Download The Nervous System

Ch 9 Notes
 Main
Function: Communication
 Sensory
– PNS -> CNS – Noticing a change in
the internal or external environment
 Integration – CNS – Signals brought together
in the CNS to create sensation, perception,
and make decisions
 Motor – CNS -> PNS – Relay signals to act on
our decisions

Effectors = muscles or glands that act on the
signal
 Within
the PNS, there are two types of motor
neurons


Somatic – Voluntary
Autonomic - Involuntary
CNS

Central Nervous
System


Brain
Spinal Cord
PNS

Peripheral Nervous
System

Nerves throughout the
body that connect to
the CNS
Neurons
Main functional unit
 Transmit information
through electrical
impulses
 Don’t easily divide

Neuroglia
Provide support,
insulation, and
nutrients to neurons
 Easily divide

 Cell
body –
contains nucleus
 Dendrites – receive
signals
 Axons – send
signals
Structure
Pg. 220
Function
Pg. 221
Sensory/afferent neurons
Association/interneurons
Motor/efferent neurons
 CNS




Microglial cells
Oligodendrocytes
Astrocytes
Ependymal Cells
 PNS

Schwann Cells
 Myelin
– an insulator found on some neurons
that helps speed up the path of the impulse.



Impulse jumps from Node of Ranvier to Node of
Ranvier
CNS – oligodendrocytes
PNS – Schwann cells
 Nerve

“processes” are dendrites and axons.
Skeletal System – prominent projection on a bone
 Where
two nerves come together is called a
synapse.
 They do not quite touch each other, but they
come very close. The space between is the
synaptic cleft.
 Sender = presynaptic neuron
 Receiver = postsynaptic neuron
 Message sending = synaptic transmission

Messages go one way


Messages are carried
by neurotransmitters


From axon of
presynaptic neuron to
dendrite of postsynaptic
neuron
Muscles = __________
Synaptic vesicles
release
neurotransmitters
into the synaptic cleft
 Neurotransmitters
can excite or inhibit.
 The overall effect depends on how much of
each kind is released.
 See Table 9.2 on pg 229
 Cell
membrane is charged – polarized – with
respect to the inside due to unequal
concentrations of positive and negative ions
on either side of the membrane.
 Action potential – a change in polarization
and a return to the resting state
 This forms a nerve impulse that moves down
an axon.
 Sodium
(Na+) and potassium (K+) are
important in cell membrane potential.
 K+ moves out of the cell faster than Na+ can
move in.
 Because more positive ions are moving out
than are moving in, the outside of the cell is
slightly more positive than the inside (which
contains many large, negative ions.)
 The
difference in the charge inside and
outside the neuron is called a potential
difference.
 When a nerve cell is at rest, this potential
difference is referred to as the resting
potential.
 As long as nothing changes, it will stay this
way.
 An
active transport mechanism also aids in
maintaining the resting potential by pumping
Na+ out and K+ in.
 Is
this cell polarized?
 What is the potential difference?
 Is it at resting potential?
 Is there an indication of an action potential?
 What would be required for an action
potential?
 Nerve
cells are excitable.
 Respond to stimuli – changes in...




Light
Temperature
Pressure
Neurotransmitters
 Stimuli
affect the resting potential of a
neuron.
 The
greater the stimuli, the greater the
potential change.
 As the potential difference changes, the cell
becomes depolarized.
 If the depolarization is enough, the
membrane potential will reach the threshold
stimulus. (about -55 mV)
 If threshold is reached, an action potential
will occur.
 Remember
– action potential occurs when
depolarization reaches threshold potential
causing a nerve impulse to be pushed down
the length of the axon.
1.
2.
3.
4.
5.
6.
7.
Threshold stimulus is reached.
Sodium channels open.
Sodium ions diffuse inward, depolarizing
the membrane.
Potassium channels open.
Potassium diffuses outward, repolarizing
the membrane
This action potential propagates a wave of
action potentials.
A nerve impulse moves down the axon.
Action Potential in Unmyelinated Axon
1.
2.
3.
4.
5.
Stimulus depolarizes the membrane enough
to reach threshold potential.
Sodium ions rush in through opened
channels.
Potassium ions rush out through opened
channels, repolarizing the membrane.
Sodium-potassium pump goes back to work
to re-establish resting potential.
An impulse of similar reactions is
propagated down the axon.
Voltage-Gated Channels and the Action Potential
 There
must be a short “resting period”
following an action potential where the
neuron can’t be stimulated. This is called a
refractory period.
 Two benefits


Ensures the impulse moves only in one direction.
It limits the frequency of the action potential.
 Just
like with muscle contraction, nerve
impulses display an all-or-none response.
 If threshold potential is reached, the entire
neuron responds.
 Also similar to muscle contraction, all action
potentials on one neuron are the same
strength. So a stronger stimulation doesn’t
create a stronger action potential, it creates
more action potentials.
 Neuronal
pools in the CNS take in and put out
impulses to other neuronal pools.
 Neurons or neuronal pools may receive
excitatory or inhibitory input.
 If the input is excitatory, but subthreshold,
then it will not create an action potential.
 The neuron/neuronal pool is, however, more
suceptible to reaching threshold, so it is said
to be in facilitation.
 Convergence
– When axons originating from
different parts of the nervous system lead to
the same neuron.
 Allows you to collect a variety of impulses
and act on them appropriately.
 Divergence – Impulse that leaves one neuron
and goes to several other output neurons.
 Amplifies an impulse so it can move to many
different places.
Unmyelinated
Nerve impulse moves
the entire length of
the axon.
 Moves more slowly

