Nervous Systems

Nervous System
-regulatory body system designed to receive, integrate, and send information from inside and outside of the body
* General Functions of Nervous System
1. Receives sensory input from your body and the world
2. Integrates & interprets input
3. Sends out Commands to your muscles and glands as needed
* Specific Names of Nervous System Functions
1. Sensory input
2. Intergration
3. Motor Output
* 2 Divisions of Nervous System
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
* Organs of Central Nervous System (CNS)
1. Brain
2. Spinal Cord
* Function of Central Nervous System
– the control center for the entire nervous system
– the primary location for INTEGRATION
* Components of Peripheral Nervous System (PNS)
1. Cranial Nerves
2. Spinal Nerves
3. Gangila
Function of Peripheral Nervous System
– provide lines of communication between the CNS and the rest of the body
-The PNS sends sensory information toward the CNS for integration
* Sensory Input
– the millions of bits of information gathered by sensory receptors inside and outside the body
* Sensory Receptors
-the sensory nerve ending that responds to stimuli
-to monitor changes occurring both inside and outside the body
* Integration
– the processing and interpreting of sensory input
* Motor Output
– the response to integration (what your body does with the information it receives)
Spinal Nerves
– carry signals to and from the spinal cord
Cranial Nerves
– carry signals to and from the brain
Ganglia
– areas where cell bodies of neurons are clustered
* Subdivisions of Peripheral Nervous System
1. Sensory (Afferent) Division
2. Motor (Efferent) Division
Identify afferent and efferent
“af-” = toward
“ef-” = away
“-ferrent” = to carry, to deliver
* Afferent Division – FUNCTION
– Conducts impulses from receptors to CNS
-Transmit information about changes in one’s environment (stimuli) from receptors toward the CNS
Afferent Division – SUBSTANCE
– Made of somatic and visceral sensory nerve fibers
* Subdivisions of Afferent (Sensory) Division
1. Somatic
2. Visceral
* Somatic body region
– EXTERNAL TO VENTRAL
CAVITY
-structures of outer tube regions (skin,skeletal musculature, bones)
* Visceral body region
– structure of body’s inner tube (digestive tube, lungs, heart, bladder)
Somatic sensory
-senses whose receptors are spread widely throughout the outer tube: (skin, body wall, and limb)
General somatic senses

Special somatic senses

-include sensory input located in the skin and body wall such as the senses of touch, pain, pressure, vibration, temperature
-include the sensory input that is localized specifically to the head such as hearing, equilibrium (balance) and vision
Proprioception
-general somatic sense that detect the amount of stretch in muscles, tendons, and joint capsules
Visceral sensory
-is made up of sensory receptors that sense information from the viscera (internal organs) and from the oral and nasal cavities)
General visceral senses

Special visceral senses

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-located in the viscera: (stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger)
-localized in the head and taste and smell
* Efferent Division – FUNCTION
– Conducts impulses from the CNS to effectors (muscles & glands)
-transmit decisions of CNS regarding necessary action toward effectors
* Targets of Somatic Efferent Division
– Muscles
– Glands
Efferent Division – SUBSTANCE
– Motor nerve fibers
* Subdivisions of Motor (efferent) Division
1. Somatic Nervous System
2. Antonomic Nervous System
(ANS)
* Somatic Motor Nervous System – FUNCTION
– Conducts impulses from CNS to skeletal muscles
– Somatic motor (voluntary)
Antonomic MotorNervous System –
FUNCTION
– Conducts impulses from CNS to cardiac muscles,
smooth muscles, & glands
– Visceral motor (involuntary)
Divisions of Autonomic Nervous System
1. Sympathetic Division
2. Parasympathetic Division
Sympathetic Division – FUNCTION
– Mobilizes body systems during activity (“fight or flight”)
Parasympathetic Division –
FUNCTION
– Conserves energy
– promotes house-keeping functions during rest (“rest and digest”)
*Effectors (targets)
* – Skeletal Muscles in the Somatic Nervous System
* – Cardiac Muscles, Smooth Muscles, & Glands in the
Autonomic Nervous System
* Special somatic senses include sensory input localized in _________ & ________
– Ear
– Eye
* A change acts as a ___________ .
– stimulus
* The nervous system gathers information in the form of _______ ________ which is carried to the CNS.
– sensory input
* The CNS processes and interprets the sensory input. It uses this information to make decisions, a process called
__________ .
– integration
* The CNS dictates a response, known as a ______ _____,
to be carried out by _______
__________ .
– motor output

