Download HUMAN PHYSIOLOGY

Chapter Goals (Neurons)
After studying this chapter, students should be able to . . .
1. describe the structure of a neuron and explain the functional significance of its principal
regions.
2. explain what is meant by the blood-brain barrier and discuss its significance.
3. describe the sheath of Schwann and explain how it functions in the regeneration of cut
peripheral nerve fibers.
4. explain how a myelin sheath is formed.
5. define depolarization, repolarization, hyperpolarization, and refractory period.
6. explain the actions of voltage-regulated Na+ and K+ channels and describe the events that
occur during the production of an action potential.
7. describe the properties of action potentials and explain the significance of the all-or-none
law and the refractory periods.
8. explain how action potentials are regenerated along a myelinated and a nonmyelinated
axon.
Chapter Goals
9. describe the events that occur in the interval between the electrical excitation of an axon and
the release of neurotransmitter.
10. describe the two general categories of chemically regulated ion channels, and explain how
these operate using nicotinic and muscarinic ACh receptors as examples.
11. explain how ACh produces EPSPs, and how IPSPs are produced, and indicate the significance
of these processes.
12. compare the characteristics of EPSPs and action potentials.
13. compare the mechanisms that inactivate ACh with those that inactivate monoamine
neurotransmitters.
14. explain the role of cyclic AMP in the action of monoamine neurotransmitters, and some of the
actions of monoamines in the nervous system.
15. explain the significance of the inhibitory effects of glycine and GABA in the central nervous
system.
16. explain how EPSPs and IPSPs can interact and discuss the significance of spatial and
temporal summation and of presynaptic and postsynaptic inhibition.
Chapter Goals (CNS)
After studying this chapter, students should be able to . . .
1. locate the major brain regions and describe their structures.
2. describe the organization of the cerebrum and the primary roles of its lobes.
3. describe the location and function of the sensory cortex and motor cortex.
4. describe the structures involved in the control of speech and explain their
interrelationships.
5. describe the structures included in the limbic system and its role in emotion.
6. describe the location of the thalamus and explain the significance of this
organ.
7. describe the location of the hypothalamus and explain the significance of this
organ.
8. explain the role of the medulla oblongata in the control of visceral functions.
9. explain how the spinal cord is organized
10. explain the structures and pathways involved in a reflex arc.
Action Potentials
• Action Potential (Transient reversal of
polarity) - concept of voltage-activated
gates or pores.
– a. Reverse polarity via increased permeability
to Na+
– b. Re-establish polarity via  permeability to
Na+ &  permeability to K+
– c. Re-establish original ion concentration via
Na+ pump.
Electrical Activity in Axons
• Ion Gates
• Action Potentials
• Conduction of Nerve Impulses
– In Unmyelinated Neurons
– In myelinated Neurons
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Neurons
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Structure
Types
Synaptic Transmission
Neural Circuits
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Neuron Types
• Myelinated - has myelin sheath.
– Speeds impulse conduction via saltatory
conduction (impulse hops from node to
node; therefore, more efficient).
– Enhances fidelity of neuron fiber
regeneration.
• Non-myelinated - has no myelin sheath
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Synaptic Transmission
• Types of Synapses
– Electrical Synapses: Gap Junctions
– Chemical Synapses
• Using Acetylcholine
• Using Other Neurotransmitters
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Synaptic Integration
• Long-term Potentiation (Facilitation)
• Inhibition
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Central Nervous System
• Organization of NS
– CNS
• Brain
• Spinal Cord
– Peripheral NS
• Afferent Division (Sensory and Visceral Stimuli)
• Efferent Division
– Somatic
– Autonomic
» Sympathetic
» Parasympathetic
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Major Brain Regions
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Cerebral Cortex
Basal Nuclei
Thalamus
Hypothalamus
Cerebellum
Brain Stem
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Cerebral Cortex
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Sensory perception
Voluntary movement
Language
Personality traits
Knowledge, memory, etc.
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Basal Nuclei
• Inhibition of muscle tone
• Coordination of slow, sustained movements
• Suppression of useless movements
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Thalamus
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Relay station of synaptic input
Crude awareness of sensations
Some degree of consciousness
Role in motor control
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Hypothalamus
• Regulator of ANS
• Link between nervous and endocrine
systems
• Involved with emotion and basic behavior
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Cerebellum
• Maintenance of balance
• Enhancement of motor tone
• Coordination and planning of skilled
voluntary muscle activity
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Brain Stem
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Origin of most cranial nerves
Control of basic life functions
Equilibrium control
Reception and integration of all synaptic
input from spinal cord; arousal and
activation of cerebral cortex
• Sleep centers
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Limbic System (Emotion)
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Spinal Cord
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Chapter Summary
Neurons and Supporting Cells
I. The nervous system is divided into the central nervous system (CNS) and the
peripheral nervous system (PNS).
