BIO 3520 Notes, 9/22/08
NEUROPHYSIOLOGY II
I. General Organization of the Nervous System.
[Widmaier, pp. 138-141]
A. The nervous system is organized to sense changes in the internal or
external environment and to respond to those changes by altering the
activity of effector organs.
II. Spinal Cord. [pp. 173-174, 177]
A. Cylinder extending from base of brain to lower back (figure).
B. Functions.
1. Link between brain and peripheral nervous system.
2. Important part of many reflexes.
C. Cross-section (fig. 6-41).
a. Gray matter -- cell bodies.
1. Nucleus = Cluster of cell bodies in the CNS.
b. White matter -- mostly myelinated axons.
1. Tract = Bundle of axons in the CNS.
2. Ascending tracts -- carry sensory info towards brain.
3. Descending tracts -- carry motor commands away from brain.
III. Brain. [pp. 173-177]
A. Located in the head.
B. Functions (see table 6-7 for functions of different brain regions).
1. Sensation and perception.
2. Homeostatic control center.
3. Motor control.
4. Higher function (memory, thought, language, emotion).
C. Three general divisions (fig. 6-38).
1. Brainstem.
2. Cerebellum.
3. Forebrain.
D. Brainstem
1. Most primitive region of brain.
2. Subdivisions.
a. Medulla.
b. Midbrain.
c. Pons.
3. Functions.
a. Life-sustaining processes -- control of breathing, heart rate, and
blood pressure.
b. Reflexes -- swallowing, cough, vomiting.
c. Reticular activating system -- sleep and arousal.
E. Cerebellum -- coordination and balance.
F. Forebrain.
1. Thalamus -- major relay center.
2. Hypothalamus -- Controls many homeostatic systems.
a. Food intake.
b. Water balance.
c. Body temperature.
d. Endocrine system.
3. Limbic system -- Ring of interconnected structures surrounding
thalamus (fig. 6-40).
a. Olfaction (smell).
b. Emotion.
c. Motivation.
d. Learning.
4. Cerebrum.
a. Most advanced portion of brain.
b. 80% of human brain.
c. Functions.
1. Sensory perception.
2. Motor control.
3. Higher functions.
d. Mostly white matter (fig. 6-39).
e. Separated into two cerebral hemispheres.
1. Connected by corpus callosum.
f. Covered by a thin (3 mm) outer shell of gray matter --
cerebral cortex.
1. Highly developed in human.
2. Many folds on surface.
3. Each hemisphere is divided into four lobes.
g. Four lobes of cerebral cortex (fig. 6-38).
1. Frontal lobe -- movement, language, expression of emotion.
2. Parietal lobe -- sensory information from skin and joints.
3. Occipital lobe -- vision.
4. Temporal lobe -- hearing, language, memory.
h. Specialization of the left and right hemispheres (figurea).
1. Sensory and motor pathways cross over.
2. Left hemisphere controls speech, math, and logic.
3. Right specializes in nonlanguage skills (ex. art, music).
4. "The Split Brain Revisited" -- Scientific American (July 1998)
(figure).
a. Ask subject what he sees --
b. Have subject point to a related object --
c. Ask why he pointed to the shovel --
a Fox, S.I. Human Physiology, 7th ed., 2002.
IV. Anatomy of the Peripheral Nervous System. [pp. 139-143, 177-180]
A. Made up of nerves arising from the CNS.
1. Nerve = Bundle of axons in the PNS.
2. Contain both sensory and motor neurons bundled together.
3. 12 pairs of cranial nerves arise from the brain (figureb).
a. Serve face and upper body.
4. 31 pairs of spinal nerves arise from spinal cord (fig. 6-42).
a. Serve upper and lower body.
b. Sensory neurons enter via dorsal roots (fig. 6-41).
c. Motor neurons exit via ventral roots.
b Moffett, Moffett, and Schauf, Human Physiology: Foundations & Frontiers,
2nd ed., 1993.
V. Afferent (Sensory) Division. [pp. 191-200, 203-204, 206-207]
A. Function -- Carry sensory information to the CNS.
B. Anatomy of sensory neuron (fig. 7-4).
1. Cell body is in dorsal root ganglion of spinal nerve.
a. Ganglion = Cluster of cell bodies in the PNS.
