Lab Exam 4 Nerves Flashcards
Nervous System Anatomical Subdivisions:
central nervous system (CNS)
peripheral nervous system (PNS)
central nervous system (CNS)
→brain and spinal cord enclosed and protected by cranium and vertebral column
peripheral nervous system (PNS)
nerves and ganglia
nerve
• bundle of nerve fibers (axons) wrapped in fibrous connective tissue
ganglion (plural, ganglia)
knotlike swelling in a nerve where the cell bodies of neurons are concentrated
Overview of the Nervous System
Endocrine and nervous systems maintain internal coordination/homeostasis
Endocrine system
communicates by means of chemical messengers (hormones) secreted into to the blood
Nervous system
employs electrical and chemical means to send messages from cell to cell
Nervous System—Coordination steps
- Sense organs and simple sensory nerve endings, receives information about changes in the body and external environment and transmits coded messages to the central nervous system (CNS)
- The CNS processes this information, relates it to past experience, and determines what response, if any, is appropriate to the circumstances
- The CNS issues commands primarily to muscle and gland cells to carry out such responses
Peripheral Nervous System Divisions
sensory (afferent) division
motor (efferent) division
Sensory afferent division does what and broken down into 2 more divisions
carries signals from receptors (sense organs and simple sensory nerve endings) to the CNS
Somatic sensory division
Visceral sensory division
Somatic Sensory Division does what
• carries signals from receptors in the skin, muscles, bones, and joints
visceral sensory division does what
•carries signals mainly from the viscera of the thoracic and abdominal cavities
The motor (efferent) division and broken down further into two more divisions
carries signals from the CNS to gland and muscle cells (effectors) that carry out the body’s responses
Somatic motor division
Visceral motor division (autonomic nervous system ANS)
Sympathetic division
Parasympathetic division
somatic motor division
carries signals to the skeletal muscles
muscular contractions→voluntary control
somatic reflexes→involuntary control
visceral motor division (autonomic nervous system, ANS)
sympathetic division
parasympathetic division
carries signals to glands, cardiac muscle, and smooth muscle→visceral reflexes (unconscious)
• sympathetic division tends to arouse the body for action
• parasympathetic division tends to have a calming effect
Nervous Tissue
specialized for communication by means of electrical and chemical signals.
• Neurons (nerve cells): detect stimuli, respond quickly, and transmit coded information rapidly to other cells
• Neurosoma (cell body)→nucleus and organelles; usually gives rise to a few thick processes that branch into a vast number of dendrites
• Neuroglia (glial cells): protect and assist the neurons
Dendrites
• branched processes that receive signals from other cells primary site for receiving signals from other neurons.
• Some neurons have only one dendrite and some have thousands
• more dendrites a neuron has, more information it can receive and incorporate into its decision making
An axon
is specialized for rapid conduction of nerve signals to points remote from the soma
Its cytoplasm is called the axoplasm and its membrane the axolemma
Schwann cells and myelin sheath that enclose the axon
At the distal end, an axon usually has a terminal arborization—an extensive complex of fine branches
• Each branch ends in a synaptic knob (terminal button), a little swelling that forms a junction (synapse) with the next cell
• It contains synaptic vesicles full of neurotransmitter
Supportive Cells (Neuroglia)
Glial cells (neuroglia) protect the neurons and help them function
Bind neurons together and provide a supportive framework for the nervous tissue
Wherever a mature neuron is not in synaptic contact with another cell, it is covered with glial cells. This prevents neurons from contacting each other except at points specialized for signal transmission
Types of Neuroglia
There are six kinds of neuroglia
4 types occur only in the CNS
Oligodendrocytes
Ependymal cells
Microglia
Astrocytes
Oligodendrocytes
(octopus) insulates the nerve fiber from the extracellular fluid (myelin sheath)
Ependymal cells
resemble a cuboidal epithelium lining the internal cavities of the brain and spinal cord.
