Lecture 20: Vertebrate Spinal Cord And PNS Flashcards
1
Q
Give the gross anatomy of the human spinal cord
A
- Approx. ½ meter in length.
- Varies from 1 to 1.5 cm in diameter
- Enlargements:
- Cervical: C3 –T1
- Lumbar region: L1 –S2
- Conus medullaris: Ends at about the level of L2
- Cauda equina.
- Filum terminale: Thin filament of meningeal tissue extending from conus medullaris to the coccyx
2
Q
List the spinal nerve pairs
A
08 cervical 12 thoracic 05 lumbar 05 sacral 01 coccygeal * Numbering System
3
Q
List the spinal nerve plexus
A
Cervical: C1 –C4
Brachial: C5 –T1
Lumbosacral: L1 –S4
4
Q
Describe Gray Matter
A
- Forms regions known as horns
- Equivalent of CNS nuclei
- Posterior (dorsal) horns:
- Receive incoming sensory fibers
- Anterior (ventral) horns:
- Site of cell bodies of alpha motor neurons to skeletal muscle fibers
- Lateral horns:
- Located only in thoracic and upper lumbar regions
- Site of cell bodies of ANS motor neurons
5
Q
Describe White Matter
A
- Forms longitudinal columns (funiculi)
- Consists of myelinated tracts
- Posterior (dorsal) columns
- Anterior (ventral) columns
- Lateral columns
6
Q
Describe Commisures
A
- White: Anterior and posterior
Gray: Anterior and Posterior - See Slide 6-7
7
Q
Describe Meninges
A
- Epidural space
- Dura mater: Tough outer layer
- Subdural space
- Arachnoid
- Subarachnoid space: Contains CSF
- Pia mater Delicate innermost layer
- Denticulate ligaments
- See Slide 8-11
8
Q
Describe Spinal Cord Anatomy in Cyclostomes, Fish, and Tetrapods
A
- Cyclostomes:
- No sharp distinction between white and gray matter
- Fish:
- Gray matter is triangular in cross section with a dorsal-pointing apex
- Paired ventral columns of gray matter
- Tetrapods:
- Spinal cord has a distinct separation between gray matter and white matter.
- The gray matter is centrally located and is organized into the shape of an “H” when viewed in cross-section.
- The arms of the “H” are called horns.
- There are a pair of dorsal horns and a pair of ventral horns.
- In humans, because of our upright posture, these are often referred to as posterior and anterior horns respectively.
9
Q
Describe the dorsal and ventral horns of the spinal cord, and the spinal canal
A
- Dorsal (posterior) horns:
- Serve as the entry point for incoming sensory neurons:
- May synapse here with secondary neurons traveling up the spinal cord to the brain
- May travel up the spinal cord in the white matter
- Ventral (anterior) horns:
- Serve as the location of the cell bodies of motor neurons
- Mark the exit of their axons from the spinal cord to the periphery
- Spinal canal:
- Located in the middle of the “H”
- Remnant of the original hollow cavity (lumen) of the neural tube
- Continuous with the ventricles of the brain
- Filled with cerebrospinal fluid.
- See Slide 14
10
Q
How is the white matter of the spinal cord organized?
A
- The white matter of the spinal cord is organized into columns or funiculi.
- Dorsal columns and carry myelinated fibers up the spinal cord to the brain.
- These, therefore, would be made up of afferent or sensory tracts.
- Lateral columns are found on either side of the gray “H”.
- Lateral columns carry both sensory and motor tracts.
- Ventral (anterior) columns are found between the ventral arms of the gray matter “H”.
- Ventral columns carry mostly motor tracts.
- See Slide 15
11
Q
Describe the Spinal Nerve
A
- The horns and columns are continuous throughout the length of the spinal column.
- Externally the spinal cord has a segmented appearance.
- Due mostly to the presence of paired nerves that enter and leave the spinal cord.
- Spinal nerves
- Approximately one pair of spinal nerves for each vertebra.
- Each spinal nerve is attached to the spinal cord by means of two branches, or roots.
- Dorsal root: Carry sensory fibers into the spinal cord
- Ventral root: Carry motor fibers from the spinal cord
- Lateral to the spinal cord the two roots unite to form the spinal nerve itself.
- Each spinal nerve divides near the spinal cord into two branches called rami (sing. ramus).
- The dorsal ramus of each spinal nerve supplies epaxial musculature.
- The ventral ramus, the hypaxial musculature.
- This pattern is retained in all vertebrates, including humans.
- Cell bodies for the motor neurons are located:
- Within the spinal cord in masses of gray matter called columns
- Within the brain within masses of gray matter called nuclei.
- Cell bodies of the sensory neurons are located outside the central nervous system in masses of gray matter called ganglia.
- These ganglia are located along the dorsal roots and are called spinal or cranial nerve ganglia.
- See Slide 18 - 20
12
Q
Describe the autonomic nervous system
A
- The autonomic nervous system is sometimes considered to be part of the peripheral nervous system.
