Functions of the Nervous SystemFunctions of the Nervous System

1. Sensory input

Monitor changes occurring inside and outside the body

2. Integration

Processes and interprets sensory input and decide what to be done

Mainly occurs in brain and spinal cord

3. Motor output

A response to integrated stimuli by activating effector organs – muscles and glands

Functions of the Nervous SystemFunctions of the Nervous System

An example of how the nervous system uses all three functions together is when you are driving and see a red light ahead (sensory input), your nervous system integrates this information (red light means “stop”, and your foot goes for the brake pedal (motor output)

Organization of the Nervous SystemOrganization of the Nervous System Classified based on structure and function

Structure

Brain

Spinal cord

Nerves

Function

Sensory

Eyes, ears, nose

Motor

Muscles and glands

Structural ClassificationStructural Classification

Central nervous system (CNS)

Brain and spinal cord

Integrating and command center

Peripheral nervous system (PNS)

Cranial nerves and spinal nerves

Communication lines between the CNS and the rest of the body

Functional ClassificationFunctional Classification

Peripheral nervous system

Two subdivisions

Sensory (afferent) division

Carry information to the CNS

Motor (efferent) division

Carry information away from the CNS

Functional ClassificationFunctional Classification

Motor (efferent) division Two subdivisions

Somatic nervous system Voluntary and conscious control Skeletal muscles

Autonomic nervous system Involuntary and subconscious Smooth muscles, cardiac muscles and glands

Functional ClassificationFunctional Classification Autonomic Nervous System

Two subdivisions Sympathetic

Fight or flight Parasympathetic

Rest and digest

Nervous TissueNervous Tissue

Two principal types of cells

Support cells (neuroglia) Support, insulate and protect the

neurons

Cannot transmit nerve impulses

Continue to divide

4 in the CNS and 2 in the PNS

Neurons

Structural units of the nervous system

Transmit electrical impulses from one area of the body to another area using neurotransmitters

Cannot divide = amitotic

Support Cells (Neuroglia) in CNSSupport Cells (Neuroglia) in CNS

Astrocytes Abundant, star-shaped cells

Anchor and brace neurons

Form barrier and make exchanges between capillaries and neurons

Control the chemical environment of the brain by cleaning up potassium ions and neurotransmitters

Microglia Small ovoid cells with

thorny processes

Spider-like phagocytes

Dispose of debris

Support Cells (Neuroglia) in CNSSupport Cells (Neuroglia) in CNS

Ependymal cells Line central cavities of the

brain and spinal cord

Cells are squamous and columnar shaped and ciliated

Circulate cerebrospinal fluid

Oligodendrocytes

Produce myelin sheath (fatty insulation) around nerve fibers

Support Cells (Neuroglia) in PNSSupport Cells (Neuroglia) in PNS

Satellite cells Surround neuron cell bodies located in the PNS

Protection and cushioning neurons

Similar to astrocytes in CNS

Schwann cells Surround and form myelin sheath in the PNS

Help with regeneration of damaged peripheral nerve fibers

NeuronsNeurons

Structural unit of the nervous system

Highly specialized cells that conduct messages in the form of impulses from one part of the body to another

Special characteristics

Extreme longevity (about 100 years)

Amitotic (cannot divide)

High metabolic rate

Vary in structure but all have a cell body and one or more slender processes

Plasma membrane is the site of electrical signaling

NeuronsNeurons Major regions of neurons

Cell body (soma)

Nucleus and metabolic center

Most are located in the CNS

Clusters of cell bodies in the CNS are called nuclei

Lie along the nerves in the PNS are called ganglia

Processes (dendrites and axons) Arm like processes extend from the body of all neurons

Brain and spinal cord contain both cell bodies and their processes

PNS consists mainly of neuron processes

Bundles of neuron processes are called tracts (CNS) or nerves (PNS)

