely related to the cerebellum and the 4th ventricle, part of the brainstem. Contains Cranial neve nuclei and relays signals to the Cerebellum.
Medulla Oblongata
Final part of the brainstem. It has functions in reflexes, autonomic function, cardiac, respiratory and vasomotor centres.
Infundibulum
The pituitary stalk, connects the hypothalamus to the posterior pituitary
Mammilary bodies
Part of the limbic system
Pineal gland
Produces melatonin, controls the wake/sleep pattern. Has photoperiodic function
Anterior commissure
Connects the right and left temporal lobe. Forms the connection between structures of the limbic system. Allows for the transfer of auditory and olfactory information.
Posterior commisure
Connection between the left and right hemispheres. Allows for the pupillary light reflex.
Fornix
Part of the limbic system
Optic chiasm
Where the optic nerves cross over
Cerebrum
1) Largest part of the brain, it is located in the anterior and middle cranial fossae.
2) It extends from the frontal bone anteriorly and the occipital bone posteriorly.
3) Split into left and right hemispheres
The medial/great longitudinal fissure
The medial/great longitudinal fissure separates the cerebral hemispheres, this is a deep groove. The fissure contains the falx cerebri and the hemispheres are covered by the meningeal layers. The corpus callosum connects the right and lefts cerebral hemispheres.
Internal structures of the Cerebrum
- Grey matter- on the surface of each cerebral hemisphere, this is known as the cerebral cortex. Contains neuronal cell bodies
- White matter- in the deeper parts of the brain, the Myelinated axons
The lobes of the Cerebrum
Each lobe is named after the bone it sits under. The lobes are just structural but contain the cortical areas that perform the function. Includes Frontal, Parietal, Temporal and Occipital. The two additional small lobes are the limbic and insular lobes
Frontal lobe of the Cerebrum
Controls voluntary movement (primary motor cortex), higher intellect, personality, mood, social conduct and language (dominant hemisphere side only). Contains the pre-motor and pre-frontal cortex
Parietal lobe of the Cerebrum
Controls somatosensory information processing (primary somatosensory cortex). Language and calculation on the dominant hemisphere side and visuospatial functions on the non-dominant hemisphere side.
Temporal lobe of the Cerebrum
The cortical association area is in charge of memory and language. Contains the primary auditory cortex which controls hearing.
Occipital lobe of the Cerebrum
Contains the primary visual cortex which controls the cortical association area which is responsible for vision.
What separates the different lobes
1) The frontal and parietal lobes are separated by the Central sulcus.
2) Separating the Occipital and Parietal lobe is the Parieto-occipital sulcus.
3) The temporal and frontal lobe are separated by the lateral fissure.
4) The Insula lobe is within the Lateral fissure.
Limbic and insular lobe
Limbic lobe- involved in memory and emotion, it is within the frontal lobe.
Insular lobe- its function is consciousness and emotion
Cingulate gyrus- considered part of the limbic lobe
Gyri and sulcus
The Cerebrum consists of depressions known as sulci in between ridges known as gyri. The pia mater follows the sulci but the arachnoid mater drapes over the surface of the cerebrum
Types of sulcus
- Parieto-occipital sulcus- separates the parietal and occipital lobe
- Lateral sulcus- separates the temporal and frontal lobe
- Central sulcus- separates the frontal and parietal lobe
- Pre-central sulcus- anterior to the central sulcus
- Post-central sulcus- posterior to the central sulcus
- Intraparietal sulcus- within the parietal lobe
- Temporal sulci- within the temporal lobe
- Frontal sulci- within the frontal lobe
- Calcarine sulcus- within the occipital lobe
- Cingulate sulcus- below the cingulate gyrus
Key Gyri
- Frontal pole- anterior part of the brian
- Occipital pole- posterior part of the brain
- Pre-central gyrus= anterior to the central sulcus
- Post-central gyrus= posterior to the central sulcus
- Frontal Gyri- sit within the frontal lobe, are split into an inferior, middle and superior zone
- Temporal Gyri- within the temporal lobe are split into a superior, middle and inferior zone
- Superior parietal lobule- within the parietal lobe
- Supramarginal gyrus
- Angular gyrus- edge of the lateral fissure
- Cingulate gyrus- part of the limbic lobe, sits above the corpus callosum
- Parahippocampal gyrus- parallel to the hippocampus
The two main types of Cortex
1) Primary cortical areas- control motor and sensory input/output
2) Association cortical areas- the areas that process and interpret the information coming to the brain through the sensory cortices or plan the movement of the motor cortices.
