BIO110 LO8/9: The Nervous System

What is the primary function of the Nervous System that must be explained?

The general role of the Nervous System in maintaining homeostasis.

What are the four main organs of the Nervous System listed in the sources?

The organs of the Nervous System are the Brain, Spinal cord, Nerves (Cranial

Spinal), and Sensory organs.

What are some of the sensory organs associated with the Nervous System?

Sensory organs include Eyes, Ears, Specialized sensory organs, and Free nerve endings (in skin).

What are the two main divisions of the Nervous System?

The two main divisions are the Central NS (CNS) and the Peripheral NS (PNS).

What structures compose the Central Nervous System (CNS)?

The Brain

spinal cord.

What is the functional role of the CNS?

The CNS is the Integrative

control centre; it interprets incoming info and dictates responses.

What structures compose the Peripheral Nervous System (PNS)?

Nerves that extend to ‘peripheral’ parts of the body (from brain

spinal cord), and All nerves (cranial

spinal).

What is the role of the PNS?

The PNS serves as the Communication network between CNS and the rest of the body.

What are the two subdivisions of the PNS (motor division)?

The two subdivisions of the PNS are the Autonomic Nervous System (ANS) and the Somatic Nervous System (SNS).

What are the characteristics and function of the Autonomic Nervous System (ANS)?

The ANS is involuntary (Visceral MOTOR nerves) and Conducts impulses from CNS → cardiac muscle, smooth muscles and glands.

What are the characteristics and function of the Somatic Nervous System (SNS)?

The SNS is voluntary (Somatic MOTOR nerves) and Conducts impulses from CNS → skeletal muscles.

What are the two divisions of the Autonomic Nervous System?

The two divisions are the Parasympathetic NS and the Sympathetic NS.

Where do the Parasympathetic NS motor neurons originate, and what is its associated function?

The Parasympathetic NS originates in the Cranial

sacral areas and is associated with ‘rest

digest’.

Where do the Sympathetic NS motor neurons originate, and what is its associated function?

The Sympathetic NS originates in the Thoracic

lumbar areas and is associated with ‘fight-or-flight’.

What are the two types of cells found in the Nervous System (NS)?

Neurons (nerve cells) and Glia/Neuroglia.

What are Neurons?

Neurons are the structural

functional units of the NS.

What are the three main parts of a Neuron?

Dendrites, Cell body, and Axon.

What are the three ways Neurons are classified according to function (direction they transmit the impulse)?

Sensory (or afferent), Motor (or efferent), and Interneurons (or central or connecting neurons).

What is the structure and function of Dendrites?

Dendrites are Branching projections that Conduct impulses to the cell body.

What is the Cell body of a neuron?

The Cell body is the Main part of the neuron and Contains the nucleus.

What is the structure and function of the Axon?

The Axon is a Long, single projection from the cell body.

What is the function of Sensory or afferent neurons?

They ‘Sense’ stimuli and Conduct impulses from receptors all over the body → brain

spinal cord.

What is the function of Motor or efferent neurons?

They Conduct impulses away from the brain

spinal cord → muscles

glands (collectively called effectors).

What are the two types of motor neurons based on function and target?

Somatic motor neurons (→ skeletal muscles) and Visceral or autonomic motor neurons (→ smooth

cardiac muscle, glands).

What is the function of Interneurons (or central or connecting neurons)?

They Conduct impulses from sensory neurons → motor neurons.

What are Glia (neuroglia)?

Glia are cells that provide support and protection for the NS.

What are the functions of Glia/Neuroglia, and how do they differ from Neurons?

They are the ‘glue’ that binds the cells of nervous tissue together structurally

functionally, but they Do NOT transmit nerve impulses.

How much more abundant are Glia than Neurons?

Glia are 5x more abundant than neurons.

What are the four types of Glia cells and where are they located?

Astrocytes, Microglia, and Oligodendrocytes (in the CNS); and Schwann cells (in the PNS).

What is the primary function of Astrocytes?

Astrocytes Wrap around

secure small blood vessels to neurons and are Part of the blood brain barrier.

What is the function of the blood brain barrier?

It Separates blood from brain tissue and Protects the brain from harmful substances that may be in the blood.

What is the function of Microglia?

Microglia act as the first and main form of active immune defense for CNS tissue (brain

spinal cord) and act as ‘macrophages’ (phagocytes) if they sense tissue damage or inflammation.

What is the function of Oligodendrocytes/Oligodendroglia?

They Help hold neurons together by extending branches to the axon of neurons, and they Form the myelin sheath (neurilemma) on axons in the CNS.

What is Myelin?

Myelin is a fatty substance that electrically insulates axons.

What is the function of Schwann cells?

Schwann cells Form myelin in the PNS.

What are the unmyelinated spaces along the neuron called?

These spaces are called nodes of Ranvier.

What type of nerve impulse transmission occurs due to the nodes of Ranvier?

The rapid and effective transmission of a nerve impulse called saltatory conduction (‘saltatory’ = ‘jumping’).

What is a Nerve?

A Nerve is made up of several bundles of axons (fascicles) in the PNS.

What is a Tract?

A Tract is a Bundle of axons in the CNS.

