Cells of the nervous system and neuromuscular junctions (1) Flashcards
What are the 4 areas in the CNS?
Cerebral hemispheres (highly convoluted surface of ridges- gyri and sulci)
Brainstem
Cerebellum
Spinal cord
What are the 4 functional regions of the cerebral hemisphere?
- frontal lobe
- parietal lobe
- temporal lobe
- occipital lobe
What parts make up the brainstem?
midbrain, pons and medulla
What is the cerebellum?
hindbrain structure attached to brainstem
–>motor coordination, balance and posture
What is the spinal cord?
extends down from medulla
- -> conduit for neural transmission
- -> coordinates some reflex actions
What are the 4 different shapes of neurons?
- unipolar–> 1 axonal projection
- pseudo-unipolar–> single axonal projection that divides into 2
- bipolar–> 2 projections from cell body
- multipolar–> numerous projections from cell body (e.g. pyramidal, Purkinje, Golgi)
What are the common features of neurons?
- non-dividing cells
- soma/cell body: contains nucleus and ribosomes…neurofilaments provide structure and transport
- axon: long, usually myelinated, originates from soma at axon hillock, can branch off
- dendrites: highly branched cell body, NOT myelinated, can receive signals from other neurons
What are astrocytes?
- most abundant cell type in CNS
- can proliferate
- structural function: blood-brain barrier
- maintain homeostasis: remove/reuptake neurotransmitter
- cell repair: synthesise neurotrophic factors
What is an oligodendrocyte?
- large glial cell found in CNS
- produce myelin sheath insulating neuronal axons
- analogous to Schwann cells in PNS
- 1 oligodendrocyte–> myelinated many axons (bc feet), but 1 Schwann cell–> myelinates 1 axon
What are microglial cells?
- specialised population of macrophages in CNS
- perform immune functions (remove damaged neutrons and infections)
What are ependymal cells?
- specialised epithelial cells
- line fluid-filled ventricles of brain
- regulate production and movement of CSF
What are the types of neuroglia?
- astrocytes (support cells)
- oligodendrocytes (myelin)
- microglia
- ependyma
What are the 4 major physiological ions?
K+, Na+, Cl- and Ca 2+
What is the uneven ion distribution in a neutron at resting membrane potential (RMP)?
- high extracellular sodium (and chloride)
- low extracellular potassium
- high concentration gradient for calcium (more extracellular)
Does a negative charge in a cell make it more or less excitable?
less excitable
Describe the process of generating an action potential at a molecular level.
- at RMP, VGSCs and VGKCs are closed
1. Membrane depolarisation- VGSC open–> Na+ influx–> further depolarisation
2. VGKCs open at slower rate and cause efflux of K+ from cell–> membrane repolarisation
3. Na+/K+ ATPase pump restores ion gradients:
resting configuration–>Na+ enter pump, phosphorylated by ATP–> conformational change–> active configuration - Na+ released outside cell and K+ bind–> dephosphorylated–> back to resting configuration–> K+ released into cell
What is the purpose of myelin in saltatory conduction?
myelin has high resistance and low capacitance (charge build up), so prevents AP conducting through it–> therefore AP transmitted along axon faster
What is the purpose of Nodes of Ranvier?
small gaps (no myelin) intermittently along axon
What is saltatory conduction?
AP ‘jumping’ between nodes
How does communication between nerve cells work?
autocrine- cell targets itself
paracrine- cell targets nearby cell
What is the axondendritic synapse?
connection between presynaptic terminal and neuronal dendrite
What is the axosomatic synapse?
connection between presynaptic terminal and neuronal soma
What is the axoaxonic synapse?
connection between presynaptic terminal and neuronal axon
What is the neuromuscular junction?
- specialised structure w/axon terminal and muscle membrane
- unidirectional chemical communication between peripheral nerve and muscle
- paracrine NT release
- nicotinic ACh receptors on skeletal muscle–> change in end-plate potential
What is the sarcolemma?
- the skeletal muscle membrane: nAChR activation–> depolarisation–> generates AP
What are T-tubules?
continuous w/sarcolemma and closely connected to sarcoplasmic reticulum
* AP travels through T-tubules
What is the sarcoplasmic reticulum?
- surrounds myofibrils- contractile units of muscle
- stores Ca2+ –> released following sarcolemma depolarisation
- Ca2+ –> myofibril contraction + muscle contraction