Function of the cortical areas
- Primary motor cortex- within the precentral gyrus of the frontal lobe, present in both hemispheres. It provides motor instructions for structures on the opposite side of the body. The left motor cortex controls the right side of the body.
- Primary somatosensory cortex- within the postcentral gyrus of the parietal lobe. Present in both hemispheres and receives sensory information from the body. The sensory information includes pain, temperature, touch, muscle stretch etc
Structure of the primary somatosensory cortex
Like a person lying along the top. With the structures controlling the head and face towards the temporal lobe
Structures in the cortex- Primary visual cortex
Within the occipital lobe in both hemispheres. Information from the opposite eye for visual processing
Structures within the cortex- Primary auditory cortex
Within the temporal lobe of both hemispheres. Contains information from the ear for auditory processing.
Structures within the cortex- Limbic association area
Anterior portion of the temporal lobe, within the Parahypocampul gyrus. Links emotion with sensory input and is important in learning and memmory
Structures within the cortex- Prefrontal cortex
Anterior in the frontal lobe, links information from other associated areas. Important in memmory, planning, higher order concept formation and personality
Structures within the cortex- Premotor cortex
Involved in planning and motor function. Links closely with the primary motor cortex. Anterior to the pre-central gyrus within the frontal lobe
Structures within the cortex- Posterior parietal association area
Links information from the primary and unimodal sensory area
Other structures within the cortex
- Primary motor cortex- sits within the pre-central gyrus
- Visual unimodal association cortex
- Auditory unimodel association cortex
- Somatosensory unimodal association cortex
- Primary somatosensory cortex- within the postcentral gyrus
- Reading comprehension area- posterior to Wernicke’s area
Unimodal association areas
The unimodal association areas only receive one type of input and work closely with multimodal association areas. They are closely linked with surrounding cortical areas. A lot of these areas work together
Broca and Wernicke’s area
• Broca’s area- motor speech area, close to the primary motor cortex. Linked to speech production. If damaged a person would be unable to talk but would be able to understand speech. Within the frontal lobe
• Wernicke’s area- involved in speech comprehension. If damaged the patient would be able to speek but what they were saying would not make sense. At the edge of the lateral sulcus.
Broca’s and Wernicke’s area are only present in the left hemisphere for most people
The 3 different types of Cortical projections
- Association fibres- link gyri in the same hemispheres. For example, Arcuate fasciculus
- Commissural fibres- link gyri across hemispheres. For example- Corpus callosum, anterior commissure and the posterior commissure.
- Projection fibres- link gyri to other CNS structures. For example, the Corticospinal and Corticobulbar pathways
Examples of damage to cortical projections
1) Arcuate fasciculus- connects Wernicke’s and Broca’s area in the left hemisphere. Damage to this pathway leads to a speech deficit called ‘conduction aphasia.
2) Damage to commissural fibres stops the two hemispheres from communicating i.e. split brain syndrome
3) Damage to the Corticospinal and Corticobulbar pathway leads to paralysis.
Cerebellum
Largest part of the hindbrain. Its function is entirely motor:
• Operates on an unconscious level
• Coordination of balance, vestibulocular reflex, output to lower motor neurons for trunk and limb stability
• Coordination and correction of trunk and limb movements
• Streamlining of cortical output
Location of the Cerebellum
Its in the posterior cranial fossa. Its beneath the tentorium cerebelli. Its embryologically related to the pons, it originates from the dorsal aspect of the brainstem. Connects to the brainstem by the 3 cerebellar peduncles. The 4th ventricle is located between the pons and the cerebellum.
