1. Organization of the nervous systemBy
Dr. Mohammed Ahamed Abuelnor

2. Objectives: At the end of the lecture, student should be able to:
List the divisions of the nervous system.
Define the terms: receptors, effectors, grey matter, white matter, nucleus, ganglion, tract, nerve.
Describe the development and derivatives of the neural tube.
List the structures protecting the brain
6/25/2019

3. The Nervous system has three major functions:
What are the functions of the nervous system?
Sensory functions – monitors internal & external environment through presence of receptors
Integration functions – interpretation of sensory information (information processing);
Motor functions – response to information processed through stimulation of effectors
muscle contraction
glandular secretion

4. General Organization of the nervous system
What are the two subsystems of the nervous system?
Two Anatomical Divisions
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
All the neural tissue outside CNS
(sensory input)
(motor output)
Somatic nervous system
Autonomic nervous system

5. General Organization of the nervous system
Brain & spinal cord

6. Neural Tissue Organization
What is the gray matter and what is the white matter?

7. The Brain
What are the major divisions of the brain?
It is one of the largest organs in the body, and coordinates most body activities.
It is the center for all thought, memory, judgment, and emotion.
There are 3 parts of the brain: forebrain, midbrain, hind brain.

8. Forebrain part 1: Telencephalon
Includes all of the cerebrum and the internal nuclei such as:
The basal ganglia, hippocampus
The olfactory bulb
The amygdala
The structures of the CNS can be group into the following divisions: telencephalon, diencephalon, mesancephalon, etc… in various anatomy texts such as Gray’s or Netter’s.
Our focus for the present is to provide a quick introduce or overview of the organization of the nervous system and its components. Over the next few weeks, we’ll examine the functions and roles of each in more detail.
Limbic system: hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix,

9. Cerebral Cortex Outermost layer of the cerebrum
Composed of 2- 4mm of gray matter
Up to 6 horizontal layers with unique neuronal projections

10. Basal Ganglia Functions
Motor control; connections with motor cortex and thalamus

11. Forebrain part 2: Diencephalon
includes the thalamus and hypothalamus
Telencephalon + diencephalon = forebrain
Thalamus functions
Main integrating centre for sensory information
Receives input from basal ganglia and cerebellum
Hypothalamus functions
Main control centre for the autonomic nervous system
Thalamus
main integrating centre for sensory information that is relayed to the cerebral cortex
receives input from the basal ganglia and the cerebellum
also important for movement control, control of arousal, and certain aspects of memory
Hypothalamus
regulates the functions of the autonomic nervous system (main control centre for ANS)
has a close connection with the pituitary gland and has important functions within the endocrine system as we’ll learn later in the semester
has nuclei that are specialized for a variety of functions, including our circadian clock, hunger, thirst, cardiovascular system, and temperature regulation
Posterior portion of the pituitary gland also part of diencephalon
Pineal gland part of epithalamus (part of diencephalon) secretes melatonin

12. Midbrain: Mesencephalon
Two divisions:
a) tectum
superior colliculi
contain nuclei for visual center
inferior colliculi
contain nuclei for auditory center
b) tegmentum

13. Hinbrain: Myelencephalon
Two divisions:
a) myelencephalon
medulla oblongata
Contains ascending and descending sensory and motor tracts connecting the cerebrum to the spinal cord
contains important control centers for ANS
The reticular formation is a set of interconnected nuclei that are located throughout the brain stem. Its dorsal tegmental nuclei are in the midbrain while its central tegmental nuclei are in the pons and its central and inferior nuclei are found in the medulla.
(from
The reticular formation has diffuse connections with the cortex and other brain regions. It’s main role is releated to level of consciousness and arousal (e.g. sleep, waking, etc…)