- It is strictly a motor system.
- Depends on sensory input from the viscera.
- It can be thought of as a visceral motor system.
- It controls all visceral activity, usually as a subconscious level.
- Two subsystems:
- Sympathetic: Motor neurons originate in the thoracic and lumbar areas of the spinal cord. Referred to as the thoracolumbar system
- Parasympathetic systems: Motor neurons arise from the brain and sacral regions of the spinal cord. Referred to as the craniosacral system
13
Q
Autonomic pathways consist of two neurons. Describe each neuron
A
- First neuron originates in the central nervous system, either the brain (cranial nerves) or the spinal cord.
- Cell bodies are located either in the gray matter of the spinal cord or specific nuclei in the brain.
- The axons are myelinated and are called preganglionic axons.
- Axons follow typical cranial and spinal nerves to the periphery.
- In the periphery the preganglionic axons synapse with a second group of neurons, the postganglionic neurons.
- The cell bodies of the postganglionic neurons are found in peripheral ganglia.
- Their axons are never myelinated.
- Axons terminate in smooth muscle of the viscera
- See Slide 24, 26-29
14
Q
What are basic characteristics of cranial nerves?
A
- Traditional pattern:
- Anamniotes have ten pairs of cranial nerves.
- Amniotes have twelve pairs of cranial nerves.
- Realistic pattern:
- May be up to 25 pairs of cranial nerves.
- Characteristics:
- Superficial origin: Site where a cranial nerve emerges from the surface of the brain.
- Deep origin: Site where motor fibers arise and sensory fibers terminate in nuclei within the brain stem.
15
Q
List the 12 Traditional Cranial Nerves (In order)
A
I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Spinal accessory XII Hypoglossal
16
Q
What are additional nerves sometimes cited?
A
* Additional nerves: 0 Terminal VN Vomeronasal E Epiphyseal P Profundus(= V1) ALL Anterior lateral line PLL Posterior lateral line
Note that the taste components of VII, IX, and X are considered to be separate cranial nerves by some authors.
17
Q
List the 7 modalities
A
- SSS: Special Sensory:
- Special senses derived from ectoderm:
- Sight, sound, balance.
- SVS: Special Visceral Sensory:
- Special senses derived from endoderm:
- Taste
- SVM: Special Visceral Motor:
- Muscles derived from pharyngeal arches.
- GVS: General Visceral Sensory: • General sensation from viscera. • GVM: General Visceral Motor:
- To smooth muscles of gut tract.
- Autonomic motor
- GSS: General Somatic Sensory:
- General senses from ectoderm (skin).
- GSM: General Somatic Motor:
- Skeletal muscles.
18
Q
What are some generalizations about the cranial nerves?
A
- Cranial nerves have same basic structure as spinal nerves.
- Dorsal root and ventral root.
- Dorsal root ganglion.
- Motor components of cranial nerves begin within brain within motor nuclei.
- Comparable to spinal cord anterior horns.
- Cell bodies of sensory fibers are located in dorsal root (cranial) ganglia.
- Special sensory cranial nerves:
- No motor nuclei and no sensory ganglia.
- Motor cranial nerves:
- Begin in cranial motor nuclei in basal plate.
- Resemble spinal nerves with only ventral roots.
- Include III, VI, and XII.
- Have no sensory roots and no sensory root ganglia.
- Mixed cranial nerves:
- Have both cranial motor nuclei and sensory ganglia.
- Sensory ganglia are usually given specific names.
19
Q
Describe the olfactory nerve (CN I)
A
- Olfactory nerve fibers pass from:
- Olfactory receptor cells (bipolar neurons)
- Through: Cribriform plate
- To: Olfactory bulbs
- Modality: SVS
20
Q
Describe the Optic Nerve (CN II)
A
- Begins in ganglionic layer of retina (not rods and cones).
- Exits orbit through optic canal.
- 50% decussation in optic chiasma in mammals but complete decussation in most other vertebrates:
- Near pituitary gland
- Near internal carotid
- Modality: SSS
21
Q
Describe the occulomotor nerve (CN III)
A
- Supplies four of the six extrinsic muscles of the eye.
- Has a parasympathetic component.
- Will be discussed in a group with other parasympathetic nerves.
22
Q
Describe the Trochlear Nerve (CN IV)
A
- Enters orbit through superior orbital fissure.
- Innervates superior oblique muscle of the eye.
- Modality: GSM.
- THE ONLY cranial nerve that emerges dorsally.
23
Q
Describe the abducens nerve (CN VI)
A
- Enters orbit through superior orbital fissure.
- Lies on medial aspect of lateral rectus muscle.
- Innervates lateral rectus muscle of the eye.
- Modality: GSM.
24
Q
Describe the vestibulocochlear nerve (CN VIII)
A
- Leaves cranial cavity via internal acoustic meatus:
- Accompanied by facial nerve.
