PHSL231 - progress test 1

What does the nervous system do?

maintains homeostasis in the body

What does the central nervous system consist of?

brain and spinal cord

What does the peripheral nervous system consist of?

peripheral nerves and ganglia

What are the two general cell types in the nervous system?

neurons and glia

What is the main difference between the CNS and PNS?

the PNS does not do its own integration and control

What are the input zones of neurons?

dendrites and cell body

Where do the inputs come from in neurons?

other neurons connected to the dendrites or cell body

What is the function of the input zone?

receive chemical signals from other neurons

What is the summation zone?

axon hillock

What is the function of the axon hillock?

where axon potentials are generated, summation of inputs

What is the conduction zone?

axon

What is the function of the conduction zone?

carry electrical signals between brain areas, to and from spinal cord, or from peripheral sensory receptors to effector cells

What is the output zone?

axon terminals

What is the function of the output zone?

contact with input zone of other neurons or effectors, release of neurotransmitters (chemical signals)

What are the four different types of neurons?

multipolar, bipolar, unipolar, anaxonic

What is a multipolar neuron?

multiple processes emanate from cell body

What is a bipolar neuron?

two processes emanate from the cell body

What is a unipolar neuron?

one process emanates from cell body and branches into a dendrite and axon

What is an anaxonic neuron?

no distinct axon, all processes look alike

What is the function of glia?

support cells for neurons

What types of glia are present in the central nervous system?

oligodendrocytes, astrocytes, microglia, ependymal cells

What types of glia are present in the peripheral nervous system?

schwann cells, satellite cells

What is the function of oligodendrocytes?

form the myelin sheath, provide insulation around neurons

What is the function of astrocytes?

provide nutrients, maintain extracellular environment, provide structural support

What is the function of microglia?

mount the immune response

What is the function of ependymal cells?

circulate and produce cerebrospinal fluid

What is the function of schwann cells?

form the myelin sheath

What is the function of satellite cells?

provide nutrients and structural support to neurons

Where do cells in the PNS get nutrients from?

circulating blood supply

What is a key difference between the blood supply to the CNS and PNS?

the brain is isolated from the normal circulating blood supply through blood-brain barrier

What is a presynaptic neuron?

has the synapse, neuron sending signal

What is a postsynaptic neuron?

neuron receiving information from the synapse

What is a nerve?

bundle of neurons travelling down the same path

What are the different types of synapses?

electrical and chemical

What are the features of electrical synapses?

very fast, ions flow from cell to cell, gap junction, continuous cytoplasm

What are the features of chemical synapses?

slower, rely on chemicals crossing gap, synapse strength can be modified, complex series of events

How do chemical synapses function?

influx of calcium causes depolarisation or hyper polarisation, bind to receptor and neurotransmitter released

What is the function of the somatosensory cortex?

detects sensory input from the body to the brain

Where is the somatosensory cortex located?

next to primary motor cortex

What is the function of the primary motor cortex?

sends signal down to muscles

Where is the primary motor cortex located?

in front of the somatosensory cortex

What is a sulcus?

groove in the brain

What is a gyrus?

ridge in the brain

What is afferent?

input, sensory information going into the brain

What is efferent?

output, motor information from the brain

What is the flow of afferent information into the brain?

receptors -\> spinal nerves -\> brain and spinal cord (where information is integrated/processed)

What is the flow of efferent information from the brain through the somatic nervous system?

brain and spinal cord -\> somatic nervous system -\> skeletal muscle

What is the flow of efferent information from the brain through the autonomic nervous system?

brain and spinal cord -\> autonomic nervous system -\> sympathetic (norepinephrine) or parasympathetic (Ach)

What is the main function of the sympathetic nervous system?

fight or flight

What is the main function of the parasympathetic nervous system?

rest and digest

What is a ganglion?

large collection of cell bodies

What neurotransmitters are used in the somatic nervous system?

acetylcholine

What neurotransmitters are used in the parasympathetic nervous system?

acetylcholine

What neurotransmitters are used in the sympathetic nervous system?

acetylcholine and noradrenaline

How is information encoded in the nervous system?

changes in membrane potential, can be sub threshold (EPSP and IPSP) or supra threshold (APs)

How is information transmitted within nerve cells?

electrically through EPSPs, IPSPs, and APs

How is information transmitted between nerve cells?

chemically through synaptic transmission

Which is a key difference between the neurotransmitters of the sympathetic and parasympathetic nervous systems?

sympathetic nervous system uses noradrenaline as postganglionic transmitter, parasympathetic uses acetylcholine

