homeostasis of the brain Flashcards
what are the three types of cortex in the cerebral cortex?
the olfactory cortex
the hippocampus
the neocortex
what is the function of the olfactory cortex?
receives sensory information about smell and chemicals
what is the function of the hippocampus?
memory
what is the function of the neocortex?
higher order thinking such as planning and consequences
what is the evolutionary oldest and newest cortex?
oldest = olfactory cortex
newest = neocortex
where is the hippocampus located and what is its structure?
in each temporal lobe
made up of 3 cellular layers
what is the basal forebrain?
a structure developed from the forebrain that contains clusters of neurons
what are the 2 main areas of the basal forebrain?
basal ganglia
amygdala
what are the 3 types of white matter fibres and what are their roles?
commissural fibres: connects the 2 hemispheres
projection fibres: link non-cortical areas
association fibres: link areas in the hemispheres
what are gyri and sulci?
gyri are bumps or ridges on the brain
sulci are grooves on the brain
how many layers does the neocortex have?
6 layers
what does golgi stain highlight?
stains neurons randomly
what does touline blue stain highlight?
cell bodies
what does Weigert-PAL highlight?
myelin
what are the 3 methods of brain imaging?
positron emission tomography (PET)
functional magnetic resonance imaging (fMRI)
electroencephalography (ECG)
what are the disadvantages of non-invasive functional imaging?
low resolution so not good at seeing specific areas
what are the 4 areas of the neocortex?
primary somatosensory cortex
secondary somatosensory cortex
primary motor cortex
the rest of the neocortex is called the association cortex
where is the primary somatosensory cortex located and what is its function?
in the parietal lobe on the post-central gyrus
processes touch
where is the primary motor cortex located and what is its function?
in the frontal lobe on the pre-central gyrus
movement planning
where is the cingulate gyrus located and what is its function?
in the limbic lope
emotions, memory and pain
where is the medial aspect of the temporal lobe located and what is its function?
in the temporal lobe
emotions and memory processing
what is the structure of the hypothalamus?
has 11 major nuclei
where is the periventricular region and what is its function?
surrounds the ventricles
links the body to the brain via the autonomic nervous system and pituitary for motor and sensory transmission
what is the function of the lateral regions?
motivated behaviour
conscious behaviour changes
how is homeostasis maintained by the brain?
leaky regions in the blood brain barrier sense changes to vital parameters
sensory inputs are fed into the hypothalamus where they are integrated into a response
the hypothalamus balances sensory inputs with contextual inputs from the amygdala and cerebral cortex
it outputs through the autonomic nervous system, neuroendocrine system and behaviour to bring about a response
what are the 2 main nuclei in the hypothalamus and what are their roles?
the paraventricular nucleus links the pituitary to the brain stem
the supraoptic nucleus which outputs to the posterior pituitary
what are the two pituitary glands?
the adenohypophysis (anterior) and the neurohypophysis (posterior)
where do the neurons of the pituitary sit and where do their axons project?
neurons sit in the hypothalamus
axons project into the pituitary stalk
what do neurons of the neurohypophysis release?
they release hormones such as oxytocin and ADH from magnocellular (large cell bodied) neurons directly into systemic circulation
what do neurons of the adenohypophysis release?
release neurohormones into portal veins (smaller blood vessels) that connect capillary bed to the anterior blood system
these neurohormones are usually releasing hormones that stimulate troph cells
what is the structure of the afferent (sensory) division of the hypothalamus?
mechanoreceptors in internal organs and blood vessels that detect stretch output through afferent fibres such as cranial or visceral nerves into the brainstem nuclei
what is the structure of the efferent (motor) division of the hypothalamus?
outputs to efferent fibres to effectors all around the body such as muscles and glands
what are the two types of neurons in the autonomic nervous system?
pre-ganglionic and post-ganglionic
where are pre-ganglionic and post-ganglionic neurons derived from?
pre-ganglionic are derived from neural tubes
post-ganglionic are derived from neural crest
where do pre-ganglionic neurons sit and project to?
cell bodies sit in the brainstem or spinal cord of the CNS
axons project into the periphery
what to pre-ganglionic neurons release?
