Nervous System

Question 1

Define the cranium of the brain.

Answer 1

The cranium is the part of the skull that encloses and protects the brain.

Question 2

Define cranial meninges.

Answer 2

The cranial meninges are the three layers of connective tissue membranes that surround and protect the brain inside the skull.

Question 3

What’s the function of the cranium and the cranial meninges?

Answer 3

The cranium and the cranial meninges surround the protect the brain.

Question 4

Are the cranial meninges continuous or discontinous?

Answer 4

The cranial meninges are continuous with the spinal meninges, have the same basic structure, and bear the same names.

Question 5

Name the different meninges.

Answer 5

1. The outer dura mater.
2. The middle archanoid mater.
3. The inner pia mater

Question 6

What’s the difference between the cranial dura mater and the spinal dura mater?

Answer 6

The cranial dura mater has 2 layers, whereas the spinal dura mater only has one.

Question 7

What are the two dural layers of the cranial dura mater?

Answer 7

The two dural layers are called the periosteal layer (which is external) and the meningeal layer (which is internal).

Question 8

Are the dural layers around the brain fused together?

Answer 8

The dural layers around the brain are fused together except where they separate to enclose the dural venous sinuses (endothelial-lined venous channels) that drain venous blood from the brain and deliver it into the internal jugular veins (veins in the neck).

Question 9

Define epidural space. Do we have any in the brain?

Answer 9

The epidural space is a potential space between the dura mater and the vertebral column. No, there is no epidural space around the brain.

Question 10

Blood vessels that enter the brain tissue -

Answer 10

Blood vessels that enter the brain tissue pass along the surface of the brain, and as they penetrate inward, they are sheathed by a loose-fitting sleeve of Pia Mater.

Question 11

What are the 3 extensions of the dura mater in the brain?

Answer 11

Three extentions of the dura mater separate parts of the brain.

1. The falx cerebri separates the two hemispheres (sides) of the cerebrum.
2. The falx cerebelli separates the two hemispheres of the cerebellum.
3. The tentorium cerebelli separates the cerebrum from the cerebellum.

Question 12

How does blood flow to the brain?

Answer 12

Blood flows to the brain mainly via the internal carotid and vertebral arteries.

Question 13

How does blood from the head return to the heart?

Answer 13

The dural venous sinuses drain into the internal jugular veins to return blood from the head to the heart.

Question 14

How much of the body weight does the brain represent?

Answer 14

In an adult, the brain represents only 2% of the total body weight, but it consumes about 20% of the oxygen and glucose used by the body, even while resting.

Question 15

How do neurons synthesise ATP?

Answer 15

Neurons synthesise ATP almost exclusively from glucose via reactions that use oxygen.

Question 16

What happens when the activity of the neurons and neuroglia increases?

Answer 16

When the activity of neurons and neuroglia increases in a particular region of the brain, blood flow to that area also increases.

Question 17

What does the brief slowing of brain blood flow cause?

Answer 17

A brief slowing of brain blood flow may cause disorientation or a lack of consiousness, such as when you stand up too quickly after sitting for a long period of time.

Question 18

What are the effects of the interruption in blood flow?

Answer 18

An interruption in blood flow for 1-2 mins impairs neuronal function. And total deprivation of oxygen for about 4 mins causes permanent injury.

Question 19

Does supply of glucose to the brain have to be continous?

Answer 19

Since there is no glucose stored in the brain, the supply of glucose to the brain must be continuous.

Question 20

What happens if the blood entering the brain has low levels of BG?

Answer 20

This can cause -
1. Mental confusion
2. Dizziness
3. Convulsions
4. Loss of consiousness

Question 21

Who must mainly be vigilant about their blood glucose levels?

Answer 21

People with diabetes must be vigilant about their blood sugar levels because these levels can drop quickly, leading to diabetic shock, which is characterised by seizure, coma, and possibly death.

Question 22

What’s BBB?

Answer 22

The blood-brain barrier (BBB) consists mainly of tight junctions that seal together the endothelial cells of brain blood capillaries and a thick basement membrane that surrounds the capillaries.

Question 23

Whats an example of a neuroglia?

Answer 23

Astrocytes are one type of neuroglia - the processes of many astrocytes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of the tight junctions.

Question 24

What can cross the BBB?

Answer 24

1. Some water-soluble substances, like glucose, cross the BBB by active transport.
2. Substances like creatinine, urea, and most ions, cross the BBB very slowly.
3. Others like proteins and most antibiotic drugs - do not pass at all from the blood into brain tissue.
4. However, lipid-soluble substances, like O2, CO2, alcohol, and most anaesthetic agents, are able to access the brain tissue freely.

Question 25

What can cause a breakdown of the blood-brain barrier?

Answer 25

Trauma, certain toxins, and inflammation

Question 26

What is CSF?

Answer 26

1. Cerebrospinal fluid (CSF) is a clear, colourless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries. 2. It also carries small amounts of oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.

Question 27

How does CSF circulate?

Answer 27

CSF continually circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space (the space between arachnoid mater and pia mater).

Question 28

What's the total volume of CSF?

Answer 28

80-150mL (3-5 oz) in an adult.

Question 29

What does CSF contain?

Answer 29

CSF contains small amounts of glucose, proteins, lactic acid, urea, cations (Na+, K+, Ca2+, Mg2+), and anions (Cl- and HCO3-). It also contains some WBCs.

