Mikhail Ness M. Buhay, MD

Nervous SystemPart 2

The Spinal Cord and Spinal Nerves

Spinal Cord Structure: Protection and Coverings◼ Vertebrae

◼ Spinal meninges

❑ Three layers of connective tissue

◼ Dura mater

◼ Arachnoid mater

◼ Pia mater

❑ Continuous with cranial meninges

◼ Cerebrospinal fluid (CSF)

Spinal Meninges and Spaces◼ Epidural space

❑ Between the vertebrae and dura mater

◼ Dura mater- tough mother

❑ Thick strong layer, dense irregular connective tissue

❑ Extends to vertebra S2 (well beyond spinal cord)

◼ Subdural space❑ Contains interstitial fluid

◼ Arachnoid mater: resembles spider’s web❑ Thin, avascular covering of loosely

arranged collagen and elastic fibers

❑ Extends into subarachnoid space

◼ Subarachnoid space ❑ CSF circulates in this space

◼ Pia mater ❑ Thin, delicate layer

❑ Adheres to surface spinal cord (and brain)

❑ Contains blood vessels

Spinal Meninges and Spaces◼ Denticulate ligaments

❑ Thickenings of pia mater

❑ Fuse with arachnoid mater and dura mater

❑ Between the anterior and posterior nerve roots of spinal nerves

❑ Suspend the spinal cord at the middle

❑ Protect the spinal cord from sudden displacement →shock

Spinal Tap◼ Spinal tap/Lumbar

puncture❑ Long hollow needle inserted

into the SA space

◼ Spinal cord – ends at L2 (superior border)

◼ Spinal meninges – extend to S2

◼ Between L2 and S2◼ (+) spinal meninges◼ (–) spinal cord

◼ Adults – (L3-L4) or (L4-L5)❑ Safe access to the SA

space

❑ Supracristal line –passes L4 spinous process

External Anatomy of Spinal Cord◼ SC is roughly oval

◼ Adults: Extends from medulla of brain to L2 superior border

◼ Newborn: Extends up to L3/L4

◼ Enlargements: cervical (C4-T1) and lumbar regions (T9-T12)❑ Points of origins of nerves to upper and lower limbs

◼ Conus medullaris – SC ends as a tapering, conical structure❑ L1-L2 intervertebral disc

◼ Filum terminale – arise from conus medullaris❑ Extensions of the pia mater; fuses with the arachnoid and dura mater❑ Anchors SC to the coccyx

External Anatomy of Spinal Cord◼ Spinal nerves – paths of communication bet. SC and body region

❑ 31 pairs of spinal nerves emerge from the intervertebral foramina❑ Cervical – 8 (C1-C8)❑ Thoracic – 12 (T1-T12)❑ Lumbar – 5 (L1-L5)❑ Sacral – 5 (S1-S5)❑ Coccygeal – 1 (Co1)

◼ Roots – bundles of axons❑ Connect each spinal nerve to a segment of the cord by even smaller bundles of axons

(rootlets)

◼ Posterior (dorsal) root & rootlets – contain only sensory axons

❑ Each posterior root has a swelling, the posterior (dorsal) root ganglion – contains the cell bodies of sensory neurons.

◼ Anterior (ventral) root & rootlets – contain only motor axons

External Anatomy of Spinal Cord◼ Spinal nerves – branch from the SC

❑ Pass laterally and exit thru the intervertebral foramina

◼ SC shorter than vertebral column❑ Lumbar, sacral and coccygeal regions – do not leave the vertebral

column at the same level they exit the cord

❑ Their roots angle inferiorly alongside the filum terminale

◼ Cauda equina (horse’s tail)❑ Extends inferior to end of spinal cord

❑ Consists of roots of lumbar, sacral and coccygeal spinal nerves

Gross Anatomy of Spinal Cord• The spinal cord extends

from the medulla oblongata of the brain to the superior border of the second lumbar vertebra.

REVIEW: Collections of Nervous Tissue

◼ Clusters of neuron cell bodies

❑Ganglion: cluster of cell bodies in PNS

❑Nucleus: cluster of cell bodies in CNS

◼ Bundles of axons

❑Nerve: bundle of axons in PNS

❑Tract: bundle to axons in CNS

Internal Anatomy of the Spinal Cord◼ A transverse section of the spinal cord reveals regions of white matter that surround an

inner core of gray matter

◼ Gray matter forms “H” (or “butterfly”) ❑ Consists of dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.

