1. A reflex arc is a short, fast pathway of response to stimuli, whose center of coordination occurs in the spinal cord.
2. Neurotransmitters are chemicals that communicate pre-synaptic and post-synaptic terminals, causing the latter to have an effect.
3. The central nervous system is formed by the brain, its structures and the spinal cord, while the peripheral nervous system is made up of the peripheral nerves.
Explanation:
1. Reflex arc
A reflex act is a rapid and involuntary motor response to an external stimulus, which is mediated by a process called reflex arc:
Once a stimulus has been produced, it is received by an external receptor and travels through sensitive nerve fibers to the spinal cord.
In the spinal cord occurs the processing of the information received and elaborates a response.
The response is conducted - in the form of a nerve impulse - through the motor nerve fibers, producing the reflex response, the muscle movement.
The reflex arc involves the somatic peripheral nervous system, the spinal cord and the effector is the skeletal muscle.
2. Action of neurotransmitters at a synapses
A synapse is formed by a presynaptic terminal, a synaptic space and a post-synaptic terminal.
Neurotransmitters are chemicals that act as a means of communication between neurons, or between a neuron and an effector organ.
The presynaptic terminal is responsible for releasing a neurotransmitter into the synaptic space.
The neurotransmitter, free in the synaptic space, binds to a specific receptor in the post-synaptic terminal.
The neurotransmitter-receptor binding causes biochemical changes in the effecting cell.
The chemical nature of a neurotransmitter changes, according to the type of synapse:
Interneuronal synapses require amino acids as neurotransmitters.
Between a neuron and a gland the neurotransmitter is a neuropeptide.
Between a neuron and a muscle the neurotransmitter is an ester.
The classic example of neurotransmission occurs in the motor plate (skeletal muscle) where the motor neuron possesses the presynaptic terminal, the neurotransmitter may be acetylcholine and the muscle constitutes the post-synaptic terminal.
3. Central nervous system (CNS) and peripheral nervous system (PNS)
The central nervous system constitutes the center of reception, integration and coordination of all the activity that occurs in the body. It consists of the brain, cerebellum, associated structures and the spinal cord.
CNS is a complex organization of nervous tissue that receives all the information from outside and inside the body, processes it, and elaborates appropriate responses that are transmitted through the nerves.
The peripheral nervous system is made up of all the nerves that come out of the central nervous system. These nerves are the set of neuronal axons responsible for the transmission of nerve impulses to and from the CNS.
PNS consists of:
12 cranial pairs, coming from the brain.
31 pairs of spinal nerves, coming from the spinal cord.
Additionally, SNP is divided into:
Somatic peripheral nervous system, with voluntary action on skeletal musculature.
Autonomic nervous system, divided into sympathetic and parasympathetic, whose function is the functioning of internal organs, in an involuntary way.
The coordination that exists between CNS and PNS is what allows a living organism to fulfill all its functions in an adequate way.
Learn more:
Central nervous system and peripheral nervous system link