- Modality: SSS
- Auditory (cochlear) component:
- Cell bodies in spiral ganglion of cochlea.
- Function: Hearing.
- Vestibular component:
- Cell bodies in vestibular ganglion.
- From receptors for balance and equilibrium.
- Function: Balance and equilibrium.
25
Describe the Spinal Accessory Nerve (CN XI)
* Arises from C1-3 (4).
* Single trunk enters cranial cavity through foramen magnum.
* Temporarily joins cranial root.
- Cranial roots leave with vagus nerve.
* Spinal accessory trunk exits cranial cavity via jugular foramen.
* Supplies: Sternocleidomastoid and trapezius.
* Modality: SVM.
26
Describe the Hypoglossal Nerve (CN XII)
* Exits cranial cavity via hypoglossal foramen.
* Descends anteriorly in neck between internal carotid and internal jugular.
* In neck gives rise to superior root of ansa cervicalis and a nerve to thyrohyoid muscle.
* Supplies extrinsic and intrinsic muscles of tongue.
* Modality: GSM.
27
List the parasympathetic cranial nerves
* Oculomotor (III)
* Facial (VII)
* Glossopharyngeal (IX)
* Vagus(X)
28
Describe the oculomotor nerve
* Modalities:
- GSM:
- - From: oculomotor complex.
- - To: 4 of 6 extrinsic muscles of the eye and levator palpebrae superioris.
- GVM:
- - Preganglionics: From Edinger-Westphal nucleus. To: ciliary ganglion.
- - Postganglionics: To: sphincter pupillae.
- See Slide 46
29
Describe the Trigeminal Nerve
* Three branches:
Ophthalmic, Maxillary, Mandibular.
* Major sensory nerve to face.
- (Also supplies tongue, but this is general sensory, not special sensory for taste.)
* Motor to muscles of mastication:
- Muscles derived from first pharyngeal arch (mandibular arch).
* Not parasympathetic.
* Modalities:
- SVM:
-- From: masticator nucleus.
-- To: muscles of mastication, tensor veli palatini, tensor tympani, mylohyoid, and anterior belly of digastric.
- GSS:
-- Cell bodies of sensory neurons in trigeminal (semilunar) ganglion.
-- Sensory to face and anterior scalp, conjunctiva, paranasal sinuses, nasal and oral cavities, anterior 2/3 of tongue, external surface of eardrum, and dura of middle and anterior cranial fossae.
- See slide 48
30
Describe the facial nerve
* Primary motor nerve to muscles of facial expression.
- Supplies muscles derived from second pharyngeal arch (hyoid arch).
- Branches:
- - Temporal. Zygomatic. Buccal. Mandibular. Cervical.
- Carries taste from anterior 2/3 of tongue.
- Carries motor to submandibular and sublingual salivary glands.
- Carries motor to lacrimal gland and mucous glands in nose.
* Modalities:
- GVM:
- - Preganglionics: From superior salivatory and lacrimal nuclei. To: submandibular/sublingual ganglia.
- - Postganglionics: To: lacrimal gland, submandibular gland, sublingual gland, and mucous glands of mouth and nose.
- GSS:
- - Cell bodies of sensory neurons in geniculate ganglion.
- - Supplies sensory to part of external ear.
- SVS:
- - Cell bodies of sensory neurons in geniculate ganglion.
- - Carries taste from anterior 2/3 of tongue.
- - Carries taste from hard and soft palates.
- See slide 51
31
Describe the glossopharyngeal nerve
* Motor to parotid gland.
* Carries taste from posterior 1/3 of tongue.
* Supplies general sensation to posterior 1/3 of tongue.
* Supplies muscles derived from third pharyngeal arch.
* Modalities:
- SVM:
- - From: Nucleus ambiguous.
- - To: Stylopharyngeus.
- GVS:
- - From: Carotid body and carotid sinus.
- GVM:
- - Preganglionics: From inferior salivatory nucleus. To: otic ganglion.
- - Postganglionics: To parotid gland.
- GSS: From: Posterior 1/3 of tongue, external ear, middle ear cavity.
- SVS: From: Posterior 1/3 of tongue (taste).
- See slide 56
32
Describe the vagus nerve
* Motor to muscles of larynx:
- Muscles of fourth and fifth pharyngeal arches.
- Important in swallowing and speaking.
* Major parasympathetic nerve to thoracic and abdominal organs:
- Parasympathetic supply distally to left colic (splenic) flexure.
* Modalities:
- SVM:
- - From: Nucleus ambiguous. To: Almost all muscles of pharynx and larynx.
- GVS:
- - From: Larynx and pharynx and from thoracic and abdominal viscera.
- GSS:
- - From: External ear and pharynx.
- GVM:
- - Preganglionics: From dorsal motor nucleus. To myenteric plexus of wall of gut tube.
- - Postganglionics: smooth muscle of pharynx and larynx and smooth muscle of most of wall of gut tube.
