Nervous Tissue

STIMULUS

Any change in the environment that is strong enough to imitate an action potential

The somatic nervous system is a branch of

the peripheral nervous system

AXON

the single axon of a neuron propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell. An axon is a Long, thin, cylindrical projection that often joins to the cell body at a cone-shaped elevation called the AXON HILLOCK.

Many neurons contain ________ or even _________ types of neurotransmitters, each with different effects on the post synaptic cell.

two, three

The pattern of dendritic branching is ________________ and _______________ for neurons in different parts of the nervous system

varied and distinctive

Fast axonal transport that occurs in RETROGRADE (backward) direction moves membrane ___________________ and other ______________ _______________ from the axon terminals to the cell body to be degraded or recycled.

vesicles, cellular materials

The nervous system can be divided into:

The central nervous system and the peripheral nervous system

Integrative function (process)

The nervous system processes sensory information by analyzing it and making decisions for appropriate responses - an activity known as integration

The Enteric Nervous system is a branch of

The peripheral nervous system

the CNS is the source of

Thoughts, emotions and memories

Both synaptic end bulbs and varicosities contain many__________ ________________-enclosed sacs called SYNAPTIC VESSICLES

Tiny, membrane

Most sensory neurons are _______polar in structure

UNIpolar

Newly synthesized proteins produced by Nissl bodies are used to replace....?

cellular components, as material for growth of neurons, and to regenerate damaged axons in the PNS.

Most signals that stimulate muscles to contract and glands to secrete originate in the?

Central Nervous System (CNS)

31 pairs of spinal nerves emerge from the

spinal cord

Both __________________ and ___________________ features are used to classify the various neurons in the body.

structural and functional

Neuroglia _____________,___________, and ______________ neurons, and maintain the interstitial fluid that bathes them.

support, nourish, and protect

In addition to forming the complex processing networks within the brain and spinal cord, neurons also ______________ all regions of the body to the brain and spinal cord.

Connect

3 Parts of a neuron

(1) cell body (2) dendrites (3) axon

the Autonomic Nervous System or ANS (a branch of the peripheral nervous system) consists of

(1) sensory neurons that convey information to the CNS from autonomic sensory receptors, located primarily in visceral organs such as the stomach and lungs and (2) motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands. -- Because its motor responses are not normally under conscious control, the action of the ANS is involuntary.

ENTERIC PLEXUS

Extensive networks of neurons located in the walls of organs of the gastrointestinal tract - The neurons of these plexuses help regulate the digestive system

NERVE FIBER

General term for any neuronal process that emerges from the cell body of a neuron. Most neurons have two kinds of processes: multiple dendrites and a single axon

TRIGGER ZONE

In most neurons, nerve impulses arise at the junction of the axon hillock and the initial segment, an area called the trigger zone, from which they travel along the axon to their destination.

Is the operation of the Enteric Nervous System (ENS) voluntary or involuntary?

Involuntary

Most interneurons are _____polar in structure

MULTIpolar

As a result of their specialization, most neurons have lost the ability to undergo _____________ __________.

Mitotic divisions

The cytoskeleton includes both...

NEUROFIBRILS, composed of bundles of intermediate filaments that provide the cell shape and support, and MICROTUBULES, which assist in moving materials between the cell body and axon.

NEURONS

Nerve cells

Functional classification of neurons (definition)

Neurons are classified according to the direction in which the nerve impulse (action potential is conveyed with respect to the CNS

What two types of cells does the nervous tissue comprise?

Neurons, and neuroglia

A ______________________ is a molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber, or gland cell.

Neurotransmitter

Motor function (output)

Once sensory information is integrated, the nervous system may elicit an appropriate motor response by activating effectors (muscles and glands) through cranial and spinal nervous. Stimulating of the effectors causes muscles to contract and glands too secrete.

DENTRITES

Receiving or input portions of a neuron. The plasma membranes of dendrites (and cell bodies) contain numerous receptor sites for binding chemical messengers from other cells. Dendrites usually are short, tapering, and highly branched. In many neurons the dendrites form a tree-shaped array of processes extending from the cell body. Their cytoplasm contains NISSL BODIES, mitochondria, and other organelles.

