3. the nervous system

The Nervous System

• A network of billions of nerve cells linked together in a highly organized fashion to form the rapid control center of the body.

• Functions include:– Integrating center for homeostasis,

movement, and almost all other body functions.

– The mysterious source of those traits that we think of as setting humans apart from animals

The nervous system also allows you to react to a stimulus.

A stimulus is a change in the environment.

Example: A hot stove

Or… tripping over a rock

Your reactions are

Automatic means that you do not have to think about your

reactions.Example: If a bug flies by your eye,

you will blink.

Basic Functions of the Nervous System

1. Sensation• Monitors changes/events occurring in and outside

the body. Such changes are known as stimuli and the cells that monitor them are receptors.

2. Integration• The parallel processing and interpretation of sensory

information to determine the appropriate response

3. Reaction• Motor output.

– The activation of muscles or glands (typically via the release of neurotransmitters (NTs))

Nervous vs. Endocrine System

• Similarities:– They both monitor stimuli and react so as

to maintain homeostasis.

• Differences:– The NS is a rapid, fast-acting system

whose effects do not always persevere. – The ES acts slower (via blood-borne

chemical signals called H _ _ _ _ _ _ _) and its actions are usually much longer lasting.

Organization of the Nervous System

2 big initial divisions:1. Peripheral Nervous System

• The nervous system outside of the brain and spinal cord

• Consists of:– 31 Spinal nerves

» Carry info to and from the spinal cord

– 12 Cranial nerves » Carry info to and from the brain

2. Central Nervous System• The brain + the spinal cord

– The center of integration and control

Peripheral Nervous System

• Responsible for communication btwn the CNS and the rest of the body.

• Can be divided into:– Sensory Division

• Afferent division– Conducts impulses from receptors to the CNS– Informs the CNS of the state of the body interior and

exterior– Sensory nerve fibers can be somatic (from skin,

skeletal muscles or joints) or visceral (from organs w/i the ventral body cavity)

– Motor Division • Efferent division

– Conducts impulses from CNS to effectors (muscles/glands)

– Motor nerve fibers

Peripheral Nervous System

• 3 kinds of neurons connect CNS to the body– sensory– motor– interneurons

• Motor - CNS to muscles and organs

• Sensory - sensory receptors to CNS

• Interneurons: Connections Within CNS

SpinalCord

Brain

Nerves

Motor Efferent Division

• Can be divided further:– Somatic nervous system• VOLUNTARY (generally)• Somatic nerve fibers that conduct impulses

from the CNS to skeletal muscles

– Autonomic nervous system• INVOLUNTARY (generally)• Conducts impulses from the CNS to smooth

muscle, cardiac muscle, and glands.

Peripheral Nervous System

Skeletal(Somatic)

Sympathetic Parasympathetic

Autonomic

Peripheral Nervous System

Autonomic Nervous System• Can be divided into:

– Sympathetic Nervous System• “Fight or Flight”

– Parasympathetic Nervous System• “Rest and Digest”

These 2 systems are antagonistic.Typically, we balance these 2 to keep ourselves in a state of dynamic balance.We’ll go further into the difference between these 2 later!

Autonomic System

• Control involuntary functions– heartbeat– blood pressure– respiration– perspiration– digestion

• Can be influenced by thought and emotion (Hypothalamus)

Parasympathetic

• “ Rest and digest” system• Calms body to conserve and

maintain energy• Lowers heartbeat, breathing

rate, blood pressure

Sympathetic

• “ Fight or flight” response• Release adrenaline and noradrenaline • Increases heart rate and blood pressure• Increases blood flow to skeletal muscles• Inhibits digestive functions

Nervous Tissue

• Highly cellular– How does this

compare to the other 3 tissue types?

• 2 cell types1. Neurons• Functional, signal

conducting cells

2. Neuroglia• Supporting cells

1.

2.

Cells of Nervous System

• Neurons or nerve cells– Receive stimuli and

transmit action potentials

– Organization• Cell body or soma• Dendrites: Input• Axons: Output

• Neuroglia or glial cells– Support and protect

neurons

Neurons• The functional and structural unit of the nervous

system• Specialized to conduct information from one part of the

body to another• There are many, many different types of neurons but

most have certain structural and functional characteristics in common:- Cell body (soma)

- One or more specialized, slender processes (axons/dendrites)

- An input region (dendrites/soma)

- A conducting component (axon)

- A secretory (output) region (axon terminal)

Neuroglia• Outnumber neurons by about

10 to 1 (the guy on the right had an inordinate amount of them).

