Chapter 12

endocrine and nervous system

What two systems maintain internal coordination?

endocrine system

communicates through hormones secreted into bloodstream

nervous system

communicates by using neurons to send messages from cell to cell using chemical and electrical means

receive stimuli from external environment and send messages to CNS

first step in the nervous system

CNS processes the information and determines response

second step in the nervous system

CNS issues commands to muscle and gland cells to carry out response

third step in the nervous system

central nervous system (CNS) and peripheral nervous system (PNS)

What are the two major anatomical subdivisions of the nervous system?

brain and spinal cord; cranium and vertebral column

What structures make up the CNS, and what encloses them?

nerves and ganglion (ganglia)

What does the peripheral nervous system consist of? (2)

nerve

A bundle of nerve fibers (axons) wrapped in fibrous connective tissue.

ganglion (ganglia)

A knotlike swelling in a nerve where cell bodies of peripheral neurons are concentrated

sensory (afferent) division

functional divison of PNS that carries sensory signals from receptors (sense organs) to the CNS

somatic sensory division and visceral sensory division

the functional division subunits of the sensory (afferent) division of the PNS (2)

somatic sensory division

What functional division of the PNS carries signals from receptors in the skin, muscles, bones, and joints?

visceral sensory division

What functional division of the PNS carries signals from viscera of thoracic and abdominal cavities (heart, lungs, stomach, and urinary bladder)?

motor (efferent) division

What functional division of the PNS carries signals from the CNS to effectors (carry out the instructions)

somatic motor division and visceral motor division

What are the functional division subunits of the motor (efferent) division in the PNS? (2)

somatic motor division

what functional division of the PNS carrires signals to skeletal muscles

visceral motor division (autonomic nervous system)

this functional division of the PNS carries signals to glands, cardiac muscle, and smooth muscle; involuntary responses

sympathetic division and parasympathetic division

what are the subunits for the visceral motor division of the PNS

sympathetic division

this functional division of the PNS stimulates and prepares the body for action; accelerates heartbeat and respiration while inhibiting digestive and urinary systems

parasympathetic division

this fuctional division of the PNS has a calming effect; slows heart rate and breathing and stimulates digestive and urinary systems

Excitability, conductivity, and secretion

What are the three universal properties of neurons?

neuron excitability

The ability to respond to environmental changes called stimuli

neuron conductivity

The ability to produce electrical signals that are quickly conducted to other cells at distant locations

neuron secretion

When an electrical signal reaches the end of an axon, a chemical neurotransmitter is secreted that crosses the gap and stimulates the next cell

Sensory (afferent) neurons, interneurons (association neurons), and motor (efferent) neurons.

What are the three functional classes of neurons?

sensory (afferent) neurons

these neurons detect stimuli and transmit information to the CNS; they begin in almost every organ and end in the CNS.

within CNS

where are interneurons (association neurons) found

interneurons (association neurons)

they receive signals from many neurons, process information, and make resulting “decisions”

motor (efferent) neurons

send signals out to effectors (muscles and glands); motor because they lead to muscles

neurosoma

this part of a neuorn is the neuron's control center; it contains a single nucleus and a cytoskeleton

neurosoma

this part of a nueron has no centrioles which means it can not undergo cell division (mitosis)

axon (nerve fiber)

this part of a neuron originates from the axon hillock

axon (nerve fiber)

this part of a nueron is cylindrical and relatively unbranched; it has rapid conduction of nerve signals

axoplasm and axolemma

what does an axon (nerve fiber) consist of

dendrites

Branches that extend from the soma and are the primary site for receiving signals from other neurons

Multipolar, bipolar, unipolar, and anaxonic

What are the four structural classes of neurons?

multipolar neuron

a neuron class with one axon and multiple dendrites; most neurons in the CNS

bipolar neuron

A neuron class with one axon and one dendrite

olfactory cells, retina, and inner ear

where are bipolar neurons found (3)

unipolar neuron

A neuron class with a single process leading away from the soma; carries sensory information from skin and organs to the spinal cord

anaxonic neuron

A neuron class with many dendrites but no axon

retina, brain, and adrenal gland

where are anaxonic neurons found

axonal transport

The two-way passage of proteins, organelles, and other material along an axon

To repair the axolemma and serve as gated ion-channel proteins, enzymes, or neurotransmitters

Why must proteins made in the cell body be transported to the axon and axon terminal? (2)

anterograde transport

Movement down the axon away from the soma

retrograde transport

Movement up the axon toward the soma; this could be for movement of other matierials (like waste products) that need to be transported from axon terminals back to cell body for disposal

neuroglia or glial cells

Supportive cells that protect neurons and help them function

neuroglia or glial cells

bind neurons togetehr and form framework for nervous tissue

neuroglia or glial cells

in fetus, guide mirgating neurons to their destination

glial cells

if mature neuron is not in synaptic contact with another neuron it is covered by _____; this prvent sneurons from touching each other and gives precision to conduction pathways

