sensory neuron, integration center, motor neuron, and eﬀector.
stretch reﬂex is important for maintaining muscle tone and adjusting it
reﬂexively by causing muscle contraction in response to increased mus-
cle length (stretch). It maintains posture. Te ﬂexor or withdrawal reﬂex
is initiated by a painful stimulus and causes automatic withdrawal of the
painful body part from the stimulus. It is protective.
Tis response is
called Babinski’s sign and it indicates damage to the corticospinal tract
or primary motor cortex.
Te vertebral column, spinal nerves, and
dermatomes are all examples of segmentation in the adult.
Review Questions 1.
(1)d, (2)c, (3)f, (4)b,
(1)f, (2)i, (3)b, (4)g, h, (5)e, (6)i, (7)c, (8)k, (9)l, (10)c, d, f, k;
(1)b 6; (2)d 8; (3)c 2; (4)c 5; (5)a 4; (6)a 3, 9; (7)a 7; (8)a 7; (9)d 1;
(10)a 3, 4, 7, 9;
(1)a, 1 and 5; (2)a, 3 and 5; (3)a, 4; (4)a, 2; (5)c, 2;
Case Study 1.
Cerebrospinal ﬂuid (CSF) is leaking out of Mr. Hancock’s
right ear. Te fracture must have torn both the dura mater and arachnoid
mater. In addition, the tympanic membrane must have ruptured. Antibi-
otics were administered to prevent infection by bacteria that might enter
through the ruptured meninges, causing meningitis. Elevating the head
of the bed decreases the CSF pressure in the skull. (Tis allows the torn
meninges to heal spontaneously in the majority of cases.)
tions on Mr. Hancock’s chart indicate: (a) Either damage to CN VIII (the
vestibulocochlear nerve, which transmits aﬀerent impulses for the sense
of hearing) or destruction of the cochlea (the sensory organ for hearing).
(b) Damage to CN V
(the mandibular division of the trigeminal nerve),
which runs through the foramen ovale. Tis nerve conveys sensory infor-
mation from the lower part of the face. (c) Damage to CN V
lary division of the trigeminal nerve), which runs through the foramen
rotundum. Tis nerve conveys sensory information from the skin of the
upper lip, lower eyelid, and cheek. (d) Damage to CN VI (the abducens
nerve), which innervates the lateral rectus muscle of the eye. Because
this muscle is responsible for pulling the eye laterally (abduction), loss
of tone in this muscle at rest will cause the eye to turn inward. Diplopia
will worsen when looking to the right because the eye cannot abduct.
Te facial nerve (cranial nerve VII) is the primary motor nerve associ-
ated with facial expression. Te facial nerve also contains parasympathetic
ﬁbers that control secretion of tears from the lacrimal glands. Damage to
this nerve explains both the motor symptoms and the dryness of his eye.
Check Your Understanding 1.
Te eﬀectors of the autonomic nervous
system are cardiac muscle, smooth muscle, and glands.
motor system relays instructions to muscles more quickly because it in-
volves only one motor neuron, whereas the ANS uses a two-neuron chain.
Moreover, axons of somatic motor neurons are typically heavily myelin-
ated, whereas preganglionic autonomic axons are lightly myelinated and
postganglionic axons are nonmyelinated.
While you relax in the sun
on the beach, the parasympathetic branch of the ANS would probably
predominate. When you perceive danger (as in a shark), the sympathetic
branch of the ANS predominates.
“Short preganglionic ﬁbers,” “origin
from thoracolumbar region of spinal cord,” “collateral ganglia,” and “in-
nervates adrenal medulla” are all characteristic of the sympathetic nervous
system. ±erminal ganglia are found in the parasympathetic nervous sys-
Te major diﬀerences are (1) the ANS has visceral aﬀerents rather
than somatic aﬀerents, (2) the ANS has a two-neuron eﬀerent chain,
whereas the somatic nervous system (SNS) has one, and (3) the eﬀectors
of the ANS are smooth muscles, cardiac muscle, and glands, whereas
the eﬀectors of the SNS are skeletal muscles.
nervous system increases digestive activity and decreases heart rate. Te
sympathetic nervous system increases blood pressure, dilates bronchi-
motor (eﬀerent) neurons.
