CHAPTER 48:
NERVOUS SYSTEM
ESSENTIAL KNOWLEDGE
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2.e.2 – Timing and coordination of physiological
events are regulated by multiple mechanisms (11.1).
3.b.2 – A variety of intercellular and intracellular
signal transmissions mediate gene expression (11.1
& 11.4).
3.d.1 – Cell communication processes share common
features that reflect a shared evolutionary history
(11.2 & 11.2).
3.d.2 – Cells communicate with each other through
direct contact with other cells or from a distance
via chemical signaling (11.1 & 11.2).
ESSENTIAL KNOWLEDGE
3.d.3 – Signal transduction pathways link
signal reception with cellular response
(11.3).
 3.d.4 – Changes in signal transduction
pathways can alter cellular response (11.4).
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INTRODUCTION
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Two types of cells:
 Glia
(supporting)
 Neurons

Nervous system is comprised of two parts:
 Central
(spinal cord, brain)
 Peripheral (outlying nerves)

Nervous system is a system of circuits of
neurons and supporting cells that work
together to communicate with rest of the
body
DIVERSITY OF NERVOUS SYSTEMS

Cnidarians:
 Ex:
hydra
 Nerve net (simplistic concentration of nerves)

Echinoderms:
 Ex:
Seastar
 Radial nerves and central nerve ring

Flatworms:
 Cephalization
(concentration of nervous system
in anterior/head region)
 Central nervous system: simple brain with 2
nerve cords
DIVERSITY OF NERVOUS SYSTEMS

Annelids/Arthropods:
 Ex:
insects, crayfish
 Cephalization with complicated brain with
ventral nerve cord
 Also contain clusters of neurons called ganglia

Vertebrates:
 Brain,
dorsal spinal cord make up CNS
 Nerves and ganglia make up PNS
NERVOUS SYSTEM ORGANIZATION
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High degree of cephalization in vertebrates
Spinal cord: integrates simple responses to
stimuli and transports info to and from brain
Cerebrospinal fluid: fluid cushions brain and
carries out circulatory functions
White matter: Axon in bundles (named for
color of their myelin sheaths)
Gray matter: Neuron cell bodies, dendrites,
and unmyelinated axons
NEURON STRUCTURE

Cell body:
 Contains

nucleus and organelles
Extensions:
 Dendrites:
received signals from other neurons,
highly branched
 Axon: transmits signals to other cells, longer
 Contains
terminal branches called synaptic terminals
which release neurotransmitters (relay of signals
across synapse)

Myelin sheath:
 Many
axons wrapped in this insulating layer
NEURON COMMUNICATION

Neurons communicate
with other cells at
synapses


Electrical synapses:
allow electrical current
to flow directly from cell
to cell (via gap junctions)
Chemical synapses:
involves release of
neurotransmitters
SUPPORTING CELLS (GLIA)

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Very numerous
Give structural integrity and physiological support
to nervous system
Astrocytes:


Radial glia:


in CNS, facilitate info transfer at synapse
(learning/memory), induce formation of blood-brain
barrier, can act as stem cells
Guide embryonic growth of neurons, act as stem cells
Oligodendrocytes (CNS) and Schwann cells (PNS):

Insulate axons in mylein sheath by wrapping around them
PROCESSING INFORMATION

Three steps:
 1)
Sensory input
 Detection
of external stimuli or internal conditions
 Sensory neurons transmit this info to CNS
 2)
Integration
 Completed
by interneurons
 Send output through motor neurons to effector cells
(muscle and endocrine cells)
 3)
Motor output
 Response
to signal/output
 Ex: reflex, hormone production and secretion
MEMBRANE POTENTIAL

Membrane potential:

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
Electrical potential difference
Exists across the plasma
membrane of all cells
Dependent upon concentration
of certain ions on either side of
the cell membrane
Outside cell: Na+ and Cl Inside cell: K+ and a number of
negatively charged amino acids
and other molecules


Sodium-potassium pumps
maintain the concentration
gradient/difference
GATED ION CHANNELS

In addition to the ungated K+
and Na+ ion channels, neurons
also have gated ion channels



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Open and closed in response to
stimuli
Stretch-gated ion channels: found
in stretch sensors, open in response
to mechanical stimuli
Ligand/Chemically-gated ion
channels: found in synapses,
respond to chemical stimuli
Voltage-gated ion channels: found
in axons, respond to change in
membrane potential
RESTING POTENTIAL
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Resting potential:



Nontransmitting neuron
Ions continually diffuse
(without energy use)
through channels down
their concentration
gradient until balanced
Equilibrium potential:


The membrane voltage
when the concentrations
are balanced
Neurons at rest have more
K+ channels open than
Na+
ACTION POTENTIAL


Action potential: when a neuron is transmitting a
signal due to the reception of a stimuli
Stimuli that open/close gated ion channels may
increase or decrease membrane potential



Graded potential: the stronger the stimuli = more
channels opens (and vice versa)
Hyperpolarization: the result of a stimuli that
OPENS K+ channels (K+ flows OUT and membrane
potential shifts)
Depolarization: the result of a stimuli that OPENS
Na+ channels (Na+ flows OUT and membrane
potential shifts)
ACTION POTENTIAL