• produce cerebrospinal fluid (CSF), a liquid that bathes the CNS and fills its internal cavities
•have patches of cilia on their apical surfaces that help to circulate the CSF
Microglia
small macrophages that develop from white blood cells called monocytes
Astrocytes
(starlike) are the most abundant and constitute over 90% of the tissue in some areas of the brain.
Functions:
• form a supportive framework , the blood–brain barrier
• Scar tissue and fill space formerly occupied by damaged neurons (astrocytosis or sclerosis)
Types of Neuroglia
The other two types of glial cells occur only in the PNS:
Schwann cells, or neurilemmocytes
Satellite cells
Schwann cells, or neurilemmocytes
envelop nerve fibers of the PNS
• Produce a myelin sheath similar to the one produced by oligodendrocytes in the CNS
• Assist in the regeneration of damaged fibers
Satellite cells
surround the neurosomas in ganglia of the PNS
• provide electrical insulation around the soma
• Regulate the chemical environment of the neurons
Myelin
insulating layer around a nerve fiber
• It is formed by oligodendrocytes in the CNS and Schwann cells in the PNS
• Its composition is like that of plasma membranes in general (20% protein and 80% lipid)
Myelination
Production of the myelin sheath (it is completed until late adolescence)
Conduction Speed of Nerve Fibers
Depends on two factors:
DIAMETER of the fiber
Signal conduction occurs along the surface of a fiber, not deep within its axoplasm
Large fibers have more surface area and conduct signals more rapidly than small fibers
PRESENCE or absence of myelin
Myelin speeds up signal conduction
The Cerebrum
83% of the brain’s volume
• Consists of a pair of cerebral hemispheres
• Thick folds called gyri (singular, gyrus) separated by shallow grooves called sulci (singular, sulcus)
• A deep median groove, the longitudinal fissure, separates the right and left hemispheres from each other
• At the bottom of this fissure, the hemispheres are connected by a thick bundle of nerve fibers called the corpus callosum
The Cerebrum Lobes
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
The insula
Frontal lobe
voluntary motor functions
motivation
planning
mood
emotion
social judgment
aggression
Parietal lobe
primary site for receiving and interpreting signals of the general senses
Occipital lobe
principal visual center of the brain
Temporal lobe
hearing
smell
learning
some aspects of vision and emotion
insula
small mass of cortex deep to the lateral sulcus, made visible only by retracting or cutting away some of the overlying cerebrum
Cerebellum
Occupies the posterior cranial fossa inferior to the cerebrum, separated from it by the transverse cerebral fissure
It consists of right and left cerebellar hemispheres connected by a narrow bridge called the vermis
Each hemisphere exhibits folds called folia separated by shallow sulci
Its most distinctive neurons→Purkinje cells
The cerebellum is connected to the brainstem by cerebellar peduncles:
- Inferior peduncles connected to the medulla oblongata (spinal input)
- Middle peduncles to the pons (cerebral input)
- Superior peduncles to the midbrain (cerebellar output)
The white matter exhibits a
branching pattern called the arbor vitae
The function of the cerebellum
center for monitoring muscle contractions and aiding in motor coordination
Gray and White Matter
The brain, like the spinal cord, is composed of gray and white matter
Gray matter
the seat of the neurosomas, dendrites, and synapses
• forms a surface layer called the cortex over the cerebrum and cerebellum, and deeper masses called nuclei surrounded by white matter
White matter
lies deep to the cortical gray matter in most of the brain, is composed of bundles of axons, which here connect one part of the brain to another and to the spinal cord
The brain is enveloped in three connective tissue
membranes→the meninges
- Dura mater
- Arachnoid mater
- Pia mater
They protect the brain and provide a structural framework for its arteries and veins
The Dura Mater
Consists of two layers
—an outer periosteal layer equivalent to the periosteum of the cranial bones, and an inner meningeal layer
Dural sinuses
spaces that collect blood that has circulated through the brain
Superior sagittal sinus
