Chapter 9

• To identify the basic structure of a neuron.
• To explain the main components of the nervous system.
• To compare and contrast the central nervous system and the peripheral nervous system. • To differentiate between the somatic and autonomic nervous systems.

• Sensory input (gathering information): to monitor changes occurring inside and outside the body o Changes = stimuli • Integration: to process and interpret sensory input and decide if action is needed • Motor output: a response to integrated stimuli o The response activates muscles or glands

• Neuron= Nerve Cell • Reacts to physical/chemical changes in surroundings • Transmit information through nerve impulses to other neurons and other cells.

• https://www.youtube.com/watch?v=ob5U8zPbAX4

• Neuroglia o o Definition: all support cells in the CNS (Central nervous system) Function: to support, insulate, and protect neurons • Neurons o Function: transmit messages o Major regions of neurons • Cell body – nucleus and metabolic center of the cell • Processes – o fibers that extend from the cell body Dendrites – body conduct impulses toward the cell o Axons – conduct impulses away from the cell body

• CNS (
Central Nervous System ):
o o Brain Spinal Cord • PNS (
Peripheral Nervous System ):
o Cranial nerves o Spinal Nerves

• Contains a sensory division and a motor division.
• Sensory Division: o o o Contains sensory receptors that convert info into a nerve impulse and transmit it back to the CNS to make sense of it.
Monitors environmental changes such as light and sound Detects changes in homeostasis ( ex: temperature, oxygen level)

• Utilize peripheral neurons to carry impulses from the CNS to an effector which will cause a response o Ex: muscle contraction, gland secretion, etc.

• Somatic Nervous System: o Controls skeletal muscle and voluntary movement.
• Autonomic Nervous System: o Controls effectors that are involuntary • Ex: heart, smooth muscle, certain glands

• To identify and explain the 3 different structures of neurons.
• To compare and contrast sensory, motor, and interneurons and explain a general pathway.
• To determine the functions of the 5 types of neuroglia.

o o
Multipolar:
Many processes stemming from cell body.
*most neurons in brain and spinal cord are multipolar

o o
Bipolar:
Only two processes (one at each end.
*found in eyes, nose, ears..

o o o
Unipolar:
One single process extending from cell body.
one side of axon cord.
is the
peripheral process
associated with body part, other side is the central process that enters brain or spinal Cell bodies
ganglia.
create a tissue mass called

• Sensory Neurons (afferent): o o o o Carry impulses from PNS to CNS Contain “receptor ends” at the tips of dendrites Changes impulse outside the body stimulate receptor ends triggering an *Most are unipolar

• Interneurons (association): o o o Completely in brain or spinal cord.
Link neurons together.
*multipolar

• Motor Neurons (efferent): o carry impulses out of brain or spinal cord to the effector and stimulate response.

*More numerous than neurons, support neurons in different ways.
• Microglial Cells: o Phagocytize bacterial cells and cellular debris • Oligodendrocytes: o Provide insulating layers of myelin • Astrocytes: o o o o Provide structural support join parts (ex: neuroncapillary) help regulate concentrations of nutrients and ions Form scar tissue in the CNS • Ependymal Cells: o Forms membrane that covers specialized brain parts and forms inner linings within the brain and spinal canal • Schwann cells: o Forms myelin sheath around axons.

• A lipid that sometimes coats axons o White matter = myelinated axons in CNS o Gray matter = cell bodies & unmyelinated axons in CNS • Produced by some neuroglial cells • Insulates neurons & increases efficiency of nerve impulses

• To explain how a nerve impulse occurs.
• To determine what types of stimuli elicit an action potential.
• To explain different things that inhibit an action potential.
• To understand components of a neuron that contribute to impulse velocity.

• The membrane is electrically charged, “polarized” due to Na+ and K+ ions o Greater concentration of sodium ions outside and potassium ions inside.
o o Potassium ions pass through more easily Active transport (sodium/potassium pump) maintains balance • This is essential in the propagation of a nerve impulse.

