Anatomy and Physiology lecture exam 3 powerpoint 1

nervous system

employs electrical and chemical means to send messages from cell to cell

nervous system (three basic steps): step 1

sensory organs receive information about changes in the body and the external environment, and transmits coded messages to the spinal cord and the brain

nervous system (three basic steps): step 2

brain and spinal cord processes this information, relates it to past experiences, and determines what response is appropriate to the circumstances

nervous system (three basic steps): step 3

brain and spinal cord issue commands to muscles and gland cells to carry out a response

the nervous system is always ______

monitoring structures inside the body and aspects of the external environment

two major anatomical subdivisions of the nervous system

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

central nervous system (CNS)

brain and spinal cord enclosed in body coverings, enclosed by cranium and vertebral column

peripheral nervous system (PNS)

all the nervous system except the brain and spinal cord

what two things is the peripheral nervous system composed of

nerves and ganglia

nerve

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

ganglion

a knot-like swelling in a nerve where neuron cell bodies are concentrated

two subdivisions of nervous system (damage)

CNS: brain and spinal cord, any damage is permanent and cannot be reversed
PNS: can repair themselves after damage

afferent

bringing something (information) in

sensory division

afferent, carries sensory signals from various receptors to the CNS

Sensory Division of PNS - function

informs the CNS of stimuli within or around the body

somatic sensory division

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

visceral sensory division

carries signals from the viscera (organs) of the thoracic and abdominal cavities (heart, lungs, stomach, and urinary bladder)

efferent

taking information (out) from the CNS

motor division

efferent, carries signals from the CNS to gland and muscle cells that carry out the body's response

somatic motor division

carries signals to skeletal muscles (voluntary), output produces muscular contraction as well as somatic reflexes (involuntary muscle contractions)

Visceral motor division - another name

autonomic nervous system (ANS)

visceral motor division

carries signals to glands, cardiac muscle, and smooth muscle - involuntary, and responses of this system and its receptors are visceral reflexes

two subdivisions of the visceral motor division

sympathetic division (fight or flight)
parasympathetic division (relax and digest)

sympathetic division (fight or flight)

tends to arouse body for action, accelerating heart beat and respiration, while inhibiting digestive and urinary systems

parasympathetic division (relax and digest)

tends to have calming effect, slows heart rate and breathing, stimulates digestive and urinary systems

sensory division = a_____

afferent

motor division = e______

efferent

somatic motor division controls what

muscles

visceral motor division/autonomic nervous system controls what

organs

three universal properties of neurons

excitability, conductivity, secretion

excitability (irritability)

respond to environmental changes called stimuli

conductivity

neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations

secretion

when electrical signals reach end of nerve fiber, a chemical neurotransmitter is secreted and crosses the gap and stimulates the next cell

sensory (afferent) neurons

specialized to detect stimuli, transmit information about them to the CNS, begin in almost every organ in the body and end in the CNS, conduct signals towards the CNS

interneurons

lie entirely within the CNS, receive signals from many neurons and carry out the integrative function, 90% of all neurons are interneurons, lie between and interconnect the incoming sensory pathways and outgoing motor pathways of the CNS

interneurons integrative function

process, store, and retrieve information and 'make decisions' that determine how the body will respond to stimuli

motor (efferent) neuron

sends signals out to muscles and gland cells, most of them lead to muscles, conduct signals away from the CNS

three major structures of a neuron

soma, dendrites, and axon

soma

control center of the neuron, also called neurosoma or cell body

soma - nucleus

has a single, centrally located nucleus with a large nucleolus

soma - cytoplasm

contains mitochondria, lysosomes, a Golgi complex, extensive rough endoplasmic reticulum and cytoskeleton

Soma - cytoskeleton

consists of dense mesh of microtubules and neurofibrils (bundles of actin filaments)

dendrites

vast number of branches coming from a few thick branches from the soma

dendrites - function

primary site for receiving signals from other neurons, the more dendrites the neuron has the more information it can receive and incorporate into decision making, provide precise pathway for the reception and processing of neural information

axon (nerve fiber)

originates from a mound on one side of the soma called the axon hillock

axon - structure

cylindrical, relatively unbranched for most of its lenght

axon collaterals

branches of axon, branch extensively on distal end

axon - specialized

for rapid conduction of nerve signals to points remote to the soma

axoplasm

cytoplasm of the axon

axolemma

plasma membrane of axon

axon - how many per neuron

only one leaving the soma

what enclose the axon

Schwann cells (PNS) and myelin sheath (CNS)

axon - distal end

has terminal arborization - extensive complex of fine branches

axon - synaptic knob

terminal button - little swelling that forms a junction (synapse) with the next cell, contains synaptic vesicles full of neurotransmitters

three types of neuron structures

multipolar, bipolar, unipolar

multipolar neuron

one axon and multiple dendrites, most common, most neurons in brain and spinal cord

