Structure and Function of the Neurologic System Chapter

Structure and Function of the Neurologic System Chapter 14 1

Overview of the Nervous System o Central nervous system (CNS) n o Brain and spinal cord Peripheral nervous system (PNS) n n n Cranial nerves Spinal nerves Pathways o o Afferent (ascending) Efferent (descending) 2 Mosby items and derived items © 2006 by Mosby, Inc.

Overview of the Nervous System o Peripheral nervous system (PNS) n Somatic nervous system o n Motor and sensory pathways regulating voluntary motor control of skeletal muscle Autonomic nervous system o Motor and sensory pathways regulating the body’s internal environment through involuntary control of organ systems n n Sympathetic Parasympathetic 3 Mosby items and derived items © 2006 by Mosby, Inc.

Cells of the Nervous System o Neuron n n Variable size and structure throughout the nervous system Cellular constituents o n Microtubules, neurofibrils, Nissl substances, and ribosomes Some neurons like olfactory neurons continue to divide 4 Mosby items and derived items © 2006 by Mosby, Inc.

Neuron o Three components n Cell body (soma) o o o n Located mainly in the CNS Densely packed cell bodies in the CNS are nuclei Densely packed cell bodies in the PNS are ganglia Dendrites o Receptive portion of the neuron 5 Mosby items and derived items © 2006 by Mosby, Inc.

Neuron o Axons n n Carry nerve impulses away from the cell body Axon Hillock o n Cone-shaped, Nissl-free area, where the axon leaves the cell body Initial segment of the axon o Area of the axon having the lowest threshold for stimulation, so the action potentials begin at this point 6 Mosby items and derived items © 2006 by Mosby, Inc.

Neuron o Axons n Myelin o o o n Endoneurium o n Segmented layer of lipid material Insulating substance Formed and maintained by the Schwann cell Delicate layer of connective tissue around each axon Neurilemma o Thin membrane between the myelin sheath and the endoneurium 7 Mosby items and derived items © 2006 by Mosby, Inc.

Neuron o Axons n Nodes of Ranvier o n Saltatory conduction o n The flow of ions between segments of myelin rather than along the entire length of the axon Divergence o n Regular interruptions of the myelin sheath Ability of branching axons to influence many neurons Convergence o Branches of numerous neurons converging on one or a few neurons 8 Mosby items and derived items © 2006 by Mosby, Inc.

Structural Classification of Neurons o Based on the number of processes extending from the cell body n n Unipolar Pseudounipolar Bipolar Multipolar 9 Mosby items and derived items © 2006 by Mosby, Inc.

Functional Classification of Neurons o Sensory n o Associational n o Transmit impulses from sensory receptors to the CNS Transmit impulses from neuron to neuron Motor n Transmit impulses from the CNS to an effector organ 10 Mosby items and derived items © 2006 by Mosby, Inc.

Neuroglia 11 Mosby items and derived items © 2006 by Mosby, Inc.

Neuroglia o o “Nerve glue” Support the neurons of the CNS n n Astrocytes Oligodendroglia (oligodendrocytes) Microglia Ependymal cells 12 Mosby items and derived items © 2006 by Mosby, Inc.

Neuroglia 13 Mosby items and derived items © 2006 by Mosby, Inc.

Nerve Injury and Regeneration o Wallerian degeneration n Occurs distal to the cut o o Swelling appears Neurofilaments hypertrophy Myelin sheath shrinks and disintegrates Axon portion degenerates and disappears 14 Mosby items and derived items © 2006 by Mosby, Inc.

Nerve Injury and Regeneration o Proximal to the cut n n Swelling and dispersal of the Nissl substance Cell increases in metabolic activity, protein synthesis, and mitochondrial activity New terminal sprouts project from the proximal segment Process limited to myelinated axons o n Generally only in the PNS Depends on location, type of injury, the inflammatory response, and scar tissue formation 15 Mosby items and derived items © 2006 by Mosby, Inc.

Neuroglia 16 Mosby items and derived items © 2006 by Mosby, Inc.

Nerve Impulse o Neurons generate and conduct electrical and chemical impulses by selectively changing the electrical portion of their plasma membranes and influencing other nearby neurons by the release of neurotransmitters 17 Mosby items and derived items © 2006 by Mosby, Inc.