A. The central nervous system includes the brain and spinal cord, which contain
nuclei and tracts.
B. The peripheral nervous system consists of nerves and ganglia.
II. A neuron consists of dendrites, a cell body, and an axon.
A. The cell body contains the nucleus, Nissl bodies, neurofibrils and other
organelles.
B. Dendrites receive stimuli, and the axon conducts nerve impulses away from the
cell body.
Chapter Summary
III. A nerve is a collection of axons in the PNS.
A. A sensory, or afferent, neuron is pseudounipolar and conducts impulses from
sensory receptors into the CNS.
B. A motor, or efferent, neuron is multipolar and conducts impulses from the CNS to
effector organs.
C. Interneurons, or association neurons, are located entirely within the CNS.
D. Somatic motor nerves innervate skeletal muscle; autonomic nerves innervate
smooth muscle, cardiac muscle, and glands.
IV. Supporting cells include Schwann cells and satellite cells in the PNS; in the
CNS they include the various types of glial cells; oligodendrocytes,
microglia, astrocytes, and ependymal cells.
A. Schwann cells form a sheath of Schwann around axons of the PNS.
B. Some neurons are surrounded by successive wrappings of supporting cell
membranes called a myelin sheath. This sheath is formed by Schwann cells in
the PNS and oligodendrocytes in the CNS.
C. Astrocytes in the CNS may contribute to the blood-brain barrier
Chapter Summary
The Synapse
I. Gap junctions are electrical synapses, found in cardiac muscle, smooth
muscle, and some regions of the brain.
II. In chemical synapses, neurotransmitters are packaged in synaptic vesicles
and released by exocytosis into the synaptic cleft.
A. The neurotransmitter can be called the ligand of the receptor.
B. Binding of the neurotransmitter to the receptor causes the opening of
chemically regulated gates of ion channels.
Chapter Summary
Acetylcholine as a Neurotransmitter
I. There are two different subtypes of ACh receptors: nicotinic and muscarinic.
A. Nicotinic receptors enclose membrane channels and open when ACh
bonds to the receptor. This causes a depolarization called an excitatory
postsynaptic potential (EPSP) in skeletal muscle cells.
B. The binding of ACh to muscarinic receptors opens ion channels
indirectly, through the action of G-proteins. This can cause a
hyperpolarization called an inhibitory postsynaptic potential (IPSP).
C. After ACh acts at the synapse it is inactivated by the enzyme
acetylcholinesterase (AChE).
II. EPSPs are graded and capable of summation. They decrease in amplitude
with distance as they are conducted.
III. ACh is used in the PNS as the neurotransmitter of somatic motor neurons,
which stimulate skeletal muscles to contract, and by some autonomic
neurons.
Chapter Summary
IV. ACh in the CNS produces EPSPs at synapses in the dendrites or cell body.
These EPSPs travel to the axon hillock, stimulate opening of voltageregulated gates, and generate action potentials in the axon.
Chapter Summary
Monoamines as Neurotransmitters
I. Monoamines include serotonin, dopamine, norepinephrine, and epinephrine.
The last three are also included in the subcategory known as
catecholamines.
A. These neurotransmitters are inactivated after being released, primarily by
reuptake into the presynaptic nerve endings.
B. Catecholamines may activate adenylate cyclase in the postsynaptic cell, which
catalyzes the formation of cyclic AMP.
II. Dopaminergic neurons (those that use dopamine as a neurotransmitter) are
implicated in the development of Parkinson’s disease and schizophrenia.
Norepinephrine is used as a neurotransmitter by sympathetic neurons in the
PNS and by some neurons in the CNS.
Chapter Summary
Other Neurotransmitters
I. The amino acids glutamate and aspartate are excitatory in the CNS.
A. The subclass of glutamate receptor designated as NMDA receptors are
implicated in learning and memory.
B. The amino acids glycine and GABA are inhibitory. They produce
hyperpolarizations, causing IPSPs, by opening Cl- channels.
II. There are a large number of polypeptides that function as neurotransmitters,
including the endogenous opioids.
III. Nitric oxide functions as both a local tissue regulator and a neurotransmitter
in the PNS and CNS. It promotes smooth muscle relaxation and is
implicated in memory.
Chapter Summary
Synaptic Integration
I. Spatial and temporal summation of EPSPs allows a sufficient depolarization
to be produced to cause the stimulation of action potentials in the
postsynaptic neuron.
A. IPSPs and EPSPs from different synaptic inputs can summate.
B. The production of IPSPs is called postsynaptic inhibition.
II. Long-term potentiation is a process that improves synaptic transmission as a
result of the use of the synaptic pathway. This process thus may be a
mechanism for learning.
Chapter Summary
Structural Organization of the Brain
During embryonic development, five regions of the brain are formed: the
telencephalon, diencephalon, mesencephalon, metencephalon, and
myelencephalon.
