chapter 11 - CNS

Question 1

primary regions of the brain

Answer 1

cerebrum
thalamus
pineal gland (part of epithalamus)
hypothalamus
pituitary gland
mid brain
pons
medulla oblongata
spinal cord
cerebellum

Question 2

brains ventricles are lined with

Answer 2

Ependymal cells.

The ependyma is made up of ependymal cells called ependymocytes, a type of glial cell. These cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord. These are nervous tissue cells with a ciliated simple columnar shape much like that of some mucosal epithelial cells.

Question 3

locations of the ventricles of the brain

Answer 3

The brain ventricles are four cavities. within each cerebral hemisphere the two large, C shaped, lateral ventricles are located in the frontal, temporal and occipital lobes. A thin membrane called ‘septum pellucidum’ separates them

the third ventricle is under the corpus callosum in the brains mid line. surrounded by the diencephalon. connected to the lateral ventricles via the intraventricular foramen.

the fourth ventricle is in the brain stem and a narrow ‘cerebral aqueduct’, which runs through the mid brain, joins it to the third ventricle.

The ventricles are all an important part of the “ventricular system.” The ventricles are interconnected with each other, and also with the central canal of the spinal cord and with the subarachnoid space (a space between two of the linings that separate the brain from the skull). CSF is produced by the lining of the ventricles. The CSF then circulates throughout the ventricular system and is eventually reabsorbed in the subarachnoid space.

Question 4

cerebrum and cerebral cortex

Answer 4

Cerebrum is the largest and the most prominent part of the brain, whereas the cerebral cortex is the outer layer of the cerebrum. Cerebral cortex is actually a part of the cerebrum. … The cerebrum has both gray and white matter, whereas the gray matter is considered to be the cerebral cortex.

Question 5

pituitary gland attachment

Answer 5

The gland is attached to a part of the brain (the hypothalamus) that controls its activity. The anterior pituitary gland is connected to the brain by short blood vessels. The posterior pituitary gland is actually part of the brain and it secretes hormones directly into the bloodstream under the command of the brain.

Question 6

cerebral hemispheres

Answer 6

cerebrum is divided into two large hemispheres, one on the left and one on the right.

they form the superior part of the brain and account for 83% of its mass.

Question 7

corpus callosum

Answer 7

the corpus callosum is a deep bridge of nerve fibers that connects the hemispheres, separated by a layer of dura mater.

it lies superior to the lateral ventricles, deep inside the longitudinal fissure.

Question 8

gyri, sulcus and fissure

Answer 8

the cerebrums surface is covered in gyri, which are separated by shallow or deep grooves.

each shallow groove is called a sulcus

each deep groove is called a fissure. The fissures separate large regions of the brain.

all these grooves form distinct patterns in normal brains, with the gyri and sulci being more prominent.

Question 9

sulci

Answer 9

divide each hemisphere into frontal, parietal, temporal and occipital lobes (as well as a structure called the insula)

Question 10

insula

Answer 10

is a brain lobe but is buried deep within the lateral sulcus, forming a portion of the brain floor.

Question 11

median longitudinal fissure

Answer 11

separates the cerebral hemispheres

Question 12

transverse cerebral fissure

Answer 12

separates the cerebral hemispheres from the cerebellum below them

Question 13

3 basic regions of each cerebral hemisphere

Answer 13

cerebral cortex - is superficial grey matter

white matter - more internal

basal nuclei - are islands of grey matter located deep inside the white matter

Question 14

Cerebrum - Cerebral Cortex

Answer 14

Thin outer layer of cerebrum made up of grey matter

Grey matter contains: dendrites, nueron cell bodies, glia, blood vessels

It lacks fibre tracts

Is the centre of the conscious mind: awareness, communication, sensation, memory, understanding and initiation of voluntary movements

Contains 75% of all neuron cell bodies of the NS.

2-4mm thick BUT makes 40% off brain mass

Surface area tripled by convolutions/folding of the surface into gyri, sulci, fissures and the Insula.

Cortical functions are specialised, which exhibits a phenomenon known as ‘lateralisation’. No functional area acts on its own, and conscious actions use the entire cortex in varying ways.

Question 15

Cerebrum - Cerebral White Matter

Answer 15

Beneath the cerebral cortex is white matter comprising most of the cerebrum.

Contains myelinated axon bundles. Some pass between hemispheres, others carry impulses from the cortex to nerve centres of the brain and spinal cord.

