2.2: Cells of the nervous system & neuromuscular junction Flashcards
What is the telencephalon also known as?
Cerebral hemisphere
What are the ridges on the telencephalon called?
Gyri
What are the valleys on the telencephalon called?
Sulci
4 lobes of the cerebral hemisphere
Frontal
Parietal
Temporal
Occipital
Function of the frontal lobe of the cerebral hemisphere
Responsible for executive functions such as personality
Function of the parietal lobe of the cerebral hemisphere
Contains the somatic sensory cortex responsible for processing tactile information
Function of the temporal lobe of the cerebral hemisphere
Contains important structures (hippocampus - short term memory, amygdala -behaviour, Wernickes area- auditory perception and speech)
Function of occipital lobe of cerebral hemisphere
Processing of visual information
3 main structures of brain stem in descending order
Midbrain
Pons
Medulla
Location and function of brain stem
Dorsal region of CNS
role in motor coordination, balance and posture
4 morphologies of neurons
Unipolar
Pseudo-unipolar
Bipolar
Multipolar ( pyramidal, purkinje, Golgi cells)
Define soma
Cell body
Most abundant cell type in CNS
Astrocyte
Morphology of unipolar neurons
1 axonal projection
Morphology of pseudo-unipolar neurons
Single axonal projection that divides into two
Morphology of bipolar neurons
2 projections from cell body
Morphology of multipolar neurons
Numerous projections from cell body
Morphology of pyramidal cells
‘Pyramidal’ shaped cell body
Where are purkinje cells and Golgi cells found
They are GABA neurons found in cerebellum
What are the functions of Oligodendrocytes and Schwann cells
Myelin producing cells
What is the difference between Oligodendrocytes and Schwann cells
O - work in CNS
S - work in PNS
O- capable of myelinating a number of axons
S- only myelinated a single axon segment
microglial cell
Performs immune functions in CNS
act as macrophages in CNS
Ependymal cells
Epithelial cells (that line fluid-filled ventricles) regulating production and movement of CSF
Resting membrane potential of neurones
Around -70mV
If membrane potential is too negative, cell is said to be
Hyperpolarised
If membrane potential becomes more positive what is the cell said to be
Depolarised
4 ions controlling resting membrane potential
K+
Na+
Cl-
Ca2+
What are the relative concentrations of RMP ions extracellularly compared to intracellularly
Higher Na+
Higher Cl-
Lower K+
Higher Ca2+ (High concentration. Gradient)
Explain how ions are involved in generating an action potential
Influx of Na+ via voltage gated sodium ion channels (VGSC) leads to further depolarisation
Explain how the ions are involved in the restoration of RMP
Voltage gated potassium ion channels open at slower rate, leading to effluent of K+ from cell which repolarises the membrane
How is the Na+/K+ ATPase involved in restoring the ion gradients
At rest - Na+ enters, phosphorylated, ions are transported through the protein against conc. gradient
Active configuration - Na+ removed from cell and K+ enters against conc. gradient. The pump returns to rest and K+ transported back into cell
Process by which AP spreads along axon
Cable transmission
What is saltatory conduction
AP “jumps” between nodes to get to pre-synaptic terminal faster
Function of myelin in speed of conduction
Prevents action potential spreading
It has a high resistance and low capacitance
What are the nodes of ranvier
Gaps of no myelin intermittently along the axon
What happens when the action potential reaches the synapse?
AP opens V gated Ca2+ channels at pre-synaptic terminal
Ca2+ influx, down conc. gradient causing exocytosis of vesicles containing neurotransmitter
Neurotransmitter released into synaptic cleft
Binds to receptors on post-synaptic membrane
Enzymes break down neurotransmitter to be uptaken again by pre-synaptic cleft / recycled by transporter proteins
How does an action potential travel across a neuromuscular junction.
Action potential propagated along axon (Na+ and K+) → Ca2+ entry at presynaptic terminal
Ca2+ entry → ACh release into synapse
ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle → change in end-plate potential (EPP)
Miniature EPP: Quantal ACh release
AP travels through T-tubules that are continuous with sarcolemma & closely connected to sarcoplasmic reticulum
Where is the sarcoplasmic reticulum in relation to myofibrils
Surrounding myofibrils (contractile units of muscle)
What is the function of the sarcoplasmic reticulum and what effect does it have?
Ca2+ storage —> Ca2+ release following sarcolemma depolarisation
Ca2+ —> myofibrils and muscle contraction
What is myasthenia gravis and what does it cause
Autoimmune disorder - antibodies directed against ACH receptor
Causes fatigable weakness
Astrocytes
structural cells
play important role in cell repair, synapse formation, neuronal maturation and plasticity
Graded potential
Membrane potential change that is not an action potential
- produce initial change in membrane potential, can initiate or prevent action potentials
Neuromuscular junction
Specialised structure incorporating axon terminal and muscle membrane, allowing unidirectional communication between peripheral nerve & muscle
Communication across neuromuscular junction
Paracrine : neurotransmitter released
Sacrolemma
skeletal muscle membrane : nAChR activation -> depolarisation -> AP
t tubules : continuous with sarcolemma, closely connected to sarcoplasmic reticulum
AP travels through T tubules
3 neuromuscular junction disorders
Botulism
Myasthenia Gravis (MG)
Lambert-Eaton myastenic syndrome (LEMS)
Botulism
BTx : irreversible
disrupts stimulation-induced Ach release from pre-synaptic nerve terminal
Lambert-Eaton myastenic syndrome (LEMS)
Autoimmune disorder - antibodies directed against VGCC
