The Human Brain Flashcards
What are the two main classes of cells that are the constituents of the nervous system- both central and periphery?
Neurons and glial cells
What is the cell body of a neuron known as?
Soma
What parts are all neurones composed of?
Dendrites A soma (cell body where the nucleus is present) Axon (only ever one of these) Axon Terminals
What do dendrites do?
Send electrical impulse to the soma (cell body)
What does the axon do?
Send electrical impulses away from the soma (cell body).
What does Glial mean?
Greek for Glue
What do glial cells do?
Play a supporting role for neurones
What does oligo mean?
It means few
What is an oligodendrocyte and what does it do?
Its a glial cell with few branches , however, the branches it does have wrap repeatedly around axons to form myelin sheaths. This cell is responsible for myelinating axons within the central nervous system.
What is the function of myelin?
It increases the speed and reliability of impulse conduction
Do oligodendrocytes myelinate neurones in the PNS?
NO myelination in the peripheral nervous sytem is done by Schwann cells
What is the difference between Oligodendrocytes and Schwaan cells?
Oligodendrocytes myelinate neurones in the CNS, whereas, Schwaan cells myelinate neurones in the PNS (periphery nerous system).
What type of cell is astrocyte or ‘star cell’?
It’s a type of glial cell. It gets it’s name as it has many processes.
What main roles do astrocytes play?
Mainly in mechanical support for neurones and their axons. A role in maintanence of the blood brain barrier in CNS. ( The have end-feet (exactly what you think it is) that wrap around the capillaries maintaining structural integrity).
What does the Central Nervous sytem comprise of?
Brain and spinal cord
What does the Peripheral nervous sytem comprise of?
Sensory and motor neurones (involunatry autonomic nervous system).
What does the human brain do for us?
Acquire knowledge (from perecption) Storing Information (as memory) Controlling Motor Behaviour Elemental movements (e.g. respiration, heart rate) Complex voluntary/‘willed’ actions (e.g, grasping) Crowning Achievement: Language & Communication What it does for us, collectively
Aprroximately how many neurones does the brain contain?
100 US billion (x10 more than the number of people on this earth).
Is bigger better when it comes to brain size?
Yes when compared to other animals scaled up.
Why is the brain very complicated?
Many different parts All with different names (sometimes several names) Each with a different, specialized function Specific brain regions interconnected by different specialized, axon pathways
What is functional specialisation in regards to the brain?
Functional specialization suggests that different areas in the brain are specialized for different functions.
When we split the brain in half laterally what do we refer to each section as?
A Hemisphere
What are the three major divisions of each hemisphere?
Cerebrum (largest) Cerebellum Brainstem (smallest)
Which of the three major divisions of each hemisphere is the biggest?
Cerebrum
Which of the three major divisons of each hemisphere is the smallest?
Brainstem
What is the brainstem directly attached to?
The spinal cord
What are the two main parts of the cerebrum?
Telencephalon (forebrain)
Diencephalon ( between brain)
What are the subdivisions of the Telencephalon?
–Cerebral Cortex: conscious sensation/perception, voluntary movements & higher cognitive (e.g., language) functions
–Basal Ganglia: movement planning & control
What are the subdivisions of the Diencephalon?
–Thalamus: various nuclei (related to the cerebral cortex)
–Hypothalamus: various nuclei for regulating appetites & endocrine functions (via connections with the pituitary gland)
–Epithalamus: pineal gland, secretes melatonin, regulates circadian rhythms
Which subdivision of the Telencephalon is the largest?
The cerebral cortex
What is the cerebral cortex responsible for?
Conscious sensation/perception, voluntary movements & higher cognitive functions (e.g., language, memory)
What is the basal ganglia and what is it responsible for?
The basal ganglia is a collection of really large nuclei within the base of the cerebrum which is mainly concerned with the planning of control and voluntary movements.
How do we know that the Basal ganglia is associated with movement planning and control?
Neurodegenerative diseases like Parkinson’s disease affect different parts of the Basal ganglia and these diseases are often characterized by struggles with voluntary movement.
What does hypo mean?
