Biological Bases Flashcards
What does the size of the brain depend on?
How much energy the body consumes
Shape of brain
- the fact that we are standing up has made the brain stem underneath, rather than behind
- placement of eyes
Organisation of reptilian brain v mammalian brain
Reptile:
- striatum (move)
- thalamus (feel)
- superior colliculus (see)
- inferior colliculus (hear)
- brainstem (pons and medulla)
Mammal: have all of the above but before striatum we have:
- limbic system and the cerebral cortex
Breaking down the cerebral cortex
Occipital cortex (see) Temporal cortex (hear) Parietal cortex (feel) Motor cortex (move) Frontal cortex (act)
Anatomical directions
neuroaxis: perceived line through the centre of the nervous system –> indicates orientation of dorsal/ventral, anterior /posterior, medial/lateral
Dorsal v Ventral
above, below
Anterior or posterior
nose v tail
Lateral v medial
outside v inside
the planes
- sagittal (arrow through head)
- coronal (crown)
- horizontal
Nervous system tree
Peripheral:
- somatic
- autonomic (sympathetic, parasympathetic)
CNS:
- spinal cord
- brain
In the Central Nervous System
cerebrum
cerebellum
brain stem
spinal cord
Somatic nervous system
Voluntary system
- receiving sensory input from the environment and producing a motor output based on that sensory input
- does not include reflexes
Process of the somatic nervous system
- information coming from the environment via sensory receptors in the skin
- they go up through the dorsal roots (the back of the spinal column)
- comes up into the spinal column up into the brain
- information is processed and comes out as a motor output (through ventral roots, coming down into the muscle)
Talking about motor neurone disease
- nerves in the ventral roots, to the muscle, are degenerating
Peripheral nerves: groups
- cranial nerves
- cervical nerves
- thoracic nerves
- lumbar nerves
- sacral nerves
- coccygeal nerves
Cerebrum lobes (cortex)
- Frontal lobe: primary motor cortex
- Temporal lobe (side)
- Parietal lobe (top): primary somatosensory cortex
- Occipital lobe (back)
The frontal lobe and parietal lobe are separated by the central sulcus
Summarise the sommatic nervous system
- receives sensory input and delivers muscle output
- sensory input is received through dorsal roots to spinal cord
- motor output is delivered via ventral roots of spinal cord to muscle
- 6 areas that the nerves join the CNS (cranial, cervical, thoracic, lumbar, sacral, coccygeal)
- the brain receives sensory information at the somatosensory cortex and once processed in the brain, produces behaviour by modulating motor output from the primary motor cortex
Autonomic nervous system
Involuntary system
Sympathetic - extends from thoracic and lumbar spine
- short preganglionic nerves
- long postganglionic nerves
- involved in the 4 Fs (fright, flight, fight, fuck)
Parasympathetic - extends from cranium and sacral spine (craniosacral)
- long preganglionic nerves
- short postganglionic nerves
- digestion, growth, etc
both are usually active, but change intensity as the need arises
parallel systems that work in OPPOSITION to each other
Sympathetic nervous system effects:
- thoracic and lumbar
- increases heartrate, blood pressure, breathing
- reduces gastrointestinal function
Parasympathetic outflow
- cranial and sacral nerves
- Increasing gastrointestinal function
- Reducing heartrate, etc
Hormones
- hypothalamus + pituitary (many different hormones released directly into blood stream)
- pineal gland (melatonin)
- consider speed and range of effect –> the nervous system is faster (electrical signal) but the hormones are a lot slower and reach a lot more areas than the nervous system
Hypothalamus and pituitary gland
PG:
- anterior lobe: neurosecretery cells that release hormones (slower than the posterior) (growth hormone and adrienocorticotropic hormone)
- posterior lobe: neurons that go from hypothalamus down to posterior lobe to release hormones (this is faster than the anterior system) (includes vasopressin and oxytocin)
How is the brain protected / nourished
- the brain is highly vascularised (many arteries and veins) which maintain a constant fresh supply of oxygen and nutrients
The brain is protected with:
- Blood brain barrier (BBB):
- -> cerebrospinal fluid (CSF)
- -> meninges
- -> glial cells
Blood Brain Barrier (protection of the brain)
Blood brain barrier (BBB): little blood vessels on the inside and outside of brain only let certain things go from the blood vessels into the brain tissue (really tightly packed cells)
- brain capillary endothelial cells have continuous tight junctions