The internal cerebral white matter controls communication between areas of the cerebrum and between the cerebral cortex and lower centres of the CNS. Myelinated fibers bundled into large tracts make up most of the white matter.

The fibers are classified by the directions in which they run.

Association fibers connect the various parts of the same brain hemisphere. Adjacent gyri are connected by short association fibers called ‘acruate fibers’. Different cortical lobes are connected by long association fibers which are bundled into tracts.

Corresponding grey areas of both hemisphere are connected by commissural fibers or commissures, which allow the hemispheres to function together. The corpus callosum in the largest commissure.

Projection fibers enter the cerebral cortex from the spinal cord or lower brain areas or descend to lower areas from the cerebral cortex. They allow motor output to leave the cerebral cortex and also sensory information to reach it.

Project fibers are different from association and commissural fibers in that they run vertically.

Projection fibers at the top of the brainstem form a compact ‘interal capsule’ passing between the thalamus and certain basal nuclei. They then have a fan like radiating pattern through the cerebral white matter and are therefore referred to as the ‘corona radiata’

Question 16

Dominant hemisphere

Answer 16

In most people one hemisphere of the cerebrum is dominant, controlling the use and understanding of language.

Left hemisphere usually responsible for activities such as speech, writing reading, and complex intellectual functions.

The non-dominant hemisphere controls non-verbal functions and intuitive and emotional thoughts.

The dominant hemisphere controls the motor cortex of the non-dominant hemisphere.

Question 17

Function of the cerebrum

Answer 17

Aside from sensory and motor control, memory and reasoning, the cerebrum also coordinates intelligence and personality. Functions overlap between regions of the cerebral cortex.

Question 18

Three functional areas of the cerebral cortex

Answer 18

The motor cortex

The sensory cortex

The association cortex

Question 19

Each cerebral hemisphere controls the motor and sensory functions of the…

Answer 19

Contralateral (opposite) side of the body

Question 20

Motor areas

Answer 20

Most of the cerebral cortex motor areas are located in the frontal lobes and are further defined as the:

Primary motor cortex
Premotor cortex
Broca’s area
Frontal eye field

Impulses from large ‘pyramidal cells’ in the motor areas travel through the brain stem in to the spinal cord via the ‘corticospinal’ tracts that form synapses with lower motor neurons. Their axons leave the spinal cord, reaching the skeletal muscle fibers.

Question 21

Tracts

Answer 21

Bundles of neuron processes in the central nervous system (CNS)

Question 22

The primary motor cortex

Answer 22

Also known as the ‘somatic motor cortex’

Located in the precentral gyrus of the frontal lobe of both hemispheres

The mapping of the CNS structures of the body is referred to as somatotopy.

Question 23

The premotor cortex

Answer 23

Lies just anterior to the precentral gyrus in the frontal lobe and helps to plan movements

Question 24

Broca’s area

Motor cortex

Answer 24

Is found anterior to the inferior region of the premotor area and is more prevelant in the left hemisphere.

It has a motor speech area and also becomes active just before speaking or when planning other voluntary motor activities.

Question 25

The frontal eye field

Motor cortex

Answer 25

Is superior to broca’s area, located partly in and anterior to the premotor cortex.

It controls voluntary eye movements.

Question 26

The central sulcus

Answer 26

separates the primary motor areas from the somatosensory areas

Question 27

Sensory areas of the cerebrum

Answer 27

Interpret impulses such as skin sensations, which are picked up in the anterior portion of the parietal lobes.

Posterior occipital lobes affect vision

Temporal lobes affect hearing

Taste and smell receptors are located deeper within the cerebrum

Sensory fibers also cross similar to motor fibers

Additional sensory areas include the insular and occipital lobes

Question 28

Primary Somatosensory Cortex

Sensory cortex

Answer 28

Lies in the post central gyrus of the parietal lobe. Just posterior to the primary motor cortex.

Its neurons receive input from the somatic sensory receptors of the skin.

It also receives input from position sense receptors in the joints, skeletal muscles and tendons.

Question 29

Somatosensory association cortex

Sensory cortex

Answer 29

Is found just posterior to the primary somatosensory cortex, is interconnected and functions primarily to integrate temperature, pressure, and related information.

Question 30

Primary visual (striate) cortex
(Sensory cortex)

Answer 30

Mostly buried in the ‘calcarine sulcus’ of the occipital lobe but also extends to the extreme posterior occipital tip.

It is the largest cortical sensory area, receiving visual information from the retinas of the eyes.

