NERVOUS SYSTEM PART 1

nervous system

is the master control and communication system of the body.

endocrine system

is a second important regulating system. produces hormones that are released into the blood.

stimuli

millions of sensory receptors to monitor changes occurring both inside and outside the body. These changes are called:

sensory input

the one that gathers information is:

integration

It processes and interprets the sensory input and decides what should be done at each moment—a process called:

motor output

It then causes a response, or effect, by activating muscles or glands

the central nervous system and the peripheral nervous system

the structural classification which includes all nervous system organs, has two subdivisions;

central nervous system

consists of the brain and spinal cord, which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system. They interpret incoming sensory information and issue instructions based on past experience and current conditions.

peripheral nervous system

includes all parts of the nervous system outside the CNS. It consists mainly of the nerves that extend from the spinal cord and brain.

spinal nerves

carry impulses to and from the spinal cord.

cranial nerves

carry impulses to and from the brain.

spinal nerves and cranial nerves

These nerves serve as communication lines. They link all parts of the body by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands or muscles.

sensory division or afferent division

consists of nerves (composed of many individual nerve fibers) that convey impulses to the central nervous system from sensory receptors located in various parts of the body.

somatic sensory fibers

Sensory fibers delivering impulses from the skin, skeletal muscles, and joints are;

visceral sensory fibers

whereas those transmitting impulses from the visceral organs are called

motor division or efferent division

carries impulses from the CNS to effector organs, the muscles and glands. These impulses activate muscles and glands; that is, they effect (bring about or cause)

somatic nervous system and autonomic nervous system

The motor division in turn has two subdivisions;

somatic nervous system

allows us to consciously (voluntarily), control our skeletal muscles. this subdivision as the voluntary nervous system.

stretch reflex

However, not all skeletal muscle activity controlled by this motor division is voluntary. Skeletal muscle reflexes, such as the— is involuntary

autonomic nervous system

regulates events that are involuntary (no conscious control), such as the activity of smooth muscle, cardiac muscle, and glands. This subdivision, commonly called the involuntary nervous system

parasympathetic and sympathetic

autonomic nervous system has 2 parts;

supporting cells (neuroglia) and neurons

Even though it is complex, nervous tissue is made up of just two principal types of cells;

neuroglia (also called as glial cells or glia)

Supporting cells in the CNS are “lumped together” as— literally “nerve glue”

support, insulate, and protect the delicate neurons

Neuroglia include many types of cells that;

astrocytes, microglia, ependymal cells, and oligodendrocytes

each of the different types of neuroglia has special functions. CNS neuroglia include the following: (4)

astrocytes

abundant star-shaped cells that account for nearly half of neural tissue. forms a living barrier between capillaries and neurons, help determine capillary permeability, they help protect the neurons from harmful substances that might be in the blood.

microglia

spiderlike phagocytes that monitor the health of nearby neurons and dispose of debris, such as dead brain cells and bacteria. and are the phagocytes in the nervous system.

ependymal cells

neuroglia that line the central cavities of the brain and the spinal cord. They participate in the production of cerebrospinal fluid (CSF) and the beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS.

oligodendrocytes

neuroglia that wrap their flat extensions (processes) tightly around CNS nerve fibers, producing fatty insulating coverings called myelin sheaths

neuroglia

never lose their ability to divide

neurons

loses their ability to divide

gliomas, or tumors

Consequently, most brain tumors are—- formed by neuroglia

schwann cells and satellite cells

Supporting cells in the PNS come in two major varieties;

schwann cells

form the myelin sheaths around nerve fibers in the PNS.

satellite cells

act as protective, cushioning cells for peripheral neuron cell bodies.

neurons

also called nerve cells, are highly specialized to transmit messages (nerve impulses) from one part of the body to another.

cell body and processes

major regions of all neurons;

cell body

is the metabolic center of the neuron. Its transparent nucleus contains a large nucleolus. The cytoplasm surrounding the nucleus contains the usual organelles, except that it lacks centrioles (which confirms the amitotic nature of most neurons).

nissl bodies and neurofibrils

The rough ER, called——(intermediate filaments that are important in maintaining cell shape) are particularly abundant in the cell body. (2)

processes, or fibers

vary in length from microscopic to over 3 feet long, reaching from the lumbar region of the spine to the great toe. fibers that extend from the cell body.

dendrites

Neuron processes that convey incoming messages (electrical signals) toward the cell body are

axons

whereas those that generate nerve impulses and typically conduct them away from the cell body are

axon hillock

each neuron has only one axon, which arises from a conelike region of the cell body called the

neurotransmitters

axon terminals contain hundreds of tiny vesicles, or membranous sacs, that contain chemicals called

synaptic cleft

Each axon terminal is separated from the next neuron or its target by a tiny gap called the

synapse

Such a functional junction, where an impulse is transmitted from one neuron to another, is called a

myelin

Most long nerve fibers are covered with a whitish, fatty material called—which has a waxy appearance. it protects and insulates the fibers and increases the speed of nerve impulse transmission

myelin sheaths

fatty insulating coverings called—-it is the tight coil of plasma membrane material surrounding the axon.

