Anatomy Ch. 12 Study Guide

The sensory nervous system

- Afferent nervous system; responsible for receiving sensory information from receptors that detect stimuli and transmitting this information TO the CNS. - The information from the receptors to the CNS is called sensory input.

Ependymal cells

- Ciliated simple cuboidal or simple columnar epithelial cells that line the internal cavities (ventricles) of the brain and the central canal of the spinal cord. - Have slender processes that branch extensively to make contact with other glial cells in the surrounding nervous tissue. - Work with blood capillaries to form a network called the choroid plexus; this helps produce cerebrospinal fluid (CSF), a clear liquid that bathes the external surfaces of the CNS and fills its internal cavities. - The cilia of ependymal cells help circulate the CSF.

The motor nervous system

- Efferent nervous system; controls effectors (muscles and glands); responsible for initiating and transmitting motor information FROM the CNS to the effectors. - The info from the CNS to effectors is called motor output.

Satellite cells

- Flattened cells arranged around neuronal cell bodies in a ganglion; physically separate cell bodies from their surrounding interstitial fluid. - Function to electrically insulate the cell body and regulate the continuous exchange of nutrients and waste products between neuron cell bodies and their environment.

Oligodendrocytes

- Large cells with a bulbous (round) body and slender cytoplasmic extensions or processes. - Extensions wrap around and insulate axons within the CNS to form a myelin sheath through a process called myelination; this insulation allows for faster propagation of action potentials along the axon.

Neurolemmocytes

- Schwann cells; elongated and flattened cells that wrap around and insulate axons within the PNS to form a myelin sheath through myelination. - As with myelin sheaths formed by oligodendrocytes in the CNS, this allows for faster propagation of actions potentials along the axon. - Myelinates a 1 mm portion of an axon, so the axons in many of the nerves in the body have hundreds to thousands of neurolemmocytes along their entire length.

Microglia

- Small cells that have slender branches extending from the main portion of the cell; represent the smallest % of CNS glial cells. - Phagocytic cells (macrophages) of the immune system; wander through the CNS and replicate in response to an infection. - Protect the CNS against microorganisms (bacteria) and other potentially harmful substances by engulfing and destroying them through phagocytosis. - Remove debris from dead or damaged nervous tissue that results from infections, inflammation, trauma, and brain tumors.

Astrocytes

- Star-like shape due to projections form their surface; numerous cell processes have contact with both neurons and blood capillaries (smallest BVs). - Most abundant glial cell in CNS and constitute 90% of nervous tissue in the brain. - They nurture, protect, support, and guide neurons by helping form the blood-brain barrier, regulating interstitial fluid composition, forming structural support, assisting neuronal development, and occupying the space of dying neurons.

Astrocytes: help form the blood-brain barrier

- The ends of astrocyte processes are called perivascular feet; they both cover and wrap around capillaries in the brain and contribute, alongside brain capillaries, to a blood-brain barrier (BBB) which strictly controls movement of substances exiting the blood and entering the nervous tissue in the brain. - BBB protects the delicate neurons of the brain from toxins and allows needed nutrients to pass through.

Amitotic behavior of neurons

During fetal development, most neurons lose the ability to form new cells through cell division. - Exceptions include the neurons in certain areas of the brain and in the olfactory epithelium of the nose.

Process and evaluate information

After processing sensory information, the brain and spinal cord determine what response, if any, is required.

Endoneurium

Areolar CT layer which provides a delicate covering that functions to separate and electrically insulate each axon.

Synaptic delay

Associated with neurotransmitter release at chemical synapses; it is the time between the neurotransmitter release from the presynaptic cell, its diffusion across the synaptic cleft, and neurotransmitter binding to receptors in the postsynaptic neuron plasma membrane.

Dorsal root ganglia

Associated with sensory neurons that extend into the spinal cord and are associated with spinal nerves.

Astrocytes: assist neuronal development

Astrocytes help direct the development of neurons in the fetal brain by secreting chemicals that regulate the formation of connections between neurons.

Astrocytes: regulate interstitial fluid composition

Astrocytes help maintain an optimal chemical composition of the interstitial fluid (fluid around cells) within the brain; regulation of potassium ion concentration by absorbing these ions to maintain the concentration critical to electrical activity of nuerons.

Glial cells found in the CNS

Astrocytes, ependymal cells, microglia, and oligodendrocytes.

