Lecture 7: The Nervous System PDF

LECTURE 5 The Nervous System Neural Tissue Spinal Cord  Nervous System Characteristics – Controls and adjusts the activity of the body – Provides swift but brief responses The nervous system includes: – Central Nervous System (CNS) Brain and the spinal cord – Peripheral Nervou...

LECTURE 5 The Nervous System Neural Tissue Spinal Cord  Nervous System Characteristics – Controls and adjusts the activity of the body – Provides swift but brief responses The nervous system includes: – Central Nervous System (CNS) Brain and the spinal cord – Peripheral Nervous System (PNS) Consist of all the peripheral nerves and the nervous tissue outise of the CNS  CENTRAL NERVOUS SYSTEM Brain Central Nervous System (CNS) Spinal cord – Responsible for integrating, processing, and coordinating sensory input & motor output – the seat of intelligence, memory learning and emotions processes and coordinates the sensor input and motor output Peripheral Nervous System (PNS) PERIPHERAL NERVOUS SYSTEM – Provides sensory information Peripheral nerves to the CNS & carries motor commands away from the CNS Afferent division: brings sensory information to the CNS Efferent division: Carries motor commands to the muscles and glands provides and carries the information to and from the cns Figure 13.1  Overview of the Nervous System CENTRAL NERVOUS SYSTEM Information (brain and spinal cord) processing Sensory information Motor commands afferent division efferent division PERIPHERAL NERVOUS SYSTEM Somatic nervous Autonomic system nervous system skeletal muscle Parasympathetic Sympathetic division division rest and digest flight or fight Special sensory Visceral sensory Somatic receptors receptors sensory Smooth muscle receptors Skeletal Cardiac muscle muscle Glands RECEPTORS EFFECTORS Figure 13.2 Cellular Organization in Neural Tissue Specialized to conduct electrical signals through the body Two cell types: 1. Neurons Responsible for the transfer and the processing of inforamtions in the nervous systems Consist of a soma, axon, and dendrites DAS 2. Neuroglia Supporting cells, protecting the neurons  1. Neuron Structure Terminal Dendrites Cell body Axon boutons Stimulated by Contains the nucleus, Conducts nerve Affect another environmental changes mitochondria, ribosomes, impulse (action neuron or effector or the activities of and other organelles and potential) toward organ (muscle or other cells inclusions synaptic terminals gland) Axon Mitochondrion hillock Nucleus Nucleolus Action protential travels down , like transportation Nissl bodies (clusters of RER and free ribosomes) Dendritic spines Figure 13.4  Nissl Bodies AND AGAIN (chromatophilic substance) Figure 13.10a  A Structural Classification of Neurons Muliple choice type questions Anaxonic Bipolar Pseudouni Multipolar neuron neuron polar neuron neuron Dendrites Dendrites Initial segment Dendrites Axon Dendrite Axon Axon Terminal Axon boutons Terminal Terminal boutons boutons a Anaxonic neurons b Bipolar neurons c Pseudounipolar d Multipolar neurons have more than two have two processes neurons have a single have a single axon and processes, but axons separated by the elongate process with multiple dendrites. cannot be distinguished cell body. the cell body situated from dendrites. to one side. Figure 13.11 Synapses 1. Synapses with another neuron - Site of intercellular Collateral branch communications Axon Neuron Neuron Synapses with Dendrites another neuron 2. Neuromuscular synapses Neuromuscular synapses Terminal arborization M Terminal boutons Skeletal muscle 3. Neuroglandular synapses Neuroglandular synapses Figure 13.10b Gland cells STRUCTURE OF A SYNAPSE the Mitochondrion supply the energy for the terminial button Figure 13.14a MULTIPLE SYNAPSES Text Multiple dendrites that can send to numberous cells Fig. 13- 14  Muliple choice questions NEURONAL ORGANIZATION CIRCUITS Serial Parallel Divergence Convergence processing processing Reverberation a Divergence; a mechanism b Convergence; a c Serial processing; d Parallel processing; e