❑ Three horns (regions) on each side

◼ Posterior (dorsal) gray horns: contain sensory neurons and interneurons◼ Sensory neuron cell bodies – located in the posterior (dorsal) root ganglion of a spinal nerve

◼ Anterior (ventral) gray horns: contain somatic motor nuclei◼ Somatic motor nuclei – clusters of cell bodies of somatic motor neurons that provide nerve

impulses for contraction of skeletal muscles

◼ Lateral gray horns: contain autonomic motor nuclei◼ Located between anterior and posterior gray horns; only in thoracic and upper lumbar SC

segments◼ Autonomic motor nuclei – clusters of cell bodies of autonomic motor neurons that regulate the

activity of cardiac muscle, smooth muscle, and glands

Internal Anatomy of the Spinal Cord

◼ White matter (surrounds gray “H”)

❑ Consists of white columns, myelinated axons of neurons

◼Posterior (dorsal), anterior (ventral), and lateral white columns◼ Contain tracts (bundles of axons)

❑Sensory (Ascending) tracts: carry nerve impulses ascending to brain

❑Motor (Descending) tracts: carry nerve impulses descending from brain

◼ Sensory and Motor tracts of the SC are continuous with the tracts of the brain.

Internal Structure of Spinal Cord• The posterior gray horn

contains axons of sensory neurons and cell bodies of interneurons; the lateral gray horn contains cell bodies of autonomic motor neurons; and the anterior gray horn contains cell bodies of somatic motor neurons.

Internal Structure of Spinal Cord

H -crossbarEntire SC; CSF; 4th Ventricle

Internal Anatomy of the Spinal Cord

◼ Nucleus/Nuclei❑ In the gray matter of the CNS (brain and SC)

❑ Functional groups formed by clusters of neuronal cell bodies

◼ Sensory nuclei – receive input from receptors via sensory neurons

◼ Motor nuclei – provide output to effector tissues via motor neurons

Internal Structure of Spinal Cord

• The posterior gray horn contains axons of sensory neurons and cell bodies of interneurons; the lateral gray horn contains cell bodies of autonomic motor neurons; and the anterior gray horn contains cell bodies of somatic motor neurons.

Spinal Nerves

◼ 31 pairs❑ Named according to level of vertebra from which they emerge

❑ C1-C8, T1-T12, L1-L5, S1-S5, 1 coccygeal

❑ Emerge from spinal cord through intervertebral foramina

❑ Connect the CNS to the sensory receptors, muscles, and glands in all parts of the body

◼ Nerves attached to spinal cord by 2 roots

❑ Dorsal root: made of axons of sensory neurons◼ Dorsal root ganglion: swelling containing cell bodies of sensory neurons

❑ Ventral root: composed of axons of motor neurons◼ Both somatic motor and autonomic motor

Spinal Nerve Composition

◼ Formed by 2 spinal nerve roots

◼ Spinal nerve is a mixed nerve:❑ Formed from dorsal root (sensory) and ventral root (motor) root

◼ Connective tissue coverings of Spinal Nerves❑ Each spinal nerve and cranial nerve consists of many individual axons

and contains layers of protective connective tissue coverings

❑ Individual axons wrapped in endoneurium (innermost layer)

❑ Axons grouped in fascicles wrapped in perineurium (middle layer)

❑ Outer covering = epineurium (outermost layer)

Spinal Nerve Composition

Distribution of Spinal Nerves

◼ Spinal nerves divides into several branches (rami) after pass through intervertebral foramina

◼ Posterior ramus – serves the deep muscles and skin of the posterior surface of the trunk

◼ Anterior ramus – serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk

◼ Meningeal branch – reenters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges

◼ Rami communicantes◼ Some join with branches from neighboring nerves to form plexuses (network of

axons)

◼ Nerve names relate to region innervated

◼ Spinal nerves T2-T12 do not form plexuses❑ They are called intercostal nerves/thoracic nerves – directly connect to the structures they

supply in the intercostal spaces

❑ Supply abdominal muscles, skin of chest and back, and muscles between ribs.

