Neurobiology Flashcards
Neuroplasticity
is a term that describes change to the brain throughout an individual’s’ life course
neuroplasticity process
Neuroplastic change can occur at small scales (e.g. individual neuron changes), large whole-brain scale (e.g. in response to injury brain function may move to a new area of the brain)
Growth of axons and dendrites is as much as part of plasticity as pruning and apoptosis
;re-growth of axons can be up to 5 nm per day
What is neurulation?
When an embryo starts to differentiate further (how the nervous system develops)
Posterior (end), Ventral (front), Dorsal (back), Anterior (beginning)
All animals in phylum chordata develop dorsal nerve cord as early stage, in process of neurulation (spine)
neurlation process
Nerve cord develops from ectoderm (outer tissue layer)
Area of ectoderm on dorsal side of embryo into neural plat
Cells on neural plate change shape→ plate folds inwards, creates groove along back, separates from rest of ectoderm→ forms neural tube, which becomes nerve cord (spinal cord)
Explain how Spina Bifida occurs
Centrum in vertebrae (series of bones) provide support + thing vertebral arch that protects spinal cord
Centrum develops on ventral side of neural tube, tissue migrates from both sides around neural tube and meets to form vertebral arch
If arch doesn’t fuse together → spina bifida occurs (usually in lower back, varies in severity)
We can discover formation of nervous systems by watching animals grow from embryo to adult; we can’t use humans for ethical reasons
E.g. C.Elegans (flat form), M.musculus (Mice), D.melanogaster (fruit fly)
steps of neurulation
- neuroectodermal tissues diffferentiate form the ecotoderm and thicken into neural plate. The neural plate border separates the ectoderm from the neural plate
- the neural plate bends dorsally with two ends; eventually joining at neural plate borders.
- closure of the neural tube disconnects the neural crest from the rest of the epidermis.Neural crest cells differentiate to form most of the peripheral nervous system
- the noctoderm degenerates and only persists as the nucleus pulposus of the interverterbral discs. Other mesoderm cells differentiate into somites, the precursos of the axial skeleton and skeletal muscle
cerebral cortex + brain damage
responsible for consciousness, perceptions, memory, manipulation of objects emotional and expressive response and judgements to our environment.
It consists of four parts; the temporal lobe, the parietal lobe, the occipital lobe and the temporal lobe.
Brain damage would affect each part differently, resulting in possible paralysis, loss of emotional control, personality changes, sense-perception and language abilities and memory loss.
brainstem
The brainstem is responsible for sleep, alertness, breathing, sense of balance and the autonomic nervous system.
Brain damage could result in vertigo, sleeping difficulties (insomnia) and issues with balance and movement.
cerebellum
The cerebellum is responsible for coordination, balance and motor reflex memory.
Brain damage could cause loss of motor functions, such as walking and quick reaction, as well as dizziness and slurred speech.
how does Brain injury affects brain activity
causing the death of neurons and glial cells, and therefore also the connections between them caused by synapses and neurotransmitters.
Alternatively, brain injury can lead to the excessive production of neurotransmitters that overstimulate neurons, therefore causing neuronal death as they ‘combust’.
stroke
blocked, or limited, supply of blood to the brain that results in the death of cells and neurological damage, as the brain is being devoid of important nutrients and oxygen.
Recovering from strokes includes reforming neurons and learning basic functions, as it generally affects the left-hand side of the brain, and it can take up to 6 months for a patient to recover.
MIGRATION OF IMMATURE NEURONS:
- neural migration can occur by the use of contractile actin filaments moving the cell and its organelles in a given direction
- migration is particularly important in brain development; MATURE neurons don’t move, but regrowth can occur if dendrites or axons become damaged
Axons
are long narrow outgrowths from the cell body that carry impulses from neuron to neuron
axon growth
-axons grow out of each immature neuron (in some cases, axons grow out of the neural tube to other parts of the embryo)
- axon reaches a favourable surface and persists
- neurones reach their fianl locaiton and make synaptic connectsion with their target cells
- target cells produce chemical messengers to which the neurone responds to
- an axon in humans maybe up to 1 m long and large in larger animals
- chemical stimuli determine the direction and length of the axon (differentiation neurons; during the growth of the embryo)
- connections between neurons are highly branched; neurons commonly possess multiple dendrites for receiving impulses from different neurons and multiple terminal ends for passing signals to different neurons
Synapse;
a structure that permits a neuron to pass an electrical or chemical signal to another neuron or effector cell
synpase growth
When a growing axon reaches the cell it’s intended to connect with, a synapse is developed
Synapses consist of specialized membranes from two cells separated by a narrow gap (cleft)
Most neurons develop multiple synapses at both the initiating dendrites and terminal ends; this allows complex patterns of communication
What is Neural Pruning?
