Chapter 7: the Nervous System
Bio 24
Organization of the nervous system
Organization of the nervous system
• Our responses to stimuli
may be voluntary or
involuntary or both
• Example: in response to
low blood pressure, you
may contract smooth
muscles to decrease the
diameter of your blood
vessels, AND feel thirsty,
causing you to take a
drink
Central and peripheral nervous
systems
• Your central nervous
system (CNS) consists
of your brain & spinal
cord
• Your peripheral
nervous system (PNS)
consists of all the
nerves that carry
information to and from
your CNS
STRUCTURE OF NERVOUS TISSUE
Cells of the nervous system
• There are two main types
of cells in the nervous
system:
• Neurons: communicate
with other cells using
electrical and chemical
signals
• Neuroglia: support and
insulate the neurons; FAR
more abundant than
neurons
Parts of a neuron
• Cell body
• Dendrites: receive
signals from other
neurons
• Axons: send signals to
other cells
• Schwann cells
(neuroglial cells) wrap
around the axons to
form myelin
Schwann cells form myelin in the PNS
• Schwann cells form
myelin by wrapping
around PNS neurons
• Oligodendrocytes form
myelin by wrapping
around CNS neurons
• “White matter” is nerve
tissue wrapped in
myelin (axons), “gray
matter” is unmyelinated
(usually cell bodies)
Multiple sclerosis
• Autoimmune disease
that attacks myelin in
both the CNS & PNS
• Multiple functions of
the nervous system may
be impaired
Many types of sensory receptors
• In response to physical
stimulation, sensory
receptor cells create
electrical signals that
travel to the central
nervous system
• Specialized senses
(hearing, sight, smell &
taste) have special
receptor cells to be
discussed in chapter 8
Electrical signals generated by neurons
are action potentials
• Electrical energy is the
result of movement of ions
• When neurons generate
action potentials it involves
ions moving across the
cell’s plasma membrane
• An action potential is an
electrical signal that starts
in a neuron and travels
down the axon
The synapse
• When electrical signals
reach the end of axons,
they trigger the release of
chemicals from the axon
terminal
• The space between the
axon terminal and another
cell is called the synaptic
cleft and the connection
between the two is called
the synapse
Neurotransmitters are released at the
synapse
• Neurotransmitters are
chemical signals released
from a neuron’s axon
terminal onto a target cell
• The target cell may be a
neuron, too, or another
cell type
• Many recreational and
therapeutic drugs work by
influencing the action of
neurotransmitters
Reflexes
• A reflex is an automatic
response to a stimulus
• Reflexes can control either
skeletal muscles (somatic
reflexes) or involuntary
muscles (autonomic
reflexes)
• Reflexes are integrated by
your spinal cord NOT your
brain, hence they are not
conscious actions
THE CENTRAL NERVOUS SYSTEM
4 major regions of the brain
• Brain stem: controls
breathing and blood
pressure; many nerves
pass through
• Cerebellum: controls
movement
• Diencephalon: integrates
sensory information &
mediates emotional
response
• Cerebrum: controls all
“higher thought”
Areas of the cerebrum are specialized
for different functions
The cerebral cortex receives sensory
information and sends motor information
The corpus callosum connects the
hemispheres
PROTECTION OF THE CNS
The CNS is vulnerable to damage
• Cells of the central nervous system have a very
limited ability to regenerate themselves
• The cells themselves are soft and easily damaged
(your brain has the consistency of tofu)
• The blood-brain barrier refers to the fact that
capillaries in the brain are less permeable than
those in other parts of the body; this helps protect
your brain from damage due to chemicals in your
bloodstream
Bones and meninges protect the CNS
• The meninges consist of
the:
– dura mater
– arachnoid mater
– pia mater
• layers of connective tissue
membrane that protect the
brain and spinal cord
• Meningitis is inflammation
of the meninges caused by
viral or bacterial infection;
can be serious or fatal!
Cerebrospinal fluid in and around the
brain and spinal cord also protects it
Hydrocephalus is caused by an
overabundance of CSF
BRAIN DYSFUNCTION
Traumatic brain injuries
• Most often caused by car accidents
• Concussion: a mild traumatic brain injury; may
result in temporary loss of consciousness
• Intracranial hemorrhage: bleeding in the
brain; can damage brain tissue
• Cerebral edema: swelling of the brain;
sometimes part of the skull is temporarily
removed to treat this
Stroke
• Stroke is the result of a blood clot that blocks
blood flow to part of the brain; if brain tissue
is deprived of blood for even a few minutes, it
dies
• Aphasia, or reduced ability to produce or
understand language, is common after stroke
affecting the left hemisphere
THE SPINAL CORD & PERIPHERAL
NERVOUS SYSTEM
The spinal cord
• Spinal nerves carry
information both to
and from the CNS
• The nerves then split
and the sensory
information goes in
through a structure
called the dorsal root;
motor information goes
out through the ventral
root
The spinal cord
• Dorsal horns (gray
matter) contain
interneurons that
connect neurons to
each other
• White matter of the
spinal cord is
myelinated axons
carrying info up and
down
Organization of the nervous system
The sympathetic and parasympathetic
divisions
• Sympathetic nervous system is activated under
“fight or flight conditions”
– Blood flow to muscles increases
– Pupils of eyes dilate
– Digestion is inhibited
– Heart rate increases
• Parasympathetic nervous system is activated
under “rest and digest” conditions
• Table 7.3 in your book lists several specific effects
each of these has!