Quick questions on Organisation of the nervous system: WACE Year 12 Human Biology Unit 3

The central nervous system (CNS) is the brain and the spinal cord. It is the control and integration centre: it receives sensory information, processes and interprets it, makes decisions, and sends out instructions. The hypothalamus, a small region of the brain, is the key homeostatic control centre, setting and defending the set points for temperature, water balance and other variables. The spinal cord carries information between the body and the brain and also coordinates fast reflexes without involving the brain.

The peripheral nervous system (PNS) is all the nervous tissue outside the brain and spinal cord, made up of the nerves that connect the CNS to receptors and effectors. Sensory (afferent) nerves carry impulses toward the CNS; motor (efferent) nerves carry impulses away from the CNS to effectors. The peripheral system is divided by function into the somatic and autonomic divisions.

The somatic division controls voluntary, conscious actions, mainly the contraction of skeletal muscle, such as deciding to pick up a pen. It also carries the sensory information that lets you feel touch, pain and temperature. The somatic reflexes (like the withdrawal reflex) are automatic but still act through somatic motor neurons to skeletal muscle.

The autonomic division controls involuntary, automatic functions, the ones you do not consciously think about, such as heart rate, breathing rate, digestion, and gland secretion. Because it acts on smooth muscle, cardiac muscle and glands without conscious effort, the autonomic nervous system is central to homeostasis. It has two branches that usually work in opposition.