7
NEURON COMMUNICATION
STRUCTURAL CLASSIFICATION OF THE
NERVOUS SYSTEM: STUDENT NOTES
• Central nervous system (CNS)
• Structures
• Brain
• Spinal cord
• Functions
• Integration; command center (brain)
• Interpret incoming sensory information
• Issues outgoing instructions
STRUCTURAL CLASSIFICATION OF THE
NERVOUS SYSTEM: STUDENT NOTES
• Peripheral nervous system (PNS)
• Nerves extending from the brain and spinal
cord
• Cranial nerves—carry impulses to and from the
brain
• Spinal nerves—carry impulses to and from the
spinal cord
• Functions
• Sensory (afferent) and motor (efferent)
divisions.
• Motor division neurons: somatic (voluntary)
and autonomic (involuntary)
FUNCTIONS OF THE NERVOUS SYSTEM:
STUDENT NOTES
• Sensory input —gathering information
• To monitor changes occurring inside and
outside the body
• Changes = stimuli
• Integration
• To process and interpret sensory input and
decide if action is needed
• Motor output
• A response to integrated stimuli
• The response activates muscles or glands
Occipital lobe
Tentorium
cerebelli
Cerebellum
Arachnoid mater
over medulla
oblongata
(b)
Skull
Scalp
Superior
sagittal sinus
Dura mater
Transverse
sinus
Temporal
bone
Figure 7.17b
MENINGES OF THE CNS
• Three connective tissue membranes
• Dura mater
• Arachnoid mater
• Pia mater
PROTECTION OF THE CENTRAL
NERVOUS SYSTEM: STUDENT NOTES
• Scalp and skin
• Skull and vertebral column
• Meninges
• Cerebrospinal fluid (CSF)
• Blood-brain barrier
NERVOUS TISSUE
COMPRISED OF TWO TYPES OF CELLS
• NEURONS
• Provide unique functions: sensing, thinking,
remembering, controlling muscle activity &
regulating glandular secretions.
• Two types of nerve fibers: axons and dendrites
• NEUROGLIA
• Support, nourish, and protect neurons
• Do not generate or propagate action
potentials
CNS NEUROGLIA
CNS
Astrocytes
Forms blood-brain barrier which protects
neurons from pathogens and harmful chemicals
Oligodendrocytes
Produces and maintains myelin (one cell can
wrap around multiple neurons)
Microglia
Provides protection against microbial organisms
Ependymal cells
Produces cerebrospinal fluid
Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
and versatile neuroglia.
Figure 7.3a
BLOOD-BRAIN BARRIER
• The least permeable capillaries of the body
What does this mean? Diffusion only allows
certain things through
Are their substances that easily cross the blood
brain barrier?
Neuron
Microglial
cell
(b) Microglial cells are phagocytes that
defend CNS cells.
Figure 7.3b
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal
fluid-filled cavities.
Figure 7.3c
Myelin sheath
Process of
oligodendrocyte
Nerve
fibers
(d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Figure 7.3d
MAJOR BRAIN REGIONS AND
THEIR FUNCTIONS
Parietal lobe
Left cerebral
hemisphere
Frontal
lobe
Occipital
lobe
Temporal
lobe
Cephalad
Caudal
(b)
Brain
stem
Cerebellum
Figure 7.13b
Precentral
gyrus
Central sulcus
Postcentral gyrus
Parietal lobe
Frontal lobe
Parieto-occipital
sulcus (deep)
Lateral sulcus
Occipital lobe
Temporal lobe
Cerebellum
Pons
Medulla
oblongata
Cerebral cortex
(gray matter)
Gyrus
Spinal
cord
Sulcus
Fissure
(a deep sulcus)
(a)
Cerebral
white
matter
Figure 7.13a
Cerebral hemisphere
Corpus callosum
Third ventricle
Choroid plexus of third
ventricle
Occipital lobe of
cerebral hemisphere
Thalamus
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Spinal cord
(encloses third ventricle)
Pineal gland
(part of epithalamus)
Corpora
quadrigemina
Midbrain
Cerebral
aqueduct
Cerebral peduncle
of midbrain
Fourth ventricle
Choroid plexus
Cerebellum
(a)
Figure 7.16a
REGIONS OF THE BRAIN: CEREBRUM:
STUDENT NOTES
Layers of the cerebrum
• Gray matter—outer layer in the
cerebral cortex composed mostly of
neuron cell bodies
• White matter—fiber tracts deep in
the gray matter (myelinated)
Corpus callosum connects right & left
hemispheres
CONNECTION TO PRACTICE: BRAIN LATERALIZATION/
DOMINANCE: FYI
Right & left sides of the brain separated by the
Corpus callosum
• Left hemisphere
• Thought to address information with more logic, linear
reasoning
• Right hemisphere
• Regarded to be more associated with artistic and