2. Axon extends from sensory receptor into gray matter of spinal cord.
a. Peripheral process -- sensory receptor to cell body.
b. Central process -- cell body to spinal cord.
c. Axon terminal -- in gray matter of spinal cord.
C. Review of terminology.
|
Axons |
Cell Bodies |
|
| CNS | ||
| PNS |
D. Sensory receptors.
1. Sensory receptors transform the mechanical energy of a stimulus into
electrical energy.
2. Receptor anatomy.
a. Some are bare nerve endings.
b. Others involve specialized membranes (ex. Pacinian corpuscle)
(figurea).
3. Receptor potential = Depolarization of the receptor membrane in
response to a stimulus.
a. Graded potential.
b. Amplitude varies with intensity of stimulus.
c. Can be summed.
d. If stimulus is adequate, action potential is triggered (fig. 7-2).
E. Sensory Coding.
1. Stimulus type.
a. Each type of sensory receptor is highly sensitive to one type of
stimulus and generally not responsive to other stimuli.
|
Type of Receptor |
Type of Stimulus |
Example |
|
Chemoreceptors |
|
|
|
Photoreceptors |
|
|
|
Thermoreceptors |
|
|
|
Mechanoreceptors |
|
|
|
Pain receptors |
|
|
2. Stimulus intensity.
a. Stimulus intensity is coded by the _____________________ of
action potentials (fig. 7-5).
b. Sensory adaptation = Decrease in receptor firing when the
stimulus is maintained at a constant level (fig. 7-3).
3. Stimulus location.
a. Stimuli from two different locations travel along separate pathways
in the spinal cord and are sent to different parts of the brain.
b. Receptive field = Area innervated by a single sensory neuron.
1. More sensitive areas have smaller receptive fields and higher
density of sensory receptors.
2. Two-point discrimination test (figurea).
c. Sensory pathways involve a series of neurons ascending to the
cerebral cortex (fig. 7-19a).
1. First order neuron (sensory neuron) -- sensory receptor to
spinal cord.
2. Second-order neuron -- spinal cord to thalamus.
a. Interneuron = Neuron contained entirely within the CNS.
b. Fibers cross over.
3. Third-order neuron -- thalamus to cerebral cortex.
F. Sensory areas of the cerebral cortex.
1. Somatosensory cortex (parietal lobe) (fig. 7-14).
a. Receives sensory information from skin and joints.
b. From opposite side of body.
c. Sensory areas are arranged according to body structure (fig. 7-20).
2. Somatic association area (parietal lobe).
a. Posterior to somatosensory cortex.
b. Interpretation of sensory information.
3. Auditory cortex (temporal lobe) -- hearing.
4. Visual cortex (occipital lobe) -- vision.
VI. Vision. [pp. 208-217, 227]
A. Vision is one of the special senses (along with hearing, taste, smell).
B. Structure of the eye (fig. 7-22).
1. Fluid‑filled sphere.
2. Outer coat.
a. Sclera ‑‑ white.
b. Cornea.
1. Anterior portion.
2. Transparent -- permits light to enter eye.
3. Iris.
a. Ring of smooth muscle.
b. Controls amount of light entering the eye.
c. Pigment determines the eye color.
d. Central opening is the pupil.
4. Lens.
a. Transparent biconvex disc behind the iris.
b. Curvature is controlled by smooth muscle attachments.
c. Focuses image on retina.
d. Cataracts.
1. Clouding of the lens.
2. Leading cause of blindness in U.S.
3. Treatment -- Surgical removal of lens and replacement with
artificial lens.
5. Cavities.
a. Anterior cavity.
1. In front of lens.
2. Filled with aqueous humor.
b. Posterior cavity.
1. Filled with vitreous humor.
2. Maintains spherical shape of the eye.
c. Glaucoma.
1. High intraocular pressure.
2. Leads to retinal damage and blindness.
6. Retina.
a. Covers inner surface of the posterior portion.
b. Reception of light images.
c. Composed of photoreceptors and neurons.
d. Fovea ‑‑ point of greatest visual acuity.
