Nervous system 1

how many bones make up the skull

22

what two groups are they divided into?

neurocranium = 8

viscerocranium = 14

name the 8 Neurocranium bones

• Frontal

• 2 parietal

• 2 temporal

• Occipital

• Sphenoid

• Ethmoid

So:

Neurocranium → 8 bones → surrounds/protects brain

what are viscerocranium bones?

Think “viscero = face.”

These are the facial bones. They form structures such as your jaws, nose, and parts of your eye sockets. They also provide attachment sites for muscles involved in chewing and facial expressions.

what is the cranium

Cranium = neurocranium + viscerocranium

where is each bone for neurocranium?

Bone	Number	Think of it as
Frontal	1	Forehead/front
Parietal	2	Top + sides
Temporal	2	Side, around your ears
Occipital	1	Back/bottom
Sphenoid	1	Deep central skull
Ethmoid	1	Deep, around nasal/orbital region

what are sutures

Sutures are joints between the bones of the skull.

what are the major sutures (3)

1. Coronal suture

2. Sagittal suture

3. Lambdoid suture

function of coronal suture

separates the frontal bone from the parietal bones. Think of it as running roughly side-to-side across the top/front of the skull

function of Sagittal suture

separates the left and right parietal bones. It runs along the midline on the top of your head, front-to-back.

function of lamdoid suture

separates the parietal bones from the occipital bone at the back.

Coronal = front boundary
Sagittal = middle line
Lambdoid = back boundary

What is the pterion?

The pterion is NOT a bone.

It's a specific region/junction on the side of the skull where FOUR bones meet: Frontal + Parietal + Temporal + Sphenoid

what is a characteristic of pterion?

The pterion is one of the thinnest and weakest areas of the skull.

• That makes trauma to this area clinically important because a major blood vessel, the middle meningeal artery, runs deep to this region. A fracture around the pterion can damage this artery and cause bleeding inside the skull, classically an epidural hematoma.

what are the three compartments of the neurocranium

1. Anterior cranial fossa - frontal lobe

2. Middle cranial fossa - temporal lobe

3. Posterior cranial fossa - cerebellum

where is the spinal cord contained?

vertebral column - consist of 5 regions

name the 5 regions

1. cervical (7 vertebrae)

2. thoracic (12 vertebrae)

3. lumbar (5 Vertebrae)

4. sacral (5 vertebrae fused)

5. coccyx

what does each vertebra have?

Each vertebra (except the coccygeal) has an opening called the vertebral foramen

• when the vertebrae are stacked on top of each other, these foramina form the vertebral canal

what is a vertebal canal?

Vertebral foramen = individual hole

Vertebral canal = long tunnel formed from those holes

The spinal cord is contained within the vertebral canal.

where do spinal nerves exit?

Spinal nerves exit through the intervertebral foramina, which are formed by adjacent vertebrae.

what is the meninges

The brain and spinal cord are covered by 3 membranous layers collectively referred to as the meninges.

what are the 3 layers?

1. Dura Mater (outermost layer)

2. Arachnoid Mater

3. Pia Mater (innermost)

what is the function of the meninges (3)

1. protection

2. compartmentalization (Dividing a larger space into smaller compartments)

3. Conduit for fluids

what does Conduit for fluids mean?

Conduit simply means a pathway or channel through which something can travel.

The meninges provide spaces/channels for two important fluids:

Cerebrospinal fluid (CSF) circulates through the subarachnoid space.

Venous blood drains through the dural venous sinuses.

how does meninges provide protection

Skull/vertebral column + meninges + cerebrospinal fluid (CSF)

You can think of the skull and vertebral column as the hard outer protection, the meninges as protective coverings, and CSF as fluid that helps cushion the CNS.

what is the dura mater

Tough, dense outer layer - “tough mother”.

• It is tightly attached to the inner surface of skull (no space between them)

what supplies blood to the dura mater

It is supplied by the middle meningeal artery, which lies right underneath the pterion

what are dural septa?

The dura mater is the outermost and toughest meningeal layer.

In certain places, the dura folds inward into the cranial cavity. These inward folds are called dural septa.

• Dural septa = folds of dura mater that divide/support parts of the brain

what two important dural septa?

1. Falx cerebri

2. Tentorium cerebelli

what is Falx cerebri

Falx cerebri → separates the left and right cerebral hemispheres.

• The falx cerebri extends vertically down between the two cerebral hemispheres

what is Tentorium cerebelli

This one separates structures vertically rather than left from right.

• Tentorium cerebelli → separates the cerebellum from the cerebral hemispheres above it.

what are dural venous sinuses?

Venous sinuses are found where the edges of the dural septae meet the skull

• channels containing venous blood associated with the dura.

  They help drain venous blood from the brain.

what is the Arachnoid mater

Thin, middle layer that is firmly attached to the dura (no space between arachnoid and dura).
It has a filmy, spider web-like appearance

what does Arachnoid mater not do?

Arachnoid mater does NOT follow the grooves of the brain.

Your brain has:

• Gyri = raised ridges

• Sulci = grooves between the gyri

Instead of dipping down into each sulcus, the arachnoid mater bridges across the top of the sulci.

what is the pia mater

Innermost and thinnest layer of the meninges. It is very delicate and translucent, which makes it
difficult to see. It is firmly attached to the outer surface of the brain and closely follows the contours of the gyri
and sulci.

what are some mingeal spaces in the skull?