A. The telencephalon and diencephalon constitute the forebrain; the
mesencephalon is the midbrain, and the hindbrain is composed of the
metencephalon and the myelencephalon
B. The CNS begins as a hollow tube, and thus the brain and spinal cord are hollow.
the cavities of the brain are known as ventricles.
Chapter Summary
Cerebrum
I. The cerebrum consists of two hemispheres connected by a large fiber tract
called the corpus callosum.
A. The outer part of the cerebrum, the cerebral cortex, consists of gray matter.
B. Under the gray matter is white matter, but nuclei of gray matter, known as the
basal nuclei, lie deep within the white matter of the cerebrum.
C. Synaptic potentials within the cerebral cortex produce the electrical activity seen
in an electroencephalogram (EEG).
II. The two cerebral hemispheres exhibit some degree of specialization of
function, a phenomenon called cerebral lateralization.
A. In most people, the left hemisphere is dominant in language and analytical ability,
whereas the right hemisphere is more important in pattern recognition, musical
creation, singing, and the recognition of faces.
B. The two hemispheres cooperate in their functions; this is aided by
communication between the two via the corpus callosum.
Chapter Summary
III. Particular regions of the left cerebral cortex appear to be important in
language ability; when these areas are damaged, characteristic types of
aphasias result.
A. Wernicke’s area is involved in speech comprehension, whereas Broca’s area is
required for the mechanical performance of speech.
B. Wernicke’s area is believed to control Broca’s area by means of the arcuate
fasciculus.
C. The angular gyrus is believed to integrate different sources of sensory
information and project to Wernicke’s area.
IV. The limbic system and hypothalamus are regions of the brain that have been
implicated as centers for various emotions.
V. Memory can be divided into short-term and long-term categories.
A. The medial temporal lobes, in particular the hippocampus and perhaps the
amygdaloid nucleus, appear to be required for the consolidation of short-term
memory into long-term memory.
B. Particular aspects of a memory may be stored in numerous brain regions.
C. Long-term potentiation is a phenomenon that may be involved in some aspects
of memory.
Chapter Summary
Diencephalon
I. The diencephalon is the region of the forebrain which includes the thalamus,
epithalamus, hypothalamus, and pituitary gland.
A. The thalamus serves an important relay center for sensory information, among its
other functions.
B. The epithalamus contains a choroid plexus, where cerebrospinal fluid is formed.
The pineal gland, which secretes the hormone melatonin, is also part of the
epithalamus.
C. The hypothalamus forms the floor of the third ventricle, and the pituitary gland is
located immediately inferior to the hypothalamus.
II. The hypothalamus is the main control center for of visceral activities.
A. The hypothalamus contains centers for the control of thirst, hunger, body
temperature, and (together with the limbic system) various emotions.
B. The hypothalamus regulates the secretions of the pituitary gland. It controls the
posterior pituitary by means of a fiber tract, and it controls the anterior pituitary by
means of hormones.
Chapter Summary
Midbrain and Hindbrain
I. The midbrain contains the superior and inferior colliculi, which are involved in
visual and auditory reflexes, respectively and nuclei that contain
dopaminergic neurons that project to the corpus striatum and limbic system
of the forebrain.
II. The hindbrain consists of two regions: the metencephalon and the
myelencephalon.
A. The metencephalon contains the pons and cerebellum. The pons contains nuclei
for four pairs of cranial nerves, and the cerebellum plays an important role in the
control of skeletal movements.
B. The myelencephalon consists of only one region, the medulla oblongata. The
medulla contains centers for the regulation of such vital functions as breathing
and the control of the cardiovascular system.
Chapter Summary
Spinal Cord Tracts
I. Ascending tracts carry sensory information from sensory organs up to the
spinal cord to the brain.
II. Descending tracts are motor tracts and are divided into two groups: the
pyramidal and the extrapyramidal systems.
A. Pyramidal tracts are the corticospinal tracts. They begin in the precentral gyrus
and descend, without synapsing, into the spinal cord.
B. Most of the corticospinal fibers decussate in the pyramids of the medulla
oblongata.
C. Regions of the cerebral cortex, the basal nuclei, and the cerebellum, control
movements indirectly by synapsing with other regions that give rise to
descending extrapyramidal fiber tracts.
D. The major extrapyramidal motor tract is the reticulospinal tract, which has its
origin in the reticular formation of the midbrain.
Chapter Summary
Cranial and Spinal Nerves
I. There are twelve pairs of cranial nerves. Most of these are mixed, but some
are exclusively sensory in function.
II. There are thirty-one pairs of spinal nerves. Each of these contains both
sensory and motor fibers.
A. The dorsal root of a spinal nerve contains sensory fibers, and the cell bodies of
these neurons are contained in the dorsal root ganglion.
B. The ventral root of a spinal nerve contains motor fibers.
III. A reflex arc is the pathway that involves a sensory neuron and a motor
neuron; one or more association neurons also may be involved in some
reflexes.