NERVOUS SYSTEM

C H A P T E R 2 8

CAN AN INJURED SPINAL CORD BE FIXED?

– Injuries to the spinal cord disrupt communication

between the central nervous system (brain and

spinal cord) and the rest of the body

– There are millions of nerve fibres make up the spinal cord, it is well

protected by vertebrae from being severed but they can be crushed

resulting in scar tissue that impedes the signals from passing

– There are different locations where these injuries can occur from resulting

in debilitating injury

CHRISTOPHER REEVE– The late actor Christopher Reeve

• Suffered a spinal cord injury during an equestrian competition

• Two vertebrae were in his neck were fractured, crushing the spinal cord at the base of his skull and causing quadriplegia

• Was an influential advocate for spinal cord research

UNIT M & N STANDARDS

• Core

– I can create a graphic organizer for the divisions of the nervous system.

– I can relate parts of the brain to various body functions.

– I can describe how the nervous and endocrine systems work together and provide a relevant

example.

– I can compare and contrast sympathetic to parasympathetic nervous responses.

– I can explain overall function of a reflex arc.

• Advanced

– I can compare and contrast structures and functions of 3 kinds of neurons.

– I can provide an overview of the nervous impulse.

– I can provide an overview of the synaptic gap process.

Crash Course – Intro to the Nervous System

28.1 - NERVOUS SYSTEM STRUCTURE AND FUNCTION

• Nervous systems receive sensory input, interpret it, and send out appropriate commands

– Nervous systems, are the most intricately organized data-processing systems on Earth

• A neuron consists of a cell body with

– A nucleus and organelles

– Long thin extensions called neuron fibres that convey signals

TWO MAIN DIVISIONS

Two main divisions are:

• The central nervous system (CNS)

– Consists of brain and spinal cord

• The peripheral nervous system (PNS)

– Is mostly made up of communication lines

called nerves that carry signals into and

out of the CNS

– The PNS also has ganglia, which are

clusters of neuron cell bodies

ORGANIZATION OF A NERVOUS SYSTEM

• The nervous system obtains and processes sensory

information

– And sends commands to effector cells, such as muscles,

that carry out appropriate responses

• It is organized as

– Sensory input: conduction from sensory receptors

– Integration: interpretation of the sensory signals

– Motor output: is the conduction of signals from the

integration centres to the;

– Effector cells, such as a muscle or gland

AUTOMATIC RESPONSES

• Our body has automatic responses called reflexes

THREE FUNCTIONAL TYPES OF NEURONS

• Sensory Neurons: convey signals

(information) from sensory receptors

into the CNS

• Interneurons: Located entirely in CNS;

integrate data and relay appropriate

signals to other interneurons or motor

neurons

• Motor Neurons: convey signals from the

CNS to effector cells

THREE FUNCTIONAL TYPES OF NEURONS

28.2 - NEURONS ARE THE FUNCTIONAL UNITS OF NERVOUS SYSTEMS

• Neurons are cells specialized for carrying signals and consist of

• A cell body

• Two types of extensions (fibers) that conduct signals,

– Numerous dendrites and axons

DENDRITES AND AXONS

• Dendrites are highly branched extensions that receive signals from other neurons and convey

this information toward the cell body

• Axons are typically longer extensions that that transmit signals to other cells which may be

other neurons or effector cells

– Axons from your spinal cord to muscle cells in your feet (1m long!)

SUPPORTING CELLS

• Supporting cells, known as glial cells are essential for the structural integrity

and normal functioning

– Schwann Cells (PNS) or Oligodendrocytes (CNS)

– Covered in a myelin sheath (insulation)

– Nodes of Ranvier: are the only point on axons where signals can be transmitted

NERVE SIGNALS AND THEIR TRANSMISSION

• A neuron maintains a membrane

potential across its membrane

• At rest, a neuron’s plasma membrane has

an electrical voltage called the resting

potential

THE RESTING POTENTIAL

• The resting potential

– Exists because of differences

in ionic composition of the

fluids inside and outside of

the cell

– K+ freely flows out, leaving

an excess of negative charge

– Is caused by the membrane’s

ability to maintain a positive

charge on its outer surface

opposing a negative charge

on its inner surface

28.4 - A NERVE SIGNAL BEGINS AS A CHANGE IN THE MEMBRANE POTENTIAL

– A stimulus alters the permeability of a portion of the

membrane allowing ions to pass through and changing the

membrane’s voltage

– A nerve signal, called an action potential

• Is a change in the membrane voltage from the resting potential

to a maximum level and back to the resting potential

28.5 - THE ACTION POTENTIAL PROPAGATES ITSELF ALONG THE NEURON• Action potentials