- only highly lipophilic drugs and small uncharged molecules can cross from blood capillaries to CSF by diffusion (O2, CO2, fat soluble molecules)
- important nutrients (amino acids and glucose) are actively transported by proteins in the capillary membrane (this requires energy)
What is the CSF
Cerebrospinal fluid and ventricles
- made up of water, a variety of salts (NaCl, KCl, CaCl2, MgSO4) and glucose
- ventricles are holes in the brain that help the CSF to flow around the brain
- CSF is made in those ventricles, goes down the spinal column and flows around the brain
- CSF is protective and has a lot of nutrients
- 3 meninges around the spinal cord are really important for the CSF to flow
Ventricles and CSF
- Cerebrospinal fluid is amde by the choroid plexus in the ventricles
- the ventricles and subarachnoid space circulate cerebrospinal fluid through and around the brain to provide nourishment
- there are 4 ventricles
- once CSF has circulated around the brain, it is reabsorbed by the arachnoid villi into venous blood (returns to heart)
White matter v Grey matter
white matter = myelinated axons
grey matter = nerve cell bodies
Sulcus v gyrus
sulcus is a valley / indent in the brain tissue
gyrus = hill in the brain tissue
Mapping out nervous system (same side, etc)
Ipsilateral = structures that lie on the same side
Contralateral = structures that lie on opposite sides
Proximal: structures that are close to one another
Distal: structures that are far from one another
What connects the hemispheres of the brain
the corpus callosum and anterior commissure
Terms referring to the nervous system:
tract = a set of axons within the CNS nerve = a sex of axons in the periphery nucleus = cluster of neuron cell bodies within the CNS ganglion = cluster of neuron cell bodies usually outside CNS
Frontal lobe functions
planning of movements, recent memory, some aspects of emotions
central sulcus
in front: precentral gyrus (primary motor cortex) which connects the frontal lobe
behind: postcentral gyrus (primary somatosensory cortex) which connects the parietal lobe
parietal lobe function
body sensations
temporal lobe functions
hearing, advanced visual processing
occipital lobe
vision
Frontal lobe case study
Phineas Gage (1848 accident) Personality changed = more impulsive
Frontal lobe: broca’s area
Broca located speech in this area of the frontal lobe
Broca’s area is really important for speech
Damage to this area causes Broca’s (expressive) aphasia (deficits in language comprehension and production)
Subcortical areas of forebrain
- nucleus accumbens
- hypothalamus
Subcortical: basal ganglia
thalamus is not apart of the basal ganglia but is important for relaying information to the basal ganglia
- globus pallidus
- caudate
- putamera
These are really important for movement and decision making
Subcortical: limbic system
Cingulate gyrus: borders the cortex and links cortex to limbi system
Thalamus: sensory and motor relay and interaction
Hypothalamus: promotes body homeostasis
Hippocampus: spatial and reward related
Amygdala: emotion: fear arousal excitement
Olfactory bulb: receives direct olfactory info from nose receptors, can lead to rapid emotional and motivating responses
Hippocampus: Case study
removal of hippocampus from henry molaison
when they took this out: intellectual and language abilities were fine, but he suffered massive anterograde amnesia (forward memories)
- he could retain new skills, but not remember learning them
- implicit (unconscious memory) intact as opposed to explicit (conscious) memory
Midbrain and Hindbrain
Midbrain:
- superior and inferior colliculi
- -> important for having fast information from either site or auditory stimuli
- midbrain
- -> contains cells that make monoamines (brain chemcials essential for motivated behaviour, movement)
Hindbrain:
- medulla
- pons (sits under medulla, important for postural reflexes)
- -> these also contain cells important for homeostasis of blood pressure, heart rate and breathing
- -> you cannot stay alive if there is damage to this
Both relay motor information from cortex - thalamus to the spinal cord
Cerebellum “little brain”
also has 2 hemispheres
attaches to pons by penduncles
integrates sensory info from cortex and modifies motor control
smooth movement and coordination
procedural memory
Summary of structures
- cerebral cortex
- subcortical areas
- midbrain
- hindbrain
- cerebellum
- spinal cord
Measuring the brain and activity: overview
- phrenology (completely inaccurate)
- electroencephalograph (EEG)
- computed tomography (CT) scan
- magnetic resonance imaging (MRI)
- positron emission tomography (PET_