under the cranium along the median line
Transverse sinus
which runs horizontally from the rear of the head toward each ear and empty into the internal jugular veins of the neck
The Arachnoid Mater and Pia Mater
The arachnoid mater is a transparent membrane over the brain surface
• A subarachnoid space separates it from the pia below, and in some places, a subdural space separates it from the dura above
The pia mater is a very thin, that closely follows all the contours of the brain, even dipping into the sulci
• It is not usually visible without a microscope
Meningitis
Inflammation of the meninges
Is one of the most serious diseases of infancy and childhood It occurs especially between 3 months and 2 years of age
Causes: a variety of bacteria and viruses that invade the CNS by way of the nose and throat, often following respiratory, throat, or ear infections
Signs and symptoms include: high fever, stiff neck, drowsiness, intense headache, and vomiting
Diagnosed by: spinal tap (lumbar puncture) - examination of the cerebrospinal fluid (CSF) for bacteria and white blood cells
Cerebrospinal Fluid
On the floor or wall of each ventricle is a mass of blood capillaries called a choroid plexus
• Ependyma, a type of neuroglia that resembles a cuboidal epithelium, lines the ventricles and canals and covers the choroid plexuses→ produces cerebrospinal fluid
clear, colorless liquid that fills the ventricles and canals of the CNS and bathes its external surface
CSF production begins with the filtration of blood plasma through the capillaries of the brain
Ventricles (CSF circulation) The brain has 4 internal chambers called ventricles
• The largest are the lateral ventricles, which form an arc in each cerebral hemisphere
• Through a interventricular foramen, each lateral ventricle is connected to the third ventricle, (inferior to the corpus callosum)
• The cerebral aqueduct passes down the core of the midbrain and leads to the fourth ventricle, between the pons and cerebellum
• Caudally, this space narrows and forms a central canal that extends through the medulla oblongata into the spinal cord
Blood Supply
• Because neurons have such a high demand for ATP, and therefore glucose and oxygen, the constancy of blood supply is especially critical to the nervous system
• A 10-second interruption in blood flow can cause loss of consciousness
• an interruption of 1 to 2 minutes can significantly impair neural function
• 4 minutes without blood causes irreversible brain damage
• Damaged brain tissue is essentially irreplaceable, and the brain therefore must be well protected
Brain Barrier System
• The brain is well protected by the blood–brain barrier (BBB), which consists of tight junctions between the endothelial cells that form the capillary walls
• The brain barrier system (BBS) is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics
The brainstem
what remains of the brain if the cerebrum and cerebellum are removed
Its major components, from rostral to caudal, are:
• Midbrain
• Pons
• Medulla oblongata
Caudally, the brainstem ends at the foramen magnum of the skull, and the CNS continues below this as the spinal cord
The Medulla Oblongata
begins at the foramen magnum of the skull and ends at a groove between the medulla and pons
• All nerve fibers connecting the brain to the spinal cord pass through the medulla
• Some of these are ascending (sensory) and some are descending (motor) fibers
The Pons
measures about 2.5 cm long, appears as a broad anterior bulge rostral to the medulla
• Posteriorly, two pair of cerebellar peduncles→connect the cerebellum to the pons and midbrain
• Exhibits continuations of the reticular formation (sleep, respiration and posture)
• Cranial nerves V to VIII begin or end in the pons
The Reticular Formation
Is a loosely organized web of gray matter that runs vertically through all levels of the brainstem, it consists of more than 100 small neural networks
The functions of these networks include :
• Somatic motor control (muscle tension to maintain tone, balance, and posture)
• Cardiovascular control
• Pain modulation
• Sleep and consciousness (Injury to the reticular formation can result in irreversible coma)
• Habituation: the brain learns to ignore repetitive, inconsequential stimuli while remaining sensitive to others
