Anatomy unit 12 nervous tissue

Endocrine system

communicates by means of chemical messengers (hormones) secreted into to the blood

helps regulate body processes over time

Nervous system

utilized neurons (nerve cells) to send messages from cell to cell by electrical and chemical means; occurs in three steps

it receives stimuli from external environment and transmits messages to central nervous system

the central nervous system process the information and determines the response

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

how the nervous system works

1. Receive

Detect a stimulus, such as touching something hot.

2. Process

The central nervous system (CNS) interprets the information and determines a response.

3. Respond

Commands go to muscles or glands, which carry out the response.

central nervous system (CNS)

brain and spinal cord

processing information and coordinates responses

Peripheral nervous system (PNS)

nerves and ganglia

carries information to and from the CNS

nerve

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

ganglion

a knot like swelling in a nerve where neuron cell bodies of the PNS are concentrated

(a cluster of neuron cell bodies in the PNS)

tract

a bundle of axons in the CNS

Nucleus

a cluster of neuron cell bodies in the CNS

sensory (afferent) division

carries signals from receptors (sense organs) to CNS

Incoming

somatic sensory division

carries signals from receptors in the skin, muscles, bone, and joints

visceral sensory division

carries signals from the viscera (heart, lungs, stomach, and urinary baldder0

motor (efferent) division

carries signals from CNS to the effectors

outgoing

effectors

glands and muscles that carry out the body’s response

somatic motor division

carries signals to skeletal muscles; causes voluntary muscle contraction and automatic reflexes

visceral motor divisions

carries signals to glands, cardiac, and smooth muscle; no voluntary control; response called visceral reflexes (without voluntary control)

sympathetic division

an ANS stimulates and prepares the body for action (fight or flight)

parasympathetic division

of ANS (automatic nervous system) has a calming effect on the body

rest and calm

Enteric plexus (enteric nervous system)

within the digestive tract wall, enables coordination and communication within the digestive tract

digestive system control

excitability

ability to respond to stimuli

conductivity

produce electrical signals that are conducted to other cells

secretion

when signal reaches end of the neuron’s axon, the neuron secretes a neurotransmitter that signals the next cell

neurotransmitter

a chemical messenger released by a neuron to communicate with another cell

interneuons

most abundant

receive signals from other neurons, process this information, and make resulting decisions

lie entirely within CNS, connecting motor and sensory pathways; most common functional type (about 90% of all neurons)

sensory (afferent) neurons

detect stimuli and transmit information about the stimuli toward the CNS

begin in every organ of body and terminate in CNS

(sense information coming in)

Motor (efferent) neurons

least abundant

send signals out to muscles and gland cells (the effectors)

(Carry commands from the central nervous system to muscles and glands)

cell body

also called a neurosoma, soma, or perikaryon; contains nucleus and many organelles

nucleus

contains the cell’s DNA

cytoskeleton

contains microtubules and neurofibrils which compartmentalize the rough Er into dark staining chromatophilic substance

dendrites

most numerous neurites, resemble branching of a tree; primary sites for receiving signals from other neurons

axon

carries nerve signals away from the cell body

axon hillock

area where the axon begins

initial segment

part of the axon just beyond the hillock; helps initiate a nerve signal

trigger zone

axon hillock plus initial segment

axoplasm

cytoplasm inside the axon

axolemma

membrane surrounding the axon

axon collateral

a branch coming off the axon

terminal arborization

branching at the end of the axon

axon terminal

end of a branch that communicates with the next cell

synapse

junction where a neuron communicates with another cell

Chromatophilic substance

dark staining materal in the cell body associated with rough ER; helps with protein production

multipolar neuron

one axon and multiple dendrites; most common type in body, most neurons in CNS

bipolar neuron

one axon and one dendrite; examples

include olfactory cells, some neurons of retina, sensory neurons of ear

unipolar neuron

single process leading away from cell

body, splits into peripheral process and central process

• Both processes comprise the axon; only short receptive endings of

peripheral process are considered dendrites

anaxonic neuron

many dendrites but no axon; found in brain, retina, and adrenal gland

mature neuron

generally cannot divide through mitosis because they lack centrioles, although neural stem cells in certain areas can divide.

axonal transport

two way passage of material along an axon

anterograde transport

Cell body → axon terminal

motor protein: kinesin

sends materials away from the cell body, such as proteins and ion channels

retrograde transport

direction: Axon terminal → cell body

motor protein: dynein

returns materials towards the cell body for recycling or disposal

rabies virus

bypasses CNS defenses by infecting the CNS though retrograde transport - the virus is transported back to the CNS from the infected nerve

neuroglia (glial cells)

are support cells that help neurons function properly. they support and protect neurons, maintain the environment around them, and help with myelin formation

Oligodendrocytes

found in the CNS

form myelin sheaths in CNS

Make myelin around axons in the CNS. One cell can wrap sections of multiple axons.

Ependymal cells

found in the CNS

line internal cavities of brain; secrete and circulate cerebrospinal fluid

Line the internal spaces of the brain and help produce and circulate cerebrospinal fluid (CSF).

Microglia

found in the CNS

macrophages; engulf debris, provide defense against pathogens

Act like immune defense cells. They engulf debris and help defend against pathogens.

astrocytes

found in the CNS

most abundant type'; wide variety of functions

Provide structural support, help maintain the blood-brain barrier, regulate the chemical environment, support neurons' energy needs, and form scar tissue after damage.

Schwann cells (neurolemmocytes)

found in the PNS

Wrap around PNS axons, produce myelin, and help damaged peripheral axons regenerate.

satellite cells

found in the PNS

surround nerve cell bodies in ganglia of PNS; provide insulation around cell body and regulate chemical environment

tumors

masses of rapidly dividing cells

arise from meninges, metastasis, and glial cells that are mitotically active throughout life

Gliomas

tumors of glial cells; grow rapidly and are highly malignant

myelin sheath

is a fatty insulating covering around certain axons. It helps nerve signals travel more efficiently.

is approximately 80% lipid and 20% protein

• In the PNS, Schwann cells wrap repeatedly around a section of one axon.

• In the CNS, an oligodendrocyte can extend processes to myelinate sections of multiple axons.

myelination

the process of creating myelin

nucleus cannot migrate around the axon like a Schwann cell does

neurilemma

thick, outermost coil

containing its nucleus and most of its cytoplasm

myelin sheath gap (node of Ranvier)

gap between segments

internodal segments

myelin-covered segments

Portion of an axon covered by myelin between nodes

initial segment

bare section of axon between the axon hillock and the first glial cell

trigger zone

axon hillock and initial segment of axon

Plays important role in initiating nerve signal (the action potential)

multiple sclerosis

• The myelin sheaths and oligodendrocytes in the CNS deteriorate.

• Nerve signal conduction becomes disrupted.

• Symptoms described in the slides include double vision, tremors, numbness, and speech difficulties.

• The slides describe a possible autoimmune cause.

Tay-sachs disease

• An inherited disorder involving the abnormal accumulation of a glycolipid called a ganglioside.

• The material normally gets broken down by a lysosomal enzyme.

• Without the necessary enzyme, the buildup interferes with nerve signal conduction.

• The slides describe blindness, loss of coordination, and dementia as possible effects.

unmyelinated axons

may be enclosed by a Schwann cell, but does not have the multilayered myelin wrapping.

nerve regeneration

the damaged part degenerates

the cel body reacts

new growth processes form

a regeneration tube guides growth

connections are re-established