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Neural Control and the Senses. Starr, Chapter 25. The Nervous System . The nervous system includes all the nervous tissue in the body plus the body’s sensory organs, such as the eyes and ears. The Nervous System . Nervous tissue is composed of two kinds of cells:

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The nervous system l.jpg
The Nervous System

The nervous system includes all the nervous tissue in the body plus the body’s sensory organs, such as the eyes and ears.


The nervous system3 l.jpg
The Nervous System

Nervous tissue is composed of two kinds of cells:

  • Neurons - transmit nervous system messages

  • Glial cells - support neurons and modify their signaling


Human nervous system l.jpg
Human Nervous System

The two major divisions of the human nervous system are:

  • Central nervous system (CNS)

    • brain

    • spinal cord

  • Peripheral nervous system (PNS)

    • nerves that thread throughout body

    • plus sensory organs


Divisions of pns l.jpg
Divisions of PNS

  • Afferent division – brings sensory info to CNS

  • Efferent division – carries action (motor) commands to bodies effectors – muscles and glands


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Divisions of the Nervous System

Central nervous

system

Central nervous system (CNS)

information

processing

brain

spinal cord

Peripheral nervous

system (PNS)

sensory infor-

mation travels

in afferent

division

motor information

travels in

efferent division

which includes...

somatic

nervous

system

autonomic

nervous

system

sympathetic

division

Sensory

receptors

in eyes nose,

etc.

parasympathetic

division

cardiac

muscle,

smooth muscle

glands

Peripheral

nervous

system

skeletal

muscle

effectors


Slide7 l.jpg

Within PNS efferent division are two subsystems:

Somatic nerves – (green)

  • voluntary control over skeletal muscles

    Autonomic nerves – (red)

  • involuntary regulation of smooth muscle, cardiac muscle, and glands


Slide8 l.jpg

Autonomic system divided into:

  • Sympathetic division –

    • stimulatory effects

    • Respond to stress or physical activity – “fight-or-flight” response

  • Parasympathetic division –

    • relaxing effects


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Opposing Systems

  • Most organs receive both sympathetic and parasympathetic signals

  • Example: Sympathetic nerves signal heart to speed up; parasympathetic stimulate it to slow down

  • Synaptic integration determines response


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The Autonomic Nervous System

Parasympathetic division (rest and digest)

Sympathetic division (fight or flight)

constrictspupil

dilatespupil

stimulatessalivation

inhibitssalivation

cranialnerves

slowsheart

acceleratesheart

cervicalnerves

constrictsbreathing

facilitatesbreathing

thoracicnerves

stimulatesdigestion

inhibitsdigestion

stimulatesgallbladder

stimulatesrelease ofglucose

lumbarnerves

secretesadrenaline andnoradrenaline

sacralnerves

contractsbladder

relaxesbladder

stimulatessex organs

inhibits sexorgans


Types of neurons l.jpg

Sensory neurons

Detect and relay info

Motor neurons

Transmit signals from inter-neurons to effectors

Inter-neurons

Receive and process info

Located entirely within CNS

stimulus

(output)

Types of Neurons

receptors

sensory neurons

integrators

interneurons of brain, spinal cord

motor neurons

effectors

muscles,

glands

response

(output)


Cells of the nervous system l.jpg
Cells of the Nervous System

Three types of neurons

sensory neuron

interneuron

motor neuron

afferentneuron

neuron within CNS

efferent neuron

effector(muscle)

Axon endings

Anatomy of a neuron

axon

synapticterminals

cell body

dendrites

Figure 27.2


Neuroglia glial cells l.jpg
Neuroglia (glial cells)

A myelinated axon

myelin nodes

  • Cells that assist, support, and protect neurons

  • Make up more than half the volume of the vertebrate nervous system

glial cells

glial cellnucleus

myelincovering

axon

glial cellcytoplasm

Anatomy of a nerve

nerve

bloodvessels

connectivetissue

axons


Nerve l.jpg
Nerve

axon

myelin sheath

  • A bundle of axons enclosed within a connective tissue sheath

many neurons

inside a connective tissue sheath


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Nervous System Communication

Understood easiest as a two-step process:

  • Signal movement down a neuron’s axon

  • Signal movement from this axon to second cell across structure known as synapse


Information flow l.jpg

interneuron

motor neuron

sensory neuron

Information Flow

  • Information from sensory neurons is relayed to interneurons in spinal cord and brain

  • Motor neurons carry signals to body


Action potential l.jpg
Action Potential

  • How nerve cell conduct signal along axon

  • Inside neuron changes from negative to more positive - based on Na+ and K+ movement along membrane

  • Repeats from point of stimulation to move signal along membrane


Myelin sheath l.jpg
Myelin Sheath

  • Sheath blocks ion movements

  • Action potential must “jump” from node to node

  • Greatly enhances speed of transmission


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Chemical Synapse

  • How nerve cells send message between cells

  • Occurs in gap between two cells (terminal of one cell to input zone of another cell)

  • Neurotransmitter diffuses across synaptic cleft and binds to receptors on membrane of second cell

plasma membrane of axon ending of presynaptic cell

plasma membrane of postsynaptic cell

synaptic vesicle

synaptic cleft

membrane receptor


Nervous system communication20 l.jpg
Nervous System Communication

sending cell

receiving cell

synapticcleft

synapticterminal

arrival ofnerve impulse

initiation ofnew impulse

mitochondrion

vesicles containingneurotransmittermolecules (such asacetylcholine)

neurotransmitterreceptors


The spinal cord l.jpg
The Spinal Cord

Gray matter (H-shaped)

