Ch. 10 Anatomy

larger axons of peripheral neurons are encased in lipid-rich sheaths formed by layers of cell membranes of neuralgia cells called (wind tightly like a bandage around a finger; layers composed of myelin); enclose but do not wind around smallest axons of peripheral neurons, so these axons lack myelin sheath

Schwann cells

every neuron has 3 features

a cell body, many dendrites, and one axon

what surrounds the myelin sheath?

a neurilemma

axon's membrane is changing in sodium permeability and cannot be stimulated; sodium channels are still open

absolute refractory period

if a neuron responds at all, it responds completely

all-or-none response

star-shaped cells; found between neurons and blood vessels; aid in metabolism, regulate concentrations of ions, respond to injury of brain tissue, form special type of scar tissue, filling spaces in CNS; nutritive; blood-brain barrier

astrocytes

CNS contains 4 types of neuroglial cells

astrocytes, oligodendrocytes, microglia, ependyma

(motor portion of peripheral nervous system) controls viscera, such as the heart and various glands, and thus controls subconscious (involuntary actions)

autonomic nervous system

longer process that carries the information away from the cell in the form of bioelectric signals; arises from slight elevation of the cell body

axon

an axon may have many fine extensions, each with a specialized ending called an

axon terminal

process in which an axon conveys biochemicals that are produced in the neuron cell body

axonal transport

two processes, one on either end; processes similar in structure but one is an axon and the other is a dendrite; found in eyes, nose, and ears

bipolar neurons

classification of neurons on structural differences

bipolar, unipolar, multipolar

brain and spinal cord

central nervous system

many membranous packets scattered throughout the cytoplasm

chromatophilic substance (Nissl bodies)

axons give off these branches

collaterals

small cellular process that receive the input; highly branched, providing receptive surfaces to which processes from other neurons communicate

dendrites

responsive structures that receive impulses from CNS carried by motor functions; outside nervous system; muscles and glands

effectors

cuboidal or columnar in shape and may have cilia; form inner lining of the central canal that extends downward through spinal cord; form a one-cell-thick epithelial-like membrane that covers the inside of spaces within the brain called ventricles; cover choroid plexuses (specialized capillaries) that are associated with ventricles of the brain; regulate composition of cerebrospinal fluid

ependyma

sensory input

gathers info; monitor changes occurring inside and outside the body; convert their info into nerve impulses, peripheral nerves to CNS, signals integrated, decisions

cell body contains

granular cytoplasm, organelles, and microtubules

lie within brain or spinal cord; multipolar and form links between other neurons; transmit impulses from one part of the brain or spinal cord to another; they may direct incoming sensory impulses to appropriate regions for processing and interpreting

interneurons (association or internuncial neurons)

smallest and fewest processes; scattered throughout the central nervous system; support neurons and phagocytize bacterial cells and cellular debris; increase when brain or spinal cord is inflamed due to injury or disease

microglia

multipolar and carry nerve impulses out of the brain or spinal cord to effectors (structures that respond, such as muscles or glands); when motor impulses reach muscles, they contract; when motor impulses reach glands, they release sections) 2 specialized groups: accelerator (increase muscular activities) and inhibitory (decrease muscular activities) neurons

motor neurons

have many processes; only one is an axon; the rest are dendrites; most of the neurons whose cell bodies lie within the brain or spinal cord

multipolar neurons

has a higher proportion of lipid than other surface membranes;

myelin

coating on Schwann cells; lipid-rich covering of the axon

myelin sheath

axons that have myelin sheaths (appears white)

myelinated axons

bioelectric signals

nerve impulses

bundles of axons

nerves

nervous system is composed predominantly of

neural tissue; blood vessels and connective tissue

surrounds myelin sheath; portions of Schwann cells that contain most of the cytoplasm and the nuclei remain outside the myelin sheath to comprise a ___

neurilemma (neurilemmal sheath)

a network of fine threads that extends into the axons and supports them

neurofibrils

specialized to react to physical and chemical changes in their surroundings

neurons

neural tissue consists of two cell types

neurons (nerve cells) and neuroglial

neuroglial cells guide

neurons to their positions and may stimulate them to specialize; also signal neurons to form and maintain synapses

biological messenger molecules that actually carry information

neurotransmitters

narrow gaps in the myelin sheath between Schwann cells

nodes of Ranvier

small; few processes; rows along myelinated axons, form myelin in the brain and spinal cord; can send out a number of processes, each of which forms a myelin sheath around a nearby axon; a single one provides myelin for many axons; do not form neurilemma

oligodendrocytes

composed of the nerves (cranial and spinal) that connect the central nervous system to other body parts

peripheral nervous system

short time following a nerve impulse that a threshold stimulus will not trigger another impulse

refractory period

the membrane reeestablishes its resting potential; a threshold stimulus of high intensity may trigger an impulse

relative refractory period

carry nerve impulses from peripheral body parts into the brain or spinal cord; have specialized receptor ends at the tips of their dendrites OR have dendrites that are near receptor cells in the skin or in certain sensory organs; changes that occur inside or outside the body stimulate receptor cells, triggering sensory nerve impulses, which travel on axons into the brain or spinal cord

sensory neurons (afferent neurons)

classification of neurons on functional differences (depending on whether they carry info into the CNS, completely within the CNS, or out of the CNS)

sensory neurons, interneurons, motor neurons

at ends of peripheral neurons; provide sensory function

sensory receptors

three general functions

sensory, integrative, and motor

neurofibrils support fibers in the

soma

(motor portion of peripheral nervous system) involved in conscious (voluntary) activities, such as skeletal muscle contraction

somatic nervous system

small spaces between neurons

synapses

space that separates synaptic knobs very close to the receptive surface of another cell (at terminal, separated from another receptive surface by __)

synaptic cleft

neuralgia cells produce

the growth factors that nourish neurons and remove ions and neurotransmitters that accumulate between neurons, enabling them to continue transmitting info

each type of neuron is specialized to send a nerve impulse in one direction, originating at a sensitive region of the axon called the

trigger zone

a single process that divides into 2 branches, which function as a single axon (one branch (peripheral process) is associated with dendrites near a peripheral body part; the other branch (central process) enters the brain of spinal cord); aggregate in specialized masses of nerve tissue called ganglia

unipolar neurons

axons that lack myeline sheaths (appears gray)

unmyelinated axons