Overview of the Nervous System Chapter 6: The Nervous System Lesson 6.1 Overview of the Nervous System

Organization of the Nervous System Our nervous system has the ability to simultaneously direct multiple functions taking place in in our bodies. Two major divisions: Central nervous system (CNS). It directs the activity of the entire nervous system. Brain Spinal cord

Peripheral nervous system (PNS). Sensory receptors: respond to stimuli such as pain Afferent (sensory) nerves: transmit impulses from the sensory receptors in the skin, muscles & joints. Efferent (motor) nerves: carry impulses from the CNS to the muscles and glands

Human Brain

Sheep Brain

Spinal Cord w/Brain

Two Major Divisions

The Efferent Nerves There are two functional subdivisions of the efferent, or motor, nerves: Somatic nervous system (voluntary) Stimulates our skeletal muscles, causing them to develop tension. Autonomic nervous system (involuntary) Controls the cardiac muscle of the heart and the smooth muscles of the internal organs. Sympathetic Parasympathetic

Nervous Tissues Two categories of tissues exist within the nervous system: Neuroglia (glial cells) These are specialized cells that perform support functions within the CNS. Astrocytes Link the nutrient-supplying capillaries to neurons and control the chemical environment to protect the neurons from any harmful substances in the blood.

Nervous Tissues Microglia Absorb and dispose of dead cells and bacteria Ependymal cells Form a protective covering around the spinal cord and central cavities within the brain. Oligodendrocytes Wrap around nerve fibers and produce a fatty insulating material called myelin.

Neuroglia Peripheral nervous system Schwann cells Form the fatty myelin sheaths around nerve fibers in the PNS. Satellite cells Serve as cushioning support cells.

Neurons Transmit nerve impulses throughout the body Dendrites Send information (stimuli) to cell body. Cell bodies Includes a nucleus and mitochondria, like all cell bodies. Axons Send information (impulses) away from cell body.

Neurons Within the PNS, the Schwann cells wrap around the axon, covering most of it with a fatty myelin sheath. The myelin sheaths insulate the axon fibers, which increases the rate of impulse transmission. The myelin sheaths are white, giving rise to the term white matter to describe tracts of myelinated fibers within the CNS. Gray matter is the term for unmyelinated nerve fibers.

Axon terminals are filled with tiny sacs (vesicles) that contain chemical messengers called neurotransmitters. Axon terminals are separated from other neurons or muscle by a microscopic gap called the synaptic cleft https://www.youtube.com/watch?v=DLN1UsvmVvM

Neuron Types by Function Sensory (afferent) neurons Send impulses from the skin and other organs toward CNS Motor (efferent) neurons Send impulses away from CNS, to the muscles and glands directing body actions. Interneurons (association neurons) Form bridges between neurons

Neuron Structures Bipolar Unipolar Multipolar one axon and one dendrite Unipolar one axon Multipolar one axon and many dendrites

Sympathetic Nervous system Review and Assessment Match these words with 1–4 below: sympathetic nervous system, myelin, synapse, axon. 1. High alert 2. Transmits impulses away from cell body 3. Fatty insulating material 4. Gap between neurons Sympathetic Nervous system Axon Myelin Synapse