The Thalamus
• Each side of the brain has a thalamus (ovoid mass)
• Nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei
• taste, smell, hearing, equilibrium, vision, touch, pain, pressure, heat, and cold
• Plays a key role in motor control
• signals from the cerebellum to the cerebrum
• Is involved in the memory and emotional functions of the limbic system (temporal and frontal lobes)
The Hypothalamus
• Forms the floor and part of the walls of the 3rd ventricle
• From the optic chiasm to the mammillary bodies
• The pituitary gland is attached to the hypothalamus by a stalk (infundibulum)
Is the major control center of the endocrine and autonomic nervous systems→homeostatic regulation
• Hormone secretion
• Autonomic effects
• Thermoregulation
• Food and water intake
• Sleep and circadian rhythms
• Memory
• Emotional behavior and sexual response
The Epithalamus
very small mass of tissue composed mainly of:
• the pineal gland (circadian rhythms)
• the habenula (a relay from the limbic
system to the midbrain), and
• a thin roof over the third ventricle
(circadian rhythms)
Spinal Cord
• cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull
• passes through the vertebral canal as far as the inferior margin of the first lumbar vertebra (L1)
gives rise to 31 pairs of spinal nerves
• The first pair passes between the skull and vertebra C1, and the rest pass through the intervertebral foramina
• The cord exhibits longitudinal grooves on its anterior and posterior sides— the anterior median fissure and posterior median sulcus
• The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions
Surface Anatomy
In two areas, the cord is a little thicker than elsewhere
• Cervical enlargement gives rise to nerves of the upper limbs
• Lumbar enlargement that issues nerves to the pelvic region and lower limbs
Medullary cone (conus medullaris)
bundle of nerve roots that occupy the vertebral canal from L2 to S5
cauda equina
innervates the pelvic organs and lower limbs.
Meninges of the Spinal Cord
enclosed in three fibrous connective tissue membranes called meninges
• These membranes separate the soft tissue of the central nervous system from the bones of the vertebrae and skull
Meninges of the Spinal Cord
From superficial to deep:
Dura mater
Arachnoid mater
Pia mater
Dura Matter
tough collagenous membrane, forms the dural sheath
The space between the sheath and vertebral bones, called the epidural space, is occupied by blood vessels, adipose tissue, and loose connective t issue
Arachnoid mater
simple squamous epithelium (arachnoid membrane)
• the gap between the arachnoid membrane and the pia mater→subarachnoid space, is filled with cerebrospinal fluid
Pia mater
transparent membrane that closely follows the contours of the spinal cord
• beyond the medullary cone→terminal filum, within the lumbar cistern
• At S2, fuses with the dura mater to form a coccygeal ligament
Cross-Sectional Anatomy
The spinal cord, like the brain, consists of two kinds of nervous tissue:
Gray matter: contains little myelin
• It contains the somas, dendrites, and proximal parts of the
axons of neurons
• It is the site of synaptic contact between neurons (neural
integration)
White matter: abundant of myelin
• It is composed of bundles of axons, called tracts, that carry signals from one part of the CNS to another
Both gray and white matter also have an abundance of glial cells
Gray Matter
Central core of gray matter that looks somewhat butterfly- or H-shaped in cross Section
• The core consists mainly of two posterior (dorsal) horns, posterolateral surfaces of the cord, and two thicker anterior (ventral) horns, anterolateral surfaces
• The right and left sides are connected by a gray commissure
• In the middle of the commissure is the central canal, lined with ependymal
cells, and filled with CSF
• Spinal nerve branches into a posterior (dorsal) root and anterior ( ventral) root • The posterior root carries sensory nerve fibers
• The anterior horns contain the large somas of the somatic motor neurons
White Matter
surrounds the gray matter
• It consists of bundles of axons that course up and down the cord and provide avenues of communication between different levels of the CNS.