Neuron ProcessesNeuron Processes Dendrites

Main receptive or input region

Receive signals from other neurons

Conduct impulses toward the cell body

Axons Each neuron has only one axon

Conducting region of the neuron

Generates nerve impulses and transmits impulses away from the cell body

Initial region of the axon arises from the axon hillock

Narrows to form a slender process the rest of the length

In some neurons the axon is very short and in others it is very long

For example: axons of toes extend from the lumbar region of your spine to your foot (about 3-4 feet) – the longest cells in your body

Axons and axonal terminalsAxons and axonal terminals

Axons can branch many times but all end in axon terminals

Axonal terminals

Knoblike distal endings also called the secretory region

When impulses reaches the terminal it causes neurotransmitters to be released

Neurotransmitters either excite or inhibit neurons

Neurons never touch other neurons

Separated from the next neuron by a gap

Synaptic cleft

Gap between adjacent neurons

Axon CoveringsAxon Coverings Many axons are covered with a whitish, fatty,

segmented myelin sheath

Myelin

Covering that protects and insulates the axons and increases the speed of transmission of nerve impulses

Myelin sheath

A tight coil of wrapped membranes encloses the axon

Axon CoveringsAxon Coverings Myelin sheaths

Peripheral nervous system

Formed by Schwann cells which wrap themselves around the axon in jelly-roll fashion

Central nervous system

Formed by oligodendrocytes

Nodes of Ranvier

Adjacent Schwann cells and oligodendrocytes do not touch each other so there are gaps in the myelin sheath

Myelinated fibers conduct nerve impulses rapidly

Unmyelinated fibers conduct impulses slowly

Axon CoveringsAxon Coverings

Multiple Sclerosis (MS)

Myelin sheath in the CNS are damaged and demyelination occurs

Affects the ability of nerve cells to communicate with each other

Caused by an autoimmune disease where the body’s own immune system attacks and damages the myelin

Electrical signals are slowed or stopped from reaching different parts of the body.

Visual disturbances, problems controlling muscles, speech disturbances, and urinary incontinence

Person loses ability to control his/her muscles

Cause is unknown and there is no cure

Neuron Cell Body LocationsNeuron Cell Body Locations

Most are found in the central nervous system

White matter

Dense collections of myelinated fibers

Gray matter

Unmyelinated fibers and cell bodies

Nuclei

Clusters of cell bodies within the white matter of the central nervous system

Outside the CNS

Ganglia

Collections of cell bodies

Neuron AnatomyNeuron Anatomy

Neuron ClassificationNeuron Classification

Neurons classified based on their structure and function

Structural Classification of NeuronsStructural Classification of Neurons Multipolar neurons

Three or more processes

One axon and the rest dendrites

Most common neuron type (motor and interneurons)

Major neuron type in CNS

Bipolar neurons

Two processes

An axon and a dendrite from opposite sides of the cell body

Rare, found in special sensory organs

Unipolar neurons

Have a short single process leaving the cell body

Mainly found in ganglia of PNS (sensory neurons)

Functional ClassificationFunctional Classification

Neurons classified based on the direction the nerve impulse travels in relation to the CNS

Sensory neurons

Interneurons

Motor neurons

Functional Classification of NeuronsFunctional Classification of Neurons Sensory (afferent) neurons

Transmit impulses towards the CNS

Sensory receptors in the skin or internal organs

Cutaneous sense organs (Meissner’s and Pacinian Corpuscles)

Proprioceptors (detect stretch or tension)

Motor (efferent) neurons

Transmit impulses away from the CNS

Muscles or glands

Association (interneuron)

Found between motor and sensory neurons

In neural pathways in the CNS

Make up 99% of the neurons of the body

Functional Classification of NeuronsFunctional Classification of Neurons

Amyotrophic lateral sclerosis (ALS) “Lou Gehrig’s Disease”

Disease of the motor neurons in the CNS that control voluntary movements

Motor neurons degenerate or die and can no longer send messages to muscles

Condition gets worse and usually ends in paralysis and death in about 3-5 years

Cause is unknown (about 10% are genetic)

Amyotrophic

Muscle without nourishment

Sclerosis

Hardening of tissue