Synapses o o o Region between adjacent neurons is called a synapse Impulses are transmitted across the synapse by chemical and electrical conduction Presynaptic neurons and postsynaptic neurons n Connections between pre- and postsynaptic neurons o o Axoaxonic Axosomatic Axodendritic Dendrodentritic 18 Mosby items and derived items © 2006 by Mosby, Inc.

Synapses 19 Mosby items and derived items © 2006 by Mosby, Inc.

Synapses o Neurotransmitters n n n o o o >30 substances Excitatory (excitatory postsynaptic potential) Inhibitory (inhibitory postsynaptic potential) Synaptic boutons Synaptic cleft Summation n n Temporal summation Spatial summation 20 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Forebrain n o Midbrain n o Cerebral hemispheres Corpora quadrigemina, tegmentum, and cerebral peduncles Hindbrain n Cerebellum, pons, and medulla 21 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Reticular formation n n Network of connected nuclei that regulate viral reflexes, such as cardiovascular and respiratory function Together with the cerebral cortex is referred to as the reticular activating system 22 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System 23 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Forebrain n Telencephalon o Cerebrum n n o Gyri, sulci, and fissures Gray matter and white matter Cerebral nuclei (basal ganglia) 24 Mosby items and derived items © 2006 by Mosby, Inc.

Forebrain 25 Mosby items and derived items © 2006 by Mosby, Inc.

Forebrain 26 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Diencephalon n n Epithalamus Thalamus Hypothalamus Subthalamus 27 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Midbrain n Corpora quadrigemina (tectum) o n Tegmentum o n Superior and inferior colliculi Red nucleus and substantia nigra Basis pedunculi 28 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System o Hindbrain (metencephalon) n n o Cerebellum Pons Myelencephalon n Medulla oblongata 29 Mosby items and derived items © 2006 by Mosby, Inc.

Central Nervous System 30 Mosby items and derived items © 2006 by Mosby, Inc.

Spinal Cord o Lies within the vertebral canal and is protected by the vertebral column n n Connects the brain and the body Conducts somatic and autonomic reflexes Provides motor pattern control centers Modulates sensory and motor function 31 Mosby items and derived items © 2006 by Mosby, Inc.

Spinal Cord 32 Mosby items and derived items © 2006 by Mosby, Inc.

Spinal Cord 33 Mosby items and derived items © 2006 by Mosby, Inc.

Spinal Cord 34 Mosby items and derived items © 2006 by Mosby, Inc.

Reflex Arc o o Receptor Afferent (sensory) neuron Efferent neuron Effector 35 Mosby items and derived items © 2006 by Mosby, Inc.

Reflex Arc 36 Mosby items and derived items © 2006 by Mosby, Inc.

Upper and Lower Motor Neurons o Upper motor neurons n n o Efferent pathways primarily relaying information from the cerebrum to the brain stem or spinal cord Synapse with interneurons Lower motor neurons n n Neurons having direct influence on muscles Cell bodies originate in the gray matter of the spinal cord, but their axons extend into the PNS 37 Mosby items and derived items © 2006 by Mosby, Inc.

Neuromuscular Junction 38 Mosby items and derived items © 2006 by Mosby, Inc.

Motor Pathways o o Lateral corticospinal Corticobulbar Basal ganglia Vestibulospinal 39 Mosby items and derived items © 2006 by Mosby, Inc.

Sensory Pathways o o Anterior spinothalamic Lateral spinothalamic 40 Mosby items and derived items © 2006 by Mosby, Inc.

Protective Structures o Cranium n Eight bones o o o n Frontal Occipital Temporal (2) Parietal (2) Sphenoid Ethmoid Galea aponeurotica 41 Mosby items and derived items © 2006 by Mosby, Inc.

Protective Structures o Meninges n Protective membranes surrounding the brain and spinal cord o o o Dura mater Arachnoid Pia mater 42 Mosby items and derived items © 2006 by Mosby, Inc.

Meninges 43 Mosby items and derived items © 2006 by Mosby, Inc.

