Nerves Flashcards
What is the nervous system composed of?
Brain
Spinal cord
Peripheral nerves
What composes the central nervous system?
Brain and spinal cord.
What composes the peripheral nervous system?
Peripheral nerves.
What does the somatic nervous system control?
Conscious activity.
What does the autonomic nervous system control?
Unconscious activity- divided into sympathetic and parasympathetic nervous systems.
What are the divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
Enteric
What does the sympathetic nervous system control?
Flight / fight response.
What does the parasympathetic nervous system control?
Rest / digest response.
What does the enteric nervous system control?
Intrinsic gut motility.
What are the meninges?
Layers of connective tissue lining the brain and the spinal cord. (dura mater, arachnoid mater, pia mater).
What are the functions of the gyrus / sulcus?
Provide the folded appearance of the brain.
Gyrus = ridges, Sulcus = depressions/furrows
What is the function of the gyrus?
Ridges within folded appearance.
What is the function of the sulcus?
Depressions/furrows within folded appearance.
What is the cerebrum?
Mass of the brain.
What is in the cerebrum?
Frontal lobe, temporal lobe, parietal lobe, occipital lobe.
What is the diencephalon composed of?
Thalmus
Hypothalamus
What is the function of the thalamus?
Final relay of sensory signals to the cerebral cortex.
What is the function of the hypothalamus?
Homeostatic control; hormone production.
What is the brainstem composed of?
Midbrain
Pons
Medulla obligata
What is the function of the midbrain?
Motor movement; visual/auditory processing.
What is the function of the pons?
Contain nuclei for signal relay.
What is the function of the medulla obligata?
Regulates subconscious breathing / heart rate / breathing etc.
What is the structure of the spinal cord?
31 pairs of spinal nerves, 12 cranial
How many pairs of spinal nerves are there?
31
How many pairs of cranial nerves are there?
12
What is the grey matter in a spinal cord?
Contains the cell bodies, dendrites and axon terminals of neurones, so it is where all synapses occur.
What is the white matter in a spinal cord?
Consists of axons connecting different parts of grey matter to each other.
Do synapses occur in the grey matter or the white matter?
Grey matter- location of cell bodies, dendrites and axon terminals.
What is the function of the dorsal horn in the spinal cord?
Afferent sensory signals are taken through the dorsal root ganglion going TOWARDS the spinal cord.
What is the function of the ventral horn in the spinal cord?
Ventral motor signals are taken through the ventral root ganglion going AWAY from the spinal cord.
What are afferent signals?
Sensory.
What are efferent signals?
Motor (eff = effect).
What are interneurones?
Interneurones exist in between dorsal/ventral routes to make sense of information- they control some information but just within the small spinal cord circuit.
Where do interneurones exist?
In between dorsal/ventral routes.
What are spinal tracts?
Spinal tracts are located in the white matter and they transfer information to the brain; some are sensory and control whether a motor response is necessary.
Where do spinal tracts exist?
White matter.
What are the parts of a neurone/nerve cell?
Cell body (soma)
Dendrites
Initial segment (axon hillock)
Axon terminals
What is the cell body of a neurone called?
Soma.
What is the function of the cell body (soma)?
Contains nucleus; protein synthesis.
What is the function of dendrites?
Receive incoming sensory information.
What is the initial segment also called?
Axon hillock.
What is the function of the initial segment?
Has machinery to fire an action potential. Evaluates whether or not this is required.
What is the function of the axon terminals?
Presynaptic area which releases a neurotransmitter when needed for continuation of the neural impulse.
What are glial cells?
Glial cells are neural cells that surround neurones and provide support and shape around them.
What are the types of glial cell?
Oligodendrocyte- produces the myelin sheath
Astrocyte- keeps neurones happy by maintaining the blood/brain barrier and keeping ion concentration to an optimum
Microglia- phagocytotic hoovers which clean up infection
What do oligodendrocytes do?
Produce the myelin sheath.
What do astrocytes do?
