Structure of the Nervous SystemCHAPTER 3

Directions in the Nervous SystemDirections in the Nervous System

Anterior/Rostral = Front Posterior/Caudal = Back Dorsal = Top Ventral = Bottom Lateral = Toward the side Medial = Toward the midline Ipsilateral= Same side Contralateral= Opposite side

Fig. 3.1Fig. 3.1

Coronal Coronal *Cross Section or *Frontal SectionTransverse section at right angles to the neuraxis.

Brain Slices and PlanesBrain Slices and Planes

CoronalCoronal

Fig. 3.2Fig. 3.2

Sagittal Section• Section parallel to neuraxis and perpendicular to the ground.• Midsagittal Plane – special type of sagittal section through the corpus callosum separating the hemispheres.

Brain Slices and PlanesBrain Slices and Planes

SagittalSagittal

Fig. 3.2Fig. 3.2

Horizontal SectionHorizontal SectionSection made through the brain parallel to the ground.

Brain Slices and PlanesBrain Slices and Planes

HorizontalHorizontalFig. 3.2Fig. 3.2

Meninges

The MENINGES MeningesMeninges Dura Mater – tough, flexible

outermost layer.

Arachnoid Membrane – middle layer of the meninges. Subarachnoid Space – space

between arachnoid membrane and pia mater filled with CSF.

Pia Mater – last layer of the meninges, which adheres to the surface of the brain.

The Ventricular System CSF surround the brain (protection) Four ventricles (lateral-2, third and fourth connected by cerebral

aqueduct) Choroid plexus- produces CSF (125 ml/day) Arachnoid granulations: absorb CSF

Figure 3.4Figure 3.4

Obstructive hydrocephalus

Figure 3.6Figure 3.6

Development of the CNS

Begins around 18th day after conception

A patch of tissue on the dorsal surface of the embryo becomes the neural plate

Development of the CNS

Figure 3.7Figure 3.7

Neural plate folds to form the neural groove

Development of the CNS

The neural groove then fuses to form the neural tube…

Walls of the neural tube become the CNS

Neural crest becomes the PNS

Figure 3.7Figure 3.7

Brain Development

Figure 3.8Figure 3.8

Early and later development of the human nervous system

Cellular Development

Totipotent – earliest cells have the ability to become any type of body cell Stem cells

Multipotent – with development, neural plate cells are limited to becoming one of the range of mature nervous system cells Progenitor cells

Migration of Neurons

Once cells have been created through cell division in the ventricular zone of the neural tube, they migrate

Migrating cells are immature, lacking axons and dendrites

Inside-out migration

Progenitor cells have limited capacity to replicate

First Step: Symmetrical Division Progenitor -> progenitor Increases the size of the ventricular zone

Figure 3.10Figure 3.10

Second: Asymmetrical Division

Asymmetrical division (7 weeks after conception) First produces radial glia Cell bodies of RG in the VZ and processes extend to

the pia Guide the migration of new neurons (neurogenesis) Ends after 3 months

•development where a progenitor cell divides into one progenitor cell and one brain cell

Cellular Development and Migration

Cajal-Retzius cells Develop after radial

glia Migrate to just

inside the pia (Layer 1)

Orderly migration: Build on each

successive layer All end up below C-R

Anatomical Subdivisions

Anatomy BasicsMajor Division Ventricle Subdivision Principle Structures

Midbrain

Hindbrain

Forebrain

Lateral

Third

Telencephalon

Diencephalon

Cerebral cortexBasal gangliaLimbic System

Cerebralaqueduct

Mesencephalon

Metencephalon

TectumTegmentum

FourthCerebellum

Pons

Myelencephalon

Thalamus

Hypothalamus

Medulla oblongata

The Forebrain

Largest section of the brain, comprised of the:

Telencephalon Cerebral hemispheres

Cerebral Cortex Limbic System Basal Ganglia

Diencephalon Thalamus Hypothalamus Figure 3.8Figure 3.8

The Forebrain

Telencephalon – contains most of the cerebrum.

