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Nervous System Overview Nervous System Overview Dr. Hugo Bergen, Ph.D. Dept. Human Anatomy & Cell Science Faculty of Medicine E-mail: [email protected] Objectives: 1. Describe the basic organization of the central and peripheral nervous systems. 2. Describe the ventricular system within the brain 3. Describe meninges and the blood supply to the brain 4. Describe the structure and function of the spinal nerves and the cranial nerves Basic Organization of NS: The nervous system consists of: 1. Central Nervous System (CNS): i. Brain carry out higher mental functions, ii. Spinal cord integrate & coordinate signals 2. Peripheral Nervous System (PNS): o Connects the CNS to tissues and organs in the periphery. Communication via nerves is both afferent/sensory and efferent/motor. i. Nerves connect CNS to peripheral targets a. Cranial Nerves (12 pairs) (Brain) b. Spinal Nerves (31 pairs) (Spinal cord) Spinal Cord From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 1.3 and 1.4 Functional Organization • Somatic Nervous System • Comprised of parts of both CNS & PNS that are under voluntary control • Uses 1 neuron connecting CNS to target tissue • Sensory: touch, pain, temperature, position • Motor: voluntary & reflexive movements • Autonomic Nervous System • Involuntary innervation to smooth & cardiac muscle, and glandular tissue • 2 neurons connecting CNS to target tissue (pre-ganglionic & post-ganglionic) • Divided into sympathetic & parasympathetic divisions Sympathetic NS Prevertebral ganglion Note: Pre-Ganglionics are blue & Post-Ganglionics are green Prevertebral ganglion Prevertebral ganglion From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 4.2 Parasympathetic NS Note: Pre-Ganglionics are purple & Post-Ganglionics are amber From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 4.4 Brain o Constitutes ~ 2% of body weight o Contains approx. 100 billion neurons o Specialized for: • Reception of stimuli • Transduction of stimuli – electrical/chemical impulse • Conduction of impulse to various sites of CNS Central Nervous System (CNS) CNS = Brain & Spinal Cord o Gray Matter = Cell bodies and dendrites of neurons. Nucleus/Nuclei = collections of nerve cell bodies and dendrites (sites of connections) o White Matter = Axons of neurons. Tracts = bundles of axons/nerve fibers that connect neighboring or distant nuclei o CNS is surrounded by membranous layers & fluid: provides structural support & protection o Recovers poorly from damage / trauma Mid-Sagittal Views Brain - divisions 1. Cerebrum • Telencephalon • Diencephalon 2. Brain stem • Midbrain • Pons • Medulla 3. Cerebellum Cerebrum / Cerebral Hemispheres Telencephalon consists of: a. Cerebral Cortex (Gray matter) / Lobes b. White matter (axons) c. Ventricles (fluid-filled cavities) d. Basal Ganglia/Basal Nuclei (Gray; Motor) Diencephalon consists of: a. Thalamus b. Hypothalamus From: The Nervous System, B. Pentland, in Medical Sciences (2nd Ed.). © 2015, Figure 8.6 Elsevier Limited. Anatomical Divisions Parietal Frontal Occipital Temporal © Dept. HACS, U. of Manitoba Cerebral Cortex Functions Coordination of complex activities: • Sensory perception • Voluntary movement • Language • Non verbal communication • Decision making processes / spatial relations • Memory • Emotions neurons These rely on white matter connections White Matter • Constitutes the ‘wiring’ of the brain • Brain function depends on connectivity • 3 categories of connections: 1. Commissural fibres: connect the left and right cerebral hemispheres to each other 2. Association Fibres: connect cortical regions within a hemisphere (don’t cross midline) 3. Projection Fibres: connect cortex to sub- cortical regions: diencephalon, brainstem, spinal cord 1. Commissural Fibres (cross midline) • Largest bundle (by far) is corpus callosum (CC) 2. Association Fibres (connect cortical areas within hemisphere) Numerous connections connecting gyri within and between lobes 3. Projection Fibres: connect cortex to sub-cortical areas (to and from cortex) • Includes corona radiata and internal capsule; projects to spinal cord, brainstem, etc. Diencephalon: Components and Functions 1. Thalamus – largest component, relay station for all sensory info. (except smell), transmits to all areas of the cortex. Also regulates consciousness and sleep 2. Hypothalamus – integrates behaviors & visceral function; controls Autonomic N.S. 3. Epithalamus – includes pineal gland: regulates circadian rhythms (releases melatonin) 4. Subthalamus – involved in the regulation of movements; part of basal nuclei Diencephalon: location • Deep within brain on either side of midline rostral to midbrain Brainstem Brainstem components are