Download - physiology : the nervous system
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Main Function: Communication system
controls and coordinates functions
throughout thebody and responds to internal and
external stimuli.
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Central and PeripheralNervous Systems
Consists of: (C.N.S.) brain, spinal cord
(P.N.S.) nerves
Cerebrum
brain
Cerebellum
Medulla OblongataSpinal Cord
Consists of: Brain and Spinal Cord
Central nervous system (CNS)
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Brain and spinal cordHoused in the skull and vertebral column
Three layers ( meninges) ,surround the brain and spinal cord (Pia matter, arechenoids and Dura matter).
The space between middle and inner layer is filled with cerebrospinal fluid (CSF).
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Includes all sensory and motor nerves
Somatic division(Motor function)
autonomic division(visceral function)
peripheral nervous system (PNS).Somatic and autonomic.
• Somatic nervous system controls voluntaryfunctions of the body, such as the musclecontractions that cause the limbs to move
Autonomic nervous system controls the rest
• ofthe involuntary functions such as heart ratebreathing, digestion and body temperatureregulation
Parasympathetic:Housekeeping tasks
Sympathetic: Fight or escape
and
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• 12 cranial nerves & 31 spinalnerves. Carry two types ofinformation:
(1) sensory impulses travelingCNS from sensory receptors in body
• to thethe
• (2) motor impulses traveling awayfrom the CNS to muscles and glands.
Picture shows hundreds ofneuron axons
A nerve is an organ containing a bundle of nerve cells called neurons.
Neurons carry electrical messages called impulses throughout thebody.
cell body
synapse
dendrite muscle
Axon tissue
cell body
TYPICAL MOTORNEURON
Parts of a Neuron
into the neuron to the cell body.
cytoplasm
from cell body
1
2 3
Dendrites: projections that bring impulses
Cell body: contains nucleus & most of the
Axon: long projection that carries impulses away
InterneuroSnynapse
Synapse
Sensory
Neuron
Motor
Neuron
Interneuron
Synapse
Muscle
Contracts
Motor
Neuron
Sensory
Neuron
Sensory Neuroncarry impulses from sense organs to
spinal cord & brain
Interneuron
-processes impulses in brain and spinal
cord
- connect sensory andmotor neurons
Axon End
Axons branching outto muscle fibers
Motor Neurons
carry impulses from the brain & spinal cord to
muscles & glands
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Neurotransmitters
(pinkspheres)
The message is transferred when RECEPTORS receiveneurotrans-
Synapse (gap) mitters.
Nerve Cell Impulses:•Flow of ions across the plasma membranes (force drive sodium & potassium ions from one side to the other)* Tiny electrodes on the outside and inside of
the plasma membrane•Potential difference (- 70 millivolts)resting•*Plasma membrane is positively charged onthe out side and negatively charged on the
inside.
P.
•* Sodium ions are found in greaterconcentration outside ,potassium ions are
found in greater concentration inside the cell.
Action Potential
(1) depolarization(voltage
from -70 millivolts to +30)
goes
(2) repolarization, the return tothe resting potential.
** Increases cell permeability, resulting in achange in the resting potential
** Protein pores in the plasma membrane open.** Sodium ions flow into the cell through the
pores.** Shift in the resting potential from
-70 to +30 (depolarization).
** After depolarization, the membranereturns to its previous state(repolarization)
(1) a sudden decrease in the membrane’spermeability to sodium (stops the influx of
sodium
(2) a rapid outflow of potassium ions
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Synaptic Transmission:.A synapse consists of•
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(1)
(2)
(3)
a terminal (presynaptica gap (synaptic cleft)
neuron)
the membrane of the dendrite orpostsynaptic cell
• Rapid influx of calcium ions into the bouton from theextracellular fluid
• Calcium stimulate the release of a chemical substancestored (neurotransmitters) into the synaptic cleft
• Bind to receptors in the plasma membrane of thepostsynaptic neuron
• Rapid increase in the permeability of the membranethe postsynaptic cell to sodium ions.
of
• Nerve impulse travels down the new nerve cell
Reflex Arc
• Nerves work together with muscles for movement. An impulse begins when one neuron is stimulated by another neuron or by the sense organs.
• The impulse travels down the axons of Sensory neurons to the brain cells called Interneurons.
• The brain will then send an impulse through motor neurons to the necessary muscle or organs, telling it to contract.