Human Anatomy & Physiology I - Chapter 11: Fundamentals of Nerves and Nervous Tissue

Key Terms

astrocytes

star-shaped glial in the CNS that support and brace the neurons and anchor them to their nutrient supply lines

ependymal cell

glial cells in the CNS that line ventricles and the central canal, produce and circulate cerebrospinal fluid (CSF), often using cilia

microglial cell

the primary immune cells of the CNS that act like tissue macrophages to patrol the brain for signs of injury or disease

oligodendrocyte

glial cells in the CNS that form the myelin sheath around neuronal axons to insulate them and speed up the transmission of electrical signals

satellite cell

glial cells in the PNS that surround neuron cell bodies, providing support and protection, similar to astrocytes in the CNS

Schwann cell

glial cells in the PNS that support neurons and form the myelin sheath

myelin

an insulating fatty sheath around axons that increases the speed of nerve impulses

The CNS consists of the _____ and ______ _____.

brain and spinal cord

The PNS consists of _____ and ______.

nerves and ganglia

ganglia

What direction do spinal nerves carry impulses?

to and from the spinal cord

What direction do cranial nerves carry impulses?

to and from the brain

What are the two functional subdivisions of the PNS?

the sensory (afferent) division and the motor (efferent) division

What does the sensory (afferent) division of the PNS do?

it carries sensory information from receptors in the body to the CNS

What do somatic sensory fibers do?

they carry sensory information from the skin, skeletal muscles, and joints to the CNS

What do visceral sensory fibers do?

they transmit impulses from the visceral organs to the CNS

What does the motor (efferent) division do?

it transmits impulses from the CNS to effector organs (muscles and glands), causing them to contract or secrete

What does the somatic nervous system do?

What does the autonomic nervous system do?

it regulates involuntary bodily functions like heart rate, breathing, digestion, blood pressure, and body temperature, ensuring homeostasis

What is another name for the autonomic nervous system?

involuntary nervous system

What are the two functional divisions of the ANS?

the sympathetic division and the parasympathetic division

neuroglia (glial cells)

small, supporting cells that surround and wrap the more delicate neurons

What are neurons?

nerve cells that are excitable and transmit electrical signals

What is excitability?

the ability of a neuron to respond to a stimulus by generating a change in membrane potential (an electrical signal)

What are the six types of neuroglia (glial cells)?

astrocytes, oligodendrocytes, ependymal cells, microglial cells, Schwann cells, and satellite cells

What neuroglia are found in the CNS?

astrocytes, microglial cells, ependymal cells, and oligodendrocytes

What neuroglia are found in the PNS?

Schwann cells and satellite cells

satellite cells

glial cells that surround neuron cell bodies in the PNS

Schwann cells (neurolemmocytes)

glial cells in the PNS that form the myelin sheath around axons and help with nerve regeneration

neurons (nerve cells)

the structural units of the nervous system

Besides their excitability, neurons have three other special characteristics:

extreme longevity, amitotic, and a high metabolic rate

What is the neuron cell body (soma or perikaryon)?

it consists of a spherical nucleus surrounded by a cytoplasm; it ranges in diameter from 5 to 140 um

The cell body is the major _________ center and ________ center of the neuron.

biosynthetic and metabolic

In most neurons, the plasma membrane of the cell body acts

as part of the ______ region that receives information from

other neurons.

receptive

What is another name for rough ER?

chromatophilic substance

neurofibrils

What types of pigments may be found in neuron cell bodies?

melanin, a red iron-containing pigment, and lipofuscin.

What is lipofuscin?

a golden-brown pigment and a harmless by-product of lysosomal activity

Why is lipofuscin called the “aging pigment”?

it accumulates in neurons of elderly individuals

nuclei

clusters of cell bodies in the CNS

ganglia

clusters of cell bodies that lie along the nerves in the PNS

neuron processes

arm-like extensions that originate from the cell body

What are the two types of neuron processes?

dendrites and axons

dendrites

short, branching extensions of a neuron that receive signals from other neurons and conduct them toward the cell body

Dendrites convey incoming messages _____ the cell body.

These electrical signals are usually ___ action potentials (nerve

impulses) but are short-distance signals called ______ potentials.

toward; not; graded

axon

the long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells

The axon rises from a cone-shaped area of the cell body called the ______ _______.

axon hillock

initial segment of the axon (trigger zone)

the specialized region where the axon begins, located at the junction between the neuron's cell body and the main axon

What is a nerve fiber?

any type of long axons

What are tracts?

bundles of axons in the CNS

What are nerves?

bundles of axons in the PNS

axon terminals

the knob-like distal endings of the terminal branches

The axon is the ______ region of the neuron.

conducting

What is an axolemma?

the plasma membrane of the neuron

The axon generates ______ impulses and ______ them, typically away from the cell body.

nerve; transmits

neurotransmitters

signaling chemicals

The axon terminal is the _____ region of the neuron.

secretory

anterograde movement

movement away from the cell body

retrograde movement

movement toward the cell body

myelin sheath

a whitish, fatty, segmented substance that covers many nerve fibers

myelinated fibers

axons bearing a myelin sheath that conduct impulses rapidly

nonmyelinated fibers

axons not bearing a myelin sheath that conducts impulses slowly

outer collar of perinuclear cytoplasm (neurilemma)

myelin sheath gaps (nodes of Ranvier)

gaps (1mm) in the sheath found in between Schwann cells

multipolar neurons

neurons that have three or more processes — one axon and the rest dendrites

bipolar neurons

neurons with two processes — an axon and a dendrite

unipolar neurons (pseudounipolar neurons)

neurons with a single, short process that divide into a proximal and distal branch

peripheral process

the distal process of a unipolar neuron that is associated with sensory receptor

central process

the process of a unipolar neuron that enters the CNS

sensory (afferent) neurons

neurons that transmit impulses from sensory receptors in the skin or internal organs toward or into the CNS

motor (efferent) neurons

neurons that carry impulses from the CNS to the effector organs (muscles and glands) of the body

interneurons (association neurons)

neurons that lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs

voltage

the measure of potential energy generated by separated electrical charges (V, mV)

potential (potential difference)

the electrical charge difference across the neuron's cell membrane between the inside and outside

current

the flow of electrical charge from one point to another

resistance

the hindrance to charge flow provided by substances through which the current must pass

Ohm’s law

current (C) = voltage (V) / resistance (R)

resting membrane potential

the potential difference in a resting neuron with a value of -40 mV to -90 mV

ion channels

membrane proteins that act as channels that are selective to ions such as potassium

chemically-gated channels (ligand-gated channels)

channels that only open when an appropriate chemical binds

voltage-gated channels

channels that open in response to changes in the membrane potential

mechanically-gated channels

channels that open in response to physical deformation of the receptor as in sensory receptor for touch and pressure

electrochemical gradient

the combined effect of both a chemical gradient and an electrical gradient across a membrane.

The direction an ion moves is determined by the __________ ________.

electrochemical gradient

concentration gradient

the difference in the concentration of particles between two areas, creating a slope from a high concentration region to a low concentration region

electrical gradient

the difference in electrical charge between two regions

polarized

a difference in electrical charge across a cell membrane, with one side being positive and the other negative

What does the sodium-potassium pump do?

it pumps three Na+ from the cell and then transports two K+ back in the cell

graded potentials

incoming signals operating over short distances that have variable (graded) strength

action potentials

long-distance signals of axons that always have the same strength

depolarization

a decrease in membrane potential, where the inside of the membrane becomes less negative than the resting potential