7. Optic nerve.
a. Bundle of axons projecting from retinal neurons.
b. Carries visual info from retina to brain.
c. Point at which optic nerve leaves the eye is the optic disc.
1. Blood supply to eye enters and exits here.
2. Blind spot (fig. 7-22).
C. Refraction.
1. Surface of cornea is convex so that light rays are bent inward.
2. Lens is convex so that light rays converge to form a focused image
on the retina.
3. Image appears on the retina upside down and reversed.
4. Central portion of image is focused on the fovea.
5. Curvature of lens can be changed by smooth muscle attachments
(fig. 7-24).
a. Accommodation = Increased curvature of the lens in order to
focus on nearby objects.
b. Objects more than 20 feet away can be focused without
accommodation.
D. Refractive problems (fig. 7-26).
1. Near‑sightedness (myopia).
a. Focal point falls short of the retina.
b. Due to an elongated eyeball.
c. Difficulty focusing on distant objects.
d. Tested using visual acuity chart.
e. Corrected with concave lenses.
f. Surgical correction -- flatten cornea.
2. Far‑sightedness (hyperopia).
a. Focal point falls beyond the retina.
b. Due to shortened eyeball.
c. Difficulty focusing on nearby objects.
d. Corrected with convex lenses.
3. Astigmatism.
a. Unequal curvature of the eye's refractive system.
b. Some areas are focused while others are not.
c. Tested using astigmatism chart.
d. Corrected by special lenses.
4. Presbyopia.
a. Gradual loss of ability to accommodate.
b. Near-point measurement.
c. Begins after age 40 (figure).
d. Corrected with convex lenses (bifocals).
E. Photoreceptors of the retina.
1. Mechanisms of photoreception.
a. Photoreceptors absorb light.
b. Produces chemical changes within the cell.
c. Results in changes in membrane potential.
d. Action potentials sent to the occipital lobe.
2. Types of photoreceptors (fig. 7-27).
a. Rods.
1. Sensitive to low levels of illumination.
2. Lack color discrimination.
3. Brain interprets their responses as shades of gray.
b. Cones.
1. Respond only to high levels of illumination.
2. Brain interprets their responses as colors.
3. Three kinds, each responding to a different range of wavelengths --
red, green, and blue (fig. 7-30).
4. Missing red or green cones results in red‑green color blindness.
3. Adaptation to light and dark.
a. Adaptation from dark to light.
1. Pupils constrict.
2. Rods bleach out (lose sensitivity) -- prevents damage.
3. Cones are active.
b. Adaptation from light to dark.
1. Pupils dilate.
2. Rods increase in sensitivity.
3. Cones are insensitive to low level of illumination.
VII. Chemoreception. [pp. 224-227]
A. Taste.
1. Sense organs are the taste buds located on the surface of the tongue
(fig. 7-44).
2. Chemicals must be dissolved in liquid in order to reach the taste buds.
3. Five distinct taste categories.
a. Sweet (simple sugars)
b. Sour (acid).
c. Salty (sodium).
d. Bitter (plant alkaloids).
e. Umami (glutamate).
B. Smell (olfaction).
1. Sense organ is the olfactory epithelium in the upper nasal cavity
(fig. 7-45).
2. Detect substances diffusing through the air.
3. About 1000 different olfactory receptor types.
VIII. Efferent (Motor) Division. [pp. 177-180, 297-299, 304-305]
A. Function -- Carries motor commands to effector organs.
B. Subdivisions.
1. Somatic motor neurons.
a. Innervate skeletal muscle.
b. Voluntary control.
2. Autonomic motor neurons.
a. Innervate smooth muscle, cardiac muscle, and glands.
b. Involuntary control.
C. Anatomy of a somatic motor neuron (fig. 6-4).
1. Dendrites and cell bodies are located in gray matter of spinal cord.
2. Axon exits spinal cord via the ventral root.
3. Axon terminal ends very close to a skeletal muscle fiber.
4. Neuromuscular junction = Synapse between a somatic motor
neuron and a skeletal muscle fiber.
D. Autonomic motor neurons.
1. Autonomic motor pathway involves two neurons.
2. Synapse between these two neurons is located outside the CNS
in an autonomic ganglion (fig. 6-43).
