Nervous Tissue and Organization of the Nervous System

Organization of the Nervous System

Nervous system can be divided structurally (by organs) and functionally (by function):

- Structural division:

central and peripheral nervous system

Organization of the Nervous System

Nervous system can be divided structurally (by organs) and functionally (by function):

- Functional division:

somatic, autonomic, and enteric nervous system

Structural Division of the Nervous System

Central Nervous System (CNS): composed of

brain and spinal cord; processes and integrates the signals coming from the peripheral nervous system and initiates the response.

Structural Division of the Nervous System

Central Nervous System (CNS):
- Neurons are located

in nuclei (plural of nucleus)

Structural Division of the Nervous System

Central Nervous System (CNS):
- The projections of neurons

are called tracts (or columns)

Structural Division of the Nervous System

Peripheral Nervous System (PNS): composed of

ganglia (group of neurons) and nerves (bundles of axons; cranial and spinal); senses the external and internal environment, sends the information to the central nervous system and carries out the response from it.

Structural Division of the Nervous System

Peripheral Nervous System (PNS):
- Neurons are located

in ganglia (plural of ganglion).

Structural Division of the Nervous System

Peripheral Nervous System (PNS):
- The projections of neurons are called

nerves when outside of the central nervous system. Cranial nerves emerge from the brain and spinal nerves exit from the spinal cord.

Basic Functions of the Nervous System

The basic functions of the nervous system

are sensation, integration and response.

Basic Functions of the Nervous System

Sensation:

the nervous system receives information on changes of the external and internal environment. These changes are called stimuli (plural for stimulus) and are perceived by peripheral sensory structures.

Basic Functions of the Nervous System

Integration:

stimuli are communicated to the brain and spinal cord where that information is processed.

Basic Functions of the Nervous System

Response:

the nervous system produces a motor response to the stimulus. The response involves movement of skeletal muscles (voluntary), cardiac or smooth muscles or glands (involuntary).

Functional Division of the Nervous System

Somatic nervous system:

responsible for conscious perception and voluntary motor responses of skeletal muscles. Includes sensory ganglia, structures of special senses, brain, spinal cord and nerves.

Functional Division of the Nervous System

Autonomic nervous system:

responsible for involuntary control of cardiac muscle, smooth muscle and glands everywhere in the body. Includes autonomic neurons in the brain and spinal cord, some cranial and spinal nerves and autonomic ganglia.

Functional Division of the Nervous System

Enteric nervous system:

responsible for involuntary control of the smooth muscle and glands in the digestive system. Includes nervous structures within the digestive system.

Somatic, Autonomic and Enteric Divisions of the Nervous System

Somatic Sensation

Somatic, Autonomic and Enteric Divisions of the Nervous System

Autonomic Sensation

Somatic, Autonomic and Enteric Divisions of the Nervous System

Enteric Sensation

Somatic, Autonomic and Enteric Divisions of the Nervous System

Somatic Intergration

Somatic, Autonomic and Enteric Divisions of the Nervous System

Autonomic Intergration

Somatic, Autonomic and Enteric Divisions of the Nervous System

Enteric Intergration

Somatic, Autonomic and Enteric Divisions of the Nervous System

Somatic Motor Response

Somatic, Autonomic and Enteric Divisions of the Nervous System

Autonomic Motor Response

Somatic, Autonomic and Enteric Divisions of the Nervous System

Enteric Motor Response

Nervous Tissue

Located in

the central and peripheral nervous system.

Nervous Tissue

Nervous Tissue

•Cells:

Neurons: responsible for the

electrical signals that communicate information about sensations, and that produce movements in response to those stimuli, along with inducing thought processes within the brain. Large, non-mitotic cells.

Nervous Tissue

•Cells:

Glia (or neuroglia, or glial cells): considered

to be supporting cells, and many functions are directed at helping neurons complete their function for communication.

Neurons

Conduct nerve

impulses from one place to another

Neurons

Special characteristics:

•High metabolic rate: rely on glucose and oxygen

•Extreme longevity: sometimes a lifetime

•Nonmitotic: cannot divide and form new cells

•Excitable: generate electrical signals

•Conductive: propagate electrical signals

Neuron Structure I

Dendrites:

processes (extensions) that receive information.

Neuron Structure I

Soma:

cell body of a neuron, containing nucleus and organelles

Neuron Structure I

Axon:

process that carry the information from the soma. Neurons have only one axon.

Neuron Structure II

Axon:

The axon emerges from the axon hillock and is covered by glial cells that form the myelin. The axon ends in branches at the axon terminal and the branches enlarge at their ends to form a synaptic end bulb. Axons that exit the CNS are bundled together in nerves.

Neuron Structure II

Nodes of Ranvier:

gaps between the myelin that expose the axon

Functional Classification of Neurons

This classification depends on

which function the neuron is carrying out: sensation, integration or motor.

Functional Classification of Neurons

Sensory neurons:

their dendrites are receiving sensory information, sometimes directly from the stimulus itself. Found in PNS. They can be unipolar, bipolar or multipolar. They can be somatic or autonomic.

Functional Classification of Neurons

Interneurons:

carry out integrative functions (such as retrieve, process and store information) and facilitate communication between sensory and motor neurons. Only found in CNS. They are multipolar neurons and the majority of neurons.

Functional Classification of Neurons

Motor neurons:

carry commands from the brain and spinal cord to muscles and glands. Found in CNS (somatic) or autonomic ganglia. They are multipolar neurons.

Glial Cells

Neuroglia (glial cells) protect

and nourish neurons; help forming synapses and maintaining them; clear out dying neurons; adjust electrical signals of neurons.

Glial Cells

Found in both

CNS and PNS

Glial Cells

Smaller and more

numerous than neurons

Glial Cells

Capable

of mitosis

Glial Cells

Brain tumors are more

likely to be derived from glial cells than neurons

Glial Cells of the CNS I

Astrocytes:

have many processes extending from their main cell body that extend to interact with neurons, blood vessels, or the connective tissue covering the CNS. Form the blood-brain barrier (BBB).

Glial Cells of the CNS I

Ependymal cells:

filter blood to make cerebrospinal fluid (CSF), the fluid that circulates through the CNS.

Glial Cells of the CNS II

Oligodendrocytes:

cover axons with myelin in the CNS. One oligodendrocyte wraps around multiple axons.

Glial Cells of the CNS II

Microglia:

smaller than most of the other glial cells. They are the CNS-resident immune cells that ingest and digest dying cells or pathogens that cause disease.

Glial Cells of the PNS

Satellite cells:

surround cell bodies of neurons in ganglia to provide support. Found in sensory and autonomic ganglia.

Glial Cells of the PNS

Schwann cells:

cover axons with myelin in the PNS. Wrap around a portion of one axon, so that one axon is covered by multiple Schwann cells.