Test 3 The Nervous System Flashcards
what does the nervous system do?
continuously monitors and processes sensory information both from the external environment and from within the body
Three overlapping function of the nervous system
1) Sensory receptors monitor changes (stimuli) inside and outside of
the body
-Gathered information: sensory input
2) Processes and interprets sensory input (integration)….makes
decisions.
3) Dictates a response by activating effector organs (motor output
• The central nervous system (CNS)
is
the integrating and command
center. It consists of the brain and
spinal cord
• The peripheral nervous system
(PNS) consists of
nerves extending from the brain (cranial nerves) and spinal cord (spinal nerves). The PNS links all regions of the body to the CNS
Sensory
(afferent- “carrying toward”) signals picked up by sensor
receptors and carried by nerve fibers of the PNS into the CNS.
• Motor
(efferent- “carrying away”) signals are carried away from
the CNS. (Innervates muscles and glands)
both sensory inputs and motor outputs are also subdivided according to the body regions they serve
- somatic body region
- visceral body region
somatic body region
structures
external to the ventral body
cavity (skin, skeletal musculature,
bone
visceral body region
the viscera
within the ventral body cavity
(digestive tube, lungs, heart,
bladder, etc.)
functional organization of the PNS results in four main subdivisions
- somatic sensory
- visceral sensory
- somatic (voluntary) motor
- visceral (involuntary) motor
somatic sensory
the sensory innervation of the of the outer part of
the body
visceral sensory
the sensory innervation of the viscera
somatic (voluntary) motor
he motor innervation of the outer tube;
specifically skeletal muscles
visceral (involuntary) motor
the motor innervation of the inner
tube; specifically smooth muscle, cardiac muscle, and glands)
basic division of the nervous system
- somatic sensory
- visceral sensory
- somatic motor
- visceral motor
somatic sensory
- general somatic senses
- proprioceptive senses
- special somatic senses
general somatic senses
senses whose receptors are widely spread throughout the outer part of the body (touch, pain, vibration, pressure, and temperature)
proprioceptive senses
detect
stretch in tendons and muscles; give
body sense of position and movement
of body in space
special somatic senses
hearing, balance, vision and smell
visceral sensory
- general visceral senses
- special visceral senses
general visceral senses
stretch, pain, temperature, nausea, and hunger; widely felt in digestive and urinary tracts, reproductive organs, and other viscer
special visceral senses
taste
somatic motor
- general somatic motor
general somatic motor
signals contraction of skeletal muscles
- under our voluntary control
- often called “voluntary nervous system”
visceral motor consists of
general visceral motor
general visceral motor
Regulates the contraction of
smooth and cardiac muscle
and secretion from glands;
-makes up autonomic nervous system (ANS);
-controls function of visceral organs; - often called “involuntary nervous system”
cells are
densely packed and intertwined
nervous tissue is composed of two main cell types
neurons support cells (glial cells)
neurons
excitable nerve cells that transmit electrical signal
support cells (glial cells)
non excitable cells that surround and wrap the neurons
neurons
- nerve cells
- the basic structural units of the nervous
system. - They are specialized cells that conduct electrical impulses
along their plasma membrane. - Neurons send and receive signal
other special characteristics of neurons
a) Longevity
b) Do not divide: fetal neurons lose their ability to undergo mitosis
c) High metabolic rate (requires an abundant amount of oxygen and
glucose)
all neurons have a?
a cell body (soma or perikaryon )…cytoplasm
contains a single nucleus and the usual organelle
chromatophilic or nissl bodies
clusters of rough ER and
free ribosomes that stain darkly
and renew membranes of the cell
neurofibrils
bundles of
intermediate filaments; form a
network between chromatophilic
bodies
where are most neuronal cell bodies located?
within the CNS and
protected by bones of the skull and vertebral column
ganglia
clusters of cell bodies not in CNS
- lie along nerves in the PNS
neuron processes extend from the?
cell bodies of all neurons
two types of processes
axons and dendrites
dendrites
(dendro = “tree”) branch from the cell body:
- All organelles that occur in the cell body also occur in the dendrites
- Bear receptors for neurotransmitters released by other neurons.