Question 31

Visual association area

Sensory cortex

Answer 31

Uses visual experiences from the past to interpret colour, form, movement, and other visual stimuli

Question 32

Primary auditory cortex

Sensory cortex

Answer 32

Lies in the superior margin of the temporal lobe and receives impulses from the inner ear, interpreting location, loudness and pitch.

Posteriorly the auditory association area perceives sound stimuli such as speech, music and environmental noises.

Question 33

Vestibular (equilibrium) cortex

Sensory cortex

Answer 33

Controls balance and is located in the posterior insula and the nearby parietal cortex.

Question 34

The primary (olfactory) smell cortex
(Sensory cortex)

Answer 34

Is present on the medial temporal lobe in the priform lobe area, which is signified by its ‘uncus’, a hook like structure.

The olfactory cortex is part of the rhinecephalon, a primitive structure that includes the orbitofrontal cortex, uncus, and related regions on or inside the medial temporal lobe as well as the olfactory tracts and bulbs extending to the nose.

Question 35

Gustatory (taste) cortex

Sensory cortex

Answer 35

Is located in the insula, deep in the temporal lobe.

Question 36

Visceral sensory area

Sensory cortex

Answer 36

Controls visceral sensations and lies in the cortex of the insula, just posterior to the gustatory cortex.

Its sensations include bladder fullness, stomach upset, and tightness in the lungs (such as from holding your breath)

Question 37

Basal Nuclei

Answer 37

Several masses of grey basal nuclei (basal ganglia) lie deep inside each cerebral hemisphere.
These are the caudate nucleus, globus pallidus and putamen.

The basal nuclei help to control skeletal muscles activities. They filter out inappropriate responses as well as being involved in cognition and emotion.

The lack of dopamine from the basal nuclei may cause parkinson’s.

Question 38

Striatum

Basal nuclei

Answer 38

Also called the corpus striatum is a collective term to the caudate nucleus, putamen and globus pallidus

The caudate nucleus arches superiorly over the diencephalon, joining the putamen to form the striatum, which has a striped appearance.

The basal nuclei are linked to the subthalamic nuclei of the diencephalon and the substansia nigra of the midbrain.

They receive input from the cerebral cortex, other subcortical nuclei and each other.

The globus pallidus and substantia nigra relay information through the thalamus reaching the premotor and prefrontal cortices. Therefore they influence muscle movements as controlled by the primary motor cortex.
However the basal nuclei do not directly access the motor pathways.

Question 39

Diencephalon

Answer 39

The diencephalon is mostly made up of the piared gray matter structures known as the thalamus, hypothalamus, and epithalamus.

It forms the central core of the forebrain.

The diencephalon is surrounded by the cerebral hemispheres and itself encloses the third ventricle.

Question 40

Thalamus structure

Answer 40

The superolateral walls of the third ventricle are formed by the egg shaped bilateral nuclei of the thalamus.

This structure makes up 80% of the diencephalon and is found deep inside the brain.

The nuclei of the thalamus are interconnected by an intermediate mass known as the ‘interthalamic adhesion’. The thalamic nuclei are mostly named based on their location, each having functional specialities, with unique fibers connected to certain regions of the cerebral cortex.

Question 41

Thalamus function

Answer 41

The thalamus processes and relays all incoming and outgoing information between the cerebral cortex and the spinal cord.

The thalamus mediates motor activities, sensation, cortical arousal, learning and memory. Related impulses are organised in groups through the internal capsule of the thalamus to the correct area of the cerebral cortex and association areas.

Afferent impulses reaching the thalamus are basically recognised as either pleasant or unpleasant. Specific stimulus discrimination and localisation occurs in the cerebral cortex, not the thalamus.

Nearly all other inputs ascending to the cerebral cortex are channeled through the thalamic nuclei: inputs from memory or sensory integration projected to areas such as the pulvinar, lateral dorsal, or lateral posterior nuclei and inputs regulating emotional and visceral function from the hypothalamus, via the anterior nuclei.

Additionally the thalamic nuclei interpret instructions aiding in direction of motor cortical activity from the cerebellum (via the ventral lateral nuclei) and the basal nuclei (via the ventral anterior nuclei).

Question 42

Integration

Answer 42

The process by which the nervous system processes and interprets sensory input.

Question 43

Nuclei

Answer 43

Clusters of cell bodies in the central nervous system

Question 44

Hypothalamus

Answer 44

The hypothalamus is the primary visceral control centre of the body. It is crucial for the homoeostasis of the body, affecting nearly all body tissues.