Visible surface of the cerebellum
Thin sheet of cortex (grey matter). This is repeatedly folded giving a large surface area, the folds are known as folia. Between the folia are fissures which vary in depth.
The hemispheres of the cerebellum
- Right
- Left
- Not as separated as the left and right cerebral hemispheres, its joined in the midline by the vermis
- The Cerebellar tonsils are inferior extensions of each hemisphere
The lobes of the Cerebellum
- Anterior lobe- regulation of muscle tone, coordination of skilled voluntary movement
- Posterior lobe- planning of voluntary lobe
- Flocculonodular lobe- split into Flocculus, Nodule. Maintenance of balance, control of eye movement
The Fissures of the Cerebellum
- Primary- between the anterior and posterior lobes
- Horizontal- in the posterior lobe, structural
- Postereolateral
Functional areas of the Cerebellum
- Vestibulocerebellum- part of the vermis and part of the Flocculo-nodular lobe. Its function is maintenance of balance and control of eye movement
- Spinocerebellum- made of the vermis and paravermis region and the anterior lobe. Functions to regulate muscle tone and coordinate skilled voluntary movement
- Cerebrocerebellum- biggest structure. Composed of the posterior lobe. Involved in planning of voluntary movement
The Cerebellar peduncles
Connects the cerebellum to the brainstem- superior cerebellar peduncle, middle cerebellar peduncle and inferior cerebellar peduncle
What side of the Cerebellum controls what side of the body
The left side of the cerebellum controls the left side of the body and the right cerebellum controls the right side of the body.
The vermis
Connects the two hemispheres of the cerebellum. The vermis is split into parts, you have the inferior vermis made up of the nodule, pyramis and uvula. The follicular is a depression where the inferior vermis will site
What can happen if there is an increase in pressure in the cerebellum
It will compress the brainstem and spinal cord
The primary fissure
Separates the anterior lobe from the posterior lobe of the cerebellum. The folia are the ridges of the cerebellum
Cerebellar peduncles- connections to the brainstem
- Superior- to the midbrain
- Middle- to the pons, largest, composed of fibres from the cortex to the cerebellum
- Inferior- to the medulla, smallest
The Microanatomy of the Cerebelum
Outer surface of grey matter (cerebellar cortex) and inner core of white matter. The Cortex has three layers:
• Outer- fibre rich molecular layer
• Intermediate Purkinje cell layer
• Inner granular layer
The white matter contains mossy and climbing fibres.
There are 4 Cerebellar nuclei
From lateral to medial- Dentate, Emboliform, Globose, Fastigial (Don’t Eat Greasy Food)
The 3 layers of the cortex
- Granular layer- contains granular cells
- Purkinje layer- Purkinje cells
- Molecular layer- contains parallel fibres
Fibre types in the Cerebellum
- Mossy- mostly afferent fibres
- Climbing- afferent fibres from the inferior olivary nucleus
- Purkinje- fibres from the leave cerebellar cortex to the deep cerebellar nuclei. Some leave the cerebellum
Division of the Cerebellum- Vestibulocerebellum
Region of the Cerebellum- Flocculonodular lobe, portion of vermis
Cerebellar nuclei- Fastigial
Function- balance, equilibrium, posture, extensor muscles
Divisions of the Cerebellum- Spinocerebellum
Region of the Cerebellum- Paravermal region, vermis and anterior lobe
Cerebellar nuclei- Interposed (globose and emboliform), Fastigial
Function- Muscle tone, stability, ongoing movement regulation (Coordination)
Divisions of the Cerebellum- Cerebrocerebellum
Region of the Cerebellum- mostly posterior lobe
Cerebellar nuclei- Dentate
Function- inititation and planning of movement, motor learning