Axon plasma membrane

Axolemma

Myelin sheath

Axons or axon collaterals may be insulated with a myelin sheath, which is formed by a certain type of glial cells (either neurolemmocytes or eliodendrocytes).

Axon cytoplasm

Axoplasm

Structural classifications of nerves

Based upon the CNS component from which the nerve extends; cranial nerves (extend from brain) and spinal nerves (extend from the spinal cord).

Functional classifications of nerves

Based upon the functional type of neuron (sensory or motor) a nerve contains; sensory nerves, motor nerves, mixed nerves.

Polio

Caused by poliovirus; preferentially infects somatic motor neurons to skeletal muscle, which may result in muscle weakness and paralysis.

Two types of synapses

Chemical synapse and electrical synapse

3 general functions of neurons

Collect information, process and evaluate information, initiate response to information.

What connects cells in an electrical synapse?

Composed of a presynaptic and postsynaptic neuron physically bound together; gap junctions are present in the plasma membrane of both neurons and facilitate the flow of ions between the cells. - The cells act as though they share a plasma membrane; the electrical signal passes between the cells with little to no synaptic delay, and is located within limited regions of the brain and eyes.

Nervous system

Composed of the brain, spinal cord, ganglia, and nerves. Regulates body activities by sending and receiving messages' primary tissue is nervous tissue.

Mixed nerves

Contain both sensory and motor neurons; most named nerves (including all spinal nerves and most cranial nerves) are mixed nerves. - Individual sensory or motor neurons still transmit only one type of information.

Sensory nerves

Contain only sensory neuros that relay information TO the CNS.

Motor nerves

Contain primarily motor neurons that relay information FROM the CNS.

Neuron nucleus

Contains chromatin and a prominent nucleolus, which synthesizes the cell body's large number of ribosomes.

Epineurium

Dense irregular CT layer of fibrous tissue wrapped around an entire nerve to protect and support it.

Perineurium

Dense irregular CT layer of rough, fibrous CT sleeves which provide protection and support to each bundle of axons (fascicles) and supports blood vessels.

Conductivity of neurons

Electrical change that is quickly propagated along the plasma membrane as voltage-gated channels open sequentially during an action potential. - Refers to the ability to propagate (move) an electrical change along the plasma membrane (AP).

Synaptic knob

End of an axon; extreme tips of the fine extensions (slightly expanded regions).

General characteristics of neurons

Excitability, conductivity, secretion (extreme longevity and amitotic)

Neurons

Excitable cells that initiate and transmit electrical signals. - Basic structural unit of the nervous system.

Synaptic cleft

Extremely narrow, fluid-filled gap (30 nm) that separates the two neurons (pre and post).

Capillaries

Microscopic blood vessels; associated with the endoneurium and function as the site of exchange of substances (oxygen, glucose, waste) between axons of neurons and the blood.

Neurotransmitters

Molecules stored in vesicles and when released, bind to an excitable cell to cause either an excitatory or inhibitory effect on these target cells (other neurons or effectors).

Brain tumors

More likely to develop from glial cells because they are more abundant and are critical for the normal function at neural synapses, maintaining the anatomic structure of synapses, and modifying transmission that occurs there.

Extreme longevity of neurons

Most neurons formed during fetal development are still functional in very elderly individuals.

Fast axonal transport

Movement along microtubules; power comes from specialized motor proteins (kinesin, dynein) that split ATP to supply the energy needed. - Materials include vesicles, organelles, and glycoproteins required at the synapse.

Retrograde transport

Movement of materials from synaptic knobs toward the cell body.

Anterograde transport

Movement of materials from the cell body toward synaptic knobs.

Structural classification of neurons

Multipolar, bipolar, unipolar, or anaxonic; based upon the number of neuron processes (axon or dendrites).

Glial cells 2

Neuroglia/ nerve glue; found in the CNS and PNS. - Smaller than neurons and produce new glial cells through cell division; do not transmit electrical signals, but do aid neurons in their function.

Myelinated axons

Neurolemmocytes are between the axon and endoneurium.

What two cell types compose nervous tissue?

Neurons and glial cells

Motor neurons

Neurons of the motor nervous system; conduct motor output from the CNS to both somatic effects (skeletal muscle) and autonomic effectors (cardiac muscle, smooth muscle, and glands). - All are multipolar.

