3 overlapping functions of nervous system
1. Sensory Input 2. Integration 3. Motor Output
A function of the nervous system. Millions of sensory receptors monitor changes (stimulus) occurring both inside and outside of the body and gather information.
A function of the nervous system. The process of interpreting the sensory input and making decisions about what should be done at each moment.
A function of the nervous system. The dictation of the integration. Nervous system activates effector organs (muscles or glands)
The central nervous system CNS
Consists of the brain and spinal cord. The integrating and command center. Interprets incoming sensory signals and dictates motor responses based on past experiences, reflexes, and current conditions.
The peripheral nervous system PNS
The part of the nervous system outside the CNS, consisting mainly of nerves that extend from the brain and spinal cord. Cranial nerves carry signals to and from brain, spinal nerves carry signals to and from spinal cord. Link all regions of the body to CNS. Contain ganglia.
areas in the PNS where the cell bodies of neurons are clustered.
Sensory (Afferent [carrying towards] division)
signals picked up by the sensory receptors located throughout the body and carried by nerve fibers of the PNS into the CNS.
Motor (efferent [carrying away] division)
signals are carried away from the CNS by nerve fibers of the PNS to innervate the muscles and glands, causing these organs to contract or secrete.
Somatic Sensory Subdivision of PNS
Sensory innervation of the outer tube: skin, body wall, and limbs. General: Touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs. Special: Hearing, equilibrium, and vision
Visceral Sensory Subdivision of PNS
Sensory innervation of the viscera. General: stretch, pain, temperature, chemical changes, and irritation in the viscera; nausea and hunger. Special: Taste and smell
Somatic (voluntary) Motor Subdivision of PNS
Voluntary Nervous System. The motor innervation of the outer tube, specifically skeletal muscles. General: Motor innervation of all skeletal muscles
Visceral (involuntary) Motor Subdivision of PNS
Motor innervation of inner tube General: Smooth muscle, cardiac muscle, and glands. Equivalent to Autonomic Nervous System (ANS)
Proprioception Somatic sensory
Sensing one's own body. A sense that detects the amount of stretch in muscles, tendons, and joint capsules.
densely packed and tightly intertwined cells made up of neurons and neuroglia.
Neurons (Nerve cells)
Body contains billions. The basic structural unit of nervous system. Highly specialized cells that conduct electrical signals from one part of the body to another via the plasma membrane in the form of nerve impulses
Nerve impulses (Action potentials)
a reversal of an electric charge that travels rapidly along the neuronal membrane.
Characteristics of neurons
-Extreme longevity: can live and function for a lifetime, over 100 yrs
-Amitotic: Do not divide: Lose their ability to undergo mitosis. Cannot be replaced if destroyed.
-Exceptionally high metabolic rate: Require continuous and abundant supplies of oxygen and glucose. Cannot survive more than a few minutes w/o oxygen
Cell body (Soma)
Vary widely in size. All consist of a single nucleus surrounded by a cytoplasm. In all but the smallest, the nucleus is spherical and clear with dark nucleolus near the center.
processes that branch from the cell body like limbs on a tree. Dendro=tree. Receptive sites, providing an enlarged surface area for receiving signals from other neurons. Conduct electrical signals toward the cell body.
A neuron has only one, whose initial segment arises from a cone-shaped region of the cell body called the axon hillock. Thin processes of uniform diameter throughout their length. Impulse generators and conductors that transmit nerve impulses away from they cell body.
the site at which neurons communicate. Most synapses in nervous system transmit info through chemical messengers. It mediates the transfer of information from one neuron to the next.
The neuron that conducts signals towards a synapse
the neuron that transmits signals away from the synapse is called the postsynaptic neuron.
When the synapse occurs between the axon terminal of one neuron and the dendrites of another. (Most)
When the synapse occurs between axons and neuron cell bodies
Membrane-bound sacs filled with neurotransmitters, the molecules that transmit signals across the synapse. Neurotransmitters are secreted from the synaptic vesicles into the synaptic cleft.
Neuron's inner, cytoplasmic side, is negatively charged with respect to its outer, extracellular side. Concentration of Potassium ions (K) is high inside the neuron, and concentration of sodium ions (Na) is high outside the neuron
When a neuron is stimulated experimentally (pinched/shocked) the permeability of the membrane at the site of the stimulus changes, allowing Na ions to rush in, making the membrane become less negative. After the impulse passes, the membrane depolarizes itself.
Synapses that result in an influx of positive ions into the post synaptic neuron, depolarizing the neuron's membrane, allowing for more generation of nerve impulses. (excite the post synaptic neuron)
increase membrane polarization, making the external surface more positive than it was, reducing the ability to generate nerve impulses.
Structural classification of neurons
Multipolar, bipolar, unipolar
Most neurons (over 99%) are multipolar. They have more than two processes. Usually have multiple dendrites and a single axon. Some have no axons and rely on dendrites to conduct signals. Motor neurons and most interneurons are multipolar.
Have two processes that extend from opposite sides of the cell body. very rare. occur in some special sensory organs (inner ear, retina of eye, olfactory epithelia) where they mostly serve as sensory neurons
short, single process that emerges from the cell body and divides like an inverted T into two long branches. Most start out as bipolar whose processes fuse together near cell body during development. AKA pseudo unipolar neurons. Make up typical sensory neurons.