14. Hinbrain: Metencephalon
b) metencephalon
pons
connect information between cerebellum and cerebrum
cerebellum
Controls posture and balance
Pons also has the primary micturation center for control of urination
The reticular formation is a set of interconnected nuclei that are located throughout the brain stem. Its dorsal tegmental nuclei are in the midbrain while its central tegmental nuclei are in the pons and its central and inferior nuclei are found in the medulla.
(from
The reticular formation has diffuse connections with the cortex and other brain regions. It’s main role is releated to level of consciousness and arousal (e.g. sleep, waking, etc…)
The pons contains somatic motor neurons that control various functions including:
mastication (chewing) = cranial nerve (CN) V (trigeminal nerve)
eye movement = CN VI (abducens nerve)
facial muscle = CN VII (facial nerve)
It receives sensory information from the face, scalp, mouth, and nose.
It processes information related to hearing and equilibrium.
It also has important connections with the cerebral cortex and the cerebellum, which are crucial for the coordination of movement.
The cerebellum lies immediately dorsal to the brainstem. It receives a very large number of inputs (ration of afferents to efferents is 40:1!)
NOTE: DO NOT CONFUSE WITH THE CEREBRUM! cerebellar ≠ cerebral
Three divisions:
vestibulocerebellum: control of balance
spinocerebellum: control of posture, muscle tone
cerebrocerebellum: coordination of motor behaviour
Much more on this later!
*the term “brainstem” refers to the medulla oblongata, pons, and the midbrain

15. Derivatives of the neural tube.
Regions named as they develop in the embryo
Embryonic development naming according to forebrain, midbrain, hindbrain, mesencephalon etc. these are called brain vesicles adult derivatives of this neural tissue are as follows
Regional specialization begins to appear around the 4th gestational week,

16. Spinal cord
Functions
Conducts afferent stimuli from sensory receptors to the brain
Conducts efferent stimuli from brain to effectors/muscles
Site of reflex
Continuous with the medulla in the brain stem down to the space between first and second lumbar vertebrae.
On transverse section of the spinal cord, you can see gray matter forming an H shape in the middle, with white matter surrounding it. What is gray matter/white matter?
In the central nervous system (CNS), central pattern
generators (CPGs) are generally considered as specialized
networks that can produce oscillatory motor output
in the absence of any oscillatory input. Micturation, locomotion, ejaculation, scratching

17. CNS Protection Against physical damage Against chemical damage Both
Skull/vertebrae
-hard external protection
Blood brain barrier
- Tight junctions form physical barrier across capillaries
Cerebrospinal fluid
Shock absorption
Stable ionic composition
Meninges
Pia mater (innermost layer)
Arachnoid mater
Dura mater
Protection of central nervous system\ vertebrae
The meninges are three layers of connective tissue membranes that surround the central nervous system.
Outer layer = dura mater
thick durable layer that is closest to the skull
contains large blood vessels
separated from the middle layer by a slight space that is filled with cerebrospinal fluid
Middle layer = arachnoid
has a cob-web like appearance caused by trabeculae that criss-cross throughout
the trabeculae was extensions that are continuous with the inner layer, the pia mater
Inner layer = pia mater
very delicate and highly vascularized
adheres very closely to the surface of the neural tissue of the brain and central nervous system

18. Peripheral Nervous System
What are the components of the peripheral nervous system?
all parts of nervous system outside the CNS
includes sensory receptors, spinal and cranial nerves and ganglia
ganglia are aggregates of nerve cells located outside the CNS
Autonomic
Somatic
Parasympathetic
Sympathetic
Sensory
Motor
Rest and digest
Flight or fight
Afferent neurons carrying information from sensory receptors to the CNS
Efferent neurons carrying information from the CNS to muscles
Somatic

19. Classification of neurons
Functional classification based on type of information & direction of information transmission:
Sensory (afferent) neurons –
transmit sensory information from receptors of PNS towards the CNS
Motor (efferent) neurons –
transmit motor information from the CNS to effectors (muscles/glands/adipose tissue) in the periphery of the body
Association (interneurons) –
transmit information between neurons within the CNS; analyze inputs, coordinate outputs

20. How do the neural pathways of the autonomic nervous system differ from the somatic nervous system?
How does the somatic nervous system differ from the autonomic nervous system?

21. References: Gray's Anatomy for Students- Second edition.
Clinically Oriented Anatomy , Keith L. Moore- Sixth edition.
Netter’s Clinical Anatomy, Second edition.