schwann cells

Axons outside the CNS are myelinated by

neurilemma

Schwann cell cytoplasm ends up just beneath the outermost part of its plasma membrane. This part of the Schwann cell, external to the myelin sheath, is called the (“neuron husk”);

rodes of ranvier

Because the myelin sheath is formed by many individual Schwann cells, it has gaps, or indentations, called—- at regular intervals

neurilemma

when a peripheral nerve fiber is damaged, it plays an important role in fiber regeneration, an ability that is largely lacking in the central nervous system;

oligodendrocytes

what forms the CNS myelin sheaths;

schwann cells

In the PNS, it takes many—-to make a single myelin sheath

oligodendrocytes

but in the CNS, the—-with their many flat extensions can coil around as many as 60 different fibers at the same time. thus, can make many myelin sheaths;

multiple sclerosis

gradually destroys the myelin sheaths around CNS fibers by converting them to hardened sheaths, it is an autoimmune disease in which the person’s own immune system attacks a protein component of the sheath.

sclerosis

what are hardened sheaths called;

nuclei

For the most part, cell bodies are found in the CNS in clusters called

well-protected location within the bony skull or vertebral column

is essential to the well-being of the nervous system;

cell body

it carries out most of the metabolic functions of a neuron, so if it is damaged, the cell dies and is not replaced

ganglia

Small collections of cell bodies called—- are found in a few sites outside the CNS in the PNS.

tracts

Bundles of nerve fibers (neuron processes) running through the CNS are called;

nerves

whereas bundles of nerve fibers running through the PNS they are called;

white matter

consists of dense collections of myelinated fibers (tracts)

gray matter

contains mostly unmyelinated fibers and cell bodies

sensory neurons, or afferent neurons

Neurons carrying impulses from sensory receptors (in the internal organs or the skin) to the CNS are

afferent

“to go toward”

a ganglion outside the CNS

The cell bodies of sensory neurons are always found in

sensory neurons

neurons that keep us informed about what is happening both inside and outside the body.

dendrite endings of the sensory neurons

are usually associated with specialized receptors that are activated by specific changes occurring nearby.

cutaneous sense organs

The simpler types of sensory receptors in the skin are

proprioceptors

those in the muscles and tendons are—- it detect the amount of stretch, or tension, in skeletal muscles, their tendons, and joints. They send this information to the brain so that the proper adjustments can be made to maintain balance and normal posture.

pain receptors

are the least specialized of the cutaneous receptors.

free nerve endings

pain and temperature receptors

Meissner’s corpuscle

touch receptor

Lamellar corpuscle

deep pressure receptor

proprioceptor

Golgi tendon organ

proprioceptor

muscle spindle

propia

comes from the Latin word meaning “one’s own,”

motor neuron, or efferent neurons

Neurons carrying impulses from the CNS to the viscera and/or muscles and glands are;

central nervous system

The cell bodies of motor neurons are usually located in the

interneurons, or association neurons

The third category of neurons consists of the—-They connect the motor and sensory neurons in neural pathways. Their cell bodies are typically located in the CNS.

the number of processes, including both dendrites and axons, extending from the cell body

The structural classification of neurons is based on;

multipolar neuron

If there are several, the neuron is a—-this is the most common structural type

bipolar neurons

Neurons with two processes—one axon and one dendrite—-are rare in adults, found only in some special sense organs (eye, nose), where they act in sensory processing as receptor cells;

unipolar neurons

have a single process emerging from the cell body as if the cell body were on a “cul-de-sac” off the “main road” that is the axon—are unique in that only the small branches at the end of the peripheral process are dendrites.

unipolar

Sensory neurons found in PNS ganglia are

irritability and conductivity

Neurons have two major functional properties:

irritability

the ability to respond to a stimulus by producing a nerve impulse;

conductivity

the ability to transmit the impulse to other neurons, muscles, or glands.

polarized

The plasma membrane of a resting, or inactive, neuron is—-which means that there are fewer positive ions sitting on the inner face of the neuron’s plasma membrane than there are on its outer face

potassium

The major positive ions inside the cell are;

sodium

the major positive ions outside the cell are;

potassium

The polarized membrane is more permeable to—-at rest, maintaining a more negative inside (fewer positive ions) compared to outside,

neurotransmitter chemicals

most neurons in the body are excited by

depolarization

This inward rush of sodium ions changes the polarity of the neuron’s membrane at that site, an event called

graded potential

Locally, the inside is now more positive, and the outside is less positive, a local electrical situation called a

resting membrane is polarized

In the resting state, the external face of the membrane is slightly positive; its internal face is slightly negative. The chief extracellular ion is sodium (Na+), whereas the chief intracellular ion is potassium (K+). The membrane is more permeable to K+ ions (which exit the cell resulting in fewer positive ions inside) at rest.

stimulus initiates local depolarization

A stimulus changes the permeability of a local "patch" of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane (the inside becomes more positive; the outside becomes more negative) at that site.

depolarization and generation of an action potential

If the stimulus is strong enough, depolarization causes membrane polarity to be completely reversed, and an action potential is initiated. (If the stimulus is not strong enough, the cell returns to a resting membrane state and no action potential occurs.)