Maintain the blood brain barrier at optimum levels of ion concentration in order to keep neurones happy.
What do microglia do?
Act as phagocytotic hoovers to clean up infection in the nervous system.
What do neurones exist to do?
Send electrical impulses.
What do action potentials do?
Send electrical impulses over long distances.
What do graded potentials do?
Decide whether or not an action potential should be fired.
What does the resting potential do?
Maintains the cell ands keeps it ready to respond.
What is the usual resting potential of a cell?
-70mV
Is the resting potential of a cell usually negative or positive?
Negative.
What maintains the negative resting potential of a cell?
Leaky potassium channels
NaKATPase action
Negative intracellular proteins
How do leaky intracellular channels help maintain the negative resting potential of a cell?
Potassium (K+) ions leak out of the cell down a concentration gradients. This creates an opposite but equal electrical gradient.
How does NaKATPase action maintain the negative resting potential of the cell?
Transporter protein NaKATPase uses ATP hydrolysis to pump 3 sodium ions out of the cell and 2 potassium ones in (only 2+ whereas 3- each time) therefore the unbalanced ratio results in a subsequent negative intracellular charge.
How do negative intracellular proteins help maintain the negative resting potential of a cell?
Maintain a negative charge within the intracellular base.
What is the concentration gradient related to potassium?
High in cell, low outside cell.
What is the concentration gradient related to sodium?
Low in cell, high outside cell.
What is the concentration gradient related to chlorine?
Low in cell, high outside cell (although opposite -ve)
What is the concentration gradient related to calcium?
Low in cell, high outside cell.
What does the graded potential do?
Determines the threshold for an action potential.
What are the 4 examples of graded potentials?
Generator potentials (sensory receptors) Postsynaptic potentials (synapses) Endplate potentials (NMJ) Pacemaker potentials (cardiac tissue)
What are the 4 properties of graded potentials?
Decremental
Graded
Depolarising / hyperpolarising
Summation
Why are graded potentials decremental?
Act as a leaky hose- neural charge reduces as it travels across. Only useful when travelling short distances.
Why are graded potentials graded?
Depolarisation caused is based on the magnitude of the initial stimulus- therefore the amplitude of the graded potential will correspond to the stimulus intensity.
Why are graded potentials depolarising / hyperpolarising?
Firing an action potential depends on activation of a threshold- graded potentials will excite or inhibit this. Neurotransmitters can be excitatory or inhibitory.
What is an EPSP?
Excitatory postsynaptic potential.
What is an IPSP?
Inhibitory postsynaptic potential.
How does summation apply to graded potentials?
Graded potentials can add together if individually small to evoke an action potential.
What is synaptic integration?
Synaptic integration occurs when the input of various graded potentials integrates to form an action potential.
What is temporal summation?
When two of the same potentials summate.
B + B
What is spatial summation?
When two different potentials summate.
A + B
Which summative graded potentials take priority?
Those closer to the axon hillock / initial segment.
What are action potentials mediated by?
Voltage-gated channels.
What are action potentials subject to?
The threshold given by graded potentials.
Are action potentials self-propogating?
Yes.
What does the self-propogating nature of action potentials mean?
Means there is a propagated spread of depolarisation across various neurones.
Are action potentials all-or-none?
Yes.
Why are action potentials all-or-none?
There is always a full movement otherwise there is none.
Do action potentials have a refractory period?
Yes.
What does the refractory period allow within action potentials?
No backwards movement.
At what speed do action potentials travel?
Travel slowly- improved through myelination and increasing the size of axon fibres.
What can increase the speed of action potentials?
Myelination
Increasing the size of axon fibres
What is myelination?
Neural insulation.
How is the peripheral nervous system myelinated?
Schwann cells form myelin sheath by wrapping themselves around axons to insulate and prevent leakage of neural impulse.
How is the central nervous system myelinated?
Oligodendrocytes.
What are microscopic gaps found within myelinated axons called?
Nodes of Ravier.
