Download Nervous System

Nervous System
Objectives
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Explain the general functions (3 Functions) of the nervous system.
Identify the two main parts of the Nervous System
Describe the structure of a neuron and the function of each major part.
Distinguish between sensory neurons, motor neurons, and interneurons.
Summarize the electrical and chemical conditions of resting potential.
Outline the electrical and chemical changes during an action potential.
Explain the role of neurotransmitters in transmitting a signal across a
synapse.
Describe the role of sensory and motor divisions of the peripheral
nervous system.
Distinguish between the autonomic and somatic nervous systems.
Summarize a spinal reflex.
Introduction
The nervous system controls and coordinates all
essential functions of the human body.
► The Nervous System has 3 main functions
►
1. SENSORY FUNCTION – gather information and
transmit to brain and spinal cord
2. INTEGRATIVE FUNCTION - Processes the
information to determine the best response.
3. MOTOR FUNCTION - Sends information to muscles,
glands, and organs (effectors) so they can respond by
muscular contraction or glandular secretions.
Divisions of the Nervous System
► Central Nervous System
 Consists of the Spinal Cord and Brain
 Spinal cord carries messages to the brain where they are
analyzed and interpreted
 Response messages are sent from the brain to the spinal
cord and the rest of the body

Peripheral Nervous System
 Consists of the neurons not found in the brain and spinal
cord
 Divided into 2 divisions: Sensory and Motor
 Afferent Neurons – Collect info and send it toward the CNS
 Efferent Neurons – Transmit info away from the CNS
The Vertebrate Nervous System
LE 48-3
Sensory input
Sensor
Integration
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
LE 48-4
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Neuron Structure
Schwann Cell
►
►
►
Neurons are the basic functional units of the nervous
system
All consist of a cell body, dendrites, and one axon
Messages take the form of electrical signals known as
impulses – Neurons carry impulses in one direction
Types of Neurons
► Sensory
Neurons
 Carry messages from sense organs to the CNS
 Receptors detect stimuli from external or internal
changes and send info to CNS by way of Afferent
neurons

Motor Neurons
 Carry impulses from the CNS to muscles and glands

Interneurons
 Connect Sensory and Motor Neurons
 Found entirely in the CNS
Anatomy of a Neuron
►
►
Neuron Video
Cell Body
 Contains nucleus and most of the cytoplasm
 Site of most of the metabolic activity including ATP production and
protein synthesis
►
Dendrites
 Short branch extensions spreading out from the cell body.
 Receive impulses (action potentials) and carry them toward
the cell body
►
Axon
 Carries action potential away from the cell body
 Each neuron only has one axon
 Axon ends with a series of swellings called axon terminals
Anatomy cont.
► Myelin
Sheath
 Lipid layer that insulates the axon
 Speeds up the transmission of action potentials
 Multiple Sclerosis Video
► Schwann
Cells
 In peripheral nervous system
 Produce the myelin that surrounds the axon
► Nodes
of Ranvier
 Gaps in the myelin sheath along the axon

Synapses
 Point of contact where impulses are passed from one
neuron to another
Supporting Cells (Glia)
► Glia
are essential for structural integrity of the
nervous system and for functioning of neurons
► Types of glia: astrocytes, radial glia,
oligodendrocytes, and Schwann cells
► In the CNS, astrocytes provide structural support
for neurons and regulate extracellular
concentrations of ions and neurotransmitters
Nerve Impulses
►
Resting potential --70 mV potential
 In a non-conducting neuron
 Result of an imbalance of charged
particles (ions) between the extracellular
and the intracellular fluids – positive
charge on the outer surface and negative
on inner surface
Remember the Na/K pump?
Well, if not…
 Mechanism
for Resting potential
1.Na/K pump pumps 3 Na+ ions to the outside
while bringing in 2 K+ ions
2.Cell membrane is more permeable to K+ than to
Na+ so that K+ diffuses out faster than Na+
diffuses in
3.Cell membrane is basically impermeable to large
negatively charged anions present inside the
neuron, therefore fewer negative particles move
out than positive
Resting Potential
ION CONCENTRATION
Action Potential
►
►
Nerve impulses carry info from one point
of the body to another by progression
along the neuron membrane of an abrupt
change in resting potential.
This traveling disturbance is called an
action potential.
ACTION POTENTIAL ANIMATION
LE 48-10
CYTOSOL
EXTRACELLULAR
FLUID
[Na+]
15 mM
[Na+]
150 mM
[K+]
150 mM
[K+]
5 mM
[Cl–]
[Cl–]
120 mM
10 mM
[A–]
100 mM
Plasma
membrane
LE 48-11
Inner
chamber
–92 mV
Outer
chamber
150 mM
KCl
Inner
chamber
15 mM
NaCl
5 mM
KCl
+62 mV
Outer
chamber
150 mM
NaCl
Cl–
K+
Potassium
channel
Cl–
Na+
Sodium
channel
Artificial
membrane
Membrane selectively permeable to K+
Membrane selectively permeable to Na+
Steps of Action Potential
1. A stimulus (chemicalelectrical-mechanical) is
sufficient to alter the
resting membrane
potential
2. The membrane’s
permeability to Na+
increases at the point
of stimulation
3. Na+ moves into the cell
rapidly; the membrane
becomes locally
depolarized
3
2.
1.
4. Na+ continues to
move inward;
inside of cell
becomes
positively charged
relative to outside
(reverse
polarization or
depolarization)
5. Reverse
polarization at
original site acts
as a stimulus to
adjacent region of
membrane
4
3
5
2.
1.
Action Potential cont.
6. At the point originally stimulated, the
membrane’s permeability to sodium
decreases, and its permeability to K+
increases.
7. K+ rapidly moves outward, again making the
outside of the membrane positive in relation
to the inside (repolarization)
8. Na+/K+ pumps transport Na+ back out of,
and K+ back into the cell. The cycle repeats
itself, traveling in this manner along the
neuron membrane.
Threshold Stimulus
 An
action potential is produced in response
to a threshold stimulus.
 Resting potential is about -70mV
 If the stimulus raises the potential to -55mV, a
threshold potential has been reached
 Complete depolarization and repolarization
occur and an action potential is generated
Impulses cont.
►
An impulse is self-propagating – once it starts it continues,
and moves in one direction
Impulses cont.
Synapse and Synaptic Transmission
►
1.
2.
3.
4.
5.
6.
AP reaches the axon terminal
Influx of Ca2+ causes synaptic vesicles with neurotransmitter to
fuse with presynaptic membrane
Neurotransmitter is released by exocytosis into synaptic cleft
Neurotransmitter binds to receptors in postsynaptic membrane
Permeability of postsynaptic membrane is altered initiating on
impulse on the second neuron
Neurotransmitter is removed from the synapse (reuptake)
Refractory Period
►


