Nervous System Overview Quiz

Nervous System Overview

• The nervous system is the primary system controlling and coordinating the body
• It constantly monitors and processes sensory information from inside and outside the body

Nervous System Divisions

• Central Nervous System (CNS): Includes the brain and spinal cord.
• Peripheral Nervous System (PNS): Includes all parts outside the CNS, including nerves and sensory receptors

Nervous Tissue Cell Types

• Neurons: Handle communication and send signals.
• Neuroglia: Support and protect neurons

Neuroglia (Glial Cells)

• Also called "nerve glue"
• CNS: Astrocytes, oligodendrocytes, microglial cells, ependymal cells
• PNS: Schwann cells (neurolemmocytes), satellite cells

Functions of Neuroglia

• Support and protect fragile neurons
• Act as phagocytes (cleaning up waste and debris)
• Produce myelin for neuron extensions (oligodendrocytes in CNS, Schwann cells in PNS)
• Help with exchanges between capillaries and neurons
• Control the chemical surroundings of neurons (astrocytes)

Neuron Structure

• Cell body: Biosynthetic center, receives signals
• Dendrites: Receive signals from other neurons
• Axons: Send signals to other neurons or effector organs

Neurons (Nerve Cells)

• The basic functional units of nervous tissue.
• Specialized to send messages (nerve impulses) throughout the body.

Neuron Cell Body

• Contains the nucleus and other organelles needed for neuron function.
• Part of the receptive region, receives signals

Neuron Cell Body Structure

• Nucleus
• Neurofibrils: Cytoskeletal elements that support and aid transport within the neuron
• Chromatophilic substance: Clusters of rough endoplasmic reticulum, involved in making proteins.

Neuron Processes

• Dendrites: Receive signals
• Axons: Carry signals away from cell bodies
• Axon terminals: Endings of axons containing neurotransmitters.

Axon Terminals and Synapses

• Endings of axons
• Contain vesicles containing neurotransmitters for transmitting signals
• Connect with other neurons or effector cells at junctions called synapses

Myelin and Myelinated Fibers

• Many long nerve fibers covered by a fatty material called myelin
• A myelin sheath is made by Schwann cells, where they wrap tightly around the axon to form it in the PNS.

Discontinuous Myelin Sheath

• The myelin sheath isn't one continuous layer
• There are gaps called myelin sheath gaps or nodes of Ranvier between Schwann cells

Neuron Types

• Multipolar - multiple processes extending from cell body
• Bipolar - two processes extending from from cell body
• Unipolar (pseudounipolar) - single process extending from cell body

Classification by Function

• Sensory (Afferent): Carry signals toward the CNS
• Motor (Efferent): Carry signals away from the CNS
• Interneurons: Connect sensory and motor neurons

Structure of a Nerve

Endoneurium: Surrounds individual axons. Perineurium: Surrounds bundles of axons (fascicles). Epineurium: Encloses all fascicles, forming the nerve covering.

Cranial Nerves

• 12 pairs connected to the brain, primarily serving the head and neck
• Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal*

Spinal Cord Anatomy

• Encased within the vertebral canal and extends from the foramen magnum to the L1-L2 vertebra
• Protected by the meninges (dura mater, arachnoid mater, pia mater)
• Contains sensory and motor tracts.

Spinal Cord Damage

• Damage leads to loss of motor and sensory function in areas below the injury.

Spinal Cord Damage Consequences

• Paraplegia: Paralysis of both legs
• Quadriplegia: Paralysis of all four limbs

Spinal Nerves

• 31 pairs of mixed nerves that exit the spinal cord
• Divided into dorsal and ventral rami, forming nerve plexuses (networks of nerves)
• Each nerve supplies specific body regions (e.g., arms, legs)

Nerve Plexuses

• Networks of nerves formed by ventral rami
• Each plexus provides nerves for specific limb regions
• Cervical, Brachial, Lumbar, Sacral*

Reflexes

• Rapid, automatic, involuntary motor responses to stimuli
• Inborn or learned
• Involve sensory neurons, integration centers, motor neurons, and effectors

Autonomic Nervous System (ANS)

• Controls involuntary bodily functions:
• Smooth muscles, cardiac muscles, glands*
• Divided into sympathetic and parasympathetic divisions

Sympathetic Division & Parasympathetic Division

• Sympathetic division: "fight or flight"
• Prepares the body to respond to stressful or emergency situations*
• Parasympathetic division: "rest and digest"
• Promotes homeostasis and a relaxed state*

Aging and the Nervous System

• The sympathetic nervous system may become less efficient with age
• This can lead to orthostatic hypotension, a drop in blood pressure upon standing up because of decreased vasoconstriction.

Five Reflex Arc Components

• Receptor: Site of stimulus
• Sensory neuron: Carries impulses to the CNS
• Integration center: Processes information (monosynaptic or polysynaptic)
• Motor neuron: Carries impulses from the CNS
• Effector: Muscle fiber or gland that responds

Types of Reflexes

• Autonomic Reflexes (involuntary): Ex. Digestion, blood pressure, defecation
• Somatic Reflexes (voluntary): Ex. Stretch reflex, crossed extensor reflex, etc