- Transmit electrical signals toward the cell body
axons
- neurons has only one
- Transmits impulses away from the cell body; no protein synthesis in
axon
function of neurofilaments, actin microfilaments, and microtubueles
provide
structural strength along length of axon; aid in the transport of
substances to and from the cell body
axon
• Axons: -Branches (axon collaterals) along length are infrequent -Multiple branches at the end of an axon called terminal branches (telodendria). These end in knobs called axon terminals. These store a neurotransmitter chemical in tiny vesicles.
neurotransmitters (NT)
chemical messenger molecules
that excite or inhibit neurons
Some examples of neurotransmitter action
- acetylcholine
- norepinephrine
- dopamine
- serotonin
- GABA
- glycine
- neuromodulars
acetylcholine
Some examples of neurotransmitter action
norepinephrine
wakefulness or arousal
dopamine
voluntary movemenet and motivation
- wanting pleasure, associated with addiction and love
serotonin
memory, emotion, wakefulness, sleep a nd temperature regulation
GABA
inhibition of motor neurons
neuromodulators
sensory transmission - especially pain
synapse
- Site at which neurons communicate
- Signals pass across synapse in one direction
each axonal terminal is
separated from the cell body or dendrites of
the next (postsynaptic) neuron by a tiny gap called the synaptic cleft
(synapse). Therefore… there is no physical contact between neurons.
what are the several types of synapse
- axodendritic synapses
- axosomatic
- less common: Axoaxonic, dendrodendritic, and dendrosomatic
axodendritic synapse
: between axon terminals of one neuron and
dendrites of another; most common type of synapse
axosomatic
between axon terminals of one neuron and neuronal
cell bodies of another
when an impulse reaches the axonal terminals, some of the synaptic vessicles
rupture and release neurotransmitter into the synaptic cleft,
which diffuses across the synaptic cleft to bind to membrane receptors
on the next neuron.
neurons conduct
electrical signals along the length of their plasma membrane
resting (unstimulated) neuron
The
membrane is polarized…the inner
cytoplasmic side is negatively charged
with respect to the extracellular side.
depolarized neuron
When a neuron is stimulated, the permeability of the plasma membrane changes at the site of the stimulus, allowing positive ions to rush in. As a result, the inner face of the membrane becomes less negative
action potentials (AP) on axons
-Strong stimulus applied to the axon triggers a nerve impulse or
AP
-Membrane becomes negative externally; Impulse travels the
length of the axon
-Membrane repolarizes itself
structural classification depends on?
the number of processes off cell body
- multipolar
- bipolar
- unipolar
multipolar
possess more than two processes; numerous dendrites
and one axon; most numerous type (99% +)
bipolar
possess two processes extending from opposite sides of
body; rare neurons…found in some special sensory organs
unipolar
- pseudounipolar
- possess one short emerging from cell
body that divides like an inverted T into two long branches, start as
bipolar neurons during development
neurons are grouped functionally according to the direction the nerve impulse travels relative to CNS
- sensory (afferent) neurons
- motor (efferent) neurons
- interneurons (association neurons)
sensory (afferent) neurons
transmit impulses toward the CNS;
virtually all are unipolar neurons; cell bodies in ganglia outside the
CNS; have short, single process divides into (1) central process –
runs centrally into the CNS and (2) peripheral process – extends
peripherally to the receptors
motor (efferent) neurons
carry impulses away from the CNS to
effector organs; most motor neurons are multipolar; cell bodies are
within the CNS; form junctions with effector cells
interneurons ( association neurons)
most are multipolar; lie
between motor and sensory neurons; confined to the CNS
supporting cells
nonexcitable cells that surround and wrap the
neurons
-Six types of supporting cells: a) 4 in the CNS and b) 2 in the PNS
function of supporting cells
provide a supportive scaffolding for neurons and
insulate the non-synaptic parts of neurons
the supporting cells in the CNS are collectively called?
neuroglia (nerve glue) or glial cells
the supporting cells in the CNS are
- Cells have branching processes and a central cell body
- Outnumber neurons 10 to 1; make up half the mass of the brain
- Can divide throughout life
- Small size and darkly staining nucle
types of neuroglial cells
cells: astrocytes, microglia, ependymal cells,
oligodendrocytes
astrocyte
most abundant glial cell type
-Take up and release ions to control the environment around
neurons
-Recapture and recycle neurotransmitters (e.g. glutamate)
-Involved with synapse formation in developing neural tissue
-Produce molecules necessary for neural growth
-Propagate calcium signals that may be involved in memory
microglia
smallest and least abundant
-They are the phagocytes and macrophages of the CNS…engulf
invading microorganisms and dead neurons; derived from blood
cells called monocytes
ependymal cells
(“wrapping garment”): Forms a simple epithelium
that lines the central cavity of the spinal cord and brain.