What are nodes of Ravier?
Microscopic gaps found within myelinated axons.
What does demyelination do?
Can lead to leakage of neural impulse.
What conditions does demyelination cause?
Autoimmune disease- including multiple sclerosis and motor neurone disorder.
What is a compound action potential?
There are small/large myelinated and non-myelinated axons. A bundle of these axons can evoke a compound action potential which correlates to an altered speed and function.
What does a compound action potential correlate to?
Altered speed and function.
What is an example of a simple synapse?
Neuromuscular junction.
What is the neuromuscular junction?
Simple synapse between synapses of motor neurones and muscle cells/
Where do NMJ synapses occur?
Between the synapses of motor neurones and muscle cells.
Where do non-NMJ synapses occur?
Central nervous system- between neurones and the next cell.
What is the function of the neuromuscular junction?
To pass on the neural signal from a motor neurone to a muscle cell where a musculoskeletal response can be generated.
What does the neuromuscular junction result in?
Musculoskeletal response.
What is the first stage of the neuromuscular junction?
The action potential across the motor neurone triggers the opening of voltage-gate Ca2+ channels. This triggers the fusion of synaptic vesicles.
What happens after the fusion of the synaptic vesicles in the neuromuscular junction?
Following fusion of synaptic vesicles, the neurotransmitter Acetylcholine is released, which travels across the synaptic cleft and binds to ACh nicotinic receptors. This opens ligand-gated Na+/K+ channels which allows the entry of sodium.
What receptors does acetylcholine bind to in the NMJ?
Nicotinic ACh receptors.
What does Ash binding to nicotinic receptors allow?
Opening of ligand-gated Na+/K+ channels which allow the entry of sodium.
What happens after the entry of sodium?
Evokes a graded (local) potential called the END PLATE POTENTIAL. This always depolarises the adjacent membrane to the threshold required for action potential generation.
What is the end plate potential an example of?
Graded (local) potential.
Does the endplate potential always depolarise the adjacent membrane to the AP threshold?
Yes.
What happens after AP threshold is reached?
Voltage-gated Na+ channels are opened which evokes a new action potential which propagates to allow musculoskeletal response.
How is acetylcholine removed?
Degradation by acetylcholinesterase.
What does acetylcholinesterase do?
Removes acetylcholine through degradation.
How does the general basis of the NMJ relate to that of the CNS synapse?
Same mechanism, however CNS synapses are more complex.
What synapses are more complex?
CNS synapses.
How do neurotransmitters differ in CNS synapses compared to NMJ?
Range of neurotransmitters, each with different receptors- ACh, noradrenaline, dopamine, serotonin, histamine, glutamate, GABA, glycine, peptides, ATP etc)
Do CNS synapses always result in an action potential?
No- they have a range of postsynaptic potentials (Slow/fast EPSPs/IPSPs)
Are postsynaptic potentials in CNS synapses usually large/small?
Generally small to enable complex synaptic integration.
Why are postsynaptic potentials in the CNS usually small?
To enable complex synaptic integration.
How does anatomical synaptic arrangement vary in the CNS compared to the NMJ?
Varied in CNS compared to NMJ always bearing the same arrangement- has significant effects on function (axo-somatic, axon-dendritic, axon-axonic).
Describe the altered synaptic connectivity in CNS synapses.
Whilst the NMJ is simply wired to a muscle cell, CNS synapses can be wired in more varied ways to allow complex pathways to occur (convergence/divergence)/
What is the difference between convergence and divergence?
Convergence starts with multiple neurones and feeds into a big synapse whereas divergence starts with a single neurone and branches out.
What can convergence and divergence give rise to?
Feedback inhibition- an inhibitory effect can be used to revert the neural pathway back to the beginning.
What are monosynaptic pathways?
Neural pathways with only one synaptic route.
What are polysynaptic pathways?
Neural pathways with multiple synaptic routes.
What do monosynaptic and polysynaptic pathway differences give rise to?
The basis of many drug functions.