Premature babies have trouble regulating
body temperature because the hypothalamus is immature.
causes of dementia include prescription drug eﬀects, low blood pressure,
poor nutrition, hormone imbalances, depression, and dehydration.
Review Questions 1.
(1)d, (2)f, (3)e, (4)g, (5)b, (6)f,
(1)a, (2)b, (3)a, (4)a, (5)b, (6)a, (7)b, (8)b, (9)a;
(1)d, (2)e, (3)c and d, (4)a;
Case Study 1.
Te four regions of the brain are the cerebral hemispheres,
diencephalon, brain stem, and cerebellum. A cerebral hemisphere is
involved in this case. Motor functions and language are both located in
this cerebral hemisphere and have been aﬀected by the injury.
le² side of the brain has been aﬀected in this case. Te motor dysfunc-
tion on the right side of the body is the primary piece of evidence used
to determine this. In addition, the brain areas serving speech are usually
located in the le² side.
Te motor dysfunction on the right side of the
body suggests that the injury has aﬀected the primary motor cortex and
possibly the premotor cortex of the le² cerebral hemisphere. In addition
to the problems with motor function, Mrs. Bryans experienced diﬃculty
with language. ±wo areas of the brain associated with language, Broca’s
and Wernicke’s area, are usually located in the le² cerebral cortex. Te
type of aphasia described suggests damage to Broca’s area.
surface of the brain to the skull, the three membranes that make up the
meninges include the pia mater, arachnoid mater, and dura mater.
subarachnoid hemorrhage involves bleeding into the region below (
below) the arachnoid mater. Te subdural hematoma involves blood
collecting between the dura mater and the arachnoid mater.
Check Your Understanding 1.
In addition to nerves, the PNS also
consists of sensory receptors, motor endings, and ganglia.
respond to painful stimuli. Tey are exteroceptors that are nonencap-
sulated (free nerve endings).
Te three levels of sensory integration
are receptor level, circuit level, and perceptual level.
adapt, whereas tonic receptors exhibit little or no adaptation. Pain recep-
tors are tonic so that we are reminded to protect the injured body part.
Hot and cold are conveyed by diﬀerent sensory receptors that are parts
of separate “labeled lines.” Cool and cold are two diﬀerent intensities of
the same stimulus, detected by frequency coding—the frequency of APs
would be higher for a cold than a cool stimulus. Action potentials arising
in the ﬁngers and foot arrive at diﬀerent locations in the somatosensory
cortex via their own “labeled lines” and in this way the cortex can deter-
mine their origin.
Ganglia are collections of neuron cell bodies in the
Nerves also contain connective tissue, blood vessels, lymphatic
vessels, and the myelin surrounding the axons.
Schwann cells, mac-
rophages, and the neurons themselves were all important in healing the
Te oculomotor (III), trochlear (IV), and abducens (VI) nerves
control eye movements. Sticking out your tongue involves the hypoglos-
sal nerve (XII). Te vagus nerve (X) inﬂuences heart rate and digestive
activity. Te accessory nerve (XI) innervates the trapezius muscle, which
is involved in shoulder shrugging.
Roots lie medial to spinal nerves,
whereas rami lie lateral to spinal nerves. Dorsal roots are purely sensory,
whereas dorsal rami carry both motor and sensory ﬁbers.
nal nerve roots were C
, the spinal nerve was the phrenic nerve, the
plexus was the cervical plexus. Te phrenic nerve is the sole motor nerve
supply to the diaphragm, the primary muscle for respiration.
cosities are the series of knoblike swellings that are the axon endings of
autonomic motor neurons. You would ﬁnd them on axon endings serv-
ing smooth muscle or glands.
Te cerebellum and basal nuclei, which
form the precommand level of motor control, plan and coordinate com-
plex motor activities.
Te ﬁve components of a reﬂex arc are receptor,