It is located below the thalamus, capping the brainstem, and forming the inferolateral walls of the third ventricle.

Paired, small, and rounded structures bulge anteriorly from the hypothalamus. Known as mammillary bodies, they act as relay stations in the olfactory pathways. A stalk of hypothalamic tissue known as the infundibulum lies between the mammillary bodies and the optic chiasma.

The infundibulum connects the pituitary gland to the base of the hypothalamus.

Question 45

Hypothalamus function

Answer 45

The hypothalamus controls the autonomic nervous system and endocrine system function.

It also initiates physical responses to emotions.

Other regulatory functions of the hypothalamus affect body temperature, intake of food, water balance, thirst, and sleep-wake cycle.

Its control of ANS activities occur by control of brainstem and spinal cord activity.

The hypothalamus is vital for the limbic system, which is the emotional part of the brain, and it acts through ANS pathways to initiate many physical expressions of emotion.

The hypothalamus is also the bodies thermostat, controls hormone secretion from the anterior pituitary gland, and produces the hormones antidiuretic hormone and oxytocin.

Question 46

Epithalamus

Answer 46

The epithalamus is the most dorsal part of the diencephalon, forming the roof of the third ventricle.

The pineal gland extends from its posterior border. This gland secretes the hormone melatonin, which helps regulate the sleep wake-cycle and also acts as an antioxidant.

The caudal border of the epithalamus is formed by the posterior commissure.

Question 47

Choroid plexus

Answer 47

The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells.

Question 48

Limbic system

Answer 48

The limbic system is a complex set of structures that lies on both sides of the thalamus, just under the cerebrum.

It includes the hypothalamus, the hippocampus, the amygdala, and several other nearby areas.

The limbic system is responsible for the experience and expression of emotion.

Question 49

Brainstem

Answer 49

Mid brain

Pons

Medulla oblongata

Behaviours needed for survival are produced in the brainstem. These behaviours are automatic and highly controlled. The brainstem create a pathway for fibre tracks that connects higher and lower neural centres. The brainstem nuclei are also linked to 10 pairs of the cranial nerves and are greatly involved with innervation of the head.

Question 50

Midbrain

Answer 50

Between the diencephalon and the pons.

The midbrain serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing.

Question 51

pons

Answer 51

Lying between the midbrain and medulla oblongata.

Is a bulge in the brainstem.

Separated from the cerebellum by the fourth ventricle.

It’s involved in the control of breathing, communication between different parts of the brain, and the sensations such as hearing, taste and balance.

Question 52

Medulla oblongata

Answer 52

The most inferior part of the brainstem.

It joins the spinal-cord smoothly, at the level of the skulls foramen magnum.

The medulla oblongata helps regulate breathing, heart and blood vessel function, digestion, sneezing and swallowing. This part of the brain is a centre for respiration and circulation.

It plays a vital role as a centre of autonomic reflexes required for homoeostasis. Important functional groups of visceral motor nuclei are controlled by the medulla oblongata.

It’s cardiovascular centre includes both the cardiac centre and vasomotor centre.

It’s respiratory centres control respiratory rhythm, rate and depth.

Various other centres of the medulla influence hiccuping, vomiting, coughing, swallowing and sneezing.

Motor nuclei send motor commands to peripheral effecters

Question 53

Cerebellum

Answer 53

It is found dorsal to the pons, medulla, and forth ventricle.

It protrudes under the occipital lobes of the cerebral hemispheres, and is separated from these lobes by the transverse cerebral fissure.

The cerebellum processes inputs from the cerebral motor cortex, brain stem, and sensory receptors. It then regulates skeletal muscle movements for many different activities, such as driving a car, playing a musical instrument, or using a computer.

All cerebellar activity is subconscious.

The cerebellum has it’s own thin outer cortex of grey matter, internalised white matter, and deep masses of grey matter.

The vermis connects its two hemispheres.

Question 54

Brain protection

Answer 54

The brain is surrounded by bones fluids and membranes. It lies inside the skulls cranial cavity and is soft and delicate.

Between the bony coverings and the soft brain tissues are layered membranes known as meninges that protect the brain and spinal cord.

The singular term Meninx describes just one of the meninges.

Also the CSF cushions the brain and the blood brain barrier protects it from harmful substances carried in the blood.

There is also a blood-CSF barrier, which is formed by ependymal cells surrounding the capillaries of the choroid plexus.

