Cells of the Nervous System/Neuroanatomy Flashcards
What are the convoluted surfaces of ridges residing within the cerebral hemispheres?
Gyri
What are the impression in the cerebral hemispheres?
Sulci
What are the four cerebral lobes?
Temporal, parietal, occipital, and frontal
What does the brainstem consist of?
Midbrain, pons and medulla
In descending order
What is the cerebellum?
Hind brain structure, attached to brainstem
Coordinates voluntary movements including posture, balance, coordination and speech
What is the role of the spinal cord?
Extends down from the medulla, conduit for neural transmission and coordinate reflex action
What are unipolar neurones?
Consists of one extension from cell body (considered as single axonal projection)
What are pseudo-unipolar neurones?
Single axonal protection that divides into two segments
What are bipolar neurones?
Two projections from the cell body- 1 axon + 1 dendrite
What are multipolar neurones?
Neurones with multiple projections from the cell body, most prevalent neuronal type
What are pyramidal cells?
Neurones with a pyramidal shape soma, two distinct dendritic trees.
Basal dendrites emerge from the base and the apical dendrites from the apex of the pyramidal cell body
What are Purkinje and Golgi cells?
GABA neurones
Where are Purkinje and Golgi cell located?
Cerebellum
What are neurones?
Excitable cells fo the CNS, generate action potentials. Non-dividing cells contemporary elements suggestive of potential division
What does heterogeneous morphology mean?
Variation in structural morphology of neurones.
What is the soma and what is its function
Connects to dendrites, transmits electrical signals to the neurone, and their axon sends information to adjacent neurones
What does the soma contain?
Nucleus, Nissl granules and neurofilaments.
What are Nissl granules?
Composed of rough endoplasmic reticulum and are polyribosomes
What is the function of neurofilaments?
Express structural and transportation properties.
What do axons contain?
Axoplasm
Where do axons originate from?
Originate from the soma at the axon hillock
What are projections from the axon called?
Collaterals
What is the function of axons?
Transmitting electrical signals to adjacent neurones/ effector cells
What protein encapsulates axons?
Myelin
Why is myelin useful?
Enhances electrical trnsmission through electrical insulation that stimulates saltatory conduction.
What is present at the axon terminal?
Telodendria
What are dendrites?
Highly branched cell body, that unmyelinated, receives signals from other neurones, and transmits electrical signals to the soma to the axon
Which cells connect neuronal signalling and CNS vasculature?
Astrocytes
What projections extend from the astrocyte soma and attach to the basement membrane?
Astrocyte end feet
How do astrocytes enable bidirectional signalling between neurones and vasculature?
Processes extend from the cell bodies towards the neurones, and to the vasculature
What are the three functions of astrocytes?
Maintenance of blood brain barrier
Cell repair
homeostasis
How do astrocytes maintain the blood brain barrier?
Paracrine interaction with the endothelial cells. Secrete classes of factors with either barrier promoting or barrier disrupting effects.
How are astrocytes involved in cell repair?
Synthesis of neurotrophic factors (endogenous soluble proteins that support growth, survival and differentiation of neurones).
CNS damage = astrocytes occupy space to form glial scar
How do astrocytes form glial scars?
Proliferate and migrate to injury site, undergo hypertrophy to develop thicker processes that aim to isolate the area
What is the process of forming glial scars referred as?
Astrocytosis
How are astrocytes involved in homeostasis?
Neurotransmitter removal and re-uptake. Express plasma membrane transporters (glutamate transporters for neurotransmitters GABA and glutamate)
How do astrocytes maintain interstitial fluid?
Release lactate into fluid, neurones have limited energy stores.
Potassium ion concentration
Which cells myelinated cells of the CNS?
Oligodendrocytes
Describe the structure of oligodendrocytes?
Consists of numerous projections that form internodes of myeline.
One oligodendrocyte myelinates multiple axons , providing myelin sheath
Which cells myelinate the PNS?
Schwann cells
How do Schwann cells myeliate neurones?
Wrap itself around the axon repeatedly to form the myelin sheath. Therefore the myelin sheath consists of many layers of Schwann cell membranes.