– Are self-propagated in a

one-way chain reaction

along a neuron

– Are all-or-none events

– The frequency of action

potentials change but

not their strength

– Will only change in

frequency with strength

in stimulus

Crash Course – Action Potentials

PROPAGATION OF THE ACTION POTENTIAL ALONG AN AXON

• 1. When this region of the axon (blue) has its

Na+ channels open, NA+ rushes inward (blue

arrows), and an action potential is generated

• 2. Soon, the K+ channels in that same region

open allows K+ to diffuse out of the axon (green

arrows), Na+ channels are closed and

inactivated. Downswing of AP

• 3. Short time later, no signs of an AP because

axon has returned to its resting potential

1

2

3

28.6 – NEURONS COMMUNICATE AT SYNAPSE

• When an action potential reaches then end of an axon, it generally stops there.

• Action potentials are not transmitted from cell to cell rather information is transmitted at a

synapse

• Synapses come in two varieties

1. Electrical

2. Chemical

ELECTRICAL SYNAPSE

• Electrical synapses pass electrical current

directly from one neuron to the next

• The receiving neuron is stimulated quickly and

the same frequency of action potentials as the

sending neurons

– Electrical synapses are found in the heart and

digestive tract, where nerve signals maintain

steady, rhythmic muscle contractions

CHEMICAL SYNAPSES

• Chemical synapses have a narrow gap called

the synaptic cleft which separates the

sending neuron from the receiving neuron

• The electrical signal of the action potential

is converted to a chemical signal

• The chemical signal consists of molecules

called neurotransmitters that are stored in

synaptic vesicles which are secreted out

into the synaptic cleft

• The neurotransmitter

– crosses the synaptic cleft and binds to a

receptor on the surface of the receiving cell

NEURON COMMUNICATION

28.7 - CHEMICAL SYNAPSES MAKE COMPLEX INFORMATION PROCESSING POSSIBLE

• A neuron may receive

information from hundreds of

other neurons via thousands of

synaptic terminals

• Neurons can have excitatory

neurotransmitters (green) and

inhibitory (red) which can create

more action potentials or

decrease action potentials

respectively.

• The summation of excitation and

inhibition determines whether or

not a neuron will transmit a

nerve signal

28.8 - A VARIETY OF SMALL MOLECULES FUNCTION AS NEUROTRANSMITTERS

• Many small, nitrogen-containing molecules serve as neurotransmitters

– Acetylcholine is important in the brain and synapses between motor neurons and

muscle cells

– They can act as both excitatory and inhibitory

– Biogenic amines are derived from amino acids

– These biogenic neurotransmitters are important in the CNS

– Epinephrine, norepinephrine, serotonin, dopamine

NEUROTRANSMITTERS

• Serotonin and dopamine – affect sleep, mood,

attention and learning

– Imbalances lead to various disorders

• Lack of dopamine – Parkinson’s Diseases

• Excess of dopamine – Schizophrenia

• Reduced norepinephrine and serotonin – types of

depression

• LSD – ‘Acid’ produces hallucinogenic effects by

binding to serotonin and dopamine receptors in the

brain

NEUROTRANSMITTERS CONT’D

• Four amino acid based neurotransmitters in CNS

– Aspartate and glutamate – excitatory

– Glycine and GABA (gamma aminobutyric acid) are

inhibitory

• Peptides can make neurotransmitters

– Substance P – mediates our perception of pain

– Endorphins are both neurotransmitters and hormones

– decrease pain during physical and emotional stress

• Dissolved gases – Nitric Oxide (NO) for E.D.