-Have cilia to help circulate the cerebrospinal fluid
oligodendrocytes
Oligodendrocytes (“few branched cells”): Have few branches than
astrocytes
-Wrap their cell processes around thicker axons in CNS
-Produce myelin sheaths
the two kinds of supporting cells in the PNS
satellite cells and
Schwann cells…similar cell types that differ in location
satellite cells
surround neuron cell bodies wtihin ganglia
schwann cells
-neurolemmocytes
- surround all axons in the
PNS and form myelin sheaths
myelin sheaths
segmented structures composed of the lipoprotein myelin -Forms an insulating layer -Increases the speed of impulse conduction
myelin sheaths are produced by?
Produced by oligodendrocytes
(CNS) and Schwann cells (PNS
myelin sheaths in the PNS
Myelin is formed by Schwann cells,
which wrap in concentric layers around the axon… creating a tightly
packed coil of membranes
since the myelin sheath is formed by many individual schwann cells, its a?
a discontinuous sheath separated by gaps called Nodes of
Ranvier
the structure of a neuron: neurilemma
During the wrapping process
the cytoplasm is squeezed from
between adjacent layers of the Schwann cell membranes…so that a
tight core of plasma membrane material encompasses the axon.
- This wrapping is called the myelin
sheath.
The Schwann cell nucleus and the bulk
of its cytoplasm ends up
just beneath the
outermost portion of its plasma membrane
The peripheral part of the Schwann cell
and its exposed plasma membrane is called
the neurilemma (sheath of Schwann).
Myelin Sheaths in the CNS
Oligodendrocytes form the myelin
sheaths in the brain and spinal cord
- In contrast to Schwann cells, each oligodentrocyte has multiple
processes that coil around several different axons
nerves
cordlike organs in the PNS;
consists of numerous axons (nerve
fibers) arranged in parallel bundles
wrapped in C.T
within a nerve, each axon is surrounded by?
Schwann cells, then a
layer of loose C.T. called endoneurium.
nerve fascicles
groups of axons
bound into bundles
perineurium
C.T. wrapping
surrounding a nerve fascicl
epineurium
whole nerve is
surrounded by tough fibrous sheath
reflex arcs
simple chains of neurons that explain reflex behaviors
and determine the basic structural plan of the nervous system.
-Responsible for reflexes…rapid,
automatic motor responses to
stimuli
reflex arcs can be either?
Can be either somatic reflexes resulting in the contraction of skeletal muscles or viceral reflexes activating smooth muscle, cardiac, or glands
• Every reflex arc has five essential components, each of which
activates the nex
receptor, sensory neuron, integration center, motor neuron, effector
receptor
site where stimulus acts
sensory neuron
transmits
afferent impulses to the CNS
integration center
consists
of one or more synapses in the
CNS
motor neuron
conducts
efferent impulses from
integration center to an effector
effector
muscle or gland
cell; responds to efferent
impulses; contracting or
secreting
types of reflexes
- monosynaptic reflex
- polysynaptic reflex
monosynaptic reflex
: simplest of all reflexes
-Just one synapse = fastest of all reflexes; example – knee-jerk
reflex
polysynaptic reflex
more common type of reflex
-Most have a single interneuron between the sensory and motor
neuron; example – withdrawal reflexes
CNS is divided into regions of?
gray matter and white matter
gray matter in the spinal cord
H-shaped region surrounds central cavity -Dorsal half contains cell bodies of interneurons -Ventral half contains cell bodies of motor neurons -Cell bodies are clustered in the gray matter
white matter in the spinal cord
located externally to the gray matter -Contains no neuronal cell bodies, but millions of axons -Myelin sheath…white color and consists of axons running between different parts of the CNS
tracts
bundles of axons
traveling to similar
destinations