Below/ low
In neuroanatomy what is a nucleus/nuclei?
Conscious sensation/perception, voluntary movements & higher cognitive (e.g., language) functions
What is the hypothalamus responsible for (general overview)?
Regulating appetite (when to eat and drink - including when to stop) and endocrine functions (via connections with the pituitary gland).
What is the Epithalmus and what does it exclusively consist of?
What does it also do?
It is a gland and consists of the pineal gland.
It secrets melatonin and regulates circadian (ser-Kay-Dee-un) rhythms.
What is a circadian rhythm?
A natural, internal process that regulates the sleep-wake cycle and repeats on each rotation of the Earth roughly every 24 hours.
What is the brain made up of?
Gray and white matter
What does Gray matter consist of and what is it a site of?
Contains the cell bodies and dendrites of neurones along with the synaptic inputs received from the terminal axons of other neurones.
It is thus a site of Information processing.
How may neuron cell bodies in the gray matter be arranged?
Neuron cell bodies may be arranged in:
- Layers or Sheets, as in the Cerebral Cortex
- Groups/Clusters (aka ‘Nuclei’), as in the Thalamus and Basal Ganglia
What is the white matter comprised of and what is it a site of?
Contains the axons of neurons (a.k.a ‘nerve fibres’) and their associated myelin sheaths formed by oligodendrocytes.
It is thus a site of information transfer.
Why is white matter white?
Many nerve fibers are surrounded by a myelin sheath. Myelin gives the white matter its colour.
What essentially is white matter and as a result what is its function?
Routes for direct, long-range connections or
‘projections’ between neurons in different gray matter
regions.
Its function is basically information transfer.
What are some examples of white matter acting as a means of information transfer?
2 large sections of white matter that act as a means of information transfer are:
- Corpus Callosum: carries axons between neuron cell bodies in the right & left cortical hemispheres (carries information between two hemispheres) - as can be seen in the diagram.
- Internal Capsule: carries axons between neuron cell bodies in different thalamic nuclei to different parts of the cerebral cortex
Understand the following schematic diagram.
:)
Why is the cerebral cortex deeply folded?
To pack its large surface area into the skull
Folds of the cerebral cortex consist of what?
Ridges known as gyri (singular = gyrus)
Furrows, known as sulci (singular= sulcus)
What do the deepest sulci divide the cortex into?
4 lobes - each with a different function
Define Cortical
relating to the outer layer of the cerebrum
Define Occiput
Relating to the back of the head.
(Occipital - main bone at the back of the head)
What are the names of the two Corticol Sulci that divide the cerebrum into four lobes?
The Central Sulcus and Lateral sulcus.
Why is the central sulcus called the central sulcus?
Its found about halfway from the front and back of the cerebral cortex thus is called the central sulcus.
What two lobes does the central cortex divide?
The frontal lobe from the Parietal lobe.
What is the main function of the frontal lobe?
To control our voluntary movements.
What is the main function of our Parietal lobe?
Conscious perception of Somatic sensation - e.g. touch, tactile, pain, and joint sensation (knowing positon of your joints in 3-dimensional space otherwise known as proprioception).
Define proprioception
perception or awareness of the position and movement of the body.
What lobes does the lateral sulcus separate?
It separates the Frontal and Parietal lobes (blue and green sections) above from the Temporal lobe (orange section) below.
What is the temporal lobe mainly concerned with (at least the part that can be seen in the diagram)?
Auditory/hearing
Why is the occipital lobe important to optometrists?
It is mainly concerned with Vision.
Which lobes of the cerebrum do not have a sulcus separating them?
The occipital lobe does not have a sulcus separating it from the Parietal lobe nor a sulcus separating it from the Temporal lobe.
What are the two methods of visualising the living brain?
X-ray Computerised Tomography (CT)
Magnetic Resonance Imaging (MRI)
How does X-ray Computed Tomography work?
A person lies in a scanner. An X-ray beam is repeatedly fired into their head but from different angles. The X-ray passes through the person’s head with different levels of attenuation (the reduction of the amplitude of a signal, electric current, or other oscillation).
