NOTES - UNIT 5 part 1: Nervous System Organization

 The nervous system has three overlapping functions: 1) SENSORY: gather information from sensory receptors; detect changes in the external or internal environment 2) INTEGRATION: information from sensory receptors is interpreted and associated with appropriate responses (sensation, memory, perceptions, decisions)   3) MOTOR OUTPUT: conduction of signals from the integration center to effector cells (muscle cells or gland cells)

The Nervous System is divided into:

*CENTRAL NERVOUS SYSTEM (CNS) brain and spinal cord integration center 

*PERIPHERAL NERVOUS SYSTEM (PNS) nerves communicate motor and sensory signals to and from CNS and rest of body made up of NERVES (ropelike bundles of neurons)

Nervous Tissue-Two Main Classes of Cells: 1) NEURONS (nerve cells): functional unit of the nervous system Specialized for nerve impulse (action potential) conduction Provide most of the unique functions of the nervous system: sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions  transmit signals from one location to another  made up of: DENDRITES, CELL BODY, AXON, & SYNAPTIC END BULBS OF AXON TERMINAL

DENDRITES (“little trees”): receiving/input parts of a neuron CELL BODY: nucleus surrounded by cytoplasm and typical organelles (rough ER, mitochondria, lysosomes, golgi)

AXON: conducts nerve impulses toward another neuron, muscle fiber, or gland cell Axons end by dividing into many fine processes called axon terminals Axon terminals swell into synaptic end bulbs which contain synaptic vesicles storing neurotransmitters

many axons are enclosed by an insulating layer called the MYELIN SHEATH Many-layered covering composed of lipid and protein Increases the speed of nerve impulse conduction Schwann cells in the PNS and Oligodendrocytes in the CNS produce myelin sheaths by wrapping themselves around and around axons Axons with a myelin sheath: myelinated and axons without: unmyelinated

Myelin producing cell; is this CNS or PNS? Unmyelinated neuron

Gaps in the myelin sheath: Nodes of Ranvier

3 Types of Neurons or Nerve Cells: sensory neurons: detect many different types of stimuli & carry information to the brain Interneurons: integrates/processes sensory information; axons extend for only a short distance & contact nearby neurons in the brain or spinal cord motor neurons: carry information from the brain toward the spinal cord or out of the brain and spinal cord to muscles and glands

2) NEUROGLIAL CELLS (SUPPORTING CELLS) 10 to 50 times more numerous than neurons provide structure; protect, insulate, nourish, & assist neurons Even though glia do not generate or conduct nerve impulses, they are actively involved in nervous tissue

2) NEUROGLIAL CELLS-(SUPPORTING CELLS) continued In contrast to neurons, some neuroglial cells can multiply & divide in the mature nervous system Example of neuroglial cells: SCHWANN CELLS and OLIGODENDROCYTES Example of neuroglial cell : ASTROCYTES: form connections between neurons; protect neurons from harmful substances; responsible for blood-brain barrier

Astrocyte Nerve cells

Functions of the Blood Brain Barrier: Protects the brain from "foreign substances" in the blood that may injure the brain. Protects the brain from hormones and neurotransmitters in the rest of the body. Maintains a constant environment for the brain.