chapter 2 - NS

• Central Nervous System (CNS) functions to receive sensory information from PNS, and then send out motor information back to PNS. Its two divisions are the brain and the spinal cord
• Peripheral Nervous System (PNS) sends sensory info from muscles, organs, and glands + sensory organs about the internal and external environment to the brain (CNS). PNS is comprised of everything outside the brain and spinal cord, and its two divisions are the Somatic NS + Autonomic NS
• the brain is a neural pathway of circuit(s) of interconnected neurons where info travels along (communication network)
• the spinal cord both receives sensory info and relays it to the brain, and receives motor info and sends it to the relevant body parts (via PNS)
• afferent or sensory neurons carry information from the body to the brain, whereas efferent or motor neurons carry information from the brain to the body
• Somatic NS is in charge of voluntary control, and initiates muscle movement. It carries motor info for voluntary movements from CNS (eg. text, talk, move, chew, dance) & carries sensory info to CNS (eg. pressure on skin)
• Autonomic NS controls many organs, glands and processes that are self-regulating (occur without conscious effort). It regulates the activity of visceral MGO's, and functions continuously to maintain survival
• Sympathetic NS is the 'fight or flight' response, where it prepares body for vigorous activity or to deal with stress or threats. Whereas, Parasympathetic NS is the 'rest and digest' response, which is dominant most of the time to maintain homeostasis
• Enteric NS is the nervous system embedded in walls of gastrointestinal tract, and is responsible for the control of gastrointestinal motility. It is referred to as ‘second brain’ because of degree of autonomy + reliance on neurons + neurotransmitters
• spinal reflex is an unconscious, autonomic response controlled by neural circuits in the spinal cord, to enable a faster reaction time before sensory info reaches brain. It is an adaptive response to save time in dangerous situations
• a conscious response is a response that involves awareness, and tends to require conscious input from the brain (like a decision). They are typically more complex, and can involve a series of voluntary responses such as movement performed by the somatic NS
• an unconscious response is a response that does not involve awareness, and can occur without conscious input from the brain. They are typically simpler tasks that involve a single response to a stimulus, and can include involuntary functions regulated by the autonomic NS
• a neurotransmitter is a chemical messenger that is released from a neuron and communicates across synapses.
• Neurotransmitters that don't bind to receptors in the postsynaptic neuron, are absorbed back into the terminal buttons by the presynaptic neuron. This is called reuptake.
• A neurotransmitter will have either an inhibitory effect (block or prevent postsynaptic neurons from firing) or an excitatory effect (stimulate or activate postsynaptic neurons to perform their functions)
• Neurohormones are neurotransmitters that also exist as hormones, such as noradrenaline. It is secreted as a hormone by the adrenal glands into the blood, and as a neurotransmitter from neurons.
• Glutamate is the primary excitatory neurotransmitter in the CNS. It has crucial roles in the synaptic changes that occur during learning and memory (helps aid synaptic plasticity)
• GABA is the primary inhibitory neurotransmitter in the brain and spinal cord. It acts to control the firing of neurons, as when this becomes unregulated, then the brain can become overactive (anxiety, phobias, etc)
• Neuromodulators are neurotransmitters that can influence the activity of other types of neurotransmitters. The two most common neuromodulators are Serotonin and Dopamine.
• An entire brain area may be influenced by exposure to a neuromodulator’s action, as neuromodulators are not limited to a single synapse. However, they exert their influence at a slower rate, while the effects last over a longer period of time than inhibitory or excitatory effects.
• Dopamine is a neuromodulator that has multiple functions, such as voluntary movement, the experience of pleasure, motivation, appetite, reward-based learning and memory (gambling). It has also been implicated in various mental conditions, including Parkinson’s disease. While dopamine is primarily an excitatory neurotransmitter, it can also have inhibitory effects (depending on where it is released).
• Serotonin is a neuromodulator that plays a role in mood regulation, sleep, appetite, sexual behaviour, aggression, cognition and pain perception. Low levels of serotonin have been linked with depression, anxiety disorders and eating disorders. Serotonin is the least abundant in the brain.
• Synaptic plasticity refers to the ability of the synapse to change in response to experience. This controls how effectively two neurons communicate with each other, through processes called Sprouting, Rerouting and Pruning.
• Synaptic sprouting is the creation of new extensions on a neuron to allow it to make new connections with other neurons. This is where dendrites may get bushier and axon terminals increase, to increase the speed/strength of the connection.
• Synaptic rerouting occurs when new connections are made between neurons to create alternate neural pathways. These alternate ‘routes’ may be entirely new neural pathways or connections to other pathways in the brain. The rerouting may involve the existing synaptic connections and/or new connections from the sprouts.
• Synaptic pruning is the elimination of weak, ineffective or unused synapses. Experience determines which synapses will be retained and strengthened and which will be pruned. The synapses that are frequently used are retained and those that are not decay and disappear.
• Changes to synaptic strength include Long-term potentiation (LTP) or Long-term depression (LTD).
• LTP is the long-lasting enhancement of synaptic transmission due to repeated strong stimulation. There is improvement in the ability of the presynaptic and postsynaptic neurons to communicate at the synapse, and the more the connection is strengthened, the efficiency in transferring information along the pathway is increased (decreasing the likelihood of forgetting it).
• LTD is the long-lasting decrease in the strength of synaptic transmission and neuronal response. This results from a lack of stimulation of pre- and postsynaptic neurons or prolonged low level stimulation. Generally, a postsynaptic neuron becomes less responsive to the neurotransmitter released by a presynaptic neuron and the effect is to weaken the synaptic connection, therefore weakening communication at the synapse.
• LTP and LTD both are activity dependent (more or less activity), involve glutamate, occur at glutamate synapses, involve changes in excitability, and both have long-lasting effects.