Hard tissue such as bone and tooth enamel doesn’t allow X-rays to pass through to the photographic beam thus are shown as a white area on the X-ray.
Soft Tissues (think air and water in the head) pass through relatively unattenuated and so appear black in conventional X-ray Scans.
Intermediate soft tissues (e.g. brain) attenuate X-rays to a certain extent and so on the scan will appear as a sort of greyscale image.
What’s beneficial about using CT scans?
Each X-ray beam produces its own point on the scan and so you can actually view the brain as different ‘slices’ or as a whole 3-dimensional image.
This is useful for looking at gross pathologies - things like strokes or tumors.
How does Magnetic Resonance Imaging (MRI) scan work?
It maps Hydrogen nuclei and water concentration.
The person lies in the scanner and the scanner passes a powerful magnetic force through the head in different directions. This causes hydrogen nuclei to spin in the same direction as the direction of the magnetic pulse.
The MRI then uses computerized systems to compile sequential ‘slices’ of the head and 3D images.
What is the advantage of MRI scans over CT scanning?
It allows a better differentiation of soft tissue - even allows you to differentiate between gray and white matter.
(Thus more useful for looking at subtle pathologies).
What is the science behind Magnetic Resonance Imaging?
The radiofrequency pulses applied from the magnetic field around the head cause nuclei with an odd proton number (e.g hydrogen/water) to align with external source and ‘resonate’ at that particular time constant.
In an MRI scan you have two ‘time constants’; T1 and T2.
T1 = all aligned: white matter lighter than grey matter
T2 = lost alignment: white matter darker than grey matter
How do we know about the different functions of different brain regions?
Clinical Neurology & Structural Brain Imaging:
•Examining Surviving patients (with stroke, trauma, diseases) which results in selective deficits resulting from localized brain damage (a.k.a ‘lesions’)
Functional Brain Imaging:
- Healthy, neurologically-intact volunteers
- Localized increases in brain activity while they perform a specific task in the brain scanner. This idea is based on fact that increased NEURAL activity is associated with increased local blood flow (oxygen & glucose) utilization in that specific brain region.
What is Lesion?
a region in an organ or tissue which has suffered damage through injury or disease, such as a wound, ulcer, abscess, or tumour.
Where is gray matter present?
On the outer surface of the cerebrum
If there is any damage to the occipital lobe what does this mean?
Most likely that the patient will experience vision loss.
Attached is a photo with an example (on the left)of damage to the right occipital lobe which can be seen from an MRI scan (it’s the black area at the bottom- where the hemorrhage occurred)
In general, terms which of the two scans, MRI and CT, is cheaper and easier to do?
A CT scan is cheaper and easier to do!
What are two methods of functional brain imaging i.e. methods for identifying regions of increased brain activity?
Positron Emission Tomography (PET scans) and Functional Magnetic Resonance Imaging (fMRI scans).
What is the principle behind both Positron Emission Tomography (PET scans) and Functional Magnetic Resonance Imaging (fMRI scans)?
To look at oxygen utilisation in different parts of the brain.
(High oxygen utilisation levels imply high brain activity).
How does a PET scan work and what does it allow us to see?
It involves injecting an isotope (15th version of oxygen) into an artery and when it reaches a part of the brain utilising a lot of oxygen, the positrons annihilate (convert into radiant energy) on collision with electrons, producing two gamma rays.
These two rays travel in opposite directions to detectors in the scanner around the head.
Thus it allows us to see localised changes in regional cerebral blood flow (rCBF)
How does functional Magnetic Resonance Imaging (fMRI) work and what does it allow us to see?
It is based on differences in the resonance of haemoglobin versus deoxy-haemoglobin molecules when exposed to a strong magnetic field provided by the scanner.
It allows us to see localised areas of Blood Oxygenation Level Dependent (BOLD) changes.
Why do we prefer functional Magnetic Resonance Imaging (fMRI) over Positron Emission Tomography (PET)?
fMRI is non invasive
Which of these cerebral cortical lobes is mainly concerned with initiating voluntary movements?
a) frontal
b) occipital
c) parietal
d) temporal
a) Frontal Lobe