Once depolarization reaches a certain
membrane potential (called the threshold) an
action potential is triggered


Stronger stimuli = higher frequency of action
potentials
Involves BOTH Na+ and K+ ion channels


Na+ channels open quickly in response to
depolarization
K+ channels open more slowly
ACTION POTENTIAL

Sequence of events:

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1) Stimulus depolarizes membrane to threshold
2) Na+ gates open causing influx of Na+ (causing
further depolarization)
3) More Na+ activation gates open, causing
membrane potential to be shifted towards Na+
concentration (rising phase)
4) Falling phase: when Na+ inactivation gates close
and K+ activation gates open (bring membrane
potential towards K+ concentration)
5) Undershoot: membrane’s permeability towards K+
is higher (than at rest), continual OUTFLOW of K+
temporarily hyperpolarizes membrane
PERIPHERAL NERVOUS SYSTEM
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Carries information to and from the CNS
Regulates movement and homeostasis
Made of:

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Paired cranial nerves and spinal nerves
Associated ganglia
Contains BOTH sensory and motor neurons
Two parts:

1) Somatic nervous system


Carries signals to and from skeletal muscles
2) Autonomic nervous system

Maintains internal environment (by controlling smooth/cardiac
muscles)
PERIPHERAL NERVOUS SYSTEM

Autonomic NS (three divisions):

1) Sympathetic division
Accelerates heart and metabolic rate
 Generates energy


2) Parasympathetic division
Carries signals for self-maintenance activities (digestion and
slow heart rate)
 Conserves energy


3) Enteric division
Networks of neurons that control secretions of digestive
tract, pancreas, gallbladder
 Control contractions of smooth muscles (peristalsis)

BRAIN

Embryonic development

Forms three portions (midbrain, hindbrain,
forebrain) – called cephalons


As fetus develops, these three portions specialized further
into 5 regions
Forebrain: becomes cerebrum (outer portion of which becomes
cerebral cortex)


Cerebral cortex: extends out and around brain
Mid/Hindbrain: become brainstem, cerebellum

Brainstem: consists of midbrain, pons, medulla oblongata
BRAINSTEM
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Controls (in part):
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Medulla oblongata (medulla):
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Control center for homestatic functions (breathing, swallowing,
heart and blood vessel action, digestion)
Pons:

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Attention span
Alertness
Appetite
Motivation
Homeostasis
Functions w/ medulla in above activities
Conducts information between the rest of the brain and spinal
cord
Midbrain:

Receives and integrates sensory information
CEREBELLUM
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Controls learning, remembering motor skills,
coordination, error-checking (during perception,
cognitive functions)
Integrates information from auditory and visual
systems together with input from joints and
muscles
Provides automatic coordination of movement and
balance
DIENCEPHALON
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Includes:
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Epithalamus
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Thalamus
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
Includes pineal gland and choroid plexus
Clusters of capillaries produces cerebrospinal fluid
Major input and sorting center for sensory information
Major output center for motor information from cerebrum
Receives input from cerebrum and other brain parts to regulate
emotion and arousal
Hypothalamus

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Major brain region for homeostatic regulation
Produces posterior pituitary hormones and releases hormones that
control anterior pituitary
Contains regulating centers for survival functions and
sexual/mating behaviors, alarm response and pleasure
CEREBRUM
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Functions:
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Determines Intelligence
Personality
Interpretation of Sensory Impulses
Motor Function
Planning and Organization
Touch Sensation
Divided into right and left hemispheres
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Communicate to each other via the corpus callosum
(thick band of axons)
Each hemisphere:


Covered with gray matter (called cerebral cortex)
Contains inner white matter (that includes group of neurons
important to planning and learning movements)
CEREBRUM
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Largest and most complex part of mammalian
brain
Divided into lobes:
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Frontal Lobe- associated with reasoning, planning,
parts of speech, movement, emotions, and problem
solving
Parietal Lobe- associated with movement, orientation,
recognition, perception of stimuli
Occipital Lobe- associated with visual processing
Temporal Lobe- associated with perception and
recognition of auditory stimuli, memory, and speech
CNS INJURIES AND DISEASES
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Schizophrenia:

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Characterized by psychotic episodes involving hallucinations
and delusions
Both genetic and environmental components
Treatments: focus on drugs that blocking dopamine receptors
Bipolar disorder:

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Involves swings of mood from high to low
Includes major depression (a persistent low mood)
Both bipolar and depression have genetic and environmental
components
CNS INJURIES AND DISEASES
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Alzheimer’s disease:




Dementia characterized by confusion, memory loss, personality
changes
Age-related (more frequency with higher age)
Progressive disease
Involves death of neurons in large areas of the
brain
CNS INJURIES AND DISEASES
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Parkinson’s Disease:

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Progressive, age-related motor disorder
Characterized by difficulty in movements, rigidity, muscle
tremors
Death of neurons lead to motor issues (from the accumulation
of a particular protein)
EXCLUSION STATEMENTS

The types of nervous systems, development
of the human nervous system, details of the
various structures and features of the brain
parts, and details of specific neurologic
processes are beyond the scope of the
course and the AP Exam.