Lecture
#21: The Vertebrate Nervous System (Fig. 48.16)
I. THE PERIPHERAL
NERVOUS SYSTEM (Fig. 48.17)
1. The sensory
(afferent) nervous system brings info from sensory receptors toward CNS,
e.g., olfactory and optic cranial nerves that are sensory.
a. somatic
sensory neurons bring info from external environment.
b. visceral
sensory neurons bring info from internal (visceral) organs.
2. The motor
(efferent) nervous system sends signals from CNS to effector cells such as
muscles and glands.
a. somatic
motor neurons are mainly voluntary since they carry out conscious control
of skeletal muscles.
b. visceral motor
neurons are mainly involuntary, automatic signals via autonomic nervous
system, which controls smooth and cardiac muscles and glandular secretions
and excretions. (Fig. 48.18)
(1) sympathetic
division originates in thoracic and lumbar segments of spinal cord and acts
via chain of sympathetic ganglia to prepare for energy expenditure in times of
crisis.
(2) parasympathetic
division originates in cranial medulla and sacral segments of spinal cord
and promotes digestion and other processes related to energy.
(3) they usually
have antagonistic actions on target tissues.
(4) norepinephrine
versus acetylcholine at axon terminus of post-synaptic neurons.
II. THE MAMMALIAN
BRAIN (and the Central Nervous System)
A. GENERAL
COMMENTS
1. The CNS is the
integration and command center.
2. It is hollow,
with ventricles in brain that are continuous with spinal canal (CS fluid).
3. White
matter (myelin around axons) vs grey matter (cells). (white inside in
brain)
4. Embryonic
development of the brain (Fig. 48.19)
B. PRINCIPAL
COMPONENTS OF THE ADULT BRAIN
1. The brainstem
consists of three major parts that function in homeostasis, movement
coordination, and conduction of information to higher brain centers: (Fig. 48.20)
a. the medulla
oblongata controls certain visceral (autonomic, homeostatic) functions,
e.g., breathing, heart/vascular, swallowing, vomiting, and digestion.
b. the pons
also influence breathing and other homeostatic functions.
c. the midbrain
contains the inferior and superior colliculi, which coordinate auditory and
visual reflexes respectively.
2. The cerebellum
functions primarily to coordinate voluntary (skeletal) movement. (Fig. 48.20)
a. it receives
sensory info of position of all of body joints and muscles.
b. it receives
"duplicates" of all motor commands from cerebrum.
c. it can then
"fine tune" the actual movements.
d. it also
cooperates closely with info from auditory and visual systems.
3. The embryonic
diencephalon consists of three parts which have variable functions. (Fig. 48.20)
a. the hypothalamus
(weighing less than 1% of the brain) has many functions in HOMEOSTASIS:
(1)
neurohypophyseal secretions and releasing factors.
(2) contains
body's thermostat.
(3) contains body's
osmoregulatory center to control body fluids.
(4) centers for
regulating hunger and eating, thirst, and drinking.
(5) site of the
"fight-or-flight" center.
(6) coordinator
of mating behavior and sexual arousal and response.
(7) seat of
pleasure and satisfaction.
b. the thalamus
is a major relay station to cerebrum:
(1) the thalamus
sorts out all incoming sensory information and sends it to the appropriate
higher brain centers.
(2) the thalamus
receives input from the cerebrum and from emotional and arousal centers (in
hypothalamus).
c. the epithalamus
includes the pineal, which produces melatonin and regulates biological rhythms.
4. The cerebrum
is massive in primates and cetaceans (Fig. 48.24)
a. the cerebral
cortex is the most complex integrator of thought processes and coordinator
of somatosensory input with motor commands.
(Fig. 48.25)
b. the corpus
callosum serves as a communications network between right and left
cortex. (Fig. 48.24)
c. the basal
nuclei are important centers for motor coordination. (switching
stations) (Fig. 48.24)
III. INTEGRATION
OF HIGHER BRAIN FUNCTIONS
1. Lateralization
refers to fact that each side of the cerebreal cortex is specialized for
different functions.
a. the left
hemisphere processes speech, language, calculation, and rapid serial processing
of details.
b. the right
hemisphere processes overall context, spatial perception, and creative
abilities.
2. The reticular
formation is a functional system of neurons in the core of the brainstem
that control sleep and arousal. (Fig. 48.21)
a. the pons and
medulla contain nuclei that cause sleep when stimulated.
b. the midbrain
has a center that causes arousal.
3. The limbic
system is associated with emotions to laugh, cry, love, hate, envy, worry, etc.
This system anatomically includes the hypothalamus, thalamus, amygdala and
hippocampus. (Fig. 48.27)
4. Learning
and memory appear to be based on synaptic changes related to the release of
the neurotransmitter glutamate by the presynaptic cell.
5. Speech and
language centers are also localized in special areas of the cerebral
cortex. (Fig. 48.24)
a. Wernicke's
area for vocabulary selection and word arrangement into grammer.
b. Broca's
area primes the motor cortex to move tongue, lips, vocal cords, etc.
6. Consciousness
is the subjective awareness of the external environment and the ability to make
conscious judgments about appropriate ways to interact with the external
environment.