Intro to Nervous System - Part 1 PDF

Neural Tissue PARA 1002 1 Nervous System Function Monitors changes from inside/outside the body in the form of stimulus/sensory input Interpret and prioritizes inputs and “makes decisions” (integration) Generates a response – activa...

Neural Tissue PARA 1002 1 Nervous System Function Monitors changes from inside/outside the body in the form of stimulus/sensory input Interpret and prioritizes inputs and “makes decisions” (integration) Generates a response – activates mechanisms to mediate responses (motor output, organ function, hormone release) The nervous system contains some of the “longest” cells in the body PARA 1002 2 1  Divisions * Note that the nervous system may be divided in a number of ways Brain (cranium) CNS Spinal Cord (vertebral canal) Cranial nerves (brain) PNS Spinal nerves (spinal cord) The PNS “relays” information to and from the CNS where the brain receives and integrates the information and initiates a response PARA 1002 3 CNS –vs- PNS (Anatomical) PARA 1002 4 2  Functional Divisions Central Nervous System –vs- Peripheral Nervous System Somatic –vs- Autonomic PARA 1002 5 Somatic –vs- Autonomic Somatic Nervous System (SNS) – The somatic motor division innervates somatic effectors or “voluntary” muscles of the body – The somatic sensory division transmits sensory information from the somatic effectors which is integrated in the somatic centre of the CNS and actions are generated PARA 1002 6 3  Somatic –vs- Autonomic Autonomic Nervous System (ANS) – Innervates autonomic (visceral) effectors: smooth muscle, cardiac muscle and glandular tissue – “Involuntary” responses are initiated in response to visceral sensory information, integrated in the autonomic centre of the CNS – Note that the ANS is influenced by the conscious mind as well (voluntary regulation) – How do the Sympathetic and Parasympathetic divisions of the ANS differ functionally? PARA 1002 7 Autonomic Nervous System The difference between sympathetic and parasympathetic is not simply “one speeds up and one slow down”! Sympathetic - Mediates responses to impending threat - Known as the “Fight or Flight” response - Enables the body to focus energy and actions on dealing with the situation at hand - EXAMPLES Parasympathetic – Coordinates normal “resting” activities – “Rest and Digest” – Generally associated with relaxation PARA 1002 8 4  Autonomic Nervous System Why is understanding the functional differences between the sympathetic / parasympathetic nervous systems so critical? Both systems work together to “fine tune” our internal environment with respect to maintaining homeostasis Many effectors are dually innervated (both types)… P/S nerves function in opposition to one another In simple terms, the parasympathetic and sympathetic branches of the ANS are responsible for: EVERYTHING PARA 1002 9 Cells of the Nervous System There are two major classifications of cells in the nervous system: Neurons – the “excitable” cells responsible for transmission of nerve impulses throughout the body Neuroglia – Originally thought to be merely a supporting “glue” – Actually play a vital role in supporting proper function of nervous tissue – May be as many as 900 billion per nervous system of various cell types – Glial cells retain their ability to reproduce (what implications does this have?) PARA 1002 10 5  Neuroglia (glia) Five major types of glial cells: Astrocytes (only in CNS) - Largest and most numerous type (star-shaped) - Transfer nutrients (glucose) from the blood to neurons - Help form the blood-brain barrier (BBB) - May actually transmit certain information in a limited way Microglia (CNS) - React to the presence of cellular debris and foreign material (microorganisms) by carrying out phagocytosis - Not functionally or developmentally related to other nervous cells PARA 1002 11 Neuroglia (glia) Ependymal cells - Similar to epithelial cells - Form this sheets that line fluid-filled cavities of the CNS and also produce the fluid - Some have cilia that help circulate fluid (CSF) Oligodendrocytes - Help hold nerve fibres together - Produce the myelin sheath surrounding neurons in CNS Schwann cells - Perform the same function in the PNS as oligodendrocytes do in the CNS - Their cell membrane form a sheath around PNS neurons called the nuerilemma (vital in nerve regeneration) PARA 1002 12 6  Typical Neuron There are several forms of neurons, but they all have the same general physical structure: Cell Body – the main cellular portion of the neuron containing the nucleus and most of the organelles Dendrites – processes of the cell body that transmit impulses toward the cell body (from synapses) Myelin sheath – an insulative barrier composed of Schwann cell (PNS) or oligodendrocyte (CNS) (prevents electrical “short circuits”) Neurolemma – covering over the myelin sheath formed by the nuclei and cytoplasm of the Schwann cells (PNS) (Not present in CNS) Neurolemma has a key role in nerve regeneration PARA 1002 13 Typical Neuron PARA 1002 14 7  Classification of Neurons Sensory neurons (afferent) – Carry impulses from sensors or receptors to the CNS – Somatic sensory neurons receive input from receptors in skin, skeletal muscle, joints – Visceral sensory neurons receive input from receptors in visceral organs Motor neurons (efferent) – Carry impulses from CNS to effectors (muscle / glands) – Somatic neurons link to skeletal muscle PARA 1002 15 Classification of Neurons Interneurons – Found within the CNS – An intermediate form of neuron designed to integrate sensory and motor function All three types of neurons work together to facilitate a characteristic nervous response PARA 1002 16 8  Classification of Neurons PARA 1002 17 9