Reverberation; a for spreading stimulation mechanism providing neurons or pools individual neurons or feedback mechanism to multiple neurons or input to a single neuron work in a sequential neuronal pools process that may be excitatory neuronal pools in the CNS from multiple sources manner information simultaneously or inhibitory Parallel key is that the information is simultanously vs the serial s in a squential manner Figure 13.15  2. Neuroglia Functions: Provide the framework for the nueral tissue maintain the intercelluar environment Act as phagocytes ( act as a immune cell) Have the ability to reproduce  Neuroglia Cell Types Neuroglia Cells of the CNS – Astrocytes – Oligodendrocytes – Microglia – Ependymal cells Neuroglia Cells of the PNS – Satellite cells – Schwann cells  Classification of Neuroglia Neuroglia Peripheral Nervous System Central Nervous System Oligodendrocytes Satellite Schwann Ependymal Cells cells Astrocytes Microglia cells Surround neuron cell Surround all axons in Myelinate CNS Maintain blood-brain barrier; Remove cell Line ventricles bodies in ganglia; PNS; responsible for axons; provide provide structural support; debris, wastes, (brain) and central regulate O2, CO2, myelination of structural regulate ion, nutrient, and and pathogens canal (spinal cord); nutrient, and peripheral axons; framework dissolved-gas concentra- by phagocytosis assist in producing, neurotransmitter levels participate in repair tions; absorb and recycle circulating, and around neurons in process after injury insolate the axons neurotransmitters; form scar monitoring ganglia tissue after injury cerebrospinal fluid immune cells of the brain Figure 13.5  Neuroglia Astrocytes Has a large number of cytoplasmic processes Control the chemical content of the interstitial environment Maintainting blood- brain barrier Isolate the neurons from general circulation Scaffolding – structural framework repair damaged neurons Guide neurogenesis Histology of the CENTRAL CANAL CNS Ependymal cells Gray matter Neurons Microglial cell Myelinated axons Internode Myelin Oligodendrocyte (cut) Axolemma Astrocyte Axon White matter Myelin sheath gap Unmyelinated axon Basal lamina Capillary Figure 13.6  Blood Brain Barrier: tight junctions and astrocytes Similar to Fig 5-3 S-K  Neuroglia Oligodentrites similar to astrocytes Smaller cell body Fewer and shorter cytoplasmic processes Wraps axons in myelin ( insulation) White matter = Myelinated axons Grey matter = Neuons bodies, dendrites and unmyelinted axons  MYELINATION CENTRAL CANAL IN THE CNS Ependymal cells Gray matter Neurons Microglial cell Myelinated axons Internode Myelin White (cut) Oligodendrocyte Astrocyte Axon matter Myelin sheath gap Unmyelinated axon Basal lamina Capillary Figure 13.6  Neuroglia of the PNS Satellite cells Regulate the exchange of material between the cell body and the environment Schwann cells Also called neurolemmocytes form a myelin sheath Every peripheral axon, whether myelinated or unmyelinated, is covered by Schwann cells, or neurolemmocytes.  PERIPHERAL AXONS & SCHWANN CELLS Node of Ranvier Fig. 13- 9  Anatomy of a Peripheral Nerve Every = Epineurium ( the outermost layer, surrounds the entire Blood vessels nerve ) neurons end Connective Tissue Layers Epineurium covering peripheral nerve E Perineurium (around one fascicle) Endoneurium Schwann cell Myelinated axon Fascicle a A typical peripheral nerve and its connective tissue wrappings Figure 14.5a  THE SPINAL CORD 1. CONDUCTS NERVE IMPULSES TO & FROM THE BRAIN 2. PROCESSES SOME SENSORY INFORMATION TO ALLOW REFLEX [MOTOR] ACTIONS  Central Nervous System Brain Integrates and processes information Can function with the spinal cord Can function independently of the spinal cord Spinal cord Integrates and processes information Can function with the brain Can function independently of the spinal cord Fig. 13- 1 Gross Anatomy of the Identify what region of the spinal cord C1 Spinal Cord C2 Cervical spinal C3 C4 nerves C5 C6 C7 C8 45 cm in length T1 T2 T3 T4 T5 T6 T7 Passes through the foramen