The Nervous System Fundamentals of the Nervous System and Nervous Tissue.
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Transcript of The Nervous System Fundamentals of the Nervous System and Nervous Tissue.
The Nervous System
Fundamentals of the Nervous System and Nervous Tissue
Function of the Nervous System
(1) Sensory Input: Monitors changes (stimuli) occurring inside and outside the body via sensory receptors (2) Integration: Processes and interprets the sensory input and decides what to do at each moment(3) Motor Function: Causes a response by activating effector organs (muscles or glands)
Homeostasis:
The nervous system is responsible to sense changes in the body (receptor), analyses the change (control centre), and cause a response (effector)
The nervous system has ultimate control over homeostasis
Divisions of the Nervous System CNS: brain and spinal
cord PNS: outside the CNS;
nerves that extend from the brain and spinal cord; spinal nerves carry impulses to and from the spinal cord and cranial nerves carry impulses to and from the brain
Peripheral Nervous System
Sensory/Afferent Division: convey impulses to the CNS from sensory receptors; (1) Somatic Afferent Fibers: from skin, skeletal muscles, and joints (2) Visceral Afferent Fibers: from visceral organs (ventral body cavity)
Motor/Efferent Division: transmits impulses from the CNS to effector organs, muscles, and glands (2 parts)
Peripheral Nervous System
Motor/Efferent Division: Somatic Nervous System: aka
voluntary NS because we consciously control our skeletal muscles; motor impulses from the CNS to skeletal muscles
Autonomic Nervous System: aka involuntary NS; visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands; 2 divisions
Peripheral Nervous System
Motor/Efferent Division: Autonomic Nervous System: (1) Sympathetic Nervous System: “Fight
or Flight” (2) Parasympathetic Nervous System:
“Rest and Digest”
Autonomic Nervous System
5 types of Adrenergic receptors Alpha one – causes??? Alpha two - TBA B1 –heart – causes ??? (three things) B2 –lungs – causes ??? Dopaminergic – renal causes patient to
pee!
Receptors
If receptor responds to acethylcholine is cholinergic and two types
= muscarinic or nicotinic
If receptor responds to norephinephrine or epinephrine
= adrenergicFive types!
ACHNOREPI
EPI
adrenergic
muscarinic
nicotinic
Sympathetic Parasympathetic
Preganglionic Preganglionic
Acetylcholine Acetylcholine
Nicotinic receptor Nicotinic receptor
Postganglionic Postganglionic
Norepinephrine Acetylcholine
Adrenergic receptor Muscarinic receptor
Nervous Tissue
2 principle types of cells (1) Neurons: the excitable nerve cells
that transmit electrical signals Basic structural & functional unit of NS (2) Neuroglia: supporting cells that
surround and wrap the more delicate neurons
Like connective tissue Together they form the structures of
both the CNS and PNS
Neurons
Cell body Nerve fibers:
Dendrites receive info into cell bodyAxons conduct info away from cell bodyAxonal terminals at ends contain neurotransmitter to permit communication between neuronsMay be myelinated or unmyelinated
Neurons
Gray & White Matter in the CNS
Gray Matter: contains mostly nerve cell bodies and unmyelinated fibers
White Matter: contains dense collections of myelinated fibers and are primarily fiber tracts
Reflexes
Rapid, predictable, automatic responses to stimuli, in which a particular stimulus always causes the same motor response; unlearned, unpremeditated, and involuntary, considered to be built into our neural anatomy
Occur over neural pathways called reflex arcs that have 5 elements: (1) receptor (2) sensory neuron (3) CNS integration center (4) motor neuron (5) effector
Reflex Arc
Resting Membrane Potential
The potential difference between the inside (cytoplasmic side) of a neuron’s membrane and the outside; the value varies from –40 mV to –90 mV (millivolts); membrane is polarized
The resting membrane potential is generated by differences in the ionic makeup of the intracellular and extracellular fluids; primarily sodium (outside) and potassium (inside)
Graded Potentials
Short-lived, local changes in membrane potential that can be either depolarizations (i.e. less negative inside) or hyperpolarizations (i.e. more negative inside); called “graded” because their magnitude varies directly with the strength of the stimulus; the stronger the stimulus, the more the voltage changes and the farther the current flows; triggered by some change in the neuron’s environment (heat, light, etc)
Action Potentials
Only cells with excitable membranes (neurons and muscle cells) can generate action potentials, which are the way neurons communicate
In neurons, a transmitted action potential is also called a nerve impulse
Action Potentials
They are generated by changes in membrane permeability to Na+ and K+ which cause depolarization (inside the membrane becomes more positive) followed by repolarization (return to negativity on the inside of membrane)
Action Potentials
Threshold: when the membrane has been depolarized by 15 to 20 mV from the resting value, an action potential will occur (same size every time)
All or None Phenomenon: the action potential either happens completely or it doesn’t happen at all
Conduction Velocities of Axons
(1) Influence of axon diameter: the larger the axon’s diameter, the faster it conducts impulses
(2) Influence of a myelin sheath: if present, the myelin sheath dramatically increases the speed of transmission because myelin acts as an insulator to prevent leakage of charge from the axon; the electrical signal jumps from node of Ranvier to node of Ranvier (1mm) along the axon
Synapse
The functional junction between two neurons or between a neuron and an effector
In order to propagate nerve impulses from neuron to neuron, they have to meet; the junctions are the synapses; the gap between them is the synaptic cleft
Neurotransmitters are released into the cleft to facilitate (or inhibit) transmission
http://www.blackwellpublishing.com/matthews/nmj.html
Happenings at the NMJ…..
Depolarization
Neurotransmitter Removal
The neurotransmitter must be removed from the synaptic cleft once its job is done
This occurs via diffusion, break down via enzymes or transport via special membrane proteins
Some drugs act on this area (E.g SSRI and MAOIs)