Nervous

Functioncommand unit provides sensessends signal between body and brainResponds to internal and external stimuli

NeuronDendrite- impulse

passes here 1st

Cell BodyAxon- covered in

myelin- acts as insulator, “white matter”-end at axon terminal

3 types of neurons

Sensory- carries impulse from body to brain or spinal cord

Motor- carries impulse from brain to muscle or gland cell(target cell)

Interneuron- connects brain to spinal cord

Impulse moves dendrite cell body axon target cell

How does impulse move along axon?

Neurons have a charge(-70 mv) on the cell membrane.This is due to more + ions on the outside of the cell than on the inside.

Neurons are excitable- charge can changeThis is called action potential- ability of

membrane to or charge.

Normal conditions of cell

More

K+inside 

More Na+ outsideThis is the resting

potential of a cellThe cell is

Polarized because of the charge difference.

Impulse cause Na+ to rush into cell (DEPOLARIZATION) through ion gates

K+ pushed out of cellCell tries to bring back to normal

Push Na+ outPush K+ back in(Reploarized)Causes impulse to move down membrane to next ion gate

How does impulse travel so quickly?Axon covered with

an insulator –MYELIN- “White matter”

Impulse jumps from node to node

ALL OR NONE THEORYAn impulse has only 1 strengthIt must be strong enough to start an impulse

in a sensory organ or reach the threshold level.

If it reaches the TL then the impulse is transmitted, if not- no transmission

How does impulse jump from axon to next nerve or cell?Need to make connection between neuron

and empty space.1.Vesicles filled with neurotransmitter2.Vesicles fuse with membrane3.Neurotransmitters released into synapse4.Neurotransmitter binds to receptor site on

next neuron or target cell5.Depolarization occurs in cell #26.Ion gates (K+ and Na+) open up7.Impulse transmitted

Synapse

There are 2 parts to your nervous systemCentral Nervous system- Spinal cord + brainPeripheral Nervous System- All nerves

coming from cord

BrainProtected in 3 ways:1.Skull2.Wrapped in connective tissue: Meninges

3 layers- inner-pia matter middle- arachnoid outer-dura matter3. Cerebrospinal fluid- found between pia matter and

arachnoid layers and serves as a shock absorberBrain must have constant supply of oxygen!!!

BRAIN CerebrumBrain StemCerebellum

Cerebrum: Site of Intelligence,Memory,LanguageMovement of skeletal muscle(voluntary)

2 halves- left brain/right brainConnected by CORPUS COLLOSUM- thick

band of connective tissue(So both sides can talk to each other)

Each hemisphere is divided into 4 lobes: frontal, parietal, occipital, and temporal. Has folds or convolutions to add surface area.

2 surfaces: Cerebral cortex or grey matter is the outer

surface Cerebral medulla- white matter is the inner

surface that contains myelinated axons.

Brain Stem : 3 parts-connects brain to cord

Medulla Oblongata- breathing/ heart rate/swallowing

Pons -above medulla, links cerebral cortex and cerebellum

Midbrain -involved in hearing and vision

 

Cerebellum:

BalancePostureCoordination

Two other parts of the brain are found between brainstem and cerebrum

Hypothalmus-control center for hunger, thirst, fatigue, anger, and temperature

Thalmus- switching station for sensory input, passes info to cerebrum

Brain is a source of weak electrical activity that can be detected by an EEG(electroencephalogram)

Sleep is when the cerebral cortex falls to its lowest possible level

Memory is thought to be short and long term

THE SPINAL CORDEmerges from the base of the skullProtected by bone, the vertebral column or

backbone; also the meninges and cerebrospinal fluid.

Links the brain with the peripheral nervous system.

Carries impulses to and from the brain and regulates reflexes.

A reflex is a response to a stimulus.31 pairs of spinal nerves branch out to the body

from the spinal cord.

The spinal cord consists of 2 kinds of nerve tissue:1.Central part is H shaped and consists of gray matter2.Outer part is the white matter and consists of myelinated axons.

Sensory neurons carry impulses from receptors to the spinal cord.

Motor neurons carry impulses from the spinal cord to the effectors (glands/muscles).

Interneurons connect the sensory and motor neurons.

2 partsSensory division- transmits impulses from

sense organs to CNS

Motor Division- transmits impulses from CNS to the effector(muscle, glands) This has 2 subdivisions:

Peripheral Nervous System

Somatic

12 pairs of cranial nerves voluntary 31 pairs of spinal nerves

Also controls reflexes- bypasses brain- signal goes directly to spinal column

sensory nerve spinal column motor nerve target cell

Autonomic -automaticcarries impulse from CNS to internal organsInvoluntary

Sympathetic- controls during time of stress “Fight or Flight”-increase heart rate, breathing, temp,blood pressure

Parasympathetic- bring back to normal

Control during rest

Sensing Chemicals

Chemoreceptors in mouth and noseNose receptors- sense chemicals –impulse

carried on Olfactory Nerve- sent to brainMouth receptors- taste buds on tongue

(10,000)

Sweet, sour, salty, bitter

Eyeconsists of 3 layers:1.outer layer contains the sclera or white of the eye

which consists of tough connective tissue and the cornea which is the transparent covering of the eye. Between the cornea and the sclera is the aqueous humor, a clear fluid.

2.middle layer is the choroid that contains the iris (colored part of the eye) which has an opening called the pupil. Just behind the pupil is the lens, that refracts incoming light. The eyeball itself consists of a large chamber filled with jellylike fluid, the vitreous humor.

3.inner layer is the retina located at the very back of the eye and contains light sensitive cells called photoreceptor cells. This is the place where light energy is converted into electrical impulses.

Sensing light-

These cells contain the pigment rhodopsin which is sensitive to different wavelengths of light. These cells fall into 2 groups;

Rods sense light and dark and the

Cones sense color. It is in these cells where

light is converted into impulses that then travel to the brain via the optic nerve.

Mechanical StimulationHearing- detect vibrations, sound waves

Outer ear consist of auditory canal-collects vibrations

Sound waves hit tympanic membrane (eardrum)Ear drum vibratesVibration passed to 3 bones- malleus, incus,

stapesVibration passed to oval window- causes fluid in

cochlea to vibrateThis causes little hairs in cochlea to bendSends impulse to brain via auditory nerveBrain interprets

Balance- center located in inner ear

Sends info to brainSemicircular canal filled with fluid and hairs

and ear stones(otoliths-CaCO2)Stones lay on hairsHair bends- stimulates nerveSends impulse to brain

Touch- receptors in dermis

Feel temperature, pressure, painReceptors located in specific areas

Light touch- tips of fingers, eyelids, mouthHeavy touch- joints, muscles, palmsFree nerve endings- itch, tickle, hot, cold,

pain

Pain- all over body, except brain Heat- deep in dermis Cold- near surface