magnum, extends from the brain to the L1 T8 Thoracic spinal T9 nerves T10 T11 Consists of: T12 L1 L2 Cervical region Lumbar spinal L3 L4 nerves Thoracic region L5 Lumbar region Sacral spinal S1 S2 S3 nerves Sacral region S4 S5 Coccygeal Coccygeal region nerve (Co1) a Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The spinal cord, however, extends from the brain only to the level of vertebrae L1–L2. Gross Anatomy of Can be found in the lab C1 C2 Cervical spinal C3 the Spinal Cord C4 nerves C5 C6 Cervical C7 C8 enlargement T1 T2 invert the upper limb T3 T4 T5 T6 T7 T8 Thoracic Posterior median sulcus 31 spinal segments spinal nerves T9 T10 Each segment consists of: T11 T12 Lumbosacral enlargement invates the lower limb Dorsal root L1 Conus medullaris L2 The point where the spine comes into a cone Dorsal root ganglia Lumbar L3 Inferior tip of spinal cord spinal Ventral root nerves L4 L5 Cauda equina Spinal nerve S1 Sacral spinal S2 S3 nerves S4 S5 Coccygeal Filum terminale nerve (Co1) (in coccygeal ligament) Horse tail a Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The spinal cord, however, extends from the brain only to Figure 14.1a the level of vertebrae L1–L2.  Spinal Meninges Specialized membranes that provide protection, physical stability, and shock absorption Continuous with the cranial (cerebral) meninges Detriculate ligaments helps anchor the spinal cord  Spinal Meninges Can be identified Dura Mater – Tough fibrous outermost layer of the meninges Stabilizes the spinal cord within the vertebral canal Arachnoid Mater – Middle meningeal layer Separated from the pia mater by subarachnoid space Cerebrospinal fluid flows within this space Pia Mater – Deepest menigeal layer Blood vessels are found in this layer Firmly bound to the brain tissue and the spinal cord tissue  Spinal Meninges Gray matter White matter Dorsal root ganglion Ventral root Spinal nerve Dorsal root Meninges * Ventral root come Pia mater together to make the spinal nerve Arachnoid mater Dura mater *Subarachnoid space CSF Figure 14.2a  Spinal cord Anterior median fissure Pia mater 3 Denticulate ligaments Arachnoid mater (reflected) 2 Dura mater (reflected) 1 Spinal blood vessel Dorsal root of sixth cervical nerve Ventral root of sixth cervical nerve c Anterior view of spinal cord shows meninges and spinal nerves. For this view, the dura and arachnoid membranes have been cut longitudinally and retracted (pulled aside); notice the blood vessels that run in the subarachnoid © to 2015 thePearson Education, of theInc. space bound outer surface delicate pia mater. Figure 14.2c Sectional Anatomy of the Spinal Cord Gray Matter – Central canal (filled with CSF) – Consists of somas (cell bodies) surrounding the central canal – Consists of glial cells White Matter – Consists of axons – Nerves are organized into tracts or columns – Located outside the gray matter area Features of the Spinal Cord In the lab should identify Dorsal root Posterior median sulcus Dorsal root ganglion White matter Central Gray Transverse view canal matter Spinal White matter nerve Anterior median fissure Ventral C 3 root Gray matter Central canal Anterior median fissure T3 Posterior median sulcus L1 S2 Figure 14.1d Sectional Anatomy of the Spinal Cord Organization of Gray Matter – Somas are organized into groups called: 1. Sensory nuclei 2. Motor nuclei – Transverse view shows: Posterior gray horns Lateral gray horns Anterior gray horns Gray commissure  Sectional Organization of the Spinal Cord Posterior median sulcus Posterior From dorsal root gray horn Posterior gray commissure Somatic Sensory Visceral nuclei Lateral some very smart people gray horn Visceral Motor Anterior nuclei gray horn Somatic To ventral Anterior gray root very smart more commissure Anterior median fissure b The left half of this sectional view shows important anatomical landmarks; the right half indicates the functional organization of the gray matter in the anterior, lateral, and posterior gray horns. Figure 14.4b Sectional Anatomy of the Spinal Cord Organization of White Matter – Consists of columns of nerves ( Funiculi) – Posterior white column – Anterior white column – Lateral white column – Columns convey either: Sensory tracts (ascending tracts) Motor tracts (descending tracts)  Posterior white Leg column (funiculus) Hip AFFERENT Trunk [SENSORY] Arm Lateral white column (funiculus) Flexors Extensors Hand Forearm Arm Shoulder EFFERENT Trunk [MOTOR] Anterior white Anterior white column (funiculus) commissure c PERIPHERAL DISTRIBUTION OF SPINAL NERVES Fig. 14- 6 Motor Commands Postganglionic fibers To skeletal to smooth muscles, muscles of back glands, etc., of back Dorsal Visceral Somatic Dorsal root root motor motor ganglion Dorsal ramus Ventral ramus To skeletal muscles of body wall, limbs Ventral root Postganglionic fibers to smooth muscles, glands, etc., of body wall, limbs Spinal nerve White ramus Sympathetic ganglion (preganglionic) Rami communicantes Gray ramus Postganglionic fibers (postganglionic) to smooth muscles, glands, visceral organs Sympathetic nerve in thoracic cavity KEY Somatic motor Preganglionic fibers to commands sympathetic ganglia innervating aboomino- Visceral motor pelvic viscera commands Figure 14.6 Sensory Information From interoceptors From exteroceptors, of back proprioceptors of back Dorsal Somatic Visceral root sensory sensory Dorsal ramus Ventral ramus From exteroceptors, proprioceptors of body wall, limbs Dorsal root ganglion From interoceptors of body wall, limbs Rami communicantes Ventral KEY root Somatic sensations Visceral From interoceptors sensations of visceral organs Figure 14.6b  Occipital bone Spinal Nerves Spinal cord emerging from foramen magnum Cervical plexus (C1–C5) Cervical 31 pairs of spinal nerves: spinal nerves (C1–C8) Brachial plexus – 8 cervical nerves (C5–T1) – 12 thoracic Thoracic – 5 lumbar spinal nerves (T1–T12) 1 – 5 sacral – Lumbar plexus Lumbar (T12–L4) spinal nerves (L1–L5) Sacral plexus Sciatic (L4–S4) nerve Sacral spinal nerves (S1–S5) Coccygeal nerves emerging from © 2015 Pearson Education, Inc. (Co1) sacral foramina  Reflexes Reflex – Immediate involuntary motor response Reflex Arc – The neural “wiring” of a single reflex – begins at a s sensory recceptor and ends at a peripheral receptor  Reflexes Pathway of a Reflex Arc 1. Activation of a sensory receptor 2. Relay of information to the CNS 3. Information processing 4. activation of a motor neuron 5. response by effectors sensory receptors—> information relay ——> information processing —> activation motor neuron ——> effectors  A Reflex Arc 1 Arrival of 2 Activation of a Dorsal Sensation stimulus and sensory neuron root relayed to activation the brain by of receptor collateral REFLEX ARC Receptor Stimulus Effector Ventral 3 Information processing root in CNS 4 Activation of a 5 Response motor neuron by effector KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron Figure 14.13 (stimulated)  Reflexes Spinal Reflexes – Stretch reflex 1. Stimulus stretches a muscle 2. Activates a sensory neuron 3. information is proceesed in the spinal cord 4. Motor neurons are activated 5. Muscle (effector) contracts streches a muscle —> sensory neurons —> s.p. processed information —> muscles contracts 1 Stimulus. Stretching of muscle stimulates muscle 2 Activation of a spindles sensory neuron 3 Information processing at motor neuron 4 Activation of motor neuron 5 Response. Contraction of muscle a Steps 1–5 are common to all stretch reflexes. Figure 14.16a  Stretch Receptor (muscle spindle) Stimulus Spinal cord REFLEX ARC KEY Effector Sensory neuron (stimulated) Motor neuron Contraction (stimulated) b The patellar reflex is controlled by muscle spindles in the quadriceps muscle group. The stimulus is a Response reflex hammer striking the muscle tendon, stretching the spindle fibers. This results in a sudden increase in the activity of the sensory neurons, which synapse on spinal motor neurons. The response occurs upon the activation of motor units in the quadriceps group, which produces an immediate increase in muscle Figure 14.16b tone and a reflexive kick. The end