12. The Nervous System Flashcards
How can neuron communication be achieved? where is this communication taking place.
Neurons communication is taking place at the synapses and it’s being achieved when a neurotransmitter chemical crosses the synapse to transmit the signal from one neuron to the next cell. When the action potential reaches an axon terminal, the electrical change opens calcium channels.
Calcium in turn causes the tiny vesicles containing the neurotransmitter chemical to fuse with the axonal membrane and pore-like openings from, releasing the transmitter.
The neurotransmitter molecules diffuse across the synapse and bind to receptors on the membrane of the next neuron.
If enough neurotransmitter is released, the whole series of events described previously will occur, leading to generation of a graded potential and eventually a nerve impulse in the neuron beyond the synapse.
The electrical changes prompted by neurotransmitter binding are very brief because the neurotransmitter is quickly removed from the synapse, either by diffusion by reuptake into the axon terminal or by enzymatic breakdown.
This limits the effect of its nerve impulse to a period shorter that the blink of an eye.
Remember that the transmission of an impulse is an electrochemical event. transmission down the length of the neuron’s membrane is basically electrical but the next neuron is stimulated by a neurotransmitter which is a chemical.
Because each neuron both receives signals from and sends signals to scores of other neurons it carries on “conversations” with many different neurons at the same time.
Describe the organisation of the nervous system
To better understand the organization of the nervous system we will classify its structure (structural classification) and its activities (functional classification).
The structural classification includes all nervous system organs. it has two subdivisions: the central nervous system and the peripheral nervous system.
The central nervous system (cns) consists of the brain and the spinal cord, which occupy the dorsal body cavity and act as a integrating and command centers of the nervous system.
They interpret incoming sensory information and issue instructions based on past experience and current conditions.
The peripheral nervous system (pns) is the part of the nervous system outside the CNS. it consists mainly of the nerves that extend from the brain and the spinal cord.
Spinal nerves carry impulses to and from the spinal cord. cranial nerves carry impulses to and from the brain. both of these nerves serve as communication lines.
They link all parts of the body by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands or muscles.
The functional classification concerns only PNS structures which are subdivided into: sensory Division and motor division.
The sensory division also called, afferent division, consist of nerves that convey impulses from sensory receptors, located in various parts of the body, to the central nervous system.
Sensory fibers delivering impulses from the skin, skeletal muscles and joints are called somatic sensory fibers.
Those transmitting impulses from the visceral organs are called visceral sensory fibers or visceral afferents. the CNS is constantly informed by the sensory division about events inside and outside the body.
The motor division also called efferent division, carries impulses from the CNS to effector organs muscles and glands. These impulses activate muscles and glands so that they effect a motor response.
The motor division has two subdivision: the somatic nervous system and the autonomic nervous system.
The somatic nervous system allows us to consciously or voluntarily control our skeletal muscles. We usually refer to this subdivision as the voluntary nervous system.
The autonomic nervous system (ANS) regulates events that are automatic or involuntary such as the activity of smooth and cardiac muscles and glands.
It can be divided into two parts: the sympathetic brands and the parasympathetic branch they typically bring about opposite effects. what one stimulates the other inhibits.
