Lecture 20

Lecture 20:The Nervous System/Senses

Covers Chapter 38 & 39

Intro to Nervous System

• Primary Purpose: receive, process and transmit information

• Messages from the environment and from the body itself go to brain and tell it what’s happening. Brain gets info and tells body how to respond. – The cells that carry these “messages” are called

NEURONS.– Neurons bundled together are called NERVES.

NERVOUS SYSTEM

• 2 parts– Central Nervous System**

• Brain• Spinal Cord

– Peripheral Nervous System**• ALL Neurons/Nerves outside the CNS

CNS & PNS

3 major types of neurons/nerves

• **Sensory Nerves – carry nerve impulses TO the CNS

• **Motor Nerves – carry nerve impulses AWAY from the CNS

• **Interneurons - located WITHIN the CNS ONLY- connect sensory and motor neurons

stimulus

sensoryneuron spinal

cord

motorneuron

dorsal root

interneuron

ventralroot

The motorneuron stimulatesthe effector muscle

The effectormuscle causes awithdrawal response

A painfulstimulus activatesa pain sensoryneuron

The signal istransmitted by thepain sensory neuronto the spinal cord

The signal istransmitted to aninterneuron and thento a motor neuron

4

3

2

1

5

Fig. 38-10

Neuron*

• 3 parts of the neuron• 1.) Cell Body- contains nucleus• 2.) Dendrites – receives information from

nearby neurons.• 3.) Axon - electrical signals are transmitted to

end of neuron (synapse)• Synapse: place where neuron communicates

with a muscle fiber, gland or another neuron• Nerve signal sent between neurons takes the

form of neurotransmitters.

Dendrites:Receive signalsfrom other neurons

2

Cell body:Integrates signals;coordinates theneuron’s metabolicactivities

3

An actionpotential starts here4

Axon: Conductsthe action potential5

Dendrites(of other neurons):Receive signals

synapse

dendritereceptors

synapticterminal

7

Synaptic terminals:Transmit signals toother neurons

6

Synaptic terminals:Transmit signals fromother neurons

1

neurotransmitters

A Neuron

Fig. 38-1

What is the impulse/signal/message?

• Information is carried in the neuron as an electrical signal (called an action potential)– When a neuron is stimulated, ions within the

neuron (Na+, K+) move in/out and change the electrical charge of the neuron momentarily as the “message” is carried through the neuron

– After the action potential passes, neuron’s charge returns to normal

How is the message carried between neurons?*

• Neurons do not actually touch• The gap between neurons is the synaptic cleft• At the end of the axon, there is a synaptic terminal. • In the synaptic terminal, vesicles containing chemicals

(neurotransmitters) release neurotransmitters from the end of the axon when an action potential reaches the end of the axon.

• Neurotransmitters cross synaptic cleft and receptor proteins on the postsynaptic neuron “catch” the neurotransmitters

• This triggers an action potential in the postsynaptic neuron• This is how the action potential travels from one neuron to the

next

Neurotransmittersbind to receptors on thepostsynaptic neuron

dendrite ofpostsynapticneuron

receptor

neurotransmitter

ions

4

synapticvesicle

synaptic cleft

The positive charge ofthe action potential causesthe synaptic vesicles torelease neurotransmitters

An action potentialis initiated

The action potentialreaches the synapticterminal of thepresynaptic neuron

1

2

3

Neurotransmittersare taken back intothe synaptic terminal,are degraded, ordiffuse out of thesynaptic cleft

6

synaptic terminalof presynapticneuron

neurotransmitters

Neurotransmitterbinding causes ionchannels to open, andions flow in or out

5

The Structure and Function of the Synapse

Fig. 38-4

Types of Neurotransmitters

• Aspartate Serotonin

• Glutamate Endorphins

• GABA Cholyecystokinin

• Glycine Vasopressin

• Acetylcholine Somatostatin

• Dopamine

• Noepinephrine

RE-UPTAKE

• After crossing synapse, neurotransmitters are removed from synapse by one of two methods:– NT are reabsorbed by the pre-synaptic

neuron to be used again– Or NT are digested by enzymes in the

synaptic cleft

Synapse-REUPTAKE

Motor Neurons

• Motor nerves START in CNS• Motor nerves end in SKELETAL

MUSCLE. • MN control the actions and movements

we initiate ourselves as well as reactions to the sensory messages we get from the brain.

