4a Introducing The Nervous System Flashcards
What is the nervous system?
A body system that integrates and generates appropriate rapid responses to maintain homeostasis
What are the functions of the nervous system?
Sensory input: detecting changes (stimuli) occurring inside and outside the body
Integration: processes and interprets sensory input and determines course of action
Motor output: a response or effect that activates muscles or glands
SIM
What kind of stimuli could be considered sensory input?
Changes in: pressure, light, taste, blood pH, sound and hormone levels
Basically anything detected by the 5 senses
What kind of response can be considered a motor output?
Movement
Changes in heart rate
Release of hormones
Sweating
Release/storage of glucose
What is a motor output caused by?
Caused by an electrochemical signal transmitted to organs from the CNS that is converted into some form of action
Nerve fibers that carry impulses away from CNS organs to effector organs
What components are the nervous system divided into? Be specific.
Structural:
-Central Nervous System: brain and spinal cord
-Peripheral Nervous System: cranial and spinal nerves
Functional:
Parasympathetic and sympathetic systems
What type of motor outputs are there?
Somatic: voluntary
Autonomic: involuntary
What do cranial and spinal nerves do?
Carry nerve impulses to and from the brain and spinal cord respectively
What is the function of the CNS vs the PNS?
CNS: integration (command center), interprets incoming sensory information, issues outgoing instructions
PNS: serves as communication lines among sensory organs, the brain and spinal cord, and glands or muscles
What are the two sensory divisions? Are they afférent or efferent?
Both afferent
Somatic sensory: fibers carry info from skin, skeletal muscles and joints
Visceral sensory: fibers carry info from visceral organs
What are the two motor divisions? Are they afferent or efferent?
Both efferent
Somatic nervous system: conscious or voluntary, controls skeletal muscles
Autonomic nervous system: automatic or involuntary, controls smooth and cardiac muscles and glands
What is the autonomic nervous system further divided into?
Sympathetic (fight or flight) and Parasympathetic (rest and digest)
Describe the path a stimulus would take to elicit a response from the body.
- Sensory organs detect the stimulus
- Sensory receptors send the information to the CNS (command center) via the nerves of the PNS
- The CNS integrates and processes the information, decides the appropriate response
- CNS sends a motor signal through the PNS to either a component of the parasympathetic or sympathetic nervous system
- If a quick reaction is required, it’ll be the sympathetic nervous system
- if it is not required, it’ll be the parasympathetic nervous system
What are the types of nerve cells/tissues? Describe.
Neuroglia: supporting cells, providing structural support, protection, growth factors and insulating sheaths
Neurons: excitable cells that generate and transmit nerve impulses
What is a nerve impulse?
An electrochemical signal or message
What is the ratio of Neuroglia to neurons?
10:1
What are the types of Neuroglia (CNS)?
-Astrocytes
-Microglial cells
-Ependymal cells
-Oligodendrocytes
Shape of astrocytes? Function?
Abundant, star shaped
Function:
-Brace and anchor neurons to blood capillaries
-Absorb excess k+ and neurotransmitter released from neurons
-Mediate exchanges between blood capillaries and neurons
-Provides nutrients to neurons
(BAMP)
What are microglial cells? Function?
Phagocytes that defend CNS cells
Monitor health of nearby neurons
Engulf debris (dead brain cells) and bacteria (défense)
What are ependymal cells? Function?
Line cerebrospinal fluid-filled cavities (brain and spinal cord)
Produce cerebrospinal fluid
Ciliated: cilia assist with circulation of cerebrospinal fluid
What is CSF?
Cerebrospinal fluid
For protection, regulation of blood pressure and chemical transport for brain
Derived from blood plasma so many of the same constituents as blood
What are oligodendrocytes? Function?
Produce myelin sheaths to wrap around multiple nerve fibers
What is the purpose/function of myelin sheaths?
Speed up conduction of nerve impulses
What are the types of Neuroglia in the PNS?
Satellite cells and Schwann cells
What do satellite cells do?
Protective cushioning of neuron cell bodies, literally a cushy blanket cocoon
What do Schwann cells do?
Produce myelin sheaths around nerve fibers
What are the differences and similarities between schwann cells and oligodendrocytes?
Schwann cells wrap around one axon, its protection is limited and localized to that axon
Oligodendrocytes wrap around multiple axons
Both produce myelin sheaths and speed up signaling
What are neurons? Characteristics and functions?
Functional unit of nervous system
High metabolic rate, requires continuous supply of O2 and glucose
Generates and conducts nerve impulses
Results in excitation or inhibition of neighbouring neuron, muscle or gland
What is the structure of a neuron?
