Intro to the Nervous System Lesson 2

The Nervous Systems  The nervous system regulates body processes and structures to help maintain homeostasis. Its highest division is the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

The Central Nervous System  The central nervous system consists of the brain and spinal cord. It integrates, processes and controls information and activity sent from the rest of the body in all bilaterally symmetrical animals. The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body, but also contains circuits that can independently control reflexes.

Peripheral Nervous System  The peripheral system is the network of nerves that carry sensory messages to the CNS, and nerves that send messages from the CNS to the muscles and glands. These are termed the sensory and motor pathways, respectively.

Autonomic vs. Somatic  The autonomic system includes sensory and motor neurons that function automatically (such as those that control internal organs), while the somatic system we control.  Somatic neurons are connected to skeletal muscle, where autonomic controls smooth or cardiac muscle and glands.

Autonomic System  The Autonomic system can be further subdivided into the sympathetic nervous system (fight or flight) or the parasympathetic nervous system (rest and digest).

Cell Types - Neurons  Neurons are the primary tissue type in the nervous system. They respond to stimuli, conduct electrochemical signals, and release chemicals called neurotransmitters.  They are surrounded by membrane, have a nucleus, contain cytoplasm, mitochondria and other organelles, and carry out basic cellular processes such as protein synthesis and ATP production.

Specialization of Neurons  Neurons are different in that they have specialized cellular extensions called dendrites and axons.  These extensions are used to receive and transmit signals throughout neural pathways through electrochemical processes. Specialized gene expression produces some specialized structures and functions in neurons.

Synapses  The axon carries an electrochemical impulse away from the cell body, which signals the release of neurotransmitters at the axon terminal. These neurotransmitters are released into a gap called the synapse, where they will bind to receptors on the dendrites of the next neuron.

Cell Types – Glial Cells  Glial cells support neurons by nourishing them, removing wastes, and defending against infection.  A specific type of glial cell called a Schwann Cell coats the axons of some neurons in a fatty, insulating layer called the myelin sheath, which drastically increases the rate of impulse transmission. In some nervous system disorders, the myelin sheath is broken down in a process called demyelination. Multiple Sclerosis is a disorder with this hallmark sign.

Nerve Pathways  Neurons are connected in pathways with multiple neural cells. They can consist of:  Sensory neurons: carry impulses from a receptor to the central nervous system  Motor neurons: carry impulses form the central nervous system to an effector (muscle or gland)  Interneurons: provide a link within the CNS between sensory and motor neurons.

Reflex Arc  The simplest nerve pathway is called a reflex arc.  It occurs without brain coordination, consisting of a sensory neuron, an interneuron in the spinal cord, and a motor neuron connected to a muscle

Review Questions  What does the central nervous system consist of?  Was a reflex arc involved in any games we played today, or something more complex? Explain.  List the two main cell types of nervous tissue and their functions.  When sitting down to write a test, what autonomic system is likely going to be more dominant?  What is the difference between a nerve and a neuron?  Why is a reflex arc important? Can you come up with a time in your life when a reflex arc helped prevent (further) injury?  Explain how the nervous system is important for homeostasis.