Crash Course – Synapses and Neurotransmitters

28.9 MANY DRUGS ACT AT CHEMICAL SYNAPSES• Many psychoactive drugs act at synapses and affect neurotransmitter action

A N I M A L N E R V O U S S Y S T E MP T 2

28.11 - VERTEBRATE NERVOUS SYSTEMS ARE HIGHLY CENTRALIZED AND CEPHALIZED

• Skip 28.10

• The spinal cord runs lengthwise inside the vertebral

column and conveys the information from the brain

and integrates simple responses to certain kinds of

stimuli like the knee-jerk reflex

• The brain includes the homeostatic centers that

keep the body functioning smoothly

• The brain capillaries are the most selective to allow

nutrients and oxygen in and keep other chemicals

out using the blood brain barrier

COMPONENTS OF THE CNS

• Both the brain and the spinal cord

have fluid-filled spaces

• Ventricles in the brain are

continuous with the narrow canal

of the spinal cord

• These cavities are filled with

cerebrospinal fluid, which is the

formed in the brain by filtering the

blood.

• Also protecting the brain are the

meninges, layers of connective

tissue

GRAY AND WHITE MATTER

• White matter is mostly composed of axons with their myelin

sheaths

• Gray matter consists mainly of nerve bodies and dendrites

• Cranial nerves originate in the brain and terminate in structures in

the head and upper body

• Spinal nerves originate in the spinal cord and extend to everything

else!

28.12 THE PERIPHERAL NERVOUS SYSTEM OF VERTEBRATES IS A FUNCTIONAL HIERARCHY

• The PNS can be divided into two functional

components

– The somatic nervous system and the

autonomic nervous system

• The somatic nervous system

– Carries signals to and from skeletal muscles,

mainly in response to external stimuli

• The autonomic nervous system

– Regulates the internal environment by

controlling smooth and cardiac muscles and

the organs of various body systems

Crash Course – PNS

28.13 OPPOSING ACTIONS OF SYMPATHETIC AND PARASYMPATHETIC NEURONS REGULATE THE INTERNAL ENVIRONMENT

• The autonomic nervous system

• The parasympathetic division of the

autonomic nervous system

– Primes the body for activities that gain and

conserve energy for the body

• The sympathetic division of the autonomic

nervous system

– Prepares the body for intense, energy-

consuming activities

Crash Course – Autonomic Nervous System

28.14 THE VERTEBRATE BRAIN DEVELOPS FROM THREE ANTERIOR BULGES OF THE NEURAL TUBE

• The vertebrate brain develops from the

forebrain, midbrain, and hindbrain

• The size and complexity of the

cerebrum in birds and mammals

correlates with their sophisticated

behavior

28.15 THE STRUCTURE OF A LIVING SUPERCOMPUTER: THE HUMAN BRAIN• The human brain is more powerful than the most sophisticated computer

• The human brain is composed of three main parts

– The forebrain, the midbrain, and the hindbrain

MAJOR STRUCTURES OF THE HUMAN BRAIN

THE BRAIN

• The midbrain and subdivisions of the hindbrain, together with the thalamus and hypothalamus

– Function mainly in conducting information to and from higher brain centers

– Regulate homeostatic functions, keep track of body position, and sort sensory information

• The forebrain’s cerebrum

– Is the largest and most complex part of the brain

THE BRAIN CONT’D

• Most of the cerebrum’s integrative

power resides in the cerebral

cortex of the two cerebral

hemispheres

28.16 THE CEREBRAL CORTEX IS A MOSAIC OF SPECIALIZED, INTERACTIVE REGIONS

• Specialized integrative regions of the

cerebral cortex include

– The somatosensory cortex and centers for

vision, hearing, taste, and smell

• The motor cortex

– Directs responses

• Association areas

– Concerned with higher mental activities such

as reasoning and language, make up most of

the cerebrum

• The right and left cerebral hemispheres

– Tend to specialize in different mental tasks

28.19 THE LIMBIC SYSTEM IS INVOLVED IN EMOTIONS, MEMORY, AND LEARNING

• The limbic system

– Is a functional group of

integrating centers in the

cerebral cortex, thalamus, and

hypothalamus

– Is involved in emotions,

memory, and learning