Chapter 35 Human Body Systems The eleven organ

Chapter 35 Human Body Systems The eleven organ systems of the human body work together to maintain homeostasis • Homeostasis is the internal balance of the body • Within the body are levels of organization and each level works with the others to keep this internal balance • These levels are: cells, tissues, organ systems, and individual organism

Levels of Organization in body

• Cells come together to form tissues - tissues are groups of cells that perform a particular function

• An organ is a group of tissues that work together to perform a complex function

• An organ system is a group of organs that perform work together to maintain a stable internal environment

Maintaining Homeostasis Feedback inhibition - the process by which the product of a system shuts down the system or limits operation - a home heating system uses feedback inhibition of maintain a stable, comfortable environment within the house (non-living example)

In the body: there must be a balance between heat production and heat loss The body regulates temperature by a mechanism that is similar to a household heating system and this takes place in a part of the brain called the hypothalamus (the body’s thermostat)

35 -2 The Nervous System FUNCTION: The Nervous System controls and coordinates functions throughout the body and responds to internal and external stimuli • messages carried by the nervous system are called impulses • specialized cells called neurons carry these messages to organs that will respond • neurons are the basic units of the nervous system

• when an impulse reaches the end of the axon of one neuron, neurotransmitters (chemicals) are released which bind to the receptor on the cell membrane of the responding cell or tissue

1. The Central Nervous System (CNS) consists of the Brain and the Spinal Cord The 3 major divisions of the brain are: a. cerebrum: conscious acts, pain, and other sensations, thinking, and memory are controlled by this part b. cerebellum: muscular coordination and balance are controlled by this part c. brain stem: many involuntary acts which help keep us alive are controlled by this part. This includes breathing, heartbeat, peristalsis, and blood pressure. The brain stem consists of the midbrain, pons, and medulla d. Some other areas of the brain are the hypothalamus and the thalamus

Parts of the Brain

2. Peripheral Nervous System (PNS): includes the neurons which are outside the brain and spinal cord. The neurons connected to the brain are called cranial nerves (stimulate the head and neck regions) and the neurons which connect to the spinal cord are called spinal nerves. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves. In terms of function, the PNS is divided into two systems; the somatic and autonomic nervous systems. The Somatic Nervous System includes both sensory and motor neurons which connect the central nervous system to skeletal muscles. It is this system that controls voluntary (under conscious control) movement

The Autonomic Nervous System includes the sympathetic and parasympathetic systems. These motor neurons regulate any of the involuntary (automatic) activities in the body (rate of heartbeat, breathing, diameter of arteries, peristalsis, gland secretions, etc. ). The sympathetic and parasympathetic systems are opposite each other in function. If the sympathetic speeds up the heartbeat, the parasympathetic slows it down to normal rate.

a. The Sympathetic Nervous System does about the same as the hormone adrenaline. It gets the body ready for action (emergencies) by increasing heart rate, increasing blood flow to muscles, increasing blood pressure, and increasing respiratory rate. b. The Parasympathetic Nervous System does the opposite. It brings the body back to normal by decreasing heart rate, decreasing blood pressure, decreasing respiratory rate, and decreasing blood flow to muscles and increasing blood flow to digestive organs