bipolar neuron

one axon and one dendrite (on each side), olfactory cells, retina, inner ear

unipolar neuron

single process leading away from the soma, soma is off to the side of the axon, sensory neurons from skin and organs to spinal cord, immediately sends signal from dendrite to axon

neurotransmitters

how neurons interact with each other

soma

where organelles are located (1 nucleus per neuron)

axonal transport

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

anterograde transport

movement down the axon away from the soma

retrograde transport

movement up the axon towards the soma

fast anterograde transport - examples

organelles, enzymes, synaptic vesicles, and small molecules

two types of axonal transport

fast and slow

fast retrograde transport - examples

for recycled materials and pathogens (polio, tetanus), delay between infection and symptoms is time needed for transport up the axon

slow axonal transport

always anterograde - moves enzymes, cytoskeletal components, and new axoplasm down the axon during repair and regeneration of damaged axons, damaged nerve fibers regenerate at a speed governed by slow axonal transport

neuroglial cells (glial cells)

support and protect the neurons, bind neurons together and form framework for nervous tissue, if mature neuron is not in synaptic contact with another neuron it is covered by glial cells - prevents neurons from touching, gives precision to conduction pathways

four types of glial cells in CNS

oligodendrocytes, ependymal cells, microglia, astrocytes

oligodendrocytes

form myelin sheaths in CNS, each arm-like process wraps around a nerve fiber forming an insulating layer that speeds up signal conduction

ependymal cells

lines internal cavities of the brain, cuboidal epithelium with cilia on apical surface, secretes and circulates cerebrospinal fluid (CSF) - a clear liquid that bathes the CNS

microglia

small, wandering macrophages formed from white blood cell called monocytes - perform a complete checkup on the brain tissue several times a day - wander in search of cellular debris to phagocytize

astrocytes

most abundant glial cell in CNS, cover entire brain surface and most nonsynaptic regions of the neurons in the gray matter of the CNS, diverse functions

astrocytes form what

supportive framework of nervous tissue

astrocytes have extensions - function

contact blood capillaries that stimulate them to form a tight seal called the blood-brain barrier (protection) - causes chemotherapy to be ineffective for the brain

astrocytes convert what

blood glucose to lactate and supply this to neurons for nourishment

astrocytes secrete what

nerve growth factors to promote neuron growth and synapse formation

astrocytes communicate ______

electrically with neurons and may influence synaptic signaling

astrocytes regulate what

chemical composition of tissue fluid by absorbing excess neurotransmitters and ions

astrocytes - scar tissue

astrocytosis and sclerosis - when the neuron is damaged, hardened scar tissue is formed and it fills space formerly occupied by the neuron

two glial cells in PNS

Schwann cells and satellite cells

Schwann cells

envelop nerve fibers in PNS, wind repeatedly around a nerve fiber, produces a myelin sheath similar to the ones produced by oligodendrocytes in the CNS, assist in the regeneration of damaged fibers

neurilemma

Schwann cells push organelles to the top of the cell - top layer

satellite cells

surround the neuromas in ganglia of the PNS, provide electrical insulation around the soma, regulate the chemical environment of the neurons

myelin sheath

an insulating layer around a nerve fiber, formed by oligodendrocytes in CNS and Schwann cells in PNS, consists of the plasma membrane of glial cells

myelin sheath - composition

20% protein and 80% lipid (phospholipid bilayer)

myelination

production of the myelin sheath

myelination - characteristics

begins 14th week of fetal development, proceeds rapidly during infancy, completed in late adolescence, dietary fat is important to nervous system development

health of myelination =

health of nervous system

Schwann cell - structure

spirals repeatedly around a single nerve fiber, lays down as many as a hundred layers of its own membrane, no cytoplasm between the membranes

neurilemma - characteristics

thick outermost coil of myelin sheath, contains nucleus and most of its cytoplasm

endoneurium

external to neurilemma is basal lamina and a thin layer of fibrous connective tissue

oligodendrocytes - myelin sheath

reaches out to myelinate several nerve fibers in its immediate vicinity, anchored to multiple nerve fibers, cannot migrate around any one of them like Schwann cells, must push newer layers of myelin under older ones - myelination spirals inward toward nerve fiber, no neurilemma or endoneurium

myelin - amount of cells needed

many Schwann cells or oligodendrocytes are needed to cover one nerve fiber - myelin sheath is segmented

nodes or ranvier

gap between myelin sheath segments

internodes

myelin covered segments from one gap to the next

initial segment

short section of nerve fiber between the axon hillock and the first glial cell

trigger zone

the axon hillock and the initial segment, play an important role in initiating a nerve signal

Two degenerative disorders of the myelin sheath

multiple sclerosis (MS) and tay-sachs disease

multiple sclerosis

autoimmune disorder - can be triggered by a virus