• These bundles are arranged in three pairs called columns or funiculi:
• a posterior (dorsal) column
• Lateral column
• anterior (ventral) column
Each column consists of subdivisions called tracts or fasciculi
Motor and descending (efferent) pathways (red)
Pyramidal tracts
- Lateral corticospinal tract - Anterior corticospinal tract
Extrapyramidal Tracts
- Rubrospinal tract
- Reticulospinal tracts -Olivospinal tract
- Vestibulospinal tract
Sensory and ascending
(afferent) pathways (blue)
Dorsal Column Medial Lemniscus System
Gracile fasciculus
Cuneate fasciculus
Spinocerebellar Tracts
• Posterior spinocerebellar tract
•Anterior spinocerebellar tract
Anterolateral System
Lateral spinothalamic tract
Anterior spinothalamic tract
Spino-olivary fibers
Spinal Tracts
• Ascending tracts carry sensory information up the cord
Descending tracts conduct motor impulses down
Several of these tracts undergo decussation as they pass up or down the brainstem and spinal cord—meaning that they cross over from the left side of the body to the right, or vice versa
• the left side of the brain receives sensory information from the right side of the body
• the right side of the brain senses and controls the left side of the body
Contrallateral→when the origin and destination of a tract are on opposite sides of the body
Ipsilateral → when a tract does not decussate, its origin and destination are on the same side of the body
General Anatomy of Nerves and Ganglia
A nerve is a cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue
• Each nerve fiber is surrounded by a basal lamina and then a thin sleeve of loose connective tissue called the endoneurium
• The fibers are gathered in bundles called fascicles, each wrapped in a sheath called the perineurium
• Several fascicles are then bundled together and wrapped in an outer epineurium to compose the nerve as a whole
Peripheral Nerve Fibers
• Sensory (afferent) fibers carrying signals from sensory receptors to the CNS
• Motor (efferent) fibers carrying signals from the CNS to muscles and glands
*Most nerves, however, are mixed nerves, which consist of both afferent and efferent fibers and therefore conduct signals in two directions
A nerve resembles a thread, a ganglion resembles a knot in the thread
• A ganglion is a cluster of neurosomas outside the CNS
The nerve then exits the vertebral canal through the intervertebral foramen
Spinal Nerves
There are 31 pairs of spinal nerves:
8 cervical (C1–C8) 12 thoracic (T1–T12) 5 lumbar (L1–L5)
5 sacral (S1–S5)
1 coccygeal (Co)
Spinal Nerves Doral and Ventral Ramus Picture
Cutaneous Innervation
• Each spinal nerve except C1 receives sensory input from a specific area of skin called a dermatome
• A dermatome map is a diagram of the cutaneous regions innervated by each spinal nerve (dermatomes overlap at their edges)
Shingles
Chickenpox (varicella) is a common disease of early childhood, is caused by the varicella-zoster virus→itchy rash
• The virus remains for life in the posterior root ganglia
• If the immune system is compromised, the virus can travel along the sensory nerve fibers by fast axonal transport and cause shingles (herpes zoster)— characterized by a painful trail of skin discoloration and fluid-filled vesicles along the path of the nerve
Postherpetic neuralgia, PHN→chronic intense pain in the site of the lesions lasting for months or even years
Vaccine: varicella vaccine in children, Zostavax in adults >60 years old
Treatment:
• aspirin and steroidal ointments→pain relief
• acyclovir (antiviral drug) can shorten the course of an episode of shingles, but only if taken within the first 2 to 3 days of outbreak
*Aspirin is for adults, kids are not supposed to take aspirin! Can cause Reye Syndrome
