Cells Of Nervous System Flashcards
CNS consists of…..
Two cerebral hemispheres (gyri and sulci), brainstem, cerebellum + spinal chord
The PNS consists of……
Nerve fibres originating from the CNS
Describe the cerebral hemispheres
Cerebral hemisphere (aka Telencephalon) consists of:
Ridges called Gyri
Valleys called Sulci
Each hemisphere separated into 4 regions:
Frontal - executive functions
Parietal - process tactile info
Temporal - hippocampus (short term memory) amygdala (behaviour) Wernicke’s area (auditory perception + speech)
Occipital - process visual info
Brainstem consists of……
And function
Midbrain Pons Medulla Multitude of functions (control of respiration + heart rate) Target/Source of cranial nerves
Describe the Cerebellum’s location + role
Located towards dorsal region of CNS and attached to brainstem
Involved in motor coordination, balance and posture
Describe spinal chord + function
Extends down from the medulla
Acts as a conduit for neural transmission + coordinate reflex actions
Name + Describe 4 types of neurones
Unipolar w/ 1 axonal projection
Pseudo-unipolar W/ 1 axonal projection that divides into 2
Bipolar w/ 2 projections
Multipolar w/ numerous projections:
Pyramidal cells (pyramid shaped cell body)
Purkinje cells
Golgi cells
What are common features between neurons?
Soma (cell body contains nucleus, ribosomes and neurotic agents for structure and transport)
Axon (long nerve fibre usually covered in myelin sending signals)
Dendrites (highly branched cell body that receives signals from other neurons)
Astrocytes
Most abundant cell type in brain
Structural cells
Take part in cell repair/synapse formation/neuronal mutation/plasticity
Oligodendrocytes
myelin producing cells of CNS
Send out numerous projections that form internodes of myelin covering MULTIPLE axons of neurones
Schwann Cells
Myelin producing cells of PNS
Send out projections forming internodes of myelin covering a SINGLE axonal segment
Microglia
specialised cells similar to macrophages performing immune functions in CNS
Ependyma
epithelial cells that line the fluid filled ventricles regulating production and movement of cerebrospinal fluid
Explain Resting Membrane Potential
Ionic imbalance between extra and intracellular fluid of a neuron
The relative concentrations of the ions gives cell membrane an EMF/potential difference between inside and outside cell
Outside of the cell (zero reference point) has 0mV while inside of the cell is between -50mV and -90mV
So neurones have RMP of -70mV
What causes neuron cells to be “excited”?
Difference in ionic composition is exploited by neurones to manipulate MP
when cell is depolarised an AP is generated where brief spike in MP from about 10mV back to RMP
This AP is transmitted along the membrane and axon by cable transmission and cells are excited due to ability to propagate APs
4 Main Physiological Ions
Potassium K+
Sodium Na+
Chloride Cl-
Calcium Ca2+
Cell membrane is impermeable to these ions so transportation regulated by channels and pumps
(Uneven distribution w/ high Na+ and Cl- + low K+ and Ca2+ outside cell vs
high K+ + low Na+ and Cl- and EVEN LOWER Ca2+ conc inside cell)
Describe generation of Action Potential
Na+ and K+ only
High Na+ outside and high K+ inside - at RMP both voltage gates Na+/K+ channels are closed
Membrane depolarisation occurs as VGSC opens due to faster kinetics, Na+ influx, further depolarisation (from -70 to higher mV)
VGKC opens at slower rate, effluent of K+ from cell, membrane repolarisation occurs (higher mV back to -70mV)
How is Na+ and K+ imbalance restored after AP
Na+K+ATPase pump restores ion gradient
Resting configuration where Na+ enters vestibule
Active configuration where Na+ is removed from the cell using ATP (against conc gradient) so K+ enters vestibule
Pump returns back to resting configuration so K+ is transported back into the cell
What is Saltatory Conduction?
AP spreads along axon by cable transmission but myelin prevents AP spreading due to high resistance and low capacitance
Nodes of Ranvier (small intermittent gaps of myelin) so AP jumps between nodes AKA Saltatory Conduction
How are signals transmitted between neurons?
Synapses consist of pre-synaptic nerve terminal, synaptic cleft and postsynaptic cell.
Electrical signal cannot jump over synaptic cleft and so is converted into a chemical signal to cross the synapse then back into an electrical signal on post synaptic cell
Describe chemical transmission across synapses
Voltage gated Ca2+ channels at presynaptic terminal causes Ca2+ influx down conc gradient
Ca2+ bind to vesicles that contain neurotransmitter who then exocytose by binding to presynaptic membrane and release contents into synaptic cleft
Neurotransmitters then bind to receptors or post-synaptic membrane who promote activity in post synaptic cell
How are neurotransmitters removed from synaptic cleft after use?
Cholinesterase enzyme binds to acetylcholine and breaks it down allowing reuptake to pre-synaptic membrane
