Lecture 2 - Central & Peripheral Nervous Systems, Anatomy of the Cranium (1) PDF

ANAT20040 – Neurosciences Review of CNS & PNS; Cranial Bones Learning Objectives At the end of this topic, you should: Know the structural make-up of the central/peripheral nervous system Review and understand the differences between sensory and motor pathways Be familiar with the l...

ANAT20040 – Neurosciences Review of CNS & PNS; Cranial Bones Learning Objectives At the end of this topic, you should: Know the structural make-up of the central/peripheral nervous system Review and understand the differences between sensory and motor pathways Be familiar with the lobes of the cerebral hemispheres and bones making up the skull  ***N.B.*** Review material from last year’s BTED course, i.e. 1) Neurons & Support Cells 2) Intro to CNS and PNS 3) Sensory Receptors 4) Neurulation Divisions of Nervous System Central Nervous System (CNS) – Brain, spinal cord (most nerve cell bodies, connections) Peripheral Nervous System (PNS) – Link between CNS and peripheral structures (e.g. skin receptors, muscles) – Cranial nerves, spinal nerves, and their branches – Autonomic nervous system  Stimulus (Input) Response (Output) Cardiac muscle, Skeletal muscle smooth muscle & glands PNS Somatic nervous Autonomic Sensory system nervous system Sensory division conducts receptors, action potentials from the nerves, Motor division conducts body to the CNS action potentials from ganglia & plexuses the CNS to the body CNS CNS processes & integrates Brain & information, initiates responses spinal & performs mental activity cord  Types of Neurones Afferent: Carry information from peripheral receptors to CNS (sensory if information reaches conscious level) Efferent: Carry impulses away from CNS (motor if they reach muscle) - (Interneurones: Vast majority; ‘relay’ neurones within CNS) Types of Nerves Sensory nerves – contain mostly sensory neurones Motor nerves – contain mostly motor neurones Mixed nerves – contain a more even combination of both Peripheral Nerve Structure, Connective Tissue Fasc Epi N Peri S CNS: Brain Made up of cerebrum, cerebellum, brain stem CNS: Brain Made up of cerebrum, cerebellum, brain stem Cerebrum Lobes, gyri (folds) and sulci (furrows) – lobes are named according to overlying skull bone Cranium (Skull) Divided into many bones that can be divided into 2 groups: Neurocranium (protects the brain) Viscerocranium (assist in formation of face)  Neurocranial Bones Parietal (paired) Temporal (paired) Frontal Occipital Sphenoid Ethmoid  Viscerocranial Bones Nasal (paired) Maxillae (paired) Palatine (paired) Lacrimal (paired) Inferior nasal conchal (paired) Zygomatic (paired) Vomer Mandibular Cranial Sutures, Foetal Skull Sutures = fibrous joints in the skull Normal to remain unfused at birth (fontanelles) Major Skull Foramina http://www.uwo.ca/cns/resident/pocketbook/pictures/skullbase.jpg Cerebellum Latin for “little brain” Located in posterior aspect of brain, just below occipital lobes, in the posterior cranial fossa Lies behind the brain stem (midbrain, pons, medulla) Bilaterally symmetrical (like cerebrum) Brainstem Connects the narrow spinal cord to the expanded cerebral hemispheres Made up of: – Medulla oblongata – Pons – Midbrain ‘Grey Matter’ vs ‘White Matter’ ‘Grey Matter’: Rich in nerve cell bodies (surface of cerebral hemisphere [good blood supply], central portion of spinal cord) ‘White Matter’: Rich in nerve processes (axons) – myelinated fibres give paler colour Nuclei & Tracts Nuclei: Groups of nerve cell bodies with similar anatomical connections and functions Tracts: Groups of nerve processes with common connections and functions, following the same course (also called fasciculus, peduncle, lemniscus.......) – Outside the CNS = nerves  CELL BODY NUCLEUS AXON TRACT  Tracts MOTOR SENSORY Tracts: Usually named according to direction of impulses – e.g. corticospinal tract – from “cerebral cortex” to “spinal cord” – e.g. spinothalamic tract – from “spinal cord” to “thalamus” Anatomy of Spinal Cord Dorsal horns – receive axons of sensory (afferent) neurones Ventral horns – send out the axons of motor (efferent) neurones  Organisation of Sensory Pathways For most somatic senses - sequence of three neurones between the receptor and perception of sensation at the cerebral cortex First order (primary) neurone: – Sends axon into cord or brainstem; cell body lies in a ganglion Second order (secondary) neurone: – Located in CNS; axon projects to thalamus (contralateral) Third order (tertiary) neurone: – Cell body is located in a specific thalamic nucleus; axon projects to a specific area of ipsilateral cerebral cortex (primary somatosensory cortex)  Organisation of Motor Pathways Sequence of two neurones between the cerebral cortex and effector (skeletal muscle) Upper motor neurone (UMN): – Cell body located in motor cortex; axon projects via internal capsule to brainstem (decussate); relays to ventral horn of spinal cord Lower motor neurone (LMN): – Cell body is located in ventral horn; axon projects to muscle unit – * Also receives and integrates inputs from various parts of the brainstem, local circuits, as well from sensory receptors – Lower motor neurone is the “final common pathway”  => In general, each cerebral hemisphere perceives sensations from, and controls movements of, the contralateral side of the body (‘Same side’ = ‘ipsilateral’) Why the Crossover? (Several theories on this…)