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.