• When a nerve cell membrane is undisturbed, the membrane remains polarized staying more negative on the inside and positive on the outside .

• If the nerve cell detects a change in light/temp/pressure it effects the resting potential and the membrane begins depolarizing.
o Sodium channels open and + ions flow in, making the inside less negative.
• Change in potential is proportional to the intensity of the stimulation.
• Stimulation + more stimulation before initial stimulation subsides is called summation .
• Once the threshold is reached, an action potential occurs.

• Definition: change in neuron membrane polarization and return to resting state • Nerve Impulse: chain of action potentials from neuron to neuron

• Depolarization: a decrease in membrane potential • Repolarization: again increase in membrane potential, causes membrane to become negatively charged Action Potential 1. Stimuli (temperature, light, pressure, other neurons) decreases membrane potential 2. When threshold potential (~55 mV) is reached, stimulus is big enough to cause neuron to send a signal.

3. Reaching threshold potential triggers equalize charges Na+ and K+ channels (located in nodes of Ranvier) to open and 3a. Na+ channels open faster, causing rapid depolarization.
3b. As K+ channels open slowly, membrane becomes more polarized, Na+ rushes out. 4. Further parts of axon are triggered nerve impulse.
and action potentials propagate down length of axon causing 5. Results in neurotransmitters being released into synapse

•
https://www.youtube.com/watch?v=ZAmUjvgoO0A • https://www.youtube.com/watch?v=HnKMB11ih2o

• Unmyelinated nerve = impulse conducted over the entire surface.
• Myelin insulates and prevents ion flow, didn’t have the nodes of ranvier.
would prevent conduction if it were continuous and • Myelinated nerve= impulse jumps from node to node and creates a saltatory response and is much faster than unmyelinated.

• Nerve impulses create an “all or none response” .
• Once the stimulus reaches threshold, it generates an action potential.

• Identify the different components of a reflex arc.
• Explain different autonomic reflexes found throughout the body.

• Ordinarily, a receptor sends a signal to the brain where the brain coordinates a response.
• What happens when you touch something hot?

• Reflex: a rapid, predictable, and involuntary response to a stimulus • Reflex Arc: Direct route from sensory neurons, to an interneuron, to an effector.
o Interneuron: neuron between the primary sensory neuron and the final motor neuron. • A reflex is a rapid action that happens without thought and does not involve the brain.

1) Receptor organ sense organ in skin, muscle, or other 2) Sensory Neuron receptor carries impulse towards CNS from 3) Interneuron carries impulse within CNS 4) Motor Neuron effector carries impulse away from CNS to 5) Effector structure by which animal responds (muscle, gland, etc).

1. Stimulus: A receptor receives a stimulus 2. Afferent Pathway: Receptor sends message to integrating center (CNS) via a sensory neuron 3. Integration: CNS makes correct connection between sensory neuron and motor neuron; usually involves an interneuron 4. Efferent Pathway: Motor neuron carries message from CNS to effector 5. Response: Effector carries out appropriate response

• https://www.youtube.com/watch?v=wLrhYzdbbpE

• Somatic reflexes: Activation of skeletal muscle o Example: when you move your hand away from a hot stove • Autonomic reflexes: Regulation of smooth muscle; regulation of cardiac muscle, regulation of glands o Example: Heart rate and blood pressure regulation; digestive system regulation; regulation of fluid balance

• Definition: chemicals that transmit signals from neurons to a target cell across a synapse • NTs can be either excitatory (excite) or inhibitory (inhibit) • Each neuron generally synthesizes and releases a single type of neurotransmitter

Neurotransmitter
Acetylcholine Dopamine
Role in the Body
Excitatory. Used by spinal cord neurons to control muscles; used by neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory.
Inhibitory. Produces feelings of pleasure when released by the brain reward system.
GABA (gamma-aminobutyric acid) Glutamate Glycine The major inhibitory neurotransmitter in the brain.
The most common excitatory neurotransmitter in the brain.
Inhibitory. Used mainly by neurons in the spinal cord. Norepinephrine Serotonin Mostly excitatory, can be inhibitory in a few brain areas. Acts as both neurotransmitter and hormone. In PNS, part of fight or flight response. it is part of the flight-or-flight response. In brain, regulates normal brain processes. Inhibitory. Involved in many functions including mood, appetite, and sensory perception.

