The functional Anatomy of the Nervous System DR. OKSANA PETRICHKO Department of Human Anatomy
Coordination and Regulation of Body Systems Nervous system. Conducts nerve impulses maintaining homeostasis (electrochemical). Endocrine system. Serves as messaging system maintaining homeostasis (chemical).
Nervous & Endocrine Systems
Main Functions of the Nervous System Connect the organism to the environments Coordinate with all processes of the body Adapt organism to the environments Specific features of the human nervous system distinguish man from the animals (social life and speech)
Divisions of the NS CNS Central Nervous System Brain & spinal cord PNS Peripheral Nervous System Cranial nerves (12 pairs) Spinal nerves (31 pairs) Nervous plexus Nerves
Divisions of the NS Somatic Nervous System Visceral (Autonomic) Nervous System Sympathetic Parasympathetic
Somatic Nervous System Somatic Sensitive General somatic sense (touch, pain, pressure, vibration) Proprioceptive sense (skin, body wall, limbsmuscles & joints) Special somatic senses (hearing, equilibrium, vision, smell) Somatic Motor Skeletal muscle
Visceral (Autonomic) Nervous System Visceral sense General visceral: stretch, pain, temperature, chemical changes, irritation in viscera, nausea, hunger Special visceral: taste Visceral motor (ANS) Smooth muscle Cardiac muscle Glands
Nervous tissue Neurons unipolar neuron pseudounipolar neuron bipolar neuron multipolar neuron Supporting cells (neuroglia)
Neuron - - The functional and structural unit of the nervous system Specialized to conduct information from one part of the body to another Cell body (soma) One or more specialized, slender processes (axons/dendrites) An input region (dendrites/soma) A conducting component (axon) A secretory (output) region (axon terminal)
Dendrites Usually numerous Branched Sends signals to soma The ends of the dendrites form receptors
Axons 1 per soma Initial segment from axon hillock Transmits AP away from soma No Nissl bodies (no protein synthesis) Neurofilaments Axonal transport Axon collaterals Terminal branches Axon terminals
Neuron
1. unipolar neuron bipolar neuron 3. pseudounipolar neuron neuron a. axon 2. 4. multipolar d. dendrite
Neuron classification by shape
CNS Neuroglia Outnumber neurons by about 10 to 1 (the guy on the right had an inordinate amount of them). 6 types of supporting cells 1. 4 are found in the CNS: Astrocytes Star-shaped, abundant, and versatile Guide the migration of developing neurons Act as K+ and NT buffers Involved in the formation of the blood brain barrier Function in nutrient transfer
CNS Neuroglia 2. Microglia 3. Specialized immune cells that act as the macrophages of the CNS Ependymal Cells Low columnar epithelial-esque cells that line the ventricles of the brain and the central canal of the spinal cord Some are ciliated which facilitates the movement of cerebrospinal fluid
CNS Neuroglia 4. Oligodendrocytes Produce the myelin sheath which provides the electrical insulation for certain neurons in the CNS
PNS Neuroglia 2 types of glia in the PNS 1. Satellite cells Surround clusters of neuronal cell bodies in the PNS Unknown function 2. Schwann cells Form myelin sheaths around the larger nerve fibers in the PNS. Vital to neuronal regeneration
Myelin sheaths Wrapping of PM around axon Phospholipid bilayers form insulation Gaps between Schwann cells are nodes of Ranvier Allow faster propagation of AP Saltatory conduction
Nerve Bundle of axons in the PNS Endoneurium around each axon Loose CT Perineurium CT around a bundle of axons Epineurium CT around a nerve
Interneurons / association neurons Located in CNS >99% of all neurons ~ all multipolar Integration of information
SYNAPSE SYNAPSE Ÿ Presynaptic Portion: Synaptic Button - synaptic vesicle - mitochondria - presynaptic membrane: tubulin Ÿ Synaptic Cleft - 20-30 nm Ÿ Postsynaptic Portion - postsynaptic membrane: actin, fodrin, spectrin - mitochondria
SYNAPSE SYNAPSE
SYNAPSE
Synapses Presynaptic neuron Postsynaptic neuron
Synapses Axodendritic synapses Axosomatic synapses Axoaxonic synapses
Synapse structure Presynaptic element Axon terminal Synaptic vesicles Neurotransmitters Mitochondria Synaptic cleft Postsynaptic elements NT receptors May generate AP
Reflex arcs Reflex = rapid motor response to a stimulus Unlearned Unpremeditated Involuntary Can involve all muscle types and/or glands
Knee-jerk stretch reflex Monosynaptic reflex arc Tap patellar tendon Stretch quadriceps femoris Stimulate stretch receptor AP to motor neuron Contract quadriceps femoris Knee extends 12.18a
Withdrawal reflex Polysynaptic