– effector organs

* Types of Nervous Tissue Cells
– neurons
– neuroglia
* Neurons (nerve cells)
-highly specialized, excitable nerve cells that transmit electrical signals
-they make up about 15% of nervous tissue cells
* Neuroglia (glial cells)
– nonexcitable supporting cells that surround and wrap the neurons
-they make up 85% of the nervous tissue cells
* Elements of a typical neuron
1. Cell Body (soma)
2. Dendrites
3. Axon hillock
4. Axons (nerve fibers)
5. Terminal Branches
6. Synaptic Terminal (axon
terminal)
* Cell Body (soma = body)
– contain typical organelles of cells
– receives signals from
dendrites
* Dentrites
– highly branched extensions of the cytoplasm of the soma
– receive incoming signals and
pass signal toward the soma
* Axon Hillock
– cone-shaped region that is the transition from the soma to the axon
– site of initiation of impulses (action potentials)
* Axons (nerve fibers)
– is a single long extension of the cytoplasm that conducts action potentials away fromthe soma to another neuron or tissue
– sometimes surrounded by a myelin sheath
* Terminal Branches
– profuse branches at the end of the axon
* Synaptic Terminal (Axon
Terminals)
– knob-like distal endings of the terminal branches that form synapses with another neuron or tissue
* 4 Special Characteristics of Neurons
1. Transmit electrical signals
2. Extreme longevity / can
live over 100 years
3. Do NOT divide
4. High Metabolic rate/cannot
survive for more than a few
minutes without oxygen
* Ways to Classify Neurons
1. Structure
2. Function
* Structural Classification of
Neurons
based on number of processes
1. Unipolar
2. Bipolar
3. Multipolar
* Unipolar Neurons (pseudounipolar)
– have short, single processes that emerges from cell body divides like and inverted “T” into 2 long branches
– characteristic of typical sensory neurons
-found mainly in the PNS
-commonly in dorsal root ganglia of the spinal cord and sensory ganglia of cranial nerves
* Bipolar Neurons
– have 2 processes that extend from opposite sides of the cell body: 1 axon & 1 dendrite
– most rare type of neuron
-rare; found in retina of eye, inner ear, olfactory epithelium of the nose
* Multipolar Neurons
– have > 2 processes (usually many dendrites & 1 axon
– most abundant in the body (99% of all neurons)
– characteristic of motor neurons and interneruons
– * found in CNS
* Functional Classification of
Neurons
1. Sensory
2. Interneuron
3. Motor Neuron
* Sensory Neurons (affarent neurons)
-transmit impulses toward the CNS from sensory receptors in the PNS
– most are unipolar & soma are housed in ganglia outside the CNS called the dorsa root ganglia
Dorsal Root Ganglia
– ganglia housed outside the CNS and houses mostly
unipolar soma (cell bodies)
* Interneurons (association neurons)
– lie between motor and sensory neurons
– found entirely within the CNS
– almost all are multipolar
– make up 99% of neurons in human body
* Motor Neurons (efferent neurons)
– carry impulses away from the CNS to muscles or glands
– stimulate muscles to contract or glands to secrete
– multipolar
– Soma are located in the spinalcord and their axons
primarily travel in cranial or spinal nerves to muscles & glands
* Neuroglia (or Glial Cells)
– cells that support neurons
– * outnumber neurons 10 to 1
– Mitotically divide throughou their lifetime
– occur in the CNS & PNS
* Neuroglia/Glial Cells of CNS
1. Astrocytes
2. Microglial Cells
3. Ependymal Cells
4. Oligodendrocytes
* Astrocytes
– largest, most abundant glial cell
– star-shaped and are in close contact with neurons
* FUNCTIONS of Astrocytes
1. Help to form the Blood-Brain barrier
2. moderating capillary permeability in active regions of the brain
3. absorb excess electrolytes and neurotransmitters
4. provide structural support to neurons, anchoring them to nearby capillaries
* Microglia Cells
– thorny appearance
– smallest, least abundant neuroglia of the CNS
– crucial to the health and well being of the CNS
* FUNCTION of Microglia Cells
– migrate toward injured or distressed neurons and phagocytize (consume) invading microorganisms & deceased neurons
* Ependymal Cells
– line the ventricles in the brain and cavities of CNS with a simple epithelial structure
– cilia on apical surface help circulate Cerebrospinal Fluid (CSF)
* FUNCTIONS of Ependymal
Cells
1. Helping to produce and circulate Cerebrospinal fluid (CSF)
2. forming tight junctions that contribute to the “blood- brain barriers”
*Oligodendrocytes
– octopus-like shape with cellular processes that wraparound multiple nerve fibers
* FUNCTION of
Oligodendrocytse
– produce myelin sheaths that insulate nearby axons within the CNS
Neuroglia in the PNS
1. Satellite cells
2. Schwann cells
* Satellite Cells
– small glial cells that wrap around cell bodies of neurons in the PNS
* FUNCTION of Satellite Cells
– protect the neuron cell bodies in ganglia
* Schwann Cells
– functionally similar to Oligodendrocytes of the CNS
– produce myelin sheaths that insulate nearby axons
* Another name for Schwann
Cells
Neurolemmocytes
* FUNCTIONS for Schwann
Cells
1. form myelin sheaths around thicker nerve fibers
2. aid in regeneration of damaged peripheral nerve
fibers
* Myelin sheaths are segmented structures formed by the plasma membranes of ____________ (in the CNS)and ___ _____(in the PNS).
– Oligodendrocytse