One Schwann cell myelinates on corresponding axon.
What are the two types of cells that are responsible for myelination?
Oligodendrocytes and Schwann cells
Which CNS cells are responsible for immunological and perform analogous functions to macrophages?
Microglial cells
What are the functions of microglial cells?
Analogous to macrophages, clearing of cellular debris and impaired neurones from nervous system by phagocytosis.
Which ion are axons permeable to?
Potassium ions
Which ions are axons impermeable to?
Sodium ions
How is resting potential maintained?
Extracellular concentrations of ions greater than that of axoplasm
Sodium/potassium ion pump
NA/K ATPase uses ATP to move 3 Na out, and 2 K in into the axon
Lowering concentrations of sodium inside the cell, due to the relative impermeability of the membrane to sodium ions, they cannot diffuse in
Potassium ions are actively moved into the axon by the pump, but then passively diffuse out again along the concentration gradient through open potassium ion channels.
Inside cell is negatively charged relative to outside- The membrane is polarised. (-70mV). The electrical gradient will put K+ back into the cell, however concentration gradient cancels tendency.
Describe the concentration gradient for sodium and chloride ions?
Extracellular concentrations of sodium and chloride ions are relatively greater than intracellular concentrations
What is the net charge of a resting neurone?
Negatively charged (-70mV)
How is an action potential triggered?
Impulse passes the threshold
What happens to the permeability of the axon membrane to sodium ions upon action potential?
Increases. Voltage gated sodium ion channels open, allowing sodium ions to rapidly diffuse down their concentration and electrochemical gradient (Sodium ion influx)
What happens due to sodium influx within the neurone?
Potential difference across the membrane is reverse and depolarised. The cell internally becomes positive with respect to the outside
Region of positive charge causes nearby sodium ion channels to open. Potential difference is +40mV (Action potential)
What occurs during the end of depolarisation?
Sodium ion channels close to excess sodium ions. Sodium ions rapidly pumped out by active sodium pump.
Permeability of potassium ions temporarily increases.
Voltage-dependent ion channels open
How are neurones repolarised?
Potassium ions diffuse out of axon down their concentration and electrochemical gradients, attached to the negative charge on the outside.
membrane becomes hyperpolarised
Why does the membrane become hyper polarised?
Voltage gated potassium ion channels close slowly, potassium ions diffuse to restore resting potential
What is an all or nothing response?
Once the threshold has been reached the action potential occurs. Size of the action potential is always the same
What is a refractory period?
Recovery time for the axon.
Time it takes for an axon to recover after an action potential, for ionic movements to depolarise the membrane and restore resting potential
What is the absolute refractory period?
After action potential, the fibre cannot re-stimulate sodium ion channels are completely blocked, and the restoring potential has not been restored
What is the relative refractory period?
There is a period the axon may be stimulated, however will only respond to stronger stimuli/
Voltage dependent potassium ion channels are still open,
What is the importance of the refractory period?
limits the impulse rate, only flow in one direction
Where do action potential occur?
Nodes of Ranvier
What are the Nodes of Ranvier?
Ions can only pass in and out of the axon freely , there are unmyelinated regions
What happens at the synaptic knob upon action potential arrival?
Increases the permeability of the presynaptic membrane to calcium ions as calcium ion channels open up
What happens when calcium ion channels open within the presynaptic membrane?
Calcium ion influx into the synoptic knob across electrochemical and concentration gradients causes the synaptic vesicles to fuse with the presynaptic membrane
What is contained within the presynaptic vesicles?
Approximately 3000 neurotransmitters
Upon presynaptic vesicle fusion with membrane, what occurs?
Exocytosis of neutrotransmitter into the synaptic cleft, diffusion across the gap, attaching onto postsynaptic receptor sites in the postsynaptic membrane of the recipient neurone
What occurs upon arrival of neurotransmitter within the post-synaptic membrane?
Opening of sodium ion channels in membrane, influx of sodium ions causing a change in the potential difference across membrane and EPSP to be setup
How is an action potential triggered within the post-synaptic membrane?
