Anatomy of the Nervous System PDF

Digitally signed by Dr Adel Bondok DN: cn=Dr Adel Bondok gn=Dr Adel Bondok c=Egypt l=EG o=Mansoura University ou=Faculty of Medicine Dr Adel Bondok [email protected]...

Digitally signed by Dr Adel Bondok DN: cn=Dr Adel Bondok gn=Dr Adel Bondok c=Egypt l=EG o=Mansoura University ou=Faculty of Medicine Dr Adel Bondok [email protected] Reason: I am the author of this document Location: Date: 2024-10-03 21:38+03:00 Dr Adel Bondok Introduction to the Nervous System https://www.youtube.com/channel/UCIABxoKdY8Q938SqD8c0qMQ?view_as=subscriber NERVOUS SYSTEM STRUCTURE OF THE NERVOUS SYSTEM The nervous system is formed of 2 types of cells and their processes: 1. Nerve cells: called neurons. They communicate together by synapses. 2. Supporting cells: called glial cells or neuroglial cells or neuroglia. NERVE CELLS (NEURONS) The nerve cell is the structural and functional unit of the nervous system. Aggregations of nerve cells may form: a. Nucleus: collection of nerve cells inside the central nervous system. b. Ganglion: collection of nerve cells outside the central nervous system. Cytology: nerve cell is formed of cell body and processes 1. Cell body (soma): nucleus and cytoplasm ❑ The nucleus is usually central in position and contains nucleolus. ❑ The cytoplasm contains organelles & inclusions. ❑ The organelles include: mitochondria, rough endoplasmic reticulum (Nissl bodies), lysosomes, Golgi apparatus, neurofilaments and neurotubules. ❑ The inclusions include: lipofuscin pigment and melanin pigment. 2. Processes: single axon and dendrites. A. Single Axon: the largest process of the nerve cell ❑ It transmits information to other nerve cells. ❑ Axons may be myelinated (faster); or unmyelinated. ❑ Importance of the myelin: insulation and impulse conduction (the thicker the myelin the faster the conduction). B. Dendrites: ❑ They are the short and highly branched processes. ❑ They receive impulses from other neurons. Myelin Producing Cells: 1. In the CNS: oligodendrocytes. 2. In the peripheral nervous system: Schwann cells. |Page1 Dr Adel Bondok Introduction to the Nervous System Classification of Nerve Cells: Nerve cells are classified according to size, function and the number of their processes A. According to Size: 1. Golgi type I: large nerve cells with long axon. 2. Golgi type II: small nerve cells with short axon. B. According to Function: 1. Motor: for movement. 2. Sensory: for perception of sensation. 3. Interneurons: connect nerve cells together. C. According to the Number of Processes: 3 types: 1. Unipolar Neurons: have one process: a. True unipolar neurons: such as amacrine cells of the retina. b. Pseudounipolar neurons: such as the dorsal root ganglia (spinal ganglia). 2. Bipolar Neurons: have 2 processes, one axon and one dendrite. They are present in the sense organs (retina, nose and inner ear). 3. Multipolar Neurons: they have one axon and several dendrites. They form most of the nerve cells in the nervous system (such as anterior horn cells of the spinal cord). Supporting (Neuroglial) Cells A. Central Neuroglia: in the CNS: 1. Astrocytes: support and transport of metabolites to the nerve cells. 2. Oligodendrocytes: formation of the myelin in the CNS. 3. Microglia: for defense against infection. 4. Ependymal cells: lining the ventricles of the brain. B. Peripheral Neuroglia: in the peripheral nervous system: 1. Schwann cells: for formation of the myelin sheath in the peripheral nerves. 2. Satellite cells: surround the nerve cells. Ependymal cells |Page2 Dr Adel Bondok Introduction to the Nervous System SYNAPSES Definition: contact point between 2 nerve cells Types: 1. Chemical Synapse: transmission occurs by chemical substance called neurotransmitter. 2. Electrical synapse: transmission occurs without chemical substance Structure of the chemical synapse: formed of 3 parts: 1. Presynaptic element: axon terminal contains synaptic vesicles and mitochondria. 2. Synaptic cleft: 20-nm space. 3. Postsynaptic element: usually dendrite. Forms of synapses: 1. Axodendritic synapse: between axon and dendrite. 