• Drugs can affect synapses at a variety of sites and in a variety of ways, including: o o Increasing number of impulses (firing of nerves) Release NT from vesicles with or without impulses o o o Block reuptake of neurotransmitters or block receptors Produce more or less NT Prevent vesicles from releasing NT

Three Drugs (of many) which affect Neurotransmission Methamphetamine Nicotine Alcohol

• Meth alters Dopamine transmission in two ways: o o Enters dopamine vesicles in axon terminal causing release of NT Blocks dopamine transporters taking dopamine back into the transmitting neuron • Result: More dopamine in the synaptic cleft o This causes neurons to fire more often than normal resulting in a euphoric feeling.

• Problems… o After the drug wears off, methamphetamine.
dopamine levels drop, and the user “crashes”. The euphoric feeling will not return until the user takes more o o Long-term use of meth causes dopamine axons to wither and die.
Note that cocaine also blocks dopamine transporters, thus it works in a similar manner.

• Similar to methamphetamine and cocaine, nicotine increases dopamine release in a synapse.
• However, the mechanism is slightly different • Nicotine binds to receptors on the presynaptic neuron

• Nicotine binds to the presynaptic receptors exciting the neuron to fire more action potentials causing an increase in dopamine release.
• Nicotine also affects neurons by increasing the number of synaptic vesicles released.

• Alcohol has receptors.
multiple effects on neurons. It alters neuron membranes, ion channels, enzymes, and • It binds directly to and gluatmate.
receptors for acetylcholine, serotonin, and gamma aminobutyric acid (GABA),

• GABA is a neurotransmitter that has an inhibitory effect on neurons.
• When GABA attaches to its receptor on the postsynaptic membrane, it allows Cl ions to pass into the neuron.
• This hyperpolarizes the postsynaptic neuron to inhibit transmission of an impulse .

• When alcohol enters the brain, of GABA.
it binds to GABA receptors and amplifies the hyperpolarization effect • The neuron activity is further diminished.
• This accounts for some of the sedative affects of alcohol.

• The brain goes through dynamic change during adolescence, and alcohol can can seriously damage long and short-term growth processes.
• Frontal lobe development and the refinement of pathways and connections continue until age 16, and a high rate of energy is used as the brain matures until age 20.
• Damage from alcohol at this time can be long-term and irreversible.

• In addition, short-term or moderate drinking impairs learning and memory for more in youth than adults .
• Adolescents need only drink half as much as adults to suffer the same negative effects.

Drugs that Influence Neurotransmitters
Change in Neurotransmission Drug that acts this way Effect on Neurotransmitter release or availability
increase the number of impulses increased neurotransmitter release nicotine, alcohol, opiates release neurotransmitter from vesicles with or without impulses release more neurotransmitter in response to an impulse block reuptake increased neurotransmitter release increased neurotransmitter release produce less neurotransmitter more neurotransmitter present in synaptic cleft less neurotransmitter in synaptic cleft less neurotransmitter released prevent vesicles from releasing neurotransmitter block receptor with another molecule no change in the amount of neurotransmitter released, or neurotransmitter cannot bind to its receptor on postsynaptic neuron amphetamines methamphetamines nicotine cocaine amphetamine probably does not work this way No drug example LSD caffeine

CNS (Brain Structure)

• Structure of cerebrum: Paired (left and right) superior parts of the brain • Function of cerebrum: Higher brain function (thought and action)

