The nervous system

McGraw Hill terms

Central nervous system (CNS)

Consists of the brain and spinal cord

Peripheral nervous system (PNS)

consists of all the nervous system except the brain & spinal cord

Nerve

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

Ganglion

knotlike swelling where the cell bodies of neurons are concentrated

PNS

this system has sensory & motor neurons

CNS

this system has only motor neurons

sensory (afferent)

this division signals are carried from receptors to the CNS

somatic sensory

this division carries signals from receptors in the skin, muscles, bone, & joints

visceral sensory

this division carries signals from the viscera (organs)

motor (efferent)

this division carries signals from the CNS to effectors (glands & muscles)

somatic motor

this division carries signals to the skeletal muscles

visceral motor (ANS)

this division carries signals to glands, cardiac, and smooth muscle

-has two further subdivisions: sympathetic & parasympathetic

ANS

this division has two further subdivisions: sympathetic & parasympathetic

sympathetic

which ANS subdivision?

tends to arouse the body for action

parasympathetic

which ANS subdivision?

adapts the body for energy intake and conservation

excitability (irritability), conductivity, secretion

the physiological properties of a neuron are:

excitability

the ability of a neuron to respond to environmental changes called stimuli

conductivity

when neurons respond to stimuli by producing traveling electrical signals that can reach other cells at distant locations

Secretion

occurs when the electrical signal reaches the end of a nerve fiber, the neuron will secrete a chemical called neurotransmitter that crosses a small gap between cells and stimulated the next cell

sensory (afferent) neurons

this type of neuron:

detects stimuli

(PNS)

interneurons (association neurons)

this type of neuron:

receives signals from other neurons

Integration (process, store, retrieve) (make decisions)

(CNS)

motor (efferent) neurons

this type of neuron:

responds to stimuli

(PNS)

multipolar

which neuron type is the most common?

-includes most neurons of the brain & spinal cord

multipolar neuron

this neuron has:

one axon, 2 or more dendrites

bipolar neuron

this neuron has:

1 axon, 1 dendrite

-e.g., cells of nasal cavity, neurons of retinal & inner ear

unipolar neuron

this neuron has:

ONLY a single process leading away from the body

-e.g., carry sensory signals to spinal cord

Anaxonic neuron

this neuron has:

multiple dendrites but no axon

(communicates over short distances)

-e.g., found in brain, retina, & adrenal medulla

Oligodendrocytes

which glial cell?

bulbous body with armlike processes

each process reaches out to a nerve fiber & wraps around it with a myelin sheath

Ependymal cells

which glial cell?

cubed shaped cells

line internal cavities of the brain & spinal cord (CNS)

produce cerebrospinal fluid (CSF)

some have patches of cilia to help circulate CSF

Microglia

which glial cell?

small macrophages

develop from stem cells

wander through CNS

perform check on brain tissue

detect foreign particles and get rid of them

concentrated in damaged areas (infection, trauma, or stroke)

Astrocytes

which glial cell?

most abundant glial cells

CNS

form a hardened scar tissue to fill spaces when neruons are damaged (sclerosis)

regulate the chemical composition of tissue fluid

secrete proteins called nerve growth factors that promote neruon growth & synapse function

communicating electrically with neurons

form a supportive framework for nervous tissue

form tight seal called the blood-brain barrier

convert glucose to lactate & supply neurons for nourishment

Schwann Cells

which glial cell?

occur in PNS

envelope nerve fibers of PNS, form a sleeve called neurilemma

wind repeatedly around nerve fibers forming a myelin sheath

assist in regeneration of damaged fibers

Satellite cells

surround neurosomas in ganglia of PNS

provide electrical insulation around soma & regulate the chemical environment of neurons

glial cells

what are most adult brain tumors composed of?

nodes of Ranvier

gaps between the segments in the myelin sheath

internodes

myelin covered segments from 1 gap to the next

diverging circuit

one nerve fiber synapses with several postsynaptic cells

-input from 1 neuron may produce output through dozens more

converging circuit

opposite of a diverging circuit, input from many different sources is funneled to 1 neuron or neuronal pool

reverberating circuit

neurons stimulate each other in a linear sequence and also circle around and restimulate the process producing a repetitive output

parallel after discharge circuit

input neuron diverges to stimulate several chains of neurons

-each chain has a different number of synapses, but they all reconverge on the same output neuron

spina bifida

occurs when 1 or more vertebrae fail to form a complete neural arch for enclosure of spinal cord

spina bifida occulta

one to a few vertebrae

no functional problems

(only external sign is a dimple or patch of hairy pigmented skin on low back)

spina bifida cystica

sac protrudes from the spine (may contain parts of spinal cord & nerve roots, meninges, and CSF)

more severe

cystica

Which spina bifida type is the worst?

anencephaly

no brain

microcephaly

small brain

L1

where does the spinal cord end?

dura mater, arachnoid mater, pia mater

What are the meninges from superficial to deep?

(D.A.P)

White matter

which one? Gray or White matter?

myelinated axons

bundles of axons (tracts)

Gray matter

which one? Gray or White matter?

Little myelin

somas, dendrites, proximal axons

Endoneurium

Connective tissue that surrounds individual axons

Perineurium

Surrounds bundles of axons forming fascicles

Epipneurium

Encloses the entire nerve

Chickenpox

caused by varicella-zoster virus

-produces an itchy rash that usually clears up without complications

-virus remains for life in posterior root ganglion, but kept in check by immune system

Quadriplegia

paralysis of all four limbs

paraplegia

paralysis of both lower limbs

hemiplegia

paralysis on one side of body

Spinal tap

a way to diagnose neurological diseases by examining CSF for bacteria, blood, and white blood cells, or abnormal chemical composition

L3, L4; L4, L5

A spinal tap is usually inserted between the spinous processes of _____-_____ or _____-_____.

Poliomyelitis (Polio)

skeletal muscles atrophy from lack of innervation

destruction of motor neurons in the brainstem & anterior horn of the spinal cord

signs: muscle pain, weakness, loss of some reflexes, paralysis, muscular atrophy, & sometimes respiratory arrest

ALS (Lou Gehrig’s disease)

astrocytes fail to reabsorb the neurotransmitter glutamate, allowing it to accumulate to a neurotoxic level

degenerates motor neurons, atrophies muscle, and sclerosis (scars) lateral regions of the spinal cord

signs: muscle weakness, difficulty speaking, swallowing, and using the hands

sensory & intellectual functions remain unaffected