Functional classification of neurons
Sensory neurons, motor neurons, interneurons
Afferent neurons. Make up the sensory division of PNS. Transmit impulses toward the CNS from sensory receptors in the PNS. Pseudounipolar. Cell bodies are in ganglia outside the CNS. Do not have dendrites, but sensory receptors at the end of the peripheral axon receive stimuli and transmit impule towards cell body
Central process (Sensory Neuron)
An axon branch of the short, single process of sensory neuron that runs centrally into the CNS.
Peripheral Process (Sensory Neuron)
An axon branch of the short, single process that extends peripherally to the receptors.
Efferent Neurons. Make up the motor division of PNS. Carry impulses away from the CNS to effector organs (muscles and glands). Multipolar. Cell bodies located in CNS (except for some neurons of the ANS). Form junctions with effector cells, stimulating muscles to contract or glands to secrete.
Association neurons. Lie between motor and sensory neurons. Confined entirely to CNS. Link together into chains that form complex neuronal pathways. Make up 99.98% of the body's neurons. Almost all are multipolar. Great diversity in size and in branching patterns.
Neuroglia or Glial Cells
non-nervous supporting cells with which all neurons associate closely. 4 types in the CNS and 2 in the PNS. Provide supportive scaffolding for neurons. Cover all non synaptic parts of the neurons to insulate and keep separate electrical activities of adjacent neurons.
Astrocytes (Glial Cells)
Star shaped. Most abundant glial cells of CNS. Processes extend between neurons and capillaries. Nourish neurons, maintain ionic concentration surrounding neurons. Take up neurotransmitters (glutamate), aid neuronal growth and synapse formation in developing neural tissue.
Microglia (Glial Cells)
Smallest and least abundant glial cells of CNS. Phagocytes that engulf and remove invading organisms and dead or damaged neural tissue.
Ependymal Cells (Glial Cells)
simple epithelium that lines the central hollow portions of the CNS: ventricles of the brain, central canal of spinal cord. Cilia aid circulation of cerebral spinal fluid (CSF)
Oligodendrocytes (Glial Cells)
Fewer branches than astrocytes. Form the myelin sheath surrounding neuronal processes in white matter of CNS.
Satellite Cells (Glial Cells)
Surround neuron cell bodies with ganglia. PNS.
Schwann Cells (Glial Cells)
Surround all axons in the PNS and form myelin sheaths around many of these axons.
Produced by Oligodendrocytes in the CNS and Schwann cells in the PNS. The lipoprotein Myelin sourrounds the thicker axons of the body. Each segment consists of the plasma membrane of a supporing cell rolled in concetric laters around the axon. Form insulating layer that prevents leakage of electrical current from axon, increasing speed of impulse.
The thin external material of a nerve axon, surrounding Myelin Sheath
Nodes of Ranvier
1mm gaps in the myelin sheath between adjacent Schwann Cells. Nerve impulses leap from one node to the next, bypassing myelin sheaths, to increase impulse conduction speeds.
Thin, slowly conducting axons that lack a myelin sheath. Schwann cells surround such axons but do not wrap around them in concentric laters of membrane. Found in portions of the ANS and some sensory fibers.
Myelin Sheath in CNS
Oligodendrocytes form the myelin sheaths in the brain and spinal cord. Each oligodendrocyte contributes myelin to several axons, whereas a Schwann cell is associated with one axon only. Nodes of Ranvier are present but spread wider.
Cablelike organ in the PNS. Each consists of many axons (nerve fibers) arranged in parallel bundles and enclosed in connective tissue. Almost al nerves contain both myelinated and unmyelinated sensory and motor fibers.
loose connective tissue that covers the Schwann cell.
Groups of axons bound into bundles by perineurium
Connective tissue wrapping binds axons/nerve fibers into a bundle. Fascicle wrapping.
The tough fibrous connective tissue wrapping that surrounds the whole nerve (groups of fascicles and blood vessel that nourish axons and schwann cells).
Neuron: Nerve cell
Nerve Fiber: A long axon
Nerve: A collection of nerve fibers in the PNS
Structure of Neuron (Image)
Two Neurons communicating at synapse (image)
Neurons classified by structure (Image)
simple chains of neurons that cause our simplest, reflexive behaviors and reflect the basic structural plan of the nervous system.
rapid automatic motor responses to stimuli. Unlearned, unpremeditated, and involuntary
5 components of a reflex arc
Receptor, sensory neuron, intergration center, motor neuron, and effector
(Reflec arc component)
Site where stimulus acts. Located at the teminal end of peripheral process of sensory neuron.
(reflex arc component)
transmits the afferent impulses to the CNS
(Reflex Arc Component)
Consists of one or more synapse in the CNS
(Reflex Arc Component)
Efferent impulses from the integration center to an effector
(Reflex Arc Component)
muscle or gland cell that responds to the efferent impulses by contracting or secreting
Has two neurons and a single synapse. Stretch reflexes that help maintain equilibrium and posture.
ie. Knee jerk reflex
One or more interneurons are part of the reflex pathway between sensory and motor neurons. Most simple reflex arcs. Withdrawal reflexes. More common.
ie. pull hand away in danger, pricking finger
Multiple sclerosis is an autoimmune disease (myelin is attacked by the body’s own immune system).
Symptoms: blindness, weakness, clumsiness
Myelin sheaths in the CNS are destroyed, forming scleroses.
The trigeminal nerve is compressed by an adjacent blood vessel and causes the myelin sheath to deteriorate.