Protective Structures o o Cerebrospinal fluid (CSF) and the ventricular system CSF is a clear, colorless fluid similar to blood plasma and interstitial fluid n n n 125 to 150 m. L Produced by the choroid plexuses in the lateral, third, and fourth ventricles Reabsorbed through the arachnoid villi 44 Mosby items and derived items © 2006 by Mosby, Inc.

Protective Structures o Vertebral column n 33 vertebrae o n 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal Intervertebral disks o Nucleus pulposus 45 Mosby items and derived items © 2006 by Mosby, Inc.

Vertebral Column 46 Mosby items and derived items © 2006 by Mosby, Inc.

Vertebral Column 47 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Brain o o 800 to 1000 m. L per minute CO 2 is the primary regulator for CNS blood flow Internal carotid and vertebral arteries Arterial circle (circle of Willis) 48 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Brain 49 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Brain 50 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Brain 51 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Brain 52 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Spinal Cord o Vertebral arteries n n o Anterior spinal arteries Posterior spinal arteries Aorta 53 Mosby items and derived items © 2006 by Mosby, Inc.

Blood Supply to the Spinal Cord 54 Mosby items and derived items © 2006 by Mosby, Inc.

Peripheral Nervous System o 31 pairs of spinal nerves n n n o Names correlate with the vertebral level from which they exit Mixed nerves Arise from the anterior and posterior horn cells of the spinal cord 12 pairs of cranial nerves n Sensory, motor, and mixed 55 Mosby items and derived items © 2006 by Mosby, Inc.

Peripheral Nervous System o Fascicles n o o Rami Plexuses n n n o Bundles of myelinated axons in the PNS Brachial plexus Lumbar plexus Sacral plexus Dermatomes 56 Mosby items and derived items © 2006 by Mosby, Inc.

Peripheral Nervous System 57 Mosby items and derived items © 2006 by Mosby, Inc.

Autonomic Nervous System o o o Located in both the CNS and PNS Coordinates and maintains a steady state among the visceral (internal) organs Neurons n n o Preganglionic (myelinated) Postganglionic (unmyelinated) Two divisions n n Sympathetic Parasympathetic 58 Mosby items and derived items © 2006 by Mosby, Inc.

Sympathetic Nervous System o Mobilizes energy stores in times of need n o Receives innervation from cell bodies located from the first thoracic through the second lumbar n o “Fight or flight response” Thoracolumbar division Sympathetic (paravertebral) ganglia 59 Mosby items and derived items © 2006 by Mosby, Inc.

Sympathetic Nervous System 60 Mosby items and derived items © 2006 by Mosby, Inc.

Parasympathetic Nervous System o Functions to conserve and restore energy n o Receives innervation from cell bodies located in the cranial nerve nuclei and sacral region of the spinal cord n o “Rest or repose response” Craniosacral division Preganglionic neurons travel to ganglia close to the organs they innervate 61 Mosby items and derived items © 2006 by Mosby, Inc.

Parasympathetic Nervous System 62 Mosby items and derived items © 2006 by Mosby, Inc.

Neurotransmitters and Neuroreceptors of the ANS o Sympathetic preganglionic fibers n o Sympathetic postganglionic fibers n o Acetylcholine and cholinergic receptors Norepinephrine and adrenergic receptors Parasympathetic pre- and postganglionic fibers n Acetylcholine and cholinergic receptors 63 Mosby items and derived items © 2006 by Mosby, Inc.

Neurotransmitters and Neuroreceptors of the ANS 64 Mosby items and derived items © 2006 by Mosby, Inc.

Aging and the Nervous System o Decrease in the number of neurons n o o o Decreased brain weight and size Senile plaques Neurofibrillary tangles Slowing of neurologic responses 65 Mosby items and derived items © 2006 by Mosby, Inc.

Tests of Nervous System Function o o o Skull and spine roentgenograms Computed tomography Magnetic resonance imaging n o o o Magnetic resonance angiography Positron emission tomography scan Brain scan Cerebral angiography 66 Mosby items and derived items © 2006 by Mosby, Inc.

Tests of Nervous System Function o o o Myelography Echoencephalography (ultrasound) Electroencephalography Evoked potentials Cerebrospinal fluid analysis 67 Mosby items and derived items © 2006 by Mosby, Inc.