Question 30

What is the CSF filled in?

Answer 30

There are 4 CSF-filled cavities in the brain - which are called ventricles. 1. There is one lateral ventricle in each hemisphere of the cerebrum (think of them as ventricles 1 and 2). 2. Anteriorly, the lateral ventricles are separated by a thin membrane, the septum pellucidum. 3. The third ventricle is a narrow slitlike cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus. 4. The 4th ventricle lies between the brain stem and the cerebellum.

Question 31

Define the brain stem.

Answer 31

The brain stem is the part of the brain between the spinal cord and the diencephalon.

Question 32

What does the brain stem consist of?

Answer 32

It consists of three structures - 1. Medulla Oblongata 2. Pons 3. Midbrain

Question 33

What is extending through the brain stem?

Answer 33

Extending through the brain stem is the reticular formation, a netlike region of interspersed grey and white matter.

Question 34

What's the Medulla Oblongata?

Answer 34

1. The Medulla Oblongata/Medulla is continuous with the superior part of the spinal cord. 2. It forms the inferior part of the brain stem. 3. The medulla begins at the foramen magnum and extends to the inferior border of the pons, a distance of about 3 cm.

Question 35

What does the Medulla consist of?

Answer 35

- The Medulla's white matter contains all sensory (ascending) tracts and motor (descending) tracts that extend between the spinal cord and other parts of the brain. - Some of the white matter forms bulges on the anterior aspect of the medulla. - These protrusions aka pyramids are formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord. - The corticospinal tracts control voluntary movements of the limbs and trunk. - Just superior to the junction of the medulla with the spinal cord, 90% of the axons in the left pyramid cross to the right side and 90% of the axons in the right pyramid cross to the left side. - This crossing is called the decussation of pyramids, and explains why each side of the brain controls voluntary movements on the opposite side of the body.

Question 36

MEDULLAAAA

Answer 36

- also contains several nuclei - A nucleus is a collection of neuronal cell bodies within the CNS) - Some of these nuclei control vital body functions. - examples of nuclei in the medulla that regulate vital activities include the cardiovascular centre and the medullary rhythmicity centre.

Question 37

What does the cardiovascular and resp centre regulate?

Answer 37

- The cardiovascular (CV) centre regulates the rate and force of the heartbeat and the diameter of blood vessels. - The medullary respiratory centre adjusts the basic rhythm of breathing.

Question 38

What else does the nuclei in the medulla control?

Answer 38

1. It also controls reflexes for vomiting, swallowing, sneezing, coughing, and hiccuping. 2. The vomiting centre of the medulla causes vomiting - the forcible expulsion of the contents of the upper gastrointestinal tract through the mouth. 3. The deglutition centre of the medulla promotes deglutition (swallowing) of a mass of food that has moved from the oral cavity of the mouth into the pharynx (throat). 4. Sneezing involves spasmodic contraction of breathing muscles that forcefully expel air through the nose and mouth. 5. Coughing involves a long-drawn and deep inhalation and then a strong exhalation that suddenly sends a blast of air through the upper respiratory passages. 6. Hiccupping is caused by spasmodic contractions of the diaphragm that ultimately result in the production of a sharp sound on inhalation.

Question 39

What's lateral to each pyramid?

Answer 39

- Lateral to each pyramid is an oval shaped swelling called an olive. - within the olive is the inferior olivary nucleus - which receives input from the cerebral cortex, red nucleus of the midbrain and spinal cord. - neurons of the inferior olivary nucleus extend their axons into the cerebellum, where they regulate the activity of cerebellar neurons. - by influencing cerebellar neuron activity, the inferior olivary nucleus provides instructions that the cerebellum uses to make adjustments to muscle activity as you learn new motor skills.

Question 40

What about the nuclei associated with sensations of touch, pressure, vibration, and conscious proprioception?

Answer 40

They are located in the posterior part of the medulla. - These nuclei are in the right and left gracile nucleus and cuneate nucleus. - ascending sensory axons of the gracile fasciculus and the cuneate fasciculus , which are two tracts in the posterior columns of the spinal cord, form synpases in these nuclei. - postsynaptic neurons then relay the sensory information to the thalamus on the opposite side of the brain. - the axons ascend to the thalamus in a band of white matter called the medial lemniscus, which extends through the medulla, pons, and midbrain. - the tracts of the posterior columns and the axons of the medial lemniscus are collectively known as the posterior column-medial lemniscus pathway.

Question 41

What else does the medulla contain?

Answer 41

- the medulla also contains nuclei that are components of sensory pathways for gustation (taste), audition (hearing), and equilibrium (balance).

Question 42

Gustatory nucleus

Answer 42

The gustatory nucleus of the medulla is part of the gustatory pathway from the tongue to the brain - it receives gustatory input from the taste buds of the tongue.

Question 43

Cochlear nuclei

Answer 43

The cochlear nuclei of the medulla are part of the auditory pathway from the inner ear to the brain - they receive auditory input from the cochlea of the inner ear.

Question 44

Vestibular nuclei

Answer 44

The vestibular nuclei of the medulla and pons are components of the equilibrium pathway from the inner ear to the brain - they receive sensory information associated with equilibrium from proprioceptors in the vestibular apparatus of the inner ear.