acetylcholine onto post-ganglionic neurons
where do post-ganglionic neurons sit and project to?
cell bodies sit in ganglions of the peripheral nervous system
axons project all around the body
what do post-ganglionic neurons release?
release neurotransmitters onto effector cells when nicotinic receptors are activated by acetylcholine
how do pre and post-ganglionic neurons change in the sympathetic and parasympathetic nervous system?
in the sympathetic nervous system they are adrenergic (norepinephrine) and in the parasympathetic they are cholinergic (acetylcholine)
what is the neuronal microenvironment made up of?
glia (mostly astrocytes), capillaries, other neurons (e.g. synapses), extracellular matrix and brain extracellular fluid
what is extracellular matrix made up of?
collagen and elastin fibres
proteins
what would happen if brain extracellular fluid (BECF) wasn’t tightly regulated?
neuronal disfunction and eventually neuronal cell death
what happens when neuronal activity increases?
BECF potassium ion concentration increases
oxygen, carbon dioxide and glucose levels change
proton levels increase making the BECF more acidic
the concentration of neurotransmitter changes
what happens if potassium ion concentration in the BECF increases?
increases the resting potential
reduces the electrochemical gradient for potassium ions
neuron repolarises slower
neuron is closer to the threshold for action potential firing
more neurotransmitter is released
neuronal activity increases
what is the blood brain barrier?
tight junctions between capillaries in the brain
what is the function of the blood brain barrier?
protects neurons from fluctuations in the concentration of substances in the blood to control the BECF
what are examples of fluctuations in the BECF?
increased amino acid concentrations after a meal
increased potassium and hydrogen ion concentrations after exercise from cellular respiration
circulating hormones
toxins
what is the structure of the blood brain barrier?
it is maintained by tight junctions between endothelial cells that prevent paracellular transport
endothelial cells sit on a thick basement membrane and astrocytic end feet surround the capillaries
which molecules can move across the blood brain barrier?
small, uncharged, or lipid soluble molecules
e.g. oxygen and carbon dioxide
how can molecules pass across the blood brain barrier?
facilitated transport using exchangers or co-transporters
what are leaky regions of the blood brain barrier?
regions without tight junctions
e.g. the choroid plexuses in the ventricular system which allows cerebrospinal fluid to be made
how is the rest of the brain protected from leaky regions of the blood brain barrier?
by ependymal cells containing tight junctions underneath the leaky regions
why are leaky regions of the blood brain barrier needed?
to release hormones into circulation
detect toxins and concentrations of molecules like glucose
pick up cytokines
what is the ventricular system?
a series of hollow cavities that runs through the brain and into the spinal cord
what is the structure of the ventricular system?
2 lateral ventricles that sit in the cerebral hemisphere
a 3rd ventricle that is connected to the 4th ventricle by a small tube called the cerebral aqueduct that runs into the central canal in the spinal cord
what are the cavities in the ventricular system filled with?
cerebrospinal fluid to provide protection by acting as a buffer
it maintains the correct concentration of ions and removes waste products
how does the cerebrospinal fluid compare to blood plasma?
it has a lower concentration of potassium to buffer increases in neuronal activity
has fewer amino acids because they can interact with neurons
how does the cerebrospinal fluid move through the body?
it is secreted by the choroid plexus and circulates around the ventricles
when it gets to the 4th ventricle it can move into the central canal or move through holes in the ventricle to around the edges of the brain and spinal cord
how is cerebrospinal fluid secreted?
plasma moves into the extracellular fluid by ultrafiltration across leaky capillaries to form ECF
substances can move into the cerebrospinal fluid by selective absorption across the choroidal epithelial cells
other substances can move freely from the cerebrospinal fluid to the BECF across ependymal cells
how is cerebrospinal fluid absorbed?
from the subarachnoid space into the venous blood system at the superior sagittal sinus
what are the meninges?
thin layers of tissue that surround the outside of the brain and spinal cord
what are the 3 types of meninges?
pia mater (inner layer) and arachnoid matter which are both leptomeninges
dura mater (thicker, tougher outer layer)
what is the subarachnoid space?
the space between the pia and arachnoid mater
substances are transferred from the BECF into the subarachnoid space through arachnoid granules
how is cerebrospinal fluid absorbed?