2. Axoaxonic synapse: between axon and axon. 3. Axosomatic synapse: between axon and cell body. 4. Neuromuscular junction (motor end-plate): between axon and muscle fiber. Divisions Of The Nervous System The nervous system is divided into 3 major divisions: 1. Central Nervous System (CNS): brain and spinal cord. 2. Peripheral Somatic Nervous System (PNS): formed of: a. Cranial nerves: 12 pairs, from the brain. b. Spinal nerves: 31 pairs, from the spinal cord. c. Associated ganglia: spinal & cranial ganglia. 3. Peripheral Autonomic Nervous System (ANS): a. Sympathetic part: thoracolumbar part. b. Parasympathetic part: craniosacral part. |Page3 Dr Adel Bondok Introduction to the Nervous System CENTRAL NERVOUS SYSTEM BRAIN Divisions of the Brain: the brain is divided into 3 parts: 1. Forebrain: formed of: a. Two cerebral hemispheres: contain higher motor and sensory centers. b. Diencephalon: formed mainly of the thalamus and hypothalamus: ❑ Thalamus: sensory relay station. ❑ Hypothalamus: the principal autonomic and endocrine center. 2. Midbrain. 3. Hindbrain: formed of the pons, medulla oblongata and cerebellum. Another Division of the Brain: the brain is divided into 3 parts: 1. Cerebrum: formed of the forebrain: c. Two cerebral hemispheres d. Diencephalon 2. Cerebellum: for coordination of muscles and maintaining equilibrium. 3. Brain stem: formed of 3 parts: a. Midbrain: upper part b. Pons: middle part. c. Medulla oblongata: lower part. Ventricles of the Brain: The ventricles are cavities inside the brain. They are filled with cerebrospinal fluid (CSF) 1. Lateral ventricle: in the cerebral hemisphere. 2. Third ventricle: in the diencephalon. 3. Fourth ventricle: in the hindbrain. |Page4 Dr Adel Bondok Introduction to the Nervous System PERIPHERAL SOMATIC NERVOUS SYSTEM 1. Spinal Nerves Distribution: 31 pairs are distributed as follows: ❑ 8 cervical nerves: in the cervical region. ❑ 12 thoracic nerves in the thoracic region. ❑ 5 lumbar nerves in the lumbar region. ❑ 5 sacral nerves in the sacral region. ❑ 1 coccygeal nerve in the coccygeal region. Formation: ❑ Each spinal nerve is formed by 2 roots: 1. Ventral Root: motor: It contains axons of the anterior horn cells to supply the skeletal muscles. 2. Dorsal Root: sensory a. It is formed of the processes of the pseudounipolar cells of the spinal ganglion. b. The spinal ganglion is attached to it; therefore, it is called dorsal root ganglion. ❑ The 2 roots unite to form the trunk of the spinal nerve. Branches (Divisions): The spinal nerve trunk immediately divides into 2 rami: 1. Anterior (Ventral) Ramus: runs anteriorly and may join each other to form plexuses 2. Posterior (Dorsal) Ramus: runs backward to supply the muscles and skin of the back 1. Lesion in the dorsal root causes sensory loss. 2. Lesion in the ventral root causes motor paralysis. 3. Lesion in the spinal nerve causes sensory loss and motor paralysis. |Page5 Dr Adel Bondok Introduction to the Nervous System 2. CRANIAL NERVES ❑ Consist of 12 pairs (I to XII), which are connected with the brain. ❑ All of the cranial nerves arise from the brainstem except the first (I, olfactory), which arises from the nose and the second (II, optic), which arises from the retina of the eye. AUTONOMIC NERVOUS SYSTEM Divisions: the autonomic nervous system is divided into: 1. Sympathetic system: thoracolumbar outflow. 2. Parasympathetic system: craniosacral outflow. 1. SYMPATHETIC SYSTEM Origin: thoracolumbar outflow ❑ From the lateral horn cells of the spinal cord segments from T1 to L2 or L3. 2. PARASYMPATHETIC SYSTEM Origin: craniosacral outflow 1. Cranial Outflow: from the brainstem through the III, VII, IX and X cranial nerves. 2. Sacral Outflow: from the spinal cord segments S2, 3, 4. |Page6 Dr Adel Bondok Introduction to the Nervous System Function of the Autonomic Nervous System See the Physiology Lectures Sympathetic System Parasympathetic System Inhibitory to everything except the heart Excitatory to everything except the heart Decrease peristalsis (movement) of the gut Increase peristalsis of the gut Contraction of the sphincters Relaxation of the sphincters Acceleration of the heart Inhibition of the heart |Page7