Sensory neurons

Neurons of the sensory nervous system; responsible for conducting sensory input from both somatic sensory (touch receptor) and sensory receptors (stretch receptors within urinary bladder) to the CNS. - Most are unipolar; some somatic sensory neurons are bipolar including the retina of the eye, olfactory, and epithelium of the nose.

Secretion by neurons

Neurons release neurotransmitters in response to conductive activity.

The peripheral nervous system (PNS)

Includes nerves, which are bundles of axons of neurons, and ganglia, which are clusters of neuron cell bodies located along nerves.

The central nervous system (CNS)

Includes the brain and spinal cord; brain is protected and enclosed within the skull, and the spinal cord is housed and protected within the vertebral canal.

Glial cells

Non-excitable cells that primarily support and protect the neurons.

Function of glial cells

Physically protect and help nourish neurons and provide an organized, supporting scaffolding for all the nervous tissue. - Do not produce action potentials; do undergo mitosis. - Glial cells far outnumber neurons; roughly half the volume of the nervous system.

Myelination

Process by which part of an axon is wrapped with myelin.

Subdivisions of sensory NS

Somatic sensory - detect stimuli that we can consciously perceive; receptors include the receptors associated with the 5 senses and proprioceptors, which are receptors in joints and muscles that detect body position. Visceral sensory - detect stimuli that we do not consciously perceive; receptors include structures located within blood vessels and internal organs.

Soma

The neuron cell body; houses both the nucleus and the cytoplasm. - Serves as the neuron's control center because it functions in many of the cell's metabolic activities and transmits graded potentials along its plasma membrane to the axon.

Neurilemma

The periphery of the neurolemmocyte which contains the cytoplasm and nucleus.

Bipolar neurons

Two processes that extend directly from the cell body - one dendrite and one axon; location of these neurons is relatively limited in humans. - Some special sense neurons (retina of eye, olfactory, epithelium in nose).

Astrocytes: occupy the space of dying neurons

When neurons are damaged and die, the space that they formerly occupied is filled by astrocytes that replicate through cell division.

Synapse 1

Where the synaptic knob ends; functional junction.

Anaxonic neurons

Only dendrites and no axons; produce graded potentials, but they do not produce action potentials. - Interneurons

Nerve

Organ composed of a cablelike bundle of axons, connective tissue layers, and blood vessels; is a component of the PNS.

What does the presynaptic neuron release into the synaptic cleft?

- Transmission between a presynaptic and postsynaptic neuron occurs when neurotransmitter molecules stored in synaptic vesicles are released from the synaptic knob of a presynaptic neuron into the synaptic cleft. - Some of the neurotransmitter diffuses across the synaptic cleft to bind to receptors within the plasma membrane of the postsynaptic neuron to initiate a graded potential.

Neurofibril nodes

- Uninsulated regions of the axon between the myelin sheaths. - Gaps in myelin; also called nodes of Ranvier; gaps between the neurolemmocytes.

Myelination in the PNS

1. The neurolemmocyte starts to encircle a 1-mm portion of an axon. 2. As it continues to wrap around the axon, the cytoplasm and nucleus of rhe neurolemmocyte are squeezed to the periphery (outside edge). 3. The overlapping inner layers of the plasma membrane form the myelin sheath. 4. The periphery of the neurolemmocyte contains the cytoplasm and nucleus and is called the neurilemma. Ex. water balloon wrapped around a pencil.

Ganglia

A bundle of neuron cell bodies within the peripheral nervous system; results in swelling, or an enlarged portion, along the length of a nerve, which is often large enough to be observed with the naked eye.

Anatomic features of neurons

A cell body, dendrites, and an axon.

Shingles

A painful skin rash caused by varicella virus; infects somatic sensory neurons extending from receptors in the skin.

Presynaptic neuron

A signal producer (releases neurotransmitter); a type of chemical synapse between two neurons is composed of this.

How many axons in a neuron?

A single axon; typically longer process emanating from the cell body to make contact with other neurons, muscle cells, or gland cells.

Multipolar neurons

Many dendrites and a single axon that extends from the cell body; most common type of neurons in the human body. - All motor neurons and most interneurons are this.