Sufficient number of EPSPs, positive charge in the postsynaptic cell exceeds the threshold level, and an action potential is set up which travels along the post synaptic neurone
What is an IPSP?
Influx of negative ions, reducing the tendency of the stimulation for action potential along the post synaptic neurone
How are synapses controlled?
Enzyme catalyses the hydrolysis of the neurotransmitter within the synaptic cleft, re-emptying the post synaptic receptors.
What is the major neurotransmitter secreted into the synaptic cleft?
Acetylcholine
How is acetylcholine synthesised?
Requires ATP produced by the present mitochondria within the synaptic knob and packaged into presynaptic vesicles
Which nerves use acetylcholine neurotransmitter?
Parasympathetic
and Sympathetic preganglionic
Cholinergic nerves
Which enzyme hydrolyses and removes acetylcholine from the synaptic cleft?
Acetylcholineesterases
What constituents form acetyl choline?
Choline and acetic acid
Where is acetylcholinesterase located?
In post synaptic membrane
What is an axodendritic synapse?
Connection between presynaptic terminal –> neuronal dendrite
What is an axisomatic synapse?
Connection between presynaptic terminal –> Neuronal soma
What is an axoaxonic synapse?
Connection between presynaptic terminal –> neuronal axon
What occurs at a neuromuscular junction?
Specialised structure incorporating axon terminal and muscle membrane, enabling unidirectional chemical communication between peripheral nerve and muscle. Paracrine: Neurotransmitter release.
which type of receptors do ACh bind onto?
Nicotinic receptors
What is a mini endplate potential?
Occurs from one acetylcholine molecule (released in quanta).
Summation is required of endplate potentials to stimulate an action potential within the postsynaptic neurone
How are action potentials transmitted into a muscle cell?
t-tubules
What is the function of the sarcoplasmic reticulum?
Releases calcium ions from ca storage
What is the mechanism of nicotine?
Mimics effects of acetylcholine and bings to acetylcholine receptor in post-synaptic membrane known as nicotinic receptors (Due to complimentary shape)
Nicotine triggers an action potential in postsynaptic neurones, receptor means unresponsive to more stimulation
What are the drug effects on increasing the response?
Increased the amount of neurotransmitter produced
Increases the release of neurotransmitter and activates/ increases effect
prevents degradation of neurotransmitter by enzymes or prevents reuptake into the presynaptic knob
What effect does nicotine exhibit:
Causes raised heart rate and blood pressure, triggers the release of dopamine associated with pleasure sensations.
What is the mechanism of organophosphates?
Anticholinesterases, organophosphates phosphorylate the acetylcholinesterase, competitively inhibiting the enzyme, reduces the ability to hydrolyse ACh and the transmission signal is thus continuously stimulated
What effects do drugs have in decreasing the response?
Blocks the synthesis of neurotransmitter
Causes neurotransmitter to leak from vesicle and be destroyed by enzymed
Blocks the receptor and prevents neurotransmitter binding
Prevents release of neurotransmitter from vesicles
What is the mechanism of lidocaine?
Molecules block voltage gated sodium channels, preventing the production of an action potential in sensory nerves
What is the mechanism of cobra venom?
A bungarotoxin is a neurotoxin preventing acetylcholine receptor channels from opening by binding specifically and irreversible to its alpha subunits. ACh cannot have effect
Muscle not stimulated, paralysis. Toxin binds to post synaptic membrane receptor sites, blocks ACh-Receptor compels formation
What is the mechanism of botulinum toxin?
Blocks the release of acetylcholine. Botulism occurs under anaerobic conditions, a toxin produced by bacteria
What is Myasthenia Gravis?
Autoimmune disorder, antibodies directed against Each receptor, preventing nerve impulses from triggering muscular contractions
What is the effect with MG?
Causes fatigable weakness
What is Lambert-Eaton Myasthenic syndrome?
Autoimmune disorder
Antibodies against voltage gated calcium channels, inhibits influx of calcium ions into the presynaptic knob, preventing neurotransmitter release and the stimulation of an action potential in the postsynaptic cells.
