Basic Nervous System

Anatomy and Physiology

Kent Rice, MS, REPT, CNIM, D-ABNM

Director of Education and Training

The Nervous System

• Central Nervous System

– Brain

– Spinal Cord

• Peripheral Nervous System

– Cranial Nerves

– Cauda Equina

– Peripheral Nerves

Divisions of the CNS

• Telencephalon – Cerebrum

• Diencephalon – Thalamus

– Hypothalamus

• Mesencephalon – Midbrain

• Metencephalon – Pons

– Cerebellum

• Myencephalon – Medulla Oblongata

• Spinal cord

Meninges – Three layers of protection for

the brain and spinal cord

P – Pia (innermost)

A – Arachnoid

D – Dura (outermost)

Cerebrospinal Fluid

(CSF) resides in

the subarachnoid

space

Circulation of

Cerebrospinal

Fluid

• CSF is formed by the choroid plexus within the ventricles of the brain

• CSF circulates around the entire brain and spinal cord

Reabsorption

into the venous

system occurs

at the arachnoid

granulations

Choroid

plexus

The Ventricles of the Brain Lateral Ventricles

Third

Ventricle

Fourth

Ventricle

The highly folded cerebrum is divided into

left and right hemispheres each controlling

the opposite side of the body

Sulcus

Groove in the cortex.

A deeper groove is

called a fissure

Gyrus

Ridge on the cortex.

Longitudinal fissure

Sylvian

fissure

Gray matter versus White matter

• Gray Matter – Nerve cell bodies

– Dense interneuronal networks

– Cortex and subcortical nuclei

– Source of surface EEG

• Cerebral blood flow and metabolic requirements of gray matter are much greater than white matter

Cortex

Putamen Thalamus

Globus Pallidum

Gray matter versus White matter

• White matter – Myelinated nerve

axons

– “Cabling” of the nervous system

– Fast conducting communication lines between cortical-cortical and cortical-subcortical areas

• White matter has lower CBF and metabolic demands

Corpus Callosum

Internal Capsule

Corona

Radiata

Typical Neuron

Upon reaching threshold, the voltage-gated Na+ channels open

causing an influx of positive charge, raising the membrane potential.

K+ channels open more gradually causing an outflux of positive

charge and repolarization of the membrane.

Residual extracellular K+ results in temporary hyperpolarization

(relative refractory period)

At rest, neurons

maintain a resting

membrane potential

of about -70 mV

Na+ is in high

concentration outside

the cell

K+ is in high

concentration inside the

cell

Nerve

conduction

• Myelin sheath increases

velocity through saltatory

conduction

• Velocity proportional to

fiber size

Thickness of myelin sheath and internodal spacing (arrows represent

Nodes of Ranvier) are proportion to axon diameter

Post-Synaptic Potentials –

Source of EEG Potentials

• EPSP

– Excitatory

• IPSP

– Inhibitory

Action potentials cannot be recorded at the surface

Frontal (Motor,

Personality)

Temporal (Language,

Hearing)

Parietal (Sensory)

Occipital (Vision)

Lobes of

the Brain

Central Sulcus

Insula

(interior

lobe)

Primary Motor Cortex

Pre-central gyrus Primary Sensory Cortex

Post-central gyrus

Homunculus

• Topographic

organization of the

sensory and motor

cortex

• Large proportions

of these areas are

devoted to hand

and face function

Cortical Speech and Language

Function

• Wernicke’s area – Language

comprehension

• Broca’s area – Speech motor

function

• Parietal operculum – connection

Relation of the brain to the

cranial fossae

Anterior Fossa (Frontal lobe)

Middle Fossa (Temporal lobe)

Posterior Fossa (Cerebellum, Brainstem)

Basal Ganglia

• The Basal Ganglia are a group of subcortical nuclei interconnected with cortex, thalamus, and brainstem and associated with motor control, cognition, emotions, and learning