– Schwann Cells

* Myelin sheaths
– are formed by oilgodendrocytes in CNS
– are formed by Schwann Cells in PNS
– by cells wrapping their plasma membranes in several concentric layers around thicker axons of CNS & PNS
* STRUCTURE of Myelin Sheath
– composed of plasma membranes from oilgodendrocytes or Schwann Cells
– composed of lipids and lipoproteins
* FUNCTION of Myelin Sheath
1. support, protect, & electrically insulate axons which increase speed
2. allow for saltatory conduction
3. help repair damaged axons
* Saltatory Conduction
-Insulation of myelin causes membrane to be only permeable to ion movement at the nodes of Ranvier.
-Signal hops from node to node
* In the PNS, the _____ ____ of ____ ___ wrap in concentric layers forming myelin sheaths around the thicker neuronal axons.
– plasma Membranes

– Schwann Cells

* Adjacent Schwann cells along an _________ do not touch one another, so there are ________ in the sheath. The gaps in the myelin sheath are called _____ __ _______.
The outermost layer of wrapping contains the _____
and most of the cytoplasm of the Schwann cell. The
outermost layer is called the_________.
– axon
– gaps

– nodes of Ranvier or nerofibrils nodes
– nucleus

– outer collar of perinuclear cytoplasm

* Unmyelinated Neurons
– axons that are not concentrically wrapped with plasma membrane of Schwann cells
* Synapses
– the site of communication between 2 individual neurons
* Presynaptic neuron
= = “before the synapse”
– the neuron that transmits signals toward a synapse
* Postsynaptic neuron
= = “after the synapse”
– neuron transmits signals away from the synapse
* 2 Types of Synapses
1. electrical synapses
2. chemical synapses
* Electrical Synapse
– occurs when ions cross between gap junctions
– * very FAST
– not common in nervous system
– * commonly found in cardiac & smooth muscle
* What type of special junction protein is present in
electrical synapses?
connexon monomer
* Chemical Synapse
– * most common type in the nervous system
– * more slow than electrical synapses
– * most commonly found ???
* Specific regions of the presynaptic cell & post synaptic cell are involved
– synaptic terminal of presynaptic neuron and the dendrite of the postsynpatic neuron
* Components of a Chemical
Synapse
1. Synaptic vessicles
2. Neurotransmitters
3. Synaptic cleft
* Synaptic Vesicles
– membrane-bound sacs that store neruotransmitters
* Neruotransmitters
– chemicals released by the synaptic terminal of one neuron which will affect the membrane potential of another neuron (by causing or inhibiting an action potential)
* Synaptic Cleft
– narrow space between 2 neurons
* What is a nerve?
– a bundle of axons located in
the PNS
* What are the bundles of axons in the nerve called?
– a nerve
Neuron
nerve cell
Nerve
a bundle of fibers or collection of axons
Nerve fiber
a long axon
Ganglion
cluster of cell bodies in PNS
* Connective tissue associated
with Nerves
1. Endoneurium
2. perineurium
3. Epineurium
* Endoneurium
– wraps around individual axons
-layer delicate loose CT surrounding each individual axons (fibers)
* Perineurium
– wraps around individual fascicles (of nerves)
* Epineurium
– wraps around entire nerve
-tough fibrous sheath that surround each nerve fascicles
* 2 Distinct regions of CNS
1. gray matter
2. white matter
* Gray Matter
– gray colored
– short unmyelinated interneurons & motor neurons
– * composed of cell bodies and dendrites
– found internal to White Matter
