Nervous System Overview

Nervous System 2 divisions central nervous system (CNS) – brain and spinal cord – control center for the whole body peripheral nervous system (PNS) – nerves and receptors in sense organs. Functions are to (inform the CNS of conditions inside and outside of the body and (2) transmit the CNS’s response to the appropriate organs (such as muscles). 2 types of cells in the nervous system neurons – nerve cells; structural and functional unit of the nervous system – receive and transmit information. neuroglial cells – provide physical support, insulation, and nutrients for neurons

Nervous System Functions (3) sensory receptors gather info from external environment (light, sound) and internal environment (body temp, blood pH, O 2 conc.) integrative collects sensory data and makes decisions motor stimulates effectors to respond detect changes  make decisions  stimulate responses

Neuroglial Cells fill spaces, provide structural frameworks, produce myelin, carry on phagocytosis 4 kinds in CNS microglial – support neurons and phagocytize bacteria and cellular debris oligodendrocytes – create myelin sheath around axons in CNS astrocytes – structural support, regulation of nutrients and ions, form scar tissue in CNS ependymal – epithelia-like membrane that covers brain parts 1 kind in PNS – Schwann cells form myelin sheath in PNS

Myelin Sheath Covers and insulates the axon so the nerve impulse moves faster. Made by oligodendrocytes in CNS Made by Schwann cells in PNS Nerves that are myelinated have gaps in the myelin (Nodes of Ranvier) that allow the signal to skip, moving the signal much faster than on unmyelinated axons.

Neuron Structure vary in size and shape – axons may be only millimeters long or several feet in length 3 basic structural components dendrites – conduct impulses to cell body cell body axon – conducts impulse away from cell body Nerve impulse (signal) moves from dendrites to cell body to axon

Cell Body & Dendrites contains granular cytoplasm, mitochondria, lysosomes, Golgi apparatus, neurofibrils Nissl bodies (chromatophilic substance) – membranous sac that functions like ER ribosomes on Nissl bodies help in protein synthesis nucleus (and nucleolus) centrally located mature neurons do not divide dendrites – short and highly branched

Axon axonal hillock – start of axon myelin – lipoprotein sheath around an axon that insulates and increases the rate of impulse conduction Schwann cells – wrap around axon like a bandaid; myelin underneath neurilemma – outer portion of Schwann cells nodes of Ranvier – narrow gaps btw Schwann cells myelinated vs. unmyelinated

Neuron Classifications bipolar – cell body + 2 nerve fibers (1 axon, 1 dendrite) unipolar – cell body + 1 nerve fiber w/2 branches multipolar – cell body + many nerve fibers (1 axon, many dendrites)

Neuron Functions (3) sensory (afferent) neurons – carry nerve impulses from peripheral body parts into brain or spinal cord most are unipolar, some bipolar interneurons – link neurons to other neurons and direct incoming sensory impulses to the appropriate places from processing and interpretation multipolar motor (efferent) neurons – carry nerve impulses out of the brain or spinal cord to effectors multipolar