73. General design of the nervous system. Major levels of central nervous system
function.
General design of the nervous system.
The nervous system includes both sensory (input) and motor (output) systems
interconnected by complex integrative mechanisms. The fundamental unit of operation
is the neuron, which typically consists of a cell body (soma), several dendrites, and a
single axon.
Much of the activity in the nervous system arises from mechanisms that stimulate
sensory receptors located at the distal termination of a sensory neuron. Signals travel
over peripheral nerves to reach the spinal cord and are then transmitted throughout the
brain. Incoming sensory messages are processed and integrated with information
stored in various pools of neurons such that the resulting signals can be used to
generate an appropriate motor response.
The motor division of the nervous system is responsible for controlling a variety of bodily
activities such as contraction of striated and smooth muscles and secretion by exocrine
and endocrine glands. Only a relatively small proportion of the sensory input received
by the brain is used to generate an immediate motor response. Much of it is discarded
as irrelevant to the function at hand. Sensory input can be stored in the form of memory.
Major levels of central nervous system function.
The human nervous system has inherited special functional capabilities from each stage
of human evolutionary development. Three major levels of the central nervous system
have specific functional characteristics:
● the spinal cord level
○ Even after the spinal cord has been cut in the high neck region, many
highly organized spinal cord functions still occur. For instance, neuronal
circuits in the cord can cause walking movements, reflexes that withdraw
portions of the body from painful objects, reflexes that stiffen the legs to
support the body against gravity, and reflexes that control local blood
vessels, gastrointestinal movements, or urinary excretion.
○ The upper levels of the nervous system often operate not by sending
signals directly to the periphery of the body but by sending signals to the
control centers of the cord, simply “commanding” the cord centers to
perform their functions.
● the lower brain or subcortical level
function.
General design of the nervous system.
The nervous system includes both sensory (input) and motor (output) systems
interconnected by complex integrative mechanisms. The fundamental unit of operation
is the neuron, which typically consists of a cell body (soma), several dendrites, and a
single axon.
Much of the activity in the nervous system arises from mechanisms that stimulate
sensory receptors located at the distal termination of a sensory neuron. Signals travel
over peripheral nerves to reach the spinal cord and are then transmitted throughout the
brain. Incoming sensory messages are processed and integrated with information
stored in various pools of neurons such that the resulting signals can be used to
generate an appropriate motor response.
The motor division of the nervous system is responsible for controlling a variety of bodily
activities such as contraction of striated and smooth muscles and secretion by exocrine
and endocrine glands. Only a relatively small proportion of the sensory input received
by the brain is used to generate an immediate motor response. Much of it is discarded
as irrelevant to the function at hand. Sensory input can be stored in the form of memory.
Major levels of central nervous system function.
The human nervous system has inherited special functional capabilities from each stage
of human evolutionary development. Three major levels of the central nervous system
have specific functional characteristics:
● the spinal cord level
○ Even after the spinal cord has been cut in the high neck region, many
highly organized spinal cord functions still occur. For instance, neuronal
circuits in the cord can cause walking movements, reflexes that withdraw
portions of the body from painful objects, reflexes that stiffen the legs to
support the body against gravity, and reflexes that control local blood
vessels, gastrointestinal movements, or urinary excretion.
○ The upper levels of the nervous system often operate not by sending
signals directly to the periphery of the body but by sending signals to the
control centers of the cord, simply “commanding” the cord centers to
perform their functions.
● the lower brain or subcortical level