3. Preganglionic neuron -- cell body in CNS, axon terminal in ganglion.
4. Postganglionic neuron -- cell body in ganglion, axon terminal in
effector organ.
E. Control of movement.
1. Somatic motor neuron receives input from other spinal neurons and
motor areas of brain.
a. Motor neuron will fire if combined EPSP's and IPSP's cause
depolarization to threshold.
2. Voluntary control of movement involves complicated interaction
between sensory stimuli and motor commands.
3. Motor areas of the brain.
a. Primary motor cortex.
1. In frontal lobe, anterior to the somatosensory cortex (fig. 10-10).
2. Initiates actions on the opposite side of the body.
3. Motor areas are arranged according to body structure
(fig. 10-11).
4. Receives constant feedback from somatosensory cortex.
b. Premotor cortex.
1. Anterior to primary motor cortex in frontal lobe.
2. Directs complex, learned patterns of movement.
c. Cerebellum -- coordination and balance.
VII. Reflexes. [pp. 9-11, 210-212, 299-304]
A. A reflex is a rapid, involuntary response to a stimulus.
B. Components of a reflex arc.
1. Sensory receptor.
2. Sensory neuron.
3. Central nervous system (brain or spinal cord).
4. Motor neuron.
5. Effector organ (muscle or gland).
C. Examples of reflexes.
1. Knee-jerk reflex (fig. 10-6).
a. Sensory receptors -- stretch receptors in quadriceps muscle.
b. Action potential travels along sensory neuron.
c. Synapse in gray matter of spinal cord with cell body and
dendrites of somatic motor neuron.
1. Triggers action potential in motor neuron.
2. Monosynaptic.
d. Motor neuron innervates same muscle that was stretched.
e. Excitation causes muscle contraction.
f. Reflex may be modified by EPSP's and IPSP's from higher level
neurons ----> facilitation or inhibition.
2. Withdrawal reflex (fig. 10-9).
a. Sequence of events leading to withdrawal of hand or foot from
painful stimulus.
b. Sensory receptors -- pain receptors.
c. Response.
1. Contraction of flexor muscles.
2. Relaxation of extensor muscles.
d. Involves interneurons in spinal cord -- polysynaptic reflex.
e. Properties (compared to monosynaptic).
1. More complex.
2. Slower, due to synaptic delay.
3. Pupillary reflex (figurea).
a. Constriction of pupils in response to a light stimulus.
b. Example of an autonomic reflex.
VIII. Reaction Times. [pp. 297-299]
A. Reaction timer measures a voluntary response to a stimulus
(this is not a reflex).
B. Differences in reaction times are due to the synaptic delay.
IX. Speech and Language. [pp. 247-249]
A. Communication of ideas through language is a function unique to
human beings.
B. Ideas are communicated by sounds or writing.
C. Language is controlled by left hemisphere in 95% of people.
D. Language comprehension.
1. Sensory input is interpreted as words by visual association area
(occipital lobe) and auditory association area (temporal lobe)
2. Wernicke's area (temporal lobe) -- comprehension of spoken or
written language (fig. 8-15).
E. Speech.
1. Wernicke's area -- develops ideas into words.
2. Broca's area (frontal lobe).
a. Arranges sequences of words into sentences.
b. Controls larynx and mouth and influences respiratory center.
3. Damage to either Broca's or Wernicke's areas causes disruption of
speech (aphasia).
a. Writing is almost always disrupted when speech is disrupted.
b. When Broca's area is damaged, speech is slow and articulation
is impaired.
c. When Wernicke's area is damaged, speech is phonetically and
grammatically normal, but the meaning is unclear.
X. Stroke. [pg. 186]
A. Blockage of blood supply to an area of the brain.
B. Causes.
1. Blood clot.
2. Broken blood vessel (aneurysm).
3. Atherosclerosis.
C. Consequences.
1. Death, if vital brain areas are damaged.
2. Disability, if less vital areas are affected.
a. Paralysis on opposite side of body.
b. Stroke affecting left hemisphere often results in damage to
speech areas (aphasia).
3. Recovery due to other brain areas taking over lost function.