is the process of synapse elimination, by retraction of the axons from unwanted synaptic connections
(elemination of un-used synpases)
neural pruning process
Neurons communicate through synapses
As a baby, you have a lot of synapses (TOO MANY CONNECTIONS; Hyperactivity)
Weak synapses are pruned (removed) as you grow older
Neurons that send a lot of messages; the stronger the pathway; the stronger the connection (unused synapses are removed)
Largest process of synaptic pruning occurs during early life but it continues throughout the entire life
neural pruning diseases
Autism can be related to hyperactivity (lack of synaptic pruning)
Too much pruning; causes memory loss/dysfunction e.g. Alzheimers
Largest process of synaptic pruning occurs during early life but it continues throughout the entire life
Apoptosis of neurons?
Apoptosis of neurons; involves killing of the cell + elimination of all connections associated with the neurons
Cerebellum:
Cerebellum: Coordinates unconscious functions, such as movement and balance
Medulla oblongata:
Controls automatic and homeostatic activities, such as swallowing, digestion and vomiting, and breathing and heart rate
Hypothalamus
Maintains homeostasis via coordination of the nervous and endocrine systems, produces hormones secreted by posterior pituitary
Produces and secretes hormones regulating many body functions - such as ADH (water retention / osmoregulation)
Cerebral Hemispheres
Acts as the integration centre for highly complex functions, such as learning, memory and emotion
HOW DO WE IDENTIFY BRAIN FUNCTION?
- autopsy
- animal experiments
- fMRI
- lesions
animal experimentation
Animal experimentation has lead to many advances in science and medicine; particularly in neurobiology and treatment of neurological disorders such as multiple sclerosis
why are animals used in experimentation?
Animals are used rather than humans as the methods are highly invasive + potentially cause permanent damage.
Experimental results have limited validity as there are differences between human + animal brains ;
Most valid comparisons use primates as they are more closely related to humans
approaches of animal experimentations
Autopsy (dissection of brain)
Stimulating regions of the brain with electrodes (and then observing behaviour and movement e.g. Ferrier work with dogs and monkeys)
Lobotomy- removing regions of the brain and observing impairment of brain function (e.g. Flourens’ experiments on pigeons)
what is fMRI
fMRI is the primary tool used in modern research; it measures changes in blood flow through the brain (indicates which regions of the brain are the most active)
Measures can be made in real-time so regional brain activity can be correlated with a stimulus
Sequencing of brain activity (e.g. language comprehension followed by production can be observed)
Tool for medicine + research (e.g. ADHD and dyslexia can be diagnosed + stroke recovery monitored)
fMRI procedure?
The procedure is non-invasive and can be performed without injury; but it’s also an indirect measure as not all brain activity is detected
why does fMRI work?
fMRI works because oxyhaemoglobin responds differently to a magnetic field than (deoxygenated) haemoglobin; computer interprets the results to produce coloured brain activity (different colours often represents different levels of activity)
brain lesions
Lesions are abnormal areas in brain tissue caused by accidents or present from birth
Presence of a lesion is usually associated with damaged and loss of caution in the affected area
Complex functions often involved brain areas making results difficult to interpret
Brain plasticity, to a degree functions to be reorganized into undamaged areas
lesions origins
In 1861- French Physician Broca heard of a patient (Leborgne) with a 21-year progressive loss of speech and paralysis but who hadn’t lost comprehension or mental function
Broca predicted the presence of a lesion in the frontal lobe on the left cerebral hemisphere (Brocas area)
After Leborgne’s death; Broca confirms lesion using autopsy
Findings further confirmed using autopsies + fMRI
Correlation between body size + brain size
Bigger body mass= bigger brain required to control body; doesn’t mean that the animal is more intelligent (that depends on the ratio of the brain areas, synapses + neurons)
Brain size is limited by the metabolism of the animal
embrynogensis
: study of the bodies development from a fertilized egg to a fully formed organism
why is a frog used as an animal mode?
