The nervous system has two main parts. The central nervous system (CNS) is the brain and spinal cord. The peripheral nervous system (PNS) is all the neurones outside the CNS: the cranial nerves from the brain, the spinal nerves from the spinal cord, and the sense receptors. It connects the CNS to every part of the body.The PNS contains two kinds of neurone, depending on the direction the impulses travel:• sensory (afferent) neurones carry impulses from receptors to the CNS
• motor (efferent) neurones carry impulses from the CNS to effectors (muscles and glands)A nerve is a bundle of many neurones wrapped in connective tissue. Most spinal nerves are mixed nerves, containing both sensory and motor neurones.The motor side of the PNS is divided according to the effectors it controls:• the somatic (voluntary) nervous system controls skeletal muscles, which are usually under conscious control
• the autonomic nervous system controls smooth muscle, cardiac muscle and glands without conscious control. It is itself split into the sympathetic and parasympathetic nervous systems.So the full classification is: nervous system → CNS + PNS; PNS → sensory + motor; motor → somatic + autonomic; autonomic → sympathetic + parasympathetic.Information usually flows around a loop: receptors detect a change, sensory neurones carry impulses to the CNS, the CNS processes the information, and motor neurones of the somatic or autonomic system carry impulses to the effectors that respond.
• motor (efferent) neurones carry impulses from the CNS to effectors (muscles and glands)A nerve is a bundle of many neurones wrapped in connective tissue. Most spinal nerves are mixed nerves, containing both sensory and motor neurones.The motor side of the PNS is divided according to the effectors it controls:• the somatic (voluntary) nervous system controls skeletal muscles, which are usually under conscious control
• the autonomic nervous system controls smooth muscle, cardiac muscle and glands without conscious control. It is itself split into the sympathetic and parasympathetic nervous systems.So the full classification is: nervous system → CNS + PNS; PNS → sensory + motor; motor → somatic + autonomic; autonomic → sympathetic + parasympathetic.Information usually flows around a loop: receptors detect a change, sensory neurones carry impulses to the CNS, the CNS processes the information, and motor neurones of the somatic or autonomic system carry impulses to the effectors that respond.