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Biology WK 4 Notes
Nervous System
-Central nervous system (CNS)and Peripheral nervous system (PNS)
PNS gathers info and relays it to CNS which is then processed and sends out action to part
of body
CNS
- Brain and spinal cord - Control Unit performing: Integration and Analysis of information and then Signal/command generation as response.
PNS
- Cranial and Spinal cord
Relays info from internal environment (for example from viscera such as
heart/intestine; afferent nerves) and from external environment (sensory such as touch, smell, taste; afferent nerves)
Cells In Nervous system - Neuron
Neuroglia: specialized cells found only in close association with
neurons, don't participate directly in information transfer.
There are four types of glia in CNS:
1. Oligodendrocytes (making myelin on many axons 1oligodendrocyte can
do myelin on up to 60 axons at the same time)
2. Astrocytes: most abundant type of glia in CNS. Their roles are;
Structural support
Provides nutrients/Homeostasis for neurons
Maintains/regulates synaptic connections
Reacts to injuries = astrogliosis
3. Microglia = resident macrophages in the brain “the brains immune
cells”. They increase in phagocytosis after injury results from migration of
cells to the injured area.
- Ependymal cells are provinding lining in the ventricles and are involved in production of Cerebro-spinal Fluid (CSF)
There TWO main types of cells in the PNS:
Schwann cells (similar function than oligodendrocyte), but divide more, myelinate faster and are more resistant to injury Satellite cells (similar function than astrocytes, meaning support neurons and enhance their function)
Neuronical Communication
The resting membrane potential (RMP) is the voltage measuring in the neuronal cell and depends on: Permeability (anions such as protein can’t go through) Electrochemical gradients (= charge and concentration of ions for example) Presence of Na+/K+ on the neuronal membrane When there is change in the resting membrane potential (RMP) that reaches a certain threshold (-55 mV), an action potential will be induced. Action potentials (APs) are electrical signals that propagate along AXONS, through rapid, transient depolarisation of the cell membrane. Depolarisation The voltage gated Sidium (NA+) channels open, sodium flows into the cell, bringing positive electrical charge and so increasing membrane potential. This phase is called DEPOLARISATION. Repolarisation
- Chemical: (unidirectional) most common ones in mammals. Examples of chemical synapse locations include; Connection between Neuron- Neurons Neuromuscular junction: synapse between neuron and muscle Neuroglandular junction: synapse between neuron and gland In the chemical synapse: there are essential components: Pre-synaptic neuron with neurotransmitter housed in the pre-synaptic neuron in vesicles Post-synaptic neuron with neurotransmitter binding sites Cleft or gap with enzymes to degrade left over of neurotransmitters (such as Acetylcholinesterase degrading Acetylcholine) Neurotransmitters Neurotransmitters are chemical messengers. They are released at presynaptic membrane(through EXOCYTOSIS) and bind to specific receptors at the postsynaptic neuronal membrane. To inactivate these neurotransmitters in the synaptic cleft, there are 3 mechanims: May be broken down by specific enzymes in synaptic cleft e.g., Acetyline cholinesterase for Ach May be reuptake at pre-synaptic button by specific transporter e.g., serotonin will be taken back inside the presynaptic button by the transporter of serotonin which is the site of action of some of anti-depressant drugs Diffuse away There are two main neurotransmitters in the brain:
- Glutamate: Major excitatory neurotransmitter in CNS, role in learning and memory. Act on both metabotropic and ionotropic (let enter Na+ and Ca++ in the cell) receptors
- GABA (Gamma-aminobutyric acid): Major inhibitory neurotransmitter in CNS. Act on GABAergic receptors which are a ligand gated channel receptors. GABA, ethanol, benzodiazepine (anxiolitic) and barbiturate are ligands of these receptors which lead to entry of chloride (Cl-) ions, which have depressant effects Other types of neurotransmitters are:
- Catecholamines such as Noradrenaline (important for concentration, energy, anxiety...), serotonin (important for memory, mood, obsessions and compulsions, appetite...) and dopamine (essential for reward, pleasure, motor control).
- Acetylcholine: important for motor activity, memory
- Peptides such as endorphins which are natural “feel-good” brain chemical. They act as natural pain and stress relievers When there is a dysregulation of these neurotransmitters and/or impairment to act on their specific receptors, this can lead to some pathologies such as: Parkinson's disease: if not enough dopamine is produced in the brain
Depression: if serotonin can act on its specific receptors and/or is not released in synapse Epilepsy: if lack of inhibitory neurotransmitters like GABA or due to the presence of excessive excitatory neurotransmitters like glutamate Brain anatomy