- verterbrate/chordata
- readily available for scintists to colelct
what is a higher chordata example
- birds
- warm blooded
- ferticle chick eggs
ectoderm
outer layer; becomes the brain and nervous system
endoderm
inner layer; forms the lining of gut and other organs
mesoderm
middle layer; develops into the skeletal, reproductive, circulatory, exxcretatory and muscular system
arscheteneron
cavity in centre of embryo
where do CNS neurone originitate?
neural trube
neuroblasts
precursors for neurones
differentiate into neurones
neurones grow towards their target cell
target cells give the chemical signals (e.g. CAM) to the neurone
neurones
Carry messages
gglial cells
do not carry messages
function; physical and nutritional support of neurone
provide a scaggolding network along with the immature neuron can migrate
CAM
- signal molecule released from target cell that acts as asignal to the growth cone
- cell adhesion moelcule located on the surface of cells in the growth environment of the axon
- growth cone of the axon has a CAM specific receptr
- CAM and receptor recognized each other + exchanged chemical messages= activates enzymes within neurone that contribute to axon elongation
chemotrophic factors
- receptors on a growth cone that can pick up signals of molecule secreted by target cells that diffuse into the extracellular environment
- can be attractive or repellent factors
chemoattractive factors; attract axon growth
chemorepellent factors; repell axon growth so it elongates in opposing direction
motor neuron axon extension
- some axons extend beyond the neural tube to reach their target s=cells
- responsible for voluntary muscle movement; motor neurones extend their axons out of the CNS to form circius
- new motor neurones; longest neurons in body
- CAM produced in enzymes to attract axons; activate enzyme to stimulate axon growth towards muscle
multiple synapses?
- many brain synpases formed during early brain development
- many synpases; test out different connections between nerve cells to find best one
- only synpases with fucntion survive while others disapperar
CAM synpase involvement
- CAM acts as lock and key; form physical but reversible bonds between cells axons
- its a neural adhesion molecule thats recruited to the site of connection
=eventually, connections are lost as their not good with their partner
neuromuscular junction
where growth cones of the axon and their target cell connect
types of plasticity
- structural; brain changes physical structure as a result of learning
- fucntional; abiliity of the brain to move functions fro a damaged to undamaged area
plasticity factors
- environmental
- heredity
EXAMPLE OF FUNCTIONAL SHIFT IN NEUROPLASTICITY
- tennis player has stroke; paralyses left arm
- during rehab; his good arm and hand are immobilized
- tennis player has to do a task with left hand; bad arm remembers how to move
- plays tennis again!
= functions in brain areas that were killed by stroke are transferred to healthy regions= new connections formed that are stimulated by activity
EXAMPLE OF STRUCTURAL SHIFT IN NEUROPLASTICITY
- study of london taxi drivers by McGill uni
- london taxi drivers; observed with MRI to see that their hippocampous is larger; for memory storage capacity
- structural change of hippocampus in taxi drivers increases with length of time driver has been doing routes
Cerebral Hemispheres: (right and left hemisphere)
The hemispheres act as the integration centres for highly complex functions, such as learning, memory and emotion
Higher order functions rely on input both from stimuli and memories
Sophisticated processes, such as reasoning, planning, self-awareness and morality, rely on a complex network of neurons (It is estimated that there are 1014 synapses in the brain)
Due to the huge complexity of these neural networks, how these functions work is only partially understood
Left and right cerebral hemisphere functions:
Some functions are limited to a particular hemisphere, but most functions are bilateral + dealt with by both sides of the brain
The right side of the brain receives stimuli from the left side of the body (and vice versa)
The left visual field from both eyes is processed by the right side of the brain (and vice versa)
The left side of the brain controls movement, muscle contraction, on the right side of the body (and vice versa)
This explains why stroke victims lose sensation and/or the ability to move limbs on half the body
Activities coordinated by the Medulla Oblongata:
Respiration + Breathing Heart and blood vessel function Digestion + Swallowing (peristalsis) + Vomiting Sneezing Pupil dilation’
cerebral hemispheres
integrating centre for higher compled functions
assosiated with; intelligence learning memory personality sensory impulses motor function organization problem solving
