Chapter 8

The Nervous System The system of cells, tissues, and organs that regulates the body’s response to internal and external stimuli.

The Nervous System Your nervous system is responsible for Maintaining consciousness Learning and remembering new things Coordinating what you sense or feel

Nervous System Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) All the nerves that branch out to the body Autonomic Nervous System (ANS) Involuntary Functions

Neurons Neurons are cells that make up nervous tissue. Neurons transmit nerve messages. This image is copyright Dennis Kunkel at

Neurons Axon endings (synaptic terminals) Nucleus Axon Dendrites Cell Body

Nerve impulses go only one way

Nerve Impulse Self propagating wave of electrical disturbance Sodium (Na+) ions racing inward Inside + Outside - Keeps going down the membrane of the axon The myelin sheath helps make it go faster

The Synapse Gap between adjacent neurons Synaptic knob, synaptic cleft, and the plasma membrane

Neurotransmitters Chemicals that move from the synaptic knob to the synaptic cleft. Ex: acetycholine, norepinepherine, dopamine, serotonin - play a role in sleep, motor functions, mood, and pleasure recognition

Neurons: 3 types Sensory neuron- go towards the spinal cord and brain, also referred to as afferent neurons Motor neuron- go away from the brain and spinal cord to the muscle and glands, also referred to as efferent neurons Interneuron- conduct between sensory and motor neurons (central or connecting neurons), also known as associative neurons

Glia Cells Glia- special type of supporting cells Hold functioning neurons together and protect them Vary in size and shape

Glia Cells: 3 types Astrocytes look like stars; attach to neurons and to small blood vessels. Form the blood- brain barrier. Microglia act as microbe- eating scavengers Oligodendrocyte help hold nerve fibers together and also produce the fatty myelin sheath (in CNS only)

Nerves Groups of peripheral nerve fibers bundled together like the strands of a cable.

Nerves Axons are wrapped by a fibrous connective tissue called the endoneurium. Groups of these wrapped axons are called fascicles. Each fascicle is surrounded by a thin, fibrous perineurium and a tough, fibrous sheath called the epineurium covers the whole nerve.

Nerves White matter – nerves that have a myelin sheath covering them (axons) Gray matter – tissue composed of cell bodies, dendrites, and unmyelinated axons

Reflex Arcs Pathway a message takes to cause a reflex 1. Sensory neurons directly to motor neurons Ex: “knee jerk”

Reflex Arcs 2. Sensory neurons to interneurons to motor neurons Ex: withdrawal reflex