Exploring the Human
Nervous System
Chapter 9 pp. 202-247
Introduction to the Nervous
System
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What is the nervous system?
It is a communication system that gathers
information, interprets that information,
and makes either conscious or
subconscious reactions.
 The fundamental unit of the nervous
system is the neuron (nerve cell)
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Vocabulary: due Wednesday
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Peripheral nervous system
(PNS)
Central nervous system (CNS)
Nerve impulse
Dendrite
Axon
Nerve
Sensory receptor
Somatic nervous system
Autonomic nervous system
Myelin
Sensory neurons
Interneurons
Brain stem
Cerebellum
Sulcus
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Motor neurons
Nerve pathways p.218
Synapse
Neurotransmitter
Excitatory response p. 214
Inhibitory response p.214
Reflex arc
Reflex
Meninges (meninx)
White matter
Grey matter
Spinal nerves
Cerebrum
Diencephalon
fissures
convolutions
The Fundamentals of the
Nervous System
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Composed of 2 types of cells
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Neurons: nerve cell that transmits impulses
Neuroglia: helper cells that aid and protect the
parts of the nervous system
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What are nerves?
– Bundles of nerve fibers
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Divided into 2 main branches
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Central Nervous System (CNS)
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Brain and spinal cord
Peripheral Nervous System (PNS)
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Consists of perpheral nerves that connect the CNS to the
rest of the body
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The nervous system provides sensory,
integrative, and motor functions to the
body.
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Motor functions can be divided into the
consciously controlled “somatic nervous
system” and the unconscious “autonomic
system”.
Neuroglial cells
Function to fill spaces, support neurons,
provide framework, produce myelin, and
carry on phagocytosis.
 The only neuroglial cell we will look at is the
Schwann cell.
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Myelin producing neuroglial cell located in the
PNS.
Myelin is a fatty covering that protects and
insulates an axon. It helps impulses transmit
easier.
Neuron Structure
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Cell body containing a
nucleus
Nerve fiber contains a
single axon and many
dendrites.
Dendrites carry
impulses from other
neurons to the cell
body.
Axons carry impulses
from the cell body to
dendrites of
neighboring neurons.
Functional Classification of
Neurons
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Sensory
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Interneurons
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gather data; detect changes in environment
Located in the PNS
located in CNS
Link other neurons
Motor
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carry impulses from the CNS to effectors (muscles
or organs responding to change).
Located in the PNS
Nerve Impulse
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Conduction
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Unmyelinated fibers conduct impulses over their
entire membrane surface.
Myelinated fibers conduct impulses from node of
Ranvier to node of Ranvier, process called
saltatory conduction.
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Saltatory conduction is faster than conduction on
unmyelinated neurons.
Follows the “All-or-None Response”
 Junction between 2 neurons is called a
synapse.
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How do impulses get across the synapse?
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Neurotransmitters or chemical messengers, are
released into the synaptic cleft.
If the neurotransmitter allows for an increase in
sodium ion permeability, then an impulse is
triggered.
If the neurotransmitter decreases the flow of
sodium ions through the path, then the impulse is
stopped.
There are at least 50 kinds of neurotransmitters
within the nervous system.
Reflexes
An automatic, unconscious response to
a stimulus
 Stretch reflexes: Occur when a muscle
is stretched by a tap over its tendon.
Stretch receptors called muscle
spindles, initiating an impulse over a
reflex arc.
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Reflexes
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Reflexes: “ Special” Responses
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Produce rapid, involuntary movement or response
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Important in times of danger
Example: Blinking eyelids when insect approaches eye or
when startled by unexpected loud noise
Why are reflexes so fast?
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Involve few neurons
Many reflexes never reach the brain; travel only as far as
the spinal cord
Example: Blinking eyelid occurs before cerebrum is even
aware of danger
Reflex Arc
Simplest type of nerve pathway
 What happens in a reflex arc?
