Notes Chapter 11: Nervous System

The Nervous System The nervous system is the master controlling and communicating system of the body The nervous system has 3 major functions: It monitors changes both inside and outside the body – sensory input It processes and interprets sensory input and decides what should be done at each moment – integration It causes a response by activating effector organs -- motor output

Organization of the Nervous System The nervous system is divided into 2 major parts: Central Nervous System (CNS) – consists of the brain and spinal cord. It is the integrating and command center of the nervous system Peripheral Nervous System (PNS) – interprets sensory input and dictates motor responses

Questions: What does the CNS do with sensory information? integration What does the PNS consist of? Nerves and ganglia outside the brain and spinal cord

Types of Nerves Spinal nerves: carry impulses to and from the spinal cord Cranial nerves: carry impulses to and from the brain

Peripheral Nervous System The peripheral nervous system has 2 subdivisions: The Sensory (Afferent) division – (means carry toward) – consists of nerve fibers that convey impulses to the CNS from sensory receptors throughout the body Motor (Efferent) division – (carry away) transmits impulses from CNS to effector organs (which are the muscles and glands). They “effect” a motor response.

The Motor Divisions Two Main Parts The Motor division has 2 main parts: Somatic nervous system – consists of somatic motor nerve fibers. It is called the voluntary nervous system because it allows us to consciously control skeletal muscle. Autonomic nervous system – consists of visceral motor nerve fibers that regulate the activities of the smooth and cardiac muscles and glands. It is involuntary.

Neuroglia Nerve cells are called neurons Neurons associate with much smaller cells called neuroglia or glia for short. These cells provide supportive scaffolding for neurons. Also… some insulate neurons so that neighboring neurons don’t interfere with each other

Glial Cells Astrocytes – most abundant and versatile. They are delicate and branching. Microglia – small ovoid cells with long “thorny” processes. They monitor the health of nearby neurons. They destroy injured neurons. Ependymal cells – range in shape from squamous to columnar. Line the central cavities of the brain and spinal cord. They help form a fluid barrier. Oligodendrocytes – they have fewer processes than astrocytes and form the myelin sheaths that protect the neurons.

Neurons There are billions of neurons in our bodies. They are the structural units of the nervous system. The function of neurons is to conduct messages in the form of nerve impulses from one part of the body to another. Besides their ability to conduct impulses … they have other special characteristics

Special Characteristics of Neurons Extreme Longevity – with good nutrition they can function for hundreds of years. Amitotic – they lose the ability to divide. There are exceptions to this like the stem cells and the cells in the hippocampus part of the brain (responsible for memory). High Metabolic Rate – require continuous and abundant supplies of oxygen and glucose. Neurons can’t survive more than a few minutes without oxygen.

Parts of Neurons Cell Body – transparent … spherical nucleus surrounded with cytoplasm. Dendrites – Short branching extensions of the neurons. They are the main reception or input region. Axon – generates nerve impulses and transmit things typically away from the body.

Basic Neuron Types Sensory (Afferent) neurons – transmit impulses from sensory receptors in the skin and internal organs toward or into the CNS. Motor (Efferent) neurons – carry impulses away from the CNS to the muscles and glands (efferent organs). Interneurons (association neurons) – lie between motor and sensory; shuttle signals through CNS pathways where integration occurs.

Neurophysiology Synapse is a junction or space between 2 neurons. The impulse of one neuron is carried across the synapse by chemicals called neurotransmitters.

How Impulses Travel Along Neurons Neurons are highly irritable (responsive to stimuli). When a neuron is stimulated an electrical impulse is generated and transferred along the axon. This response is called the action potential.

How Impulses Travel Along Neurons, continued When a neuron is stimulated it begins to actually generate a tiny electrical pulse This electricity and chemical change travels the full length of the neuron. But when it gets to the end of the axon at the end of the neuron…it needs help getting across the cleft to the dendrite of the next neuron. The electrical pulse in the cells trigger the release of neurotransmitter that carry the pulse to the next cell. This is a repeating process. The brain then processes the information and dictates the proper response.