• 6 types of supporting cells– 4 are found in the CNS:

1. Astrocytes• Star-shaped, abundant, and

versatile• Guide the migration of

developing neurons• Act as K+ and NT buffers• Involved in the formation of the

blood brain barrier• Function in nutrient transfer

Neuroglia

2. Oligodendrocytes

• Produce the myelin sheath which provides the electrical insulation for certain neurons in the CNS

Neuroglia of CNS

3. Ependymal Cells– Line brain ventricles and spinal cord central canal– Help form choroid plexuses that secrete CSF

4. Microglia– Specialized macrophages

• 2 types of glia in the PNS

1. Satellite cells• Surround clusters of

neuronal cell bodies in the PNS

• Unknown function

2. Schwann cells• Form myelin sheaths

around the larger nerve fibers in the PNS.

• Vital to neuronal regeneration

Neuroglia

The Central Nervous System is made of the brain and the spinal

cord.

The Central Nervous System controls everything in the body.

An organ that controls your emotions, your thoughts, and every movement you make.

Spinal cord •conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain •conducts motor information from the brain to our various effectors

•skeletal muscles •cardiac muscle •smooth muscle •glands

•serves as a minor reflex center

SpinalCord

Brain

White Matter vs. Gray MatterBoth the spinal cord and the brain consist of: white matter = bundles of axons each coated with a sheath of myelin gray matter = masses of the cell bodies and dendrites — each covered with synapses.

In the spinal cord, the white matter is at the surface, the gray matter inside

The MeningesBoth the spinal cord and brain are covered in three continuous sheets of connective tissue, the meninges. From outside in, these are the -dura mater — pressed against the bony surface of the interior of the vertebrae and the cranium -arachnoid -pia materThe region between the arachnoid and pia mater is filled with cerebrospinal fluid (CSF).

CSF Flow

• CSF– Produced in the

lateral ventricles

– Absorbed by thearachnoid villi

Arachnoid Villi

Arachnoid

Dura

The arachnoid villiare specialized“absorbing” filters

Brain Support

• Bone– Face Attachment– Holds CSF and Supports Meninges

• Meninges– Main brain support– Suspends, Compartmentalizes, and Coats

• Cerebrospinal Fluid– In a bony container, allows dissipation of

sudden shocks (forces)

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

Parts of the Brain

The HindbrainThe main structures of the hindbrain (rhombencephalon) are the medulla oblongata ponscerebellum

Medulla oblongataNerve impulses arising here rhythmically stimulate the intercostal muscles and diaphragm — making breathing possible. •regulate heartbeat •regulate the diameter of arterioles thus adjusting blood flow.

The neurons controlling breathing have mu (µ) receptors, the receptors to which opiates, like heroin, bind. This accounts for the suppressive effect of opiates on breathing. Destruction of the medulla causes instant death

Pons•serve as a relay station carrying signals from various parts of the cerebral cortex to the cerebellum. •Nerve impulses coming from the eyes, ears, and touch receptors are sent on the cerebellum. •The pons also participates in the reflexes that regulate breathing.

Cerebellum

•It represents only 10% of the weight of the brain, it contains as many neurons as all the rest of the brain combined. •Its most clearly-understood function is to coordinate body movements. People with damage to their cerebellum are able to perceive the world as before and to contract their muscles, but their motions are jerky and uncoordinated. •So the cerebellum appears to be a center for learning motor skills.

The Forebrain•The human forebrain (prosencephalon) is made up of a pair of large cerebral hemispheres, called the telencephalon. •the left hemisphere of the forebrain deals with the right side of the body and vice versa. •a group of structures located deep within the cerebrum, that make up the diencephalon

Diencephalon•Thalamus

All sensory input (except for olfaction) passes through these paired structuressignals from the cerebellum pass through them on the way to the motor areas of the cerebral cortex.

•Lateral geniculate nucleus (LGN). All signals entering the brain from each optic nerve enter a LGN and undergo some processing before moving on the various visual areas of the cerebral cortex.

Hypothalamus. •The seat of the autonomic nervous system. Damage to the hypothalamus is quickly fatal as the normal homeostasis of body temperature, blood chemistry, etc. goes out of control. Posterior lobe of the pituitary. Receives •vasopressin and •oxytocin from the hypothalamus and releases them into the blood.

Parts of the Brain

Parts of the Brain

Left hemisphere: Logical, Analytic, Quantitative, Rational and Verbal

Right hemisphere: Conceptual, Holistic, Intuitive, Imaginative and Non-Verbal

The left brain process information in logical analytical stages

Right side – The Artistic Brain

Look at the chart and say the COLOUR not the word

YELLOW BLUE ORANGEBLACK RED GREEN

PURPLE YELLOW REDORANGE GREEN BLACK

BLUE RED PURPLEGREEN BLUE ORANGELeft - Right Conflict

Your right brain tries to say the colour butyour left brain insists on reading the word.

Are both smiling figures?

Problem in recognizinginvertedimages

Are both smiling figures ?

* The spinal cord sends messages to the brain.

* The spinal cord is the part of the nervous system that connects the brain to the rest of the nervous system.