Question 55

Meninges

Answer 55

There are three layers of membranes in the meninges:
Dura mater
Arachnoid mater
Pia mater

Question 56

Dura mater

Answer 56

The outermost layer which is made up of fibrous, tough, white connective-tissue. It has many blood vessels and nerves and attaches to the inside of the cranial cavity. It also extends inward between the brain lobes to form protective partitions. It continues into the vertebral canal to surround The spinal-cord, ending in a sack at its end.

Dura mater has two layers of fibrous connective tissue:
It’s periosteal layer, which is more superficial, attaches to the periosteum (inner surface of the skull). Around the spinal-cord there is no dural periosteal layer.
The meningeal layer actually covers the brain, continuing caudally as the spinal dural mater in the vertebral canal.

The two dural layers of the brain fused in most areas. In certain places they separate, enclosing dural venous sinuses, which collect blood from the brain and channel it to the internal jugular veins in the neck.

Question 57

Dural septa

Answer 57

Dural septa limit excessive brain movement and are formed from the meningeal dura mater.

It contains three primary features. It’s falx cerebri is a large fold that dips into the longitudinal fissure between the hemispheres of the cerebrum. It contains two large venous sinuses known as the superior sagittal and inferior sagittal sinuses.

The falx cerribelli continues inferiorly from the more posterior falx cerebri, along the vermis of the cerebellum.

The tentorium cerebelli is a nearly horizontal dural fold extending into the transverse fissure and cerebellum. It contains the transverse sinus.

Question 58

Epidural space

Answer 58

The membrane around the spinal-cord has an epidural space separating it from the vertebrae. The epidural space contains loose adipose and connective-tissues, protecting the spinal cord.

Question 59

Arachnoid mater

Answer 59

A thin, weather like arachnoid mater lies between the dura and Pia maters. the subdural space is a narrow serious cavity that contains a fluid film.

Question 60

Pia mater

Answer 60

The thin pia mater has many blood vessels and nerves that nourish the brain and spinal cord. The pia mater is closely aligned with the surfaces of these organs.

It is comprised of many tiny blood vessels and delicate connective-tissue. The pia mater is bound tightly to the brain and its convolutions.

Small ragged bits of pia mater are briefly carried by small arteries entering the brain.

Question 61

Cerebrospinal fluid

Answer 61

Between the arachnoid and pia mater is a subarachnoid space containing the watery and clear cerebrospinal fluid and the primary brain blood vessels.

Inside the subarachnoid space are web like extensions that function partially to bind the arachnoid mater to the pia mater.

CSF surrounds the brain and spinal-cord, maintaining a stable ionic concentration and protecting CNS structures. The brain floats in CSF, which cushions it and prevents the bottom of the brain from being crushed by its own weight.

CSF also helps to nourish the brain and may assist in carrying chemical signals concerning sleep and appetite. It also may carry hormones.

The total CSF volume is about 150 mL, which is replaced every eight hours.

Question 62

Arachnoid villi

Answer 62

Knob like projections that protrude superiorly through the dura mater into the superior sagittal sinus. They absorb CSF into the venous blood of the sinus.

In adults, clusters of arachnoid villi form large arachnoid granulations, where CSF is actually absorbed into the venous circulation.

Question 63

Choroid plexus

Answer 63

Small red choroid plexuses (specialised capillaries) secrete CSF and project into the brain ventricles. Most CSF is formed in the lateral ventricles. CSF also enters the meninges’ sub arachnoid space via the two lateral apertures and the single median aperture and is reabsorbed into the blood.

Question 64

Blood-brain Barrier

Answer 64

The blood–brain barrier (BBB) is a highly selective semipermeable border that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS).

3 layers: capillary wall endothelium, basal lamina, astrocytes

Not effective against fat soluble molecules.

Hypothalamus does not have a barrier so it can sample the bloods chemical composition and regulate metabolic activities.

Question 65

Spinal cord

Answer 65

Thin column of nerves leading from the brain to the vertebral canal.

Starts at the cranial cavity, foramen magnum.

Terminates at first and second lumbar. Cauda equina.

42cm long

1.8cm thick

Provides two way communication to and from the brain.

Contains spinal reflex centres.

Divided into right and left halves by a deep anterior median fissure and a shallow posterior median sulcus.

Spinal meninges continuous with those of the brain.

Epidural space between dura mater and vertebrae, padded by fat and veins.

Inner core is grey matter surrounded by white matter.

Motor fibres pass out from grey matter through spinal nerves to skeletal muscles. However most of the grey matter neurons are interneurons.