Cells of Nervous System and Neuromuscular Junction Flashcards
What are the surfaces on the cerebral hemispheres?
Highly convoluted surface of ridges -> gyri & valleys -> sulci
What are the 4 functional regions in the cerebral hemispheres?
frontal, parietal, temporal and occipital
What does the brainstem consist of?
-midbrain, pons and medulla -Target or source of all cranial nerves and has numerous important functions
Describe the cerebellum
•Hindbrain structure attached to brainstem •Important role in motor coordination, balance & posture
What is the spinal cord?
- Extends down from medulla:
- Conduit for neural transmission
- Co-ordinates some reflex actions
What are the different neurones? Describe them
- Unipolar: 1 axonal projection
- Psuedo-unipolar: Single axonal projection that divides into two
- Bipolar: 2 projections from cell body
- Multipolar: Numerous projections from cell body •Pyramidal cells: ‘pyramid’ shaped cell body
•Purkinje cells: GABA neurons found in the cerebellum •Golgi cells: GABA neurons found in the cerebellum
Describe neurones
- Excitable cells of CNS
- Heterogeneous morphology
- Non-dividing cells
- Share common features:
Describe the Soma (cell body, perikaryon) of the neurone
- Contains nucleus & ribosomes
- Neurofilaments -> structure & transport
Describe the axon
- Long process (aka nerve fibre) - originates from soma at axon hillock
- Can branch off into ‘collaterals’
- Usually covered in myelin
Describe dendrites
•Highly branched cell body - NOT covered in myelin •Receive signals from other neurons
Describe astrocytes
- Most abundant cell type within CNS
- Able to proliferate
What is the fucntion of astrocytes?
- Structural cells: blood-brain barrier
- Cell repair: synthesise neurotrophic factors
- Homeostasis: neurotransmitter removal & reuptake
Describe oligodenocyte
- Variable morphology & function
- Numerous projections that form internodes of myelin
- One oligodendrocyte to myelinates many axons
Descrieb Shwaan cells
- Produce myelin for peripheral nerves
- One Schwann cell to myelinates one axon segment
What are microglial cells?
- Specialised cells - similar to macrophages
- Perform immune functions in CNS
What are ependymal cell?
- Epithelial cells - line fluid filled ventricles
- Regulate production & movement of cerebrospinal fluid (CSF)
Summarise the other cells in the CNS Anatomy
1.Neuron
- Excitable cells of CNS
- Responsible for electrical transmission
2.Oligodendrocyte
•Glial cell - produces myelin
3.Astrocyte
•Most abundant cell type in CNS
4.Microglia
•Neuronal macrophages
What are the 4 major physciological ions in RMP?
potassium (K+), sodium (Na+), chloride (Cl-) and calcium (Ca2+)
What is the distributioin of ions in the cell like and what does this cause?
- Cell membranes - impermeable to these ions -> transportation regulated by channels & pumps
- This causes an uneven ion distribution:
- High extracellular - Na+ & Cl-
- Low extracellular - K+
- High concentration gradient for Ca2+
- Difference in concentration -> creates a potential difference across the membrane
What is the charge like the neuronal cells?
- Neuronal cells -
- Negative charge inside compared to outside
- RMP of between -40 to -90mV
•Positive and negative charges are concentrated around the membrane
What happens at RMP?
•Voltage-gated Na+ channels (VGSCs) & voltage-gated K+ channels (VGKCs) are closed
1) Membrane depolarisation - opening of VGSC to Na+ influx to further depolarisation
2) VGKCs opens at a slower rate and causes tp efflux of K+ from cell to membrane repolarisation
What happens during an action potential?
•AP leaves Na+ & K+ imbalance to need to be restored
•Na+-K+-ATPase (pump) restores the ion gradients
1)Resting configuration - Na+ enters vestibule & upon phosphorylation to ions are transported through protein
2)Active configuration - Na+ removed from cell to K+ enters the vestibule
3)Pump returns to resting configuration to K+ is transported back into the cell
Describe salatory conduction
- AP spreads along the axon by ‘cable transmission’
- Myelin prevents AP spreading because it has - high resistance & low capacitance
- Nodes of Ranvier - Small gaps of myelin intermittently along axon:
- AP ‘jumps’ between nodes - saltatory conduction
- AP is unable to ‘jump’ across the gap at the axon termina
What if the first step in the neurotransmission in a synapse?
1.Propagation of the action potential (AP)
- AP is propagated by VGSCs opening
- Na+ influx -> membrane depolarisation -> AP ‘moves along’ neuron
- VGKC opening -> K+ efflux -> repolarisation
What is the second step in neurotranmission in a synapse?
2.Neurotransmitter (NT) release from vesicles
•AP opens voltage-gated Ca2+ channels at presynaptic terminal
•Ca2+ influx -> vesicle exocytosis
What is the third step in neurotranmission in a synapse?
3.Activation of postsynaptic receptors
•NT binds to receptors on post-synaptic membrane
•Receptors modulate post-synaptic activity
What is the fourth step of neurotransmission in a synpase?
4.Neurotransmitter reuptake
•NT dissociates from receptor and can be:
•Metabolised by enzymes in synaptic cleft
•Recycled by transporter proteins
What are the different types of communication in nerve cells in post-synpatic cell?
Communication between nerve cells
•Autocrine & paracrine: neurotransmitter release
What are the different types of synpatic organisation in post-synaptic cell?
A.Axodendritic synapse: connection between presynaptic terminal -> neuronal dendrite
B.Axosomatic synapse: connection between presynaptic terminal -> neuronal soma
C.Axoaxonic synapse: connection between presynaptic terminal -> neuronal axon
Whta is a neuromusculasr junction?
Specialised structure incorporating axon terminal & muscle membrane allowing unidirectional chemical communication between peripheral nerve & muscle
What is the communcation like between nerve and effector cells?
•Paracrine: neurotransmitter release
What happens at neuromusuclar junction?
- Action potential propagated along axon (Na+ & K+) -> Ca2+ entry at presynaptic terminal
- Ca2+ entry -> acetylcholine (ACh) release into synpase
- ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle -> change in end-plate potential (EPP)
- Miniature EPP: quantal ACh release
Describe the sarcolemma
- The skeletal muscle membrane: nAChR activation -> depolarisation – action potential (AP)
- T-tubules: continuous with sarcolemma & closely connected to sarcoplasmic reticulum
- AP travels through T-tubules
Describe the sarcoplasmic reticulum
- Location: surrounds myofibrils – contractile units of muscle
- Function: Ca2+ storage -> Ca2+ release following sarcolemma depolarisation
- Effect: Ca2+ -> myofibril contraction & muscle contraction
What is botulism (disorder of neuromuscular junction)?
•Botulinum toxin (BTx): irreversible disrupts stimulation-induced ACh release from presynaptic nerve terminal
What is Myasthenia Gravis (disorder of neuromusuclar junction)?
- Autoimmune disorder: antibodies directed against ACh receptor
- Cause fatigable weakness (i.e. becomes more pronounced with repetitive use)
What is Lambert-Eaton myastenic syndrome (LEMS) (disorder of neuromsuuclar junction)?
•Autoimmune disorder: antibodies directed against VGCC