Interneurons (association neurons)

Lie entirely within the CNS; receive stimulation from many other neurons and carry out the integrative function of the nervous system - they receive, process, and store information and 'decide' how the body responds to stimuli. - Interneurons facilitate communication between sensory and motor neurons; they outnumber all other neurons (99%). - Either multipolar or anaxonic neurons.

Synapse location

It may be between the axon of the presynaptic neuron and any portion of the surface of a postsynaptic neuron (dendrite, cell body, or axon), except the regions covered by a myelin sheath; a synapse is usually with a dendrite of the postsynaptic neuron. - The synaptic knob of the presynaptic neuron does not make contact with the postsynaptic neuron.

Neuron ribosomes

Readily absorb basic dyes when a nervous tissue sample is stained so they appear as a dark-staining body and are called chromatophilic substance.

Collect information

Receptors are specialized nervous system structures that monitor changes in both the internal and external environment called the stimuli. - Ex: receptors in the skin detect stimuli with touch - this sensory info is relayed along neurons to the spinal cord and brain.

Dendrites

Relatively short, small, tapered processes that branch off the cell body; not insulated with myelin and transmit graded potentials along their plasma membrane toward the cell body. - More dendrites = more input a neuron may receive.

Excitability of neurons

Responsiveness to a stimulus (chemical, stretch, pressure change). - This stimulus causes a local electrical change in the resting membrane potential in the excitable cell by initiating the movement of ions across the plasma membrane of the excitable cell.

Slow axonal transport

Results from flow of the axoplasm and is also called axoplasmic flow; materials only moved from the cell body toward the synaptic knob (anterograde). - Substances include enzymes, cytoskeletal components, and new axoplasm for regenerating axons.

Glial cells found in the PNS

Satellite cells and neurolemmocytes; specialized glial cells which function in insulating neurons.

Functional classification of neurons

Sensory neurons, motor neurons, and interneurons; based on the direction the action potentials are propagated relative to the CNS.

Axon collaterals

Side branches at the distal end into an array of fine terminal extensions.

Postsynaptic neuron

Signal receiver or target (binds neurotransmitter).

Unipolar neurons

Single, short neuron process that emerges from the cell body and branches like a T; also called pseudounipolar because they start out as bipolar neurons during development, but the two processes fuse into a single process. - Short, multiple branched receptive endings are dendrites (exhibit graded potentials); other portion is axon (generates and conducts APs). - Axons are composed of the combined peripheral process (from dendrites to the cell body) and central process (from the cell body into the CNS). - Most are sensory neurons.

Subdivisions of motor NS

Somatic motor - initiates and transmits motor output from the CNS to skeletal muscle. Autonomic motor - innervates and regulates cardiac muscle, smooth muscle, and glands without our conscious control. (sympathetic and parasympathetic)

Initiate response to information

The brain and spinal cord initiate a response as motor info is relayed along neurons to structures called effectors. - Effectors contain all 3 types of muscle tissue and glands; the effect may be muscle contraction/relaxation or change in gland secretion activity.

Structural divisions of the nervous system

The central nervous system and the peripheral nervous system

Astrocytes: form structural support

The cytoskeleton in astrocytes strengthens these cells to provide a structural framework to support and organize neurons within the CNS.

Neuron structure

The dendrites and axon are cellular extension that project from the spherically shaped cell body - with the axon emanating from the triangular, cone-shaped region of the cell body called the axon hillock.

Myelin color

The high lipid content of the myelin gives an axon a distinct, glossy-white appearance and effectively insulates an axon (myelin also contains a small amount of proteins).

Axon function

The initiation and propagation of action potentials along their axolemma, which trigger synaptic vesicles to release neurotransmitter from the synaptic knobs.

Myelin

The insulating covering around the axon that is composed of many concentric layers of plasma membrane of glial cells.

Functional divisions of the nervous system

The sensory nervous system and the motor nervous system

Syanpse

The specific location where a neuron is functionally connected to either another neuron or an effector (muscle or gland).

Fascicle

Within a nerve, many axons are bundled into a structure called a __.

Synaptic vesicles

Within synaptic knobs; contain neurotransmitter.

Neuron cytoplasm

Within the cell body, called the perikaryon; composed of the typical cellular organelles such as the ER, golgi apparatus, ribosomes, and mitochondria.

Do nerves have blood vessels?

Yes, nerves are vascularized by an extensive network of BV, which branch and extend through both the epineurium and the perineurium to become capillaries.