⚙️ | Chapter 11: Nervous System and Nervous Tissue

Central nervous system (C N S)

Brain and spinal cord; Integration and command center.

Peripheral nervous system (P N S)

Spinal and cranial nerves; Carries messages to and from the spinal cord and brain.

Receptors

Detect changes in internal or external environment.

Sensory division of the P N S

Sends information to the C N S from receptors in peripheral tissues and organs.

Information processing

Integration and distribution of information occurs in the C N S.

Motor division of the P N S

Carries motor commands from the C N S.

Effectors

Respond to motor commands and change their activities.

Sensory receptors

Detect position, touch, pressure, pain, temperature.

Special sensory organs

Involved in smell, taste, sight, balance, hearing.

Somatic nervous system (SNS)

Voluntary nervous system; conscious control of movement to skeletal muscles.

Autonomic nervous system (AN)

Involuntary nervous system; automatically regulates activities to smooth muscle, cardiac muscle, glands, adipose tissue.

Neurons

Nerve cells specialized for intercellular communication.

Neuroglial cells

Support cells that are non-excitable and surround and wrap neurons.

Dendrites

Receive stimuli from the environment or other neurons; highly branched.

Cell body

Contains nucleus and organelles that provide energy and synthesize neurotransmitters.

Axon

Carries information toward other cells.

Anaxonic neurons

Small neurons lacking features distinguishing axons from dendrites; located in brain and special sense organs.

Unipolar neurons

Dendrites and axons continuous (fused); cell body off to one side; includes most sensory neurons in peripheral nervous system.

Bipolar neurons

Have two distinct processes; occur in special sense organs.

Multipolar neurons

Have two or more dendrites and a single axon; most common neurons in CNS.

Sensory neurons

Deliver information from exteroceptors, interoceptors, or proprioceptors.

Motor neurons

Form the efferent division of the PNS.

Interneurons

Located entirely within the CNS; usually between sensory and motor neurons.

Synapse

Where neuron communicates with another cell.

presynaptic cell

The cell that sends the signal in a synapse.

postsynaptic cell

The cell that receives the signal in a synapse.

Chemical Synapses

Most common, use chemical messengers to transmit signals.

synaptic cleft

Narrow space between the cells in a chemical synapse.

Neurotransmitter

Released from presynaptic membrane into synaptic cleft; binds receptors on postsynaptic membrane.

Electrical Synapses

Occur in certain CNS areas, use gap junctions for direct electrical communication.

Interoceptors

Monitor internal organs/systems; detect distension (stretch), deep pressure, pain.

Proprioceptors

Monitor position/movement of skeletal muscles/joints.

Exteroceptors

Monitor external environment (touch, temperature, pressure, input for special senses).

Neuroglia (or glial cells) of CNS

Cells that support/protect neurons; comprise ~ half the total volume of the nervous system.

Ependymal cells

Simple cuboidal to columnar epithelium that lines central canal (spinal cord) and ventricles (brain).

Microglia

Smallest and least abundant neuroglia in the CNS; act as phagocytes (macrophages of the CNS).

Astrocytes

Star-shaped glial cells; the most abundant in the CNS; maintain the blood-brain barrier.

Oligodendrocytes

Produce myelin sheaths around CNS axons.

Myelinated axons

Axons with myelin sheaths; appear white because of lipid content of myelin.

Unmyelinated axons

Axons without myelin sheath.

CNS white matter

Areas with many myelinated (whitish) axons.

CNS gray matter

Areas with mostly cell bodies, dendrites, unmyelinated axons; lack of myelin makes them appear gray.

Multiple Sclerosis (MS)

Autoimmune disorder where the immune system attacks the myelin sheath, causing inflammation and disrupting nerve communication.

Wallerian degeneration

The repair process where Schwann cells assist in repairing damaged nerves.

Neurilemma

Outer surface of Schwann cells.