Myelinated
Nerve impulse moves
from one node of
Ranvier to the next.
 Moves more quickly.

 synapse
 threshold
potential
 neurotransmitter
 refractory period
 polarized
 facilitation
 resting potential
 neuronal pools
 action potential
 convergence
 potential difference  divergence
 So
far, we’ve spent most of our time talking
about neurons – nerve cells. When you
bundle a group of neurons together, you get
nerves.
 We call axons “nerve fibers”


Sensory fibers/afferent fibers
Motor fibers/efferent fibers
 There



are three kinds of nerves:
Sensory nerves – conduct impulses to the CNS
Motor nerves – conduct impulses from the CNS
Mixed nerves – contain both kinds of fibers
 Nerve
pathway – route a nerve impulse
follows as it travels through the nervous
system.
 Reflex
arc – simplest pathway involving only
a few neurons
 Reflexes – involuntary actions

Somatic or autonomic?
 Reflexes
help maintain homeostasis
 Layered
membranes between bones and CNS.
 Dura mater – outer layer


Blood vessels
Inside the skull, inward between lobes of brain,
and inside the vetebral canal.
 Arachnoid


mater – middle layer
No blood vessles
Has a subarachnoid space between it and the pia
mater which contains CSF (cerebrospinal fluid).
 Pia


mater – innermost layer
Blood vessels
Very thin and covers brain and spinal cord
 Continuous
with the brain; starts at the
foramen magnum.
 31 segments each with a pair of spinal
nerves.

See Fig 9.35 – p 249
 Anterior
median fissure and posterior median
sulcus separate into left and right halves.
 Sections: cervical enlargement (upper limbs)
and lumbar enlargement (lower limbs)
 Gray



matter – looks like a butterfly
Posterior horns – upper
Anterior horns – lower
Lateral horns – middle
 White




matter – separated by gray matter
Posterior funiculus
Anterior funiculus
Lateral funiculus
Has bundles of neurons called tracts.
 Gray
comissure surrounds the central canal
and contains CSF.
 Two


basic functions
Conducting nerve impulses to and from the brain
Serving as a center for spinal reflexes
 Tracts


Ascending = carry information to the brain
Descending = carry information from the brain
 Four




Regions
Cerebrum
Diencephalon
Brain stem
Cerebellum
 Structure
 Right


and Left Hemispheres
Connected by corpus callosum
Separated by dura mater
 Ridges
– gyri
 Grooves – sulcus and fissures
 Lobes




Frontal
Parietal
Temporal
Occipital
 Cerebral
Cortex – gray matter on outer
surface.
 The rest is white matter.
 Function
 Sensory
area – interpret incoming info;
produce feelings/sensations

Wernicke’s area – visual and auditory info
 Association
area – analyze, interpret,
verbalize, reason, judgement, emotion,
concentrating, planning, problem solving...
 Motor area – Takes info to brainstem and
beyond

Broca’s area – generates muscle movements for
speech.
 Location:
Above midbrain and between
cerebral hemispheres.
 Made mostly of gray matter
 Parts


Thalamus – receives sensory input and channels it
to cerebral cortex for interpretation; Produces
general sensations of pain, touch, and temp.
Hypothalamus – Maintains homeostasis – links
nervous and endocrine systems. Regulates temp,
blood pressure, hunger and more.
 Other

parts
Optic tracts, optic chiasma, infundibulum,
posterior pituitary gland, mammillary bodies,
pineal gland
 Also
contorls emotional responses through
the limbic system.


Fear, anger, pleasure, sorrow – can affect
actions.
Acts as a mechanism to protect the organism to
increase the chances of survival.
 Connects
cerebrum to spinal cord.
Three parts
 Midbrain – Connects diencephalon


Two corticospinal tracts – main motor pathways
between cerebrum and lower parts of N.S.
Also has reflex centers
 Pons
– Separates midbrain from medulla
oblongata


Transmits impulses between M.O. And cerebrum
Transmits impulses between cerebrum and
cerebellum.
 Medulla
Oblongata – from pons to foramen
magnum



All ascending and descending fibers pass through
Three centers: cardiac, vasomotor, respiratory
Reticular formation – Keeps you awake and alert.
 Two
hemispheres connected by vermis.
 Cerebellar cortex – thin layer of gray matter
surrounding the white matter.
 Three pairs of nerve tracts for
communication with CNS – cerebellar
peduncles.

Sense, integrate, and move body parts.
 Coordinates
movements.
complex skeletal muscle
 Created
in the choroid plexus in the pia
mater of the ventricles.
 Travels through other ventricles in the
cerebrum and brainstem and into the spinal
cord.
 Completely fills the subarachnoid space
which surrounds the brain and spinal cord.
 Protects organs by absorbing energy that
might otherwise damage them.
 Also maintains homeostasis – ions, blood,
wastes, etc.
 Four
lobes
 Cerebellum
 Cerebrum
 Brainstem – all three parts
 Diencephalon
 Meninges – distinguish among them
 Somatic
vs Autonomic
 Cranial nerves vs Spinal nerves
 Cranial

Twelve pairs – Pg 247
 Spinal


nerves
nerves
Thirty-one pairs – Pg 249
Most form plexuses – cervical, brachial,
lumbosacral