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Sensory receptor at the dendrite end of
sensory neuron detect a change
 Sensory neuron communicates with
interneurons in CNS
 Interneurons communicate with motor
neurons, whose axons lead out to effector
muscles or glands.
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Examples of Reflexes
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Knee-jerk reflex
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Ankle-jerk reflex
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Response: knee
extension
Effector muscle:
quadriceps
Response:
Effector muscle:
Biceps-jerk reflex
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Response:
Effector muscle
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Triceps-jerk
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Response:
Effector muscle
Plantar reflex
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Response:
Effector muscle:
Babinski:
Meninges
Layered membranes that lie between bony
coverings and the soft tissues of the CNS
 Act to protect the brain and spinal cord.
 Three layers:
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Dura mater: outermost layer; tough, white, fibrous
connective tissue; many blood vessels and nerves
Arachnoid mater: middle layer; weblike; no blood
vessels
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Subarachnoid space: contains watery cerebrospinal fluid
Pia mater: inner most; contains many nerves and
blood vessels that nourish the cells of the brain
and spinal cord.
The CNS: Spinal Cord
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The slender nerve
column that passes
downward from the
brain through the
vertebral column.
Consists of 31
segments, each giving
rise to a pair of spinal
nerves.
Spinal nerves are
accessory organs to the
PNS.
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Two major functions
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Conducting nerve
impulses
Center for spinal
reflexes.
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Knee-jerk reflex
Withdrawal reflexes
Spinal cord innervations
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Cervical vertebrae (1-7)
located in the neck
Thoracic vertebrae (1-12) in
the upper back (attached to
the ribcage)
Lumbar vertebrae (1-5) in the
lower back
Sacral vertebrae (1-5) in the
hip area
Coccygeal vertebrae (1-4
fused) in the tailbone
The CNS: Brain Anatomy
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Four regions of the brain:
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Cerebrum:
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Cerebellum:
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Sits below and behind the cerebrum
Coordination and balance
Brain Stem:
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Largest region
Nerve centers associated with sensory and motor functions/
provides higher mental functions
Involuntary life processes (ie. Breathing and heart rate)
Diencephalon:
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Processes sensory information
The Cerebral Cortex
Structure of the cerebrum
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Divided into two cerebral
hemispheres connected
internally by the corpus
callosum.
Surfaces ridges are called
convolutions. A shallow
groove is a sulcus; a deep
groove is a fissure.
Cerebral cortex: thin layer of
gray matter which is the
outermost portion of the
cerebrum. Contains 75% of
all neuron cell bodies
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4 lobes
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Frontal: reasoning; planning,
parts of speech and movement,
emotions, and problem solving
Parietal: perception of stimuli
related to touch, pressure,
temperature and pain
Temporal: perception and
recognition of sound and
memory
Occiptal: vision
Answer the following!
If Christopher is in a car accident and due to brain
damage loses his sight, which lobes of the brain
were probably damaged?
 When you go to the refrigerator and reach for a
can of pickles, which lobe of the brain are you
using?
 When you are listening to music on earphones,
which lobe of the brain are you using?
 When an Olympic gymnast does a flip on the
balance beam, which lobe(s) of the brain is she
using?
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Diencephalon and Brain Stem
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Diencephalon
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Located between
cerebral hemispheres,
below the corpus
callosum.
Includes the thalamus,
hypothalamus, optic
chiasma, pituitary gland,
mammillary bodies, and
pineal gland
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Brain Stem
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Located from the
diencephalon to the
spinal cord.
Includes the:
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Midbrain
Pons
Medulla oblongata
Cerebellum
Reflex center for processing information
concerning body position
 Injuries to this area could lead to:
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Tremors
Inaccurate movements of voluntary muscles
Loss of muscle tone
An awkward walk
Loss of equilibrium
The PNS
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Somatic nervous
system
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Cranial and spinal
nerves that connect
to skin and skeletal
muscles
Conscious activities
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Autonomic nervous
system
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Connects CNS to the
lining of hollow
organs and glands
Controls unconscious
activities
Cranial and Spinal
nerves