What is a chemical gradient?

energy provided by the difference in concentration across the plasma membrane

What is an electrical gradient?

energy associated with moving charged molecules across the membrane when a membrane potential exists

What is the membrane potential in neurons?

around -70mV

What is an electrochemical gradient?

set up by the ionic distribution across the membrane, positively charged ion has a chemical driving force to leave cell, electrical driving force to enter cell

What does an electrochemical gradient rely on in order to work?

specific ion channels to open and a few ions to flow

What is equilibrium in an electrochemical gradient?

number of K+ ions entering and leaving the cell is equal

What does the Nernst equation tell us?

equilibrium potential for each ion

What is the resting membrane potential altered by?

number of channels in the membrane, number of channels open

What drives the membrane potential?

K+, lots of K+ channels in the membrane

Why is the resting membrane potential closer to the K+ membrane potential?

cell membrane is more permeable to K+ than Na+

How is the RMP maintained?

by sodium potassium ATP-ase which ensures K+ and Na+ do not reach equilibrium, ATP used to pump ions against gradient

What are local potentials?

changes in membrane potential that can be small/big, current spreads but decreases in amplitude over distance

Where do local potentials summate?

in space and time (spatial or temporal summation)

What is the function of local potentials?

influence the generation of action potentials

What is hyper polarisation?

cell goes below RMP

What is the function of action potentials?

how neurons transmit their signals

What are the features of action potentials?

all or nothing phenomenon, threshold around 10 mV above RMP

What is depolarisation?

change in the RMP that is more positive

What is after hyperpolarisation?

more negative than RMP

What causes the RMP to be depolarised?

opening of ion channels, influx of Na+ ions into the cell

Why does transport of ions require channels?

ions cannot freely diffuse across the membrane

What does conductance of an ion across the membrane depend on?

permeability (ion channels) and equilibrium potential (driving force)

What is the function of the selectivity filter in voltage gated Na+ channels?

ensures that only Na+ goes through

What is the function of blockers?

stop nerve conduction by blocking voltage-gated Na+ channels, can be irreversible or short acting/reversible, block pain receptors

What are some examples of blockers?

tetrodotoxin, saxitoxin, lidocaine

What is the inactivation gate?

ball and chain model, inactivation molecule not part of pore blocks pore preventing Na+ conductance and AP

What are the three states of the channel at the inactivation gate?

closed, open, inactivated (cannot be opened)

What is happening at the inactivation gate when the pore is closed?

pore closed, positive charge is in the way, no Na+ conductance

What is happening at the inactivation gate when the pore is activated?

pore open, positive charge nearby for selectivity, sodium free to travel across the membrane, areas of neurons that have lots of voltage-gated Na+

What is happening at the inactivation gate when the pore is inactivated?

pore still open but ball on end of chain blocks it, cannot be opened, sudden drop in sodium conductance causes repolarisation of AP

What are the features of voltage gated potassium channels?

largest ion channel family, have a selectivity filter (specific for K+), activated by depolarisation, slower than voltage gated Na+ channels, blocked by TEA (tetraethyl ammonium), remain open longer than Na+ channels

What is the absolute refractory period?

cannot generate another action potential, 1-2 ms while inactivation molecule is in voltage gated Na+ channel

What is the relative refractory period?

occurs during afterhyperpolarisation (more negative than RMP), can reach threshold if stimulus is large enough causing an AP

What is the threshold for action potentials?

+10mV above RMP (-70), enough change in RMP for all voltage gated Na+ channels to open

Why are action potentials regenerative?

Na+ channels open, current flows, membrane depolarises, more channels open, more current flows

What does opening of voltage gated Na+ channels cause?

rapid depolarisation

What does opening of voltage gated K+ channels cause?

depolarisation

What happens during repolarisation?

inactivation molecule blocks voltage-gated Na+ channels causing them to close, voltage-gated K+ channels open, Na+ leaks out of the cell, membrane potential repolarises, absolute refractory period

What happens during afterhyperpolarisation?

K+ channels open, K+ enters the cell, membrane potential closer to Ek (less than -70 mV), Na+ channels ready to be opened, relative refractory period

Why is it harder to cause an AP during the relative refractory period?

RMP is further from threshold and increased K+ permeability means that a larger stimulus is needed

What direction do action potentials travel in?

down the axon away from cell body/axon hillock, due to absolute refractory period

What factors increase the speed of conduction of action potentials?

increasing diameter and membrane resistance (myelination)