Plexuses

◼ Cervical plexus❑ C1-C4 roots + C5

contributions

❑ Supplies the skin and muscles of the head, neck, and superior part of the shoulders and chest, diaphragm

❑ Important nerves: phrenic to diaphragm

Plexuses

◼ Brachial plexus ❑ Formed by roots of

spinal nerves from C5-C8 and T1

❑ Supplies upper limbs + some neck and shoulder muscles

❑ Important nerves: radial, ulnar, median

Plexuses

◼ Lumbar plexus❑ Formed by the anterior

rami spinal nerve roots L1-L4

❑ Supplies anterolateral abdominal wall, external genitalia, and part of lower limbs

❑ Important nerves: femoral (to anterior thigh: quads)

Plexuses

◼ Sacral plexus❑ Sacral plexus formed by the

anterior rami spinal nerve roots of L4-L5 and S1-S4

❑ Supplies buttocks, perineum, and most of lower limbs

❑ Sciatic nerve – largest nerve in the body

❑ Important nerves: gluteal, sciatic (to posterior thigh and all of leg and foot)

Plexuses

◼ Coccygeal plexus❑ Formed by the anterior

rami spinal nerve roots of

S4-S5 and the coccygeal

nerves

Dermatomes

◼ A dermatome is an area of skin that provides

sensory input to the CNS via the posterior roots of

one pair of spinal nerves or via the trigeminal (V)

nerve.

◼ The nerve supply in adjacent dermatomes

overlaps somewhat.

◼ Knowing which spinal cord segments supply each

dermatome makes it possible to locate damaged

regions of the spinal cord.

◼ If the skin in a particular region is stimulated but

the sensation is not perceived, the nerves

supplying that dermatome are probably damaged.

The Brain and Cranial Nerves

Mikhail Ness M. Buhay, MD

◼ The brain and spinal cord develop from the ectodermal neural tube

◼ The anterior part of the neural tube expands, along with the associated neural crest tissue. Constrictions in this expanded tube soon appear, creating three regions called primary brain vesicles: ◼ Prosencephalon◼ Mesencephalon◼ Rhombencephalon

Brain

Brain: Major Parts◼ Brain stem: continuous with spinal cord

❑ Medulla oblongata, pons, midbrain

◼ Diencephalon: superior to brain stem

❑ Thalamus, hypothalamus, and pineal gland

◼ Cerebrum: largest part and most superior

❑ Surface covered with gray matter: cortex

❑ Deep to cortex is cerebral white matter

◼ Cerebellum: posterior and inferior

❑ Means “little brain”

◼ Cranial meninges: dura mater, arachnoid mater, and pia mater

Brain: Major Parts

Brain: Major Parts

Brain Blood Flow and the Blood-Brain Barrier (BBB)◼ Internal carotid & vertebral arteries →

brain

◼ Dural venous sinuses → internal jugular veins → heart

◼ Requires 20% of the body’s O2 supply❑ 4 min lack → permanent damage

◼ Requires continuous glucose supply

◼ Protected by blood-brain barrier❑ Allows passage of lipid soluble materials: O2,

CO2, alcohol, anesthetic agents

❑ But controls entry of most harmful materials

◼ Created by tight capillaries and astrocytes

Cerebrospinal Fluid (CSF)

◼ CSF is a clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries.

◼ It also carries small amounts of oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.

◼ CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space

Cerebrospinal Fluid (CSF)

◼ Formed in the 4 ventricles of brain❑ Lateral (#1 and 2) → 3rd → 4th ventricle

❑ Formed in choroid plexuses◼ By filtration and secretion of blood plasma

◼ In specialized capillary networks (covered by ependymal cells) in walls of ventricles

◼ Pathway❑ Through 4 ventricles → central canal of spinal cord and within

subarachnoid space →

❑ Reabsorbed through arachnoid villi into blood in superior sagittal sinus

◼ Cushions brain and provides nutrients

Locations of ventricles within a “transparent” brain.

• One interventricular foramen on each side connects a lateral ventricle to the third ventricle, and the aqueduct of the midbrain connects the third ventricle to the fourth ventricle.

• Ventricles are cavities within the brain that are filled with cerebrospinal fluid.

Cerebrospinal Fluid (CSF)

• CSF is formed from blood plasma by ependymal cells that cover the choroid plexuses of the ventricles.

