06 The Nervous System
Learn how the nervous system detects and processes information, coordinates responses, and works with other body systems to maintain stable internal conditions.
Organization and role
The nervous system detects changes inside and outside the body, processes information, and coordinates responses. It works closely with other body systems by activating muscles, adjusting organ and gland activity, and helping maintain .
The consists of the brain and spinal cord. The includes nerves and ganglia outside the central nervous system.
Neurons and communication
Neurons receive and transmit information. A typical has a cell body, which maintains the cell; dendrites, which receive many incoming signals; and an axon, which carries signals away from the cell body. Axons may be insulated by myelin, which helps signals travel efficiently. Supporting cells called protect, nourish, and support neurons.
A can carry an electrical signal called an along its axon. At most -to- connections, or synapses, an arriving signal prompts the release of chemical messengers called neurotransmitters. These bind to receptors on a neighboring cell and can increase or decrease the likelihood that it will signal. The combined effects of incoming signals help determine a 's response.
Neurons are also classified by their roles. carry information from sensory receptors toward the CNS. connect and process signals within the CNS. carry commands from the CNS to muscles or glands.
Brain and spinal cord
The brain and spinal cord receive, integrate, and respond to information. The is involved in conscious perception, thought, memory, and voluntary movement. The helps coordinate movement and balance. The connects the brain with the spinal cord and supports essential functions such as breathing and cardiovascular regulation. The includes the thalamus and hypothalamus; the hypothalamus helps regulate internal conditions, including temperature, thirst, and hormone-related functions.
The spinal cord is both a communication route and a processing center. Ascending pathways carry sensory information toward the brain, while descending pathways carry motor commands toward the body. In the spinal cord, gray matter contains many cell bodies and synapses; surrounding white matter contains bundles of axons traveling in pathways.
Sensory and motor pathways
A sensory pathway begins when a receptor detects a stimulus, such as light, pressure, tissue damage, or a change in body position. Sensory signals travel through peripheral nerves to the spinal cord or , then along pathways to brain regions that interpret the information. Some sensory pathways also trigger rapid protective reflexes.
A motor pathway carries output from the CNS to an , which is a muscle or gland. In many movements, motor areas of the brain send commands down the spinal cord, where circuits and motor neurons help activate the appropriate muscles. Sensory feedback from muscles, joints, and skin helps adjust movement as it happens.
In the , motor neurons control skeletal muscle. This supports voluntary movement as well as reflexes.
Spinal reflexes
Some responses are organized as reflexes. In a withdrawal , receptors detect a painful stimulus and a sensory carries the signal into the spinal cord. Spinal circuits activate motor neurons, and muscles pull the body part away. The brain also receives information, but the spinal response can begin before conscious awareness of pain.
Autonomic regulation
The regulates many functions that usually occur without conscious effort, including heart activity, digestion, pupil size, and the activity of smooth muscle and glands. Its helps coordinate responses to challenge or increased demand, such as raising heart output during exertion. Its supports functions such as digestion and recovery, including slowing the heart in some situations.
The sympathetic and parasympathetic divisions do not simply switch on and off as opposites. Their effects depend on the organ and the body's needs. Autonomic output commonly travels from a CNS to a peripheral ganglion, then from a second to the target tissue.
The is a network in the digestive tract. It helps control gut movement and secretion and communicates with the CNS.
Coordination and
Nervous control interacts with the endocrine system. The hypothalamus links neural regulation with hormone control, while autonomic signals can influence glands and internal organs. Rapid neural signaling and hormone-based regulation work together to coordinate responses and help preserve stable internal conditions.