Nervous System Introduction

• 1. Astrocyte
• 2. Oligodendrocyte
• —3. Microglial
• 4. Ependymal
• 5.Schwann Cells
• —6.Satellite Cells

—Outnumber neurons by about 10 to 1.

6 types of supporting cells

4 are found in the CNS:

Blood/Brain Barrier, Housekeeping, Etc.

Star-shaped, abundant, and versatile

—Guide the migration of developing neurons

—Act as K+ and NT buffers

—Involved in the formation of the blood brain barrier

—Function in nutrient transfer

Production Of Myelin In CNS

• —•Produce
• the myelin sheath which provides the electrical insulation for certain neurons
• in the CNS

Cell Macrophage

—Specialized immune cells that act as the macrophages of the CNS

Cell Production Of CSF & Tight Junction Boundaries

Low columnar epithelial-esque cells that line the ventricles of the brain and some of the central canal of the spinal cord

• —
• Some are ciliated which facilitates the movement of cerebrospinal fluid

Production Of Myelin In PNS

Surrounding PNS Neurons

– contains more than 100 clusters of neurons

• dispersed gray matter (sometimes called the “central gray”

1. Somatic motor control (primarily of extensor muscles)

2. Cardiovascular control

3. Pain modulation

4. Sleep and consciousness

3 cm long (1 inch)

—forms inferior part of brain stem

• —lateral side - Olive
• – contains inferior olivary nuclei (relay nuclei)
• – communicates with the cerebellum

1. autonomic nuclei controlling visceral activities

• cardiac center

• vasomotor center

• two respiratory centers

2. relay stations along sensory or motor pathways nucleus gracilis and nucleus cuneatus

– sensory information crosses over to other side decussation of pyramids

– descending motor tracts

– majority of fibers cross over throughout the brain stem

1. telencephalon

2. diencephalon

3. Mesencephalon (Midbrain)

4. metencephalon

5. myelencephalon

– surface gray -cerebrum cortex

– deep gray - basal nuclei

– white matter

– epithalamus

– thalamus

– Hypothalamus

– corpora quadrigemina

– cerebral peduncles

– substantia nigra

– red nucleus

–cerebellum

– pons

– medulla oblongata

– olive

• water, glucose
• lipid soluble substances - oxygen, carbon dioxide, caffeine, nicotine, heroin, and anesthetics

sodium, potassium, chloride, creatinine, and urea

proteins, most antibiotics neurotransmitters, formed elements

—Normal capillary bed in the human body is very permeable

—Two different barriers

• 1. blood brain barrier
• 2. Blood-CSF barrier

capillary bed has tight junctions protoplasmic pseudopodia of astrocytes cover capillary and release chemicals that control the permeability of the endothelium

ependymal cells in choroid plexus have tight junctions

– portions of the hypothalamus

– posterior pituitary gland

– pineal gland

– choroid plexus

nasal sprays can travel up the olfactory nerve fibers

– very different from plasma

– lower pH, proteins, K, Ca, HCO3 and glucose

– Na is about the same

a.Buoyancy

• human brain weighs about 1500 g in air but 50 g when suspended in CSF

b. Protection

• protects brain from striking the cranium

c. Chemical Stability

• • Helps provide means of rinsing metabolic
• wastes from

• •formation
• – formed in the choroid plexus

• • in roofs of the ventricles
• – volume = 100 - 160 ml

• • produce about 500 ml per day
• – 160 mm pressure

– between L3 and L4

– CSF from subarachnoid space

– spinal tap: 3-9 ml

– myelogram

– into the epidural space

– steroids and anastethetics

1. lateral ventricles

2. 3rd ventricle

3. 4th ventricle

– in each cerebral hemisphere

– 1st two ventricles fuse to form the lateral ventricles

– connected to third ventricle by interventricular foramen

– between left and right thalamic clusters

-the floor is the hypothalamus

– connected to 4th ventricle by mesencephalic (cerebral) aquaduct

– between inferior brain stem and the cerebellum

– connects to the spinal canal in the spinal cord

dura mater

arachnoid

pia mater

– double layer over most of brain

• outer periosteal layer

• inner meningeal layer

• separated by dural sinus which empty into the internal jugular veins

– single layer over spinal cord

• epidural space between dural sheath and bone

– middle cob-web layer

– separated from dura mater by subdural space some feel this my be an artifact

• – separated from pia mater by
• subarachnoid space

• 2 spaces contain cerebrospinal fluid

• subarachnoid space is much larger

– arachnoid villi

–inner most delicate areolar connective tissue

Satellite cells

Schwann cells

-Surround clusters of neuronal cell bodies in the PNS

-Probably serve as “replacement” cells for damaged neurons

-Form myelin sheaths around the larger nerve fibers in the PNS.

- Vital to neuronal regeneration

Axolemma = axon plasma membrane.

Surrounded by a myelin sheath, a wrapping of lipid which:

– Protects the axon and electrically isolates it

– Increases the rate of AP transmission

The myelin sheath is made by ________ in the CNS and by _________ in the PNS.

—This wrapping is never complete. Interspersed along the axon are gaps where there is no myelin – these are nodes of Ranvier.

—In the PNS, the exterior of the Schwann cell surrounding an axon is the neurilemma

• Neurons
• -Functional, signal conducting cells

• Neuroglia
• -Supporting cells

The functional and structural unit of the nervous system

• Specialized to conduct information from one part of the body
• to anotherThere are many, many different types of
• neurons but most have certain structura and
• functional characteristics in common:

Cell body (soma)

• —One
• or more specialized, slender processes (axons/dendrites)

• — An
• input region (dendrites/soma)

• — A
• conducting component (axon)

• —-A secretory
• (output) region (axon terminal)

Clusters of somata in the CNS are known as nuclei.

Clusters of somata in the PNS are known as ganglia

Armlike extensions emanating from every neuron.

• The CNS consists of both somata and processes
• whereas the bulk of the PNS consists of processes.

Tracts = Bundles of processes in the CNS

Nerves = Bundles of processes in the PNS

—•Dendrites are thin, branched processes whose main function is to receive —incoming signals.

—•They effectively increase the surface area of a neuron to increase its ability to —communicate with other neurons.

—•Small, mushroom-shaped dendritic spines further increase the SA

—•Convey info towards the soma thru the use of graded potentials – which are —somewhat similar to action potentials.

—Most neurons have a single axon – a long (up to 1m) process designed to convey info away from the cell body.

—Originates from a special region of the cell body called the axon hillock.

—Transmit APs from the soma toward the end of the axon where they cause NT release.

—Often branch sparsely, forming collaterals.

—Each collateral may split into telodendria which end in a synaptic knob, which contains synaptic vesicles – membranous bags of NTs.


—

• —Nervous system has
• two branches, CNS and PNS.

• —CNS contains the
• brain and spinal cord.

• —PNS contains, Sensory
• afferent and a Motor efferent sub region.

• —The sensory PNS has
• visceral and somatic divisions

• —The motor PNS has a
• somatic and visceral sub division but the visceral subregion has an autonomic
• branch with both parasympathetic and sympathetic divisions.