Nerve Plexuses
• Cervical plexus in the neck
• Brachial plexus near the shoulder • Lumbar plexus of the lower back • Sacral plexus
• Coccygeal plexus
Nerve plexus→trunks→anterior and posterior divisions→cords
Somatosensory signals are for touch, heat, cold, stretch, pressure, pain, and other
sensations
• Proprioception (body position and movements) to maintain equilibrium (balance) and coordination
The motor function of these nerves is primarily to stimulate the contraction of skeletal muscles
Cervical Plexus
Receives fibers from the anterior rami of nerves C1 to C5 and gives rise to:
• Lesser occipital nerve
• Greater auricular nerve
• Transverse cervical nerve
• Ansa cervicalis
• Supraclavicular nerve
• Phrenic nerve→innervate the diaphragm, and play an essential role in breathing
Brachial Plexus
Is formed predominantly by the
anterior rami of nerves C5 to T1
It passes over the first rib into the axilla and innervates the upper limb and some muscles of the neck and shoulder
The subdivisions of this plexus are called roots, trunks, divisions, and cords
• Musculocutaneous nerve • Axillary nerve
• Radial nerve
• Median nerve
• Ulnar nerve
Lumbar Plexus
Is formed from the anterior rami of nerves L1 to L4 and some fibers from T12
It gives rise to the following nerves
• Iliohypogastric nerve
• Ilioinguinal nerve
• Genitofemoral nerve
• Lateral femoral cutaneous nerve • Femoral nerve
• Obturator nerve
The Sacral and Coccygeal Plexus
formed from the anterior rami of nerves L4, L5, and S1 through S4
• it is connected to the lumbar plexus by fibers that run through the lumbosacral trunk, the two plexuses are sometimes referred to collectively as the lumbosacral plexus
• The tibial and common fibular nerves travel together through a connective tissue sheath; they are referred to collectively as the sciatic nerve
• At the popliteal fossa, the tibial and common fibular nerves diverge
• Tibial nerve descends through the leg→medial and plantar nerves in the foot
• Common fibular nerve divides into deep and superficial fibular nerves
The coccygeal plexus is formed from the anterior rami of S4, S5
Common fibular + Tibial = Sciatic nerve
*above the popliteal fossa
The Nature of Reflexes
Reflexes are quick, involuntary, stereotyped reactions of glands or muscles to stimulation
Properties of a reflex:
1. Reflexes require stimulation→they are a response to stimuli
2. Reflexes are quick→involve few interneurons, or none, and minimum synaptic delay
3. Reflexes are involuntary→they occur without intent, often without our awareness, and they are difficult to suppress
4. Reflexes are stereotyped→they occur in essentially the same way every time; the response is very predictable
Reflex Activity
Inborn (intrinsic) reflex→rapid, predictable motor response to a stimulus
• Unlearned, unpremeditated, and involuntary
• Built into our neural anatomy→regulated by the brain steam and spinal cord
•
Learned (acquired) reflex→results from practice or repetition • Example: driving a car
*The distinction between inborn and learned reflexes is not clear-cut and most inborn reflex actions can be modified by learning and conscious effort
Reflex Arc
Functional Classification
• Somatic Reflexes→if they activate skeletal muscle
• Autonomic Reflexes→if they activate visceral effectors (smooth or cardiac muscle, glands)
Spinal Reflexes are somatic reflexes mediated by the spinal cord
• Tests of somatic reflexes are important clinically to assess the condition of the nervous system
• The most commonly assessed reflexes are:
• Stretch reflex
• Flexor reflex
• Superficial reflexes
• Spinal Shock→occurs when the spinal cord is transected, immediately depressing all functions controlled by the cord.
