Lecture 1: Cells of the nervous system and neuromuscular junction Flashcards
What are the highly convoluted surface of ridges on the brain called?
Gyri
What are the valleys in the brain called?
Sulci
What are the 4 functional regions of the brain?
- frontal
- parietal
- temporal
- occipital
What does the brainstem consist of?
- midbrain
- pons
- medulla
NOTE: descending disorder
What is the cerebellum?
Hindbrain structure attached to brainstem, important in motor coordination, fine movement, balance and posture
What is the function of the spinal cord?
- conduit for neural transmission
- coordinates some reflex actions
Where does the spinal cord extend down from?
The medulla
What is a unipolar neuron?
1 axonal projection
What is a pseudo-unipolar neuron?
single axonal projection that divides into 2
What is a bipolar neuron?
2 projections from cell body but still only 1 axon
What is a multipolar neuron?
numerous projections from cell body but still only 1 axon
What are the different types of multipolar neurons?
- pyramidal: ‘pyramid’ shaped cell body
- purkinje cells: GABA neurons found in cerebellum
- Golgi cells: GABA neurons found in cerebellum
What are the shared common features of neurons?
- Soma (cell body, perikaryon)
- Axon
- Dendrites
What is the soma of a neuron?
Cell body that contains nucleus and ribosomes.
Neurofilaments for structure and support
What is the axon of a neuron?
- long process (a.k.a nerve fibre) - originates from soma at axon hillock
- can branch off into ‘collaterals’
- usually covered in myelin
What is the dendrite of a neuron?
- highly branched cell body, not covered in myelin
- branches receive signals from other neurons
What is the most abundant cell type within the CNS?
Astrocytes
What are astrocytes?
- able to proliferate
- structural cells: blood-brain barrier, keeping neurones in place
- cell repair: synthesis of neurotrophic factors, growth + maintenance
- homeostasis: neurotransmitter removal and reuptake
What are oligodendrocytes?
- myelin-producing cells for CNS
- numerous projections that form internodes of myelin
- variable morphology and function
How many axons can one oligodendrocyte myelinate?
Many axons
What is a Schwann cell?
- myelin-producing cell for peripheral nerves
How many axons can 1 Schwann cell myelinate?
1 cell myelinates one axon segment only
What are microglial cells?
- specialised cell, similar to macrophages
- immune cells of CNS, perform immune functions
What are ependymal cells?
- epithelial cells lining fluid-filled ventricles
- regulate production and movement of cerebrospinal fluid (CSF)
What are glial cells?
The glial cells surround neurons and provide support for and insulation between them
What cells are included within glial cells?
- astrocytes
- oligodendrocytes
- microglia
- ependymal
What are the 4 major physiological ions?
- potassium (K+)
- sodium (Na+)
- chloride (Cl-)
- calcium (Ca2+)
How is transportation of important ions regulated?
By channels and pumps because cell membrane is impermeable to these ions
Which ions have a high extracellular concentration?
Na+ and Cl-
Which ion has a low extracellular but high intracellular concentration?
K+
Which ion has a high concentration gradient across the cell membrane?
Ca2+
What creates the potential difference across the cell membrane?
the difference in ion concentrations
What charge do neuronal cells have inside?
negative compared to outside
What is the range of the resting membrane potential?
-40 to -90mV
Where are the positive and negative charges concentrated?
Around the membrane
What is the state of the ion channels at RMP?
voltage-gated Na+ and voltage -gated K+ channels are closed
What happens at membrane depolarisation?
voltage-gated sodium channels open which leads to an influx of Na+ and further depolarisation
What happens at membrane repolarisation?
voltage-gated potassium channels open at a slower rate and cause efflux of K+ from cell
What does an action potential leave?
a sodium and potassium imbalance
How is the Na+ and K+ imbalance restored?
Using Na+-K+-ATPase pump to restore ion gradients
What is the resting configuration of Na+-K+-ATPase?
Na+ enters vestibule and upon phosphorylation ions are transported through protein
What is the active configuration of Na+-K+-ATPase?
Na+ removed from cell, K+ enters vestibule
What happens when the pump returns to resting configuration?
K+ is transported back into the cell
What is saltatory conduction?
action potential jumps between nodes of Ranvier to speed up transmission
How does myelin prevent action potential from spreading?
It has high resistance and low capacitance
What are the nodes of Ranvier?
small gaps of myelin intermittently along axon
Outline how a synapse works. (4 steps)
1) Propagation of the action potential (AP) - Na+ influx, AP moves along neuron, K+ efflux for repolarisation
2) Neurotransmitter release - AP opens voltage-gated Ca2+ channels at presynaptic terminal, Ca2+ influx leads to vesicle exocytosis
3) Activation of postsynaptic receptors - NT binds to receptors on post-synaptic membrane, receptors modulate post-synaptic activity
4) Neurotransmitter reuptake - NT dissociates from receptor and can be metabolised by enzymes in synaptic cleft or recycled y transporter proteins
What type of communication occurs between nerve cells?
Autocrine and paracrine via neurotransmitter release
What is an axodendritic synapse?
connection between presynaptic terminal to neuronal dendrite
What is an axosomatic synapse?
connection between presynaptic terminal to neuronal soma
What is an axoaxonic synapse?
connection between presynaptic terminal to neuronal axon
What is the neuromuscular junction?
Specialised structure incorporating axon terminal and muscle membrane allowing unidirectional chemical communication between peripheral nerve and muscle
What type of communication occurs between nerve and effector cells?
paracrine via neurotransmitter release
What 4 steps happen at the neuromuscular junction?
1) AP propagated along axon –> Ca2+ entry at presynaptic terminal
2) Ca2+ entry leads to acetylcholine (ACh) release into synapse
3) ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle –> change in end plate potential (EPP)
4) 1 ACh vesicle (quantal ACh release) results in mini EPP so need summation of lots of mini EPPS for transmission
What is the sarcolemma?
skeletal muscle membrane with nAChR receptors which when activated lead to depolarisation and so an action potential
What are the T-tubules?
tubes that are continuous with sarcolemma & closely connected to sarcoplasmic reticulum
Where does the AP travel through in skeletal muscle?
T-tubules
Where is the sarcoplasmic reticulum?
surrounds myofibrils - contractile units of muscle
What is the function of the sarcoplasmic reticulum?
Ca2+ storage - Ca2+ is released following sarcolemma depolarisation
What is the effect of Ca2+ in skeletal muscle?
causes myofibril contraction and muscle contraction
What are some disorders of the neuromuscular junction?
- botulism (botulinum toxin irreversibly disrupts stimulation-induced ACh release)
- myasthenia gravis (MG): antibodies directed against ACh receptor, autoimmune
- Lambert-eaton myastenic syndrome (LEMS): antibodies against VGCC, autoimmune