- functional MRI (fMRI)
- magnetoencephalography (MEG)
electroencephalograph (EEG)
electrical impulses in the cortex generate waves of current - measured using an eeg
because you’re getting input from various regions, its difficult to know where this is coming from
high amplitude = high synchronicity of neurons
Anatomical imaging
- CT scan
- -> 3D reconstruction of multiple xrays
- MRI
- -> release of energy from water in the tissue when you expose it to a magnetic field
- -> good for detecting soft tissue changes (tumour, or blunt damage to neural tissue)
Functional Imaging
- PET - measures radioactive tracers (such as glucose)
- -> this is invasive
- Functional MRI - measures blood oxygenation (=activity)
Magnetoencephalography
- measures of small magnetic fields
- provides measure of electrical activity in brain
Ratio of neurons from cerebrum to cerebellum
Cerebrum: 14 billion neurons
Cerebellum: 70 billion neurons
Hindbrain and spinal cord: 1 billion (tend to be longer tho)
Types of brain cells
- neurons
- glial cells
- -> astrocytes
- -> oligodendrocytes (help make the white matter - myelin)
- ependymal cells (line the CSR-filled ventricle, involved in making new neurons = neurogenesis)
- microglia (remove dead or degenerating neurons or glia = phagocytosis)
structure of neurons
Most have 4 main parts
- soma (cell body)
- dendrites
- axon
- presynaptic terminals
neurons are classified by:
- number of neurites (from cell body: unipolar, bipolar or multipolar)
- their dendrites (how many and if they have spines –> spines are important for regulating information to lots of different cells, whereas aspiny neurons are more targeted)
- their axon length
- -> long ‘internuncial’ = golgi type 1
- -> small ‘interneurons’ = golgi type 2
- the neurotransmitter released by the neuron
- neuronal connections –> primary sensory neurons or motor neurons
classification by dendrites
- stellate (starshaped) vs pyramidal (triangular)
- spines (spinous) or don’t have spines (aspinous)
- dendritic spines are involved in learning and memory (provides more surface area for communication)
- dendritic trees constantly change (grow or recede) - aids in neuroadaptation
- dendrites are sources of information for the neuron - the more dendrites, the more information the neuron receives
afferent vs efferent
- refers to the synaptic connection
- afferent (to the connection) / Arriving to the connection
- efferent (from the connection) / Exiting the connection
skin of the neuron / PLASMA CELL MEMBRANE
- phospholipid bilayer: will let uncharged molecules through, but not ions
- ions require channels in the form of large protein molecules in the membrane to travel from one side to the other
resting membrane potential
- resting membrane potential is an electrochemical gradient (i.e. intracellular ion concentration is different from extracellular ion concentration) –> since these are different, it has the potential to change
- extracellular vs intracellular fluid ion concentration at rest
- the ions important for neurophysiology:
- -> cation = Na+, K+, Ca2+
- -> anion = Cl-
When at rest: -70mV
extracellular fluid: high amount of Na, low amount of K
intracellular fluid: low amount of Na, high amount of K, also negatively charged proteins (which can’t move over the membrane) and negative chloride ions
the inside of the cell is negative at rest
depolarise
make more positive
hyperpolarise
more negative
at rest: potassium channels are
always open (therefore can flow in or out) electrical gradient: the difference in electrical charge between two adjacent areas: the potassium should flow to where it is more negative
concentration gradient: the difference in concentration of a particular ion between two adjacent areas: if an area has many K ions, the K ions will flow to an area with less (therefore will flow outside)
the sodium potassium pump
- the pump brings 2 Ka into the cell, and takes 3Na out of the cell
- this uses energy (ATP) –> both travel against their concentration gradients
- this allows the actions potential
Na channels
- these are closed in a resting neuron
- Na channels are voltage gated, meaning they can only open with certain membrane potentials (e.g. -50mV to +30mV)
voltage gated K channels
- these are closed in a resting neuron
- these only open when the cell becomes very positive (+30mV) `
measuring the action potential
- the intracellular and extracellular electrical potential can be measured by recording electrodes and an oscilloscope
- action potentials produce a rapid reversal in potentials (happening across 4 miliseconds)
where do axon potentials begin
- axon hillock