  • Mostly cell bodies of neurons (no myelin)

    White matter

  • Mostly axons

  • Sensory and motor neurons

    Meninges

  • Protective coverings


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Functions of Spinal Cord

  • Expressway - channels sensory impulses between brain and peripheral nerves

  • Communication center – receives input from sensory neurons and directs motor neurons with no input from the brain

    • spinal impulses do not involve the brain


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Reflexes

  • Automatic movements in response to stimuli

  • In simplest reflex arcs, sensory neurons synapse directly on motor neurons

  • Most reflexes involve an interneuron


Reflex arc l.jpg
Reflex Arc

The signal from the receptor reaches asensory neuron cell body in the dorsalroot ganglion.

Stimulus (tapping) arrivesand receptor is activated.

afferentsignal

spinalcord

receptor

reflexarc

stimulus

motorneuron

efferentsignal

effector

The signal arrives at a sensoryneuron/motor neuron synapsein the spinal cord. Informationprocessing takes place promptinga signal to be sent through the

motor neuron.

The motor neuron signal stimulatesthe effector (the quadriceps muscles)to contract. Note that CNSprocessing for this reaction washandled entirely in the spinal cord;the brain was not involved.

response



The human brain l.jpg
The Human Brain

  • There are six major regions in the adult brain:

    • Cerebrum

    • Thalamus and hypothalamus

    • Midbrain

    • Pons

    • Cerebellum

    • Medulla oblongata


Slide27 l.jpg

The Vertebrate Brain*

corpus callosum

hypothalamus

thalamus

pineal gland location

part of optic nerve

midbrain

cerebellum

pons

medulla oblongata

Fig. 25-15, p.434


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Cerebrospinal Fluid

  • Surrounds the spinal cord

  • Fills ventricles within the brain

  • Blood-brain barrier controls which solutes enter the cerebrospinal fluid


Anatomy of the cerebrum l.jpg
Anatomy of the Cerebrum

  • Largest and most complex part of human brain

  • Divided into right and left cerebral hemispheres

  • Thin outer layer (cerebral cortex) is site of our highest thinking


Lobes of the cerebrum l.jpg
Lobes of the Cerebrum

primary somatosensory cortex

primary motor cortex

parietal

frontal

occipital

temporal


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The Human Brain

  • The brainstem is a collective term for three brain areas—the midbrain, pons, and medulla oblongata

  • These brainstem structures are active in:

    • Controlling involuntary bodily activities (such as breathing and digesting).

    • Relaying information.

    • Processing sensory information.


The brain stem l.jpg
The Brain Stem

cerebralcortex

cerebrum

cerebellum

thalamus

hypothalamus

pituitarygland

midbrain

pons

brainstem

medullaoblongata

Figure 27.9


The human brain33 l.jpg
The Human Brain

  • Most of the body’s sensory perceptions are channeled through the thalamus before going to the cerebral cortex.

  • The hypothalamus is important in sensing internal conditions and in maintaining stability or homeostasis in the body, largely through its control of many of the body’s hormones.



Our senses35 l.jpg
Our Senses

Each sense employs cells called sensory receptors that do two things:

  • Respond to stimuli

  • Transform these responses into the language of the nervous system – electrical signals that travel through action potentials



Smell l.jpg
Smell

  • A special sense

  • Olfactory receptors

  • Receptor axons lead to olfactory lobe

olfactory

bulb

receptor

cell


Taste l.jpg
Taste

  • A special sense

  • Chemoreceptors

  • Five primary sensations:

    • sweet, sour, salty, bitter, and umami


Our sense of vision l.jpg
Our Sense of Vision

  • Perceives visual field

  • Lens collects light

  • Image formed on retina


Human eye l.jpg
Human Eye

sclera

retina

choroid

iris

fovea

optic

disk

lens

pupil

cornea

part of

optic

nerve

aqueous

humor

ciliary muscle

vitreous body


Pattern of stimulation l.jpg
Pattern of Stimulation

  • Image on retina is upside down and reversed right to left compared with the stimulus

  • Brain corrects during processing


Slide42 l.jpg

Retinal Stimulation Patterns

a Light rays from an object converge on the retina, form an inverted, reversed image.

muscle contracted

b When a ciliary muscle contracts, the lens bulges, bending the light rays from a close object so that they become focused on the retina.

close

object

slack fibers

c When the muscle

relaxes, the lens

flattens, focusing light

rays from adistant object

on the retina.

muscle relaxed

distant

object

taut fibers

Fig. 25-26, p.442


Organization of retina l.jpg
Organization of Retina

  • Photoreceptors at back of retina, in front of pigmented epithelium

  • For light to reach photoreceptors, it must pass layers of neurons involved in visual processing


Organization of retina44 l.jpg
Organization of Retina

  • Signals from photoreceptors are passed to bipolar sensory neurons, then to ganglion cells

  • Axons of ganglion cells form the two optic nerves

Cone

Rod

Bipolar sensory neuron

Ganglion cell


The photoreceptors l.jpg
The Photoreceptors

  • Rods

    • Contain the pigment rhodopsin

    • Detect very dim light, changes in light intensity

  • Cones

    • Three kinds; detect red, blue, or green

    • Provide color sense and daytime vision


Hearing l.jpg
Hearing

  • Outer ear

  • Middle ear

  • Inner ear