What is White matter composed of, and what color does it appear?

White matter is tissue composed primarily of myelinated axons and appears white in color.

What is Gray matter composed of?

Gray matter is tissue composed primarily of cell bodies and unmyelinated fibers/axons and dendrites.

What are the three layers of fibrous connective tissue that cover a nerve, based on location?

Endoneurium (surrounds individual axons), Perineurium (surrounds individual fascicles), and Epineurium (surrounds the entire nerve).

What is a Reflex arc?

A reflex arc is a specialized neuron pathway that results in a rapid involuntary or automatic response to a stimulus (called a reflex).

What are the two types of reflex responses?

A contraction by a muscle or a secretion by a gland.

What are the five components of a reflex arc?

A receptor (detects change), Sensory/afferent neuron (transmits impulse to CNS), CNS (integrating centre), Motor/efferent neuron (transmits impulses from CNS to effector), and Effector (a muscle or gland).

What are the two types of reflex arcs based on neuron components?

Two-neuron arcs (sensory neurons synapsing with motor neurons – no interneuron) and Three-neuron arcs (sensory neurons synapsing with interneurons that synapse with motor neurons).

Where are Interneurons located?

Interneurons are located entirely within the gray matter of the brain or spinal cord.

In a three-neuron arc, what is the role of the interneurons?

They ‘determine’ what, if any, action needs to happen in response to a stimulus and communicate this information to the motor neuron.

What are Two-neuron reflex arcs often referred to as, and what are they used for?

They are Simple, unlearned or ‘true reflexes’ (e.g., knee jerk; pupil dilation).

What are Three-neuron arcs associated with?

They are associated with more ‘complex responses such as response to injury/pain (WITHDRAWAL REFLEX).

What is a Nerve Impulse (or Action Potential)?

A self-propagating wave of electrical disturbance that travels along the surface of a neuron’s plasma membrane.

What is the initial mechanism that triggers a nerve impulse?

A stimulus triggers the opening of Na

How does the nerve impulse travel along the entire length of the neuron’s membrane?

The ‘electrical disturbance’ stimulates Na

What is a Synapse?

A microscopic junction between neurons (or a neuron and an effector).

What are the three structures that comprise a Synapse?

Synaptic knob, Synaptic cleft, and Plasma membrane of postsynaptic neuron.

What is the function of a Synapse regarding impulse transmission?

A synapse ensures there is only one-way transmission of a nerve impulse.

What is the Synaptic knob and what does it contain?

A Tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that Contains vesicles full of neurotransmitters.

What is the Synaptic cleft?

The Microscopic space between a synaptic knob

the plasma membrane of a postsynaptic neuron.

How does a nerve impulse get across the synapse?

With the help of chemical compounds called neurotransmitters.

What are Neurotransmitters?

Chemicals by which neurons communicate.

How is neurotransmitter action ended in the synaptic cleft?

By Reabsorption back into the synaptic knob.

What is the major neurotransmitter of autonomic nervous system responses?

Acetylcholine (ACh).

What are the functions associated with Catecholamines (noradrenaline/norepinephrine, adrenaline/epinephrine, dopamine, serotonin)?

Sleep, mood, pleasure recognition, motor function.

What is the function of Endorphins and enkephalins?

They are Morphine-like.

What two major structures compose the Central Nervous System (CNS)?

The Brain and Spinal cord.

What structures provide protection for the brain and spinal cord?

The cranial bones/skull, vertebral column/spine, and meninges.

What are the four main divisions of the Brain?

Brainstem, Cerebellum, Diencephalon, and Cerebrum.

What are the three parts of the Brainstem?

Medulla oblongata, Pons, and Midbrain.

What substance is the reticular formation in the medulla oblongata composed of?

Bits of scattered white

gray matter that are closely mixed together.

What is the function of the gray matter in the Brain Stem?

It functions as autonomic reflex centres (e.g., heartbeat, respiration, blood vessel diameter), which are called ‘vital centres’ (located in the medulla oblongata).

What is the Cerebellum?

The 2nd largest part of the brain.

What is the primary function of the Cerebellum?

It helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal posture.

What are the two major structures that compose the Diencephalon?

The Hypothalamus and Thalamus.

What is the Hypothalamus often referred to as functionally?

‘The Heart of Subconsciousness’.

What are the two major functional roles of the Hypothalamus?

It is the Major centre for controlling the ANS (involuntary actions) and Connects nervous

endocrine system.

What specific hormones are affected by the Hypothalamus?

It Controls hormone secretions via anterior and posterior pituitary glands (making hormones like ADH secreted by the posterior pituitary gland).

What other functions does the Hypothalamus control?

Appetite control, body temp, water balance, sleep

wakefulness, pleasure, anger, sexual arousal, and pain.

What is the structure of the Thalamus?

A Dumbbell shaped mass of grey matter in each cerebral hemisphere.

What is the main function of the Thalamus regarding sensory information?

It Receives all sensory information (except for smell), then directs impulses from sensory organs to sensory areas in the brain for conscious interpretation.

What emotional and survival functions is the Thalamus associated with?

Association of sensations with emotions (pleasant or unpleasant) and playing a role in the body’s arousal/alertness mechanism (alerting us to danger).