Cell body: metabolic center, has organelles, neurofibrils for cell shape but no centrioles
Dendrites: fibers conducting impulses toward the cell body, a single neuron may have hundreds of dendrites
Axon: fibre conducts impulse away from cell body, a neuron has only 1 axon
Why do neurons, specifically the cell body, not have centrioles?
Because they are non-mitotic (will not divide)
Where does the axon of the neuron begin? End? Whats in between?
Begin: axon hillock (little tail from cell body leading to axon, before the myelin sheath)
End: axon terminals, contain neurotransmitters
Between the end of a neuron and the beginning of the next: synapse or synaptic cleft
What is a myelin sheath?
A white fatty material that covers most of the axons in the PNS and some in the CNS
What is an axon covered in myelin sheaths called?
Myelinated axons
What type of cells form myelin sheaths in the CNS? PNS?
CNS: Oligodendrocytes
PNS: Schwann cells
Describe myelin sheath formation in Schwann cells and oligodendrocytes.
Schwann
Schwann cell rolls around the axon at the same spot in layers
The cytoplasm and nucleus are forced to the outer region of the cell (external to the sheath) called the neurilemma
Oligodendrocytes
Same as Schwann process except there is no neurilemma
Why is there no neurilemma in the myelin sheaths in the CNS? Consequences?
Myelin sheaths in the CNS are formed by oligodendrocytes which do not fully wrap around the axon but rather their extensions do, so the nucleus and cytoplasm doesnt wrap as in Schwann cells
Consequence: the axons and myelin sheaths in the CNS are not capable of regeneration, but those in the PNS are to some extent
What is the function of myelin sheaths?
To protect the axon
Ions cannot enter or exit the axon in regions surrounded by myelin
-This provides electrical insulation that increases the rate of conduction of a nerve impulse (faster communication)
What are the gaps between schwann cells called and what is their purpose?
Nodes of Ranvier
To allow Saltatory conduction
What is saltatory conduction?
The transmission of electrical signals by “jumping” from gap to gap to increase the speed of conduction
What is MS?
Multiple Sclerosis
An autoimmune disease in which the myelin sheaths in the brain and spinal cord are progressively destroyed in a process called demyelination
The scars (scleroses) slow the transmission of nerve impulses and eventually stop the transmission altogether
What are the consequences of MS? Treatment?
Can result in paralysis and loss of sensation
Loss of vision
Affects primarily young adults
Treatment: drugs that modify immune system
What differentiates the different structural classifications of neurons and what are they?
The number of processes that extend from the cell body
Multipolar: multiple processes
Bipolar: 2 processes extending from body
Unipolar: only one process extending from cell body into dendrites
Where can you find multipolar neurons?
In motorneurons and interneurons
Where can you find bipolar neurons?
Special sense organs (nose, eyes, ear)
Special note: rare in adults
Characteristic of unipolar neurons?
Majority of sensory neurons
What are the functional classifications of neurons?
Sensory neurons
Interneurons
Motor neuron
What does the sensory neuron do and is it afférent or efferent?
Afférent
Carries impulse from sensory receptors to CNS
Note: all receptors, dendrites and cell bodies are located in PNS, only axons are occasionally in the CNS
What does the motor neuron do and is it efferent or afférent?
Efferent
Carries impulses from CNS to visceral, muscles and glands
Note: dendrites and cell body located in CNS (to talk to interneurons)
What do the interneurons do and what are they also known as?
Association neurons
Connect sensory and motor neurons
Cell bodies located in the CNS, whole thing
What are sensory receptors and what are the types?
Specialized receptors formed by dendritic ends of sensory neurons
Cutaneous receptors and proprioreceptors
Where are cutaneous receptors located?
Located in skin (touch, pain, temperature, pressure)
Where are proprioreceptors located?
Located in muscles and tendons (stretching and tension)
How many motor and inter neurons are there typically?
Interneuron: 1-3
Motor neuron: 1-2
What words are used to describe clusters of cell bodies in both the CNS and PNS?
CNS: nuclei
PNS: ganglia
What words are used to describe the bundles of fibres running together in the PNS and CNS?
CNS: tract
PNS: nerve
What words are used to describe large area of nuclei (and unmyelinated axons) in the CNS and PNS?
CNS: gray matter
PNS: no term
What words are used to describe large areas of tracts in the CNS and PNS?
CNS: White matter
PNS: no term
Describe the organization of a nerve from small to big.
Endoneurium: connective tissue sheath that surrounds each myelinated axon
Perineurium: wraps around groups of fibres (endoneuriums) bound into a fascicle
Epineurium: binds groups of fascicles
What is a mixed nerve?
A nerve that contains both sensory and motor fibres
Ex: spinal cord contains mixed nerves
Differentiate gray matter from white matter.
Gray: unmyelinated, mainly cell bodies and dendrites, very little axon
White: shiny, white, has myelin