• Corpus Striatum – Caudate Nucleus

– Lentiform Nucleus

• Putamen

• Globus Pallidus

• Amygdaloid Body

• Subthalamic Nucleus

• Substantia Nigra

Thalamus

Basal Ganglia and related

structures Caudate

Putamen

Globus

Pallidum

Internal

Capsule

Thalamus

Motor circuitry within the basal

ganglia

• GPe – Globus Pallidus

externa

• GPi – Globus Pallidus

interna

• STN – Subthalamic

Nucleus

• SNc – Substantia Nigra

pars compacta

• SNr – Substantia Nigra

pars reticulata

Cortex

Striatum

GPe

GPi STN

SNc

SNr

Thalamus

Excitatory

Inhibitory

Diencephalon

• Thalamus – Made up of multiple nuclei

– Highly connected with all parts of the cortex

– Sometimes thought of as a “sensory relay” station

– Important for regulating states of arousal

• Hypothalamus – The “Master Gland”, controls the

pituitary

– Links nervous activity to the endocrine system

– Hunger, temperature, metabolism, sexual behavior

Brainstem

Midbrain

Pons

Medulla

Fourth ventricle

III IV

V

VI VII VIII

IX X

XI

XII

Cerebellum

Anterior View Posterior View

Medullary

Pyramids

Decussation

IV

Superior

Colliculus

Inferior

Colliculus

Facial

Colliculus

Cranial Nerve Nuclei in Brainstem

Sensory Motor

III

III

IV

IV V

V

VI

VI

VII VII

VIII

VIII

IX

IX

X

X

XI

XI XII

XII

A1 A2

Cz

Lateral

Lemniscus

Inferior

Colliculus

Medial Geniculate

Body

(in Thalamus)

Auditory

Cortex

Posterior

View

Cochlear

Nuclei

Superior

Olivary

Complex

Auditory

Nerve

Auditory Pathway in the CNS

Cerebellum

• Serves to coordinate

motor activity

• Separated from the

cerebrum by the

tentorial membrane

Posterior Anterior

Neurovascular Supply

Supplying Arteries to the Brain

Common

carotid artery

Subclavian artery

Brachiocephalic

trunk

Internal

Carotid

Artery Supplies anterior

circle of Willis

External

carotid

artery

Vertebral

Artery Supplies

posterior

circle of Willis

Circle

of

Willis

Internal

Carotids

Middle

Cerebral

Artery

Anterior

Cerebral

Artery

Anterior

Communicating

Artery

Posterior

Cerebral

Artery

Vertebral Arteries

Posterior

Communicating

Arteries

Basilar Artery

Superior Cerebellar

Pontine Arteries

Anterior Inferior Cerebellar

Circle

of

Willis

Internal

Carotids

Middle

Cerebral

Artery

Anterior

Cerebral

Artery

Anterior

Communicating

Artery

Posterior

Cerebral

Artery

Vertebral Arteries

Posterior

Communicating

Arteries

Basilar Artery

Superior Cerebellar

Pontine Arteries

Anterior Inferior Cerebellar

Communicators

provide collateral

flow (we hope!)

Inferior View of

Circle of Willis

Vertebrals

Basilar

Internal

Carotids

Posterior

Cerebral

(PCA)

Middle

Cerebral

(MCA)

Anterior

Cerebral

(ACA)

Posterior Communicating

(PComm)

Anterior Communicating

(AComm)

Superior Cerebellar

(SCA)

Anterior Inferior

Cerebellar

(AICA)

Pontine Vessels

MCA

ACA

PCA

Coronal View of MCA and ACA

Anterior Cerebral

Middle Cerebral

Lenticulostriate

Arteries Supply posterior limb

of internal capsule

and portions of basal

ganglia

Arteries of Brain – Lateral View

Left Middle Cerebral

Supplies lateral

frontal, temporal and

parietal lobes

Left Anterior Cerebral

Left Internal Carotid

Arteries of Brain – Medial View

Posterior Cerebral Artery Supplies inferior temporal and

occipital lobes

Anterior

Cerebral

Artery

Supplies

medial

frontal and

parietal

lobes

Cortical Perfusion

Middle Cerebral

Anterior Cerebral

Posterior

Cerebral

Watershed

Areas

(most

sensitive to

ischemia)