2 Main Paths Convergence and Divergence
Saltatory Conduction Appear the jump from node to node. Speed of impulses is much faster on myelinated nerves then unmyelinated ones. Speed also increases with increase in diameter. Ex.) 120m/s skeletal muscle.5m/s skin
Neuron Communication
Developmental Aspects
Development
Structure of the Spinal Cord
Meninges of the Spinal Cord
A Reflex Arc
Spinal Cord Reflex
Simple Nerve Path
The Spinal Cord The spinal cord extends from the foramen magnum to the level of the 1st or 2nd lumbar vertebrae It is enclosed within the vertebral column
The Spinal Cord The spinal cord is a provides a two way conduction pathway to and from the brain It is a major reflex center
The Spinal Cord The spinal cord is protected by bone, cerebrospinal fluid, and meninges Dura mater, arachnoid, pia mater
The Spinal Cord Between the bony vertebrae and the dural sheath is a large epidural space filled with a soft padding of fat and a network of veins Cerebrospinal fluid fills the subarachnoid space
The Spinal Cord Inferiorly, the dural and subarachnoid membranes extend to the level of S2 while the spinal cord ends at L1 Subarachnoid space beyond L1 is an ideal site for a spinal tap
The Spinal Cord The spinal cord terminates in a tapering cone shaped structure called the conus medullaris
The Spinal Cord A fiberous extension of the pia mater, the filum terminale extends inferiorly from the conus medullaris to attach to the posterior surface of the coccyx
The Spinal Cord There are 31 pairs of spinal nerves that arise from the cord by paired roots and exit from the vertebral column via the intervertebral formina Each segment of the spinal cord is defined by a pair of spinal nerves that lie just superior to their corresponding vertebra
The Spinal Cord The spinal cord has obvious enlargements where the nerves serving the upper and lower limb arise Cervical enlargement Lumbar enlargement
Cross Section of Spinal Cord The spinal cord has two grooves that mark its surface Anterior median fissure / Posterior medial sulcus
Gray Matter and Spinal Roots These grooves run the length of the cord and partially divide it into right and left halves Gray matter inside, the white matter outside
Gray Matter and Spinal Roots The gray matter consists of a mixture of neuron cell bodies, their unmyelinated processes, and neuroglia (support cells)
Gray Matter and Spinal Roots The white matter is composed of myelinated and unmyelinated nerve fibers that represent ascending, descending and transverse pathways
Gray Matter and Spinal Roots The gray matter consists of mirror-image lateral gray masses connected by a cross-bar of gray matter called the gray commissure that encloses the central canal
Gray Matter and Spinal Roots The two posterior projections of gray matter are the posterior (dorsal) horns; the anterior pair are the anterior (ventral) horns with lateral horns in the lumbar and thoracic portions of the cord
Gray Matter and Spinal Roots The anterior horns house nerve cell bodies of the somatic motor neurons These send their axons out via ventral roots of the spinal cord to the skeletal muscles
Sectional Anatomy of the Spinal Cord
Gray Matter and Spinal Roots The amount of ventral gray matter present at a given level of the spinal cord reflects the amount of skeletal muscle innervated at that particular level Thus, the anterior horns are the largest in the areas where the innervation for limbs is present Cervical enlargement / arms Lumbar enlargement / legs
Meninges and Ventricles of the Brain
Nerve Plexuses Plexus = braid Nerves supplying the limbs form plexuses when they leave the spinal cord Cervical Brachial Lumbosacral Lumbar Sacral
Nerve Plexuses
Cervical Plexus Formed by spinal nerves C1 C5 Nerves innervate the neck and shoulder region Phrenic nerve to the diaphragm
Cervical Plexus
Brachial Plexus Formed T1 by spinal nerves C5 C8 and Nerves innervate the arm and shoulder Radial nerve Ulnar nerve Median nerve (between radial & ulnar nerve)
Brachial Plexus Human Anatomy, 3rd edition Prentice Hall, 2001
Brachial Plexus Human Anatomy, 3rd edition Prentice Hall, 2001
Lumbar Plexus Formed L4. by spinal nerves T12 and L1 Innervates the medial and anterior portions of the thigh and lower abdominal regions Lateral femoral cutaneous nerve
Lumbar Plexus Human Anatomy, 3rd edition Prentice Hall, 2001
Lumbosacral Plexus Human Anatomy, 3rd edition Prentice Hall, 2001
Sacral Plexus Formed by spinal nerves L4 and L5, and S1 and S2 Innervates the posterior portion of the hip, thigh, and leg, and the genital region Sciatic nerve
Sacral Plexus
Sacral Plexus