The Muscle Spindles
Muscle spindles are stretch receptors embedded in the muscles (proprioceptors)
They inform the brain of muscle length and body movements→the brain sends motor commands back to the muscles that control muscle tone, posture, coordinated movement, and corrective reflexes
The Stretch Reflex
When a muscle is suddenly stretched
→it contracts, increases tone, and feels
stiffer than an unstretched muscle
→helps to maintain equilibrium and posture
The Tendon Reflex
Tendon organs are proprioceptors located in a tendon near its junction with a muscle
• The tendon reflex is a response to excessive tension on the tendon
• This serves to moderate muscle contraction before it tears a tendon
Tendon reflex→the reflexive contraction of a muscle when its tendon is tapped, as in the familiar patellar reflex
*Tendon organs measure tension
The Flexor (Withdrawal) Reflex
quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus
The Crossed Extension Reflex
The crossed extension reflex is the contraction of extensor muscles in the limb opposite from the one that is withdrawn
• It extends that limb and enables you to keep your balance
Superficial Reflexes → Are elicited by gentle cutaneous stimulation
Plantar Reflex→tests integrity of spinal cord from L4 – S2 and corticospinal tracts
• Draw a blunt object downward along the lateral aspect of the plantar surface of the foot
• Normal→toes flex
• Abnormal→toes dorsiflexion of great toe and the smaller toes fan laterally (Babinski’s sign)
Superficial Reflexes
Abdominal Reflex→check the integrity of the spinal cord and ventral rami from T8 – T12 and corticospinal tracts
• Stroking the skin of the lateral abdomen above the umbilicus, the reflex induces a movement of the umbilicus toward the stimulated site
The Cranial Nerves
• Brain must communicate with rest of body
• Cranial nerves are part of Peripheral Nervous System
(PNS)
• 12 pairs
• Most of them arise from the base of the brain
• Numbered with Roman numerals according to their
position
• Name of nerve often related to its function
• Lead to muscles and sense organs located mainly in the head and neck
12 Cranial Nerves
Olfactory
Optic
Oculomotor
Throchlear
Trigeminal
Abducens
Facial
Vestibulocochlear
Glassopharayngeal
Vagus
Accessory
Hypoglossal
Nerve (I)
The Olfactory
• Sense of smell
• Damage causes impaired sense of
smell
• Begins in the nasal cavity
• Contains sensory fibers
(II) cranial nerve
The Optic Nerve
• Begins at the retina of the eyes
• Provides vision
• Damage causes blindness in part or all of visual field
(III) cranial nerve
(IV) cranial nerve
(VI) cranial nerve
Oculomotor Nerve (III)
Trochlear Nerve (IV)
Abducens Nerve (VI)
They innervate the 6 extrinsic muscles that perform voluntary eye movements
Trigeminal (V)
This nerve has 3 branches:
• Ophthalmic
• Maxillary
• Mandibular
It is mainly Sensory! Sensation of the face
Cranial Nerve (VII)
Facial Nerve (VII)
• Sensory component→ sensation from the anterior 2/3 of the tongue
• Motor component→muscles of facial expression, secretion from lacrimal and salivary glands
Cranial Nerve (VIII)
Vestibulocochlear
• Vestibular branch: detect movements that are linear and angular (turning)
• Cochlear branch: responsible for hearing sounds
Cranial Nerve (IX)
Glossopharyngeal (IX)
• Sensory→neurons for taste to posterior 1/3 of tongue, sensory neurons of pharynx and eardrum
• Motor→stylopharyngeus muscle (swallowing) and parotid salivary glands
Cranial Nerve (X)
Vagus Nerve (X)
• Sensory→pharynx, external acoustic meatus, diaphragm, and internal organs of the thoracic and abdominopelvic cavities
• Motor→motor fibers to the palate, pharynx, and autonomic motor fibers to internal organs
This nerve is almost everywhere!!
Cranial Nerve (XI)
Accessory Nerve (XI)
Entirely Motor and innervates the Trapezius and Sternocleidomastoid muscles
*It actually origins from spinal cord!
Cranial Nerve (XII)
Hypoglossal Nerve (XII)
Entirely Motor and innervates the muscles that move the tongue
External Anatomy of the Orbital Region (picture)
Lacrimal Apparatus
The lacrimal apparatus works to produce tears that are needed to wet the front of the eye and flush debris from the ocular surface
Extrinsic Eye Muscles
Strabismus
• Congenital weakness of the external eye muscles
• The affected eye rotates laterally or medially
• Eyes alternate in focusing objects
• The brain shuts off the deviant eye→
functional blindness
Which muscle is affected in this patient?