1. Cerebral Cortex – thin, wrinkled layer of tissue covering the brain consisting of sulci (groove), fissures (big groove), and gyri (convolution). Frontal Lobe Parietal Lobe Temporal Lobe Occipital Lobe

Figure 3.8Figure 3.8

Figure 3.16Figure 3.16

The Forebrain

Telencephalon Primary cortices

Visual cortex Auditory cortex Somatosensory cortex Motor cortex

Association cortices Associated with all

primary cortices

Figure 3.16Figure 3.16

Figure 3.15Figure 3.15

Figure 3.16Figure 3.16

Limbic System

2. Limbic System – set of structures involved in learning, memory, and emotion. Major structures of the limbic system include: Limbic Cortex (cingulate!) Hippocampus Amygdala Fornix Mammillary Bodies (part of

the hypothalamus)Figure 3.19Figure 3.19

Basal Ganglia

3. Basal Ganglia – set of structures involved in processing information for motor movement. Major structures of the basal ganglia motor system include: Caudate Nucleus Putamen Globus Pallidus

Figure 3.20Figure 3.20

Forebrain: The Diencephalon

Thalamus and hypothalamus

ThalamusThalamus: Dorsal diencephalon Two lobes connected by

the massa intermedia Many nuclei

LGN MGN Cerebellum->VLN->

motor

Figure 3.8Figure 3.8

Forebrain: The Diencephalon

Figure 3.21Figure 3.21

Hypothalamus Below thalamus Many nuclei Many diverse

behaviours Endocrine- Pituitary

Hypothalamus regulates the autonomic nervous system, controlling the pituitary gland, and integrating species-typical behaviors.

Hypothalamic Portal System

Endocrine system Hormones are secreted from the hypothalamus through the

venous portal system to anterior pituitary

These stimulate hormone release from AP Can control other glands or the hormones are the messengers AP- ‘master gland’

Gonadotropin-releasing hormone causes the anterior pituitary gland to secrete gonadotropic hormones, which play a role in reproductive physiology and behavior

Hypothalamus also releases hormones in the posterior pituitary

oxytocin - stimulates milk ejection and uterine contractions during childbirth Vasopressin - regulates urine output by the kidneys

The Midbrain

Figure 3.8Figure 3.8

Also known as the mesencephalon and is comprised of the tectum and tegmentum.

Tectum (roof) – contains the superior (vision) and inferior (auditory) colliculi (singular is colliculus).

Tegmentum (floor) – contains the periaqueductal gray matter, reticular formation, red nucleus, and substantia nigra all of which share a role in motor movement.

Figure 3.23c and dFigure 3.23c and d

The Hindbrain

The Hindbrain

Contains both the metencephalon and the myelencephalon.

Figure 3.8Figure 3.8

The Hindbrain

Metencephalon – a structure comprised of the cerebellum and the pons.

Cerebellum – appears as a mini brain and is involved in motor coordination.

Pons – contains part of the reticular formation and is involved in sleep and arousal.

Figure 3.23Figure 3.23

The Hindbrain

Myelencephalon – contains the medulla oblongata containing portions of the reticular formation

Is involved in basic life functions, such as respiration and regulation of the cardiovascular system. Figure 3.23Figure 3.23

The Central Nervous System

The Spinal Cord Function: distribute

motor fibers to the effector organs of the body (glands and muscles) and to collect somatosensory information to be passed on to the brain

Protected by the vertebral column Composed of 24

individual vertebrae

Primary Components of the Spinal Cord

Spinal Roots – a bundle of axons surrounded by connective tissue that occur in pairs, which fuse and form a spinal nerve

Dorsal Roots – the spinal roots that contain incoming (afferent) sensory fibers

Ventral Roots - the spinal roots that contain outgoing (efferent) motor fibers

The Peripheral Nervous System

Somatic Nervous System Portion of the PNS comprised of the spinal nerves

and cranial nerves involved in transmitting sensory information and controlling voluntary movement. Spinal Nerves

Peripheral nerves attached to the spinal cord. Cranial Nerves

Set of 12 motor and/or sensory nerves attached to the ventral surface of the brain.

The Autonomic Nervous System Portion of the PNS concerned with the regulation of

smooth muscle, cardiac muscle, and glands

The Autonomic Nervous System Sympathetic Division of the

ANS Nervous system components

involved in arousal and preparing the body for the expenditure of energy.

‘Fight or flight’

Parasympathetic Division of the ANS Nervous system components

involved in relaxing the body, often competing with those of the sympathetic division.

‘rest and digest’