How nerves work 1-5 Flashcards
Nervous system (2 areas)
CNS and PNS
CNS
Brain and spinal cord encased in bone
PNS
Somatic and autonomic
Autonomic
Sympathetic and parasympathetic
Meninges
3 membranes that envelop brain and spinal cord and protect the spinal cord
Gyrus
Ridge on cerebral cortex - high
Sulcus
Ridge on cerebral cortex - low
Where is the cerebellum?
Back of the brain for balance
4 cerebral cortexes
Frontal, parietal, temporal and occipital
Diencephalon
In forebrain below cerebrum
Thalmus and hypothalamus
Thalmus
Last relay of information from spinal cord q
Hypothalmus
Hormones and endocrine gland
3 parts of brainstem
Pons, midbrain and medulla
How many spinal nerves are there?
31
Name how many nerves there are at each vertebrate level
7 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Axon hillock/initial segment
Make action potential
Axon terminal
Release neurotransmitter
Astrocytes
Maintain external environment and make blood brain barrier and surround blood vessels
Oligodendrocytes
Wrap feet around axon to form myelin sheath in CNS
Microglia
Little cells in immune system and mop up infection
What is the function of the resting membrane potential?
Keep cell ready to respond
Is the inside of the cell negative or positive to the outside of the cell
Negative = -70mV
Why is the inside of the cell negative in comparison?
Leaky potassium membrane moves out of cell down concentration gradient
Equilibrium potential
Membrane potential at which the electrical gradient is equal and opposite to the concentration gradient
Why is more K+ in ECF bad?
Less concentration gradient
Smaller electrical gradient
RMP reduced so fire at random time due to less -ve
Capillaries in blood brain barrier prevent this but heart ==>ventricular fibrillation
Why is normal RMP -70mV
- leaky channels
- Electrogenic nature of the pumps
- large intracellular proteins
When RMP is an action potential fired at?
-55mV
Name the 4 graded potentials
- Generator => sensory
- endplate => neuromuscular
- pacemaker => heart
- Post synaptic => at synapses
Name some properties of graded potentials
- Decremental - current leaks out
- non propagated
- graded - more channels= bigger potential
- electrotonic potentials
In graded potentials where is the intensity encoded?
Amplitude
Are graded potentials hyperpolarising or depolarising?
Both
Hyperpolarising
- inhibitory IPSP
- fast - CL- in
- slow - g protein coupled K+ out
eg GABA and glycine
Depolarising
fast = ATPase slow = gprotein coupled stop K+ leaving
Ligand gated ion channel
Neurotransmitter
Voltage gated ion channel
Depolarisation of membrane potential
Temporal summation
2 EPSP added together
Spatial summation
2 different stimulations added together
Postsynaptic inhibition
Straight on to dendrite
Synaptic integration
the process of summing all those inputs in space and time, to determine whether or not the initial segment reaches threshold.
Action potentials
- Have a threshold = fired once depolarised
- all or none - all the same size
- Encodes stimulus intensity in frequency, fire more
- Self propagate - Can’t travel back as all neurons in the refractory period
Gaps in myelin
Nodes of ranvier
Big axons
Lower axial resistance
Depolarisation travel further and spread out sodium channels
Myelination
Increase resistance - AP spreads
less leaky and saltatory reduction
Demyelination
MS - resistance so low so will decay and not big enough to fire AP
Compound action potential
Axons variable size and myelination with different conduction velocities
A alpha big and myelinated and C opposite
Endplate
Where sarcolemma invaginates
Neurotransmitter released in vesicles to fuse with presynaptic membrane due to what?
Exocytosis triggered by calcium concentration changes
Brief steps
AP-Calcium channels open- vesicles of acetylcholine released, NA/K, graded potential, depolarise, Na and acetylcholinesterase
CNS receptors
Acetylcholine, NO, serotonin, dopamine, GABA
axo somatic synapse
Synapse on cell body
axo dendritic synapse
Synapse on dendrite
axo axonial
Synapse on axo dendritic
Feedback inhibition
Inhibitory interneuron close to axon hillock
Why is CNS more complex than neuromuscular?
- Bigger range of receptors
- Range of postsynaptic potentials
- small potentials - integration
- variations on connectivity and anatomical arrangement