considered together: • 10 of the 12 cranial nerves attach to it (III – XII; form component of Peripheral NS) and cranial nerve nuclei (origin/termination) • Reticular formation: controls vegetative functions and consciousness/arousal; critical for life o Respiratory and cardiovascular centres; autonomic reflexes; pain modulation o Non-conscious adjustments in posture & locomotion o e.g., large lesions may result in coma Brainstem (cont.) • Ascending tracts destined for cortex pass through the brainstem o All somatosensory information (pain, temp. touch, vibration, & proprioception) from the periphery (ascending from the spinal cord) passes through the brainstem • Descending tracts pass through brainstem o Responsible for controlling motor activity of the body • These tracts are essential for maintaining normal motor and somatosensory function Cerebellum (lat.: ‘little brain’) • Gray matter surrounds core of white matter • Attached to midbrain, pons, and medulla • Critical for coordinating motor activity and is important for precision and timing of movements • Motor learning • Important for maintaining posture • Cerebellar lesions can result in incoordination of movements Brainstem & Cerebellum C. Callosum Midbrain Pons Medulla Cerebellum C. Callosum Midbrain Cerebellum Pons Medulla © Dept. HACS, U. of Manitoba Thalamus Nuclei (e.g. CNs & RF) Cranial Nerves Cerebellum Ascending and Descending Tracts © H. Bergen, University of Manitoba Cerebellum: Inputs and Outputs Inputs: • Motor-related input from cerebral cortex • Proprioceptive input from spinal cord • Vestibular input from vestibular apparatus Integrates sensory info. with motor info. to produce normal movement patterns Acts like a comparator; it adjusts motor activity in response to proprioceptive feedback Cerebellum (cont.) Outputs: • Projects to higher centres (cortex via thalamus) to adjust activity of descending motor pathways (from cortex to spinal cord) • Projects to brainstem circuits to adjust posture and balance; automatic adjustments in posture and locomotion Spinal Cord • Rostrally it is continuous with the medulla • Contained within spinal canal of vert. column • 31 pairs of spinal nerves (component of PNS) are attached to cord White matter surrounds core of gray matter White Matter: o Ascending tracts carry somatosensory information from the periphery to higher centres o Descending tracts carry fibres that control the motor neurons that innervate voluntary muscle From: The Nervous System, B. Pentland, in Medical From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) Sciences (2nd Ed.). © 2015, Figure 8.15 Elsevier Limited. by Crossman & Neary. © 2015, Elsevier Limited. Figure 1.19 Brainstem & Cerebellum Spinal Cord Midbrain Pons Medulla Spinal Cord Vertebrae © Dept. HACS, U. of Manitoba Spinal Cord • Spinal nerves are the source of the segmental innervation of the body • Each spinal nerve is formed from a dorsal root (sensory fibres) and a ventral root (motor fibres) • Dorsal root contains the cell bodies of the sensory neurons that convey pain, temp., touch, etc. (cell bodies are in dorsal root ganglion) • Ventral root contains motor axons Dorsal Vertebra Dorsal Root Dorsal Root Ganglion Spinal Nerve Ventral Root Gray Matter White Matter AMIRSYS | Reference Centers Spinal Reflexes Ventricular System & Cerebrospinal Fluid • Within the cerebral hemispheres are the large bilateral C-shaped lateral ventricles (n=2) filled with cerebrospinal fluid (csf) • These drain into the midline 3rd ventricle via the interventricular foramen (foramen of Monro) • The 3rd ventricle drains into midline 4th ventricle via the cerebral aqueduct • Total of 4 fluid-filled ventricles From: The Nervous System, B. Pentland, in Medical Sciences (2nd Ed.). © 2015, Figure 8.19 Elsevier Limited. From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 6.7 Cerebrospinal Fluid • CSF is a clear fluid derived from plasma of the highly vascularized choroid plexus • Choroid plexus (CP) appears as tufts of material in all 4 ventricles • Regulates extracellular environment of CNS • Absorbed into venous circulation Meninges • Brain & spinal cord are covered with 3 membranous layers: 1. Dura Mater: tough, dense layer tightly attached to inner surface of skull 2. Arachnoid Mater: thinner layer attached to dura; extensions from arachnoid to pia (‘spider- web’ like) 3. Pia Mater: very thin translucent layer attached to cortical surface; follows contours of the gyri Meninges - Functions 1. Protection (together with CSF, skull, vertebral column) 2. Compartmentalization of cranial cavity which provides structural support and suspends spinal cord within the dural sleeve 3. Conduit for cerebrospinal
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