Anatomy of the Eye
Three layers (tunics) that form the wall of the eyeball
- Retina:
• Photoreceptors - Choroid:
• Vascular
• Brown (melanocytes) - Sclera:
• White
• fibrous connective tissue
• Avascular
Anatomy of the eye
Conjunctiva —a transparent mucous membrane that lines eyelids and covers anterior surface of eyeball, except cornea
Sclera: dense, collagenous white of the eye
Conjunctivitis (pink eye)
Anatomy of the Eye
Cornea: Transparent cover on anterior surface of eyeball
Pupil: central opening
Iris: colored diaphragm controlling size of pupil
Cornea Donation
Anatomy of the Eye
Optical components
Lens: suspended by suspensory
ligaments from ciliary body
• Changes shape to help focus light
• Rounded with no tension or flattened with pull of suspensory ligaments
Cataracts
Cataract —clouding of lens
• Lens fibers darken with age, fluid-filled bubbles and clefts filled with debris appear between the fibers
• Induced by diabetes, smoking, drugs, ultraviolet radiation, and certain viruses
• Replace natural lens with plastic one
Glaucoma
Glaucoma —elevated pressure within the eye due to obstruction of scleral venous sinus and improper drainage of aqueous humor
• Death of retinal cells due to compression of blood vessels and lack of oxygen
• Illusory flashes of light are an early symptom
• Colored halos around lights are late symptom
• Lost vision cannot be restored
Anatomy of the Eye
Retina
• Attached to the rest of the eye only at optic disc and at ora serrata
Detached retina causes blurry areas in field of vision and leads to blindness
Ophthalmoscopy Picture
Microscopic Anatomy of the Retina
• Outer layer→pigmented cells • Inner layer (neural):
• Photoreceptors
• Rods→dim light (night vision)
• Cones→color (day vision)
• Bipolar cells
• Ganglion cells
Color blindness
• Congenital lack of one or more cone pigments
• X-linked condition, more common in males
• 8-10% of males have some form of colorblindness
• Most common type is red-green color blindness
Visual Pathway
• The axons of the ganglion cells of the retina converge at the posterior aspect of the eyeball and exit as the optic nerve
• At the optic chiasm, the fibers crossover
• The optic tracts formed contain fibers from the lateral side of the eye on the same side and from the medial side of the opposite eye
The Ear: Hearing and Balance
• Divisions:
• External ear (hearing) • Middle ear (hearing)
• Internal ear (hearing and equilibrium)
External Ear
Tympanic Membrane (eardrum)
• Auricle (pinna)
• Elastic cartilage
• Rim
• Lobule
External acoustic meatus (Auditory canal) Ceruminous glands secrete cerumen (ear wax)
Middle Ear
Malleus
Incus
Tympanic Membrane
Oval Window
Round Window
Pharyngotympanic Tube
Otitis Media → Middle Ear Inflammation
• Common result of a sore throat
• Most common cause of hearing loss in children
• Eardrum bulges and becomes inflamed and red
• Treatment→Antibiotics
Internal Ear (labyrinth)
Lies in the Temporal Bone, behind the eye socket
• Bony Labyrinth→ channels in the bone, contains perilymph
• Membranous Labyrinth→sacs and ducts contained within the bony labyrinth, contain endolymph
Inner Ear
• Vestibule (bone cavity)
• Saccule and Utricule
(membranous sacs)
• House of equilibrium receptor region called maculae→respond to the pull of gravity and report changes of head position
Inner Ear
• Semicircular Ducts:
• Anterior
• Posterior • Lateral
• They communicate with the Utricle
• Each duct has an ampulla that houses an equilibrium receptor region called crista ampullaris
Inner Ear
• Cochlea (“snail”)
• Cochlea (“snail”) houses the cochlear ducts which have the receptor organ of hearing→ Organ of Corti
• The cochlea is divided into chambers:
• Scala vestibuli • Scala media
• Scala tympani
• Scala media (membranous labyrinth) is filled with Endolymph
• Scala vestibuli and tympani (bony labyrinth) are filled with Perilymph
Sense of Smell
• Chemoreceptors→respond to chemical in an aqueous solution
Smell receptors are excited by airborne chemicals that dissolve in fluids coating nasal membranes
Sense of Taste
• Dissolved chemicals are detected by receptor cells in taste buds (sensory organs for taste)
• Gustatory epithelial cells are the receptor cells for taste (taste cells)