hypothalumus
control pituitary gland which secretes hormones
- coordinates nervous and endocrine systems
- maintains homeostatis
cerebellum
assosiated with regulation and coordination of movement and balance
- two hemispheres + highly folded surface
- coordinates UNCONSCIONS FUNCTIONS
medulla oblongata
maintains vital body functions such as breathign and heart rate (autonomic and homeostatic activities)
piutitary gland
secretes hormones; has two lobes;
- posterior lobe
- anterior lobe
each love controlled by hypothalmus to secrete hormones
role of medulla oblongata
- swallowing centre; coordinates mouth, throat and adams apple movement to make sure food goes own oesuphogus and not wind pipe
- controls breathing by controlling carbon dioxide levels in blood
- cariovascular centre; controls heard rate by excersixe or stress exposre
right hemisphere
recieving and analyzing information that comes from our senses
left hemisphere
all forms of communication
autonomic nervous system
has two divisions;
1. central nervous system; brain and spinal cord
- peripheral nervous system;
. peripheral nervous system
- peripheral nervous system;
- somatic (voluntary); infromation recieved by senses + messages sent to skeletal muscles; takes sensory information from sensory receptors in CNS and then returns them to motor commands from CNS to muscles (e.g. reflex arc)
ANS: invountaryl regulates glands, muscle and heart activitty (medulla oblongata)
- autonomic (involuntary); controls cardiac mucle, smooth muslce
- sympathetic system
- parasympathetic system
sympthatetic system of PNS
important in emergency
response is fight or flight
neutrotransmitter is noadrenanline
exictatory
parasynpathetic system
important in returning to normal
response is to relax
neurotransmitter is acetylecholine
inhibitory
pupil reflex
The pupil reflex originates in the brainstem and is under the control of the autonomic nervous system
pupil reflex process
Stimulus: bright light
Receptor: photoreceptors on the retina detect potential damaging levels of light
Coordination; sensory neurons in the optic nerve send impusles to the medulla oblongata.
Relay and then motor neurons direct the impulse to the irsis muscles
Effect: Radial muscles relax + circular muscles contract to constrict the size of the pupil
Failure of the pupil reflex indicates the damage to the medulla oblongata (brain stem)
If brain stem fails; basic automatic brain function can fail
sensory and motor neurones in pupil reflex
connect in brain rather than spinal cord (cranial reflex)
pathway of pupil reflex
- optic nerve recieves messages from retina at back of the eye; retina contains photorecetpors that recieving light stimulues
- photoreceptors synpase with bipolar neurons and then with ganglion cells (nerve fibres of the ganglion cell become the opitc nerve)
- optic nerve connects with pretectal nuclear of brain stem
- from the pretectal nucleus; a message is sent to the Edinger-Westphal nucleus; axons of which run along the oculomotor nerves back to the eye
- oculomotor nerves synpase on the ciliniary ganglion
- axons of ciliary ganglion stimulate the circualr muscle of the iris
brain death
- its possible to artificialyl maintain the body without the impulses that come from the brain (e.g. heart rate, breathing and blood flow, temperature, fluid retention etc)
- people can live on life support; but brain shows no electrical activity
- ‘the time when a physician has determined that the brian and brain stem have irreversibly lost all neurologiacal function”
what tests must a physician do to test for brain death?
- . toxicology test (make sure the patient isnt under drugs)
- test movement of extremeties (no movement or hesitation in arm/leg fall)
- eye movement; no eye rolling
- corenal reflex; no eye blinking
pupil reflex; no constriction in response to light
gag reflex; insercetion of small tube into throat causes no reaction
respiration; no breathing response when patient is removed from ventilator
issues with brain dead people?
they can still have spinal refelxes;
knee jerk response canstill be functional
what further tests are ussd to confirm brain death?
- electroencephalogram (EEG); measures brain activity in microvolts
- cerebral blood flow (CBF); radioactive isoptopes injected into blood stream and seen if there is brain activity
cerebral cortex
- front part of nueral tube
- consits of left and right cerebral hemispheres
- covered by thin layer of grey mater; cerebral cortex
cerebral cortex functions
- reaosning
- language
- complex thought
- visual processing
- motor movement
- remembering
- speech
prefrontal cortex
organizes thoughts, solves problems, formats strategiest
motor assosiciation cortex
coordinates movement
primary motor cortex
plants and executes movements