• Frontal lobe Area) : problem solving, judgment, motor function (Primary Motor Area), speech (Broca’s • Parietal lobe : sensation, handwriting, body position (Primary Somatic Sensory Area) • Occipital lobe: visual processing system • Temporal lobe: memory and hearing

• Structure: sits on top of brain stem; enclosed by cerebral hemispheres

Three parts • Thalamus: relay station for sensory impulses • Hypothalamus: autonomic nervous system center; involved in emotion o o o Helps regulate body temperature Controls water balance Regulates metabolism • Epithalamus: houses the pineal gland (involved in sleep); forms CSF (Cerebrospinal fluid)

Structure: Attached to the spinal cord • Midbrain o o Mostly composes of tracts of nerve fibers Function: reflex center for vision and hearing • Pons o o Structure: bulging center part of the brain stem Function: control of breathing • Medulla Oblongata o Structure: most inferior part of the brain stem; merges into spinal cord o Functions: heart rate control, blood pressure regulation, breathing, swallowing, vomiting

• Structure: looks like a “little cerebrum”, sits inferior to cerebrum, posterior to brain stem • Function: provides involuntary coordination of body movements

• Structure: four chambers within the brain filled with cerebrospinal fluid o Lateral Ventricles: within Cerebrum o Third Ventricle: in Diencephalon o Fourth Ventricle: between pons and cerebellum

• Functions 1. Transport of waste and nutrients 2. Protects cerebrum from trauma 3. Contain signaling molecules that direct development and function

Spinal Cord Anatomy and PNS

• Structure: extends from foramen magnum of skull to the first two lumbar vertebra

• Internal gray matter – central canal o mostly cell bodies; surrounds Central canal is filled with cerebrospinal fluid • Exterior white matter axons

• Definition: nerves and ganglia outside the central nervous system • Ganglia: mass of nerve cell bodies • Nerve: bundle of neuron fibers

• Mixed nerves: both sensory and motor fibers • Sensory (afferent) nerves: carry impulses toward the CNS • Motor (efferent) nerves: carry impulses away from the CNS

• Definition: 12 pairs of nerves that serve the head and neck

• I Olfactory nerve – • II Optic nerve – sensory for smell sensory for vision • III Oculomotor nerve – • IV Trochlear – motor fibers to eye muscles motor fiber to eye muscles • V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles • VI Abducens nerve – • VII Facial nerve – the face motor fibers to eye muscles sensory for taste; motor fibers to • VIII Vestibulococlear nerve – and hearing sensory for balance

• IX Glossopharyngeal nerve – fibers to the pharynx • X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera • XI Accessory nerve – upper back sensory for taste; motor motor fibers to neck and • XII Hypoglossal nerve – motor fibers to tongue

• Structure: formed by the combination of the ventral and dorsal roots of the spinal cord o 31 pairs of spinal nerves arise from the spinal cord • Cauda equina: collection of spinal nerves at the inferior end

• Definition: involuntary nervous system • Function: regulates activities of cardiac and smooth muscles and glands • Two subdivisions o Sympathetic divisions o Parasympathetic division

• Sympathetic Function – o “fight or flight” Response to unusual stimulus o o Takes over to increase activities Remember the “E” division: Exercise, excitement, emergency, and embarrassment • Neurotransmitters o Norepinephrine o Epinephrine

• Parasympathetic function – activities o o o “housekeeping” Conserves energy Maintains daily necessary body functions Remember as the “D” division: digestion, defecation, and diuresis • Neurotransmitter o Acetylcholine

Difference between Somatic and Autonomic Nervous System • Nerves o o Somatic: one motor neuron Autonomic: preganglionic and postganglionic nerves • Effector organs o o Somatic: skeletal muscle Autonomic: smooth muscle, cardiac muscle, and glands • Neurotransmitters o Somatic: acetylcholine o Autonomic: acetylcholine, epinephrine, or norepinephrine

• https://www.youtube.com/watch?v=UabDiuTtU0M