Myelin and the Myelin Sheath

• Many (not all) motor neurons have a covering over their axon called a myelin sheath.

• MS helps action potential (the message) travel faster along the axon to the next neuron.

• MS made of schwann cells.• Schwann cells contain lipids, which make the the

neuron look white, hence the term “white matter” • Unmyelinated neurons look gray, hence the term

“gray matter”.

The Sensory Nervous System

• Things that we “sense” in the world is picked up from sensory receptors, and sent by sensory nerves to the CNS.– 1.) General Senses*– 2.) Special Senses*

Receptors for the sensory nervous system*

• Receptors are specialized cells that can register stimuli from outside or inside the body and send the message (via action potential) to the CNS– Receptors can be

• Thermoreceptors: detect heat/cold• Mechanoreceptors: detect vibration, pressure, motion

and gravity• Photoreceptors: detect light• Chemoreceptors: detect odors & tastes• Nociceptors: detect pain

General Senses*

1.) Temperature (thermoreceptors)

2.) Pain (nociceptors)

3.) Touch (mechanoreceptors)

4.) Pressure (mechanoreceptors)ALL OF THE ABOVE RECEPTORS ARE

LOCATED IN THE SKIN.

5.) Proprioception- position of your limbs in space. (mechanoreceptors)

RECEPTORS LOCATED IN MUSCLES AND JOINTS.*

Paciniancorpuscle(vibration,rapid pressurechanges)

Meissner’scorpuscle(light touch,rapidmovement)

Ruffini corpuscle(pressure)

epidermis

dermis

subdermalconnective and adiposetissue

free nerve ending(hair movement)

free nerve ending(touch, heat, cold, pain)

Receptors in the Human Skin

Fig. 39-3

Special Senses*

Receptor location and type:

• 1.) Smell NOSE chemoreceptor• 2.) Taste TASTE BUDS chemoreceptor• 3.) Hearing INNER EAR

mechanoreceptor• 4.) Vision RETINA photoreceptor• 5.) Equilibrium INNER EAR mechanoreceptor

(gravity, motion, acceleration)

Sensory neurons of the special senses

Sense of taste. This map was later proven wrong. Receptors for each taste are spread

evenly over the tongue.

sclera

choroid

vitreous humor

retina

fovea

bloodvessels

opticnerve

blind spotlens muscle

aqueoushumor

cornea

lens pupil

eyelash

iris

ligaments

rod cone

signal-processingneurons

ganglioncells

light

(photoreceptors)

membrane discsbearing photopigmentmolecules

ganglion cellaxons formthe optic nerve

(a) Eye anatomy

(b) Cells of the retina

The Human Eye

Fig. 39-9

calcium carbonatestones

semicircularcanals

ampullae

ampullagelatinous material

hairshair cells

axons from theauditory nerve

cochlea

auditorynerve

saccule

utricle

gelatinous matrixhairshair cellsaxons from theauditory nerve

The Vestibular Apparatus

Fig. 39-6

The Brain

• Housed inside the skull for protection• Bathed in Cerebrospinal Fluid

(H20, proteins, glucose, WBC’s)• 100-200 BILLION NEURONS • 100 TRILLION GLIAL CELLS• *Glial Cells: Supportive cells that hold neurons in

place*– Supply nutrients and O2 to neurons*– Insulate one neuron from another*– Destroy bacteria and remove dead neurons*

Parts of the Brain***

• Forebrain: – Cerebrum: decision-making, emotion, language, interpreting

sensory information– Thalamus: pain, pressure, temperature– Hypothalamus: sex, hunger, thirst, body temp

• Midbrain: relay center. Coordinates information sent from hindbrain to forebrain

• Hindbrain:– Cerebellum: balance, coordination, movement– Medulla & Pons: swallowing, breathing, heart rate,

wakefulness

The Human Brain

Fig. 38-12

(a) A lateral section of the human brain (b) A cross-section of the brain

hypothalamus

meninges skull

corpuscallosum

thalamus

cerebellum

pons

medulla

spinal cord

cerebral cortex(gray matter)

myelinated axons(white matter)

basalganglia

hypothalamus

hippocampus

thalamus

corpuscallosum

substantia nigra

MIDBRAIN

HINDBRAIN

FOREBRAIN(within dashedblue line)

cerebralcortex

pituitarygland