imaginative thought
• ¾ of population is right-handed; the rest are lefthanded
CEREBRUM
LOBES: FRONTAL; PARIETAL; TEMPORAL; OCCIPITAL
Figure 7.14
Cerebral
hemisphere
Diencephalon
Cerebellum
Brain stem
(b) Adult brain
Figure 7.12b
Cerebral hemisphere
Corpus callosum
Choroid plexus of third
ventricle
Occipital lobe of
cerebral hemisphere
Third ventricle
Thalamus
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Spinal cord
(encloses third ventricle)
Pineal gland
(part of epithalamus)
Corpora
quadrigemina
Midbrain
Cerebral
aqueduct
Cerebral peduncle
of midbrain
Fourth ventricle
Choroid plexus
Cerebellum
(a)
Figure 7.16a
REGIONS OF THE BRAIN:
DIENCEPHALON: STUDENT NOTES
• Made of three parts
• Thalamus
• Hypothalamus
and
• Limbic system (a functional system)
Cerebral hemisphere
Corpus callosum
Choroid plexus of third
ventricle
Occipital lobe of
cerebral hemisphere
Thalamus
(encloses third ventricle)
Pineal gland
(part of epithalamus)
Corpora
quadrigemina
Midbrain
Cerebral
aqueduct
Third ventricle
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Spinal cord
Cerebral peduncle
of midbrain
Fourth ventricle
Choroid plexus
Cerebellum
(a)
Figure 7.16a
REGIONS OF THE BRAIN: BRAIN STEM
STUDENT NOTES
• Midbrain
• Pons
• Medulla oblongata
and
• Reticular formation (a
functional system)
What are the functions of the
brain stem?
CEREBELLUM FUNCTIONS: STUDENT NOTES
Main: maintaining proper posture and balance.
Four activities involved:
Monitoring intentions for movement
Monitoring actual movement
Comparing command signals with sensory information
Sending out corrective feedback
What is found in skeletal muscles that work in conjunction with
the cerebellum?
CEREBROSPINAL FLUID (CSF)
What is the purpose of CSF?
- Protects brain and spinal cord
4
Superior
sagittal sinus
Arachnoid villus
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
Right lateral ventricle
(deep to cut)
Choroid plexus
Corpus
callosum
1
Interventricular
foramen
Third ventricle
3
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Choroid plexus
of fourth ventricle
2
Central canal
of spinal cord
(c) CSF circulation
Figure 7.18c
SOMATIC SENSATIONS
The major components and functions of the nervous system
Central Nervous System
The central nervous system
(CNS) consists of the brain and
spinal cord and is responsible
for integrating, processing, and
coordinating sensory data and
motor commands.
Information processing
includes the integration and
distribution of information in
the CNS.
Peripheral Nervous
System
The motor division of the
PNS carries motor commands
from the CNS to peripheral
tissues and systems.
The peripheral
nervous system
(PNS) includes all the
neural tissue outside
the CNS.
includes
The sensory division of the PNS
brings information to the CNS
from receptors in peripheral
tissues and organs.
Somatic sensory
receptors provide
position, touch,
pressure, pain, and
temperature sensations.
The somatic
nervous
system
(SNS)
controls
skeletal
muscle
contractions.
Special sensory
receptors provide
sensations of
smell, taste,
vision, balance,
and hearing.
Visceral sensory receptors
monitor internal organs.
Receptors are sensory structures that detect
changes in the internal or external
environment.
Skeletal
muscle
The autonomic
nervous system
(ANS) provides
automatic regulation
of smooth muscle,
cardiac muscle,
glands, and adipose
tissue.
• Smooth muscle
• Cardiac muscle
• Glands
• Adipose tissue
Effectors are target organs whose
activities change in response to neural
commands.
SENSATIONS: STUDENT NOTES
• Conscious or subconscious awareness of
changes in environmental stimuli (Can occur in
all parts of the CNS; transmission involves PNS)
• Somatic sensations:
• Tactile, pain, temperature, proprioception
• Visceral sensations: within internal organs
• Pain, blood pressure changes, chemical
levels, hunger, nausea, temperature.
• Specialized sensations:
• Smell, taste, vision, hearing, balance
(equilibrium)
Figure 7.7a
PAIN SENSATION: PAIN RECEPTORS
Pain Sensation
o Free nerve endings
o Protective function by signaling the presence of
noxious, tissue-damaging conditions.