Sensory Function (input)

Sensory receptors detect internal stimuli, such as an increase in blood pressure, or external stimuli (for example, a raindrop landing on your arm). This sensory information is then carried into the brain and spinal cord through cranial and spinal nerves.

Multipolar neurons

Structural classification of neuron that usually have several dendrites and one axon. Most neurons in the brain and spinal cord are this type, as well as motor neurons.

The autonomic nervous system is a branch of

The peripheral nervous system

SYNAPSE

The site of communication between two neurons or between a neuron and an effector cell

SLOW AXONAL TRANSPORT

The slower transport system, which moves materials about 1-5 mm per day. It conveys axoplasm to developing or regenerating axons and replenishes axoplasm in growing and mature axons.

VARICOSITIES

The tips of some axon terminals that exhibit a string of swollen bumps

How many types of transport systems are used to carry materials from the cell body to the axon terminals and back? and why?

Two, because some substances synthesized or recycled in the neuron cell body are needed in the axon or at the axon terminals

NERVE

a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord

The brain is part of the ______________ that is located in the __________ and contains about __________ billion neurons

central nervous system (CNS), skull, 85

Interneurons - Functional Classification of Neurons

or association neurons - are mainly located within the CNS between sensory and motor neurons. Interneurons integrate (process) incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons. Most interneurons are multipolar in structure.

Because rough endoplasmic reticulum is not present, protein synthesis does ________ ___________in the axon.

not occur

Sensory - functional classification

or afferent neurons, either contain sensory receptors at their distal ends (dendrites) or are located just after sensory receptors that are separate cells. Once an appropriate stimulus activates a sensory receptor, the sensory neuron forms an action potential in its axon and the action potential is conveyed into the CNS through cranial or spinal nerves. Most sensory neurons are unipolar in structure.

Motor - functional classification

or efferent neurons convey action potentials away from the CNS to effectors (muscles and glands) in the periphery (PNS) through cranial or spinal nerves. Motor neurons are multipolar in structure.

Fast axonal transport that occurs in ENTEROGRADE (forward) direction moves _________________ and synaptic ___________________ from the cell body to the axon terminals.

organelles, vesicles

Neuroglia are smaller cells but they greatly______________ neurons, perhaps by as much as 25 times.

outnumber

Each nerve follows a defined _________ and serves a specific _________ of the __________

path, region, body

Structurally, neurons are classified according to the number of _________________ extending from the cell body

processes

Ribosomes are the site of

protein synthesis

SENSORY RECEPTOR

refers to a strucuture of the nervous system that monitors changes in the external or internal environment Examples of sensory receptors include touch receptors in the skin, photoreceptors in the eye, and olfactory receptors in the nose

The Central Nervous System (CNS) processes many different kinds of incoming

sensory information

Neurons display great diversity in what?

size and shape

GANGLIA

small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside of the brain and spinal cord. Ganglia are closely associated

peripheral nervous system (PNS) is divided into a

somatic nervous system (SNS), an autonomic nervous system (ANS), and an enteric nervous system (ENS)

ELECTRICAL EXCITABILITY

the ability to respond to a stimulus and convert it into an action potential

INITIAL SEGMENT

the part of the axon closest to the axon hillock

The somatic nervous system (a branch of the peripheral nervous system) consists of

(1) sensory neurons that convey information to the CNS from somatic receptors in the head, body wall, and limbs and from receptors for the special senses of vision hearing, taste and smell (2) motor neurons that conduct impulses from the CNS to skeletal muscles only. Because these motor responses can be consciously controlled, the action of this part of the PNS is voluntary

Structural classifications of neurons

1. Multipolar neurons 2. Bipolar neurons 3. Unipolar neurons

Functional classifications of neurons (3)

1. Sensory 2. Motor 3. Interneurons

Functions of the nervous system include

1. Sensory function (input) 2. Integrative function (process) 3. Motor function (output)

The spinal cord contains about ____ million neurons

100

Neuron cell bodies range in diameter from _______ up to _______

5 micrometers, up to 135 um

PERKINJE CELLS

Also known as "perking neurons" are neurons in vertebrae animals located in the cerebellar cortex of the brain. Shaped like a flask and have many threadlike extensions called dendrites, which receive impulses from other neurons called granule cells

Gliomas

Brain tumors derived from glia. Tend to be highly malignant and grow rapidly.

