Organization of the nervous system By Dr. Mohammed Ahamed Abuelnor

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

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

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

General Organization of the nervous system Brain & spinal cord

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

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.

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,

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

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

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

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

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 http://www.csuchico.edu/~pmccaff/syllabi/CMSD%20320/362unit6.html) 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…)

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 http://www.csuchico.edu/~pmccaff/syllabi/CMSD%20320/362unit6.html) 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

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,

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

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

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

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

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?

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