1. Subarachnoid Space

2. Epidural space (only if injury)

3. Subdural space (only if injury)
   
   

funciton of subarachnoid space

1. Cerebrospinal fluid (CSF)
   This space is filled with CSF, which surrounds and cushions the CNS.

2. Cerebral blood vessels
   Superficial arteries and veins of the brain travel through this space.

3. Continuous with the ventricles, which are
   also filled with CSF

what is epidural space

between skull and dura

If bleeding separates the dura from the skull → epidural hematoma

what is subdural space

between dura & arachnoid

Bleeding there → subdural hematoma

is the dura attached to the spinal cord?

dura is not attached

• Epidural space — this time it's a REAL space

• Skull → potential epidural space → dura

  But in the vertebral column, the dura isn't attached to the vertebrae. Therefore there is a real epidural space:

What is the dural sac?

Contains the spinal cord
◦ Extends from the foramen magnum to the 2nd
sacral vertebra (S2)
◦ Also contains the nerves attached to the spinal
cord

what is Epidural space

Between the dura and vertebrae
◦ Contains fat, connective tissue and veins (different from the skull

where is the arachnoid on the spinal cord?

Arachnoid is attached to the dura and ends at S2 (with the dura

what about Subarachnoid space in spinal cord?

◦ Between the arachnoid and pia
◦ Filled with CSF

what is Lumbar cistern

The subarachnoid space also continues down to S2 and contains CSF. Below the end of the spinal cord, this space becomes enlarged. called lumbar cistern
◦ used for obtaining CSF samples (lumbar puncture) and spinal anesthesia

is pia mater attched to spinal cord? what structures does it make

yes

1. Denticulate ligaments

2. Filum terminale

what are Denticulate ligaments

The denticulate ligaments are lateral projections of the pia mater.

They extend outward from the spinal cord and attach toward the dura, helping keep the spinal cord suspended and stabilized within the dural sac

what are Filum terminale

The filum terminale is also derived from the pia mater, but instead of projecting sideways, it's a thin strand that extends downward.

It begins from the:

Conus medullaris → extends inferiorly toward the base of the dural sac

Its purpose is also to help stabilize/anchor the spinal cord.

what are two categories of cells in the nervous system

1. neuron

2. glia

function of neuron

specialized cells for reception, transduction and conduction of stimuli
◦ rapidly conduct signals (action potentials) from one part of a neuron to another, and these
signals are then transmitted to other neurons

function of glia cells

: the support, insulate and nourish the neurons cells
◦ 5x as abundant as neurons (~70% of all cells in the brain

feutures of neurons (4)

1. cell body/soma

2. dendrites

3. axon

4. axon temrinals

fuction of dendrites

The dendrites are the many branching structures coming off the cell body.

Their main function is:

Receive incoming signals from other cells

A neuron usually has many dendrites

function of cell body

The cell body, also called the soma, contains the:

• Nucleus

• Most of the cell's organelles

It keeps the neuron alive and performs the normal metabolic activities of the cell.

It's also where incoming information is integrated before a signal is sent down the axon.

function of axon

The axon is the long projection extending away from the cell body.

Its main job is:

Carry electrical signals (action potentials) away from the cell body.

Unlike dendrites, a neuron generally has one axon, although that axon can branch.

Axons can vary dramatically in length—some are less than 1 mm, while others can extend more than a metre.

what is Myelin

insulation around the axon

Not every axon is myelinated, but when myelin is present, it acts as electrical insulation and allows signals to travel along the axon more efficiently and rapidly.

what is Axon terminals

end of the neuron

At the end, the axon branches into axon terminals.

These allow the neuron to communicate with another cell.

what is synapse

The junction where one neuron communicates with another cell

what are glia cells in the cns (4)

1. ependymal

2. astrocytes

3. oligodendrocytes

4. microglia

what about pns?

1. Schwann cells

2. satellite cells

function ependymal

produce CSF, line the ventricles in the
brain and the central canal of the spinal cor

function of astrocytes

provide physical and metabolic support,
secrete growth factors, limit neurotransmitter
diffusion

function of oligodendrocytes

myelination of axons

function of Microglia

immune cells of the brain, activated
during inflammation

what do Schwann cells do

myelination of axons

what do Satellite cells do

support cells found within ganglia

what is gray matter?

Gray matter is where relaying and processing of information occurs

what is gray matter made up of (3)

◦ Neuronal cell bodies
◦ Dendrites (sites of synaptic connections)
◦ Glia are also present

where is Gray matter is located

◦ Cerebral cortex: Outer surface of the brain
◦ Nucleus: Collection deep within the brain
◦ H-shaped horns within the spinal cord

what is white matter

White matter is the interconnecting fiber tract system (“wiring” of the brain

◦ Consists of myelinated axons
◦ Brain function depends on this connectivity
◦ Called “white matter” because of the high lipid content of myelin

what happens to axons with similar functions

Axons with similar functions and connections are organized into bundles
◦ referred to as a tract, fasciculus, pathway, or lemniscus

what is the Corpus callosum

◦ largest white matter structure in the brain
◦ connects the left and right cerebral hemispheres