Lecture 5 Flashcards
Do neurons have action potentials without sensory input?
Yes. Some express channels that generate ongoing spiking without stimuli
The firing rate is sensitive to change in sensory input, inhibitory or excitatory so they can convey a broader range if information.
If neurons spike at a steady state in the absence of sensory input do they have a resting potential?
It is defined as the membrane potential they sit at when all voltage-gated Ka+ channels are blocked and there is no sensory input
If neurons keep firing all the time, how long do they maintain their ionic concentration gradient across their membranes?
Until death
Receptor protein
Protein that is sensitive to and can communicate a signal. Can be ionotropic or metabotropic
Ionotropic receptor
Receptor protein that has an ion channel.
Direct effect is always short lived and immediate change to the permeability of the membrane to certain ions
Metabotropic receptor
Receptor proteins that is not an ion channel
Signal intracellular signaling cascades, usually with g proteins which can change gene expression, or open/close a g protein gated ion channel
The effects are slow and long lasting as they rely on signaling cascades and diffusion
Trophic means
Turn towards
ionotropic turn towards ions to mediate their effects
metabotropic turn towards metabolism
Metabotropic receptors and g proteins
Metabotropic receptors use metabolism to affect changes. The use g proteins to start a cascade.
g proteins use GTP instead of ATP.
When they are bound to GTP they are on and catalyze things. WHen the g protein clips off a P from GTP it becomes GDP and is inactivated.
Inactivated g proteins cannot release GDP. When a ligand binds to the extracellular part of a metabotropic receptor, it changes its intracellular configuration. This then binds to the g protein and allows it to release its GDP. Then the g protein can bind GTP and become active again.
G-protein ion channels
Are activated by g proteins
Metabotropic receptor is activated, cleaves GDP from a g protein which then binds GTP, becomes active, binds with the ion channel and activates it
Why use metabotropic receptors when you already have ionotropic ones?
While the metabotropic receptor is active, it can activate many g proteins.
While the g protein is active, it can catalyze many things.
ie gene expression, ion channels, secretion from the cell (anything more or less)
So scats to amplify many things.
It is slow to act >30ms but has a bigger, longer effect.
Synapses can form between the axon terminals and (4 things)
Dendrites (dendritic shafts) - led toward cell body
Dendritic spines
The soma (cell body)
Other axon terminals cause presynaptic inhibition or facilitation
presynaptic inhibition or exitation
Inhibition - causes the synapse to release less neurotransmitter. hyperpolarizes presynaptic axon terminal so that less voltage gated Ca2+ channels open
Excitation -depolarizes it so more ca2+ comes in
Autoreceptors
On pre synaptic membranes
Sensitive to the neurotransmitter the presynaptic neuron releases
Usually metabotropic and inhibitory
prevent excess release
A strong source of presynaptic inhibition.
2 parts to nervous systen
central nervous CNS = brain and spinal chord
Peripheral (PNS) everything outside the CNS including the bits attached to it
Oligodendrocytes in CNS … in PNS
Schwann cells
Interstitial fluid in the body and brain
It is extracellular fluid
OUTSIDE the CNS = comes from blood
Blood plasma can leak through holes in capillary
Is now called lymph
Picks up waste and bacteria
Collected in lymph nodes and goes back to blood
Immune function at lymph nodes
INSIDE CNS = no leaky capillaries, GLYMPHATIC SYSTEM
Glymphatic system
The blood brain barrier is the layer between blood and brain which is NOT LEAKY
Cerebrospinal fluid is made by the CNS directly
The ventricular system (4)
The LATERAL ventricles are the largest. They sit under the cerebrum
goes to the THIRD VENTRICLE which is between the two thalamic nuclei
The FOUUTH ventricle is between the pons and the cerebellum
Cerebral aqueduct is a long tube that connects the third and fourth ventricle.
Cerebrospinal fluid is produced where and goes where?
Produced in the choroid plexus of the lateral ventricle. Flows to the third ventricle, then via the cerebral aqueduct to the fourth ventricle and then around the superior sagittal sinus to the arachnoid granulation and back into the blood
The meninges 3 layers
Dura matter is hard and sits below bone. Thick, tough and inflexible.
Arachnoid membrane is the middle layer, soft spongy and has blood vessels in it which supply oxygen to the brain (but are not leaky)
The pia matter is like surround wrap. Thin, clear and holds stuff in place.
Neuraxis (imagine 4 legged creature)
An imaginary line that runs along the CNS
Anterior (rostral)
Front end/ toward beak/ toward head
Posterior (Caudal)
Tail end
Dorsal
(superior)
towards the back OR top of the head
can mean two things
Ventral
Infererior
Towards the belly, front surface that faces ground
Lateral
Distal
Away from center
Medial
proximal
towards the middle
3 types of brain slices
Transverse plane (frontal section, cross section Coronal
Sagittal plane (mid sagittal)
Horizontal plane
Brain nuceli
Group of neighboring neurons that have roughly similar connections and function
Developmental brain
Neural plate - neural tube within the first month. Tube is made of neural progenitor cells.
2 months, divide in symmetrical division
after 2 months asymmetrical division
4-5 months in, this stops
Symmetrical division
Neural progenitor - 2x neural progenitors
Occurs for the first two months of development
Hug the inner section of the neural tube called the ventricular zone
Asymmetrical division
Neural progenitor - 1x neural progenitor and one other cell (glia, neuron etc)
Lasts 2-3 months
Makes all the brains neurons. More produced now than will exist at birth.
Cortical development
One radial glial cell forms that grows up through the cortex. Is used as a scaffold by other neurons when they divide during asymmetrical division. Each migrates up the radial glial cell until there is space to settle. Hence they form layers. This is how the cortex forms, layer by layer.
Neurogenisis
Production of neurons
Stops at 4-5 months when a signal cascade goes out and signals it
Apoptosis
Programmed cell death
regulated and controlled. All neuro progenitor cells do this at 4-5 months (or at least most).
If cells ignore these signals due to mutation, glial cells signal them. If they ignore this they may accumulate (possible cause of ageing). If they ignore apoptosis and keep dividing = cancer.