Cerebrospinal Fluid (CSF)

Cerebrospinal Fluid (CSF)

Brain Stem: Medulla Oblongata

◼ Most inferior part of brainstem❑ White matter connects spinal cord

and other parts of brain

◼ Contains vital nuclei❑ Cardiovascular center

◼ Regulates heart rate, blood pressure

❑ Medullary rhythmicity area ◼ Adjusts respiratory rhythm

◼ Other sensory and reflex motor areas

◼ Cranial nerves VIII-XII attached here

Brain Stem: Pons

◼ Serves as a “bridge”❑ Connects medulla to midbrain

and above

❑ Contains ascending and descending tracts

❑ Connects left and right sides of cerebellum

◼ Contains nuclei ❑ Motor relays from cerebrum to

cerebellum

❑ Helps control breathing

❑ Cranial nerves V-VIII attached here

Brain Stem: Midbrain

◼ Connects pons to diencephalon❑ Large tracts: cerebral peduncles

◼ Nuclei: ❑ Substantia nigra: related to

Parkinson disease❑ Red nuclei: help coordinate

movements❑ Origin of cranial nerves III and IV

(control eye movements)❑ Superior colliculi: nuclei involved in

◼ Scanning eye movements ◼ Responses to visual stimuli

❑ Inferior colliculi: responses to auditory input

Brain Stem

Midbrain

Reticular Formation

◼ Netlike arrangement of gray and white matter

◼ Contains ascending and descending tracts

◼ Ascending part = reticular activating system (RAS)

❑ Carries sensory pathways to cerebral cortex

❑ Helps maintain consciousness

❑ Helps induce sleep

Reticular Formation

Reticular Formation

Diencephalon

◼ Thalamus: major sensory relay center❑ Also motor, autonomic, and consciousness functions

◼ Hypothalamus: lies inferior to thalamus❑ Control of pituitary and hormone production

❑ Works with ANS regulating many viscera

❑ Involved with feelings and behavior patterns

❑ Regulation of eating, drinking, fluid levels

❑ Control of body temperature

❑ Regulation of circadian rhythms, sleep, waking

◼ Pineal gland: secretes melatonin❑ Controls sleep, biological clock

Diencephalon

Cerebellum

◼ Location: posterior to medulla and pons, inferior to

cerebrum

❑ Attached to brain stem by cerebellar peduncles

◼ Structure:

❑ Two cerebellar hemispheres

❑ Cerebellar cortex: gray matter

❑ Tree-like appearance (seen in sagittal section) of white matter

and gray nuclei

Cerebellum

Cerebellum

◼ Functions❑ Receives wide range of sensory input from muscles, joints,

tendons, eyes, inner ears

❑ Compares actual movements with intended ones

❑ Helps produce smooth, coordinated movements

❑ Helps execute skilled motor activities

❑ Regulates posture and balance

Cerebrum: Structure

◼ Cerebral cortex

◼ Internal white mater

◼ Deep gray nuclei

◼ Surface folds of cerebral cortex: gyri

◼ Grooves between gyri: sulci

◼ Longitudinal fissure: divides cerebrum into left and right hemispheres

◼ Hemispheres connected by corpus collosum

Cerebrum: Structure

◼ Each hemisphere has 4 lobes❑ Frontal, parietal, temporal, occipital

❑ Central sulcus separates frontal, parietal

❑ Precentral gyrus anterior to sulcus: primary motor area

❑ Postcentral gyrus: primary somatosensory area

◼ Deep gray nuclei: basal ganglia❑ Globus pallidus, putamen, caudate nucleus

Cerebrum

Cerebrum

Limbic System

◼ Ring of structures on inner border of cerebrum and floor of

diencephalon

◼ Called “emotional brain”: plays primary role in pain,

pleasure, anger, affection and in behavior

◼ Involuntary activity related to survival

◼ Important in memory development

Limbic System

Functional Areas of Cerebral Cortex

◼ Specialized areas in specific regions of cerebral cortex

◼ Sensory areas receive input → perception

◼ Motor areas → initiate movements

◼ Associative areas → complex integration: memory, emotion, reasoning, judgment

Sensory Areas

◼ Primary somatosensory area: postcentral gyrus❑ Input includes: touch, proprioception, pain, itching, tickle, temperature

◼ Primary visual area: occipital lobe

◼ Primary auditory area: temporal lobe

◼ Primary gustatory (taste) area: base of postcentral gyrus

◼ Primary olfactory (smell) area: medial aspect of temporal lobe

Motor Areas

◼ Located anterior to central sulcus

◼ Primary motor area: precentral gyrus

◼ Broca’s speech area

❑ Interacts with premotor area and primary motor area to regulate

breathing and speech muscles

❑ Is in left hemisphere in 97% of persons

Association Areas

◼ Adjacent to sensory and motor areas and connected via association tracts

◼ Integrate and interpret information

◼ Examples❑ Somatosensory association area

◼ Posterior to primary somatosensory area

◼ Integrates sensation: exact shape and texture of object compared with stored memories