Oligodendrocytes, ependymal cells, microglia, and astrocytes

What are the four types of neuroglial cells of CNS

oligodendrocytes

Form myelin sheaths in the CNS; arm-like processes wrap around nerve fibers to form insulating layers that speed signal conduction

ependymal cells

Line the internal cavities of the brain and spinal cord; secrete and circulate cerebrospinal fluid (CSF).

microglia

macrophages, engulf debris, provide defense against pathogens

WBCs (monocytes) and in areas of damage

Where do microglia develop from, and where do they become concentrated?

astrocytes

cover entire brain surface and most nonsynaptic regions (most abundant glial cell); diverse functions

a supportive framework

what do astrocytes form

blood-brain barrier

astrocytes have perivascular feet hat contain blood capillaries and stimualte them to form _____

by absorbing excess neurotransmitters and ions

How do astrocytes regulate the chemical composition of tissue fluid?

blood glucose to lactate

what do astrocytes convert so that they can supply this to the neurons for nourishment

communicate electrically with neurons

what do astrocytes communicate with and what way do they communicate

Schwann cells/neurilemmocytes and satellite cells

What are the two types neuroglial cells of PNS?

Schwann cells/neurilemmocytes

Envelop PNS nerve fibers/axons and wind repeatedly around a nerve fiber

Schwann cells/neurilemmocytes

produce myelin sheaths and and assist regeneration of damaged fibers

satellite cells

Surround neurosomas in ganglia of the PNS and provide electrical insulation around the soma

satellite cells

regulate the chemical environment of neurons and assists in clean-up

tumor

masses of rapidly dividing cells

They have little or no capacity for mitosis

Why are mature neurons seldom form tumors?

meninges, metastasis from tumors in other organs, and glial cells that are mitotically active throuhgout life

Brain tumors arise from (3)

glioma

type of tumor that grows rapidly and is highly malignant

It decreases the effectiveness of chemotherapy

How does the blood-brain barrier affect chemotherapy for brain tumors?

Radiation or surgery

Treatments for brain tumors

myelin sheath

Spiral layers of insulation around a nerve fiber

Oligodendrocytes in the CNS and Schwann cells in the PNS

Which cells form myelin sheath in the CNS and PNS?

plasma membrane and glial cells

What does the myelin sheath consist of (2)

myelination

The production of a myelin sheath

during fetal development

when does myelination begin

infancy and late adolescence

when does rapid myelination occur and when is it completed

Dietary fat

What factor is important to CNS development? (bc myelin is mostly made of this)

How does a Schwann cell form a PNS myelin sheath?

It spirals repeatedly around a single nerve fiber and lays down as many as 100 layers of its own membrane, with no cytoplasm between the membranes.

What is the neurilemma?

The thick, outermost coil of the PNS myelin sheath; it contains the Schwann cell nucleus and most of its cytoplasm.

What lies external to the neurilemma?

The endoneurium.

How does CNS myelination differ from PNS myelination?

One oligodendrocyte myelinates several nearby nerve fibers and is anchored to multiple fibers. It pushes newer layers under older layers, so myelination spirals inward.

What structures are absent from CNS myelin?

The neurilemma and endoneurium.

What is a node of Ranvier?

A gap between segments of the myelin sheath.

What are internodes (internodal segments)?

The myelin-covered segments between nodes of Ranvier.

What is the initial segment of a nerve fiber?

The short section between the axon hillock and the first glial cell.

What is the trigger zone?

The axon hillock and initial segment; it plays an important role in initiating a nerve signal.

What happens to oligodendrocytes and CNS myelin in multiple sclerosis (MS)?

They deteriorate, and myelin is replaced by hardened scar tissue.

What is the effect of MS on nerve conduction?

Nerve conduction is disrupted.

What MS symptoms are listed in the slides?

Double vision, tremors, numbness, and speech defects.

What MS onset age and prognosis are listed in the slides?

Onset between ages 20 and 40; the slides state it is fatal 25 to 30 years after diagnosis.

How do the slides describe the cause of MS?

As an autoimmune disease triggered by a virus.

What is Tay-Sachs disease?

A hereditary disorder described in the slides as occurring mainly in infants of Eastern European Jewish ancestry.

What accumulates abnormally in Tay-Sachs disease?

The glycolipid/ganglioside GM2 accumulates in the myelin sheath.

How is GM2 normally broken down, and what happens in Tay-Sachs disease?

A lysosomal enzyme normally decomposes GM2; the enzyme is missing in individuals homozygous for the Tay-Sachs allele.

What are the effects of GM2 accumulation in Tay-Sachs disease?

It disrupts nerve-signal conduction and causes blindness, loss of coordination, and dementia; the disease is fatal before age four.

Are all CNS and PNS axons myelinated?

No. Many CNS and PNS axons are unmyelinated.