AXON COLLATERAL

Branches/forks off a neuron, typically at a right angle to the axon.

FAST AXONAL TRANSPORT

Capable of moving materials a distance of 200-400 mm per day, uses proteins that function as "motors" to move materials along the surfaces of microtubules of the neurons cytoskeleton. Fast axonal transport moves materials in both directions-away from and toward the cell body.

Unipolar neurons

Structural classification of neurons that have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body. These neurons are more appropriately called pseudo unipolar neurons because they begin In the embryo as bipolar neurons. During development, the dendrites and axon fuse together and become a single process. The dendrites of unipolar neurons function as sensory receptors that detect a sensory stimulus such as touch, pressure, pain, or thermal stimuli. The trigger zone for nerve impulses in a unipolar neuron is at the junction of dendrites and axon.

Bipolar neurons

Structural classification of neurons that have one main dendrite and one axon. They are found in the retina of the eye, in the inner ear, and the olfactory area of the brain.

what are the two branches of the Autonomic Nervous System (ANS)?

Sympathetic division, and the parasympathetic division

The tips of some axon terminals swell into bulb-shaped structures called

Synaptic end bulbs

TRUE OR FALSE? Aging neurons also contain LIPOFUSCIN

TRUE

AXON TERMINAL

The axon and its collateral end by dividing into many fine processes called axon terminals

The Central Nervous System consists of:

The brain and spinal cord

LIPOFUSCIN

a pigment that occurs as climbs of yellowish brown granules in the cytoplasm - product of neuronal lysosomes that accumulates as the neuron ages, but does not seem to harm the neuron

The Peripheral Nervous System (PNS) consists of?

all nervous tissue outside of the CNS

CELL BODY

also known as the perikaryon or soma, contains a nucleus surrounded by cytoplasm that includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex. Neuronal cell bodies also contain free ribosomes and prominent clusters of rough endoplasmic reticulum, termed NISSL BODIES.

A few small neurons lack an ______________, and many others have very ____________ axons.

axon, short

The cytoplasm of an axon, called ___________, is surrounded by a plasma membrane known as the ______________

axoplasm, axolemma

12 pairs of cranial nerves emerge from the

brain

Unlike neurons, neuroglia continue to _____________ throughout an individual's lifetime.

divide

With a few exceptions, ______________ receive nerves from both the sympathetic division and the parasympathetic division of the autonomic nervous system, and usually the two divisions have _______________ actions.

effectors, opposing

Neurons possess _____________ excitability

electrical

Substances that enter the neuron at the axon terminal are also moved to the cell body by what?

fast retrograde transport - These substances include trophic chemicals such as nerve growth factor and harmful agents such as tetanus toxin and the viruses that cause rabies, herpes simplex, and polio.

The spinal cord is connected to the brain through the?

foramen magnum of the occipital bone, and is encircled by the bones of the vertebral column

ACTION POTENTIAL (NERVE IMPULSE)

is an electrical signal that propagates (travels) along the surface of the membrane of a neuron. It begins and travels due to the movement of ions (such as sodium and potassium) between interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane. Once begun, a nerve impulse travels rapidly and at a constant strength.

Neuroglia

make up about half of the CNS. Their name derives from the idea of early histologists that were in the "glue" that held the nervous tissue together. Generally, smaller than neurons, and they are 5 to 25 times more numerous. In contrast to neurons, glia do not generate or propagate action potentials, and they can multiply and divide in the mature nervous system. In cases of injury or disease, neuroglia multiply to fill the spaces formerly occupied by neurons. Of the six types of neuroglia, four-astrocytes, oligodendrocytes, microglia, and ependymal cells - are found only in the CNS. The remaining two types - Schwann cells and satellite cells - are present in the PNS.

An AXON contains what?

mitochondria, microtubules, and neurofibrils

Components of the PNS include

nerves, ganglia, enteric plexuses, and sensory receptors