Pain Receptors : Nococeptors
o Found in every tissue of the body except the brain
o Pain often from internal/visceral organs felt over a
larger area than what was stimulated = referred
pain
TRANSMISSION OF
MESSAGES
Figure 7.2
Mitochondrion
Dendrite
Cell
body
Nissl substance
Axon
hillock
Axon
Neurofibrils
Nucleus
Collateral
branch
One
Schwann cell
Axon
terminal
Node of
Ranvier
Schwann cells,
forming the myelin
sheath on axon
(a)
Figure 7.4a
Figure 7.1
PERIPHERAL NERVOUS SYSTEM :
STUDENT NOTES
NERVES:

bundles of neuron fibers found outside the CNS

each neuron fiber protected by several layers
(connective tissue) creating a cordlike structure
SENSORY (AFFERENT) AND MOTOR (EFFERENT) PATHWAYS
Classified according to their direction of impulse
transmission.
Sensory
Motor
Mixed
Interneuron carrying sensory
information to cerebral cortex
Integration (processing
and interpretation of
sensory input) occurs
Cerebral cortex
(gray matter)
White matter
Interneuron carrying
response to
motor neurons
Thalamus
Cerebrum
Interneuron
carrying response
to motor neuron
Brain stem
Cell body of sensory
neuron in sensory
ganglion
Interneuron carrying
sensory information to
cerebral cortex
Nerve
Skin
Sensory
receptors
Cervical spinal cord
Muscle
Motor output
Motor neuron
cell body
White matter
Gray matter
Interneuron
Figure 7.22
Central process (axon)
Cell
body
Sensory
neuron
Spinal cord
(central nervous system)
Ganglion
Dendrites
Peripheral
process (axon)
Afferent
transmission
Interneuron
(association
neuron)
Peripheral
nervous system
Receptors
Efferent transmission
Motor neuron
To effectors
(muscles and glands)
Figure 7.6
FUNCTIONS OF THE NERVOUS SYSTEM
STUDENT NOTES
Sensory (input):
detect internal or external stimuli (changes) that
are carried to the brain and spinal cord via
cranial and spinal nerves
Integrative function: processes sensory
information by analyzing it and making
decisions for appropriate responses
 Interneurons or Association neurons:
mostly within CNS between the sensory and motor
neurons; mostly multi-polar in structure.
Motor (output):
activates effectors (muscles and glands) through
cranial nerves and spinal nerves.
Stimulation of the effectors causes muscles to
contract and glands to secrete.
Axon of
transmitting
neuron
Receiving
neuron
Dendrite
Axon terminal
1 Action
potential
arrives.
Vesicles
Synaptic
cleft
Figure 7.10, step 1
NERVOUS TISSUE: NEURONS:
STUDENT NOTES
• Axons
• Axon terminals contain vesicles with
neurotransmitters
• Axon terminals are separated from the
next neuron by a gap
• Synaptic cleft—gap between adjacent
neurons
• Synapse—junction between nerves
SPINAL CORD: KEY POINTS
• Extends from the foramen magnum of the skull to
the first or second lumbar vertebra
• Provides a two-way conduction pathway from
the brain to and from the brain
• 31 pairs of spinal nerves arise from the spinal
cord
• Cauda equina is a collection of spinal nerves at
the inferior end
Cervical
nerves
Thoracic
nerves
Lumbar
nerves
Sacral
nerves
C1
2
3
4
5
6
7
8
T1
2
3
4
5
6
7
8
9
10
11
Ventral rami form
cervical plexus
(C1 – C5)
Ventral rami form
brachial plexus
(C5 – C8; T1)
No plexus
formed
(intercostal
nerves)
(T1 – T12)
12
L1
2
3
4
Ventral rami form
lumbar plexus
(L1 – L4)
5
(a)
S1
2
3
4
Ventral rami form
sacral plexus
(L4 – L5; S1 – S4)
Figure 7.25a
Dorsal root
ganglion
White matter
Central canal
Dorsal (posterior)
horn of gray matter
Lateral horn of
gray matter
Spinal nerve
Dorsal root of
spinal nerve
Ventral root
of spinal nerve
Ventral (anterior)
horn of gray matter
Pia mater
Arachnoid mater
Dura mater
Figure 7.21
Axillary nerve
Humerus
Radial
nerve
Musculocutaneous
nerve
Ulna
Radius
Ulnar nerve
Radial nerve
(superficial
branch)
Median nerve
(a) The major nerves
of the upper limb
Figure 7.26a
PNS: SPINAL NERVE PLEXUSES:
STUDENT NOTES
• Sacral Plexus
• Important nerves:
• Sciatic
• Areas served:
• Lower trunk and posterior thigh
• Lateral and posterior leg and foot
• Gluteal muscles of hip area
Superior
gluteal
Inferior
gluteal
Sciatic
Posterior
femoral
cutaneous
Common
fibular
Tibial
Sural (cut)
Deep
fibular
Superficial
fibular
Plantar
branches
(c) Sacral plexus, posterior view
Figure 7.26c
Figure 7.2
PNS: DIFFERENCES BETWEEN SOMATIC