❑ Wernicke’s area: left temporal, parietal lobes◼ Interprets meaning of speech: words → thoughts

◼ Right hemisphere adds emotional content

Cerebrum: Functional Areas

Somatic Sensory Pathways

◼ Relay sensory information from periphery to cerebral cortex

◼ 3 neurons in each pathway

❑ Cell body #1 in dorsal root ganglion

❑ Cell body #2 in spinal cord or brain stem

❑ Cell body #3 in thalamus; axon extends to cerebral cortex (somatosensory area in postcentral gyrus)

◼ Most sensory input to right side of body reaches left side of brain (and vice versa)

Somatic Sensory Pathways

◼ Posterior column - medial lemniscus pathway senses

❑ Fine touch: body location, texture, size

❑ Proprioception: position and motion of body parts

❑ Vibrations: fluctuating touch stimuli

◼ Spinothalamic pathways❑ Anterior and lateral spinothalamic tracts

❑ Relay impulses for pain, tickle, itch, hot, and cold sensations

Somatic Sensory Pathways• The posterior column–medial lemniscus

pathway conveys nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head to the cerebral cortex.

Somatic Motor Pathways

◼ Signals come from

❑ Upper motor neurons: via corticospinal tracts

❑ Basal ganglia: help with muscle tone

❑ Cerebellum: coordination

❑ Sensory neurons or interneurons via reflexes

◼ Impulses activate lower motor neurons

❑ Cell bodies in anterior gray of spinal cord

❑ Axons → ventral root → spinal nerve → muscle → voluntary

movements

Somatic sensory and somatic motor maps in the cerebral cortex, right hemisphere.

• (a) Primary somatosensory area (postcentral gyrus) and (b) primary motor area (precentral gyrus) of the right cerebral hemisphere. The left hemisphere has similar representation. (After Penfield and Rasmussen.)

• Each point on the body surface maps to a specific region in both the primary somatosensory area and the primary motor area.

Lateralization

◼ Brain controls opposite side of the body: all sensory and motor pathways cross in CNS

❑ Left side of the brain controls right side of body

❑ Right side of brain controls left side of body

◼ Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning

◼ Right side more involved with spatial and pattern recognition and emotional content

Memory

◼ Process for storing and retrieving information

◼ Involves structural and functional changes

◼ Involves association areas, parts of limbic system, and diencephalon

◼ Skill memory also involves cerebellum and basal ganglia

Cranial Nerves

I. Olfactory: special sensory—smell

II. Optic: special sensory—vision

III.Oculomotor: motor—control of eye movements

IV.Trochlear: motor—control of eye movements

V. Trigeminal: mixed

❑General sensory: touch, pain, pressure, hot, cold in face

❑Motor: to muscles used for chewing

Cranial Nerves

VI.Abducens: motor—control of eye movements

VII.Facial: mixed

❑ Special sensory (taste) from anterior of tongue

❑ Motor to muscles of facial expression, tear glands, and some salivary glands

VIII.Vestibulocochlear: special sensory—ear

Cranial Nerves

IX.Glossopharyngeal: mixed

❑ Sensory for posterior of tongue, pharynx, and palate; blood

pressure

❑ Motor to pharyngeal muscles (swallowing), salivary gland

(parotid

Cranial Nerves

X. Vagus: mixed (the major parasympathetic nerve)

❑ Sensory from pharynx, ear, diaphragm, visceral organs in

thoracic and abdominal cavities

❑ Motor to palatal and pharyngeal muscles (swallowing and

voice); to viscera in thoracic and abdominal cavities

Cranial Nerves

XI.Accessory: motor to voluntary muscles including

sternocleidomastoid and trapezius (move head,

shoulders)

XII.Hypoglossal: motor to tongue (swallowing and speech)

Aging

◼ Rapid brain growth during first few years of life❑ Due to increase in size of neurons and proliferation of neuroglia

❑ Increase in development of dendritic branches and synaptic

contacts

◼ From early adulthood through old age:

❑ Decline in brain mass

❑ Fewer synaptic contacts brain function

❑ Some decrease in brain function

Mikhail Ness M. Buhay, MD

ThankYou!