* White Matter
– white color
– * containes myelinated axons (Myelin is fatty=white)
– fiber tracts of myelinated & unmyelinated axons
* Reflex
– a rapid, automatic motor response to a stimulus
* Characteristics of Reflexes
(properties)
1. a stimulus is required
2. they are VERY FAST
3. they are automatic & occurthe same way every time
4. they are involuntary & unlearned
* Components of Reflex Arc
1. Receptor
2. Sensory Neuron
3. Integration Center
4. Motor Neuron
5. Effector
* Receptor
– the site where the stimulus is detected
* Sensory neuron
– neuron that transmits afferent impulses to CNS
* Integration Center
– one or more synapses in the CNS
* Motor neuron
– neuron that conducts efferent impulses from integration center to an effector organ or cell
* Effector
– the muscle cell or gland cell that responds to efferent impulses by physically contracting or secreting product
* Monosynaptic Reflex Arc
– has ONLY ONE SYNAPSE in the pathway located between sensory neuron and motor neuron
– FASTEST REFLEXES
– STRETCH REFLEXES
* Polysynaptic Reflex Arc
– has AT LEAST 2 SYNAPSES
– involves at least one interneuron between the
sensory and motor neuron
– More common than monosynaptic reflexes
2 directional terms associated with CNS
1. Rostral: toward the nose/forehead (anterior)
2. Caudal: toward the tail/cord (posterior)
3 Structures associated with the spinal cord
1. Conus medullaris
2. Finum terminale
3. Cauda equina
Conus Medullaris
– the inferior, tampered end of the spinal cord
Finum terminale
– (“end filament”) which attaches to the coccyyx inferiorly, anchoring the spinal cord in place so that it is not jostled by body movements
Cauda equina
– (“horse’s tail”) the collection of spinal nerve roots at the inferior end of the vertebral canal
Spinal cord segment
– used clinically to indicate the region of the spinal cord from which the nerve fibers that form a given spinal nerve emerge
2 depressions that run the length of the spinal cord
1. Dorsal median fissure (posterior median sulcus)
2. Ventral median fissure (anterior median fissure)
Dorsal median fissure (posterior median sulcus)
– a narrow furrow
Ventral median fissure (anterior median fissure)
– a wide furrow
How many pairs of spinal nerves?
– 31 pairs of spinal nerves that attach to the spinal cords via spinal root
Are they part of the CNS or PNS?
– spinal nerves are part of PNS since they are outside of the spinal cord
Functions of the spinal cord
1. its responsible for sensory and motor innervation body, inferior to the head
2. it provide 2-way conduction pathway for signals between the body and the brain
3. the major integration center for reflexes.
Gray matter of spinal cord composed of:
1. cortex – (bark on a tree) at the surface of the brain
2. cerebral nuclei – deep within the brain
Gray commissure
– the crossbar of the H. It is bundle of axons that crosses form one side of the CNS to the other and allows the two sides of the spinal cord to communicate
White matter composed of
1. “inner” white matter
2. corpus callosum
3. septum pellucidum
4. internal capsule
Ascending tracts
-carry information form the body to the brain
types of classification of white matter
1. ascending tracts – carry information from body to the the brain
2. descending tracts – carry information from brain to body
3. commisural – carry information from one side of the spinal cord to the other
4 Lobes of the Cerebrum
Frontal, Parietal, Occipital, and Temporal