A period when a neuron is unable to conduct an impulse
Na+/K+ pumps are restoring the resting potential
SYNAPSE FUNCTION VIDEO
LE 48-17
Presynaptic
cell
Postsynaptic cell
Synaptic vesicles
containing
neurotransmitter
Na+
K+
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
Ca2+
Synaptic cleft
Ligand-gated
ion channels
Neurotransmitters
► Ach
- acetylcholine
► Norepinephrine
► Epinephrine
► Dopamine
► Serotonin
► GABA
► Derived
acids
from amino
Neuroglia
► Make
up more than half the volume of the
vertebrate nervous system
►A
variety of cells that metabolically assist,
structurally support, and protect the
neurons
Fig. 34-14, p.583
Peripheral Nervous System
►
►
All nerves not in the spinal cord and brain
Sensory Division (Afferent)
 Transmits impulses from the sense organs (e.g. ears and eyes) to
the CNS
►
Motor Division (Efferent)
 Transmits impulses from the CNS to the muscles and glands
 Two divisions: Somatic and Autonomic
Somatic System
► Regulates
activities that are under conscious
control (ex: skeletal muscle movement)
► Many nerves are part of reflexes and can
act automatically
 Patellar reflex – By passes the brain completely
Reflexes
► Automatic
movements made in response to
stimuli
► In
the simplest reflex arcs, sensory neurons
synapse directly on motor neurons
► Most
reflexes involve an interneuron
Stretch Reflex
STIMULUS
Biceps
stretches.
sensory
neuron
motor
neuron
Response
Biceps
contracts.
Figure 34.16
Page 585
Central and Peripheral Nervous
Systems
► Central
nervous system (CNS)
 Brain
 Spinal cord
► Peripheral
nervous system
 Nerves that thread through the body
Peripheral
Nervous System
► Somatic
external
nerves-
 Motor functions
 (Shown in green)
► Autonomic
internal
nerves -
 Visceral functions
 (Shown in red)
Two Types of
Autonomic Nerves
► Sympathetic
► Parasympathetic
► Most
organs receive input from both
► Usually
have opposite effects on organ
Sympathetic Nerves
► Originate
in the thoracic and lumbar regions
of the spinal cord
► Ganglia
are near the spinal cord
► Promote
responses that prepare the body
for stress or physical activity (fight-or-flight
response)
Parasympathetic Nerves
► Originate
in the brain and the sacral
region of the spinal cord
► Ganglia
are in walls of organs
► Promote
housekeeping responses such
as digestion “Rest & Digest”
Both Systems Are
Usually Active
► Most
organs are continually receiving both
sympathetic and parasympathetic
stimulation
► For
example, sympathetic nerves signal
heart to speed up; parasympathetic
stimulate it to slow down
► Which
dominates depends on situation
Function of the Spinal Cord
► Expressway
for signals between brain and
peripheral nerves
► Sensory
and motor neurons make direct
reflex connections in the spinal cord
► Spinal
reflexes do not involve the brain
Structure of the Spinal Cord
spinal cord
ganglion
nerve
vertebra
meninges
(protective
coverings)
Figure 34.18
Page 587
Anatomy of the Brain
Cerebrospinal Fluid
► Surrounds
the spinal
cord
► Fills
ventricles within
the brain
► Blood-brain
barrier
controls which solutes
enter the cerebrospinal
fluid
Figure 34.20
Page 588
The Brainstem
► “Lower
Brain”
► Medulla oblongata – controls automatic,
homeostatis functions (breathing, hear and
blood vessels, swallowing, vomiting,
digestions
► Pons – breathing regulation & other
homeostatic functions
► Midbrain – recipt and integeration of
sensory info
Cerebellum
► Coordination,
error checking in motor,
perceptual & cognitive functions (learning,
consciousness)
► Sensory info about joint position and length
of muscle – how you “know” where your
parts are
► Auditory & visual information
Cerebrum
► Right
and Left Cerebral Hemispheres which
are responsible for opposite sides of body
► Gray matter outside; white matter inside
► CORPUS CALLOSUM – connection between
two halves
Sensory Receptors
Convert the energy of a stimulus into action
potentials
Mechanoreceptors
Chemoreceptors
Thermoreceptors
Osmoreceptors
Pain receptors
Photoreceptors
Assessing a Stimulus
► Action
potentials don’t vary in amplitude
► Brain tells nature of stimulus by:
 Particular pathway that carries the signal
 Frequency of action potentials along an
axon
 Number of axons recruited
Somatic Sensations
► Touch
► Pressure
► Temperature
► Pain
► Motion
► Position