Homeostasis maintaining a constant internal environment despite changes in external environment

Regulatory Systems: 1. Nervous System  brain, spinal cord, nerve bundles 2. Endocrine System  endocrine organs, hormones, target organs

Feedback Systems Negative Feedback System:  change detected, system(s) work to recover homeostasis  common in body  ex. thermostat in house

Positive Feedback System  Very rare in living organisms  change detected, system(s) further amplify or speed up change  ex. oxytocin during birth

1. Structure & Function of the Nervous System 2 Major Parts to NS 1. CNS (central nervous system):  brain & spinal cord 2. PNS (peripheral nervous system)  nerves to and from CNS

PNS made of 2 parts: 1. Sensory Division (Afferent)  impulses from receptors to CNS  Informs CNS of the state of the body (interior and exterior)  Sensory nerve fibers can be somatic (from skin, skeletal muscles or joints) or visceral (from organs w/in body)

2.Motor Division (Efferent)  Conducts impulses from CNS to effectors (muscles/glands)  motor nerve fibres

Division of Motor NS  Motor NS further divided into 2 parts: 1. Somatic NS  Under voluntary control – responses can be consciously controlled  motor nerves that carry commands from CNS to skeletal muscles, external sensory organs like skin  Reflex reactions are an exception – we’ll see these soon.

2. Autonomic NS  Controls involuntary muscles (cardiac and smooth).

 The autonomic NS is made from 2 antagonistic systems always trying to balance each other  sympathetic NS controls things like dilating pupils, increasing heart rate, relaxing bladder. fight/flight (controls organs under high stress situations) parasympathetic NS Constricts pupils, relaxes heart rate, contracting the bladder rest/digest (controls organs at rest)