the arachnoid membrane has invaginations containing arachnoid granules and villi
the CSF moves through the arachnoid mater and the membrane evaginates to form vesicles containing CSF
the vesicles transport CSF across the subarachnoid space
what happens to absorption of cerebrospinal fluid as intercranial pressure increases?
absorption increases as more CSF is engulfed by the cell
this prevents intercranial pressure from getting too high
what is hydrocephalus?
a condition that occurs when CSF can’t circulate properly
what causes hydrocephalus?
blockages in the cerebral aqueduct that cause the 3rd and 4th ventricles to expand and dilate
this increases intercranial pressure which leads to loss of cells in the brain
what is the role of neurons and astrocytes?
terminate neurotransmission
they take up neurotransmitters so they are removed from the synaptic cleft
they recycle the components into the presynaptic terminal
how do neurons and astrocytes remove potassium ions from the extracellular space?
using sodium-potassium ATPase pumps
astrocytes increase their uptake of potassium ions
this triggers glucose and glycogen metabolism
how do astrocytes facilitate transport?
they move potassium ions away from active neurons to a less active area of the brain
they form a syncytium through gap junctions so they can do cell-cell communication
they allow transport of sugars, amino acids, cAMP and calcium ions
what is neurovascular coupling?
the way that astrocytes communicate with arterioles and capillaries that run through the brain
what do astrocytes do when the neuron firing rate increases?
they sense an increase in the neuron firing rate and their calcium ion concentration increases
this causes them to release vasoactive substances that cause the diameter of blood vessels to increase
this increases blood flow to neurons so they receive more glucose and oxygen for respiration
what is the disadvantage of using magnetic resonance imaging (MRI)?
can’t tell us what parts of the brain are active
how does positron emission tomography (PET) work?
glucose is radioactively labelled and moves around the body
it is detected in blood vessels around neurons to see where is more active because active neurons need more glucose
how does functional magnetic resonance imaging (fMRI) work?
it detects blood oxygen levels because oxygenated haemoglobin and deoxygenated haemoglobin have different magnetic resonances
it is called blood oxygen level dependent (BOLD) imaging
what is the neural plate?
tissue that develops to form the entire central nervous system
what are the 3 layers of the neural plate and what do they form?
the endoderm which develops into the lining of the organs
the mesoderm that develops into bones and somites that form muscles
the ectoderm that develops into the skin and nervous system
what is the process of neurulation and when does it happen?
around 22 days after fertilisation
the neural plate starts to fold inwards to form the neural tube
neural folds are pinched off and move apart to form the neural crest
what does the neural tube develop into?
the hollow part develops into the ventricular system
it is where all neurons in the CNS are derived from
what does the neural crest develop into?
all the nervous tissue of the peripheral nervous system
it is where sensory neurons are derived from
what are 3 examples of sensory neurons?
dorsal root ganglion cells
chromaffin cells
schwann cells
what is anencephaly?
a disease in developing embryos where the forebrain doesn’t develop properly
what causes anencephaly?
when the neural tube doesn’t close properly
what is the process of differentiation?
when the areas of the neural tube start to change into the parts of the brain
what are the 3 primary vesicles that develop from the neural tube?
prosencephalon that forms the forebrain
mesencephalon that forms the midbrain
rhombencephalon that forms the hindbrain
what develops from the forebrain?
olfactory bulbs that contains the olfactory nerves
telencephalon that forms into the lateral ventricles and grey matter
diencephalon that forms into the 3rd ventricle, hypothalamus and thalamus
what does the grey matter of the forebrain contain?
the cerebral cortex and basal telencephalon
what does the white matter of the forebrain contain?
the corpus callosum, cortical white matter and the internal capsule
it is myelinated tissue
what does the midbrain develop into?
the tectum and the tegmentum
it contains lots of white matter for transfer of information
what is the role of the midbrain?
takes in information from auditory and visual processes
what does the hindbrain differentiate into?
the pons, cerebellum and medulla
what does the cerebellum contain and what is its function?
folium folds, deep cerebellar nuclei and the cerebellar cortex
it receives sensory information for muscle contraction, balance and movement planning