Lower extremity

sensory-motor

function

ACA

Upper extremity

and face

sensory-motor

function

MCA

Arteries of the Posterior Cranial

Fossa – The Vertebrobasilar System

Internal

Carotid Artery

Basilar Artery

Anterior spinal artery

Vertebral Artery

Posterior

Cerebral

Artery

Superior

Cerebellar

Anterior Inferior

Cerebellar (AICA)

Posterior Inferior

Cerebellar (PICA)

Perforating

branches from the

basilar and

posterior cerebral

artery supply the

brainstem and

thalamus

Spinal Cord Anatomy

Spinal Cord • The spinal cord

extends from the medulla down to the L2 vertebral level

• It is divided into functional spinal segments, each giving a pair of spinal nerves derived from dorsal and ventral roots

• The spinal cord is thicker at the cervical and lumbar segments due to the neuronal requirements of the limbs

Dorsal View

Segment

Root

Spinal Cord • The tapered end of the

spinal cord is called the conus medullaris

• The nerve roots exiting the lumbosacral segments of the conus descend as the cauda equina (“horse’s tail”)

• The tip of the spinal cord is connected to the coccyx by a string of connective tissue, the filum terminale.

Dorsal View

Spinal nerve root

positions relative

to the vertebrae

• Cervical roots exit above their respective vertebra

– Exception: C8 root exits above T1

• All other roots exit below their respective vertebra

Spinal Cord Meninges

Arachnoid

Pia Mater overlying

Spinal Cord

Dura Mater

Ventral Root of

Spinal Nerve

Dorsal Root of

Spinal Nerve

Spinal cord features

Gray Matter

White Matter

Ventral Nerve Root Outgoing motor fibers

Dorsal Nerve Root Incoming sensory fibers

Dorsal Root Ganglion houses

sensory cell bodies

Spinal Cord Cross Sections

C5

L1 L2 S2 S3

T2 T7

A greater proportion of gray matter is observed at the enlargements

Spinal cord relative to vertebra

(thoracic region)

Vertebral

Body

Epidural

Space

Spinal

Cord

Lamina

Cauda Equina relative to

vertebra (lumbar region)

Cauda

Equina

Filum

Terminale

Spinal Tracts

Fasciculus Gracilis

(Lower SSEP)

Fasciculus Cuneatus

(Upper SSEP) Lateral

Corticospinal

(TCMEP)

Lateral

Spinothalamic

Anterior

Spinothalamic

Anterior

Corticospinal

Spinal Cord Blood Supply - Thoracic

Aorta

Anterior Spinal

Artery

Posterior Spinal

Arteries

Intercostal

Arteries

Arteries of the Spinal Cord

Anterior

Spinal

Artery

(Supplies

Anterior 2/3

of cord) Radicular

Arteries

Posterior

Spinal

Arteries

(Supplies

Posterior 1/3

of cord)

Spinal Cord

Vasculature

• Anterior spinal artery receives fewer segmental suppliers (6-8) compared to posterior spinal arteries (10-23)

• Artery of Adamkiewicz is a major supplier to the spinal cord, located variably at a low thoracic level

• Mid-thoracic spinal cord is most vulnerable to hypoperfusion

Anterior Spinal Posterior Spinal

Posterior

Column –

Medial

Lemniscus

Pathway

1. Primary sensory fibers

enter the dorsal root and

ascend the ipsilateral

fasciculus cuneatus tract

2. Termination in the nucleus

cuneatus, synapse, and

decussation via internal

arcuate fibers in the medulla

3. Secondary fibers ascend

the medial lemniscus to the

ventral posterolateral

nucleus of the thalamus

4. Thalamocortical fibers conduct to

the hand region of the contralateral

post-central gyrus

Nucleus

cuneatus

Dorsal

Root

Medial

Lemniscus

VPL nucleus

of thalamus

Fasciculus

cuneatus

Pyramidal

Pathway

Internal

Capsule

Pre-central

Gyrus

Primary Motor

Cortex

Decussation of

the Pyramids Approximately 85% of

the corticospinal fibers

cross

Controls

voluntary

discrete skilled

motor function

Monitored via

Transcranial

Motor Evoked

Potentials

Lateral

Corticospinal

Tract

Anterior

Corticospinal

Tract

Lower motor

neuron exits

the ventral

root

Corticospinal Fiber

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