The Nervous System

• The master controlling and communicating system of the body

• Method of communication? Electrical impulses

The Three Overlapping Functions

• It uses millions of sensory receptors to monitor changes called stimuli inside and outside the body.

• It processes and interprets this gathered information called sensory input and makes decisions on what should be done. This process is called integration.

• It effects a response by activating muscles or glands via motor output.

Figure 7.1 page 223

Organization of the Nervous System• Structural Classification–Central Nervous System (CNS) – brain and

spinal cord. They interpret incoming sensory information and issue commands in response–Peripheral Nervous System (PNS) – mainly

nerves that extend from the CNS and act as communication lines.• Spinal nerves carry impulse to and from the

spine• Cranial nerves carry impulse to and from the

brain

Functional Classification (PNS only)

• Sensory or afferent division – nerve fibers that carry impulses to the CNS from sensory receptors– Somatic sensory fibers come from the skin,

skeletal muscles and joints–Visceral sensory fibers or visceral afferents

come from the visceral (internal) organs

Functional Classification (PNS only)• Motor or efferent division – go from CNS to

effector organs (muscles and glands)– Somatic nervous system – the voluntary

nervous system. Allows us to consciously control skeletal muscles–Autonomic nervous system – the

involuntary nervous system. Regulates events that need to be automatic and has two complimentary parts called Sympathetic and Parasympathetic

Flow Chart from Page

224

Cells of the Nervous System

Neurons

• Also known as nerve cells• Highly specialized to transmit messages from

one part of the body to another• The neuron has several important parts.

Cell Body

• Metabolic center of the neuron. • Contains the normal organelles except

centrioles. • The neuron’s shape is the result of the rough

ER (called Nissel substance) and the intermediate filaments (called neurofibrils)

Armlike Processes or fibers

• Dendrites – many processes that carry information to the cell body

• Axon – the one process that carries information away from the body. The axon arises from the conelike region called the axon hillock. It may have an occasional collateral branch (a split of the axon), but all axons branch profusely at their ends.

The Axon Terminals (Ends)

• The end of the axon can branch hundreds or thousands of times. Each branch is known as an axon terminal

• These contain hundreds of tiny vesicles that contain neurotransmitters.

• When a signal reaches the end of the axon, the neurotransmitters are released across the synaptic cleft or synapse (a space between the axon and the next cell)

Myelin

• A whitish, fatty material that covers nerve fibers

• It helps insulate and increase the transmission rate of nerve impulses

Types of Supporting Cells

Known as neuroglia (“nerve glue”) or glia or glial cells

Astrocytes

• Abundant star-shaped cells (make up almost 50% of neutral tissue)

• Their numerous projections have swollen ends that cling to neurons. They then brace and anchor the neurons next to blood capillaries.

• They form a living barrier between the capillaries and the neurons that keeps out harmful materials from the blood.

• They also pick up extra ions and released neurotransmitters

Microglia

• Spiderlike phagocytes that dispose of debris, including bacteria and dead brain cells

Ependymal Cells

• Line the cavities of the brain and spinal cord. • Their beating of their cilia helps to circulate

the cerebrospinal fluid.• This fluid fills the cavity and cushions the CNS

Oligodendrocytes

• Cells that create a myelin sheath around axons inside the CNS

• It has several cell extensions that wrap themselves around many different neurons.

Schwann cells

• Cells that create a myelin sheath around axons outside the CNS

• They roll around the nerve cell like a Swiss Cake Roll

• Most of its cytoplasm is squished to the outmost part of the cell. This is called the neurilemma

• The spaces in between the Schwann cells are called the nodes of Ranvier

Picture Time

• From Page 225 and 227• Now on the SMART Board

Interesting fact

• Most brain tumors are the result of glial cells forming the tumor. This is because neurons have lost their ability to divide. This is also why nerve damage can be so catastrophic for a person.

Cluster Terms• Nuclei – well protected clusters of cell bodies in

the CNS• Ganglia – small collections of cell bodies found

outside the CNS• Tracts – bundles of nerve fibers running through

the CNS• Nerves – bundles of nerve fibers running in the

PNS• White matter – dense collection of myelinated

fibers• Gray matter – contains mostly unmyelinated fibers

Classification of Neurons

• Functional classification– Sensory or afferent – carry messages from sensory

receptors to the CNS. Have dendrite endings associated with specialized receptors

– Motor or efferent – carry message to muscles or glands

– Association – connect the motor and sensory neurons in neutral pathways

Classification of Neurons

• Structural– Multipolar neuron – most common type. It has

several processes branching from the neuron– Bipolar – only has two processes, axon and a

dendrite.– Unipolar – have a single process emerging from

the cell body. But this process doesn’t go too far before it splits into a peripheral (distal, dendrite) and central (proximal, axon) branch

Draw types from 231

• And physiology of the nerve assignment