AND AUTONOMIC NERVOUS SYSTEMS
Somatic Nervous
System
Autonomic Nervous
System
Nerves
One-neuron; it
originates in the CNS
and axons extend to
the skeletal muscles
served
Two-neuron system
consisting of
preganglionic and
postganglionic
neurons
Effector organ
Skeletal muscle
Smooth muscle,
cardiac muscle,
glands
Subdivisions
None
Sympathetic and
parasympathetic
Neurotransmitter
Acetylcholine
Acetylcholine,
epinephrine,
norepinephrine
FUNCTIONAL CLASSIFICATION OF THE PERIPHERAL
NERVOUS SYSTEM STUDENT NOTES
• Motor (efferent) division
• Two subdivisions
• Somatic nervous system = voluntary
• Consciously controls skeletal muscles
• Autonomic nervous system = involuntary
• Automatically controls smooth and cardiac
muscles and glands
• Further divided into the sympathetic and
parasympathetic nervous systems
SOMATIC NERVOUS SYSTEM
SYMPATHETIC DIVISION OF ANS
• Responds to the “Es”
•
•
•
•
Exercise
Emergency
Excitement
Embarrassment
• Increased heart rate, force of contraction, blood
pressure, vasodilation, blood flow to organ and
muscles
• Dilated airways and increased rate of breathing
• Breaking down glycogen and fatty acids and
releasing glucose
• Inhibiting digestion to conserve blood for muscle
action
AUTONOMIC NERVOUS SYSTEM:
PARASYMPATHETIC DIVISION
PNS: AUTONOMIC FUNCTIONING
Parasympathetic—“housekeeping” activities
• Conserves energy
• Maintains daily necessary body functions
• Remember as the “D” division
• digestion, defecation, and diuresis
Central
nervous system
Peripheral nervous system
Effector organs
Acetylcholine
Skeletal
muscle
Somatic nervous system
Acetylcholine
Autonomic
nervous
system
Sympathetic
division
Smooth muscle
(e.g., in stomach)
Norepinephrine
Ganglion
Acetylcholine
Epinephrine and
norepinephrine
Adrenal medulla
Acetylcholine
Blood
vessel
Glands
Cardiac
muscle
Parasympathetic
division
Ganglion
KEY:
Preganglionic
axons
(sympathetic)
Postganglionic
axons
(sympathetic)
Myelination
Preganglionic
axons
(parasympathetic)
Postganglionic
axons
(parasympathetic)
Figure 7.27
THE REFLEX ARC
• Somatic reflexes
• Reflexes that stimulate the skeletal
muscles
• Example: pull your hand away from a
hot object or something sharp
• Autonomic reflexes
• Regulate the activity of smooth
muscles, the heart, and glands
• Example: Regulation of smooth
muscles, heart and blood pressure,
glands, digestive system
1 Sensory receptor
2 Sensory (afferent) neuron
3 Interneuron
4 Motor (efferent) neuron
5 Effector organ
Figure 7.11c, step 5
Stimulus at distal
end of neuron
Spinal cord
(in cross section)
Skin
2 Sensory neuron
1 Receptor
4 Motor neuron
5 Effector
3 Integration
center
Interneuron
Figure 7.11a, step 5
KEY POINTS
Major areas of the brain have specific functions that impact
the homeostasis of the body.
Specific anatomical structures within the CNS are designed to
protect the homeostatic functioning of the brain and spinal
cord.
Both the somatic and the autonomic nervous systems are
necessary for the homeostatic functioning of other body
systems.
Specific areas of the brain are related to specific reactions.
KEY POINTS
Peripheral nerve impulses travel on specific pathways toward
and away from the central nervous system.
Neurotransmission of nerve impulses requires the presence of
specific chemicals and ions to be successful.
Nerves are transmitted through myelinated and unmyelinated
pathways.
Reflexes are involuntary and involve both the CNS & PNS and
indicate a pathological condition when they are
exaggerated, distorted or absent.
CRANIAL NERVES
• Cranial nerves classified as motor, sensory or mixed
Which cranial nerve extends to the thoracic and
abdominal cavities?
• Twelve pairs of
cranial nerves
• I, II, VIII sensory only
• III, IV, VI, XI, XII
motor only
• V, VII, IX, X
sensory and motor
III Oculomotor
IV Trochlear
VI Abducens
I Olfactory
II Optic
V Trigeminal
V Trigeminal
VII Facial
Vestibular
branch
Cochlear
branch
VIII Vestibulocochlear
X Vagus
IX Glossopharyngeal
XII Hypoglossal
XI Accessory
Figure 7.24
CRANIAL NERVES
 Oh – Olfactory
 Oh – Optic
 Oh – Oculomotor
 To – Trochlear
 Touch – Trigeminal
 And – Abducens
 Feel – Facial
 Very – Vestibulocochlear
 Green – Glossopharyngeal
 Vegetables – Vagus
 A – Accessory
 H – Hypoglossal
CRANIAL NERVES: