WEEK 12 NOTES FOR BIOLOGY 03048, ANATOMY:
OVERVIEW OF BRAIN AND CRANIAL NERVES; INTRODUCTION TO EXTREMITIES
11/16/99 W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc/academ/faculty/crone/index.html)
Moore and Dalley, Ch. 5 (aspects); Ch. 7, pp. 887; Ch. 9.
Young and Young, aspects of Chs. 3, 4, 5, 6, 9, 12, 15, 19, 21, Appendix A
some possible HVCC library a/v resources:
VT 2604,"A Visual Guide to Physical Examination: Cranial Nerves" (Bates tape)
CD-R 70,"Basic Neurochemistry" (probably more useful for Physiology)
CD-R 71,"Whole Brain Atlas" (many MRI views and case studies)
possible web site: http://thalamus.wustl.edu/course/ (Washington U. Med School Neuroscience Tutorial)
MAJOR REGIONS OF THE BRAIN:
Brain development:
forebrain with telencephalon (cerebral hemispheres) and diencephalon (thalamus)
midbrain with mesencephalon (midbrain)
hindbrain with metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata)
The cerebrum is found in the forebrain, and is the largest part of the brain-80% of brain mass. It is responsible for higher mental functions, which include memory and reason. It consists of five paired lobes and two hemispheres. Left and right hemispheres are partially divided by a longitudinal cerebral fissure. The falx cerebri portion of the meninges extends into this fissure. The corpus callosum (large tract of white matter) connects the two hemispheres, making sure that each side is aware of the other and can share memories.
Functions of the hemispheres:
left: analytical and verbal skills
right: spatial and artistic skills
Convolutions are evident, with elevated gyri (s. - gyrus) and grooves of sulci (s. - sulcus) that help to increase the gray matter area. Fissures (deep sulci) separate the cerebral hemispheres into lobes. Immediately in front of the central sulcus is the precentral gyrus (important motor region). Immediately behind the central sulcus is the postcentral gyrus (important somatesthetic area).
HAL (head-arm-leg): the homunculus functionally represented on the precentral and postcentral gyri.2
|
anterior cerebral artery lesion |
loss of strength and sensation of contralateral lower part of body |
|
middle cerebral artery lesion |
loss of strength and sensation of contralateral upper portion of body (or with lateral striate branches to the internal capsule, a contralateral hemiplegia) |
|
posterior cerebral artery lesion |
contralateral homonymous hemianopsia |
|
post. inf. cerebellar lesion |
Wallenberg syndrome or PICA syndrome: contralateral loss of pain/temp and ipsilateral ataxia and Horner's syndrome |
|
Lobe |
Function |
|
frontal |
functions include voluntary motor impulses for skeletal muscles, and dealing with responses relating to personality, reason, emotions, etc. |
|
parietal |
functions in interpretation of texture and shapes |
|
temporal |
auditory sensation, processes many memories, and is involved in the limbic system. |
|
occipital |
integrates eye movements, correlates visual images with previous stimuli, and performs conscious perception of vision. |
|
insula |
poorly-specified integrative functions |
Most (80%) of the diencephalon is the thalamus, an ovoid mass of gray matter, a paired structure found underneath the lateral ventricles of the cerebral hemispheres. The thalamus is a relay center for all sensory impulses (except smell) to the cerebral cortex.
The hypothalamus forms the floor and (part of) the lateral walls of the third ventricle, functioning to maintain homeostasis via autonomic nervous, endocrine, and limbic systems. The pituitary gland (cerebral hypophysis) is inferior and attached to the hypothalamus via the infundibulum. The circle of Willis surrounds the pituitary.
The cranial nerves:1,2
Oh, Oh, Oh, To Touch And Feel Very Green Vegetables, AH!
|
number |
name |
basic functions |
where found |
lesion |
|
CN I |
olfactory |
sense of smell |
nerve tracts from the cerebral hemispheres |
loss of smell |
|
CN II |
optic |
sense of vision |
diencephalon (thalamus) |
loss of vision, depends where along the nerve. Also concern with papilledema (swollen optic disc), from increased intracranial pressure |
|
CN III |
oculomotor |
pupil constricting, eye opening, most eye movements |
midbrain |
pupil dilation, inability to focus, ptosis (eyelid drooping), eyeball directed downward and out. |
|
CN IV |
trochlear |
downward and outward eye movement (superior oblique m.);. SO by itself is down and out (and works in conjunction with the other extraocular muscles) |
midbrain |
rare by itself, but when looking downward, diplopia (double vision). |
|
CN V |
trigeminal |
motor for mastication m., sensory for facial region |
pons |
trigeminal neuralgia or tic douloureux, or pain along the distribution of a branch of the trigeminal nerve.2 Also, depending on damage, could have anesthesia, loss of mastication function. |
|
CN VI |
abducent(s) |
lateral deviation of eye (lateral rectus m.) |
pons/medulla junction |
inability to move eye laterally beyond midpoint. |
|
CN VII |
facial |
motor for facial m., front 2/3 tongue taste, sublingual & submandibular glands |
pons/medulla junction |
Bell's palsy and paralysis of the facial muscles. |
|
CN VIII |
vestibulocochlear |
hearing (cochlear division) and balance (vestibular division) |
pons/medulla junction |
hearing loss (cochlear) and equilibrium disturbance (vestibular) |
|
CN IX |
glossopharyngeal |
carotid sinus and carotid body (along with CN X), posterior 1/3 tongue taste, sensory for pharynx |
medulla |
loss of taste in posterior 1/3 of tongue and loss of sensation in pharynx (loss of gag reflex) |
|
CN X |
vagus |
motor for palate, pharynx, larynx; sensory: pharynx and larynx; parasympathetic supply for most of thoracoabdominal cavity |
medulla |
most noticeably, the hoarseness due to lack of the laryngeal innervation. If both vagi cut, alterations in heart and respiratory rate |
|
CN XI |
accessory |
motor to sternocleidomastoid and trapezius |
medulla and spinal cord |
paralysis of trapezius and sternocleidomastoid |
|
CN XII |
hypoglossal |
motor to tongue |
medulla |
atrophy of affected side of tongue,"pointing to the lesion." |
Head autonomics: unlike in the thorax/abdomen, the parasympathetic ganglia in the head are not small and directly on the target organ. Instead, there are a few specific ganglia (ciliary, pterygopalantine, submandibular, otic) receiving preganglionic fibers from different cranial nerves (III, VII, IX). The superior cervical ganglion of the sympathetic chain is the site from which postganglionic sympathetic neurons travel to head.
Our limbs are masses of hypertrophied hypaxial muscle innervated by ventral rami of the segmented spinal nerves. As several segments (somites) contribute to the limbs, so do the rami form from nerve plexuses at the base of the limbs and have several spinal nerves contributing to limb innervation. The developing muscles in the limb bud will keep subdividing after innervation, leading to a pattern of muscle groups sharing a common nerve. They are separated by intermuscular septa, near which major nerves and vessels tend to run to avoid being squished by muscle groups. The septa blend into deep fascia surrounding limb muscles.
LOWER EXTREMITY:
The lower extremity is used for weight bearing, locomotion, and maintainence of equilibrium. One can divide up the lower extremity to three main joints and three main regions: hip joint; thigh between hip and knee; knee joint; leg between knee and ankle; ankle joint; foot
The pelvis with its acetabulum, or socket for the head of the femur. The femur (thigh bone), the longest bone in the body, has specialized ends for its attachment to the hip and to the knee. At the hip end of the femur, the neck supports the head, and distal to the neck are the greater trochanter (glutei, lateral rotators) laterally, and the lesser trochanter (iliopsoas) posteromedially. In the shaft of the femur, the main feature is the linea aspera on the posterior side.
Inside the hip joint, the head of the femur fits inside of the acetabular socket attached by a ligament. There is an extensive fibrous capsule around the hip joint, with a synovial membrane lining this fibrous capsule. Inside, the ball and socket joint allows the extensive movements associated with the hip joint: flexion, extension, medial and lateral rotation, abduction, adduction, and circumduction. A major clinical concern, especially in older osteoporotic women, is a fracture through the neck of the femur. The main blood supply to the head is the medial femoral circumflex artery off of the profunda femoris artery, which can be compromised with a fracture here, leading to avascular necrosis and poor healing.1
Our lower limb innervation is from a plexus with two subdivisions:
lumbar plexus: L1-L4 (femoral [L2-4] and obturator [L3-4] nerves), and sacral plexus: L5-S4 (sciatic [L4-S3]à tibial and common peroneal/fibular nerves).
Gluteal group/abductors:
a) Deep glutei: gluteus medius and gluteus minimus muscles are abductors that assist in walking.
b) Anteriorly, the tensor fasciae latae m. arises from anterior ilium and inserts into the deep fascia of thigh or fascia lata, particularly the iliotibial tract laterally.
c) Gluteus maximus m. is an extensor of the hip joint when power is needed, eg, hill climbing.
The gluteus maximus/medius mm. is often considered to be a site for intramuscular (IM) injections. These should be directed to the upper lateral quadrant of gluteal region to avoid the sciatic nerve. Sciatica: pain resulting from irritation of sciatic nerve. Given that the sciatic nerves is the major component of the sacral plexus, possible cause of L4/L5 or L5/S1 lumbar disc protrusions (or other causes, e.g., inappropriate intergluteal injection). Straight leg raising or dorsiflexion may increase pain because of pulling action on nerve.
Lateral rotator group:
From the back of the pelvis to the greater trochanter to create their action: piriformis, obturator internus and externus, superior and inferior gemellus, quadratus femoris mm..
The muscles of the thigh are elongated and can be put into three groups, clearly marked by intermuscular septa of the fascia lata attaching to the femur:
1) Extensors of knee joint or muscles of the front of the thigh: this anterior compartment contains the quadriceps. Femoral nerve.
2) Flexors of knee joint or muscles of the back of the thigh: this posterior compartment contains the hamstrings. Sciatic nerve (tibial division).
3) Adductors or muscles of the medial side of the thigh. Obturator nerve.
|main page| |background| |03028: Physiology| |03048: Anatomy|
|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|
Please send comments and questions to: cronewil@hvcc.edu
Copyright 1999 by Wilson Crone
External and unofficial links are not endorsed by Hudson Valley Community College
This page updated on November 15, 1999