Division of the Nervous System Parts of the CNS and PNS
The Nervous System The nervous system has two main functions: 1) To regulate body functions 2) To respond to stimulus
The nervous system has two major divisions: 1) The Central Nervous System (CNS) 2) The Peripheral Nervous System (PNS)
The Central Nervous System The CNS is where sensory information is received and motor control is initiated. It is made up of two parts.
The Brain protected by the skull and a membrane known as meninges. Between the meninges and the skull there is a fluid which cushions and protects known as cerebrospinal fluid (CSF). Made up of four ventricles – two lateral ventricles, the third ventricle and the fourth ventricle Ventricles are hollow interconnecting cavities which connect with the hollow central canal of the spinal cord. They serve as a reservoir for CSF (cerebral spinal fluid).
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The Spinal Cord Extends from the base of the brain through an opening in skull and into the vertebral canal. Each vertebra in the vertebral column (spinal column) protects the spinal cord. The spinal nerves project from the cord between the vertebrae. Intervertebral disks are fluid-filled disks that separate and cushion the vertebrae. Also protected by the meninges. The central canal within the cord contains CSF. Provides a means of communication between the brain and the peripheral nerves that leave the cord
The Peripheral Nervous System The PNS carries sensory messages to the CNS and motor commands from the CNS to the muscles and glands. It is made up of two parts
Nerves Bundles of axons (fibers that conduct nerve impulses away from the cell). Fibers in the nerves can either be sensory fibers (carry info to CNS) or motor fibers (carry info away from CNS). Humans have 12 pairs of cranial nerves attached to the brain which take impulses to and from the brain and 31 pairs of spinal nerves emerging from the openings in the vertebral column which take impulses to and from the spinal cord.
Ganglia Swellings associated with nerves that contain collections of cell bodies.
The PNS is divided into two parts: Somatic System Serves the skin, skeletal muscles, and tendons. Includes nerves that take sensory info from external receptors to the CNS and motor commands away from the CNS to the skeletal muscles. Some actions are due to reflexes – programmed, built in circuits that allow for protection and survival; require no conscious thought; rapid response.
Autonomic System Regulates the activity of the cardiac and smooth muscle and glands. Divided into two divisions: Sympathetic Division – brings about those responses we associate with “fight or flight” (ie. accelerates heartbeat, dilates bronchi, inhibits digestive tract). Parasympathetic Division – brings about the responses we associate with a relaxed state (ie. promotes digestion of food, retards heartbeat, contracts pupils).