Nervous system - overview.pdf

THE NERVOUS SYSTEM OVERVIEW  Functions The Nervous System is the master controlling and communicating system of the body. It controls and coordinates all the essential function of the Human Body 1) Receives information about your environment 2) Controls voluntary effectors, and medi...

THE NERVOUS SYSTEM OVERVIEW  Functions The Nervous System is the master controlling and communicating system of the body. It controls and coordinates all the essential function of the Human Body 1) Receives information about your environment 2) Controls voluntary effectors, and mediates voluntary reflexes. None of your other systems would function 3) Controls involuntary effectors and without your nervous mediates autonomic reflexes system 4) Stores memories 5) It is responsible for conscious thought and perception, emotions, personality. Allows you to think. It makes us unique as individuals  Structural classification of the Nervous System CENTRAL NERVOUS SYSTEM (CNS) -Consists of the brain and the spinal cord, which act as the integrating and command centres of the nervous system. PERIPHERAL NERVOUS SYSTEM (PNS) - It is the part of the Nervous system outside the CNS -It consists mainly of the nerves that extend from the brain and the spinal cord: - Cranial nerves carry impulses to and from the brain - Spinal nerves carry impulses to and from the spinal cord - Ganglia  Functional organization of the Nervous System The nervous system has three overall functions: – Sensory function: sensory receptors detect the changes in the external environment and the environment within the organism. – Integrative function: the central nervous system integrates this information. – Motor function: effectors (muscles and glands) bring about a response.  Practical example You are driving a car… When you come to a red light, what do you do? 1.Seeing the red light is your sensory input. 2. Your nervous system integrates this information (red means stop – integrative function). 3. Your foot goes for the break (motor output ) and you stop the car. Functional organization of the Nervous System  Nervous Tissue Types of nervous tissue cells: - Neurons - largest cells, trasmit impulses - Neuroglial cells - smaller, more abundant and act as support for neurons Neuron  Types of neurons – functional classification Sensory (afferent) neurons: - specialized to detect stimuli - transmit information about them to the CNS Interneurons (association) neurons: - lie entirely within the CNS - receive signals from many neurons and carry out the integrative function (process, store and retrieve information and “make decisions” that determine how the body will respond to stimuli) - 90% of all neurons are interneurons - lie between and interconnect the incoming sensory pathways, and the outgoing motor pathways of the CNS Motor (efferent) neurons: - send signals out to muscles and gland cells (the effectors) Types of neurons – structural classification Glial cells  Gray and White matter The CNS has two kinds of tissue: grey matter and white matter Grey matter contains the cell bodies, dendrites, axon terminals of neurons, (so it is where synapses are), glial cells and capillaries. Forms cortex over cerebrum and cerebellum and central portion of spinal cord. Forms nuclei within brain (a localized collection of neuron cell bodies) White matter is made of axons connecting different parts of grey matter to each other, together with glial cells and capillaries  CNS - SPINAL CORD - DIENCEPHALON - BRAIN STEM BRAIN - CEREBRAL HEMISPHERES - CEREBELLUM Spinal Cord  Cerebral hemispheres The two cerebral hemispheres form the largest part of the brain, called the CEREBRUM. Its surfaces, called CEREBRAL CORTEX surrounds the white matter, in which depth are located the basal nuclei.  Cerebral hemispheres The cerebral cortex, in addition to being divided into lobes, can be divided into areas in relation to its structural features (sensory areas, motor areas, association areas)  Diencephalon Consists of structures that are lateral to the third ventricle, and includes the thalamus, the hypothalamus (including the Posterior pituitary), the epithalamus  Brainstem Connected to the spinal cord. From above downwards: MIDBRAIN, PONS and MEDULLA OBLONGATA Controls processes basic for survival, such as heart rate, breathing, digestion and sleep. Most of the cranial nerves arise from brainstem  Cerebellum It consists of a mantle of grey matter (cerebellar cortex), which surrounds a mass of white matter containing the cerebellar nuclei The cerebellum plays an important role in motor control: it contributes to coordination, precision, and accurate timing; it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity.  The adult spinal cord About 45 cm long, 14 mm wide CNS tissue ends between vertebrae L1 and L2 31 segments (31 pairs of spinal nerves) Each pair of nerves exits the vertebral column at the level it initially lined up with at birth ➔ Spinal cord is the link between the CNS and the rest of the body It receives sensory information both from the limbs and from the whole trunk, retrasmitting it, through ascending projections tracts to the higher centres and, at the same time, receives from the latter, through descending projection tracts, motor orders that it retrasmits to the muscles and target organs Gross anatomy of the spinal cord Gross anatomy of the spinal cord Organization of the gray matter Organization of the white matter  THE PERIPHERAL NERVOUS SYSTEM  The Peripheral Nervous System The peripheral nervous system lies outside the central nervous system. The peripheral nervous system consists of the peripheral nerves throughout the body (outside of spinal cord and brain), ganglia and the sensory organs  The Peripheral Nervous System NERVES that connect the central nervous system to the rest of the body - Motor Division – impulses from CNS to muscles or glands Two Parts: – Somatic Nervous System – Autonomic Nervous System - Sensory Division – transmits impulses from sense organs to CNS  Nerves Nerves are mainly formed by neuronal extensions of axons that originate from cell bodies located within the neuroaxis or in ganglia Nerve Fibers  Motor Division Somatic and Autonomic Nervous System  Motor Division – Somatic Nervous System Controls voluntary movement of the skeletal muscles. Motor neurons have direct control over skeletal muscles. Somatic motor neurons have cell bodies in the spinal cord or in the brain stem and just one neuron traveling from spinal cord/brain stem to effector.  Motor Division – Autonomic Nervous System Controls involuntary actions - Heart beat, blood pressure, sweating ect…(we do not control the autonomic nervous system). It allows for homeostasis to occur. The autonomic nervous system has two sets of neurons in the PNS. - The first has cell bodies in the brain or spinal cord and synapses in an autonomic ganglion (Preganglionic neuron) - The second has cell bodies in the ganglion and synapses on the effector (Postsynaptic neuron)  Motor Division – Autonomic Nervous System The autonomic nervous system is subdivided into two system that have opposite effects on the same organs: Parasympathetic – slow down systems (like a brake). Controls internal organs during normal activity Sympathetic – speed up systems (like a gas pedal) Controls internal organs during high stress activity Motor Division – Autonomic Nervous System Parasympathetic Nervous System Oculomotor nerve (III) Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X) Sympathetic Nervous System Cranial Nerves  Spinal Nerves Spinal nerves are the means by which the CNS receives information from, and control the activities of, the trunk and limbs. 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) They contain a mixture of sensory and motor fibers. Enteric Nervous System