- communication with dendrites from other neurons brings positive or negative ions in the cell –> enough positive charge at the hillock will fire the neuron
- less negative charge in axon (depolarisation) opens sodium channels
- there is a threshold of excitation (potential) required to open these channels (-50mV)
- massive influx of positive charge into the cell
- polarity of the membrane switches for miliseconds
process of an action potential
- the Na+ channels closest to the change in potential change their molecular conformation - they open, massive influx of Na ions (DEPOLARISATION)
- some K ions leave as now more negative outside (the Na / K pump is closed)
- the depolarised part of the cell continues to open sodium channels along the length of the axon, the first part of the axon is now in it’s refractory period (too positive to fire) – >this forces the signal to move down towards the terminal
- voltage gated K ions channels open - big efflux of K ions
- now because the K has leaved, it is hyperpolarised (-80mV)
- the Na and K pump has kicked in to go back to resting membrane potential
- the membrane of the neuron is ready to fire again approximately 4ms after the action potential has occurred in it’s section of the membrane
brief summary of action potential
- triggering event (positive charge)
- voltage gated Na channels open
- depolarisation because of Na influx
- Na channels close, voltage gated K channels open
- repolarisation (efflux of K)
- undershoot occurs because of hyperpolarisation
- return to resting membrane potential
TTX / tetradotoxin
sodium channel blocker
excitatory post synaptic potentials (EPSP)
communications with dendrites from other neurons can bring positive ions into the cell
positive ions produce a small depolarisation (EPSP)
small epsps are not enough to produce an action potential (need to at least -50mV)
inhibitory post synaptic potentials (IPSP)
communication with dendrites from other neurons can bring negative ions into the cell (Cl)
negative ions produce a small hyperpolarisation - an inhibitory post synaptic potential (IPSPs will not produce an action potential)
big ESPS will produce an action potential
needs to be bigger than -50mV
potential will occur
a big IPSP can cancel the effect of EPSP
neural integration
many dendrites receive info from different neurotransmitters at the same time - polarity of these dendrites may differ on the one neuron
some may cause IPSP and some may cause EPSP
all of these polarities are produced by chemical transmission are integrated at the axon hillock
a neuron will only fire if the hillock has an overall increase in positive charge which exceeds the excitability threshold
–> depolarisation of the neuron will occur - action potential
why have action potentials ?
- action potentials allow the transfer of information through the release of neurotransmitters
chemical release at the synaptic ocnnection
- neurotransmitter release from the afferent neuron
- this will bind to the efferent neuron
EPSPs:
increase the likelihood of generating an action potential by elevating the mV at the axon hillock
IPSPs
reduce the likelihood of generating an action potential by lowering the mV at the axon hillock
neural integration is
the sum of the EPSP and IPSP
myelin sheath
- reduces leakiness
- the neuron is insulated with myelin (oligodendrocytes :glial cells)
- therefore neurons leak instead at the nodes of ranvier (small gaps in the myelin)
- the nodes of ranvier are where channels and pumps are concentrated along the axon
what is the process of propagation of the action potential along myelinated neurons
saltatory conduction
how does one cell talk to another?
- electrical communication: gap junctions (electrical synapses)
- chemical communication: synaptic cleft (chemical synapses)
THIS IS IMPORTANT
how big is the synapse
20-50nm wide
neurotransmitter release process
- action potential (cause a release in neurotransmitter)
2; vesicle docks (where the neurotransmitter is released) which binds to the presynaptic membrane due to the action potential
3: causes release of NT
4: NT binds to receptor
5: unbound NT transported into presynaptic terminal (reuptake by transporters)
When they have been returned to the presynaptic terminal they either under metabolism through a reaction with an enzyme or they are repackaged into the neurotransmitter vesicle
Neurotransmitters and their dysfunction
- dopamine: reduced in Parkinson’s disease (motor impairment)
- serotonin: reduced in depression (very low mood)
- acetylcholine: reduce in alzheimer’s disease (memory loss)
- GABA: increased activation in alcohol intoxication
